Lidar observations of stratospheric gravity waves from 2011 to 2015 at McMurdo (77.84°S, 166.69°E), Antarctica: 1. Vertical wavelengths, periods, and frequency and vertical wave number spectra
27 May 2017-Journal of Geophysical Research (John Wiley & Sons, Ltd)-Vol. 122, Iss: 10, pp 5041-5062
TL;DR: In this article, the authors used an Fe Boltzmann lidar to characterize the vertical wavelengths, periods, vertical phase speeds, frequency spectra, and vertical wave number spectra of stratospheric gravity waves from 30 to 50 km altitude.
Abstract: Five years of atmospheric temperature data, collected with an Fe Boltzmann lidar by the University of Colorado group from 2011 to 2015 at Arrival Heights, are used to characterize the vertical wavelengths, periods, vertical phase speeds, frequency spectra, and vertical wave number spectra of stratospheric gravity waves from 30 to 50 km altitudes. Over 1000 dominant gravity wave events are identified from the data. The seasonal spectral distributions of vertical wavelengths, periods, and vertical
phase speeds in summer, winter, and spring/fall are found obeying a lognormal distribution. Both the
downward and upward phase progression gravity waves are observed by the lidar, and the fractions of
gravity waves with downward phase progression increase from summer ~59% to winter ~70%.
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TL;DR: In this article, a new high-resolution general circulation model with regard to secondary gravity waves in the mesosphere during austral winter was proposed, and the model resolved gravity waves down to horizontal and vertical wavelengths of 165 and 1.5 km, respectively.
Abstract: This study analyzes a new high-resolution general circulation model with regard to secondary gravity waves in the mesosphere during austral winter. The model resolves gravity waves down to horizontal and vertical wavelengths of 165 and 1.5 km, respectively. The resolved mean wave drag agrees well with that from a conventional model with parameterized gravity waves up to the midmesosphere in winter and up to the upper mesosphere in summer. About half of the zonal-mean vertical flux of westward momentum in the southern winter stratosphere is due to orographic gravity waves. The high intermittency of the primary orographic gravity waves gives rise to secondary waves that result in a substantial eastward drag in the winter mesopause region. This induces an additional eastward maximum of the mean zonal wind at z ∼ 100 km. Radar and lidar measurements at polar latitudes and results from other high-resolution global models are consistent with this finding. Hence, secondary gravity waves may play a significant role in the general circulation of the winter mesopause region. Plain Language Summary We present a new gravity-resolving general circulation model that extends into the lower thermosphere. The simulated summer-to-winter-pole circulation in the upper mesosphere is nearly realistic and driven by resolved waves. We find a new phenomenon that results from the generation of secondary gravity waves in the stratosphere and lower mesosphere. The effect is characterized by an eastward gravity drag that causes a secondary eastward wind maximum around the polar winter mesopause. Analysis of the simulated gravity waves shows consistence with other gravity wave resolving models and with observational studies of the austral winter middle atmosphere, including the mesopause region.
135 citations
01 May 2006
TL;DR: In this article, the authors summarize what has been learned from traditional temporally and spatially averaged analyse of gravity wave data and present a global map of averaged gravity wave temperature variance from a variety of different instruments on Earth-orbiting platforms.
Abstract: Abstract Small-scale gravity waves are common features in atmospheric temperature observations. In satellite observations, these waves have been traditionally difficult to resolve because the footprint or resolution of the measurements precluded their detection or clear identification. Recent advances in satellite instrument resolution coupled to innovative analysis techniques have led in the last decade to some new global datasets describing the temperature variance associated with these waves. Such satellite observations have been considered the best hope for quantifying the global properties of gravity waves needed to constrain parameterizations of their effects for global models. Although global maps of averaged gravity wave temperature variance have now been published from a variety of different instruments on Earth-orbiting platforms these maps have not provided the needed constraints. The present paper first summarizes what has been learned from traditional temporally and spatially averaged analyse...
124 citations
TL;DR: In this paper, the results of the Kühlungsborn Mechanistic general circulation model were analyzed at McMurdo Station (166.69∘E and 77.84∘S), where strong downslope eastward winds create strong mountain wave (MW) events.
