Tests conducted to evaluate sonde accuracy have shown the data to be satisfactory if the observers have been fully trained in equipment operation and data evaluation. 

TEMPERATURE. Under controlled condi-tions, comparisons of sonde-recorded tempera-tures to those measured by thermometer show the sonde temperatures to be accurate within 1C over 90% of the time. 

PRESSURE. The average sonde pressure error is from 2 to 4 mb. The absolute maximum error evaluated was 5 mb, and this occurred in only one percent of the sondes tested.

HUMIDITY. This element is accurate to within 5% up to 700 mb, but maybe in error by as much as 20% at 300 mb. Because this element is recorded with respect to water (never ice) when a sonde passes through an ice crystal cloud layer the relative humidity computes at 70 to 80 per-cent.

This is an accurate reading. A very rough estimate of humidities in below-freezing temperatures is obtained by decreasing the humidity 10% for every 10C decrease in temperature.

UPPER WINDS. The reliability of upper-wind data is dependent on the manner in which the data is obtained. Rawinsonde winds are for the most part very accurate. Winds obtained by radar tracking are the most accurate. See probable errors listed in table 8-1-1. This table is used by the National Weather Analysis Center.

Learning Objective: Identify the analysis procedures and use of thickness, time differential, jet stream, tropopause, and individual analyses.

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