Study on a Stochastic Model of Birth-Death Process of Rain Cells and Rainfall Forecasting

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How to analyze and make a model for variation of meso-beta and meso-gamma rainfall area in time and space is important to study flood runoff phenomena in basin-scale. This study investigated the way for separating rain cells, cell clusters, and rain-bands, and tracking them and analyzed stochastic properties those elements.To analyze the variation properties in time of rain-bands, we got the data observed dy Okinawa Radar Rain gauge most of the observation area of which is over sea. The use of weather rader data is desirable for analtyzing the properties of rain cells, because we need to consider them in the scale of kilometers.We proposed "rainfall area growth curve analysis" and "tangential valley analysis" to analyze the hierarchy structure of rainfall fields. Rainfall area growth curves are considered around each local maximal points of rainfall intensity, with taking the difference between rainfall intensity at local maximal point and given rainfall intensity in the y axis and squ … More are roof of area where the rainfall intensity is greater than the given rainfall intensity in the x axis. The application of those method told us that the rainfall field can be modeled as the field in which rain cells ride on rain-bands. We separated using tangential valley analysis rain cells and rain-bands, and investigated the distribution of speed of movement and life time of rain cells.Because it has been known already that rain-bands of typhoon is on logarithmic spirals, we introduced curvilinear two-dimensional coordinates based on logarithmic apirals into rainfall fields and processed the data about rain cells on those curvilinear coodinates. The result of this analysis told us that rain areas in meso-beta scale move along spirals so that they go away off the eye. Within spirals, rain area in meso-beta scale move faster than the beginning and ending points of rain-bands and at ending points of rain-bands new inner rain areas are born and at beginning points of rain-bands inner rain areas die.Our analysis showed that life time and size of rain areas in meso-gamma scale follow exponential distribution and beta distribution, respectively. The analysis about correlation between meso-gamma scale rain area (Mg) and meso-beta scale rain area (Mb) showed us that 1) the number of Mg in Mb is constant in time, 2) the distribution of distance of Mg's in Mb folows exponential distribution, 3) the birth points of Mg's are uniform in Mb, and 4) the distance of birth points of Mg's from the eye follows exponential distribution. Less