Indian Journal of Radio & Space PhysicsVol. 21,April 1992,pp. 119-122

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Linkage between north pole winter temperatures and summer monsoonrainfall over India ' - r:

.•K Indira &' B K MukherjeeIndian Institute of Tropical Meteorology, Pune 411 008 /

Received 18 April 1991; revised received 3 September 1991

An investigationof the possiblelinkageof the north pole temperatures at 30mbar (lowerstratosphere) for26 pre-winters (November, 1955-1980),winters (December, 1955-1980;and January, 1956-1981),andsprings (March, 1956-1981)with rainfall activity over India for the following 26 summer monsoons(June-September, 1956-1981)has been made. The study suggests an association of the mean warm/coldanomalies in the north pole temperatures at the lower stratosphere during pre-winter, winter and spring withthe mean positive/negative percentage departures of rainfall over India during the following summermonsoon. The relationships betweenanomalies in the north pole temperatures during November and Marchand the rainfall activityduring the followingsummermonsoons over India are, however,significantand maybe responsiblefor 20and 10%variabilitiesin monsoon rainfall.On most of the occasionsthe wet/dry summermonsoons (percentage departures of rainfall being more than ± 10) in India are preceded by warm/coldanomalies in the north pole winter temperatures at the lower stratosphere during winter. It seemsthat warmand cold anomalies in the north pole winter temperatures at the lower stratosphere are inter-locked with theoscillations of 500mbar ridge during the following April over the Indian tropics in some manner which. inturn, influence the rainfall activity over India during the following summer monsoon. \ '~h" (~I .

1 IntroductionUnderstanding of coupling mechanism between

the middle atmosphere and the tropospheric events isone of the prime motivations for enhancement ofknowledge of the dynamics of the middleatmosphere. Recently McGuirk and Douglas! havereported severe weather anomalies over the UnitedStates that are associated with the major suddenstratospheric warming (SSW) events. It has also beenreported that the stratospheric disturbances areaccompanied by tropospheric blocking eventsbetween 85 and 95% of the tirne-. The features ofinteraction between stratosphere and troposphereduring SSW events at high latitudes have beendiscussed at length by several workers? -7.

Mukherjee et al+? have suggested an association ofthe phases of the low latitude quasi-biennialoscillation (QBO) with variability of the summermonsoon rainfall over India. Using a short period (6years) temperature and wind data, they have alsomade an effort to link inter-annual variability of thestratospheric warming events over high latitudeswith the variability of following summer monsoonrainfall over India 10. The objective of the presentstudy is to examine the anomalies in the north poletemperatures at the lower stratosphere (30 mbar)during pre-winter (November), winter (Decemberand January) and spring (March), and their linkage

with the forthcoming summer monsoon rainfallactivity (June-September) over India.

2 DataSince the present investigation deals with the

relationship of the lower stratospheric parameterswith the tropospheric events, the monthly meantemperatures at only 30 mbar which represents lowerstratosphere for the north pole are considered.Mukherjee et al,? and Labitzke and van Loonll alsoconsidered the same level (30 mbar) to representlower stratosphere to find out influence of QBO onIndian summer rainfall and of solar cycle on thestratospheric temperature, respectively. The dataconsidered in the present study consist of 26 northpole temperatures for pre-winter (November,1955-1980), for winter (December, 1955-1980; andJanuary, 1956-1981) and for spring (March,1956-1981) and of rainfall over India during thefollowing 26 summer monsoon seasons (June-September, 1956-1981). Analysis of thestratospheric temperatures at the northernhemisphere is being carried out regularly at the FreeUniversity of Berlin. The monthly mean 30 mbartemperature data discussed in the paper are exactlyfor the north pole, thus representing only one singlepoint. They are, however, derived from the dailyanalysis since 1964. The data related to the penod

120 INDIAN J RADIO & SPACE PHYS. APRIL Il)l)~

prior to that have been extracted from the monthlyanalysis. There is no upper air station located exactlyover the north pole. The mean temperatures forNovember and March are considered separately andthe mean temperatures for December and January,which represent the temperature field at the northpole during winter are considered together. Thedeviations of the pre-winter (November), winter(December and January) and spring (March) fromtheir 26-year long-term mean are then derived foreach year. The percentage departures of the summermonsoon rainfall (June-September) for entire India(26 years from 1956-1981) are also worked out.

