Distribution of the Variability of Seasonal Character of in the World
Climate
Yoshinari AMBE
INTRODUCTION
Clima七e at any point on七he earth is considered 七〇 be an accumulation of year clima七es． The year clima七e is exl）ressed as an annual march of seasons， and， 七hough 七he main I）rocess of 七he seasonal march of climate is almos七 similar in every year， minor charac七eristics of seasons fluc七ua七e yearly．
For example， in Tokyo， 七here are two rainy seasons in mos七years before and af七er s㎜mer called， Baiu，， and
S hurin，， respec七ively， and in some years one or bo七h of 七hese rainy seasons do no七 appear significantly． The main sequence of seasons spring−一一summer−一一au加mn−一一win七ertt is of course re七ained．
の
Such a varia七ion of 七he「七ype of annual progress of season is a reflec七ion of 七he secular variation of atmos 一一 pheric circula七ion． In some region， like India， where a dry season and a rainy season°by monsoon aI）pear cons−tan七ly every year，七he seasonal process of clima七e is relatively stable．
On the other hεmd， in such a region as 七he cen七ral I）art of七he Uhi七ed S七ate， where 七he 七racks of lows ahd highs show a complicated figure，七he 七ype of seasonali七y is very variable．
The dis七ribu七ion of 七he varia bili七y of the 七ype of seasonal march，七herefore， represen七s 七he regional charac七er of world clima七e as well as of the recen七 clima七ic varia＿
tions．
While u．⊥ere have been some s七udies on 七he regionali七y of 七he secular varia七ion of 七he −annual change of any one clima七ic elemen七 such as air 七empera七ure， precipi七ation etc． （for examples；Wall6n l955， Dingle l955）， those on 七he variation of annual se（luence of seasons as a syn七hesis
■
of these climaもic elemen七s are scarcely found．
The charac七er of any season is bes七 represen七ed by com＿
posi七‡ng each clima七ic elemen七 such as wea七her I）a七七ern，
wind， air 七empera七ure， precipi七a七ion e七c． The hydrome七e＿
orological condi七ion can also be used as one of 七he adequa＿
七e indica七〇rs of syn七hesized character of a season． In the former s七udies （Ambe l966）， 七he au七hor discussed 七he secular varia七ions of aridi七ies of 七he world， based on 七he variabili七y of 七he number of humid and dry mon七h in −bhe year． Using 七he da七a calcula七ed in七hese s七udies，七he geogral）hical dis七ribu−ti on of 七he varia「bili七y of seasonal charac七er of clima七e of 七he world is studied in 七his paper．
TYPES OF SEASONALITY OF CLIMATE
Dry mon七hs and humid mon七hs for abou七 600 s七a七ions in 七he world， excepting regions north of 500N，七he central part of Asian con七inent and the islands in Sou七h Eas七 Asia，
are dis七inguished for every mon七h from 1931 − 1960， af七er the cri七erion whe七her mon七hly precipi七a七ion is larger or smaller 七han monthly values corresponding 七〇 七he values of evapora七ion．
The amoun七 〇f evaporation is es七ima七ed from o−bher climatological da七a．
The annual process of season in each year are clas＿
sified in七〇 七he following 七ypes according 七〇 七he mode of occurrence of humid mon七h．
1）ry year 七ype （ O ） ．・… t・
Win七er七ype Spring type Summer七ype
C・mp・si七e七ype Win七er−Spring Win七er−Summer Win七er＿Au七umn
（w）＿＿．
（ F ） ．．．。．．．
（S）。。。．．．．
七ype 七ype 七ype
Another 七ype （ D ）
（WF）
（ws）
（WH）
e七c．
● ■ o ● ● ● ● ●
No humid mon七h appeεしrs 七hrough七he year．
Humid mon七hs apPear mainly
in ・w・in七er．
Humid mon七hs al）pear mainly ln sp「lng・
レ
Humid mon七h apPear mainly in au七umn．
No sI）ecific seasonali一七y can be found七hrough 七he year．
Table l．
Bombay
（India）
Examples of the secular se quences seasonal charac七er of climate．
Ha七七eras
（U．S。A．）
コ
Sao Paulo Cloncurry （Brazil） （Aus七ralia）
of the types of
Mi lano Kano Cairo
（工七aly） （Nigeria） （U． Aral））
DIS TRIBUT工ON OF THE PREVIAIL工NG TYPE OF S EAS ONAL I TY
The fre quency of occurrence of もhe types of seasonali七y of climate during l931 − 1960 is calcula七ed a七 every s七a七ion
