Dynamic effects of the South Asian high on the ozone valley over the Tibetan Plateau

Abstract

In this study, the TOMS/SBUV (Total Ozone Mapping Spectrometer/Solar Backscatter Ultraviolet Radiometer) data and SAGE (Stratospheric Aerosol and Gas Experiment) II data were employed to calculate the monthly total zonal ozone deviations over the Tibetan Plateau and the 150–50-hPa zonal ozone variations. The results show that there is a significant correlation between the two, with a correlation coefficient of 0.977. From 150 to 50 hPa, the ozone valley over the Tibetan Plateau (OVTP) becomes the strongest based on the SAGE II data, and the South Asian high (SAH) is the most active according to the 40-yr reanalysis data of the European Centre for Medium-Range Weather Forecasts (ERA40), so a correlation between the SAH and the OVTP may exist. The WACCM3 (Whole Atmosphere Community Climate Model version 3) simulation results show that both SAH and OVTP could still present within 150–50 hPa with reduced strength even when the height of the Tibetan Plateau was cut down to 1500 m. It is also shown that the seasonal variation of SAH would result in a matched seasonal variation of the OVTP, which suggests a meaningful effect of SAH on the OVTP. Meanwhile, it is found that the atmospheric circulation would impose different effects on the OVTP, depending on the SAH’s evolution stages and movement directions. At 150–50 hPa, as the SAH approaches the plateau, the SAH zonal (meridional) transport would make the OVTP deeper (shallower), while the vertical transport of ozone produces a deeper (shallower) OVTP at the lower (higher) level; the combined dynamic effects lead to a weakened OVTP. When the SAH stabilizes over the plateau, the zonal (meridional) transport results in a shallower (deeper) OVTP while the vertical transport would create a deeper (shallower) OVTP at the middle (bottom and top) levels; the combined dynamic effects produce a deeper OVTP. As the SAH retreats from the plateau, the OVTP becomes deeper (shallower) under the zonal (meridional) effect or shallower under the vertical effect; the combined dynamic effects contribute to a deeper (shallower) OVTP at the middle (bottom and top) levels. The SAH would have a weak effect on the OVTP over the plateau when positioned over the tropical Pacific.