The influence of summertime convection over Southeast Asia on water vapor in the tropical stratosphere

Abstract

[1] The relative contributions of Southeast Asian convective source regions during boreal summer to water vapor in the tropical stratosphere are examined using Lagrangian trajectories. Convective sources are identified using global observations of infrared brightness temperature at high space and time resolution, and water vapor transport is simulated using advection-condensation. Trajectory simulations are driven by three different reanalysis data sets, GMAO MERRA, ERA-Interim, and NCEP/NCAR, to establish points of consistency and evaluate the sensitivity of the results to differences in the underlying meteorological fields. All ensembles indicate that Southeast Asia is a prominent boreal summer source of tropospheric air to the tropical stratosphere. Three convective source domains are identified within Southeast Asia: the Bay of Bengal and South Asian subcontinent (MON), the South China and Philippine Seas (SCS), and the Tibetan Plateau and South Slope of the Himalayas (TIB). Water vapor transport into the stratosphere from these three domains exhibits systematic differences that are related to differences in the bulk characteristics of transport. We find air emanating from SCS to be driest, from MON slightly moister, and from TIB moistest. Analysis of pathways shows that air detrained from convection over TIB is most likely to bypass the region of minimum absolute saturation mixing ratio over the equatorial western Pacific; however, the impact of this bypass mechanism on mean water vapor in the tropical stratosphere at 68 hPa is small (<0.1 ppmv). This result contrasts with previously published hypotheses, and it highlights the challenge of properly quantifying fluxes of atmospheric humidity.

Sub-seasonal Variability in the Boundary Layer Sources for Transport into the Tropopause Layer in the Asian Monsoon Region

“…The seasonal BL sources presented here are largely consistent with those that have been found in previous tracer-independent studies by Wright et al (2011) (2015) argued that the contributing sources are primarily located in Southeast Asia, India, and eastern and southern China. However, these studies are limited to short 25 time periods or are case studies, which may hinder the ability to draw more general conclusions.…”

“…shown to enter the lower stratosphere in the Northern Hemisphere (e.g., Bannister et al, 2004;Fu et al, 2006;Randel and Park, 2006;Park et al, 2009;Randel et al, 2010;Wright et al, 2011;Vogel et al, 2014;Vogel et al, 2015;Müller et al, 2016).…”

“…Fu et al (2006), Wright et al (2011), andHeath andFuelberg (2014) emphasized the regions of the Tibetan Plateau (TP) and the southern slope of the Himalayas as the most important BL sources transporting air into the lower stratosphere. Based on a perspective of the whole ASM region, Chen et al (2012) found that the Tibetan Plateau is less important than the western Pacific as a source region for tracers in the 10 TL.…”

Simulation of stratospheric water vapor and trends using three reanalyses

“…These parameters are: (1) supersaturation, which is frequently observed to be >100 % near the tropical tropopause (Jensen et al, 2005;Kramer et al, 2009) -increasing the supersaturation threshold will increase the water vapor concentration; (2) the magnitude of high frequency gravity wave temperature fluctuations (Jensen and Pfister, 2004) -gravity waves reduce the water vapor by increasing the probability of parcels encountering colder temperatures; (3) the convective overshooting and ice injection -this will increase the water vapor concentration on the average (e.g. Wright et al, 2011). To parameterize convective ice injection we use the scheme developed by Dessler et al (2007).…”

Quantifying pollution transport from the Asian monsoon anticyclone into the lower stratosphere

“…Transport by the Asian monsoon includes convection over the Bay of Bengal, northern India and the South China Sea (e.g., Tzella and Legras, 2011;Wright et al, 2011;Bergman et al, 2012). At higher levels monsoon transport is dominated by a strong anticyclonic circulation (Randel and Park, 2006) with confinement and slow uplift of air in the upper troposphere and lower stratosphere (UTLS; e.g., Park et al, 2009).…”