Entry 17

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Authors

  • Joseph Hardin

Abstract

This figure shows the results of electromagnetic scattering simulations for data retrieved from a disdrometer. A disdrometer is a device that gives a distribution of drop sizes for rainfall at the ground. In this case, we have a pseudo-pdf that tell us how many drops of each diameter were measured per minute, and the velocity of those drops. The drop size distribution is the image in the upper left panel. We take this information, and using the pytmatrix package by Jussin Leinonen, calculate the radar parameters that we would measure with an X-Band Radar. These parameters, and the rainfall rate, are listed down the first column. Next we show a histogram of the different parameters to allow an easy visual classificatin of the severity of the storm (In this case, primarily stratiform convection evidenced by the low values, but moderate rainfall) down the 2nd column. These parameters arise from the flattening of raindrops as they fall from clouds. The larger a raindrop, the more the drag from the air overwhelms hydrostatic tension causing drops to become oblate. This causes larger returns in the horizontal channel compared to the vertical channel. The differential reflectivity then forms a sort of proxy for the average size of the drops. The number of drops and axis ratio causes the phase to delay more in the horizontal direction. This is shown as specific differential phase.

Finally one of the main goals is to use these radar parameters to estimate the rainfall. This has applications in flooding, hydrology, and severe weather. Rain rate scales proportional to drop diameter to the 3.67 power. Reflectivity scales approximately as the 6th power of drop diameter. Specific differential phase however scales as approximately D to the 4th. We fit a power law relation between each of the parameters and rain rate and then plot the cumulative rainfall over the course of a day. We can see that the specific differential phase makes a much better estimator than reflectivity or differential reflectivity. In addition, specific differential phase does not suffer from the attenuation effects that usually plague reflectivity and differential reflectivity.

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