Use of two profilers during MCTEX for unambiguous identification of Bragg scattering and Rayleigh scattering

A 2835-MHz (10.6-cm wavelength) profiler and a 920-MHz (32.6-cm wavelength) profiler were collocated by the NOAA Aeronomy Laboratory at Garden Point, Australia, in the Tiwi Islands during the Maritime Continent Thunderstorm E xperiment (MCTEX) field campaign in November and December 1995. The two pro filers were directed vertically and observed vertical velocities in the cle ar atmosphere and hydrometeor fall velocities in deep precipitating cloud s ystems. In the absence of Rayleigh scatterers, the profilers obtain backsca ttering,a from the refractive index irregularities created from atmospheric turbulence acting upon refractive index gradients. This kind of scattering is commonly referred to as Bragg scattering and is only weakly dependent o n the radar wavelength provided the radar half-wavelength lies within the i nertial subrange of homogeneous, isotropic turbulence. In the presence of h ydrometeors the profilers observe Rayleigh backscattering from hydrometeors much as weather radars do and this backscatter is very dependent upon rada r wavelength, strongly favoring the shorter wavelength profiler resulting i n a 20-dB enhancement, of the ability of the 2835-MHz profiler to observe h ydrometeors. This paper presents observations of equivalent reflectivity, D oppler velocity, and spectral width made by the collocated profilers during MCTEX. Differential reflectivity is used to diagnose the type of echo obse rved by the profilers in the spectral moment data. When precipitation or ot her particulate backscatter is dominant, the equivalent reflectivities are essentially the same for both profilers. When Bragg scattering is the domin ant process, equivalent reflectivity observed by the 1-GHz profiler exceeds the equivalent reflectivity observed by the 3-GHz profiler by approximatel y 18 dBZe. However, when the 3-GHz profiler half-wavelength is smaller than the inner scale of turbulence, the equivalent reflectivity difference exce eds 18 dBZe, and when both Rayleigh scattering and Bragg scattering are obs erved simultaneously, the equivalent reflectivity difference is less than 1 8 dBZe. The results obtained confirm the capability of two collocated profi lers to unambiguously identify the type of echo being observed and hence en able the segregation of "clear air" and precipitation echoes for studies of atmospheric dynamics and precipitating cloud systems.