Quantifying “Convective Influence” on Upper Tropospheric and Lower Stratospheric Composition using Lagrangian Trajectories and Aura Microwave Limb Sounder Observations

Rapid uplift of boundary layer air by deep convection is one of the key processes affecting the humidity and composition of the Upper Troposphere and Lower Stratosphere (UTLS) at low- and mid-latitudes. Convection in the summertime Asian and North American Monsoons leads to a build up of pollution in the UTLS as the convective outflow is “trapped” in the large-scale circulations. By contrast, convection of “pristine” air in the southwest Pacific contributes to persistently low values of UTLS ozone in this region. Here we apply the “convective influence” approach, developed for airborne measurements, to the multi-year record of UTLS observations from the Aura Microwave Limb Sounder (MLS). Lagrangian trajectories are used to track the motion of air masses observed by MLS up to 15 days prior to each measurement. Cases where these tracked air masses encounter convection (as identified by a combination of precipitation data and geostationary satellite imagery) are recorded. We describe the MLS observations and the convective influence approach. The relationship between convective influence (i.e., the location, depth and timing of any convection previously encountered) on the MLS-observed airmasses and their composition and humidity is explored and described.