Abstract: We analyze the results of the gravity wave (GW)-resolving, high-resolution Kühlungsborn Mechanistic general Circulation Model in July at McMurdo Station (166.69∘E and 77.84∘S), where strong downslope eastward winds create strong mountain wave (MW) events. These MWs have horizontal wavelengths of λH ≃ 230 km, propagate to z ∼ 40–60 km, and can have upward phases in time if the eastward wind accelerates in time. Additionally, inertia-GWs (IGWs) with λH ∼ 500–800 km and ground-based periods of τr ∼ 5–6 hr are generated in the troposphere from unbalanced, large-scale flow. The density-scaled GW amplitudes are ∼10 times smaller at z ∼ 80–100 km than at z < 50 km because of severe wave dissipation. “Fishbone” structures are seen at z ∼ 30–60 km with upward (downward) phases in time below (above) the “knee” at zknee. We horizontally filter the perturbations to isolate the GWs in a fishbone structure for a particular MW event. We find that these GWs have strikingly similar parameters below and above zknee = 46 km, with ground-based horizontal phase speeds of cH ∼ 40–60 m/s, τr ∼ 9–10 hr, λH ∼ 1,600–2,050 km, vertical wavelengths of λz ∼ 18–25 km, and azimuths of Υ = 145∘ –151∘ east of north. We show that these are secondary GWs excited by a body force at zknee created by MW dissipation approximately 400 km northwest of McMurdo 2.5 hr earlier and that the secondary GW scales and propagation directions are consistent with this force. Importantly, we show that most of the GWs at z> 70 km are secondary GWs not primary GWs from the troposphere.
75 citations
TL;DR: In this paper, the effects on the mesosphere and thermosphere from a strong mountain wave (MW) event over the wintertime Southern Andes using a gravity wave (GW)-resolving global circulation model were investigated.
Abstract: We investigate the effects on the mesosphere and thermosphere from a strong mountain wave (MW) event over the wintertime Southern Andes using a gravity wave (GW)-resolving global circulation model. During this event, MWs break and attenuate at z ∼ 50–80 km, thereby creating local body forces that generate large-scale secondary GWs having concentric ring structure with horizontal wavelengths λH = 500–2,000 km, horizontal phase speeds cH = 70–100 m/s, and periods τr ∼ 3–10 hr. These secondary GWs dissipate in the upper mesosphere and thermosphere, thereby creating local body forces. These forces have horizontal sizes of 180–800 km, depending on the constructive/destructive interference between wave packets and the overall sizes of the wave packets. The largest body force is at z = 80–130 km, has an amplitude of ∼2,400 m/s/day, and is located ∼1,000 km east of the Southern Andes. This force excites mediumand large-scale “tertiary GWs” having concentric ring structure, with λH increasing with radius from the centers of the rings. Near the Southern Andes, these tertiary GWs have cH = 120–160 m/s, λH = 350–2,000 km, and τr ∼ 4–9 hr. Some of the larger-λH tertiary GWs propagate to the west coast of Africa with very large phase speeds of cH ≃ 420 m/s. The GW potential energy density increases exponentially at z ∼ 95–115 km, decreases at z ∼ 115–125 km where most of the secondary GWs dissipate, and increases again at z > 125 km from the tertiary GWs. Thus, strong MW events result in the generation of mediumto large-scale fast tertiary GWs in the mesosphere and thermosphere via this multistep vertical coupling mechanism.
68 citations
References
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TL;DR: ERA-Interim as discussed by the authors is the latest global atmospheric reanalysis produced by the European Centre for Medium-Range Weather Forecasts (ECMWF), which will extend back to the early part of the twentieth century.
