Precipitation radar

Robertson FR, Fitzjarrald DE, Kummerow CD (2003) Effect of uncertainty in TRMM precipitation radar path integrated attenuation on interannual variations of tropical oceanic rainfall. Geophy Res Lett 30(4). doi 10.1029/2002GL016416... 

Fibrillated Fibers. Instead of extmding cellulose acetate into a continuous fiber, discrete, pulp-like agglomerates of fine, individual fibrils, called fibrets or fibrids, can be produced by rapid precipitation with an attenuating coagulation fluid. The individual fibers have diameters of 0.5 to 5.0 ]lni and lengths of 20 to 200 )Jm (Fig. 10). The surface area of the fibrillated fibers are about 20 m /g, about 60—80 times that of standard textile fibers. These materials are very hydrophilic an 85% moisture content has the appearance of a dry soHd (72). One appHcation is in a paper stmcture where their fine fiber size and branched stmcture allows mechanical entrapment of small particles. The fibers can also be loaded with particles to enhance some desired performance such as enhanced opacity for papers. When filled with metal particles it was suggested they be used as a radar screen in aerial warfare (73). 

Seliga, T. A., and V. N. Bringi, 1976. Potential use of radar differential reflectivity measurements at orthogonal polarizations for measuring precipitation, J. Appl. Meteorol., 15, 69-76. 

By the 1940s, upper-level measurements of pressure, temperature, wind and humidity clarified more about the vertical properties of the atmosphere. In the 1950s, radar became important for detecting precipitation over a remote area. Also in the 1950s, with the invention of the computer, weather forecasting became not only quicker but also more reliable, because the computers could solve the mathematical equations of the atmospheric models much faster. In 1960, the first meteorological satellite was launched to provide 24-hour monitoring of weather events worldwide. 

A network of 8 radar stations provides information on the position and movement of clouds, as well as on the wind speed. These data are crucial for precipitation forecasts. The radars use the Doppler effect to measure clouds speed and by this way wind speed. Their observation range (the radius of the circle covered) is 200 kilometers. The resolution of cloud distribution measurements ranges from 1 kilometer to 4 kilometers, and that of wind speed is 0.5 kilometer per hour. The data are updated every 10 minutes. 

Cloud physicists draw on the well-developed sciences of chemistry, physics, and fluid dynamics to study these phenomena. Such topics as the thermodynamics of moist air, the physics of the growth of water droplets and ice particles, radiation, effects of clouds on climate, electrification, and chemical conversion processes are all part of this discipline. Major research tools include computers for numerical simulation and aircraft and radars for observation, along with wind firrmels and cold rooms for the study of the properties of cloud and precipitation particles. 

The TRMM precipitation retrievals are based on the emission of microwave radiation from raindrops. The PR is the first space-based radar to measure precipitation [41 3]. It operates at 13.8 GHz frequency with a 2.17 cm wavelength. The instrument is capable of detecting echoes of >17 dbz. However, due to the strong reflection of the earth s surface, PR measures precipitation rates close to the ground surface, thus affecting the reflectivity profile above the surface [43]. 

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