Directional Absorption of Parameterized Mountain Waves and Its Influence on the Wave Momentum Transport in the Northern Hemisphere

Xu, Xin; Tang, Ying; Wang, Yuan; Xue, Ming

doi:10.1002/2017jd027968

Cited by 10 publications

(12 citation statements)

References 48 publications

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“…On the other hand, the mean value of both distributions is approximately equally justifying the utilization of composites from spatially averaged OGWD for dynamical analysis. The magnitude of higher-order moments (especially kurtosis as a measure of the "tailedness" of the distributions) is another measure of the intermittency (Zel'Dovich et al, 1987;Mahrt, 1988). The spatially averaged OGWD represents still a highly intermittent forcing in the LS.…”

Section: Composite Analysismentioning

confidence: 99%

On the intermittency of orographic gravity wave hotspots and its importance for middle atmosphere dynamics

Kuchař

Šácha

Eichinger

et al. 2020

Weather Clim. Dynam.

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Abstract. When orographic gravity waves (OGWs) break, they dissipate their momentum and energy and thereby influence the thermal and dynamical structure of the atmosphere. This OGW forcing mainly takes place in the middle atmosphere. It is zonally asymmetric and strongly intermittent. So-called “OGW hotspot regions” have been shown to exert a large impact on the total wave forcing, in particular in the lower stratosphere (LS). Motivated by this we investigate the asymmetrical distribution of the three-dimensional OGW drag (OGWD) for selected hotspot regions in the specified dynamics simulation of the chemistry-climate model CMAM (Canadian Middle Atmosphere Model) for the period 1979–2010. As an evaluation, we first compare zonal mean OGW fluxes and GW drag (GWD) of the model simulation with observations and reanalyses in the Northern Hemisphere. We find an overestimation of GW momentum fluxes and GWD in the model's LS, presumably attributable to the GW parameterizations which are tuned to correctly represent the dynamics of the Southern Hemisphere. In the following, we define three hotspot regions which are of particular interest for OGW studies, namely the Himalayas, the Rocky Mountains and East Asia. The GW drags in these hotspot regions emerge as strongly intermittent, a result that can also quantitatively be corroborated with observational studies. Moreover, a peak-detection algorithm is applied to capture the intermittent and zonally asymmetric character of OGWs breaking in the LS and to assess composites for the three hotspot regions. This shows that LS peak OGW events can have opposing effects on the upper stratosphere and mesosphere depending on the hotspot region. Our analysis constitutes a new method for studying the intermittency of OGWs, thereby facilitating a new possibility to assess the effect of particular OGW hotspot regions on middle atmospheric dynamics.

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Section: Composite Analysismentioning

confidence: 99%

On the intermittency of orographic gravity wave hotspots and its importance for middle atmosphere dynamics

Kuchař

Šácha

Eichinger

et al. 2020

Weather Clim. Dynam.

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“…Recently, Xu et al (2018) designed an OGW parameterization scheme taking into account the directional absorption of OGWs (hereafter, the X18 scheme). Offline evaluation using reanalysis data in X18 showed that the scheme can produce weaker (stronger) OGWD in the lower stratosphere (upper stratosphere and lower mesosphere) because directional absorption tends to a transfer of wave breaking to higher levels.…”

Section: Introductionmentioning

confidence: 99%

Parameterization of Directional Absorption of Orographic Gravity Waves and Its Impact on the Atmospheric General Circulation Simulated by the Weather Research and Forecasting Model