The monthly mean north pole temperatures areobtained from NaujokatP.

3 Results and discussionExamination of the north pole temperatures at 30

mbar during winter suggested an existence of a littlerelationship of warm/cold anomalies in thestratospheric polar temperatures with the rainfallactivity over India during the following summermonsoon, the correlation coefficient being +0.18.But, it would be noteworthy to mention here that thepositive anomalies in the north pole temperatureswere noticed during December and January for 10winters [i.e. 1958-1959, 1959-1960, 1960-1961,1965-1966, 1967-1968, 1968-1969, 1969-1970,1970-1971,1974-1975, 1976-1977]. The average ofthese positive anomalies was + 6.T'C, while theaverage of the percentage departures of the rainfallfor the following 10 summer monsoons over India(i.e. 1959,1960,1961,1966,1968,1969,1970,1971,1975, 1977) was + 3.6. The negative anomalies in thenorth pole temperatures, on the other hand, werenoticed during the 16 winters [i.e. 1955-1956,1956-1957, 1957-1958, 1961-1962, 1962-1963,1963-1964, 1964-1965, 1966-1967, 1971-1972,1972-1973. 1973-1974, 1975-1976, 1977-1978,1978-1979, 1979-1980, 1980-1981]. The average ofthese negative anomalies for these 16 years was- 4.1°C and the average of the percentage departuresof rainfall for the following 16summer monsoons was-0.9. The average of the warm/cold anomalies forNovember (pre-winter) and March (spring) and thepercentage departures of the following summermonsoon rainfall for 26 years are also worked out.Similar type of result as noticed for winter can also benoticed for pre-winter and for spring. But therelationship between the anomalies in the north poletemperature at 30 mbar during November and Marchwith the percentage departures of rain fall during thefollowing summer monsoon is more meaningful. Thecorrelation coefficient worked out for November

stratospheric temperatures and the followingsummer monsoon rainfall is +0.47, and that forMarch stratospheric temperatures and the followingsummer monsoon rainfall is +0.33. The averagewarm anomaly noticed in 13 cases was + 2.8°C andthe average cold anomaly noticed in another 13caseswas - 2.8OCduring November, while the respectivepercentage departures in rainfall were + 3.9 and- 2.3, respectively. In March, the average warmanomaly was + 5.6°C in 13cases and cold anomalywas - 4.6°C in another 13cases, while the percentagedepartures of rainfall were, respectively, + 2.8 and-1.8.

The rainfall data for the 26 summers are thenstratified into two groups--one with rainfalldepartures more than + 10% (wet years) and theother with the rainfall departures less than - 10%(dry years). There are 9 such years (1959,1961, 1965,1966, 1970, 1972, 1975, 1978 and 1979) when suchcontrasting rainfall was reported during the span of26 years considered in this study. The warm/coldanomalies in the north pole temperatures at 30 mbarduring the 9 preceding winter years, namely,1958-1959, 1960-1961, 1964-1965, 1965-1966,1969-1970, 1971-1972, 1974-1975, 1977-1978 and1978-1979 are then examined and shown in Table I.Table I shows that out of5 occasions of wet monsoonyears [i.e. 1959(+13.8%),1961 (+12.4 %),1970(+ 10.6%), 1975(+ 18.9%) and 1978 (+ 11.9%)], on 4occasions good monsoon was preceded by warmanomalies in the north pole winter temperatures at 30mbar. Only on one occasion (1978) the good rainfallactivity was preceded by the cold anomaly, instead ofexpected warm anomaly, indicating that 80% of thewet monsoon years during 1956-1981 was precededbv warm anomalies in polar lower stratosphere.Scrutiny of the data for the monthly mean north poletemperatures at 30 mbar suggests that the mean northpole temperature during December 1977 wasabnormally cold and inconsistent with the trend ofthe monthly mean temperatures for November 1977and January 1978. If the mean temperature forDecember 1977 is worked out from the linearinterpolation of the monthly mean temperatures ofNovember 1977 and January 1978, a warm anomalyin the north pole at 30 mbar during winter could beascertained. The mean north pole winter temperatureduring 1977-1978 would then show a warm anomalyof + 1.8T in place of the cold anomaly of - 2.T'C.asshown in Table I.

