Experience from one year of operating a boundary-layer profiler in the center of a large city

Abstract

Abstract. Since May 1992 a small, 915-MHz profiler has been operated continuously in downtown Montreal. It is a five-beam system employing a microstrip array antenna, located atop a 14-story office building that houses several academic departments of McGill University. The data are used for research on precipitation physics and the clear-air reflectivity in addition to wind profiling. We are especially interested in situations in which the reflectivities of the clear air and the precipitation are comparable. This permits the study of interactions between the precipitation and the clear air, a new area of research made possible by wind profilers. On clear days in the summer, 30-min consensus winds can often be measured to an altitude of 3 km, but ground clutter in the antenna sidelobes interferes with measurements below 600 m. Rain when present often permits wind profiling down to 100 m and up to 6 km or higher. On cold winter days there are some periods when the reflectivity is too weak at all levels to permit wind estimation. Falling snow, however, provides readily detectable echoes and serves as a good tracer of the wind and so allows profiling over its full altitude extent. The best conditions for observing interactions between precipitation and the clear air are when light rain falls through a reflective layer associated with a frontal surface or inversion. Unexpectedly, flocks of migrating birds sometimes completely dominate the signal at night in the spring and fall seasons.

Interactions between clear‐air reflective layers and rain observed with a boundary layer wind profiler

“…Spatial irregularities in the refractivity are caused by turbulence acting on mean gradients of the potential refractive index [Tatarski, 1961 ]. Because vertical gradients of potential refractive index are generally much stronger than those in the horizontal, a common model is to consider this vertical gradient as it is mixed by turbulent eddies.…”

“…Since May 1992, a 915-MHz boundary layer wind profiler has been operated in downtown Montreal as a collaborative project of the National Oceanic and Atmospheric Administration (NOAA) and McGill University. Rogers et al [1994] have described the profiler and have given examples of data from the first year of operation. The profiler is fundamentally an improved version of the prototype model of the small UHF profiler described by Ecklund et al [1988Ecklund et al [ , 1990 and the profiler employed on the Hawaiian Rainband Project [Rogers et al, 1993].…”