. Compendium of meteorology. Meteorology. Fig. 10.—Photograph of RHI scope showing horizontal layer of strong echo signal (bright band) at altitude of about 11,000 ft. Tall vertical showers are indicative of convective activity. (1930 EST, 9/25/47, X-band radar.) { Weather Radar Research.) pulse resolution of the radar used to observe it, and since it has occasionally been determined to be no more than this amount for a given radar system, there is evi-. FiG. 11.—Photograph illustrating appearance of R scope when antenna is directed vertically and echoes are received from rain and snow.
. Compendium of meteorology. Meteorology. Fig. 10.—Photograph of RHI scope showing horizontal layer of strong echo signal (bright band) at altitude of about 11,000 ft. Tall vertical showers are indicative of convective activity. (1930 EST, 9/25/47, X-band radar.) { Weather Radar Research.) pulse resolution of the radar used to observe it, and since it has occasionally been determined to be no more than this amount for a given radar system, there is evi-. FiG. 11.—Photograph illustrating appearance of R scope when antenna is directed vertically and echoes are received from rain and snow. The weaker echo signal of the snow is due to its greater range and lower dielectric constant. The echo from rain shows much greater intensity variations because of the wider range of fall velocities of the water particles. (X- band radar, range 5 miles, 1-mile markers.) ( Weather Radar Research.) dence that the thickness of the band may vary from as little as a few tens of meters to several hundred meters in thickness or more. It has been observed in connec- tion with thunderstorms after convective activity has subsided [10, 19]. Two theories have been advanced to explain this phenomenon: 1. The region of strong echo is due to drop formation in the colloidally unstable layer of heterogeneous ice- water mixture. Any precipitation detected above that altitude would therefore probably be caused by con- vective transport [19]. 2. Snow particles, too small to give more than a weak echo, fall to the zero degree isotherm, and melt at or just below this level. While melting, they have the low fall velocity of snowflakes, but the high reflectivity of water. Coalescence, often observed near melting tem- peratures, also serves to increase the reflectivity. After the snowflakes have completely melted, the fall velocity increases and the drops become widely spaced. The re- sult is a region of weaker echo below the level of melt- ing [10, 24, 52]. Most investigators are inclined to
Size: 1366px × 1830px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookcollectionbiodivers, booksubjectmeteorology
