Some features of water vapor mixing ratio in tropical upper troposphere and lower stratosphere: Role of convection V. Panwar a, b, ⁎, A.R. Jain a , A. Goel b , T.K. Mandal a , V.R. Rao c , S.K. Dhaka d a Radio and Atmospheric Sciences Division, National Physical Laboratory, New Delhi, India b Department of Physics and Astrophysics, University of Delhi, New Delhi, India c Satellite Meteorology Division, India Meteorology Department, Mausam Bhawan, New Delhi, India d Department of Physics and Electronics, Rajdhani College, University of Delhi, New Delhi, India article info abstract Article history: Received 26 January 2011 Received in revised form 2 February 2012 Accepted 2 February 2012 Spatial and temporal variation of water vapor mixing ratio (WVMR) is examined for its associ- ation with the convective activity in upper troposphere and lower stratosphere over tropical region particularly Asian monsoon region (AMR) and Indonesian–Australian West Pacific region (IAWPR) using WVMR obtained from MLS satellite with simultaneous daily mean OLR from NOAA and daily mean wind from NCEP reanalysis. An examination of WVMR at various pressure levels during high water vapor regime (moist Phase) indicates that water vapor (WV) transport, in troposphere, is rather fast up to a level of ~147 hPa. Seasonal variation of WVMR over tropical lower stratosphere (TLS) is noted to be closely associated with seasonal northward movement of intertropical convergence zone (ITCZ). Convection activity over AMR appears to be a prominent contributor to the moist phase of WVMR seasonal cycle in TLS. However, other tropical regions may also be contributing to the seasonal variability of WVMR. Low WV (dry) phase of the WVMR seasonal cycle in TLS observed during NH winter and early spring months may be caused by the appearance of extreme cold temperatures (≤191 K) close to tropopause heights over IAWPR. Mechanisms that could cause such low tem- peratures over IAWPR are discussed. Intraseasonal oscillations with period of 30–40 days are observed in WVMR at various pressure levels. At 100 hPa level such oscillations are noted to be closely associated with similar oscillation in OLR and temperature. These observations sug- gest that variations in OLR (proxy of convection activity) produce such oscillation in WVMR. Present analysis thus report signature of convection in upward transport of WV, seasonal and intraseasonal oscillation in WVMR in upper troposphere and lower stratosphere (UTLS). © 2012 Elsevier B.V. All rights reserved. Keywords: Convection Water Vapor Upper troposphere Lower stratosphere 1. Introduction Water vapor (WV) is an important minor constituent of atmosphere. Observation of WV at tropospheric height is important as it actively participates in the formation and dissipation of the weather phenomena over tropics. This is also an important green house gas at tropospheric height. At stratospheric height humidity content is important as the available amount of WV present determines the radiative energy balance and thereby plays an important role in heat balance at these heights (Foster and Shine, 1999). WV also affects the stratospheric chemistry as it acts as a planetary source of HOx and for the activation of chlorine on polar stratospheric clouds (PSC's) that leads to ozone destruction (Solomon et al., 1986). Tropical regions are the major source of global atmospher- ic moisture because of the presence of active convection and large cyclonic activity. This moisture is then distributed to higher heights and latitudes. Vertical and spatial structure of tropical tropopause region or the tropical tropopause layer Atmospheric Research 108 (2012) 86–103 ⁎ Corresponding author at: Radio and Atmospheric Sciences Division, National Physical Laboratory, New Delhi, India Tel.: + 91 45609448; fax: + 91 45609448. E-mail address: vivek_panwar83@yahoo.com (V. Panwar). 0169-8095/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.atmosres.2012.02.003 Contents lists available at SciVerse ScienceDirect Atmospheric Research journal homepage: www.elsevier.com/locate/atmos