An evaluation of the effects of idealized ice nuclei on the apportionment of upper tropospheric water vapor in the UWNMS

As much as we know about the radiative properties of clouds and the radiative effects caused by changing cloud properties such as particle size, clouds also affect atmospheric chemistry. The best known examples of this are acid rain and the process of ozone destruction involving polar stratospheric clouds. Can changes in cloud properties influence the distribution of a chemical species? This study investigates a potential link between the observed increase in Tower stratospheric moisture and changing ice particle sizes in the tropics. Since increasing numbers of cloud condensation nuclei have been seen to decrease cloud water droplet sizes, it seems likely that increasing numbers of ice nuclei would act to decrease ice particle sizes. A decrease in ice particle size should lead to decreased sedimentation and an increased lofting of moisture into the tropical tropopause layer and even into the lower stratosphere.;To this end, populations of idealized IN have been modeled using the University of Wisconsin Non-hydrostatic Modeling System (UWNMS) to investigate the sensitivity of water vapor and ice concentrations and distributions to IN concentration, activation temperature, and initial location within the study volume: the Amazon Basin, where biomass burning represents a large potential source of organic IN in a highly convective environment. These studies span a 60-hour period from the 26th - 28th of September 1992, coincident with frontal and mesoscale convective activity.;The expected results are evident in the UWNMS experiments---there are clear areas with increases in vapor and ice above areas with IN activity. However, the results are complicated by areas with negative changes in vapor and ice. The extent and location of areas with negative changes give rise to interesting patterns which are highly dependent on vertical velocities and altitude, as well as the initial IN concentration, activation temperature, and location. This work explains the mechanisms that cause these patterns with a view toward expanding the understanding of how the distribution of humidity in the upper troposphere/lower stratosphere may be impacted by aerosol.