Contribution of air-mass transport via the South Asia High to the deep stratosphere in summer

Abstract. This study proposes a method for estimating meridional and vertical air-mass transport in the stratosphere based on the mass conservation equation. The method does not require calculation of the velocity and flux, and avoids the uncertainty in vertical velocity estimates. Using satellite observations of hydrogen cyanide (HCN) concentrations in summer (June–September), the relative contributions of air mass originating from the troposphere and transporting into the deep stratosphere via the tropical tropopause and South Asia High (SAH) were estimated as 7.72 % and 14.55 %, while those of HCN were 7.17 % and 15.72 %, respectively. These results indicate that the air-mass contributions of the SAH are greater than those of the tropical troposphere, and that the SAH is the most important air-mass transport pathway from the troposphere to the deep stratosphere in summer. This suggests that the impact of pollutants from Asia on the stratosphere is greater than that reported by previous studies.