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Postcards from IHC, Part II: remote pressure measurements

By: Dr. Jeff Masters, 12:39 PM GMT on March 05, 2009

I'm at the 63rd Interdepartmental Hurricane Conference (IHC) in St. Petersburg, Florida this week, catching up on the latest hurricane research results and plans. About 150 scientists and administrators from all the major U.S. hurricane research agencies are here, and I'll present a few of the highlights of the conference in my next few posts.

We can make crude measurements of atmospheric wind and temperature using remote sensing instruments mounted on aircraft on satellites, but we currently have no way to take such measurements of pressure. Accurate pressure measurements of the inital state of the atmosphere are key in making accurate computer model forecasts, since it is differences in pressure that drive all winds, as air flows from high pressure to low pressure in an attempt to equalize the pressure. Currently, sea surface air pressure measurements can only be obtained from in-situ observations including buoy, ship and dropsonde measurements, which are expensive and sparse in spatial coverage. Dr. Roland Lawrence of Old Dominion University and Qilong Min of SUNY Albany presented a new technique to make remote pressure measurements, in a talk titled "Flight Test Results of a Differential Microwave Radar for Remote Sensing of Atmospheric Pressure". Scientists at NASA's Langley Research Center have built a prototype instrument that has successfully taken remote pressure measurements on aircraft test flights over the ocean. The instrument can measure surface pressure to an accuracy of 4 mb, and possibly as good as 1 mb, when averaged over a several kilometers of ocean area. While flights tests into a hurricane and real-time assimilation of the data in hurricane forecast models are still probably several years away, this is one technology that has the potential to make a big improvement in hurricane track and intensity forecasts. One potential problem with using the instrument in hurricanes is that since the device is measuring the total amount of oxygen in the air along its beam to derive the air pressure, one also needs to know the amount of water vapor along this beam (since water vapor contains oxygen). This quantity will usually need to be modeled, since we don't have detailed humidity measurements available in hurricanes.

I'll post another postcard from IHC on Friday.

Jeff Masters

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