Influence of enhanced Asian NO$_{x}$ emissions on ozone in the Upper Troposphere and Lower Stratosphere (UTLS) in chemistry climate model simulations

Asian summer monsoon convection plays an important role in efficient vertical transport from the surface to the anticyclone. In this paper we investigate the potential impact of convectively transported anthropogenic nitrogen oxides (NOx) on the distribution of ozone in the Upper Troposphere and Lower Stratosphere (UTLS) from simulations with the fully-coupled aerosol chemistry climate model, ECHAM5-HAMMOZ. We performed anthropogenic NOx emission sensitivity experiments over India and China. In these simulations, anthropogenic NOx emissions for the period 2000–2010 have been increased by 38 % over India and by 73 % over China in accordance with satellite observed trends over India of 3.8 % per year and China of 7.3 % per year. These NOx emission sensitivity simulations show that strong convection over the Bay of Bengal and the Southern slopes of the Himalayas transports Indian emissions into the UTLS. Convective transport from the South China Sea injects Chinese emissions into the lower stratosphere. Indian and Chinese emissions are partially transported over the Arabian Sea and west Asia by the tropical easterly jet. Enhanced NOx emissions over India and China increase the ozone radiative forcing over India by 0.112 W/m2 and 0.121 W/m2 respectively. These elevated emissions produces significant warming over the Tibetan Plateau and increase precipitation over India due to a strengthening of the monsoon Hadley circulation.However doubling of NOx emissions over India (73 %); equal to China, produced high ozone in the lower troposphere. It induced a reverse monsoon Hadley circulation and negative precipitation anomalies over India. The associated subsidence suppressed vertical transport of NOx and ozone into the anticyclone