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thesis entitled
"Cyclone Tracks in Relation to the Upper Flow

Pattern in the Middle East, December-March

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presented by

Bohloul Alijani A

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CYCLONE TRACKS IN RELATION TO THE
UPPER FLOW PATTERN IN THE MIDDLE EAST
DECEMBER-MARCH 1964-67

By
Bohloul Alijani

A THESIS

Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of

MASTER OF ARTS
Department of Geography
1979

 

 

ABSTRACT
CYCLONE TRACKS IN RELATION TO THE
UPPER FLOW PATTERN IN THE MIDDLE EAST
DECEMBER-MARCH 1964-67
BY
Bohloul Alijani

This study was undertaken to relate the spatial dis—
tribution of surface cyclone tracks to the positions of mean
long wave trough and polar front jet axes in the Middle East,
particularly Iran. Daily lZGMT surface and 500mb weather
maps of the northern hemisphere for December-March, 1964-67,
were analyzed. Both seasonal and monthly cyclone tracks were
determined by plotting the paths of individual systems mean
axes of the associated polar front jet and mean long wave
trough were determined for each monthly track.

The spatial distribution and orientation of the sur-
face tracks were best explained by the upper level flow
pattern. From December to March the Mediterranean trough
was displaced eastward while the polar front jet shifted
southward. These changes displaced the cyclonic tracks in-
creasingly eastward and southward during each winter investi-
gated and caused cyclogenesis in the lee of the southern

zagros later in the season.

Dedication
To my cousin Mr. Ali Akbar Alijani
whose spiritual and material support

is always with me.

ACKNOWLEDGEMENT

I would like to express my sincere appreciation to
my advisor, Dr. J.R. Harman, for all his helpful advice and
constructive assistance. I also thank Professors H.A. Winters
and J.M. Hunter of the Geography Department for their time
and effort serving on my Committee and critically reading
the final manuscript. Special thanks should go to Professor
D.H. Brunnschweiler whose valuable assistance has contributed

to the accomplishment of this project.

ii

CHAPTER

II

III
IV

VI

VII

TABLE OF CONTENTS

INTRODUCTION .
PHYSICAL SETTING .

Relief . . . . .
Climate .

LITERATURE REVIEW
METHODS

Area and Method of Study . .
Determination of Cyclone Tracks
Upper Level Investigation .

RESULTS

Seasonal Cyclone Tracks
Monthly Cyclone Tracks .

December .
January

February .
March .

Displacement of Monthly Cyclone Tracks .
Cyclone Tracks of Iran . . . .

DISCUSSION .

Possible controls of cyclone track position.

Redevelopment of December pattern in
February . .

The Seasonal Displacement of the Flow
Pattern . .

Cyclogenesis in othe lee of the Southern
Zagros . . .

Limitations of the Study .

SUMMARY AND CONCLUSION .

LITERATURE CITED .

iii

TABLE

LIST OF TABLES

Seasonal Cyclone Tracks .

Monthly Cyclone Tracks

Cyclone Tracks Affecting Iran .

iv

FIGURE

10

LIST OF FIGURES

Important Physical and Political Features
of the Study Area .

Principal Seasonal Cyclone Tracks for
December-March, 1964-67 in the Middle East

Mean Mbnthly Cyclone Tracks and Associated
500mb. Flow Pattern for December, 1964-67

Mean Monthly Cyclone Tracks and Associated
500mb Flow Pattern for January, 1965-67 .

Mean Mbnthly Cyclone Tracks and Associated
500mb Flow Pattern for February, 1965-67

Mean Mbnthly Cyclone Tracks and Associated
500mb Flow Pattern for March, 1965-67 .

Mean Mbnthly Cyclone Tracks for December and
March, 1964-67 . .

Estimated Mean Mbnthly 500mb Flow Pattern
for all Cyclone Days in December and March

1964-67 .

Principal Cyclone Tracks Affecting Iran in
December-March, 1964-67 .

Estimated Mean 500mb Flow Pattern Associated

‘with Cyclone Tracks AffeCting Iran in
December-March, 1964-67 .

32

35

37

41

43

45

46

49

51

CHAPTER I

INTRODUCTION

The weather of the mid-latitudes is characterized
by the development and movement of migratory extratropical
cyclones. Their importance on the climatic patterns of
these latitudes, especially on precipitation, is unquestion-
able (1,2,3). Many studies have attempted to explain their
paths in relation to the atmospheric and surface conditions.
These extratropical cyclones develop when an area of upper
level divergence ahead of a westerly short wave is super-
imposed on a surface baroclinic zone (4,5,6). These short
waves are usually associated with propagating jet maxima
(5). Thus, each surface cyclone has an associated short
wave and a jet stream (7,8,9). Once they develop, these
cyclones are steered by the upper level short waves as they
move through the long wave features (10,11). Accordingly,
changes in the upper flow pattern cause changes in the sur-
face cyclone tracks.

Cyclogenesis takes place wherever the above mention-
ed conditions combine. Within Eurasia these conditions

occur over the Mediterranean Sea during the cold months of

2
the year, and some of the resultant cyclones migrate east-
ward through the Middle East as far as India, although many
of the cyclones develop within the area itself in some
regions as the lowlands of Iraq (12,13,14,15). These
migratory cyclones are responsible for the winter precipi-
tation of the Middle East (16,17,18,19).

This preliminary study is concerned with the geo-
graphical distribution of major cold season surface cyclonic
tracks in relation to the upper level flow pattern over the
Middle East, particularly Iran. To investigate this rela-
tionship, the surface tracks were determined and the mean
jet stream and long wave trough axes associated with each
cyclone track were located. The specific objectives of the
study can be outlined as follows: 1, to describe carto-
graphically both the principal surface cyclone tracks and
the position of associated upper level jet and long wave
axes; 2, to relate seasonal changes in the spatial distribu-
tion of these surface tracks to seasonal shifts of jet and
trough positions; 3, to summarize the characteristics of each
track in terms of its frequency, pressure, and origin.

Cyclone paths are a most important source of pre-
cipitation in the area (17,20), and the seasonal distribu-
tion of precipitation in the Middle East reflects vari-
ations in the paths of winter cyclones (14). To my know-
ledge, there has been no comprehensive study of the relation-

ship between surface tracks and upper level flow pattern in

3
this area, and, for these reasons, this study was under-

taken .

10.

11.

12.

CHAPTER I - REFERENCES

Patton, P.C. et al. 1974. Physical Geography, Duxburg
Press, Belmont, California.

Reitan, C.H. 1974. Frequencies of Cyclones and Cyclo-
genesis for North America, 1951-1970. Mon. Wea. Rev.,
Vol. 102, pp. 861-68.

Pichler, H.I. 1973. On the Theory of Cyclogenesis in
Middle Latitudes. Geoforum, vol. 14, pp. 7-10.

El-Tantawy, A.I. 1964. The Rule of the Jet Stream With
Formation of Desert Depressions in the Middle East.
WMO, Tech;‘NOte No, 64.

Hovanec, R.D. and Lyle, H.H. 1975. Static Stability
and 300mblbotach Field in the Colorado Cyclogenetic
Area. Men. wea. Rev., vol. 103, pp. 628-38.

 

Bjerknes, J. 1951. Extratropical Cyclones. In
Compendium of Meteorology, Boston.

Petterseen, S. 1956. weather Analysis and Forecasting,
Vol. 1, Motion and MotiOn Systems. McGraw Hill BOOK
Co., Inc., New York.

Riehl, H. 1972. Introduction to the Atmosphere, McGraw
Hill, Inc., New York.
Harman, J.R. 1971. TropospheriC'Waves,'Jet'Streams,'and
‘United'States'Weather Patterns. Asso. Amer. Geogr.,
Resor. Pap. No. 11, washington.

and Harrington, Jr. J.A. 1977. In Support of
Synoptic Climatology. In Winters, H.A. and Winters,
M.K. (eds.), In“ApplicatiOn'of'GeographiC'Research.
Dept. of Geog., M.S.U., E. Lansing, Michigan.

 

Abdel-Hady, 3.8. 1964. Upper Cold Pools in the
Mediterranean, Middle East and Adjacent Areas, WMD,
Tech;'the‘No;‘64.

 

Meteorological Office. 1962. ‘Weather in the
' Mediterranean, Vblg'1‘Genera1‘MeteoroIogy. HMSO,
London.

4

13.

14.

15.

16.

17.

18.

19.

20.

5

Klein, W.H. 1957. Principal Tracks and Frequencies of
' Cyclones and Anticyclones in the Northern Hemisphere.
U.S. weather Bureau, Res. Pap. No. 40.

El-Fandy, M.G. 1950. Effects of Topography and Other
Factors on the MOvement of Lows in the Middle East
and Sudan. Bull. Amer. Meteor. Soc., Vol. 31,
pp. 375-81.

Pieter, J.F. 1973. The Role of Deep Convection and
Strong Winds Aloft in Triggering Gales Over the
Persian Gulf: Comparative Case Studies. Mon. Wea.
§§2,, Vol. 101, pp. 455-60.

Ali, F.M. 1953. Prediction of Wet Periods in Egypt
Four to Six Days in Advance. J. of Meteor., Vol. 10,
pp. 478-85.

