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- Author or Editor: Michael Istok x
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Abstract
The Next Generation Weather Radar (NEXRAD) may use a 5-min volume scan to monitor thunderstorms and provide hazard warnings. Short-lifetime, low-altitude wind shear near airports is a hazard to safe flights that deserves special attention. An interlaced scanning strategy is examined for its effects on the accuracy and reliability of some NEXRAD storm analysis and tracking algorithms that require noninterlaced data. By increasing the elevation step to twice its normal value and starting every other scan at the second step of the corresponding 5-min sequence, a pair of 2½-min sequences is achieved. These can be recombined for use in the NEXRAD algorithms while providing a shorter period between observations of rapidly developing phenomena such as low-altitude wind shear. It is found that differences between storm cell attributes derived from successive non-interlaced scans are about the same as differences between values obtained from interlaced and noninterlaced volume scans for the same time period. Thus, interlaced scanning may halve the wind shear warning time to be provided by the proposed NEXRAD noninterlaced scan strategy without significantly compromising the evaluation of storm attributes. Growth rates of reflectivity and updraft speed for several cells during the growth stage of a severe thunderstorm have been assessed in relation to the need for 2½-min updates to resolve severe thunderstorm phenomena. Results indicate that the growth rates are not so rapid as to require interlaced scanning for this purpose.
Abstract
The Next Generation Weather Radar (NEXRAD) may use a 5-min volume scan to monitor thunderstorms and provide hazard warnings. Short-lifetime, low-altitude wind shear near airports is a hazard to safe flights that deserves special attention. An interlaced scanning strategy is examined for its effects on the accuracy and reliability of some NEXRAD storm analysis and tracking algorithms that require noninterlaced data. By increasing the elevation step to twice its normal value and starting every other scan at the second step of the corresponding 5-min sequence, a pair of 2½-min sequences is achieved. These can be recombined for use in the NEXRAD algorithms while providing a shorter period between observations of rapidly developing phenomena such as low-altitude wind shear. It is found that differences between storm cell attributes derived from successive non-interlaced scans are about the same as differences between values obtained from interlaced and noninterlaced volume scans for the same time period. Thus, interlaced scanning may halve the wind shear warning time to be provided by the proposed NEXRAD noninterlaced scan strategy without significantly compromising the evaluation of storm attributes. Growth rates of reflectivity and updraft speed for several cells during the growth stage of a severe thunderstorm have been assessed in relation to the need for 2½-min updates to resolve severe thunderstorm phenomena. Results indicate that the growth rates are not so rapid as to require interlaced scanning for this purpose.
Abstract
Radar echoes from insects, birds, and bats in the atmosphere exhibit both symmetry and asymmetry in polarimetric patterns. Symmetry refers to similar magnitudes of polarimetric variables at opposite azimuths, and asymmetry relegates to differences in these magnitudes. Asymmetry can be due to different species observed at different azimuths. It is shown in this study that when both polarized waves are transmitted simultaneously, asymmetric patterns can also be caused by insects of the same species that are oriented in the same direction. A model for scattering of simultaneously transmitted horizontally and vertically polarized radar waves by insects is developed. The model reproduces the main features of asymmetric patterns in differential reflectivity: the copolar correlation coefficient and the differential phase. The radar differential phase on transmit between horizontally and vertically polarized waves plays a critical role in the formations of the asymmetric patterns. The width-to-length ratios of insects’ bodies and their orientation angles are retrieved from matching the model output with radar data.
Abstract
Radar echoes from insects, birds, and bats in the atmosphere exhibit both symmetry and asymmetry in polarimetric patterns. Symmetry refers to similar magnitudes of polarimetric variables at opposite azimuths, and asymmetry relegates to differences in these magnitudes. Asymmetry can be due to different species observed at different azimuths. It is shown in this study that when both polarized waves are transmitted simultaneously, asymmetric patterns can also be caused by insects of the same species that are oriented in the same direction. A model for scattering of simultaneously transmitted horizontally and vertically polarized radar waves by insects is developed. The model reproduces the main features of asymmetric patterns in differential reflectivity: the copolar correlation coefficient and the differential phase. The radar differential phase on transmit between horizontally and vertically polarized waves plays a critical role in the formations of the asymmetric patterns. The width-to-length ratios of insects’ bodies and their orientation angles are retrieved from matching the model output with radar data.
