Direct numerical simulation of VHF radar measurements of turbulence in the mesosphere

Abstract

We simulate very high frequency (VHF) radar backscatter from turbulent irregularities in the mesosphere and examine the process of calculating key turbulence parameters from radar Doppler spectral moments. Mesospheric turbulence is represented by a three‐dimensional (3‐D) direct numerical simulation (DNS) of a turbulent layer generated by Kelvin–Helmholtz instability, which exhibits inertial range turbulence characteristics. A subgrid‐scale turbulence advection model is used to parameterize the unresolved small‐scale structure of mesospheric temperature, ion species, and electron mixing ratios and to derive the radar backscatter cross sections. Energy and thermal dissipation rates are calculated from the 3‐D velocity and temperature derivatives of the DNS. Doppler spectral widths relevant to various mesospheric radar observations are then determined from explicit calculation of spectral moments. We then present a comparison between the turbulence parameters calculated from the DNS and those calculated from the Doppler spectral moments.