Radar Observations Of The Effects Of Changing Electric Fields On The Orientations Of Hydrometeors

The changing orientations of hydrometeors due to rapidly changing electric fields in clouds have been observed for the first time at a radar wavelength of 11 cm (S-band) with the polarimetric Doppler radar operated in Sudbury, MA by the Geophysics Directorate of Phillips Laboratory. During 1991 the radar was operated in a half-matrix mode, transmitting a signal of right circular polarization and receiving signals of right and left circular polarization. Observations of electrified storms on nine days during the spring and summer of 1991 revealed several occurrences of lightning that coincided with significant changes of the circular depolarization ratio (CDR), the cross- correlation, or the phase of the cross-covariance of the two received signals. Changes up to 2 dB in CDR, 50% in cross-correlation, and 40 deg in phase were observed. However, many occurrences of lightning observed by radar were not accompanied by detectable changes of hydrometeor orientations, and there were no observations of the cyclical changes of the polarimetric quantities that have been observed elsewhere with radars of shorter wavelength. Examples of observations are presented and implications for future measurements with this radar are discussed.

Rapid progress during the last twenty years has created a host of new technologies for studying electrical storms, including lightning mapping systems, new radars, satellite sensors, and new ways of measuring electric field and particle charge. This book explains how these advances have revolutionized our understanding. The books provides substantial background material, making it accessible to a broad scientific audience.

This 2001 book provides a detailed introduction to the principles of Doppler and polarimetric radar, focusing in particular on their use in the analysis of weather systems. The design features and operation of practical radar systems are highlighted throughout the book in order to illustrate important theoretical foundations.