Variability of Gravity Wave Effects on the Zonal Mean Circulation and Migrating Terdiurnal Tide as Studied With the Middle and Upper Atmosphere Model (MUAM2019) Using a Nonlinear Gravity Wave Scheme

Friederike Lilienthal,Nadja Samtleben,Christoph Jacobi,Erdal Yiğit

doi:10.3389/fspas.2020.588956

Friederike Lilienthal, Nadja Samtleben + Show 2 more

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https://doi.org/10.3389/fspas.2020.588956

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Abstract

Implementing a nonlinear gravity wave (GW) parameterization into a mechanistic middle and upper atmosphere model, which extends to the lower thermosphere (160 km), we study the response of the atmosphere in terms of the circulation patterns, temperature distribution, and migrating terdiurnal solar tide activity to the upward propagating small-scale internal GWs originating in the lower atmosphere. We perform three test simulations for the Northern Hemisphere winter conditions in order to assess the effects of variations in the initial GW spectrum on the climatology and tidal patterns of the mesosphere and lower thermosphere. We find that the overall strength of the source level momentum flux has a relatively small impact on the zonal mean climatology. The tails of the GW source level spectrum, however, are crucial for the lower thermosphere climatology. With respect to the terdiurnal tide, we find a strong dependence of tidal amplitude on the induced GW drag, generally being larger when GW drag is increased.

Highlights

The opposite phenomenon prevails in the summer SH. This distribution of gravity wave (GW) drag is clearly seen by the eastward GW drag in the SH and westward GW drag in the NH between 80 and 100 km (Figure 3A), which is primarily responsible for the reversal of the zonal mean flow above 90 km, from eastward to westward direction ( ∼ − 40 m s−1) in the winter NH and from westward to eastward direction in the SH ( ∼ 50 m s−1)
Maximum GW drag is in the order of ±100 m s−1 d−1 and is stronger in the summer SH than the winter NH, which is in line with radar observations of GW fluxes and variance (Placke et al, 2011a; Placke et al, 2011b)
The zonal mean horizontal wind patterns in the middle atmosphere as well as the global temperature distribution reasonably agree with respect to established climatologies such as CIRA-86 (Fleming et al, 1988) or URAP (Swinbank and Ortland, 2003), Global Empirical Wind Model (GEWM) (Portnyagin et al, 2004; Jacobi et al, 2009), HWM-14 (Drob et al, 2015), and other general circulation models (GCMs) predictions like WACCM-X (Liu et al, 2018) or Kühlungsborn Mechanistic General Circulation Model (KMCM) (Becker, 2017)

Summary

Introduction

Atmospheric gravity waves (GW) are known to cause a variety of effects in the middle and upper atmospheres of Earth (e.g., Hines, 1960; Richmond, 1978; Taylor et al, 1998; Fritts and Alexander, 2003; Snively and Pasko, 2003; Yue et al, 2009; de la Torre et al, 2014; Becker and Vadas, 2020) and all planetary atmospheres that have been studied so far (e.g., Creasey et al, 2006a; Creasey et al, 2006b; Parish et al, 2009; Medvedev et al, 2011; Miyoshi et al, 2011; Spiga et al, 2012; Walterscheid et al, 2013; Yigit and Medvedev, 2019). GWs are acknowledged as an important physical mechanism that contributes to the vertical coupling in the atmosphere-ionosphere system as has been discussed in contemporary reviews (e.g., Hocke and Schlegel, 1996; Nicolls and Heinselman, 2007; Nicolls et al, 2014; Yigit and Medvedev, 2015). During transient events such as sudden stratospheric warmings, thermospheric effects of GWs can be extremely variable depending on the nature of the warming (Yigit and Medvedev, 2016; Nayak and Yigit, 2019). For mechanistic models with limited resources, the scheme by Yigit et al (2008) is the one that is most state-of-the-art

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