Dehydration and low ozone in the tropopause layer over the Asian monsoon caused by tropical cyclones: Lagrangian transport calculations using ERA-Interim and ERA5 reanalysis data

Abstract

<p><strong>Abstract.</strong> Low ozone and low water vapour values near the tropopause over Kunming, China were observed using balloon-borne measurements performed during the SWOP (sounding water vapour, ozone, and particle) campaign in August 2009 and 2015. Here, we investigate low ozone and water vapour signatures in the upper troposphere and lower stratosphere (UTLS) using FengYun-2D, FengYun-2G, Aura Microwave Limb Sounder (MLS) satellite measurements and backward trajectory calculations driven by both ERA-Interim and ERA5 reanalysis data. Trajectories with kinematic and diabatic vertical velocities were calculated using the Chemical Lagrangian Model of the Stratosphere (CLaMS) trajectory module.</p> <p>All trajectory calculations show that air parcels with low ozone and low water vapour values in the UTLS over Kunming measured by balloon-borne instruments originate from the western Pacific boundary layer. Deep convection associated with tropical cyclones over the western Pacific transports boundary air parcels with low ozone into the cold tropopause region. Subsequently, these air parcels are mixed into the strong easterlies on the southern side of the Asian summer monsoon anticyclone. Air parcels are dehydrated when passing the lowest temperature region (< 190 K) over the western Pacific during quasi-horizontal advection. However, trajectory calculations show different vertical transport via deep convection depending on the employed reanalysis data (ERA-Interim, ERA5) and vertical velocities (diabatic, kinematic). Both the kinematic and the diabatic trajectory calculations using ERA5 data show faster and stronger vertical transport than ERA-Interim primarily due to ERA5's better spatial and temporal resolution, likely resolving more convective events.</p>

Confinement of air in the Asian monsoon anticyclone and pathways of convective air to the stratosphere during summer season

“…The large differences between kinematic and diabatic trajectories transport properties in the ERA-Interim have already been noticed in a number of previous studies (e.g., Bergman et al, 2015;Bucci et al, 2019;Li et al, 2019).…”

“…This set-up is quite similar to that of, e.g., Bergman et al (2013). Some other studies where the tracers are initialized in the boundary layer used instead the total heating rate (Vogel et al, 2015;Ploeger et al, 2017;Vogel et al, 2019;Li et al, 2019). Above the level of maximum cloud cover, the total heating rate converges rapidly to the radiative heating rate as a function of increasing potential temperature.…”