Description
Calculate the mean wind in the lowest 150m layer of a dropsonde sounding. WL150 is reported as a national-practice level in the 62626 section of a TEMPDROP message.
A depth-weighted average wind is calculated over a 150m thick layer, from the lowest wind measurement, upward. The mean u and v wind components are averaged separately to provide the final result.
The bottom of the 150m layer starts at the lowest available QC wind, no matter how far it is above the surface. There must be at least three winds avaiable, and they must span at least 75% of the 150m layer (i.e. 112.5m).
The algorithm finds each interval bounded by two winds, and sums the product of the interval thickness and the wind average. The interval thicknesses are also summed. The resulting value is the summed products divided by the summed intervals.
The algorithm depends upon there being altitude avaiable in order to determine the interval thickness. These altitudes are interpolated at the time of the wind observation. If there is a time gap in altitudes of more than 40 seconds (due to missing temperaature or pressure), then the calculation will stop at that gap. 40 seconds is the aproximate time for a falling sonde to traverse 50mb, which was specified in the original defintion of this function.
Source
Editsonde, and James Franklin.
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