Turbulence-induced fluctuations in ionization and application to PMSE

Abstract

The temporal evolution of a turbulent layer is calculated in detail by solving the hydrodynamic equations. The turbulence is initiated by a Kelvin-Helmholtz instability. The field of potential-temperature fluctuations serves as a tracer for modeling entrainment of the mixing ratios of ionized constituents hypothesized to be present in the upper polar mesosphere. This entrainment modeling provides the input to a turbulence advection model capable of calculating the spectra and cospectra of ions and electrons. The turbulence advection model is used as a subgrid-scale model and is required because, given present or foreseeable computer capabilities, numerical solutions cannot span the enormous range of spatial scales from the depth of the shear layer to the smallest scales on which the most massive ions diffuse. The power spectrum of electron number-density fluctuations obtained from the turbulence advection model is compared with that measured by a rocket during the STATE (Structure and Atmospheric Turbulence Environment) experiment; agreement is found for a case of massive ions. The radar cross section for Bragg scattering is calculated from the electron number-density power spectrum and is used to calculate the signal-to-noise ratio (S/N) for the Poker Flat 50 MHz radar. The resultant S/N is then compared with the radar measurements obtained during the STATE experiment. These comparisons support the hypothesis that massive ions can cause polar mesosphere summer echoes from turbulent layers. Large-scale morphology of the turbulent layer obtained from rocket and radar measurements is reproduced by the hydrodynamic solution.

Wave influence on polar mesosphere summer echoes above Wasa: experimental and model studies

“…It should be noted that while Varney et al (2011) used q = 4.08 following Hill and Mitton (1998) and Hill et al (1999), Rapp et al (2008) and Li et al (2010) have used q = 2.…”

Frequency domain interferometry mode observations of PMSE using the EISCAT VHF radar

“…It is believed that these instabilities are common near the mesopause and, although never directly observed, there have been several reports in the literature in which evidence has been found to support the belief (Pan and RoÈ ttger, 1996;Czechowsky and RuÈ ster, 1997). High-resolution computer simulations are also being developed that can be used to study the impact on KH instabilities on PMSE Hill et al, 1999). Although this work is still newly developing, it appears that these simulations oer a powerful tool for investigating the links between PMSE and atmospheric small-scale dynamics.…”

“…Results of KH instability simulations have been directly applied to the study of PMSE by Hill et al (1999). They compare height pro®les of the dimensionalized potential temperature from KH simulations with rocket data of electron number densities from the STATE experiment, see their Fig.…”

Estimates of eddy turbulence consistent with seasonal variations of atomic oxygen and its possible role in the seasonal cycle of mesopause temperature

“…However, when we try to model such long-time seasonal variations, we need mean values for the statistically steady turbulent motion. Numerous experimental data on eddy turbulence exist (see, for example, Fukao et al, 1994;Lübken, 1997;Hill et al, 1999), and these data facilitate inferring the mean values of eddy turbulence and their longtime seasonal variations. It is important to emphasize that the meridional wind and wind shears are very intermittent in altitude, as can be seen from the measurements (Larsen, 2002), meaning that vertical motion driven by the meridional wind is very intermittent as well.…”