Beaumont, P. et al. 1974. The Middle East, A Geo-
graphical Study, John'WiIey‘& Sons,vNew Ybrk.

 

Ganji, M.H. 1954. A Contribution to the Climatology of
Iran, Ph.D. Thesis, ClarE’Univ., W6rcester,
Missachusetts.

Perrin de Brichambeaut and wallen, C.C. 1963. A Study
of Agroclimatology in Semi-arid and Arid Zones of the
Near East. WMO, Tech. NOte No. 56.

Winstanley, D. 1973. Recent Rainfall Trends in Africa,
the Middle East and India. Nature, Vol. 243,
pp. 464-5.

CHAPTER II

PHYSICAL SETTING

Relief

The term "Middle East" was applied for the first
time in 1902 by Americans to a region centered on the
Persian Gulf (1). Since then, the term.has defined several
different geographical regions. In this study the defini-
tion of Beamont (1) has been followed, so that it includes
the countries of Turkey, Iran, Lebanon, Israel, Jordon,
Syria, Iraq, Egypt, and Libya as well as the Arabian Penin-
sula (Fig. 1). Topographically, the region is divided into
a northern mountainous belt, comprising the states of Turkey
and Iran, and a southern region of plains and plateaus.
Because topography may help determine cyclogenetic regions,
I will describe the major mountain patterns in some detail.

In Turkey, the Anatolian plateau, approximately
above 500m'in altitude, is located between the Pontus
Mbuntains on the north and the Taurus Mountains in the south.
The Pontus Mbuntains run parallel to the Black Sea coast
and increase in altitude from the west to the east. This
range is dissected by rivers; its highest peak is about 3000m
above sea level. On the south lie the Taurus Mbuntains,

less dissected by rivers and wider and higher than their

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northern counterparts. In Eastern Turkey the Pontus and
Taurus ranges coalesce near Mbunt Ararat (5165m) into a
complex upland with average height of more than 3000mb.
Eastward from Mount Ararat the mountain chain divides into
two main ranges, the Elburz Mbuntains in northern Iran and
the Zagros Mountains of southwestern Iran.

The Elburz Mbuntains extend eastward south of, and
parallel to, the Caspian Sea until they merge with the Hindu
Kush Mountains in Afghanistan. The average height of this
system.is about 3000m; The highest peak of the Middle East,
Mount Demavand (567lm), is located in this range north of
Tehran (2). The Elburz Mountains are relatively narrow but
high enough to block the climatic influence of the Caspian
’Sea from the interior parts of Iran (3). The Sefid Rud
river dissects the Elburz Mountains at the Menjil Gap as it
makes its way to the Caspian Sea. In the northeastern part
of Iran this range consists of scattered low mountains with
many vast north-south trending valleys. It is these valleys
which lead the cold winds of the Siberian winter high pres-
sure to Iran.

The Zagros Mountains run southeastward from Mount
Ararat, separating the central plateau of Iran on the east
from.the Mesopotamian lowlands on the west. The Zagros sys-
tem consists of a number of parallel ranges making up an
kmi

unbroken and impenetrable wall of mountains about 100 n

length and often more than 200km in width (2). The Zagros

9
Mountains attain heights of more than 4000m andtherefore
are important from a climatological standpoint. The lowe
lands between the Elburz and the Zagros form the central
plateau of Iran and are bounded by the Eastern Iranian
Highlands which attain only about 2500m in altitude and
lie on the eastern border of Iran.

The southern region of plains and plateaus is
generally homogeneous with some exceptions: the Red Sea
Hills on the west coast of the Red Sea; the uplands of the
Levant where its highest peak, Mount Hermon, attains an
altitude of about 3000m; the Asir Mountains of southwestern
Arabia reaching heights of more than 3700m; and Gebel a1
Akhdar in the eastern-most tip of Arabia with a maximum

height of more than 3000m.

Climate

The Middle East has a Mediterranean climate and is
located in a transitional zone between mid and low lati-
tudes (4,5). In summer all the region is dominated by a
large belt of thermal low pressure centered over the Persian
Gulf and of secondary lows over the highland areas (3,6).
The sub-tropical jet stream, which lies above the sub-tropical
high pressure centers, is shifted northward over the Caspian
Sea (7), hence the region comes under the influence of
steady trade winds (4,5), and CT air masses dominate the

entire region (8). Due to subsidence and dry CT air mass,

10

there is little precipitation in the region except in the
very narrow coastal lands (4,5).

In winter, usually from.mid-October to April, the
subtropical jet stream.shifts southward and is centered
over the Persian Gulf (7). The thenmally-induced intense
Siberian high pressure center is developed over central
Asia and secondary highs appear over the Anatolian and
Iranian plateaus (9). In association with the southerly
displacement of general circulation features, the polar
front assumes a modal position over the Mediterranean Sea.
Thus the polar front jet stream appears over this area and
steers the Mediterranean depressions to the Middle East (7,
10). Because of the passage of these cyclones the area
experiences different air masses such as CP, MP, and CT,
and winter is the wet period in much of the Middle East (2,

3,4,5,9).

10.

CHAPTER II - REFERENCES

Beaumont, Peter, et a1. 1974. The Middle East: A
Geographical Study, John Wiley & SOns,*New”YOrk.

 

Ganji, M.H. 1954. A Contribution to the Climatology of
Iran Ph.D. Thesis, Clark Univ., WOrcester,

Massachusetts.

Beaumont, P. 1968. Climatological Traverse from.the
Caspian Sea to the watershed of the Elburg Mountains,
Iran. weather, Vol. 23, pp. 515-17.

Brice, W.C. 1966. Southwest Asia, Univ. of London Press,_
London.

Perrin de Brichambaut and Wallen, C.C. 1963. A Study
of Agroclimatology in Semi-Arid and Arid Zones of the
Near East, WMO, Tech. Note No. 56.

Lahey, J.F. et a1. 1958. Atlas of Five Day Normal Sea
Level Pressure Charts for'the'Northern'Hemisphere,
Univ. ofIWISconsin Press, Madison.

weickmann, L. 1961. Some Characteristics of the Sub-
Tropical Jet Streams in the Middle'EESt’and Adjacent
Re ions,TMeteor. Pub. ser. A., No. l, Minist. of’
Roads, Meteor. Dept., Tehran, Iran.

Mazumdar, S. 1965. Some Features of Synoptic Meteorol-
ogy of South west Asia,’WMO,;Tech.‘N0te'No.‘69.
Fisher, W.B. 1971. The Middle EaSt: A Physical, Social,
'and‘Regional'Geography, Methuen & C0. Ltd., London.

 

Reed, R.J. 1960. Principal Frontal Zones of the
Northern Hemisphere in Winter and Summer, Bu11.'Amer.
Meteor. Soc., Vol. 41, pp. 591-8.

 

11

CHAPTER III

LITERATURE REVIEW

There are many studies, mostly by meteorologists
but to some extent by geographers, about cyclone frequen-
cies and tracks in various areas of the world. Klein (1)
contends that the migratory nature of cyclones was under-
stood by Benjamin Franklin as early as l8th century. The
demonstration of cyclone tracks began with the preparation
of the modern synoptic weather maps during the first half
of the 19th century (1). Most of the earlier studies,
dealing either with cyclone frequency distribution or
tracks, were restricted to local areas. The first compre-
hensive work for the entire hemisphere was compiled by
Garriott under the supervision of Dunwoody (2). This work
contained cyclone frequencies for each month of the year as
well as their tracks.

Since the beginning of this century, much attention
has been paid to cyclone tracks. The first worldwide study
of cyclones in this century was carried out by Mitchel in
1930 (3). He illustrated the cyclone and anticyclone
tracks on a monthly basis for the period of January-April
1925 for almost all of the Northern Hemisphere. He also

mapped the origin, life period, and decay of the preSsure

12

13
centers for each month separately. Sheridan (4) also exam:
ined cyclone frequencies and their characteristics. By
utilizing the ten year series of Northern Hemisphere sea-
level historical weather maps for the years 1929-38, he
studied the life cycle, intensity, speed of movement, fre-
quency distribution in So-squares, and direction of movement
of cyclones in the Northern Hemisphere.

In response to military needs, synoptic climatology
received more attention during and after WOrld war II.

Like the other climatic features, surface pressure centers
and their behavior were related to the general circulation.
In 1951, Bjerknes (5) presented his widely-quoted model con-
cerning the development and movement of extratropical
cyclones in relation to the general circulation. Petersen
(6) summarized the July and January frequencies of cyclones
and anticyclones and their movement for the period 1899-1939
for the entire Northern Hemisphere in So-squares.

Perhaps the most comprehensive study on cyclone
climatology was compiled by Klein (1); be plotted the fre-
quencies, regions of formation, and tracks of both cyclones
and anticyclones of the Northern Hemisphere. By utilizing
the historical weather maps of the Northern Hemisphere of
1899-1939 period, he averaged the daily frequency of cyclones
within 5°-grid squares for each month of the year. One year
later in another article (7) he related the frequency of

cyclones and anticyclones to the mean 700mb circulation.

