A robust method for tropopause altitude identification using GPS radio occultation data

Abstract

A robust method to determine the tropopause altitude directly from GPS Radio Occultation (RO) measurements of bending angle is presented. An objective covariance transform method is applied to identify transitions in a bending angle profile. The tropopause is identified by the maximum in the convolution of the natural logarithm of an observed bending angle profile with a gradient window function. Identification of the tropopause from bending angles is of particular value since they are directly derived from climate benchmark observations. This method avoids additional RO data processing and assumptions to derive parameters such as dry temperature, and use of subjective tropopause identification criteria. The RO tropopause altitude is compared with lapse rate and cold point criteria using dry temperatures and radiosonde temperature profiles. A longer-term tropopause altitude analysis for May to November 2008 using the RO bending angle method shows good agreement with tropopause altitudes computed from dry temperature parameters.