Katabatic wind

Nylen, T.H., Fountain, A.G., Doran, P.T. 2004. Climatology of katabatic winds in the McMurdo dry valleys, southern Victoria Land, Antarctica, Journal of Geophysical Research, 109, 9. 

Figure 2. Diurnal variation of DMS in air and surface seawater observed at a station in Gerlache Strait during a high pressure weather situation with intense daylight and strong katabatic winds at night. (Reprinted with permission from Ref. 12. Copyright 1987 by the American Geophysical Union).

To develop our novel micro-meteorological instruments, we used a large cow-pasture east of Pasadena, which gently sloped up toward the San Gabriel mountains. We had a favorite demonstration of katabatic wind. We had a pole with eight wind vanes spaced about every half meter apart. In the afternoon, the sea breeze caused all the wind vanes to point toward the Pacific Ocean. As sunset approached, first the lowest wind vane on our pole turned and pointed toward the mountain as a shallow current of cold air flowed downhill. Somewhat later the second vane turned, then the third, fourth, fifth, sixth, seventh, and finally the eighth turned as the katabatic wind built up to be a deep gentle flow of cold air. Before sunset, we could almost tell the time of day by how many wind vanes pointed uphill. 

The army representative said that the town was four miles away, and war gases don t travel that far. The Berkeley group mentioned the slope, the terrain, and katabatic winds, but the army was unconvinced. Ruben and Gwinn came up with another idea and went ahead with their proposed novel experiment. 

At low wind speed at night, the surfece was cooled by emission of heat radiation, air was cooled upon contact with the surface, and cold dense air pooled on the surface as if a separate fluid. We had an inversion. Where the ground sloped, the cold surface air flowed downhill, a katabatic wind, and mechanical turbulence was induced by this wind. When there was a prevailing wind, its mechanically induced turbulence was reduced by the... 

The local conditions that affect the weather alluded to above include the katabatic wind that blows from the polar plateau through the valleys of the outlet glaciers in the Transantarctic Mountains. The wind is generated when the layer of cold air that forms directly above the surface of the polar plateau drains downslope toward the coast. The speed of the wind on a gentle slope... 

During cloudy weather a condition known as white-out may occur when surface definition deteriorates because of the absence of shadows and because the horizon disappears. These conditions are dangerous because they can lead to accidents that result from poor visibility and associated disorientation. Whiteout conditions in Fig. 2.4 can also occur during dense fog and may be caused by ground blizzards when strong katabatic winds inject snow into the air. Travel on the polar platean and in the mountains is not indicated under whiteont conditions. 

Former residents of McMurdo Station will also recall the windstorms that suddenly reduce visibility to less than 100 ft (30.48 m), with wind speeds in excess of 55 knots (101.9 km/h), and wind-chill temperatures that drop below -100°F (-73.3°C). Under these conditions, all personnel in McMurdo are required to remain in-doors (Condition 1) and all travel is suspended for the duration of the storm that may last several days. The classification of weather conditions detailed in Table 2.3 is the responsibility of the McMurdo Weather Office (Mac Weather). Condition 1 storms can occur anywhere within the Transantarctic Mountains during the austral spring and fall especially on major outlet glaciers, such as the Reedy Glacier in Fig. 2.11, that channel the katabatic winds from the polar plateau to the Ross Ice Shelf or to the Ross Sea. Field parties that experience such storms learn first-hand that weather still rules in Antarctica. 

Fig. 2.11 Strong katabatic wind on the Reedy Glacier caused near whiteout conditions in this geological field camp in November of 1964 (Photo by G. Faure)...

The blue ice areas are of great interest because they expose old ice that formed in the central accumulation area that may be up to 1,000 km distant in the up-ice direction. Moreover, meteorites, cosmic spherules, fly-ash, and other kinds of object or particles that fell on the surface of the ice sheet in the area of accumulation emerge from the ice in the ablation area and can be recovered for scientific study (Chapter 18). Blue ice is typically slippery and rippled by the katabatic winds which polish its surface. Many unwary travelers have slipped on the ice and fallen unexpectedly, sometimes with painful consequences. 

The source of the wind, e.g. whether it is a mild south-westerly, or whether it is cold polar air from the north or from the Continent in winter, and hot, dry wind from the south in summer. Wind direction depends mainly on the position of areas of high and low pressure in the immediate vicinity of the British Isles, although local winds, e.g. offshore breezes, Fohn effect winds (warm) and katabatic winds (cold) from high ground, can occur independently of the cyclonic system. 

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