Re: Earlier this morning when the dropsonde splashed down at 9:08AM EDT on 10/17: 890mb
Posted by Chris in Tampa on 10/17/2010, 9:07 pm
It's not just rain, more of the really heavy rain. While storms do have a lot of rain, it's those really heavy rains that can really have an impact.

Here is a paper that goes into some technical details:
http://ams.confex.com/ams/29Hurricanes/techprogram/paper_167846.htm

I don't understand all the science behind it, but basically this is the important part, keeping in mind that the SFMR estimates rain rate and the surface wind:

"Past work with the rain model led to a frequency
component that was too dependent on rain rate.
Because this model produces rain rate estimates with a
degree of uncertainty and because the wind model
depends upon the rain model, the rain dependence is
believed to have a negative impact (i.e. overestimation)
on the wind model within high rain rate circumstances.
By weakening this dependence, these negative
influences are expected to be lessened, producing more
realistic wind speeds in the presence of heavy rain."

Here is something about SFMR from the manufacture:
http://www.prosensing.com/Hurricane%20Wind%20Speed%20Radiometer.htm

"The SFMR is a compact, airborne radiometer designed to measure surface brightness temperature in 6 frequency bands spanning 4.5 to 7 GHz. Calibrated values of brightness temperature generated by SFMR are reported in real time to a windspeed retrieval algorithm, developed in cooperation with NOAA's Hurricane Research Division. This algorithm generates a real time measure of surface level wind speed and rain rate in hurricanes and tropical storms."

(You can own your own for the low, low price of $159,200.00 to $169,840.00, includes a one year warranty!)

A little about brightness temperature:

http://en.wikipedia.org/wiki/Brightness_temperature
http://disc.sci.gsfc.nasa.gov/data-holdings/PIP/brightness_temperature.shtml

I'm not sure what about the rain has an impact on the what comes back to the instrument. It must interfere the more rain you have, but I don't really know how. It's one of those things where I know to be cautious of the wind value if the rain rate is high, but don't know the specifics why.
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Typhoon MEGI - hanna, 10/15/2010, 9:51 am
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