Comparing and Verifying WRF Simulations of Water Vapor for TC Ingrid (September 2013)

Atmospheric water vapor is a potent greenhouse gas. Variations of water vapor in the upper troposphere and lower stratosphere (UTLS) are important in determining climate impacts. However, the water vapor budget of tropical cyclones (TCs) and its impact on the UTLS remain under-studied. Therefore, this paper will describe high-resolution simulations from the Weather Research and Forecasting (WRF) model version 3.6 with finest grid spacing of 1.33 km to calculate the water vapor budget of TC Ingrid during September 2013. After extensive testing on the 12 km domain, the WRF Double Moment 6-class Scheme and the New Simplified Arakawa-Schubert Scheme are chosen for microphysics and cumulus parameterization, respectively. The cumulus parameterization scheme is incorporated only on the coarsest 12 km domain, with the 4 km and 1.33 km domains simulating convection explicitly.

Our WRF simulations of TC Ingrid closely correspond to the National Hurricane Center's (NHC's) best track data. Thus, model results of the water budget are compared to the in situ airborne data of Ingrid collected during NASA's Studies of Emissions and Atmospheric Composition, Clouds, and Climate Coupling through Regional Surveys (SEAC4RS). Comparisons between ER-2 in situ data in the UTLS of TC Ingrid from 13-16 September are used to further verify the WRF model runs. In addition, a variety of satellite imagery is used to validate the structure of TC Ingrid. Time series of water vapor depict spatial and temporal changes of water vapor in the UTLS throughout Ingrid's lifecycle. The paper will describe the physical processes contributing to these changes using the model output.

Since TC Ingrid is a relatively weak and short-lived TC, with maximum sustained winds of category one intensity on the Saffir-Simpson scale, a stronger and longer-lived TC also is modeled in WRF for comparison. Similar options within WRF are used to simulate the water budget of the stronger TC, with results compared to those of TC Ingrid. This paper will benefit the scientific community by showing whether and how TCs hydrate or dehydrate the UTLS, helping to answer a question posed during the SEAC4RS mission. The paper highlights the mechanisms by which water vapor is injected into the UTLS, and the widespread horizontal and vertical transports of water vapor within TCs of varying intensities.