(Formerly Poster 42) Convectively Injected Water Vapor in the Asian and North American Monsoon Anticyclones observed with the Aura Microwave Limb Sounder

Anderson et al. (A2012) report in situ observations of convectively injected water vapor (H2O) in the North American (NA) summer lowermost stratosphere (LMS), occasionally exceeding 12 ppmv. They contend that, in such cold/wet conditions, heterogeneous chemistry on binary water-sulfate aerosols will activate chlorine, leading to catalytic ozone destruction. Aura Microwave Limb Sounder 100-hPa, 83-hPa and 68-hPa H2O measurements show that, indeed, both the Asian monsoon anticyclone (AMA) and NA monsoon anticyclone (NAMA) are unusually wet, in mean values and in outliers reaching 18 ppmv. In this work, we examine the statistics of extreme AMA and NAMA H2O observations within the global context of the 8-year MLS record. We discuss the implications of MLS vertical resolution on observation of ~1-km layers of enhanced H2O such as are reported in A2012, and discuss the usefulness of MLS hydrochloric acid (HCl), ozone (O3) and chlorine monoxide (ClO) measurements in putting observational limits on chlorine activation and ozone loss. Monsoon LMS parcels that are cold enough (T < ~205 K) to be candidates for aerosol growth and chlorine activation typically have much less chlorine, in the form of HCl, to activate and much less O3 to destroy than is used in A2012 as model initial conditions, regardless of whether they are wetter or drier than A2012's activation threshold. Parcels that are wet enough for activation will have been diluted with tropospheric air, and so will have lower O3 and HCl than dry parcels of similar temperature. A2012 almost certainly overstates the potential for chemical chlorine loss in the monsoon anticyclones under current climate conditions.

Copyright 2013 California Institute of Technology. Government sponsorship acknowledged.