School of Earth Sciences - Theses
Permanent URI for this collection
Search Results
1 - 1 of 1
-
ItemRemote sensing tropical cyclone rainfall over the southwest Pacific region( 2018)The south-west Pacific (SWP) region is susceptible to the catastrophic effects of tropical cyclones (TCs). The region, therefore, has received adequate attention in terms of scientific research pertaining to TC genesis, tracks and intensity. It (especially the island countries), nonetheless, has not received much attention, in comparison to studies elsewhere (e.g. the Atlantic and western North Pacific region), on additional important aspects of TCs such as rainfall estimation and characteristics of the TC-related rainfall drop size distribution (DSD). The latter has implications for radar rainfall estimation and cloud modelling studies. In this thesis, we first validate the Tropical Rainfall Measuring Mission (TRMM) Multi-satellite Precipitation Analysis (TMPA) 3B42 quantitative precipitation estimates (QPEs) during the passage of TCs over New Caledonia and Fiji. It is shown that TMPA has skill in representing the rainfall during the passage of TCs over New Caledonia and Fiji. TMPA overestimates light rainfall and underestimates moderate to heavy daily rainfall. The skill deteriorates with increasing elevation, as underestimation is greater at large altitudes. The ability of TMPA also varies with TC intensity and distance from the TC centre, whereby it is more skilful for less intense TCs (category 1-2) and near the TC centre than in the outer rainbands. The rainfall DSD during the passage of TCs over Darwin, Australia, is evaluated next and this is compared with the DSD associated with non-tropical cyclone (non-TC) events. It is shown that the TC-related DSD is statistically different from the non-TC related DSD, the former encompassing a larger concentration of small to moderate size drops. The TC related drop diameter is lower than the non-TC values at all rain rates and also for the different precipitation types (convective, transition and stratiform). The TC DSD also varies with distance from the TC centre, as rainfall near the TC centre comprises of relatively smaller drops which are strongly evident at small to moderate rainfall rates (< 30 mm hr-1). These variations in the DSD have implications for the parameters used in the algorithm that converts radar reflectivity to rainfall rate, as well as for the analytical expressions used in describing the observed DSD employed in cloud modelling parameterizations. Finally, the feasibility of estimating the DSD parameters using (i) the TRMM precipitation radar (PR) and (ii) a combined PR and TRMM Microwave Imager (TMI) algorithm (COM) is investigated using the Darwin C-band dual polarised (C-POL) ground radar (GR) as the reference. The correspondence of the TRMM instruments with the GR is generally dependent on the precipitation type: the PR and the COM usually overestimate (underestimate) the reflectivity and the rainfall rate from events that are highly stratiform (convective) whereas they mostly overestimate the median volume diameter (Do) of all rainfall types whereby the overestimation increases with an increase in the percentage of convective fraction. Also, the COM reflectivity estimates are similar to the PR estimates but it has a smaller bias in the Do for most of the greater stratiform events. This suggests that combining the TMI with the PR adjusts the Do towards the “correct” direction if the GR is taken as the reference. Moreover, for the TC events considered in this study, the association of the TRMM estimates with the GR is similar to the highly stratiform non-TC events (there is no significant difference) but it differs largely from the majority of the highly convective non-TC events.