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Roughness length is a parameter of some vertical wind profile equations that model the horizontal mean wind speed near the ground. In the log wind profile, it is equivalent to the height at which the wind speed theoretically becomes zero in the absence of wind-slowing obstacles and under neutral conditions. In reality, the wind at this height ...
Consequently, a wind blowing from the north has a wind direction referred to as 0° (360°); a wind blowing from the east has a wind direction referred to as 90°, etc. Weather forecasts typically give the direction of the wind along with its speed, for example a "northerly wind at 15 km/h" is a wind blowing from the north at a speed of 15 km/h ...
Presented in a polar coordinate grid, the wind rose shows the frequency of winds blowing from particular directions. The length of each spoke around the circle is related to the proportion of the time that the wind blows from each direction. Each concentric circle represents a different proportion, increasing outwards from zero at the center.
A wind atlas contains data on the wind speed and wind direction in a region. [1] These data include maps , but also time series or frequency distributions . A climatological wind atlas covers hourly averages at a standard height (10 meters) over even longer periods (30 years) but depending on the application there are variations in averaging ...
Wind roses typically use 16 cardinal directions, such as north (N), NNE, NE, etc., although they may be subdivided into as many as 32 directions. [ 4 ] [ 5 ] In terms of angle measurement in degrees, North corresponds to 0°/360°, East to 90°, South to 180° and West to 270°.
Such maps have been in use since the mid-19th century and are used for research and weather forecasting purposes. Maps using isotherms show temperature gradients, [2] which can help locate weather fronts. Isotach maps, analyzing lines of equal wind speed, [3] on a constant pressure surface of 300 or 250 hPa show where the jet stream is located.
A trough is an elongated area of lower air pressure. Since pressure is closely linked to wind, there are often changes in wind direction across a trough. If a trough forms in the mid-latitudes, a temperature difference at some distance between the two sides of the trough usually exists and the trough might become a weather front at some point.
Along with wind direction, cloud cover is one of the oldest atmospheric conditions to be coded on a station model. [ 7 ] [ 8 ] The circle in the middle of the station model represents cloud cover. In the United Kingdom , when the observation is taken from an automated weather observation site, the shape is a triangle. [ 10 ]