14

Few recent publications have dealt with cyclone
tracks except in a regional scale. However, Taljaard (8)
summarized cyclone frequencies and tracks of the Southern
Hemisphere south of 1508. for the International Geophysical
Year. At the regional scale, the work of Reitan (9) is very
valuable and methodologically relevant to the present study.
He studied cyclogenesis, cyclone frequencies, and cyclone
tracks over North America during 1951-70 period. Reitan
criticized the method of previous authors in counting cyclone
frequencies. He suggested that cyclonic frequencies and
tracks were better determined by counting the cyclone paths
in a grid rather than the frequency of occurrence of indivi-
dual cyclones to avoid multiple count for the stationary or
31 w moving storms.

The significance of the migratory cyclones to the
climatic patterns of the Middle East, especially during the
cold period of the year, has been examined. weickmann, in his
book on the climate of Turkey (10), studied the seasonal
frequency of the Mediterranean cyclones passing north and
south of the Anatolian plateau during the 1915—1918 period.
He found that the frequency of cyclones is highest in winter,
with a maximum in February. The same tracks were mentioned
by Kendrew (11). Another notable study is the Climatologi-
cal Atlas of Iraq (12), published in 1945, which depicts
the tracks of individual storms moving into, or generating

in, Iraq for the months of October through May during the

15

1938-40 period.

By utilizing the Climatological Atlas of Iraq,
Ganji (13) investigated the monthly frequency and tracks
of cyclones entering Iran. He calculated that all of the
127 depressions he examined entered Iran between 30°N.and
38°N.latitudes. He concluded that three principal channels
existed through which cyclones invaded Iran due to the pre-
sumed influence of topography and local pressure patterns.
These channels are 1, Rowandouz gap at about 37°N.and 450E.
leading to northwestern Iran; 2, the Kermanshah gap at about
34°N. and 450E. leading to the interior of the country; and
3, the Khuzistan lowlands around 30°N. leading to the south-
‘western portion of Iran. Also, he discussed the monthly
distribution of each track.

weickmann(l4) conducted a comprehensive and detailed
investigation of cyclone frequencies and paths over the
Middle East, particularly Iran, during the winter months of
1956-59. The frequencies were plotted within each lO-square
for all days of the 19 months of the period. He tried to
explain the regions of frequency maxima and minima as
related to topography and zonal wind maxima and drew six
‘major tracks over Iran all oriented southwest-northeast.
This orientation was determined by the location of upper
level troughs. He concluded that the major factor steering
the surface cyclones in the Middle East is the westerly jet

S tr eam .

16

The cyclones affecting the Middle East usually
originate over the Atlantic Ocean, North Africa, the
Mediterranean Sea, and the Middle East itself (13,15,16,17).
The lows generating over North Africa are known as Khamsin
depressions and invade the Middle East in spring but rarely
in Winter (17). Some of the North African lows develop
south of the Atlas Mountains as lee depressions and enter
the central and eastern Mediterranean Sea (16). However,
the majority of cyclones entering the Middle East develop or
rejuvenate over the Mediterranean Sea. These depressions
originate mostly in two areas: as lee depressions in the
Gulf of Genoa, the Adriatic Sea, and Cyprus, or as wave
depressions in the area between Tunisia and Sicily (16,18,19).
The lows generating in the Gulf of Genoa may divide into
two branches; the northern branch extends into the Balkan
peninsula but the southern branch enters the Ionian Sea from
a northwesterly direction (1,16,20). From the Ionian Sea
some of the lows migrate north of the Anatolian plateau
toward the Black Sea and some of them migrate eastward to
Cyprus (16,21,29).

Nearly all of the lows entering the Middle East
originate from.Cyprus and are known as Cyprus lows. They
are either the rejuvenated shallow lows moving from the
western and central Mediterranean and North Africa or begin
as IOWS‘WhiCh develop over Cyprus itself (1,16,23). El-Fandy
(20) related the deVelopment of Cyprus lows to the pressure

distribution over the central Mediterranean. These Cyprus

17

lows generally migrate to the Middle East through two
principal tracks (24). Besides the migratory cyclones
some of the lows develop within the Middle East itself in
such areas as the Mesopotamian lowlands (13,21,25), the lee
side of the Zagros Mountains, south of the Caspian Sea (14),
and the northwestern part of the Arabian peninsula (26).
More recently, cyclonic paths have been studies from
an explanatory rather than descriptive viewpoint. Until the
beginning of modern meteorology, the movement of the cyclones
was believed to be controlled mostly by topography and the
surface pressure distribution. As an example, the division
of the Mediterranean cyclones over the Ionian Sea or over
Iran was related to the orographic influence of the plateaus
of Anatolia and Iran, respectively. These high areas are
dominated by high pressure centers which augment their oro-
graphic influence (13,27,28,29). In winter, an important
feature of the surface circulation of the Middle East is the
oscillation of the Siberian High. Gupta (30) found a
relationship between the oscillation of the Siberian High
and the movement of the cyclones. Pedgley (26) maintained
that the southward intrusion of the Siberian High is inter-
rupted by the arrival of the Mediterranean cyclones. Also,
in 1960, weickmann(l4) concluded that the mmuntain ranges do
not directly influence the cyclone tracks, but may modify
them by splitting upper jet stream or altering the regional
wave pattern. Therefore, it is the features of the upper

fIOW’WhiCh basically control the surface climatic patterns,

18
including the cyclone tracks (31). Many other studies have
since confirmed the important role played by features of
the upper level flow (especially long waves) in determining
the movement of surface weather features (32,33,34).

There have been many studies in the Middle East
regarding local-regional jet streams. The main and pre-
dominant jet stream in the area is the sub-tropical jet
stream which overlies the surface sub-tropical high centers
about 200mb (35,36,37). Its mean position shifts from.25°N.
in winter to about 36°N. in summer (28,36,38). Since it lies
over the subtropical high centers and is not associated with
the surface frontal zone, it is not usually associated with
any cyclonic activity at the surface (36). As in other
parts of the world, cyclones in the Middle East are associ-
ated with the polar front jet stream.(35,36,39,40), the prin-
cipal cold-period jet in the Middle East. In winter one
branch of the polar front jet stream moves to lower latitudes
(41). This jet is associated with the Mediterranean polar
front at the surface (42). The southward shift of this jet
stream is particularly pronounced during low index flow
(43). Generally, the low circulation is characterized by
two jet maxima at 500 mb, one around 60°N. and the other
around 25°N. (44). The core of the polar front jet stream is
best developed between 500mb and 300mb in the Middle East
(35,41,42).

19

Several studies have focused on the frequency and
position of the upper level troughs. Among these studies
the work of Klein and Winston (45) and Stark (46) are most
relevant to this paper. Klein and Winston studied the geo-
graphical frequency of troughs and ridges at 700mb during
the 1932-55 period for the Northern Hemisphere. Later in
1965 Stark studied the monthly position of troughs and
ridges during the 1949-63 period. In contrast with Klein
and Winston, he examined all troughs with amplitude of 50
latitude or more rather than 100 latitude. Although no
such studies have been confined to the Middle East, the
steering influence in this area exerted by the upper level
troughs in relation to surface cyclones generally is sub-
stantiated by several authors (l4,l7,19,22,24,26,27,48,49).
Most of these have found that the orientation and position
of upper-level long wave trough over the Mediterranean Sea
is by far the most important factor in steering the surface
cyclones through the Middle East.

All of the previous studies, however, have consider-
ed either the surface tracks or upper level flow pattern
separately. In some cases they have traced the surface
cyclones with respect to the upper level flow pattern for
only a few days. But until now there has been no known
attempt to determine the associated flow pattern for each
surface track. Therefore it seems there is a need to study
the spatial relationship of surface cyclone tracks with the

upper level flow pattern in the Middle East.

10.

ll.

 

CHAPTER III - REFERENCES

Klein, W.H. 1957. Principal Tracks and Mean Frequencies
of Cyclones and AnticypIOnes in the NOrthern Hemis-
phere, U.S. Weather Bureau, Res. Pap. No. 40.

 

Dunwoody, H.H.C. 1893. Summary of International Meteor-
ological Observations. U.S. Weather Bureau, Bull.
A. In Klein, W.H. 1957, Principal Tracks and Mean
Frequencies of Cyglones'and'AnticycIones in the
'Northern'HEmisphere, UiS. Weather Bureau, Res.Pap. No.40.

 

Mitchell, C.L. 1930. Cyclones and Anticyclones of the
Northern Hemisphere, January-April, inclusive, 1925.

 

Sheridan, L.W. 1945. A Study of Northern Hemisphere
Pressure Center Tracks. Trans. Amer. Geoph. Un.,
' vol. 26, pt. 2, pp. 49-57.

Bjerknes, J. 1951. Extratropical Cyclones. In Compen-
dium of Meteorology, Boston.

Petterssen, S. 1950. Some Aspects of the General Circu-
lation of the Atmosphere. Centenary Proc. R4M.S.,
pp. 120-55.

Klein, W.H. 1958. The Frequency of Cyclones and Anti-
cyclones in Relation to the Mean Circulation,
J. of Meteor., vol. 15, pp. 98-102.

Taljaard, J.J. 1967. Development, Distribution, and
Movement of Cyclones and Anticyclones in the Southern
Hemisphere During the IGY. “J;'of‘App1.‘MeteOr,
vol. 6, pp. 973-87.

