Characterization of thermal structure and conditions for overshooting of tropical and extratropical cyclones with GPS radio occultation

Abstract. The thermal structure of tropical cyclones (TCs) in different ocean basins is studied using global positioning system (GPS) radio occultation (RO) measurements co-located with TCs' best tracks. The objective of this work is to understand the mutual influence of TCs and atmospheric parameters in different regions. We selected more than 20 000 GPS RO profiles co-located with TCs in a time window of 6 h and space window of 600 km from the TC center in the period 2001–2012 and classified them by intensity of the cyclone and by ocean basin. The results show that TCs have different characteristics depending on the basin, which affects the cloud top altitude and the TC thermal structure which usually shows a negative temperature anomaly near the cloud top altitude. In the Northern Hemisphere ocean basins, the temperature anomaly becomes positive above the cloud top while in the Southern Hemisphere ocean basins it stays negative up to about 25 km in altitude.
Furthermore, in the Southern Hemisphere the storms reach higher cloud top altitudes than in the Northern Hemisphere ocean basins, indicating that possible overshootings overpass the climatological tropopause more deeply at extratropical latitudes. The comparison of the TC thermal structure with the respective monthly mean tropopause altitude allows for a detailed analysis of the probability for possible overshooting. While the co-locations between GPS ROs and TC tracks are well distributed in all the ocean basins, conditions for possible overshootings are found to be more frequent in the Southern Hemisphere basins and in the northern Indian Ocean basin. However, the number of possible overshootings for high intensity storms (i.e., TC categories 1–5) is the highest in the western Pacific Ocean basin.