Observations from four Global Position System (GPS) Radio Occultation (RO) missions: Global Positioning System/Meteorology, CHAallenging Minisatellite Payload, Satellite de Aplicaciones Cientificas-C, and Constellation Observing System for Meteorology, Ionosphere and Climate and Taiwan's FORMOsa SATellite Mission #3 (COSMIC/FORMOSAT-3) are collected within a 600？km radius and ±180 minute temporal window of all observed tropical cyclones (TCs) from 1995 to 2006 that were recorded in the global hurricane best-track reanalysis data set (Jarvinen et al. (1984); Davis et al. (1984)). A composite analysis of tropical cyclone radial mean temperature and water vapor profiles is carried out using the GPS RO retrievals which are colocated with global analysis profiles and available in situ radiosonde observations. The differences between the respective observations and analysis profiles are quantified and the preliminary results show that the observations collected within TCs correspond favorably with both the analysis and radiosonde profiles which are colocated. It is concluded that GPS RO observations will contribute significantly to the understanding and modeling of TC structures, especially those related to vertical variability of the atmospheric state within TCs. 1. Introduction A tropical cyclone (TC) spends most of its lifetime over the global oceans and often in regions where regularly collected in situ observations are scarce. As a result, the kinematic and thermodynamic structures of TCs were largely unobserved using the conventional observation network. During the mid-1960s through the late 1970s, the advent of aircraft reconnaissance missions provided scientists the ability to create composite analyses of the energy budgets within these events. Many case studies have been executed using the collected data which include Riehl and Malkus [1], Miller [2], LaSeur and Hawkins [3], Gray and Shea [4], Shea and Gray [5], and Jorgensen [6]. More recent advancements, especially for those which apply remote sensing technologies, have provided even more detailed insight into the kinematic and thermodynamic structure for TCs. Example applications include the use of airborne Doppler radar [7–10], stereoscopic and infrared satellite observations [11, 12], and field programs [13]. As a result of these observations, further studies investigating the inner-core structures, dynamics, and wind fields of TCs have been performed, which have led to further understandings of the characteristics for TCs. In 1995, a proof-of-concept mission, GPS/MET (Global Positioning
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