Reitan, C.H. 1974. Frequencies of Cyclones and Cyclo-

genesis for North America, 1951-1970. Mon. wea. Rev.
vol. 102, pp. 861-68.

 

weickmann, L. 1922. Zum Klima der Turkei, und Ergehisse
Dreijahiger Behachtungen, 1915-18. In Ganju, M.H.
1954. A COntribution to the Climatology of Iran,
Ph.D. TheSis, Clark Univ., worcester, Massachusetts.

Kendrew, W.G. 1961. The Climate of the COntinents,
Oxford Univ. Press, London.

20

12.

13.

14.

15.

16.

l7.

18.

19.

20.

21.

22.

23.

24.

25.

26.

21

Iraq Government, 1945. Climatological Atlas of Iraq,
Gov. Pub. No. 8, Baghdad.

Ganji, M.H. 1954. A Contribution to the Climatology
of Iran, Ph.D. Thesis, Clark Univ., warcester,

Mas sacHus 8121: S .

Weickmann, L. 1960. Haufigkeitisnerteilung und
Zughahnen von depresionen im mitleren osten.
Meteor. Rund. Berlin, Vol. 13, No.2, pp. 33-8.

 

Fisher, W.B. 1971. The Middle East; a Physical, SOcial,
and Regional Geography, Methuen & Co. Ltd., LondOn.

 

Meteorological Office. 1962. weather in the Mediterranean,
Vol. 1, General Meteorology,HMSO, London.

 

El-Tantawy, A.I. 1964. The Role of the Jet Stream in the
Formation of Desert Depressions in the Middle East,
WMO, Tech. Note No. 64.

Conrad, V. 1943. The Climate of Mediterranean Area,
Bull. Amer. Meteor. Soc., Vol. 24, pp. 127-45.

 

Gordon, J.C. 1965. Mediterranean Synaptic Weather and
the Associated 1000-500mb Thickness Pattern. WMOz
Tech. NOte No. 69.

 

El-Fandy, M.G. 1946. Barometric Lows of Cyprus.
Q;J.R;M.S., Vol. 72, pp. 291-306.

 

1950. Effects of Topography and Other Factors
on the Movement of Lows in the Middle East and Sudan.
Bull. Amer. Meteor. Soc., Vol. 31, pp. 375-81.

 

 

Levi, W;M; 1963. The Dry Winter of 1962/63, Synoptic
Analysis, Israel ExploratiOn J., Vol. 13, pp. 229-41.

Ali, F;M. 1953. Prediction of Wet Periods in Egypt
Four to Six Days in Advance, J. of Meteor., Vol. 10,
pp. 478-85.

Perrin de Brichambaut and wallen, C.C., 1963. A Study of
Agroclimatology, WMO, Tech. NOte No. 56.

Pieter, J.F. 1973. The Role of Deep Convection and
Strong Winds Aloft in Triggering Gales Over the

Persian Gulf: Comparative Case Studies. 'Mon. wea.
Rev., Vol. 101, pp. 455-60.

Pedgley, D.E. 1974. Winter and Spring Precipitation at
Riyadh, Saudi Arabia, MeteOr. Mag., Vol. 103,
pp. 225-36.

27.

28.

29.

30.

31.

32.

33.

34.

35.

36.

37.

38.

39.

40.

22

Mazumdar, S. 1965. Some Features of the Synoptic
Meteorology of South West Asia. WMD,’Tech.'Note
No. 69.

Brice, W.G. 1966. Scuth west Asia, Univ. of London
Press, London.

 

Beaumont et al. 1974. The Middle East; A Geographical
Study, John Wiley & Sons, New York.

Gupta, B.R.D. 1972. Periodiatry in the Average Daily
Strength of Siberian Anticyclone from.November 67-
April 68. Tellus, Vol. 24, pp. 380-82.

Barry, R.G. and Perry, A.H. 1973. Synoptic Climatology;
Methods and Applications. Methuen & Co. Etd.,
London.

 

Petterssen, S. 1956. Weather Analysis and Forecasting,
Vol. 1, Mbtion and Mbtion‘SyStems, McGraw Hill Book
Co. Inc., New Y6rk}

Harman, J.R. 1971. Tropospheric waves, Jet Streams, and
United States weather Patterns. Assoc. Amer. Geogr.
Resor. Pap. No. 11, Washington, D.C.

Riehl, H. 1972. IntroduCtion to the Atmosphere, McGraw
Hill Inc., New York}

El-Tantawy, A.I. 1964. The Role of the Jet Stream in
the Formation of Desert Depressions in the Middle
East, WMO,'Tech. NOte No. 64.

Weickmann, L. 1961. Some Characteristics of Subtropical
Jet Stream.in theIMidHIe East and'Adjacent RegiOns,
Meteo.'PuEi, Ser. A.,INo. 1, Minist. of‘Roads, Meteor.
Dept., Tehran, Iran.

Bannon, J.R. 1954. Note on the Structure of the High
Altitude Strong Wind Belt in the Middle East in
Winter. Q.J.R;M.S., Vol. 80, pp. 218-21.

 

Krishnarouti, T.N. 1961a. The Subtropical Jet Stream
of Winter,'J.'of'MeteOr., Vol. 18, pp. 172-91.

 

Walker, J.M. 1967. Some Ideas on Winter Atmospheric
Processes Over South West Asia, Meteor. Mag., Vol.
96, pp. 161-67.

Lamb, H.H. et al. 1957. Jet Streams Over North Africa
and Central Mediterranean in January and February
1954. MeteOr. Mag., Vol. 86, p. 97.

 

41.

42.

43.

44.

45.

46.

47.

48.

49.

23

Winstanly, D. 1973. Rainfall Patterns and General
Atmospheric Circulation, Nature, Vol. 245, pp. 190-94.

Reed, R.J. 1960. Principal Frontal Zones of the North-
ern Hemisphere in Winter and Summer, Bull. Amer.
Meteor. Soc., Vol. 41, pp. 591-8.

Bradbury, D.L. 1958. On the Behavior Patterns of Cyclones
and Anticyclones as Related to Zonal Index, Bull.
Amer. Meteor. SOC., Vol. 39, pp. 149-51.

 

Gupta, M.G. and Rajagoplun, K.S.V. 1969. Formation of
Upper Anticyclones and Their Blocking Activity During
Winter Over Asia. Indian J. Meteo. GeOph, Vol. 21,
pp. 567-76.

Klein, W.H. & Winston, J.S. 1958. Geographical Fre-
quency of Transfers and Ridges on Mean 700mb Charts.
Mbn.‘ ea. Rev., Vol. 86, pp. 344-58.

 

 

 

Stark, L.P. 1965. Positions of Mbnthly Mean Troughs
and Ridges in the Northern Hemisphere, 1949-63.
Men. Wea. Rev., Vol. 93, pp. 705-20.

Krown, L. 1966. An Approach to Forecasting Seasonal
Rainfall in Israel, J. of Appl. Meteor., Vol. 5,
pp. 590-94.

Datta, R.K. & Gupta, M.G. 1967. Synoptic Study of the
Formation and Movement of Western Depressions.
Indian J. Metro. Geoph., Vol. 18, pp. 45-50.

Singh, M.S. 1963. Upper Air Circulation Associated
With a western Disturbance. Indian‘JL'Meteor.
‘Geoph., Vol. 18, pp. 45-50.

CHAPTER IV

METHODS

Area and Method of Study

The Middle East was chosen as the study area. How-
ever, since the majority of the cyclones affecting this
area are generated in the Mediterranean Sea, the study
area was extended to include the western part of the Medi-
terranean Sea as well. The North Atlantic Ocean was not
included in the study because cyclones affecting the Middle
East which develop there travelled through the same tracks
as the Mediterranean cyclones. Latitude 20°N. was chosen
as the southern limit of the area because extratropical
cyclones in this region rarely penetrate south of this lati-
tude (l). The north and east boundaries of the area were
defined according to Beaumont's political definition of the
area (2). Thus these boundaries are roughly 45°N. and 650E.

According to several authors, some of whom were
‘mentioned in the previous chapter, extratropical cyclones
reach the Middle East during mainly the cold period of the
year, particularly December to March. In this study daily
12 GMT surface and 500mb synoptic weather maps of the
Northern Hemisphere for the months December through March,

1964-67, (3) were analyzed. First, the cyclone tracks for

24

 

 

25
each calendar month were determined and then the associated

upper level jet and long wave trough positions were plotted.

Determination 'Of' Cyclone Tracks

The study area was divided into So-square units;
this grid size was chosen following Petterssen (4) and Klein
(5) in order to plot the occurrence of cyclones within each
of the 24 hour interval. A cyclone was defined as a low
pressure region which has at least one closed isobar, and
only the paths of moving cyclones were plotted, according to
the method of Reitan (6). This procedure was used because
1, a cyclone track exists only where a cyclone moves along
it, so that stationary cyclones cannot be used to determine
a track; 2, the direction of movement of cyclones deter-
‘mines the orientation of cyclone tracks; and 3, only the
migratory cyclones reflect the configuration of the upper
flOW'pattern.

A transparent overlay with a square grid ruled on
it was used to plot the locations of cyclones and determine
their movement. As a cyclone appeared in a grid square, a
dot was put in its center on the overlay and an arrow was
drawn connecting this dot with other dots which represented
the path of the cyclone. In those few cases when the path
of an individual cyclone was difficult to follow on the sea-
level charts, the location of the system was approximated
by examining the motion of the associated 500mb short wave.

