Distribution and Sources of Trace Gases and Aerosols in the Asian Summer Monsoon Anticyclone - Aircraft Observations and Model Simulations

We report aircraft observations of trace gases and aerosols from recent field campaigns in the Asian summer monsoon anticyclone. Measurements were performed with the DLR Falcon and HALO aircraft at altitudes up to 15 km across the boundary of the anticyclone over the Arabian Sea during June, July and September conditions. Sharp gradients in chemical tracer mixing ratios were observed at the boundary of the anticyclone. In particular, sulfur dioxide and aerosols were enhanced inside the anticyclone. Ozone and carbon monoxide were enhanced or reduced in the anticyclone depending on the degree of in-mixing of air from the stratosphere inferred from observations of the stratospheric tracer hydrochloric acid. Backward trajectory analysis, tracer dispersion calculations, and simulations with the chemistry-climate model EMAC, nudged to the meteorological conditions of the measurements, were used to investigate the origin and transport of trace gases in and in the vicinity of the anticyclone. A chemistry-aerosol box model was used to simulate the formation of sulfate aerosol from sulfur dioxide inside the anticyclone uplifted by deep convection over northern India and in the Gulf of Bengal.