The Effect of the North American Monsoon Anticyclone on Cross-Tropopause Convective Outflow

We analyzed the interaction between the North American monsoon anticyclone (NAMA) and summertime cross-tropopause convective outflow by applying a trajectory analysis to a climatology of convective overshooting tops (OTs) identified in GOES satellite images which covers the domain from 29° S to 68° N and from 205° W to 1.25° W. With this analysis we identified seasonally, geographically, and altitude dependent trends in both NAMA strength and in cross-tropopause convection that control their interaction. We find that the NAMA has the strongest impact on the circulation of convectively influenced air masses in August, when both the NAMA strength and the frequency of cross-tropopause convection are at a maximum. Additionally, we find that the average residence time for these air masses in the NAMA is 69 hours at 370 K and 71 hours at 400 K. Below 400 K, the intertropical convergence zone contributes the greatest fraction (up to 66.3%) of convectively influenced air masses into the NAMA circulation, while at potential temperatures greater than 400 K, convection over the Sierra Madres and the central U.S. contribute the dominant fraction (up to 58.6%). When evaluating the impact of cross-tropopause convection on the composition and chemistry of the upper tropopause and lower stratosphere, the effects of the NAMA on both the distribution of convective outflow and the residence time of convectively influenced air masses within the NAMA region must be considered.