| Popis: |
Wind-profiling Doppler radars measure the radial component of motion in the “clear atmosphere” along the radar beam. At lower VHF (e.g., 50 MHz) the backscattering process is highly anisotropic with maximum returns from stable layers near vertical incidence. By contrast, at UHF the backscattering process is very nearly isotropic. Because of these differences in scattering mechanism it is of interest to intercompare vertical velocities measured by collocated profilers, one operating at lower VHF and the other at UHF. An observational campaign was undertaken at Platteville, Colorado, to intercompare vertical motions measured by two collocated profilers. The VHF (50 MHz) wind profiler was operated in a vertical-only mode interrupted every half hour for radio accoustic sounding system (RASS) measurements. The UHF (404 MHz) profiler was operated in low and high modes that are customary for the Demonstration Network of profilers in the central United States. Observations made by these two systems in October and November 1991 are intercompared. The overall agreement in vertical motions is quite good above 8 km with both profilers showing downward mean velocities in the lee of the Colorado Rocky Mountains as large as 6 cm s−1. Below 8 km the UHF velocities are systematically more downward than the VHF velocities. This systematic difference is attributed to the influence of hydrometeors on the UHF observations, as can be seen clearly in daily and hourly profiles. |
Plný text