At the same time the central pressure and the date of

 

 

26
appearance of each low were recorded. If the low was
shaped irregularly, a dot was placed in the approximate
center of it. When the center of a low was located on the
boundary between two units, the dot was put in the unit
where the major part of the low existed. If a cyclone began
one month and continued into the next, its location during
the first day of the second month was treated as a continu-
ation of the path from the preceding month.

To construct the monthly cyclone tracks all charts

 

for every calendar month we combined on a single chart

for each month. On this composite chart the primary monthly
cyclone tracks were drawn through the grids where the cyclone
paths appeared to be concentrated. Each track begins in its
respective region and continues until it is no longer recog-
nizable, with the direction of tracks shown by arrows. The
monthly tracks were ranked according to the frequency of
cyclonic activity, determined by counting the number of
cyclones crossing the 400E. and 55°E.meridians which were
selected arbitrarily to represent the central and eastern
portions of the study area. A principal track accounted for
the highest percentage of the cyclones crossing either meridian;
lesser concentrations were regarded as secondary tracks. On
the maps, the type of track is indicated by its width propor-
tional to its relative frequency; that is, the principal
tracks are wider than the secondary tracks. By compiling the
monthly tracks the map of overall cyclone tracks (seasonal

tracks) for the Middle East was prepared. All cyclone paths

 

27

either entering, or originating within, Iran were extrapol-
ated from all charts, compiled, and presented on one map.

The mean central pressure of each cyclone along
its entire path was determined by averaging the daily
values; the mean pressures were then averaged for each
track, yielding the mean central pressure of each track.
Also, to determine the frequent cyclogenetic region of each
track the origin of all cyclone paths of that track was
plotted on the overlay. In counting and summing the number
of cyclone centers the areal correction coefficient* was
not applied because of the limited latitudinal extent of the
study area and because the number of cyclones within each
unit was very small. Tables were constructed to show the
frequent cyclogenetic area, mean central pressure, and fre-
quency of cyclone passages along each track. The frequency
of cyclone passages for each track across the 400E. and 550E.
‘meridians is shown as the percentage of all cyclones cross-

ing those meridians.

Upper Level InveStigation
Among the conditions favorable for the development
of the extratropical cyclones, two are important: the exist-

ence of upper level divergence ahead of a westerly trough and

 

*Due to difference in size of 5°-squares units at high and low
latitudes, the observed frequencies may be adjusted to the
size of a selected latitude by multiplying to the areal
correction coefficient. This correction coefficient is ex-
pressed as the ratio of the cosine of the selected latitude to
the cosine of each latitude (Klein & Winston, 1958).

  
  

28

a surface baroclinic zone. The upper level divergence causes
the convergence at the surface which results in cyclone
development. The connection between upper divergence and
surface convergence is achieved by vertical motion. Thus,

in general, the stronger the vertical motion the stronger

the surface cyclone. The rate of vertical motion is related
to the amplitude, wind speed, and length of the upper trough.
If the wind speed and amplitude are held constant, the verti-

cal motion is higher when the length of the trough is short.

 

Thus the surface cyclones develop in association with the
short waves with approximate lengths less than 700 longitude
(7). If wave length and amplitude are constants, the verti-
cal motion varies directly with the speed of the wind through
the upper trough. Higher wind speeds (jet maxima) are usually
associated with short waves (8). Thus the superposition of
the upper short wave troughs over surface baroclinic zones
may stimulate cyclonic development. Once formed, the sur-
face cyclone usually migrates with the upper level short wave
trough, which follows the general configuration of the mean
long wave features. As a result, the long wave pattern and
jet stream.are decisive factors in the movement of surface
cyclones.

Two jet streams can be recognized around the Northern
Hemisphere. The sub-tropical jet stream lies at about 200mb
level over the surface sub-tropical high centers and is not

associated with any frontal zone at the surface. The polar

 

29

front jet (PFJ) lies at heights of between 500mb - 300mb,
is associated with the polar front at the surface, and is
primarily responsible for surface extratropical cyclogenesis.
Thus the positions of the long wave features and the PFJ
are important controlling factors of surface cyclone tracks,
and for this reason they were considered closely in connec-
tion with surface cyclone paths in this study.

To determine the mean position of long waves and

PFJs associated with surface cyclone tracks in the Middle

 

East, the 500mb daily weather maps were inspected. The dates
of appearances of all cyclones in each track were first
extrapolated from the surface track charts, and the 500mb
level maps of these days were inspected. By examining the
500mb charts of the date of development of each cyclone, the
position of the long wave trough was approximated. Height
contours depicting the mean trough position affecting every
traveling cyclone thus were approximated, and trough axes
were drawn by connecting minimum latitudes of height contours.
At the same time the position of the PFJ was determined by
drawing a line parallel to the most concentrated regions of
height contours. This was done because the wind speed is
higher in the regions of the great height contour concentra-
tion (9). By inspecting all the 500mb maps relevant to the
cyclones passing along a specific surface track the axes of
all jets and troughs were drawn. On the final maps the axes
for each track were smoothed to a single line. The results

‘were superimposed on the related track maps.

 

CHAPTER IV - REFERENCES

. Mazumdar, S. 1965. Some Features of the Synoptic

. Beaumont, et al. 1974. The Middle East, A Geographical

Meteorology of Southwest Asia. WMO, Tech. Note No.
69.

 

 

Study, John Wiley & Sons,*New’York.

. NoAA. Daily Series Synoptic weather Maps, Part 1,
Northern Hemisphere Sea-Level and 500mb. Asheville,
North Carolina.

 

. Petterssen, S. 1950. Some Aspects of the General Cir-
culation of the Atmosphere, Centenary Proc. R.M.S.,
pp. 120-55.

. Klein, W.H. 1957. Principal Tracks and Mean Frequencies

 

of Cyclones and Anticyclones in fhe‘Northern
Hemisphere, UZS. Weather Bureau, Res. Pap._No. 40.

 

 

. Reitan, C.H. 1974. Frequencies of Cyclones and Cyclo-
genesis for North America, 1951-1970, Mon. Wea. Rev.,
Vol. 102, pp. 861-68.

 

. Boucher, K. 1975. Global Climate. Halsted Press, A

 

Division of John Wiley & Eons, Inc., New York.

. Hovanec, R.D. & Lyle, H.H. 1975. Statistic Stability and

the 300mb lsotach Field in Colorado Cyclogenesis
Area. ’Mon;'Wea.‘Rev., Vol. 103, pp. 628-38.

. Harman, J.R. 1971. ‘TrowospheriC'waves,‘Jet‘Streams,'and

 

 

‘United’States”weat.er‘Patterns; Assoc. Amer. Geogr.
Res.’Pap.‘No. 11,7washington,’D.C.

 

30

CHAPTER V

Results
Seasonal Cyclone Tracks

By combining all monthly surface cyclone tracks for
the study period the seasonal cyclone tracks for the Middle
-East were derived (Fig. 2). Sixty-five cyclones affected
the area during the study period (Table 1). Most of these
cyclones developed in four major cyclogenetic regions: the
Adriatic Sea, the Ionian Sea, Cyprus, and the lee side of
the southern Zagros; only a few generated in the lowlands of
Iraq and North Africa. During the study no cyclone from.the
Atlantic Ocean affected the Middle East. A11 cyclones
which generated in the Mediterranean Sea or North Africa
migrated toward the Aegean Sea where they divided into three
distinctive tracks. The northerly track (A) continued frOm
western Turkey, after crossing the Pontus and the Caucasus
Mountains, to the Caspian Sea. The mean central pressure of
cyclones moving along this track was about lOOSmb. This
track included 26% of all cyclones passing 400E. and 6% of

those passing at 550E. Thus, most of these cyclones dissi-

pated in the Caucasus region. The frequent cyclogenetic

31

 

32

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33
regions for this track were the Adriatic Sea and the Ionian
Sea.

Track B, the principal track, extended from south-
western Turkey (north of Cyprus) northeastward to the east
of the Caspian Sea. Some of the cyclones of this track
branched off southeastward in the lowlands of Iraq to the
northeast of the Persian Gulf (B1 in Fig. 2). Sixty-one
percent of all the cyclones passing 400E. migrated through
track B; only 34 percent reached 550E. (Table 1). This

decrease reflected the division of the track in the lowlands

TABLE 1. Seasonal Cyclone Tracks

 

 

Total Map Mean Z at Z at Most fre-
No.of Designa- Central 40E. 55E. quent
cyclones tion of pressure cyclo-
track in mb. genetic
area
A 1005 26 6 Adriatic
Sea and
Ionian Sea
65 B 1006 61 34 Eastern
Mediter-
ranean
C 1006.5 13 60 Lee of the
Southern
Zagros
Mbuntains

 

of Iraq. The mean central pressure for the track was about
1006mb. Mest of the cyclones of this track developed over
the eastern Mediterranean around the Ionian Sea; few of them

developed over Iraq.

