What Is a Weather Radar?

Weather radar is a kind of meteorological radar. It is a main tool for monitoring and early warning of strong convective weather. Its working principle is to emit a series of pulsed electromagnetic waves and use the scattering and absorption of electromagnetic waves by precipitation particles such as clouds, rain, and snow to detect The spatial distribution and vertical structure of precipitation are used as a warning to track the precipitation system. ^[1] The wavelengths commonly used by weather radars are mostly in the range of 1-10cm. Because the attenuation of the 10cm wavelength is small, it is better for detecting typhoons, heavy rain and hail. Currently domestically used are 713 mines (5.6cm), 714 radars (10cm) and 711 radars (3.2cm), which can detect weather systems within hundreds of kilometers of radar stations.

Weather radars are mostly pulse radars. They emit pulse waves of short duration (0.25 to 4 microseconds) at a certain repetition frequency, and then receive echo pulses scattered by precipitation particles. The scattering and absorption of precipitation by radar are related to the characteristics of raindrop spectrum, rain intensity, phase of precipitation particles, shape and orientation of ice grains (see

The weather radar is composed of the following basic parts: the transmitter-generating high-frequency pulses, directional antennas-transmitting detection pulses and receiving echo pulses, pressing the receiver-amplifying the echo pulse signal, and the display-displaying meteorological targets (Such as precipitation areas, storms) relative to the radar's position, echo strength, and structure. There are three kinds of displays commonly used in weather radar: distance display (A display or A / R display). An instrument that displays the echo strength of meteorological targets at different distances. Planar Position Display (PPI). A radar station is used as a display center, and a flat view of the azimuth and distance of a meteorological target is displayed in polar coordinates. It can reflect the horizontal distribution of precipitation areas, storms, etc. Distance and Height Indicator (RHI). An indicator that displays the distance and height of a meteorological target in a vertical plane at a given azimuth in the form of rectangular coordinates. It can reflect the vertical structure of precipitation areas, storms, etc. After the 1970s, quantitative weather radars were accompanied by digital processing systems with small computers.

The structure of the weather radar has the following characteristics: It uses a logarithmic intermediate frequency amplifier. It can make the output approximately proportional to the logarithm of the input signal strength, so as to ensure that the cloud and precipitation echo intensity with a wide range of change can be displayed accordingly. There is a distance correction. Since the received power Pr is inversely proportional to the square of the distance R (see

The detection principle of conventional weather radar is to use cloud and rain targets to scatter the echo of electromagnetic waves emitted by the radar to determine its spatial position, strength distribution, vertical structure, etc. In addition to the role of conventional weather radar, the new generation Doppler weather radar can also use the physical Doppler effect to determine the radial movement speed of precipitation particles, and infer the moving speed of precipitation cloud bodies and wind field structure. Characteristics, vertical air velocity, etc. The new generation of Doppler weather radar can effectively monitor the occurrence and development of catastrophic weather such as heavy rain, hail and tornado; meanwhile, it also has good performance of quantitative measurement of echo intensity, and can quantitatively estimate large-scale precipitation; Doppler In addition to providing various image information in real time, weather radar can also provide automatic identification and tracking products for a variety of severe weather. ^[2]

The new generation Doppler weather radar plays an irreplaceable role in the monitoring and early warning of severe weather. The new generation of Doppler weather radars that have been built in China are mainly divided into S and C bands. S-band radars are mainly distributed in coastal areas and major rainfall basins. C-band radars are mainly distributed in inland areas. By the end of the "Eleventh Five-Year Plan," there will be a weather radar network consisting of 158 Doppler weather radars nationwide.

1. C-band weather radar (CINRAD / CC)

The C-band Doppler weather radar of the Beijing Meteorological Bureau can monitor typhoons, heavy rain and other large-scale heavy precipitation weather at a distance greater than 400 and can obtain precipitation and wind field information within a 150 km radius. Rainfall within the range is more accurately estimated. Compared with the conventional weather radar, the CINRAD / CC radar adds wind field information, which can effectively monitor and forecast gust fronts, downbursts, tropical cyclones, wind shear and other catastrophic weather.

2. S-band radar (CINRAD / SA)

Beijing's new generation of S-band Doppler weather radar can monitor typhoon, heavy rain, squall line, hail, tornado and other heavy precipitation weather in a radius of 400 kilometers. The effective monitoring and identification distance of the phenomenon can reach 230 kilometers, and it can identify the nuclear area of hail clouds with a mesoscale of 2 to 3 kilometers at a distance of 150 kilometers from the radar, or tornadoes with a scale of about 10 kilometers. Its advanced technology will significantly enhance the ability to monitor and warn of catastrophic weather such as heavy rain and hail, further improve the temporal and spatial resolution of precipitation forecasting, and realize the fixed-point, quantitative, and timing of precipitation forecasting. Life provides better weather forecasting services. ^[2]