Dynamics and composition of the Asian summer monsoon anticyclone

Abstract

Abstract. This study places HALO research aircraft observations in the upper-tropospheric Asian summer monsoon anticyclone (ASMA) into the context of regional, intra-annual variability by hindcasts with the ECHAM/MESSy Atmospheric Chemistry (EMAC) model. The observations were obtained during the Earth System Model Validation (ESMVal) campaign in September 2012. Observed and simulated tracer-tracer relations reflect photochemical O 3 production as well as in-mixing from the lower troposphere and the tropopause layer. The simulations demonstrate that tropospheric trace gas profiles in the monsoon season are distinct from those in the rest of the year, and the measurements reflect the main processes acting throughout the monsoon season. Net photochemical O 3 production is significantly enhanced in the ASMA, where uplifted precursors meet increased NO x , mainly produced by lightning. An analysis of multiple monsoon seasons in the simulation shows that stratospherically influenced tropopause layer air is regularly entrained at the eastern ASMA flank and then transported in the southern fringe around the interior region. Radial transport barriers of the circulation are effectively overcome by subseasonal dynamical instabilities of the anticyclone, which occur quite frequently and are of paramount importance for the trace gas composition of the ASMA. Both the isentropic entrainment of O 3 -rich air and the photochemical conversion of uplifted O 3 -poor air tend to increase O 3 in the ASMA outflow.

Modeling the aerosol chemical composition of the tropopause over the Tibetan Plateau during the Asian summer monsoon

“…The geographic distribution patterns of the columnintegrated aerosol properties are similar to those given in the work of Pringle et al (2010), who also used EMAC but with a different grid resolution (T42L19) and for an earlier simulation period (2001)(2002). However, the concentration levels of anthropogenic aerosols, especially sulfate, over the Middle East, India, and northeastern China are significantly higher in our simulations due to increasing emission trends over the period of 2001 to 2010 (Granier et al, 2011). The concentration levels of dust aerosols from our simulation are similar to those of Pringle et al (2010), but there are some differences in the fine structure, probably due to different meteorological conditions for different periods and/or an improved scheme used in our simulation .…”

“…We used an emission inventory of the Representative Concentration Pathways scenario 8.5 (RCP8.5), namely MAC-City emission inventory, for fossil fuel combustion and biomass burning emissions in our simulation (see Jöckel et al, 2016, and references therein). The RCP8.5 global emission inventory has a horizontal grid resolution of 0.5 • × 0.5 • at monthly intervals and vertical distributions as described in Pozzer et al (2009), and it is a reasonable choice for anthropogenic emissions over the period from 2000 to 2010 (Granier et al, 2011;Pozzer et al, 2015). The monthly cycles of the RCP8.5 emissions in 2010 are used in this study.…”

High tropospheric ozone in Lhasa within the Asian summer monsoon anticyclone in 2013: influence of convective transport and stratospheric intrusions

“…During the ASM period, deep convective clouds occurred over the South Asian subcontinent, the southern Himalayan region, and the Tibetan Plateau that caused lightning activity (Qie et al, 2014). NO x produced by lighting has the potential to impact upper tropospheric ozone via photochemical reactions (Kita et al, 2002;Schumann and Huntrieser, 2007;Fadnavis et al, 2015;Gottschaldt et al, 2018). Uplifted ozone precursors and NO x produced by lighting contribute to photochemical ozone production in the upper troposphere in the ASM anticyclone.…”

“…Vogel et al (2016) show that the northeastern flank of the ASM anticyclone is a region where air masses from the ASM anticyclone are separated from the anticyclone and are subsequently transported into the extratropical lower stratosphere. When air parcels enter into the stratosphere, they have the potential to impact the regional climate in Asia (Vernier et al, 2015;Gu et al, 2016). Ozone concentrations in the planetary boundary layer over the Tibetan Plateau are most likely affected by intense deep stratospheric intrusion (Škerlak et al, 2014).…”

Modelling the aerosol chemical composition of the tropopause over the Tibetan Plateau during the Asian summer monsoon

“…2005;Jöckel et al, 2010). EMAC has been extensively used at a range of spatial resolutions and evaluated against site, aircraft and satellite measurements of trace gases and aerosols in both the troposphere and stratosphere Lelieveld et al, 2007;Pozzer et al, 2007;Pringle et al, 2010;Astitha et al, 2012;Brühl et al, 2012;Pozzer et al, 2012;Brühl et al, 2015;Eichinger et al, 2015;Pozzer et al, 2015;Tsimpidi et al, 2016;Abdelkader et al, 2017;Gottschaldt et al, 2017;Karydis et al, 2017;Bacer et al, 2018;Brühl et al, 2018;Gottschaldt et al, 2018;Khosrawi et 5 al., 2018;Klingmüller et al, 2018;Lelieveld et al, 2018). The model spectral resolution used in this study is T106L90, which corresponds to a horizontal grid resolution of approximately 1.125º×1.125º and 90 vertical layers extending from the surface to an altitude of 0.01 hPa (~80 km) with a vertical resolution of about 500m in the tropopause region.…”