 

34

The southerly track (C) lay from Cyprus southeast- 2
ward to the north of the Persian Gulf. This track was
secondary until it reached the area northeast of the Persian
Gulf where it became a principal track, because many cyclones
developed here on the lee side of the southern Zagros. Some
of these cyclones migrated northeastward (C1 in Fig. 2) and
joined with the track B to the east of the Caspian Sea.

Track C contributed only 13% of all cyclones passing 400E.

 

but more than 60% of those at 550E. The mean central pressure
of this track was about 1005.5mb.

Since the overall cyclone tracks were a combination of
the monthly tracks, the upper level features were not drawn
and the reader can refer to the contributory monthly pattern

of each overall track.

Monthly Cyclone Tracks
December

During the three Decembers studied, fourteen cyclones
developed either within the Middle East itself or entered
from areas to the west. Most of the cyclones followed a
single track (Fig.3). The most important cyclogenetic area
was the Adriatic Sea (Table 2). After generation, the
cyclones migrated southeastward to southwestern Turkey where
they turned east-northeastward across the southern edge of
the Anatolian Plateau to the Caspian Sea. Almost all of the
cyclones followed this track at 40°E., but only about 70% of

them.reached 550E. Normally their central pressure increased

 

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36

 

 

 

TABLE 2. Monthly Cyclone Tracks
Month No. of Map Mean %‘at % at Most fre-
cyclones desig- central 40E. 55E. quent
nation pressure cyclo-
of in mb. genetic
track area
Dec. 14 D 1005.8 100 75 Adriatic {
Sea I
Jan. 17 J1 1008 33 00 Central
Mediterranean
J2 1009 50 25 " "
J3 1006 17 75 " "
Feb. 14 F 1004 100 100 Aegean Sea'
and Cyprus
South of the
Atlas
Mountains
March 20 M1 1005.5 75 16 Central Medi-
terranean
M2 1005 25 84 Lee of the
Southern
Zagros
Mbuntains

 

as they moved onto the land area from the sea.

pressure for the track was about 1005mb.

The mean central

Few of the cyclones

of. this track passed north of Iran; within Iran only a few

shallow depressions generated on the lee of the southern Zagros,

but most did not continue for more than 24 hours.

cyclone track coincided with the seasonal track B.

The December

Most of

the Middle East except Turkey was free of cyclonic activity.

The associated mean upper level trough axis was

aligned in a north-south direction over the Aegean Sea (Fig.

3). The polar front jet extended from northeastern Egypt

 

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37

           

 

 

 

 

 

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38
northeastward along and south of the position of the surface
track. The agreement between the position of the surface
track and mean position of the upper level jet and trough

axis is depicted in Figl 3.

January
Seventeen cyclones developed during the three
Januarys and followed three tracks over the Middle East (Fig.

4). Most of the depressions began over the central Medi-

 

terranean (Table 2) and a few over Italy. Most moved south-

 

eastward over the Mediterranean Sea until they arrived over
Cyprus and then followed one of three tracks eastward. The
northern track (J1) (which coincides with seasonal track A)
crossed the Anatolian Plateau toward the northern parts of
the Caspian Sea. The cyclones of this track were relatively
shallow (about 1008mb) and of all cyclones passing the 400E.
meridian, 33% migrated through this track. The associated
jet axis extended from central Mediterranean northeastward to
the northern Caspian Sea. The upper level trough axis was
located over the eastern Mediterranean in a northeast-
southwest direction.

The other track (J2) coincided with seasonal track B;
it began near Cyprus and, after crossing northern Syria and
Iraq, made its way over the high mountains of the Zagros and
Elburz to the southern part of the Caspian Sea. Of all

cyclones passing 40°E., 50% followed this track, whereas the

 

 

39

percentage was 25% at 550E. The central pressure for the
track was higher than others (1009mb). Some of these
depressions crossed the northern part of Iran. The associ-
ated long wave trough axis was located east of the J1 trough
axis over the Black Sea and eastern Mediterranean in a north-
east-southwest direction. The associated jet was also south
of that for J1 and was located over northeastern Egypt extend-
ing northeastward to the Southern Caspian Sea.

The southern track (J3) again diverged southeastward

 

from near Cyprus and crossed the lowlands of northern Jordan
and Iraq and the Zagros Mountains north of the Persian Gulf
toward the central plateau of Iran (track C in Fig. 2). Only
17% of all cyclones followed this track across the 400E.
‘meridian, whereas about 75% followed it at 550E. This indi-
cates that most of the cyclones migrating along this track
generated over the lowlands of Iraq and the Persian Gulf.
Cyclones of this track were deeper than other tracks (1006mb).
All cyclones of this track entered Iran; some of them diverg-
ed northeastward on the lee of the southern Zagros. The long
wave trough associated with this track was situated over Syria
and the Arabian Peninsula in a northwest-southeast orienta-
tion; the jet also was farther south than those of other
tracks, and extended from the Sinai Peninsula eastward over
the Persian Gulf.

In general, in January two cyclogenetic areas were

active. Many originated over the Adriatic Sea and followed

 

40
either tracks J1 and J2. Others originated over the
Mesopotamia and the Persian Gulf lowlands and followed the

J3 track which was the principal track of the month.

February
About 70% of the fourteen cyclones identified in
February traveled through a single track (Fig. 5). Three
cyclogenetic areas were active this month (Table 2). One

region was located south of the Atlas Mountains and another

 

region near Cyprus, but cyclogenesis occured most frequently
in the region of the Aegean Sea. All of these cyclones com-
bined into one track over southwestern Turkey where they con-
tinued eastward. After crossing the highlands of Turkey,

the Caucasus, and the northern parts of Iran (especially the
Caspian Coast), these storms reached the deserts east of the
Caspian Sea (similar to seasonal track B). Almost all
cyclones passing both 400E. and 550E. followed this track.
Most of these cyclones passed through the northernmost parts
of Iran. The mean central pressure of cyclones of this

track was about 1004mb. The upper level jet was located near
34°N. latitude extending from the eastern Mediterranean to
the south of the Caspian Sea. The associated mean long wave
trough axis was situated northeast-southwest over Greece and
the Ionian Sea. The comparison of figures 3,4 and 5 shows

that the general patterns of December recurred in February

and that both months differed from January, when the principal

41

 

 

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42
cyclone track and associated upper flow were farther south.

This contrast will be discussed in the ensuing chapter.

March
Twenty cyclones affected the Middle East during the
period of investigation (Table 2). Most of these cyclones
developed within the Middle East itself. The cyclones began
either over North Africa or the central Mediterranean and

traveled to Cyprus, where most of them migrated northeastward

 

toward the Caspian Sea as a single track, again like seasonal
track B. (M1 in Fig. 6) This track crossed the southern
edge of the Anatolian Plateau and affected the northwestern
part of Iran. The principal cyclogenetic region was the
central Mediterranean and the mean central pressure of the
cyclones was about 1005.5mb (Table 2). Along the 400E.
meridian, 88% of all cyclones followed this track but only
14% of these cyclones passed 550E. In other words, along
550E. only about 16% of all passing cyclones followed this
track. Mbst of the cyclones of this track dissipated over
northwestern Iran. The associated upper level long wave
trough axis was positioned over Greece in a northeast-
southwest alignment. The polar front jet was shifted further
south so that its southern position lay over North Africa at
about 25°N. From North Africa the jet continued northeastward
in such a way that along 500E. its position was over the
northern Caspian Sea.

The region of frequent cyclogenesis for the southern

track (M2) was the lee of the southern Zagros (Table 2).

43

 

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44

Only 12% of all cyclones passing 400E. followed this track,
whereas the percentage was 84% at 55°F. This is again indi-
cating cyclogenesis on the lee of the southern Zagros. The
track was generally west to east but some of the cyclones
migrated northeastward to the east of the Caspian Sea after
development. The mean central pressure for the track was
about 1005mb. This track corresponds to seasonal track C.
The mean upper trough axis was located roughly along 32°E.,

crossing the Black Sea, Turkey, Syria, and Jordan. The

 

associated jet stream also was further south than the pre-
vious months over the Middle East, crossing northern Arabia

and the Persian Gulf.

Displacement of Monthly Cyclone Tracks

The months of December and March were compared to
determine the displacement of both the surface tracks (Fig. 7)
and the upper level features (Fig. 8) as the winter season
advanced. In review, the December track (D) began in the
Adriatic Sea, a major cyclogenetic region, and extended south-
eastward to Cyprus and then continued northeastward to the
Caspian Sea region. Only a few cyclones developed in the
eastern Mediterranean in DeCember and travelled along the
principal track of March (M3) southeastward to India; actually
‘most of the cyclones of track M3 originated on the lee of
the southern Zagros. It appears, therefore, that not only
did the cyclone track shift southward from December to March,

but also that the cyclogenetic area shifted from the Adriatic

 

 

45

 

 

 

 

  

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47

Sea in December eastward to the lee of the southern Zagros.
The upper features, naturally, displayed a similar shift
(Fig. 8). The axis of the long wave trough shifted east-
ward from the central Mediterranean in December to over
Syria in March. In the same manner over the Middle East
the polar front jet shifted southward from.its December
position over Turkey to over the Persian Gulf in March.

