Friday, August 24, 2007

Discussion of the TWC Sounding for 0000 UTC 24 August 2007

The TWC sounding taken yesterday afternoon Figure 1 illustrates several of the serious problems with data from the NWS RRS Sippican sondes. I discuss the sounding layer by layer beginning at the surface:

* Abrupt jump in Td at release - reason for this is unknown. See my earlier post on the Madweather webpage regarding the roof-top launch conditions at TWC.

* The afternoon boundary layer (BL) in T extends upward to 700 mb; however, the Td trace from 900 to 780 mb does not depict a well-mixed BL in moisture. My guess is that this reflects a slow response of the hygrister back toward actual values, after the abrupt Td excursion at release.

* A realistic portion of the BL is is sampled from 780 to 700 mb.

* The sonde apparently entered a towering cumulus at about 660 mb and experienced severe wetting of the thermistor and perhaps of the hygrister. The data are extremely bad from 600 to 400 mb affected by evaporation, and perhaps freezing, and sublimation. Note - I was inthe immediate vicinity of the launch site and there were no thunderstorms present; however, a deep and thick mesoscale anvil covered the sky from the WSW through the ENE. The equally absurd ASOS surface observation from TUS at this time was "CLR."

* From 400 to 300 mb the sensors are apparently slowly recovering toward values present in the actual atmosphere.

* Above 300 mb the data remain suspect; are extremely smooth; and do not reflect the presence of the ice saturated anvil cloud.

* The temperature data from at least 600 to 300 mb appear too cool. Since the thermodynamic data are used to compute the heights of the pressure surfaces, it is not surprising that heights at and above 300 mb appear 20 to 40 m too low.

Thus, it is likely that this sounding had physically realistic data for a single layer that was only about 80 mb deep!

I certainly hope that these data do not end up in the NCDC sounding data archive.

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