An analysis of pre-tornadic low-level moisture-flux convergence and the utility of GOES and GIFTS sounder data

The availability of high time resolution boundary-layer wind, temperature and moisture around the tornadic thunderstorms which developed on 3 May 1999 offers an unprecedented opportunity to study the evolution of the lower-level moisture flux convergence fields needed to support the development and continued growth of these storms, both for objective NWP and nowcasting and for subjective forecaster use.

For this case, data were available not only from the inner-core of the Wind Profiler network, but also from five co-located Atmospheric Emitted Radiance Interferometers (AERI), which provided detailed temperature and moisture data for the lowest three kilometers of atmosphere at ten minute resolution in clear sky and to cloud base. Although the AERI data alone can be used to monitor the evolution of the convective available potential energy (CAPE) and convective inhibition (CIN) at each of the instrument locations, the combination of the moisture and temperature information with wind profiler observations facilitates detailed studies of the dynamical processes involved in modifying the pre-convective environment and focusing the energy needed to subsequent convection. The results shown will focus on:

- Determining the dynamical processes responsible for both increasing the depth of the low-level moisture source and enhancing the convective instability,

- Evaluating the relative roles of divergence and advective processes in supporting the low-level moisture convergence structure, and

- Assessing the implications that these findings have on the relative roles that improvements in depicting wind field dynamics (e.g., numerical models) and observations of moisture gradients (e.g., observing systems) will have in future severe storm prediction systems.

These data sets are also used to determine the ability of future generation Geostationary sounders such as the Geostationary Imaging Fourier Transform Spectrometer (GIFTS) to provide sufficient information to support future forecasting and nowcasting systems. For this purpose, the AERI data are used to emulate high-time frequency moisture and temperature retrievals typical of those available from the current GOES sounders and from the future GIFTS. These data are then compared with the original observations and derived combined-profiler kinematic results to assess the role of current and future geostationary sounders in our future integrated mesoscale observing systems.