Abstract
Abstract. This paper addresses various characteristic features associated with the hydration of the tropical upper troposphere and lower stratosphere (UTLS) in association with the boreal monsoonal convective activity occurring over three different tropical regions viz. Asian region, American region and African region. Analysis of water vapor mixing ratio (WVMR) data obtained from AURA MLS (v3.3), ISCCP D1 cloud top pressure data and outgoing long-wave radiation data (OLR) from NOAA reanalysis has brought out two significant results. Firstly, high altitude clouds and high WVMR regions are mostly associated with the low OLR region. Convection over Asian region is very deep and spread over a large geographical area as compared to African or American region. Magnitude of WVMR in the pressure range of 261.0–146.8 hPa is observed to be higher over the Asian region, whereas, close to the tropopause level (~ 100 hPa) it is comparable or more over the American region as compared to Asian and African regions. Secondly, the vertical ascent rate of water vapour obtained from AURA MLS data suggest that convection associated transport might have dominated up to 146.8–121.2 hPa in addition to slow large scale diabatic transport, which appears to be prominent above the pressure range of 100–82.5 hPa. Within the pressure levels of 121.2 to 82.5 hPa, the influence of convective transport appears to be gradually decreasing. However, there are other possible processes like ice sublimation or cirrus jumping which could contribute to the hydration of the tropical lower stratosphere. Present analysis has, thus, brought out the significance of convection in water vapour transport and distribution in the tropical UTLS. Another interesting feature which is observed is the anomalous increase in temperature during boreal winters (November–April) over all three convective regions. Such phenomenon is only observed within the pressure range of 100.0–261.0 hPa; however it is relatively weaker for levels > 177.8 hPa.
Highlights
Climate of the Past high water vapor mixing ratio (WVMR) regions are mostly associated with the low Discussionsoutgoing long-wave radiation data (OLR) region
Three independent low OLR regions (< 220 W m−2) i.e., organised convective regions are observed over the tropics, viz., Asian region (5◦ S–30◦ N, 70–150◦ E), African region (0–15◦ N, 0–30◦ E) and American region (5– 20◦ N, 70–110◦ W)
The convective regions contain a central region for which OLR is lowest and a gradual increase in OLR values is observed towards the peripheral region
Summary
Climate of the Past high WVMR regions are mostly associated with the low Discussions. Convection over Asian region is very deep Water vapour is an important greenhouse gas which traps and spread over a large geographical area as compared to the infrared outgoing long-wave radiation (OLR) and raises. Abatic cooling occurring in the upper troposphere and lower the vertical ascent MLS data suggest rate that ocof nwvaetcetriovnapaosusorcoibattaeidnterGdanfersopomosrtAcmUieiRgnhAttific stratosphere tion acts as (UTLS). Stratospheric water vapour concentraa planetary source of HGOexoasncdieinnittiiaftiecs enhave dominated up to 146.8–121.2 hPa inInadsdtirtuiomn teonstloawtion hanced ozone depletion (SolomoInnest tarlu.,m19e8n6)t.aTthioernefore, large scale diabatic transport, which appears toMbeepthroomdinsenat nd asubroevelevtheelsporef s1s2u1re.2ratong8e2.o5fh1P0a0,–th8e2.i5nhflPuae.nWcDeiatohftiancotSnhveyepcsrttievese-ms tthroepsicoaulrcloews werhsictrhatloesapdhteorethaendavhayildarbaiMtliiotyentoohffowUdaTtseLrSavnanpedeodusr in to be examined in order to better underDstaantdaanSdypsretdeicmt tshe futransport appears to be gradually decreasing. Present significance of convection ainnaMwlyasoteisrdhveaaspl,otDhuurest,rvabneroslpuoogrphttmaonudet nt of Mwaotsetrovfatphoeusrtrfartoomsphtheeriuc-ptproepr otrsopphGoesrepichoeexrsecchtoaienlgonewtaeinfridscternattroysphere occurs through tMropoicdaletlroDpoepvaueselolpaymer e(Bnrtewer, 1949; Holton et al, 1995; Highwood and HDiossckusinssio,n1s998; distribution in the tropical UTLS
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