Kelly M. Howell, M.S.

1. THESIS TITLE: Quasi-Global and Regional Water Vapor and Rainfall Rate Climatologies for a 35 Month Period Kelly M. Howell, M.S. ABSTRACT Atmospheric water vapor and rainfall are crucial elements in the global water cycle. The spatial and temporal variations of total precipitable water (TPW) and rainfall rate (RR) between 60N and 60S are investigated. In addition, nine oceanic locations in different climate regions are further studied in order to clarify regional differences in a more detailed manner. The Blended Total Precipitable Water (bTPW) product from the Cooperative Institute for Research in the Atmosphere (CIRA) provides the water vapor observations, and the Climate Prediction Center morphing method (CMORPH) product is used for the rainfall rate. These six-hourly datasets were analyzed at 0.25 × 0.25 resolution during the period between February 2006 and December 2008. The variations present in these quasi-global TPW and RR climatologies are found to be similar to the variations presented in previous studies. For instance, oceanic TPW maximizes around 7N at 45 mm, the most land-falling rain occurs around 2S, and the most oceanic rainfall occurs around 7N. However, both datasets over the 35 month period indicate an occurrence of the double Intertropical Convergence Zone during the boreal spring that is not evident in the previous TPW studies presented. Over the study period, the quasi-global CMORPH mean daily RR is 2.63 mm day-1 and the quasi-global bTPW mean oceanic TPW is 24.94 mm. Regionally, the rainfall rate distributions were found to approximate exponential decay, with typically drier regions corresponding with faster decay rates. This pattern is also evident on a global scale. While one might expect an increased TPW to correspond with an increased RR, it was found that rainfall is possible at nearly any TPW value. On a global scale, higher TPW values are associated with higher probabilities of rainfall, although global patterns of moisture convergence and vertical motion are key factors in the production of this rainfall. The RR algorithms used to form the CMORPH product are less sensitive to stratiform light rain, which means that rainfall is likely underestimated in areas receiving mostly this type of rain, such as the subtropical eastern Pacific Ocean. The results demonstrate that the bTPW and CMORPH products produce observations consistent with past climatologies and that TPW on its own is not an accurate indicator of rainfall; other dynamical and thermodynamical effects must be considered. Kelly Howell SELECTED RESULTS Threshold = 0.1 mm hr-1