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Dual-Polarization Radars Used to Predict Heavy Rainfall in China

China is one of the countries which experiences severe damage due to high-impact weather and associated mudslides and floods. Dual-polarization (dual-pol) radars, first built in the US in the late 1970s, have been widely used for tracking and nowcasting these high-impact weather occurrences.

This is Nanjing University’s C-band radar. (Image credit: Gang Chen)

Dual-pol parameters comprise an abundant amount of microphysical information on these heavy precipitation systems, according to Prof. Kun Zhao, Director of the Joint Center for Atmospheric Radar Research of the CMA/NJU, and Vice Dean of the School of Atmospheric Sciences, Nanjing University.

In the last couple of years, with the arrival of dual-pol radar technologies in China, numerous dual-pol radars have been designed by research institutes, universities, and weather observatories. China’s countrywide radar network is presently being advanced to dual-pol capability.

Professor Zhao is the study’s lead author that was recently published in Advances in Atmospheric Sciences, which reviews dual-polarization radar research and applications in China. The paper has been added into a special issue on the National Report (2011-2018) to the International Union on Geophysics and Geodesy (IUGG) Centennial by the China National Committee for IAMAS.

"To date, the data collected from these dual-pol radars in China have been used and analyzed to improve understanding of precipitation microphysics as well as quantitative precipitation estimation and forecasting in China", says Prof. Zhao.

To enhance the data quality and alleviate the interference of non-meteorological objects, researchers and engineers in China have formulated wide-ranging approaches for data quality control of dual-pol radars.

These include:

  • Attenuation correction
  • Calibration
  • Calculation of specific differential phase shift
  • Identification and removal of non-meteorological echoes to improve hydrometeor classification, raindrop size distribution retrieval, and quantitative precipitation estimation in China.

Researchers have also attempted to use dual-pol radar data to verify the microphysical parameterization and initialization of numerical models and integrate dual-pol data into numerical models.

Emerging technology includes multiple frequency radar and phased array radar. Phased array dual-pol radars have also been employed in weather surveillances in China. The temporal resolution of radar scans has radically improved. It is now possible to sample the 3D information of weather systems within two minutes.

However, the H- and V-polarized beam matching off the broadside affecting dual-pol measurements remains a challenge for radar engineers. Multi-frequency dual-pol radars provide information on the sizes of hydrometeors based on the wavelength dependence of the Mie scattering effect.

Kun Zhao, Professor and Director, Joint Center for Atmospheric Radar Research, CMA/NJU

Professor Zhao is assured that these two kinds of technologies will advance in the next ten years and make substantial contributions to the future of radar meteorology.


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