Synoptic Scale Vertical Effluent Redistribution: A Comparison of Two Modeling Approaches

Synoptic-scale vertical motion can strongly influence the trans-continental transport of effluent in the atmosphere. In addition to vertical mixing driven by the diurnal heating cycle, large-scale ascent and descent due to forcing by synoptic scale disturbances redistribute material throughout the troposphere.

The Global Atmospheric Multilayer Transport (GAMUT) model has modeled the large-scale vertical motion in the atmosphere by using static energy, a nearly conservative thermal property of the atmosphere, as a tracer of atmospheric motion. This approach performed well in middle and high latitudes where air mass interactions are strongest. In tropical regimes, static energy is nearly constant or decreases with height, which renders it a poor tracer.

A recent upgrade to GAMUT now allows it to utilize the vertical motion fields calculated within global analysis and forecast models. This modification should improve the estimates of vertical effluent redistribution, particularly under more tropical conditions. This paper will describe the approaches to vertical motion available within GAMUT. A comparison of results obtained using the static energy tracer and the global models' vertical velocity fields will be presented. Analyses from the NCAR/NCEP Reanalysis Project will be used to drive the GAMUT transport/dispersion calculations. Measurements from the Across North America Tracer Experiment (ANATEX) will be utilized to evaluate the model predictions.