This thesis assesses regional and temporal dependent biases in several microwave rainfall climatologies and considers their implications for monitoring the El Nino Southern Oscillation. Seasonal rainfall climatologies from the Tropical Rainfall Measuring Mission (TRMM) are evaluated during the transition from the 1997/1998 El Nino to the 1998/2000 La Nina. The satellite algorithms include version 5 TRMM rainfall products (GPROF (2A12), COMBINED (2B31) and PR (2A25ยป, several passive microwave algorithms and GPCP (Global Precipitation Climatology Project) satellite-gauge estimates. All are compared to GPCC (Global Precipitation Climatology Centre) gauge estimates and two benchmark climatologies. The passive microwave algorithms are spatially and temporally calibrated to the Precipitation Radar using the histogram matching approach, which minimises spatial and temporal algorithm biases. Each algorithm detects seasonal and inter-annual variations in the rainfall distributions, although absolute values are shown to be significantly different. Despite three year quasiglobal averages converging to within -20%, zonal averages show large variations in the magnitude of the biases, e.g. >55% (-30%) for the austral (boreal) summer over land and >40% (-20-25%) during El Nifio (La Nina) over the ocean. Fine-scale comparisons show regional differences vary from <20% to >200%. Biases are attributed to variations in cloud microphysical characteristics, sampling problems and passive microwave coastal and surface artefacts. Unless temporal and spatial algorithm biases are accounted for, all satellite retrievals should be restricted to qualitative assessments of climatic rainfall.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:403605 |
| Date | January 2003 |
| Creators | Sanderson, Victoria Louise |
| Publisher | University of Birmingham |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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