Studies related to Tropical Rainfall Measuring Mission (TRMM): Sampling a cyclostationary field and a climatology of reflectivity profiles

The Tropical Rainfall Measuring Mission (TRMM) was designed to obtain multi-year precipitation data sets in the tropics. These data will be used to understand tropical precipitation processes and their roles in global climate and also to improve satellite rainfall measurement algorithms. Although it was known that some of the biases associated with sampling and unfilled beams were reduced due to the TRMM orbit, there are still a few unresolved problems on these biases.; This dissertation is first intended to investigate whether the non sun-synchronous orbit of the TRMM satellite allows the statistical errors that might be encountered in sampling the field having an inherent period (so-called cyclostationary) to be decreased. For this study, a sampling error formula was developed based on a spectral approach, which can compare errors contributed separately by stationary background, cyclostationary effect and the interference between them. This formula was applied to the case of a diurnally or semidiurnally varying field for monthly averaging and two different satellite sampling designs revisiting every 12h (sun-synchronous) and 11.75h (TRMM). It was shown that the TRMM satellite was less affected by either the diurnal or semidiurnal cycle and the phase shift between the satellite revisiting cycle and the diurnal cycle than the sun-synchronous satellite.; Secondly, a preliminary climatology of the melting-layer altitude precipitation, from January 1998 to January 1999, was derived for the nadir reflectivity profiles of the precipitation radar. This analysis is intended to provide a clue to a free parameter (the rain-column thickness), which is important to the current (or future) microwave radiometric estimations of rain rates. The geographical, seasonal and diurnal variations, and spatial correlations of the melting-layer altitudes, obtained from a gradient-checking method, were presented over 10° x 10° longitude-latitude boxes and for 8 selected domains. The results indicate that the melting-layer altitudes appear to respond to atmospheric phenomena such as El Nino and the Asian summer monsoon and to have a latitudinal dependency on their distributions, suggesting a strong relationship with surface temperatures. On the other hand, the analysis of the second moment statistics shows that the occurrence of the melting layer was rather irregular at small scales.