of 七he ・w・orld．
The dis七ribu七ion of七he most prevailing （fre quency of occurrence is larger than 50％） もype is i llus七ra七ed in』Fig． 1．
Eleven kinds of regions are dis七inguished in 七he world．
Dry七ype， summer 七yl）e， winter type region and七he
regions where not any one 七ype predomina七es are di s七ribu七ed wide ly， while 七he coml）osi七e type regions are rather limited to the eqロaもorial zone of Sou七h America， small areas of w est coas七 〇f Eq｝1a七〇rial Africa and七he coas七 〇f the Bay of Bengal．
Regions where the summer type or winter七ype predomina土e show a zonal pa七七ern reflecting 七he seasonal shifも of the frontal zones・ For examples，七he winter 七ype in 七he eas七 p昂r七 〇fUnited S七ate， Mediterranean region an《1七he south
・・ast・f Au・七ralia・・rresp・nd t・七h・p・・iti・n・・f th・p・lar
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fron七in win七er． The s㎜mer type regions at七he bo七h sides of e（lua七〇rial zone in Africa， nor七hern coas七 〇f Aus七ralia and Cen七ral America coincide −bo 七he posi七ions of 七he in七er＿
七ropical fron七in summer． The summer七ype in India and in Sou七heas七 Asia are related七〇 七he summer monsoon．
The region Vi七h no pre do minan七 七yl）e of seasonali七y
consis七s of more もhan 七hree 七ypes， having very uns七able con＿
di七ions of clima一七e with high variabili七y．
For ins七ance， Milano 層belongs to 七his kind of region as shown in Table l， having 七he following 七ypes：もype−D （30％），
七ype−W （16％），『むype＿H （16％），七ype＿F （13％）， 七ype−WH （lO％o），
七ype−WF （7％） and 七ype−［FH （7％）．
This kind of a region are found widely on the eas七 side of 七he dry 七ype regions in bo七h．North and Sou七h America，
while in Africa i七 does noも neighbo U r 七he arid region。
The larger part of Europe， excep七ing 七he winもer もype regions in 一むhe Medi七erranean， also belongs to 七his 七ype of a−region．
The region with no specific seasonal charac七er are found only in 七he limi七ed area of islands in 七he Eas七ern Asia．
STABIL昌ITY OF SEASONAL CHARACTER EACH CONTINENT OF THE WORLD
OF CLIMATE IN
To describe 七he s七abili−ty of seasonal charac七er， or 七he secular variabili七y of clima七e，七he con七inuity of −bhe occur＿
rence of 七he 七ype of season is calculated as follows：
Σ（Cl・i＋1一αブ）
v；
n−1
V n ai
● ● ● ● ■ ● o ● ● ■ ● ・
● ● ● ■ ● ● o ● ■ ・ ●
● ● ● ● o ● o ● ■ ● ● ●
ai＋1−ai＝1 ・
＝0
−つ
o ● o ● ■ ● o ● ■ ・ ・
■ ● ■ ■ ● ■ ● ● ● ●
の
variabili七y．
number of years・
七ype of seasonali七y in 七he i−th year．
when 七he 七ype of the 七wo
con七inued years are differen七．
when 一しhe 七ype s of the two continued years are 七he same・
when 七he 七ype s of 七he 七wo
COn七inUed years are Similar bu七 no七 exac七ly the same； for an example， summer一七ype − Sum−
me r−au加mn一七ype．
When all of 七he もypes are the same during 七he period，
七his value of the variabili七y is na七urally zero， and if none of 土he 七wo con七inued years have the same type 七he variabili七y becomes maximum value l． The dis七ribu七ion of 七he value in each con七inen七 is shown in Fig． 2 （a−f）．
Nor七h America
The wes七ern half of 七he con七inen七 belongs 七〇 七he dry I）revailing region， 七he cen七ral par七 and 七he Florida Peninsula are uns七able regions， and 七he eas七ern par−b of 七he con七inent is a win七er type region． The sou七hern もwo 七hird of Cen七ral America is summer or summer−autumn七ype region． The varia−
bili七y is high in the eas七ern half of the con七inent and七he nor七hern par七 〇f 七he dry 七ype region． The nor七heastern par七
〇f 七he con七inen七 has a very stable 七ype of 七he annual march of seasons． In Central America， 七he variabili七y is higher in 七he coas七al area 七han in 七he inland area．
South America
The I）attern of the types of 七he seasonali七y is very com＿
