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<br />4 <br /> <br />it has been shown that the character of the orographic airflow depends <br /> <br />upon the upwind airflow, topography, and stability (Corby, 1947; Queny, <br /> <br />~; <br /> <br />1947; Scorer. 1949, 1951, 1953a,b, 1954; Schaffer, 1950; Queny, et a1., <br /> <br />1960; Sawyer, 1960; Elliott and Schaffer, 1962; Myers, 1962; Berkofsky, <br /> <br />.. <br /> <br />1964; Wallington, 1970; Willis, 1970; Orgill, 1971; Grant, et a1., 1974; <br /> <br />Mahrer and Pie1ke, 1975; Rhea, 1978). For broad mountains, half width <br /> <br />>20 km, the height at which the orographic vertical velocity first <br /> <br />becomes zero is proportional to one over the square root of the Scorer <br /> <br />parameter (Willis, 1970). <br /> <br />Q,2 = g/u2 ClLn8e b <br /> dZ <br />Q,2 g/u2 ClLn8 <br /> dZ <br /> 1 - Y /Y <br /> m d <br />b = 1 c T/EL <br /> P <br /> <br />(Scorer parameter for saturated air) <br /> <br />(Scorer parameter for dry air) <br /> <br />(Fraser, 1970; Fraser, et a1., 1973). <br /> <br />. <br />"" <br /> <br />Ym = saturated adiabatic lapse rate <br /> <br />Yd = dry adiabatic lapse rate <br /> <br />~ <br /> <br />T = temperature <br /> <br />E = .622 <br /> <br />L = latent heat of vaporization <br /> <br />c = specific heat at constant pressure <br />p <br /> <br />By calculating Scorer parameters for typical winter airmasses which <br /> <br />impinge upon the Colorado Rockies, Rhea (1978) showed that the height <br /> <br />at which the orographic vertical velocity first becomes zero is between <br /> <br />2 to 3 1/2 times as far above the mountain ridge for cloudy air as for <br /> <br />clear air over the Colorado Rockies. Therefore, even the presence of <br /> <br />'t, <br /> <br />moisture within the stabi1y stratified air can change its flow charac- <br /> <br />'l <br /> <br />teristics. WIlen the cloud system becomes unstable and convection sets <br />