Differential O2 Absorption Barometric Pressure Radar (DIAR_BAR): Improvements in tropical storm forecasts

Currently, sea surface air pressure measurements can only be observed from in situ measurements using buoy, ship and dropsonde techniques, which are sparse in spatial coverage and expensive to implement. There are no pressure remote sensing methods available even in experimental stages. This study considers use active microwave systems to obtain the differential O2 absorption at 50-56 GHz bands to fill the observational gap. The numerical simulation results show that the rms errors of the instantaneous sea surface pressure estimates can be as low as 4 mb. With multiple radar measurements the uncertainty in radar sea surface pressure estimates would drop to about 1 mb which is similar to conventional in situ buoy measurements. A prototype system of the DIfferential O2 Absorption Radar for Barometry (DIAR-BAR) has been developed and integrated it into an aircraft. The flight test results show the instrument performance meets or exceeds the all system requirements indicting the concept of the differential O2 absorption for the pressure remote sensing measurements could be realized with existing radar technologies.

Motivated by the potential application of DIAR-BAR, the importance of using surface pressure distribution in three dimensional variational data assimilation system for WRF is investigated in a case study of hurricane Katrina. Hurricane Katrina crossed Florida peninsula on August 26, 2005, which provides us surface pressure data with good spatial distribution that is rarely available for other hurricanes in their developing stage over the ocean. Various patterns of surface pressure distribution are assimilated, and the bias in landfall position for 84-hour forecasting decreases from 360 km in the control run up to 38 km in assimilation runs. It demonstrates the DIAR-BAR system will have great potential for weather observations and other meteorological applications, especially for forecasts of hurricanes.