Casebook 22 September 2003
From CHILL
CSU-CHILL Casebook: 22 September, 2003
PPI volume scans conducted on 22 September 2003 detected widespread boundary layer echo with a "dumbell" Zdr pattern characterized by maximum positive values of nearly +9 dB that are separated by ~180 degrees in azimuth. (See the first VCHILL example image below.) This Zdr pattern is observed when insects are flying in a preferred direction. The positive Zdr peaks occur when the radar is observing a side view of the insects, giving the largest horizontal / vertical axis length ratio. When the radar is illuminating an end-view of the insects, Zdr values are minimized. The broadside view of the insects also gives a larger backscattering cross section, so reflectivity maxima coincide with the Zdr peaks. The second VCHILL example is an RHI scan that passes through the layered insect echo.