Abstract: ERA-Interim is the latest global atmospheric reanalysis produced by the European Centre for Medium-Range Weather Forecasts (ECMWF). The ERA-Interim project was conducted in part to prepare for a new atmospheric reanalysis to replace ERA-40, which will extend back to the early part of the twentieth century. This article describes the forecast model, data assimilation method, and input datasets used to produce ERA-Interim, and discusses the performance of the system. Special emphasis is placed on various difficulties encountered in the production of ERA-40, including the representation of the hydrological cycle, the quality of the stratospheric circulation, and the consistency in time of the reanalysed fields. We provide evidence for substantial improvements in each of these aspects. We also identify areas where further work is needed and describe opportunities and objectives for future reanalysis projects at ECMWF. Copyright © 2011 Royal Meteorological Society
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TL;DR: In this article, a review of gravity wave sources and characteristics, the evolution of the gravity wave spectrum with altitude and with variations of wind and stability, the character and implications of observed climatologies, and the wave interaction and instability processes that constrain wave amplitudes and spectral shape are discussed.
Abstract: [1] Atmospheric gravity waves have been a subject of intense research activity in recent years because of their myriad effects and their major contributions to atmospheric circulation, structure, and variability. Apart from occasionally strong lower-atmospheric effects, the major wave influences occur in the middle atmosphere, between ∼ 10 and 110 km altitudes because of decreasing density and increasing wave amplitudes with altitude. Theoretical, numerical, and observational studies have advanced our understanding of gravity waves on many fronts since the review by Fritts [1984a]; the present review will focus on these more recent contributions. Progress includes a better appreciation of gravity wave sources and characteristics, the evolution of the gravity wave spectrum with altitude and with variations of wind and stability, the character and implications of observed climatologies, and the wave interaction and instability processes that constrain wave amplitudes and spectral shape. Recent studies have also expanded dramatically our understanding of gravity wave influences on the large-scale circulation and the thermal and constituent structures of the middle atmosphere. These advances have led to a number of parameterizations of gravity wave effects which are enabling ever more realistic descriptions of gravity wave forcing in large-scale models. There remain, nevertheless, a number of areas in which further progress is needed in refining our understanding of and our ability to describe and predict gravity wave influences in the middle atmosphere. Our view of these unknowns and needs is also offered.
2,206 citations
TL;DR: In this article, the effects of mean winds and gravity waves on the mean momentum budget were investigated and it was shown that the existence of critical levels in the mesosphere significantly limits the ability of gravity waves to generate turbulence.
Abstract: It has been suggested (Lindzen, 1967, 1968a, b; Lindzen and Blake, 1971; Hodges, 1969) that turbulence in the upper mesosphere arises from the unstable breakdown of tides and gravity waves. Crudely speaking, it was expected that sufficient turbulence would be generated to prevent the growth of wave amplitude with height (roughly as (basic pressure)−1/2). This work has been extended to allow for the generation of turbulence by smaller amplitude waves, the effects of mean winds on the waves, and the effects of the waves on the mean momentum budget. The effects of mean winds, while of relatively small importance for tides, are crucial for internal gravity waves originating in the troposphere. Winds in the troposphere and stratosphere sharply limit the phase speeds of waves capable of reaching the upper mesosphere. In addition, the existence of critical levels in the mesosphere significantly limits the ability of gravity waves to generate turbulence, while the breakdown of gravity waves contributes to the development of critical levels. The results of the present study suggest that at middle latitudes in winter, eddy coefficients may peak at relatively low altitudes (50 km) and at higher altitudes in summer and during sudden warmings (70–80 km), and decrease with height rather sharply above these levels. Rocket observations are used to estimate momentum deposition by gravity waves. Accelerations of about 100 m/s/day are suggested. Such accelerations are entirely capable of producing the warm winter and cold summer mesopauses.
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TL;DR: In this paper, it was shown that the least-squares estimation method of fitting the best straight line to data points having normally distributed errors yields identical results for the slope and intercept of the line as does the method of maximum likelihood estimation.
Abstract: It has long been recognized that the least-squares estimation method of fitting the best straight line to data points having normally distributed errors yields identical results for the slope and intercept of the line as does the method of maximum likelihood estimation. We show that, contrary to previous understanding, these two methods also give identical results for the standard errors in slope and intercept, provided that the least-squares estimation expressions are evaluated at the least-squares-adjusted points rather than at the observed points as has been done traditionally. This unification of standard errors holds when both x and y observations are subject to correlated errors that vary from point to point. All known correct regression solutions in the literature, including various special cases, can be derived from the original York equations. We present a compact set of equations for the slope, intercept, and newly unified standard errors.
883 citations