Graphical Abstract

Ohigashi, T., T. Maesaka, S. Suzuki, Y. Shusse, N. Sakurai, and K. Iwanami, 2021: Clear-air echoes observed by Ka-band polarimetric cloud radar: A case study on insect echoes in the Tokyo metropolitan area, Japan. J. Meteor. Soc. Japan, 99, 101-112.
https://doi.org/10.2151/jmsj.2021-006 Graphical Abstract Published

Plain Language Summary: The clear-air echoes (CAEs), that appeared on May 21, 2016 in the Tokyo metropolitan area, Japan, were investigated to establish the potential for distinguishing CAEs and hydrometeor echoes in the initial stage of cloud formation using Ka-band polarimetric cloud radar. The polarimetric variables obtained by Ka-band polarimetric cloud radar are useful in distinguishing between clear-air echoes and hydrometeor echoes.

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Highlights:

The upper limit of the equivalent radar reflectivity ( Ze ) and the distributions of the differential reflectivity ( Z_DR ) and the copolar correlation coefficient ( ρ_hν ) were inconsistent with the characteristics of Bragg scattering observed by S-band (10-cm-wavelength) radar in previous studies.
The larger Z_DR , smaller ρ_hν , and larger variability of the total differential phase ( Ψ_DP ) in the range direction, associated with the horizontally widespread echoes, were consistent with the characteristics of insect echoes.
The depolarization ratio, defined using Z_DR and ρ_hν , could be effective in distinguishing this type of CAE and hydrometeor echoes observed by Ka-band polarimetric cloud radar.

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