Validity on radar observation of middle- and upper-atmosphere dynamics

Abstract

Doppler radar observations have made a large contribution towards improving our understanding of middleand upper-atmosphere dynamics. This radar echo is mainly due to radiowave scattering by atmospheric turbulence, which occurs almost universally throughout the atmosphere as a result of gravity wave (GW) breaking. In the strictness sense, the radar pulse is back-scattered by radio refractive index (RRI) perturbations caused by turbulence whose size along the radar beam is half of the radar wavelength. Understanding of the validity of the MST (mesosphere, stratosphere and troposphere)-radar observation requires a precise knowledge of how RRI perturbations are formed and behave. A basic property of the RRI of the atmosphere is that it has a static vertical gradient in terms of distribution and the turbulence velocity is divergence-free. The RRI depends on three atmospheric properties-humidity, air density and electron density. These three elements each have a static vertical gradient along which turbulence transports each element, hereby perturbing the density distribution of each element; that is to say, it produces the RRI irregularity for scattering the radar pulse. Since the turbulence motion and winds are divergence-free, PRI perturbation co-moves with the total air flow, i.e. turbulence motion plus winds. This can be true even in the mesosphere where the perturbation is controlled electromagnetically. Co-movement of turbulence with local winds has been shown from a comparison of observations with radars and radiosondes. In addition to tracking turbulence as wind-tracers, MST-radar observations provide important data in the study of atmosphere turbulence dynamics.

Mid‐Latitude Mesospheric Responses of the Solar Eclipse on 21 June 2020 Observed by the Wuhan MST Radar

“…The advent of Mesosphere‐Stratosphere‐Troposphere (MST) radar makes it possible to observe the mesosphere by radio waves (Hocking, 1997). Due to photo‐ionized electrons in the upper mesosphere, the MST radar can receive the echoes in Very‐High‐Frequency (VHF) band through the turbulent scattering (Kato, 2009). In the daytime, the MST radar can receive much more scattered echoes from the mesospheric turbulent irregularities as the solar radiation has ionized neutral atmospheric components in the D‐layer.…”

Wind observation around the tops of the midlatitude cirrus by the MU radar and Raman/Mie lidar

“…Atmospheric radars which receive echoes from fluctuations of refractive index are useful for directly observing height profiles of vertical and horizontal winds both in clear and cloud regions (Fukao, 2007). Mesosphere-Stratosphere-Troposphere (MST) atmospheric radars (hereafter MST radars) to observe winds and turbulence up to the mesosphere are useful for observing uppertropospheric winds with high time and vertical resolutions (Kato, 2009). It has been shown that a combination of atmospheric radar and cloud profiling radar is useful for knowing dynamical processes in and around cirriform clouds (Yamamoto et al, 2008).…”