Again it can be noticed from Table I that out of 4occasions of dry monsoon years. [i.c. 1965( - 15.0%),1966(- 11.1'1'0),1972(- 17.8%) and 1979(- 15.4%)],on 3 occasions weak monsoon activity was preceded

)

INOIRA& MUKHERJEE: UNKI\(;r OF NORTH POLE WINTER TEMP. WITH SUMMER MONSOON RAINFALL 121

Table I-Mean warm and cold anomalies in polar temperatures at 30 mbar for winter. location of 500 mbar ridge at 75°E in April andpercentage departures of summer monsoon rainfall over India

Winter years(December and

January)

Warm ( + )/cold( - )anomaly in polartemperatures at30 mbar during

winter CC)+ 2.3+ 7.8- 3.7+ 5.3+ 11.8- 5.7+ 3.3- 2.7- 1.7

1958-19591960-1%11964-19651965-19661969-19701971-19721974-19751977-19781978-1979

Location ofridge at

500 mbaralong 75"E

in April

16.0oN15.0oN14.0oNI3.5"N15.8°N11.0oN17.5°N14.0oN12.5°N

Percentagedeparturesof rainfallover India

(June-September)

+ 13.8+ 12.4-15.0- 11.1+ 10.6-17.8+ 18.9+ 11.9- 15.4

Summeryears

195919611965196619701972197519781979

by cold anomalies in the north pole wintertemperatures at 30 mbar. On one occasion the warmanomaly, instead of expected cold anomaly, wasnoticed in the pole during the winter of 1965-1966.The above result could lead to the conclusion that75% of the dry monsoon years during 1956-1981 waspreceded by cold anomalies in the north pole wintertemperature at 30 mbar. It may not be out of contextto mention here that the mean temperature forJanuary 1966was cooler by as much as 4.4°C than the26-year mean temperature for January, showing acold anomaly existing in the month of January.

Similar type of analysis has been done for themonths of November and March. During November,80% of occasions (4 out of 5 years) of warm anomalieswas associated with more than 10% ofexcess rainfalland 75% of occasions (3 out of 4 years)of cold anomalieswas associated with more than \0% of deficientrainfall during the following summer monsoons. Butthe relationship of warm/cold anomalies duringMarch with the rainfall activity during the followingsummer monsoon is not, however, encouraging.

Shukla and Mooley!", on the basis of their analysisof 46 years' data, have made an attempt to correlatethe location of the 500 mbar ridge at 75°E over tropicsduring April with the following summer monsoonrainfall activities over India. In order to examine theposition of the ridge at 500 mbar at 75°E during Aprilpreceding the 9 occasions of contrasting monsoonrainfall (wet and dry years), the anomalies in thewinter polar temperatures at 30 mbar and thelocations of the ridge at 500 mbar at 75°E for these 9years are also shown in Table I. During these 9occasions, the ridge position has oscillated betweenlIoN and 17SN. On 5 occasions of excess rainfall(wet years), i.e. in 1959, 1961, 1970, 1975and 1978, theridge oscillated between l4.0oN and 17-5"N.But on 4

