High Surface Wind Research Articles

An observational study of the structure of stratiform cloud sheets: Part I. Structure

AbstractResults from six flights with an instrumented aircraft in marine, stratiform cloud‐topped boundary layers are presented. The flights took place around the U.K. in a variety of conditions, both during the day and at night. The data comprise simultaneous, high resolution turbulence, cloud microphysics and radiation measurements.On five of the flights, turbulent mixing in the cloud layer was found to be primarily maintained by convection resulting from cloud top radiative cooling. In four cases, this mixed layer was observed to be decoupled from the surface, i.e. the cloud‐induced mixing did not extend down to the surface, and the cloud formed part of a detached turbulent layer. One flight in high surface wind conditions displayed a significantly different structure. Possible reasons for this are suggested.The mean microphysical features of the different cloud layers are compared, as are the measured and theoretically calculated radiation fluxes. The latter show good general agreement, but some systematic differences are apparent. Again, possible causes of these disparities are discussed.Features of the turbulent velocity field are presented and a number of similarities between data from the convective cases and cloud‐free boundary layers driven by heating from below are found. Values of the entrainment velocity are estimated directly from the measured cloud top water fluxes in all but one case, together with an estimate of the errors incurred. The measured vertical turbulent fluxes are found to be reasonably well predicted by diagnostic mixed‐layer models using the measured boundary conditions as long as the heights of the mixed‐layer boundaries are also specified from observations. Such a model is also used to help explain the main observed features of the mixed‐layer structure and the differences between the various cases.

Deep-sea sediments in the eastern equatorial Atlantic off the African coast and meteorological flow patterns over the Sahel

Deep-sea mineral dust deposits are a powerful tool allowing to deduct atmospheric flow patterns. Here deep-sea sediments from the eastern tropical Atlantic were used to derive climatic conditions over the African continent where in summer the dust is lifted in the transition zone of the Sahara and the Sahel. The meteorological process causing this aeolian dust injection are the squall lines, the rain bearing disturbances of the Sahel. They produce a high surface wind velocity area in their northern vicinity. The deep-sea deposits of sediments and their spatial patterns allowed to conclude that the dust raising mechanism connected with the squall lines were similar for present day conditions and for the time of the last glacial maximum. The Saharan trades and the African monsoon had about the same extension in either time slice coupled with an identical travel belt of the squall lines. However, the intensity and the frequency of the squall lines were lower in glacial times.

Analysis of low-altitude wind speed and direction shears

Horizontal wind profile measurements recorded at the NASA 150-Meter Ground Winds Tower Facility at the Kennedy Space Center, Fla., are analyzed to evaluate wind shears known to be hazardous to the ascent and descent of conventional aircraft and the Space Shuttle. Twenty 5-s intervals of high (between 10 and 18 m/s) and gale force (18 to 33 m/s) surface winds provided instantaneous recordings every 0.1 s per speed, direction, and tower level from 3-150 m. Mathematical (maximum, mean, standard deviation) and graphical (percentage frequency distribution) descriptions of absolute, positive, and negative speed and direction shears with altitude (six vertical layers) and along flight path (one horizontal distance) are presented as functions of the intensity categories and significant values.

NOAA satellite set for launch

The latest in a series of National Oceanic and Atmospheric Administration (NOAA) meteorological satellites is scheduled for launch from Vandenberg Air Force Base, Calif., on December 1, 1984. High surface winds delayed the launch from the originally scheduled date of November 8. The 1712‐kg satellite, the NOAA‐F, is to be launched to an altitude of approximately 870 km into a circular near‐polar orbit. The satellite is the sixth in the current series of 11 NOAA satellites that collect meteorological readings and transmit the data to ground stations for local weather analysis and forecasting.

Response of Stratified Flow in the Lee of the Olympic Mountains

The behavior of stratified air flowing around an isolated mountain is dependent on an internal Froude number (F), which indicates the relative importance of upstream velocity and vertical stratification. Three cases of the flow in the lee of the Olympic Mountains in the State of Washington are studied where the measured F was in the range 1.0–1.4 but apparently dominated by stable stratification. This study combined measurements of spatial variation of low-level winds and other parameters from a NOAA P-3 research aircraft with a dense network of surface stations including eight meteorological buoys and six upper-air stations. Results from these cases show the presence of an area of light winds in the lee of the Olympic Mountains. The characteristics of the flow are shown to be similar to laboratory results for low Froude number flow around an isolated obstacle where the flow is confined to quasi-horizontal planes. These cases are contrasted with a situation which led to the formation of a mesoscale low-pressure area and high surface winds in the lee of the mountains. The latter case was the Hood Canal Bridge storm on 13 February 1979 where local winds in the lee of the Olympic Mountains were in excess of 50 m s−1. The flow at the surface was produced by down-pressure-gradient acceleration in the confined channels of Puget Sound toward the orographically produced low-pressure center. The measured internal Froude number in this situation was 4.6, and the pressure fields are shown to agree with the linear hydrostatic model developed by Smith (1980) for F > 1. It is suggested that the Froude number calculated from routine, upper-air sounding data is an index that forecasters can use to determine the potential for severe wind conditions over the inland waters of Puget Sound.

PREDICTION OF THE MOTION OF OIL SPILLS IN CANADIAN ARCTIC WATERS

ABSTRACT An oil spill movement prediction model operating as part of a real-time Environmental Prediction Support System for the Canadian Beaufort Sea has been developed. The present version of the model considers spills only in open waters, that is, the sea surface is considered to be ice free. The model has been partially verified with data obtained from oil simulation experiments conducted in the Bay of Fundy, off the east coast of Canada during the months of August and September, 1978. With the use of observed winds, the model-predicted locations of “Orion” buoys used to simulate the motion of oil on water, agreed fairly well with their observed locations. These verification tests also pointed out the need for high resolution surface wind forecasts — essential data for computing wind-driven water currents which move the oil.

The wind stress over the ocean from observations in the trades

AbstractThe method of geostrophic departure is used to determine the surface drag of the ocean in the Trade‐wind belt, this region being particularly suitable for the technique because the opposition of the thermal wind to the surface geostrophic wind leads to a maximum in wind speed at a few hundred metres elevation. This pilot study is based on balloon winds at three very small Pacific islands and the U.S.W.B. Northern Hemisphere Charts of surface pressure. A drag coefficient of 1·0 × 10−3 is found from two of the stations, and 1·5 × 10−3 at the third and there is no systematic variation with surface‐wind speed from 3 m/sec to 12 m/sec. The higher value of drag coefficient may be due to excessive roughness caused by reefs, or possibly to thermal instability.A similar analysis for San Juan in the West Indies shows the disturbing effect of a larger land area on the geostrophic departure so that only in high surface winds does the apparent drag tend to the probable value. Some other features of the Trade‐wind regime are briefly described.