Enig­matic dis­tur­bances

Down to Earth - - COVER STORY - THERE IS

not much data on west­ern dis­tur­bances. Ac­cord­ing to A P Dimri, pro­fes­sor, school of en­vi­ron­ment science, Jawa­har­lal Nehru Uni­ver­sity, New Delhi, there has been very lit­tle re­search on west­ern dis­tur­bances be­cause most re­searchers pre­fer to study the mon­soon which is con­sid­ered life­line of In­dian agri­cul­ture. R Kr­ish­nan,a sci­en­tist at the In­dian In­sti­tute of Trop­i­cal Me­te­o­rol­ogy, says that even defin­ing or count­ing a dis­tur­bance is tricky be­cause when west­ern dis­tur­bance moves over a long dis­tance, its strength changes and one can never be sure when a new dis­tur­bance gets formed or an ex­ist­ing one un­der­goes change. Th­ese dis­tur­bances orig­i­nate thou­sands of kilo­me­tres away and travel over coun­tries where data col­lec­tion is sparse. In­dia has fa­cil­i­ties to study the weather but ob­ser­va­tional data from Afghanistan and Pak­istan is vir­tu­ally non-ex­is­tent, says A Ja­yara­man, direc­tor, Na­tional At­mo­spheric Re­search Lab­o­ra­tory, Depart­ment of Space.

B P Ya­dav, head of IMD's Na­tional Weather Fore­cast­ing Cen­tre, says that more dis­tur­bances are be­ing ob­served th­ese days be­cause the tech­nol­ogy to de­tect, mon­i­tor and pre­dict has im­proved. IMD is now un­der­tak­ing stud­ies to un­der­stand west­ern dis­tur­bance, Ya­dav adds. plateau in re­cent decades has in­creased the in­sta­bil­ity of the West­er­lies and this has in­creased the vari­abil­ity of the west­ern dis­tur­bances. Ac­cord­ing to the study, the west­ern Hi­malayan re­gion has seen a sig­nif­i­cant rise in sur­face tem­per­a­tures since the 1950s.Ob­ser­va­tions from the area show a sig­nif­i­cant in­crease in pre­cip­i­ta­tion in re­cent decades. The re­searchers looked at a va­ri­ety of cli­mate data to un­der­stand the in­creas­ing fre­quency of heavy pre­cip­i­ta­tion. They say tem­per­a­tures have risen in the mid­dle- and up­per-tro­po­spheric lev­els over the sub­trop­ics (area be­tween the Tropic of Can­cer and the Tropic of Capricorn) and the mid­dle lat­i­tudes. “Our study sug­gests that hu­manin­duced cli­mate change is the rea­son for the in­creased vari­abil­ity of west­ern dis­tur­bance,” says R Kr­ish­nan,one of the re­searchers.“The find­ings are based on di­rect ob­ser­va­tions and we are now us­ing cli­mate mod­els to con­firm if the im­pact is hu­man-in­duced,” says Kr­ish­nan.

An­other study which blames global warm­ing is by Jen­nifer Fran­cis of Rut­gers Uni­ver­sity, New Jer­sey, and S J Vavrus of Uni­ver­sity of Wis­con­sinMadi­son, both in the US. The study, pub­lished in the Jan­uary is­sue of En­vi­ron­ment Re­search Let­ters, sug­gests that heat­ing up of the Arc­tic has weak­ened the jet streams in the north­ern hemi­sphere. The west to east flow of jet streams in the north­ern hemi­sphere is main­tained by the “gra­di­ent of heat” be­tween the cool Arc­tic and warmer ar­eas near the equa­tor. But the Arc­tic has been warm­ing since the past 20 years due to which the jet streams have be­come weaker. Rather than cir­cling in a rel­a­tively straight path, jet streams now

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