Impact of the Horizontal Wind Profile in the Lower Stratosphere on the Convective Transport of Chemical Species

The impact of the vertical profile of the horizontal wind in the troposphere and lower stratosphere on the develo pment of vertical transport of chemical species induced by deep convective events has been studied using a two-dimensional cloud ensemble model. Seven horizontal wind profiles, including one observed during the Central and Equatorial Pacific Experiment (CE PEX) have been chosen. These represent typical wind profiles over the tropical Pacific including upper level westerly and easterly cases, and have been applied to the model as initial conditions to carry out the sensitivity runs. We have found that the pattern of the shear in the horizontal wind in the vicinity of the tropopause plays a significant role in controlling the development of deep convective clouds. As a result, fluxes of chemical species from the planetary boundary layer to the free troposphere and from the free troposphere to the lower stratosphere are very different for different assumed profiles. It has been found specifically that a moderate wind shear crossing tropopause favors vertically advective transport of chemical species. Strong positive shear, though enhancing turbulent mixing from the troposphere to the stratosphere, generates the weakest vertically advective transport primarily due to its influence in limiting the vertical development of convective turrets. In addition we have found that the smoothed wind profile derived from a more fluctuating observed profile produces clear differences in cloud development and associated tracer vertical transport compared to the results of the run with the non-smoothed profile.