THE TIBETAN PLATEAU AND THE INDIAN MONSOON

TO WHAT EXTENT DOES THE TIBETAN

PLATEAU INFLUENCE THE SOUTHWEST

MONSOON?

SOME 130 YEARS AGO, SIR H.F. BLANFORD,

CHIEF REPORTER OF THE NEWLY

ESTABLISHED INDIA METEOROLOGICAL

DEPARTMENT (IMD) , NOTICED THAT MORE

HIMALAYAN SNOW COVER DURING THE

PRECEDING WINTER PRESAGED A POOR

MONSOON. ON THAT BASIS, IMD BEGAN

ISSUING THE FIRST MONSOON FORECASTS

FROM 1882. BUT MONSOON PREDICTION

WAS NOT SO EASILY DONE AND REMAINS A

DIFFICULT PROBLEM TO THIS DAY.

YEARS LATER, THE ESTABLISHED VIEW

CAME TO BE THAT THE HIMALAYAS ACTED

ON THE MONSOON IN TWO WAYS. THE

TIBETAN  PLATEAU, HEATED UP DURING

SUMMER AND THEREBY ESTABLISHED AN

ATMOSPHERIC CIRCULATION THAT WAS

CONDUCIOVE FOR THE MONSOON.

THE VAST MOUNTAINN RANGE ALSO ACTED

AS A TALL BARRIER, PREVENTING COLD,

DRY AIR IN THE NORTHERN LATITUDES

FROM ENTERING THE SUBCONTINENT AND

SUBDUING THE WARM, MOISTURE LADEN

WINDS FROM THE OCEANS THAT DRIVE

THE MONSOON.

IN A PAPER PUBLISHED IN THE JOURNAL

NATURE IN 2010, WILLIAM BOOS A

DNZHIMING KUANG OF HARVARD

UNIVERSITY IN THE U.S ARGUED THAT THE

HIMALAYAS' ROLE AS A BARRIER WAS THE

CRUCIAL FACTOR FOR THE MONSOON.

USING A GENERAL CIRCULATION MODEL

THAT SIMULATED WHAT HAPPENED IN THE

ATMOSPHERE, THEY FOUND THAT EVEN IF

THE TIBETAN PLATEAU DID NOT EXIST,

THE MONSOON WOULD BE UNAFFECTED

PROVIDED THE HIMALAYAS AND

ADJACENT MOUNTAIN RANGES WERE

THERE TO PREVENT INTRUSION OF

NORTHERN AIR.

HOWEVER, BALAJI RAJAGOPALAN AND

PETER MOLNAR OF THE UNIVERSITY OF

COLORADO AT BOULDER IN THE U.S. HAVE

TAKEN THE VIEW THAT THE TIBETAN

PLATEAU SHOULD NOT BE WRITTEN OFF

SO EASILY. THE HEATING OF THE PLATEAU

CORRELATED WITH MONSOON RAINFALL

BUT ONLY DURING THE EARLY AND LATE

PARTS OF THE SEASON, THEY OBSERVED IN

A PAPER PUBLISHED RECENTLY IN

JOURNAL OF GEOPHYSICAL RESEARCH:

ATMOSPHERES.

AS THE VAST TIBETAN PLATEAU, HIGH UP

IN THE MOUNTAINS, WARMED DURING THE

SUMMER ABOVE, WHICH THEN ROSE AND

CREATED AN AREA OF LOW PRESSURE,

EXPLAINED DR. RAJAGOPALAN. THAT BELT

OF LOW PRESSURE SUCKED IN MOISTURE

FROM THE OCEANS, THUS INITIATING THE

MONSOON.

THE HEATING OF THE TIBETAN PLATEAU

CORRELATED WELL WITH RAINFALL OVER

INDIA FROM MAY 20 TO JUNE 15 WHEN THE

MONSOON WAS SETTING IN. BUT THEN THE

CORRELATION DISAPPEARED ONLY TO

REAPPEAR AGAIN FOR RAINFALL BETWEEN

SEPTEMBER 1 AND OCTOBER 15 WHEN THE

MONSOON WAS TAILING OFF. "WE DON'T

HAVE A VERY GOOD ANSWER YET" ABOUT

HOW THE TIBETAN PLATEAU COULD BE

INFLUENCING THE LATE STAGE OF THE

MONSOON, HE SAID.

IN AN EARLIER  PAPER, HE AND DR.

MOLNAR HAD NOTED THAT SWINGS IN THE

TEMPERATURE OF THE TROPICAL PACIFIC

OCEAN'S SURFACE WATERS NEAR THE

INTERNATIONAL DATELINE, KNOWN AS EL

NINO-SOUTHERN OSCILLATION(ENSO) ,

ALSO STRONGLY INFLUENCED RAINFALL

OVER CENTRAL INDIA AND ITS WEST COAST

DURING THE EARLY AND LATE PHASES OF

THE MONSOON.

WITH THE TIBETAN HEATING AND ENSO

ACTING INDEPENDENTLY OF EACH OTHER,

THE TWO FACTORS TAKEN TOGETHER

COULD HAVE PREDICTIVE VALUE FOR

RAINFALL IN THE MONSOON'S EARLY AND

LATE PHASES.

PRELIMINARY RESULTS LOOKED

PROMISING,DR.RAJAGOPALAN TOLD THIS

CORRESPONDENT. THOSE TWO PHASES OF

THE MONSOON ACCOUNTED FOR OVER

ONE-THIRD OF THE TOTAL RAINFALL

DURING THE ENTIRE SEASON AND WAS

"NOTHING TO BE SNEEZED AT".