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Variation of upper tropospheric clouds and water vapour over the Indian Ocean
Author(s) -
Bhawar Rohini L.,
Jiang Jonathan H.,
Su Hui,
Schwartz Michael J.
Publication year - 2014
Publication title -
international journal of climatology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.58
H-Index - 166
eISSN - 1097-0088
pISSN - 0899-8418
DOI - 10.1002/joc.3942
Subject(s) - indian ocean dipole , climatology , teleconnection , el niño southern oscillation , sea surface temperature , indian ocean , troposphere , environmental science , walker circulation , atmospheric sciences , oceanography , geology
The objective of this paper is to understand the response of upper tropospheric ( UT ) clouds and water vapour ( H 2 O ) to sea surface temperature ( SST ) changes over the Indian Ocean. UT ice water content ( IWC ) and H 2 O observed by Aura Microwave Limb Sounder (MLS) show dominant dipole mode variability over the Indian Ocean. This is characterized by the oscillating differences between the western and eastern Indian Ocean ( WIO and EIO ) with greater amplitude in September, October and November ( SON ) as compared with other seasons. We denote δX = X_WIO − X_EIO, with X being H 2 O and IWC at three UT levels ( 215 , 147 and 100 hPa ) or SST , following the documented definition for Indian Ocean Dipole ( IOD ). We find a strong positive correlation between δIWC at the three UT levels and δSST , and a relatively weak positive correlation between δIWC and Niño 3.4 SST , suggesting that the UT clouds over the Indian Ocean are largely controlled by the local thermally driven circulation, while teleconnection to El Niño and Southern Oscillation (ENSO) plays a secondary role. The change per degree of δSST for δIWC in SON is 5.5 mg m −3 C −1 at 215 hPa , 1.6 mg m −3 C −1 at 147 hPa and 0.13 mg m −3 C −1 at 100 hPa (i.e. 96% C −1 , 87% C −1 and 46% C −1 increase at 215 , 147 and 100 hPa , respectively). We find 36% C −1 increase in δH 2 O at 215 hPa with increasing δSST , associated with a sharp contrast in convective strength (indicated by δIWC ) over the Indian Ocean region. On the other hand, δH 2 O at 100 hPa decreases with increasing δSST because cold temperature is observed above convective clouds and 100 hPa H 2 O is largely controlled by temperature. The Niño 3.4 SST has a relatively weak positive (negative) correlation with δH 2 O at 215 hPa ( 100 hPa ).