Observations of complex-terrain flows using acoustic sounders: Experiments, topography, and winds

Abstract

Acoustic sounders have now been used extensively in a series of noctural drainage flow experiments carried out by the U.S. Department of Energy's Atmospheric Studies in Complex Terrain (ASCOT) program. Doppler acoustic sounders, located in three different valleys during the sequence of experiments, reveal drainage-wind profiles that depend strongly on the ambient meteorological conditions and the elevation of each observing site relative to surrounding terrain. In elevated sites that drain easily, Doppler-sounder derived wind profiles show a simply-structured flow; in lower lying areas, subject to topographic constriction and cold-air pooling, and where Archimedean forces are comparable to those due to synoptic and mesoscale pressure gradients, the wind profiles show considerable vertical and temporal variation. In particular, in the Geysers area ofnorthern California, the seabreeze and the depth ofthe Pacific Coast marine inversion affect not only the initiation of drainage winds but also their subsequent evolution.

Observations of complex terrain flows using acoustic sounders: Echo interpretation

“…Neff and King (1987) using tethered balloon data, described typical temperature profiles that occur in nocturnal inversions in complex terrain. On steep slopes, radiative cooling, and the subsequent redistribution of heat by long-wave radiation and turbulent mixing near the surface, causes a shallow katabatic inversion layer, often less than 50 m depth.…”

“…Because of the lesser slopes, Archimedean forces were comparable to those of synoptic and mesoscale origin. Neff and King (1987) also described characteristic wind profiles observed in both simple and complex drainage flows using both Doppler sodars and tethered balloon soundings: over simple slopes and in draining valleys, wind profiles were simple, usually with a single wind maximum; in basins subject to topographic constriction and/or blocking by an ambient pressure gradient (such as the marine inversion in the Geysers), winds were light and variable with height and in time. In these data, the Doppler sodar wind profiles had a typical vertical resolution of 25 m, the tethered balloon of about 4 to 10 m.…”

“…The first part of this series (Neff and King, 1987), outlined a sequence of experiments carried out by the U.S. Department of Energy's Atmospheric Studies in Complex Terrain (ASCOT) program in which Doppler sodars were used. That paper described the topography and meteorology of the sites used in the experiments, and the behaviour of the Doppler-derived wind fields in a variety of circumstances.…”

Meteorological Variables Associated with Population Density of Culturable Atmospheric Bacteria at a Summer Site in the Mid-Willamette River Valley, Oregon

“…Figures 2, 3, 4, and 5 shows that there are distinct meteorological conditions associated with the natural prevalence of culturable airborne bacteria at the observation location during the summer: (1) daytime moderate ascending winds from the ENE traversing bacterial sources, plant and dry soil surfaces of the Willamette River Valley, and (2) nighttime light descending vwnds from the V^JWover and through gaps in the Douglas fir forests of the Pacific Coast Mountain Range from the Pacific Ocean. The ocean air could be the source of the relatively clean air (Schroeder, Fosberg, Cramer and O'Dell, 1967;Olsen and Tuft, 1970;Neff and King, 1987;Lighthartand Shaffer, 1995).…”

Boundary Layer Characteristics over Aindanda Low-Mountain Pass of Kathmandu Valley, Nepal

“…Because of their low cost, versatility, portability and ability to operate unattended for long periods of time, they have been extensively used in various terrain structures for various purposes. For example, sodars have been used to study coastal land-/sea breeze circulations (Aggarwal et al 1980, Bacci et al 1984, Prakash et al 1992, the Antarctic stable boundary layer (King et al 1989, Argentini et al 1992, wind flow in complex terrain (Neff 1988, Neff & King 1987, 1988, gravity waves (Einaudi et al 1987, Cheung & Little 1990, Ralph et al 1993, low-level jets (Kataoka et al 1991, Kotroni et al 1994, and frontal passages (Gera & Weill 1987. Techniques have been developed to derive turbulence parameters such as the sensible heat flux (Sen Gupta et al 1986), turbulence kinetic energy budget (Greenhut & Mastrantonio 1989), and temperature structure functions (Moulsley et al 1981, Singal et al 1982.…”