occasions of deficient rainfall (dry years), i.e. in 1965,1966, 1972 and 1979, it oscillated between II ONand14°N. The above feature suggests an associationbetween north/southward shift of the ridge at 500mbar at 75"E during April and the following wet/drysummer monsoon years. Since warm/cold anomaliesin the winter polar temperatures at 30 mbar weremostly linked with the excess/deficient rainfall in thefollowing summer monsoon years, it may not befarfetched to conceive that the weakening/strengthening of the grip of the stratospheric polarvortex during the winter would be conducive to thenorthward/southward shift of the ridge at 500 mbarover Indian tropics during the following April,which, in turn, could influence the performance of thefollowing summer monsoon (June-September) overIndia. Wallace and Chang':' have shown ateleconnection of the southern oscillation withintensity of the stratospheric polar vortex. They haveput forward an impressive evidence envisaging thelinkage between 'high/dry' winters and winters withstrong polar vortex, and between'Iow/wet winterswith weak polar vortex. It has been hinted I 0.15 thatthe early breaking of the stratospheric polar vortexcould be helpful to the better performance of thefollowing summer monsoon over India. Significantweather anomalies over the United States werereported in association with the January andFebruary SSW events'. A teleconnection ofinter-annual variability in the tropical wind field at200 mbar with the southern oscillation has also beensuggested!". Two plots of warm/cold anomalies inthe north pole at 30 mbar during pre-winter andspring for the block 1955-1980 and 1956-1981,respectively, and the percentage departures ofrainfall during the following summer monsoon overIndia have also been included (Figs I and 2). The

122 I]\;()L\]\; J RADIO 8:.SPNT PHYS. APRIL 1992

24 24 u 24 24 .'-!- TEMPERATURE ANOMALY. NOV

o._ TEMPERATURE ANOMALY, MARCH n:a: ~~ :l o--~ PERCENTAGE DEPARTURE6 OF '"0---<)PERCENTAGE DEPARTURE OF UJ •..~ RAINFALL (JUNE - SEP)

•.. ..• RAINFAll (JUNE - SEP) 16 a:~ 16 16 a: ... 16 ..•zz ..• :c ~0 R 0<l a: Q.

rr a. ... "u. ~ 0 I I !!::0

'" 8 9 , ~w ~ a:ex ..• :::> , ..•:::> •..

I ~r ~ II:c; ~ : 'I z<l0

..•n.0 <I '" 0 I I'w 0

" I '"w " ':l0 ..•e" •.. 0:" 0 z -e u7 -8 -8 u '" -8 ....•..w --- UU :;.- IX +rr '"w

Q.

:::Eo,-16 ~ -16 ~-16 -16

~-20 -20 -20 -20

1955 59 63 67 71 75 79 81 1955 59 63 67 71 75 79 111YEAR YEAR

Fig. l=-Warm/cold anomalies in the north pole temperatures at30 mbar during pre-winter (November) and departures of rainfallduring the following summer monsoon (June-September) over

India

values of correlation coefficients are, respectively,+ 0.47 (significant at less than 5% level) in Novemberand +0.33 (significant at less than 10% level) inMarch. The above feature suggests that about 20 and10% variabilities in the summer monsoon rainfallover India could be attributed to the warm/coldanomalies at 30 mbar north pole temperatures duringthe preceding November and March, respectively.

4 ConclusionSummer monsoon rainfall affecting Indian

subcontinent and the other Asian region is theproduct of the global and local anomaly in thecirculation features. Moreover, ifthere is, at all, anyinfluence of the middle atmospheric parameters onthe rainfall activity, it could not be expected to be aspectacular one. It has been shown earlier":" thatabout 15% of rainfall variability could be linked withphases of the low-latitude QBO in the zonal wind.Besides, the present investigation has suggested thatabout 20 and 10% variabilities in the rainfall duringthe following summer monsoon could be associatedwith the anomalies in the north pole temperatures at30 mbar during the preceding November and March.Also the anomalies in the 30 mbar north poletemperatures during the preceding winter (Decemberand January) may be considered as an indicator ofexcess/deficient rainfall activity noticed during thefollowing summer monsoon over India. The resultsof the earlier study? and the present study haveindicated that the dynamical parameters of the lower

Fig. 2-Same as Fig. I but for March

stratosphere of the tropics as well as of the north polemay have some bearing towards judging theperformance of the rainfall activities over India. Withthe availability of more stratospheric data, thelinkage between the middle atmospheric parametersand the monsoon rainfall would become furtherclear.

AcknowledgementThe authors express their sincere gratitude to Dr

Barbara Naujokat of Free University of Berlin forhaving kindly made available to them the 30 mbarpolar temperature data.

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