Effects of Latitude-Dependent Gravity Wave Source Variations on the Middle and Upper Atmosphere

Erdal Yiğit,Manfred Ern,Alexander S Medvedev

doi:10.3389/fspas.2020.614018

Abstract

Atmospheric gravity waves (GWs) are generated in the lower atmosphere by various weather phenomena. They propagate upward, carry energy and momentum to higher altitudes, and appreciably influence the general circulation upon depositing them in the middle and upper atmosphere. We use a three-dimensional first-principle general circulation model (GCM) with implemented nonlinear whole atmosphere GW parameterization to study the global climatology of wave activity and produced effects at altitudes up to the upper thermosphere. The numerical experiments were guided by the GW momentum fluxes and temperature variances as measured in 2010 by the SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) instrument onboard NASA’s TIMED (Thermosphere Ionosphere Mesosphere Energetics Dynamics) satellite. This includes the latitudinal dependence and magnitude of GW activity in the lower stratosphere for the boreal summer season. The modeling results were compared to the SABER temperature and total absolute momentum flux and Upper Atmosphere Research Satellite (UARS) data in the mesosphere and lower thermosphere. Simulations suggest that, in order to reproduce the observed circulation and wave activity in the middle atmosphere, GW fluxes that are smaller than observed fluxes have to be used at the source level in the lower atmosphere. This is because observations contain a broader spectrum of GWs, while parameterizations capture only a portion relevant to the middle and upper atmosphere dynamics. Accounting for the latitudinal variations of the source appreciably improves simulations.

Highlights

Atmospheric gravity waves (GWs) play an important role in the dynamics and thermodynamics of the middle (Fritts and Alexander, 2003) and upper atmosphere (Kazimirovsky et al, 2003; Yigit and Medvedev, 2015) of Earth
It is important to note that the GW scheme exclusively accounts for GWs unresolved by the general circulation model (GCM), whose scales depend on the model resolution, while SABER observes a broad range of GW scales
We rely on the recent findings, which all indicate a latitudinal variation, such as SABER and HIRDLS satellite observations that are sensitive to horizontal wavelengths > 100 − 200 km and vertical wavelengths in the range 2–25 km (Ern et al, 2018); dedicated high-resolution convection-permitting model simulations by ICON, NICAM, and IFS (Stephan et al, 2019a, b) that resolve horizontal wavelength >50 km and vertical wavelengths greater than 2 km; and AIRS satellite observations of GWs that are sensitive to horizontal wavelengths >30 km and vertical wavelengths > 15 km (Ern et al, 2017; Meyer et al, 2018)

Summary

Introduction

Atmospheric gravity waves (GWs) play an important role in the dynamics and thermodynamics of the middle (Fritts and Alexander, 2003) and upper atmosphere (Kazimirovsky et al, 2003; Yigit and Medvedev, 2015) of Earth. While models primarily designed for the middle atmosphere show fluxes similar to observations, GW activity measured by satellites falls off more strongly with altitude. This indicates that probably the extent to which GWs are captured between the different models and observations can substantially vary at higher altitudes (Geller et al, 2013) The different approaches to observations provide various views of GW activity at different spatiotemporal scales in the atmosphere. We perform sensitivity studies guided by GW momentum flux measurements of the SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) instrument onboard NASA’s TIMED satellite

Methods

Findings

Discussion

Conclusion