Formation of the summertime ozone valley over the Tibetan Plateau: The Asian summer monsoon and air column variations

Total ozone over the Tibetan Plateau in summer was ~33 Dobson units (DU) lower than zonal mean values over the ocean at the same latitudes during the study period 2005-2009. Satellite observations of ozone profiles show that ozone concentrations over the ASM region have lower values in the upper troposphere and lower stratosphere (UTLS) than over the non-ASM region.

This is caused by frequent convective transport of low-ozone air from the lower troposphere to the UTLS region combined with trapping by the South Asian High. This offset contributes to a ~20-DU deficit in the ozone column over the ASM region. In addition, along the same latitude, total ozone changes identically with variations of the terrain height, showing a high correlation with terrain heights over the ASM region, which includes both the Tibetan and Iranian plateaus.