A study of radar echo patterns related to mesoscale network observations and topography

Graduation date: 1964This investigation studies the relationship of the reflectivity in\ud the radar beam depicted by the radar echo patterns to the computed\ud reflectivity at surface observing stations under the radar beam.\ud Drop size distributions at stations in the Oregon State University\ud Mesometeorological Network during the storm period of 27-30 March\ud 1963 provided data for computation of the radar reflectivity at the\ud surface. Films of the Weather Radar Set AN/CPS-9 PPI scope\ud simultaneously recorded the reflectivity in the radar beam presented\ud by the radar echo patterns as the beam scanned above the Mesometeorological\ud Network. The derivation of the theoretical relationship\ud between the reflectivity Z in the radar beam and the receiver\ud gain step G[subscript r], which gives a relative measure of the average\ud returned power, yielded a final result in the form:\ud log Z(m³/mm⁶) = 0.1 G[subscript r](db⁻¹) + constant, where 0.1 represents\ud the regression coefficient. Replacing the reflectivity Z in the\ud beam by the computed reflectivity at the surface Z[subscript s] yielded a set\ud of data pairs (Z[subscript s], G[subscript r]) for each surface observing station. The\ud method of least squares computed for each set of data the sample\ud regression curve of the form: log Z[subscript s](m³/mm⁶) = b(G[subscript r])(db⁻¹) +\ud constant. Statistical methods determined if significant differences\ud from the theoretical relationship occurred when the reflectivity at\ud the surface substituted for the reflectivity in the beam. Statistical\ud tests on the sample regression curves determined for the population\ud of data pairs (Z[subscript s], G[subscript r]) at different stations that the new relationships\ud remained linear in 90 percent of the cases, testing at the five percent\ud level of significance. Testing at the ten percent level of significance,\ud the regression coefficient remained equal to 0.1 in 90\ud percent of the cases. The correlation coefficients between the two\ud independent values of reflectivity, log Z[subscript s] (m³/mm⁶) and G[subscript r](db⁻¹),\ud showed a tendency toward lower correlation for one synoptic case\ud of postfrontal showers than in another synoptic case of continuous\ud prefrontal rain