Sunday, August 19, 2007

Overview of Problems with Data from the RRS Sippican Sondes

I have seen a copy of an internal NWS issue paper on the RRS sonde, including "talking points" for the media. After reading this document, I have a number of concerns:

The sonde problem is apparently being approached by higher levels of the NWS as if it is essentially a problem related to the performance of the Sippican hygrister in dry, desert environments.

In my opinion, nothing could be further from the truth.

After looking at many RRS soundings during the past month and a half, I conclude that there are serious problems with both the hygrister and the thermistor and, probably, with the sonde's internal electronic components. This last statement is just a hypothesis, since I don't know much about the technical details.

I am collecting bad RRS soundings from all over the country so that I can provide an extensive documentation of the problems. I provide here a quick overview of theproblems I have seen to date:

1 - Extreme dry layers above the surface with a slow recovery, leading to soundings that are too dry. (Note that this "too dry in low levels" problem was first detected by NWS personnel in the Southwest. However, the NWS instruction manual for operators of the RRS system indicates that other of the sonde's problems were detected during evaluation; however, implementation proceeded regardless.) See Fig. 1.

2 - Slow response to dry layers aloft when sonde is launched in a relatively humid environment, leading to occasional soundings that are too wet. See Fig. 2 and post of August 8th.

3 - Both the thermistor and hygrister are apparently poorly vented and one or both are easily wetted, leading to a plethora of problems caused by the latent heat effects of condensation, evaporation, freezing, and sublimation. (The wetting problems apparently relate to the compact size of the new overall instrument package that was evidently developed initially for military field use.) See Fig. 3 and Fig. 4.

4 - The RRS soundings are sometimes missing winds through significant layers (the ultimate example of which I distributed the other day - for a MN sounding, hardly a desert environment!) - See a previous post made today. The problems the missing winds can cause are many, some of which have serious implications for forecasting. This problem may be related to the sonde's internal electronic components. See both Fig. 1 and Fig. 5.

5 - Other problems, again probably related to internal electronics, cause high to veryhigh frequency noise leading sometimes to many many "special" points - in bothT and Td. See Fig. 6.

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