Radar Observations of the Effects of Changing Electric Fields on the Orientations of Hydrometeors PDF Download

Author: James I. Metcalf
Publisher:
ISBN:
Category : Atmospheric electricity
Languages : en
Pages : 38

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Book Description
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. We observed changes up to 2 dB in CDR, 50% in cross-correlation, and 40° in phase. However, many occurrences of lightning observed by radar were not accompanied by detectable changes of hydrometeor orientations, and we did not observe the cyclical changes of the polarimetric quantities that have been observed elsewhere with radars of shorter wavelength. We present examples of our observations and discuss implications for future measurements with this radar.