Doppler radar



The Use of Doppler Radars for Studying the Turbulence 

of Air Masses in Clouds.

http://www.slideshare.net/rf1002/the-use-of-doppler-radars-for-studying-the-8007328

Abstract – A method for estimating the turbulent pulsations of the velocity of air masses in clouds has been proposed. This method is based on the spectra of scattered signals and makes use of the moment characteristics of the scattered signal spectrum and deviations of the characteristics from trend changes for estimating the shear characteristics of the air stream in terms of both the average speed and its spread.

A lot of atmospheric phenomena constitute a danger for the air and maritime transport. For needs of aviation and fleet it is necessary to improve the methods for forecasting the weather, conditions of meteorological quantities (atmospheric pressure, wind, and air temperature), movements and evolutions of hazardous synoptic object, such as cyclones, their troughs with atmospheric fronts, anticyclones, ridges, etc. One of such dangerous phenomenon is the wind shear.

Wind shear is the change of the wind vector (its speed and direction) per unit of distance. Wind shear is an indicator of the instability of atmosphere condition capable of causing the bumpy-air flight (bucketing) and at certain values of the wind shear it may endanger the safety of flights.

The vertical wind shear of more than 4 m/s per 60 m height is considered to be a meteorological phenomenon hazardous for flights.

The history of the radar meteorology began in the forties of the last century. At the first stage it had a descriptive character, when observations of reflections from meteorological formations and their classification were carried out, and the correlation between the reflections of different types and synoptic data was established. Beginning from the 1960s the quantitative interpretation of radar reflections was performed as well as the search for their dependence on such parameters as the rain intensity distribution, size of water drops, velocity of particles, and the atmospheric turbulence. The state and future trends of the development of meteorological radars were analyzed in paper.

The recognition of the nature of hydrometeors is a relatively new field of radiometeorology. In this connection the search for and investigation of the stable informative criterions is considered to be most topical direction of studies. In this case the use of polarization characteristics significantly improves the information capacity of radar signals reflected from hydrometeors. Also known are the methods of increasing the information capacity at the expense of applying the coherent processing of reflected signals based on measuring their spectral characteristics. New methods of describing the field polarization structure are applied for determining the microstructure of clouds, estimating the turbulence, and vibration of drops.

The majority of available studies involve the investigation of polarization spectral characteristics of signal backscattering and adsorption by hydrometeors for solving the inverse problem – determination of the spatial distribution of precipitation intensity, estimation of their potential hazard level.

In recent years the studies have appeared, where attempts are made to reconstruct the turbulent pulsations of air masses on the basis of the characteristics of scattered signal by using the movements of elementary scatterers (rain drops, snowflakes and hail particles). This involves the use of the polarization and spectral differences of scattering for different elements of space.

The present study proposes an approach to the analysis of turbulent pulsations, including those having the shear pattern, by using characteristics of the signal scattered by hydrometeors.