1）lica七ed on this con七inen七． Dry type region lies in 七he coas七al par七 〇f Peru and Chile and the sou七hern part of Argen七ina． The drainage basin of 七he Amazon belongs largely 七〇七he win七er．．summer−au七㎜n type and winter七ype has a ra七her low varia『bili七y． The major par七 〇f Argentina， southern half of Chi le and 七he area north of 七he e（lua七〇r have high varia＿
bility， belonging to 七he region withou七 a prevailing 七ype．
Aus七ralia
Almost all of 一七he con七inent， a dry 七yl）e and high stabili七y predominate． The variabili七y is higher in 七he coastal areas
of もhe eas七 and nor七hwes七ern par七 〇f 七he con七inen t．
Both the win七er 七yI）e region in 七he sou七hwest and七he summer 七ype region in the nor七hern part have ra七her low vari 一一 abili七y．
The main par七 〇f Europe belongs 七〇 七he region wi七hou七 a predominaもing 七ype． Sou七heast Europe， par七s of France and Spain have a win七er 『しype and a small area of dry 七ype lies in Greece． The variabili七y is high as a whole compared七〇 the o七her conもinen七s of 七he world， showing a decrease toward north．
Africa
In Africa a zonal pa七七ern of もhe types of seasonali七y
，
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Fig．2− ． Disもribu』七ion of the
of clima七e variabili七y of seasonal character
are found，七ha七 is， from sou七h to nor七h； dry 七ype， summer 七ype， wiもhou七 a predomina七ing type， summer 七ype， dry 七ype and win七er 七ype in 七he medit（ミrranean coas七 are no七ed． The region wi七h high variabi li ty occupies a large part of cen七ral and southern Africa．
The nor七hern arid region is very s七a¶ble and 七he neigh＿
bouring region wi七h a s㎜er七ype also has a lower varia−
bili七y compared 七〇 七ha−t of 七he area surrounding 七he sou七hern arid region。
Asia
As 七〇 Asia， only sou七hwes七 and eas七 Asia are considered，
the main inland par七 〇f 七he c ontinen七 and 七he islands in 七he Wes七 Pacific Ocean are excluded because of 七he incomple七eness
of da七a． Avas七 dry七ype region lies in wes七Asia where 七he variabili七y is nearly zero， eas七 coas七al region of 土he con七i−
nen七belongs 七〇 summer 七ype and I）ar七ly七〇 the no prevailing 七ype region， showing a ra七her high s七abili七y． In 七he south＿
wes七，七〇七he inland par七〇f工ndia，七he s㎜mer七ype is very stable， reflec七ing 七he regular occurrence of monsoons．
In west Pakistan， where −bhe dry type and the summer types are adjacen七，七he variabili七y is very high．
SUMIMARY AND C ONC LUS I ONS
The distribution pat−tern of the types of seasonal charac＿
七・r・fw・rld・1ima七・and its s七ability ar・illu，七ra七。d．
Th・r・gi・n with high v・riability ar・f・und in Eur・p・，
cen七ral and・・u七h・a・七part・・f Uni七・d S七a七es，main par七。。f Argen七ina and Venezue la， west coas七 〇f Aus七ralia and some par七・・f cen七ral Afri・a． The ev・ry arid regi・n。 ar。 in七h。
n・rthw・・t・rn part・f Uni七・d S七a七es， Ama・・nian ba・in， n。r七h。rn par七・fエndia and・・m・ar・a・n・ar七he・・uth・rn b・undary。f n・rth・rn arid r・gi・n in Afri・a having v・ry・七abl・七yp・。f七he
seasonali七y of clima一もe．
。f七漉翻gm畿臨9と「；。盤翻y°儲㍊㌢｝｛毛e呈とen・y
P・in七・d・ut七ha七七h・七ran・i七i・nal・・n・wh・r・humid and dry years appear al−terna七ely has very variable type of seasonali一 七y in South America， in 七he eastern half of Uni七ed S−bates and in India， whi le 七he transi七ional zones on もhe o七her con七i＿
n・nt・hav・ra七h・r・tabl・七ypes、．
By combining 七hese figures a more detailed clima七ic clas−
sifica七ion map will be accomplished．
AC KNOWLEDGEMENT
The au七hor wishes 七〇 express his sincere thanks もo
Professor Taiji Yazawa for his many advices and sugges七ions．
REFERENC ES
Ambe， Y． （1966）；Secular varia七ions of arid regions in 七he
world。 Japan． Jour． Geol． Geogr． （in prin七）
Am be， Y。 （1966）；Regionalities in七he variations of aridity
in七he world．
Japan．Jour． Geol． Geogr． （in prin七）
Dingle， A．N． （1955）；Pa七もerns of changes of precipi七a七ion
in the Uni七ed Sta七es．
Jour． Me七．， 12， 220 − 225．
Wall（≦n， C．C。 （1955）； Some charac七erisl）ics of I）recipi七a七ion
in MexicO．
Geograf． Ann．， 37， 51 − 85．
