Numerical simulations of NASA research instrumentation in hurricane environments

Tropical cyclone intensity prediction is an issue at the forefront of mesoscale numerical weather prediction efforts because it is an area where historically there have been only small improvements, and yet much more progress is needed to improve advance warnings for land- falling tropical cyclones (TCs). In recent years, research instrumentation has been developed for deployment aboard aircraft that remotely study tropical cyclones in order to answer critical intensity questions about TCs. One such instrument is the NASA Hurricane Imaging Radiometer (HIRAD) that has been developed to observe hurricane surface wind speeds and rain rates. This study explores the expected benefits of this instrument's data to numerical simulations of tropical cyclones using two different data assimilation methods within the experimental framework of Observing System Simulation Experiments (OSSE). The HIRAD instrument performed its inaugural hurricane flights during the summer 2010 NASA Genesis and Rapid Intensification Processes (GRIP) field program, when it first studied Hurricane Karl undergoing Rapid Intensification (RI) during its brief transit over the southern Gulf of Mexico. RI events such as this one are particularly difficult to forecast given the short duration and distance over water between landmasses. The aims of this study are four-fold: first, the creation of two Nature Run simulations of Hurricane Karl as a strong and a weak hurricane; second, the accurate simulation of the HIRAD instrument's rain rate and wind speed observations; third, the development and use of two data assimilation schemes for use with the Weather Research and Forecasting (WRF) model using simulated HIRAD data for both Nature Runs; and fourth, the improvement of Hurricane Karl's intensity forecast at the end of the data assimilation period due to the inclusion of HIRAD observations and potential use for aiding the forecast of landfalling intensity. The two data assimilation schemes in this study include the creation of an update to the Krishnamurti et. al, technique of Physical Initialization of rain rates for a mesoscale model, and the adjustment and use of an Ensemble Kalman Filter (EnKF) data assimilation scheme developed by Zhang et al. for use with tropical cyclone wind speeds. Additionally, since HIRAD currently flies in the NASA HS3 field campaign on the same Global Hawk as the NASA High-altitude Radar (HIWRAP)- a dual-frequency, dual-beam conical scanning Doppler radar system- a few OSSE experiments are performed combining simulated data from both instruments. These assess the potential benefits of assimilating HIRAD wind speeds alongside HIWRAP radial velocities to further improve the initialization of TC intensity.