Trends and Variability of the Tropical Width from GPS Radio Occultation

Abstract:

GPS radio occultation (RO) measurements have been shown to be useful in the study of the tropical width as defined from the thermal tropopause and subtropical jet. In Ao and Hajj (2013, doi: 10.1002/2013GL058203), we inferred the linear trends of the hemispheric tropical widths using 10 years (2002–2011) of RO measurements from the CHAMP and COSMIC missions and found widely different seasonal trends in the North and the South. In this study, we extend our previous analysis to include three additional years of measurements (2012–2014). The inferred hemispheric seasonal trends will be compared with the ECMWF and MERRA reanalyses for the same period as well as for the period extending back to 1979. In addition, we present preliminary results on the use of free tropospheric specific humidity as a new definition of the tropical boundary and compare the hydrologically-defined tropical width with other definitions.