A Case Study of the Effects of Random Errors in Rawinsonde Data on Computations of Ageostrophic Winds

Abstract

Input data from the AYE-SESAME I experiment are utilized to describe the effects of random errors in rawinsonde data on the computation of ageostrophic winds Computer-generated random errors for wind direction and speed and temperature are introduced into the station soundings at 25 mb intervals from which isentropic data sets are created. The ageostrophic wind and its components are computed for both the 312 K and 324 K isentropic surfaces. The total form of the ageostrophic wind components consists of the local wind tendency and inertial-advective contributions. The geostrophic momentum form of the ageostrophic wind components consists of the isallobaric and inertial-geostrophic-advective contributions. All winds are computed for 2000 GMT 10 April 1979 except the isallobaric and the local wind tendency, which are calculated for the 1700?2000 GMT time period. The ageostrophic wind components were quite strong during this time. Quantitative analyses utilizing various statistical parameters and qualitative analyses from a visual comparison of fields are discussed. Results show that the geostrophic momentum forms of the ageostrophic wind components are generally less sensitive to rawinsonde error than their total form counterparts. This is most likely due to the fact that the mass field is observed more accurately by a rawinsonde than the momentum field. Divergence fields generated from the various ageostrophic wind components are presented as they are more sensitive to rawinsonde error than the various ageostrophic wind components themselves. These divergence fields revel that the isallobaric and inertial-geostrophic-advective divergences are less affected by rawinsonde random errors then the divergence of the local wind tendency or inertial-advective winds. Finally, this study indicates that the ageostrophic wind can be reliably diagnosed from the rawinsonde data gathered during the AYE-SESAME I experiment in 1979.