Taking into consideration the "steering principal"

and analyzing all the monthly results, it appears that in the

 

Middle East as in other parts of the world the surface tracks
are controlled primarily by the upper level long wave pat-
tern and jet position. Each track seems to coincide with a
specific upper level long wave and jet pattern, and the dis-
placement of the surface tracks follows the displacement of
the upper long wave trough and jet axes. These findings

will be discussed more fully in the next chapter.

Cyclone Tracks of Iran

 

During the study period sixteen cyclones entered

Iran and sixteen developed inside Iran, mostly on the lee of
the southern Zagros (Table 3). Most of the cyclones affecting
Iran migrated through two distinctive tracks, P and I (Fig. 9).
The track P, which coincides with seasonal track B, began in
the Eastern Mediterranean, its frequent cyclogenetic region,
and extended northeastward to northern Iran. Over the low-
lands of Iraq this track divides into two branches, the major

branch going eastward and the minor track (P1- in Fig. 9) going

 

 

 

48

TABLE 3. Cyclone tracks affecting Iran

 

 

Total Map Mean central Most frequent
No. of designation pressure in cyclogenetic
cyclones , of track. .mb.. area
P 1006 Eastern Medi-
32 terranean
I 1008 Lee of the
Southern

Zagros Mountains

 

southeastward to the Persian Gulf, where it turns northeastward
to join Track I. Over northwestern Iran another minor track
(P3 in Fig. 9) diverges from.track P2 and extends southeastward
to join track I.

The southern track (I) coincides with the seasonal
track C. The frequent cyclogenetic area for this track is
the lee of the southern Zagros. Some of its cyclones moved
northeastward (I, in Fig. 9) to join track P2. It appears,
however, that most of the cyclones which affected Iran
developed either in the eastern Mediterranean or the lee of
the southern Zagros. In terms of cyclone frequencies, both
tracks P and I are nearly equal. The track P consisted of
migrating cyclones whereas track I consisted mostly of
cyclones which developed inside Iran. Also, the cyclones of
track P were generally deeper than that of track I; the mean
central pressure for track P was about 1006mb vs. 1008mb for

track I (Table 3).

 

 

 

 

49

 

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50

The upper level features for each track are shown
in Figure 10. The associated long wave trough axis of track
P was located over the Aegean Sea in a northeast-southwest
direction and the associated jet extended from Cyprus north-
eastward to the east of the Caspian Sea. But the trough
axis of track I was shifted eastward over Syria, having a
northsouth direction, and the associated jet was displaced

southward over the Persian Gulf.

 

51

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CHAPTER VI

DISCUSSION

The results of the study suggest the following
important patterns: 1, the spatial distribution of cyclone
tracks in the Middle East was more closely related to the
upper flow than to the surface topography or pressure pat-
terns; 2, the flow pattern of February was more similar to
that of December than that of January; 3, from December to
March the mean monthly long wave trough axis shifted east-
ward and the mean jet was displaced southward; and 4, in
March cyclones developed to the lee of the southern Zagros
Mountains, Iran, in addition to the usual cyclogenetic area

in the Mediterranean.

Possible controls of cyclone track position

 

The results presented in Chapter V indicated that
the location and orientation of each cyclone track in the
Middle East were closely related to the position of the axes
of the mean long wave trough and Polar Front jet streams.
The results also agreed with the findings of Klein (1), in
that almost all cyclone tracks were located north of the 500mb
jet maxima. In December the jet extended from Cyprus north-

eastward to the Caspian Sea, and cyclones travelled parallel

52

 

53

to it through the northern parts of the study area. In this
month the axis of the mean long wave trough was over the
Aegean Sea, implying the existence of southwesterly flow
over the northern parts of the Middle East, along which
cyclones migrated. As is apparent from Figure 3, cyclones
crossed the Taurus Mountains and the highlands of eastern
Turkey and northern Iran without by-passing them. This
agrees with the findings of Pedgly (2) who demonstrated that
in the Middle East as elsewhere the movement of cyclones is
linked with the upper level short waves; thus, surface
cyclones, like those short waves, are not strongly influenced
by the surface relief, but rather by wave patterns (3). This
fact holds true in other months as well. All of the cyclone
tracks crossed the mountain ranges without undergoing import-
ant deflection. The best example is track Jl (Fig. 4) and
coincident track A (Fig. 2) which radiate from southwestern
Turkey and extend to northern Caspian Sea, crossing the high-
lands of Turkey and the Caucasus Mbuntains. Previous studies
indicated that this track was believed to branch northward in
the Aegean Sea to continue along the southern coast of the
Black Sea due to the highaltitude of the Anatolian Plateau
(4,5,6).

The influence of upper flow adjustments as a control
in inter-monthly variations of the mean cyclone tracks in the
region is clearly apparent from the results. In December and

February when the mean jet position was in the northern parts

 

 

54
of the region, cyclones passed only through that area. But
the displacement of the mean jet southward in January and
particularly in March steered the cyclones through the south-
ern parts of the Middle East. Concurrent with this southward
displacement of the jet, the long wave trough is by far the
most important factor in determining the orientation of
cyclone tracks in the Middle East. When the long wave trough
axis was located over the central Mediterranean, as was the
case in December and February (Figs. 3,5), the cyclones
migrated toward the northern parts of the Middle East. At
this time the Middle East was dominated by a long wave ridge
which blocked the cyclones from the rest of the area. But as
the trough axis shifted eastward over eastern Mediterranean,
upper level divergence dominated the Middle East and permitted
the cyclones to affect the entire area, as was the case in
January and March (Figs. 4,6). These findings agree with the
studies of Levi (7) who found that the position of long wave
trough over the Mediterranean correlates with precipitation
in the Middle East.

Except for a small discrepancy in their latitudinal
positions, the cyclone tracks plotted for this study agreed
with the findings of weickmann(4,8) and Klein (1), and con-
firmed that nearly all of the cyclones affecting the Middle
East radiated from a point near Cyprus. These cyclones
developed mainly over central Mediterranean, the Gulf of Genoa,

the Adriatic Sea, North Africa, and Cyprus (Tables 1 & 2).

 

 

55
The reasons for their concentration near Cyprus, as is
apparent from.the map, are the existence of the mean jet
axis and the recurrent location of an area of positive
vorticity advection (upper level divergence) over Cyprus.
Thus, traveling cyclones pass near Cyprus and enter the
Middle East. East of Cyprus, the position of the different
tracks appears to be related to the orientation and ampli-

tude of the mean trough and the position of the jet.

Redeve10pment of December Pattern in February
Analysis of the Figures 3,4 and 5 shows that the

distribution of cyclone tracks of February corresponded to
that of December, i.e. most of the storms affected only the
northern parts of the Middle East. Both months differ with
January when the principal track and upper flow pattern
shifted farther south. Monthly variations of the 500mb pat-
terns over the Middle East, which accounted for similar vari-
ations in surface cyclonic patterns, appear to be related to
hemisphere-wide readjustment of the circulation that occurred
during the study period. Inspection of the 500mb maps
revealed that the immediate reason for the monthly changes was
the flow condition upstream over the Atlantic Ocean. During
December, the flow over the ocean was meridional with a strong
north-south-oriented blocking high over the eastern Atlantic
or northern Europe. This condition resulted in a deep down-
stream trough over the central Mediterranean. Since this

trough also was oriented generally north-south, it steered

 

56
most of the cyclones northeastward toward the Black Sea and
the northern Caspian Sea. The same flow pattern redeveloped
over the Atlantic Ocean in February. During this period the
eastern Mediterranean and all the Middle East were dominated
by a ridge.

In January the conditions differed. The flow over
the Atlantic Ocean was zonal and strong. The Azores anti-
cyclone was farther south and over the central Atlantic
Ocean and the westerlies were divided into two branches
around 3OON. The southern branch contained two troughs, one
over northwest Africa and the other over the Arabian penin-
sula with a ridge between them. This bifurcation of the
westerlies brought the southern branch of the polar front jet
stream over Arabia and the Persian Gulf; this branch steered

the cyclones to the southern parts of the Middle East.

The Seasonal Displacement of the Flow Pattern

Figure eight portrays the southward shift of the
mean jet position and the eastward displacement of the long
wave trough axis from December to March. Between December
and March the westerly circumpolar wortex expanded. In
December only one jet was located in Eurasia extending from
Cyprus northeastward to the Caspian Sea, whereas in March,
as just described, the westerlies bifurcated over the Atlantic
Ocean as the southern branch passed through North Africa and
the southern parts of the Middle East, with the mean jet

extending from the Sinai Peninsula to the Persian Gulf. Thus,

 

 

 

57
this branch steered the cyclones toward the southern parts
of the Middle East.

The mean long wave trough axis of December was
located over the central Mediterranean with a ridge upstream
over the eastern Atlantic Ocean. In March, however, the up-
stream ridge over the eastern Atlantic was displaced to
southern Europe and North Africa, forcing the downstream
trough to establish over the eastern Mediterranean. This

trough which was very deep and extended to the subtropical

 

latitudes as a result, displaced the jet stream southward.

I could not determine whether the circulation conditions in
the North Atlantic play a determinate role in March, because
both zonal and meridional patterns were present. The Azores
high, however, showed a remarkable change from December to
March; in December its orientation was north-south over the
northeast Atlantic, whereas it changed to an east-west direc-
tion in March, and its eastern part extended over northwest

Africa.

