Description of the images deduced from the radar ST data

For every day, the horizontal wind continuously measured at different altitudes above the radar has been averaged over each hour of measurement. This mean wind has been drawn in a time-altitude image, in which the abscissa is the time expressed in UTC hour. UTC is the Coordinated Universal Time which is an acronym chosen to satisfy both the English and French speaking communities since it does not have a direct equivalent in either language - in French UTC reads as Temps Universel Coordonné. UTC is based on an atomic standard, but for all practical purposes is equivalent to GMT and, for Clermont-Ferrand, it is the local time -1 h in winter and - 2 h in summer. In the time-altitude image, the ordinate is the altitude above the sea level, expressed in m ASL. On these images, each vector represents the strength (length of the vector) and the direction with respect to the North (arrow direction) of the mean horizontal wind obtained at the time corresponding to the abscissa of the arrow foot and at the altitude of its ordinate. Therefore, a pointing upward arrow represents a wind coming from the South et blowing towards the North.

The color of each vector of the horizontal wind depends upon its speed following :

         0 m/s =< V < 10 m/s  = > black
        10 m/s =< V < 15 m/s  = > dark green 
        15 m/s =< V < 20 m/s  = > green
        20 m/s =< V < 25 m/s  = > blue-green
        25 m/s =< V < 30 m/s  = > blue
        30 m/s =< V < 35 m/s  = > light blue
        35 m/s =< V < 40 m/s  = > purple
        40 m/s =< V < 45 m/s  = > pink
        45 m/s =< V < 50 m/s  = > red
        50 m/s =< V < 55 m/s  = > brown
        55 m/s =< V < 60 m/s  = > dark brown
        60 m/s =< V < 65 m/s  = > orange
        65 m/s =< V < 70 m/s  = > yellow
        70 m/s =< V < 75 m/s  = > light gray
        75 m/s =< V < 80 m/s  = > mean gray
        80 m/s =< V < 85 m/s  = > dark gray

During the continuous measurements by the radar, each image covers a 3 day period, the last day of which corresponds to the date indicated in the image list of the previous page. During the starting periods of measurements, the corresponding image may cover only 1 or 2 days ending at the date indicated in the image list.

Since the beginning of 2002, the images are in the PNG (Portable Network Graphics) format and red isolines of the vertical velocity (1., 2. et 3. m/s in full lines and -1., -2. et -3. in dashed lines) are overlaid over the horizontal wind vectors.

Yves Pointin

Back to the WEB page of La.M.P./O.P.G.C.

This page has been modified on November 23, 2007