Variability of the Brunt–Väisälä frequency at the OH&amp;lt;sup&amp;gt;∗&amp;lt;/sup&amp;gt;-airglow layer height at low and midlatitudes

Sabine Wüst,Jeng-Hwa Yee,James M Russell Iii,Martin G Mlynczak,Michael Bittner

doi:10.5194/amt-13-6067-2020

Abstract

Abstract. Airglow spectrometers, as they are operated within the Network for the Detection of Mesospheric Change (NDMC; https://ndmc.dlr.de, last access: 1 November 2020), for example, allow the derivation of rotational temperatures which are equivalent to the kinetic temperature, local thermodynamic equilibrium provided. Temperature variations at the height of the airglow layer are, amongst others, caused by gravity waves. However, airglow spectrometers do not deliver vertically resolved temperature information. This is an obstacle for the calculation of the density of gravity wave potential energy from these measurements. As Wüst et al. (2016) showed, the density of wave potential energy can be estimated from data of OH∗-airglow spectrometers if co-located TIMED-SABER (Thermosphere Ionosphere Mesosphere Energetics Dynamics, Sounding of the Atmosphere using Broadband Emission Radiometry) measurements are available, since they allow the calculation of the Brunt–Väisälä frequency. If co-located measurements are not available, a climatology of the Brunt–Väisälä frequency is an alternative. Based on 17 years of TIMED-SABER temperature data (2002–2018), such a climatology is provided here for the OH∗-airglow layer height and for a latitudinal longitudinal grid of 10∘×20∘ at midlatitudes and low latitudes. Additionally, climatologies of height and thickness of the OH∗-airglow layer are calculated.

Highlights

Climatologies of height and thickness of the OH∗-airglow layer are calculated. This is the succeeding publication to Wüst et al (2017a), where the angular Brunt–Väisälä (BV) frequency was calculated for the OH∗-layer height between 43.93–48.09◦ N and 5.71–12.95◦ E using Thermosphere Ionosphere Mesosphere Energetics Dynamics, Sounding of the Atmosphere using Broadband Emission Radiometry (TIMEDSABER) data from 2002 to 2015
We described seasonal variations of the three parameters, height and full width at half maximum (FWHM) of the OH∗ layer as well as the BV frequency weighted according to the parameters of the OH∗ layer and provided a climatology of the yearly course of this BV frequency
85 % of all spectrometers and photometers listed in the database of Network for the Detection of Mesospheric Change (NDMC) address at least one of the various OH emissions (Schmidt et al, 2018); TIMED-SABER OH-B channel and temperature measurements are used for the BV frequency climatology

Summary

Introduction

This is the succeeding publication to Wüst et al (2017a), where the angular Brunt–Väisälä (BV) frequency was calculated for the OH∗-layer height between 43.93–48.09◦ N and 5.71–12.95◦ E using Thermosphere Ionosphere Mesosphere Energetics Dynamics, Sounding of the Atmosphere using Broadband Emission Radiometry (TIMEDSABER) data from 2002 to 2015. The angular BV frequency N, which is, for example, needed for calculation of the density of gravity wave potential energy, varies with the temperature T and its vertical gradient At a poorer horizontal resolution scanning OH∗ spectrometers can deliver horizontally resolved temperature information (see, e.g. Wachter et al, 2015; Wüst et al, 2018) In these cases, the temperature is vertically averaged over the OH∗ layer; the BV frequency cannot be calculated. 85 % of all spectrometers and photometers listed in the database of NDMC address at least one of the various OH emissions (Schmidt et al, 2018); TIMED-SABER OH-B channel and temperature measurements are used for the BV frequency climatology. We provide an uncertainty range of the BV frequency due to tides in this publication

Data and analysis

Results and discussion

The 60 d oscillation

Annual and semi-annual variation

Summary and outlook