Cyclogenesis in the Lee of the Southern Zagros
Table two shows the frequent cyclogenetic areas
during the period of study. In December the Adriatic Sea was
very active, whereas in March the lee of the southern Zagros
showed the highest activity. It seems that cyclogenesis to
the lee of the southern Zagros is related to the orographic
influence of this range. Since the altitude and orientation

of Zagros are similar to those of the Rocky MOuntains (9),

 

 

58
though on a smaller scale, their effects can be compared
(10).

The orographic influence of the Zagros weakens
atmospheric stability on the lee side. The air, while des-
cending the steep slope to the east of the Zagros, warms
adiabatically and the surface pressure falls; this pressure
causes low level convergence (11,12). Both the warming
process and the subsequent low level convergence are most

detectable near the jet stream; when an area of upper level

 

divergence ahead of a short wave trough is superimposed over
the developing cyclone, intensification of this lower level
cyclone occurs (12,13). Inspection of the maps revealed the
existence of the upper level jet maximum over the southern
Zagros during cyclogenetic conditions which caused the in-
tense adiabatic warming and subSequent cyclogenesis in this
part of Zagros.

Although most of the previous authors (6,14,15) have
referred to the generation of desert depressions on the lee
of the Atlas Mountains in March, during this study period no
depression was observed in this area. Analysis of the March
500mb charts showed that most of the time either a ridge or
the eastern part of the Azores High was located over the area,

suppressing cyclonic development.

Limitations of the'Study

 

During this investigation certain limitations were

recognized. One possible source of error was in the

 

59
procedure used to draw the cyclone tracks and the mean axes
of the associated jets and troughs which were visually deter-
mined as the areas of the highest concentration. It is
doubtful that this procedure, although subjective, affected
the accuracy of the results because the cyclone path concen-
trations were highly developed.

The 24-hour interval between individual weather
charts can be considered another limitation of the study,
since some lows could possibly develop and dissipate within
24 hours and thus not appear on these charts. Also, it is
possible that a low crossing a mountain barrier could fill
and another low could develop on the lee of the barrier within
24 hours and may be shown on the chart as one continuous cy-
clone. However, the long interval between the maps did not
affect the broad results of this study, since its objective
was to determine the spatial relationships between surface
tracks and upper flow patterns regardless of the origin of
the lows.

One may consider the length of the study period as a
limitation, inasmuch as the result may differ with those of a
longer period. Fortunately the gross resultant patterns
(such as the cyclone tracks) agreed with those of the pre-
vious studies (1,4,5,15), and any small discrepancy between
these results and those of a longer period would not affect
the overall validity of this study because it was concerned

with the relationship between surface tracks and upper flow

 

 

6O
patterns in general rather than in great detail. However,
to avoid even these minor limitations, some changes in the
research design of such future studies can be suggested:
1. The axes of the associated jets and trough should be drawn
according to the numerical values of the frequencies in each
grid square rather than rely on visual estimations.
2. Select daily syndptic weather charts with intervals of 12
hours rather than 24 hours.

3. Extend the time period of investigation.

 

 

CHAPTER VI - REFERENCES

l. Klein, W.H. 1957. Principal Tracks and Mean Frequen-
cies of Cyclones and Anticyclones in the Northern
Hemisphere, U.S. Weather Bureau, Res. Pap. No. 40.

 

 

2. Pedgley, D.E. 1974. Winter and Spring Precipitation at
Riyadh, Saudi Arabia, Meteor. Mag., Vol. 103,

 

p. 225-
3. Boucher, K. 1975. Global Climate. John Wiley & Sons,
New York.

 

4. Weickmann, L. 1922. Zumklima der Turkei, und Ergehisse
Dreijahiger Behachtungen, 1915-18. In Ganju, MQH.
1954. A ContributiOn to the Climatology of Iran.
Ph.D. Thesis, Clark Univ., worcester, Massachusetts.

5. Ganju, M.H. 1954. A Contribution to the Climatology of
Iran. Ph.D. Thesis, CIakaUniv , Wbrcester,
Hassachusetts.

6. Meteorological Office. 1962. 'Weather in the Mediterranean
Vol. 1,‘General‘MeteOrology, HMSO, London.

 

7. Levi, W}M. 1963. The Dry Winter of 1962/63, A Synoptic
Analysis. Israel Exploration J., Vol. 13, pp. 229-41.

8. Weickmann, L. 1960. Haufigkeitisverteilung und Zughahnan
von Depresionan in mitleren Osten. 'Meteor. Rand.
' Berlin, Vol. 13, No. 2, pp. 33-38.

 

9. Berkofsky, L. and Bertoni, E.A. 1955. Mean Topographic
Charts for the Entire Earth. Bullg'Amer.'MeteOr.‘SOc.
Vol. 36, pp. 350-54.

lO.Weickmann, L. 1961. ‘Some CharaCteriStiCS'of‘the‘Sub-
TroPical'Jet‘Stream;in‘the'Middle'EaSt'and'Adjacent
‘Re ions, Meteor.'Pub. Ser.*A., No.‘l, Minist. of‘
Roads, Meteor. Dept., Tehran, Iran.

ll.Palmer, E. and Newton, C.W. 1969. AtmosPheric Circulation
Systems, Academic Press, New York.

 

12.Harman, J.R. 1971. Tropospheric WaVes, Jet Streams, and
United'StateS'Weatner Patterns,‘Assoc. Amer. Geogr.
‘ Res. Pap. No. II, waShington, D.C.

 

 

61

 

62

13. Hovanec, R.D. and L.H. Horn. 1975. Static Stability and
300mb Isotach Field in the Colorado Cyclogenetic
Area. Mbn. Wea. Rev., Vol. 103, pp. 628-38.

 

l4. Perrin de Brichambaut and wallen, C.C. 1963. A Study of
Agroclimatology in Semi-Arid and Arid Zones of the
Near East, WMO, Tech. Note No. 56.

 

15. Pedgley, D.E. 1972. "Desert Depressions Over North East
Africa", Meteo. Mag., Vol. 101, pp. 228-45.

 

 

 

CHAPTER VII

SUMMARY AND CONCLUSION

The purpose of this study was to relate the spatial
distribution of surface cyclone tracks to the position of
mean long wave trough and polar front jet axes in the Middle
East, particularly Iran. Data were obtained from 12 GMT
surface and 500mb weather charts of the orthern emisphere
for the months December through March, 1964-67. Mean cyclone
tracks were determined by plotting the paths of individual
traveling depressions and then visually generalizing them in-
to monthly and seasonal tracks for both the Middle East and
Iran. The mean position of the upper level long wave trough
axes and polar front jet axes were determined for each monthly
track separately.

The results of this study strongly suggested that
the spatial distribution and orientation of the surface cyclone
tracks were best explained by the upper level circulation
rather than by terrain or surface pressure patterns; the
position of cyclone tracks in almost all cases was north of
the mean position of polar front jet stream. In contrast to
that reported in other studies, I found evidence that the

mountains did not block the movement of cyclones, and only

63

 

64
the Zagros Mountains caused lee cyclogenesis (when the upper
jet was over the Persiaanulf).

The invasion of cyclones into the Middle East dur-
ing the winter began with the eastward displacement of the
long wave trough axis in the Mediterranean Sea that is, when
the trough axis was over the central Mediterranean (December)
only the northern parts of the Middle East were affected by
cyclones, but when the trough axis shifted to the eastern
Mediterranean (March) all the Middle East fell under the in-
fluence of the cyclones. Concurrent with the eastward shift
of the Mediterranean trough axis, the polar front jet also
was displaced southward, producing a southward shift of the
surface tracks as winter progressed. This displacement of the
upper level features was probably related to circulation
changes occurring over the Atlantic Ocean. Almost all of the
cyclones affecting the Middle East originated in the Medi-
terranean Sea except in late winter when some cyclones develop-
ed on the lee of the southern Zagros Mountains in Iran.

The results of this study might be influenced by
such limitations as the time interval of the synoptic maps,
the visual method used to determine the cyclone tracks or
flow patterns, and the brevity of the study period. These
limitations are not regarded as serious because the study was
concerned with determining the spatial relationship between
the distribution of cyclone tracks and the upper flow pattern
rather than the long term climatologyof either the upper

level features or the surface cyclone tracks. However, it is

 

 

65

suggested that in future studies synoptic weather maps with
twelve rather than twenty-four hour intervals be used over
a longer time period and that the cyclone tracks and their
associated jet and trough axes be determined numerically
rather than visually.

This study raised several questions which need to be
studied in more detail in the future.
1. Although the upper level circulation appears to play the
major role in determining the spatial distribution of cyclone
tracks, a quantitative study is necessary to determine pre-
cisely the degree of control exerted by the upper circulation
or any other possible factors, such as terrain.
2. The eastward shift in the position of the Mediterranean
long wave trough from.December to Marsh should be analyzed
further. Is this related to the flow pattern over the North
Atlantic Ocean or are there other factors? Is it seasonally
forced? If the flow pattern of the North Atlantic is the
control (as the results of this study suggested), precisely
which aspect of this flow is most important? What aspects of
this circulation are most probable each winter?
3. Do the Zagros Mountains impose any dynamic influence, by
creating mountain waves, on the northeastward movement 6f the

cyclones over Iran?

 

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