Xue

Teixeira

et al. 2019

Journal of the Atmospheric Sciences

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In this work, a new parameterization scheme is developed to account for the directional absorption of orographic gravity waves (OGWs) using elliptical mountain-wave theory. The vertical momentum transport of OGWs is addressed separately for waves with different orientations through decomposition of the total wave momentum flux (WMF) into individual wave components. With the new scheme implemented in the Weather Research and Forecasting (WRF) Model, the impact of directional absorption of OGWs on the general circulation in boreal winter is studied for the first time. The results show that directional absorption can change the vertical distribution of OGW forcing, while maintaining the total column-integrated forcing. In general, directional absorption inhibits wave breaking in the lower troposphere, producing weaker orographic gravity wave drag (OGWD) there and transporting more WMF upward. This is because directional absorption can stabilize OGWs by reducing the local wave amplitude. Owing to the increased WMF from below, the OGWD in the upper troposphere at midlatitudes is enhanced. However, in the stratosphere of mid- to high latitudes, the OGWD is still weakened due to greater directional absorption occurring there. Changes in the distribution of midlatitude OGW forcing are found to weaken the tropospheric jet locally and enhance the stratospheric polar night jet remotely. The latter occurs as the adiabatic warming (associated with the OGW-induced residual circulation) is increased at midlatitudes and suppressed at high latitudes, giving rise to stronger thermal contrast. Resolved waves are likely to contribute to the enhancement of polar stratospheric winds as well, because their upward propagation into the high-latitude stratosphere is suppressed.

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“…These differences may be explained by the fact that the parameterization of OGWs is tuned to represent a missing drag in the SH resulting in the overestimation in the NH (McLandress et al, 2012). Using horizontal propagation and directional absorption of OGWs in the parametrization may bring the GWD in the middle latitudes closer to observations (Xu et al, 2017(Xu et al, , 2018, particularly considering that GW momentum fluxes as derived from satellite observations may be underestimated (Trinh et al, 2015;Ern et al, 2018). Still, the high bias in the NH emerges as deficiency of current GW parameterizations in GCMs https://doi.org/10.5194/wcd-2020-21 Preprint.…”

Section: Discussionmentioning

confidence: 99%

On the intermittency of orographic gravity wave hotspots and its importance for middle atmosphere dynamics

Kuchař¹,

Šácha²,

Eichinger³

et al. 2020

Preprint

View full text Add to dashboard Cite

Abstract. When orographic gravity waves (OGWs) break, they dissipate their momentum and energy and thereby influence the thermal and dynamical structure of the atmosphere. This OGW forcing mainly takes place in the middle atmosphere. It is zonally asymmetric and strongly intermittent. So-called OGW hotspot regions have been shown to exert a large impact on the total wave forcing, in particular in the lower stratosphere (LS). Motivated by this we investigate the asymmetrical distribution of the three-dimensional OGW drag (OGWD) for selected hotspot regions in the specified dynamics simulation of the chemistry-climate model CMAM (Canadian Middle Atmosphere Model) for the period 1979–2010. As an evaluation, we first compare zonal mean OGW fluxes and GW drag (GWD) of the model simulation with observations and reanalyses in the northern hemisphere. We find an overestimation of GW momentum fluxes and GWD in the model's LS, presumably attributable to the GW parameterizations which are tuned to correctly represent the dynamics of the southern hemisphere. In the following, we define three hotspot regions which are of particular interest for OGW studies, namely the Himalayas, the Rocky Mountains and East Asia. The GW drags in these hotspot regions emerge as strongly intermittent, a result that can also quantitatively be corroborated with observational studies. Moreover, a peak-detection algorithm is applied to capture the intermittent and zonally asymmetric character of OGWs breaking in the LS and to assess composites for the three hotspot regions. This shows that LS peak OGW events can have opposing effects on the upper stratosphere and mesosphere depending on the hotspot region. Our analysis constitutes a new method for studying the intermittency of OGWs, thereby facilitating a new possibility to assess the effect of particular OGW hotspot regions on middle atmospheric dynamics.

show abstract

Directional Absorption of Parameterized Mountain Waves and Its Influence on the Wave Momentum Transport in the Northern Hemisphere

Cited by 10 publications

References 48 publications

On the intermittency of orographic gravity wave hotspots and its importance for middle atmosphere dynamics

On the intermittency of orographic gravity wave hotspots and its importance for middle atmosphere dynamics

Parameterization of Directional Absorption of Orographic Gravity Waves and Its Impact on the Atmospheric General Circulation Simulated by the Weather Research and Forecasting Model

On the intermittency of orographic gravity wave hotspots and its importance for middle atmosphere dynamics

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