Showing papers on "Winds aloft published in 1978"

Comparison of Meteorological Aspects of the Big Thompson and Rapid City Flash Floods

Abstract: Analyses and descriptions of the meteorological conditions that produced devastating flash floods in the Big Thompson Canyon on 31 July 1976 and in the Black Hills on 9 June 1972 are presented. The storms developed when strong low-level easterly winds pushed moist, conditionally unstable air masses upslope into elevated, mountainous terrain. Orographic uplift released the convective instability and light winds aloft allowed the storm complexes to remain nearly stationary. Meteorological conditions that produced these flash floods were found to have been very similar. A set of meteorological features is defined for the purpose of identifying the potential for this type flash flood along the eastern slopes of the Rocky Mountains.

The influences of weather and topography on water bird migration in the southwestern United States.

Abstract: Radar and visual observations were made on water bird migration throuh the Southwest at six stations from February 1973 through November 1974. The influence of weather on nocturnal non-passerine migration in the Southwest is less significant than reported for passerine migration elsewhere. Both seasonality and weather factors influence water bird migration, but the relative contribution of each is strongly dependent on the specific migration season. Spring migration, which has more extreme weather conditions, shows a stronger correlation to meteorological factors. Autumn migration in the Southwest rarely experiences severe weather, and consequently shows a stronger correlation to seasonality than to weather. The intensity of spring non-passerine migration was highly correlated with height of freezing level, temperature at sunset and midnight, humidity at sunset, cloud height at sunset and midnight, following winds aloft, and inversely related to change in temperature and day of the year. The most important variables listed by the stepwise linear multiple regression analysis were freezing level, following winds aloft, day of the year, and surface wind speed. When the height of the lowest cloud layer was allowed to enter the regression analysis, freezing level and cloud height were the most significant variables, with the intensity of migration higher with higher freezing level and higher cloud base. The most important variables predicting the occurrence or absence of migration were freezing level, barometric pressure and dew point. Autumn water bird migration was most highly correlated with cloud height and day of the year, and inversely correlated with humidity. The most important variables from the stepwise regression analysis and discriminant function analysis were day of the year, 670 m following-wind speed, and temperature. When cloud height was allowed to enter the model, it was the only significant factor influencing migration. As in spring, higher rates of autumn migration occurred with higher freezing levels. More migration occurred on the Great Plains than in the Rocky Mountains; but within the mountains, geography had little influence on the intensity of migration. Indirect evidence indicates that waterfowl and shorebirds move over the mountains (up to 2000 m above the surrounding terrain and 3500 m above sea level), rather than around them.

The Earth's neutral upper atmosphere

Abstract: This paper was intended as an introductory and superficial survey of the earth's neutral upper atmosphere, mainly at heights between 100 and 1000 km, to prepare for the more specialized papers which followed. The density, temperature, and winds and their variations are briefly discussed.

Doppler Velocities in Rain Bands of Hurricane Belle

Abstract: : Hurricane Belle skirted the east coast of the US during the evening of 9 August 1976, crossed Long Island just east of New York City shortly after midnight, and dissipated in the mountainous country of western and northern New England Several of the hurricane rain bands passed over the AFGL Doppler radar site at Sudbury, Mass, providing an excellent opportunity for monitoring local winds aloft in the hurricane circulation, using the VAD technique of Lhermitte and Atlas In the outer and middle bands there was a low-level wind maximum from the northeast quadrant at heights well under 1 km, with strong directional shear up to 3-5 km where there was generally a wind maximum from the SSE Generally the winds veered with height but during a brief period they backed Winds at the cirrus level of 6-9 km were consistently from the south Maximum wind speeds were 25 to 30 m/sec Interesting velocity information was also acquired at low elevation angles in remote portions of bands Velocity patterns in the innermost rain band indicated a period of intense deformation, pronounced curvature of the wind field, and speeds up to at least 35 m/sec, which is consistent with the proximity of the center of low pressure