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

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 ozone deviations over the Tibetan Plateau and the 150-50 hPa zonal ozone variations. The results show that there is a significant correlation between these 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-year reanalysis data of the European Centre for Medium Range Weather Forecasts (ERA-40), so a correlation between the SAH and the OVTP may exist. The WACCM3 (Whole Atmosphere Community Climate Model version 3) simulations with the height of the Tibetan Plateau cut down to 1500 m also show that the seasonal variation of SAH would result in a matched seasonal variation of the OVTP, which suggests a meaningful effect of 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), combined dynamic effects lead to a weakened OVTP. When the SAH stabilizes over the Tibetan 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 Tibetan Plateau, the OVTP becomes deeper (shallower) due to the zonal (meridinal) effect or shallower due to 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 Tibetan Plateau when it positioned over the tropical Pacific.