THERMO Spoken Here! ~ J. Pohl ©  ( B0600~2/15)

( B0800 -  Torricelli's Barometer)

Hurricane Wilma

The very large hurricane, Wilma, set some records in October, 2005. At times its winds reached 185 miles per hour. Measure­ments showed the barometric pressure in her eye to be 882 mbars of mercury. These were "static" pressure measurements.

One meaning of static pressure of air is the pressure exhibited by air that is motionless ~ not moving relative to the Earth surface. Individual molecules of air move but the air, in a bulk manner, does not move relative to earth. But in a hurricane hardly any air is motionless relative to Earth. How then, is the static pressure within hurricane force winds measured? These pressure measurements are taken by instrument packages, called "sondes," which are parachuted from Hercules C-130 aircraft into the hurricane winds at altitudes less than 10,000 feet.

As the sonde slowly descends, it moves with the prevailing wind and its devices measure "static," undisturbed properties of the air: pressure, temperature, humidity (along with the time and GPS locations). The electronics of the sonde radio-transmit this data to aircraft where computers use it to calculate the wind speed, direction, temperature gradients and such. Static means "undisturbed." If the air is not moving - measure away. If the air is moving, move with the air to take the measurements.

Hurricane Wilma

This very large hurricane set some records in October, 2005. At times its winds reached 185 miles per hour. Measurements showed the barometric pressure in her eye to be 882 mbars of mercury. These pressure measurements were "static."

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