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On the Type‐A and Type‐B 150‐km Radar Echoes
Author(s) -
Patra A. K.,
Chaitanya P. Pavan,
Rao M. Durga,
Reddy G. Janardana
Publication year - 2020
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
eISSN - 2169-9402
pISSN - 2169-9380
DOI - 10.1029/2020ja028551
Subject(s) - spectral line , physics , type (biology) , radar , doppler effect , echo (communications protocol) , quasiperiodicity , astrophysics , doppler broadening , computational physics , geology , astronomy , condensed matter physics , quasiperiodic function , telecommunications , paleontology , computer network , computer science
Type‐A (weaker and wider Doppler spectra) and Type‐B (stronger and narrower Doppler spectra) echoes are inherent to the puzzling 150‐km echoing phenomenon. In this paper, we investigate the characteristics and possible origin of the Type‐A and Type‐B 150‐km echoes using high‐resolution 53‐MHz radar and Digisonde observations from Gadanki. Results show that the Type‐A echoes dominate the echoing phenomenon and they always precede the Type‐B echoes. Intriguingly, the Type‐B echoes are fundamentally not narrower than the Type‐A echoes as was originally thought. The primary reason that distinguishes the Type‐B echoes from the rest is the confinement of a few high PSD values at the center of the spectra, resulting in narrow spectral width. Spectral spreads of both types of echoes are found to increase with echo signal‐to‐noise ratio (SNR), and in fact, the spectral spreads of the Type‐B echoes are higher than those of the Type‐A echoes. Observations also show spectral evolution displaying the occurrence of Type‐A and Type‐B echoes in tune with the quasiperiodicity in the echo strength (SNR). We propose that both types of echoes primarily are of common origin, presumably linked with naturally enhanced incoherent scattering. Looking at the simultaneously observed short period variations in the lower F region electron density, we propose a gravity wave induced pathway as a plausible mechanism accounting for echo intensity modulation as well as spectral transition.