scholarly journals Scale Analysis of Moist Thermodynamics in a Simple Model and the Relationship between Moisture Modes and Gravity Waves

2019 ◽  
Vol 76 (12) ◽  
pp. 3863-3881 ◽  
Author(s):  
Ángel F. Adames ◽  
Daehyun Kim ◽  
Spencer K. Clark ◽  
Yi Ming ◽  
Kuniaki Inoue
Keyword(s):  
Gravity Wave ◽  
Gravity Waves ◽  
Reanalysis Data ◽  
Scale Analysis ◽  
Convectively Coupled Equatorial Waves ◽  
Propagating Waves ◽  
Static Energy ◽  
Complex Phenomena ◽  
Fast Waves ◽  
The Relationship

Abstract Observations and theory of convectively coupled equatorial waves suggest that they can be categorized into two distinct groups. Moisture modes are waves whose thermodynamics are governed by moisture fluctuations. The thermodynamics of the gravity wave group, on the other hand, are rooted in buoyancy (temperature) fluctuations. On the basis of scale analysis, it is found that a simple nondimensional parameter—akin to the Rossby number—can explain the processes that lead to the existence of these two groups. This parameter, defined as Nmode, indicates that moisture modes arise when anomalous convection lasts sufficiently long so that dry gravity waves eliminate the temperature anomalies in the convective region, satisfying weak temperature gradient (WTG) balance. This process causes moisture anomalies to dominate the distribution of moist enthalpy (or moist static energy), and hence the evolution of the wave. Conversely, convectively coupled gravity waves arise when anomalous convection eliminates the moisture anomalies more rapidly than dry gravity waves can adjust the troposphere toward WTG balance, causing temperature to govern the moist enthalpy distribution and evolution. Spectral analysis of reanalysis data indicates that slowly propagating waves (cp ~ 3 m s−1) are likely to be moisture modes while fast waves (cp ~ 30 m s−1) exhibit gravity wave behavior, with “mixed moisture–gravity” waves existing in between. While these findings are obtained from a highly idealized framework, it is hypothesized that they can be extended to understand simulations of convectively coupled waves in GCMs and the thermodynamics of more complex phenomena.

scholarly journals Vortex Preconditioning due to Planetary and Gravity Waves prior to Sudden Stratospheric Warmings

2014 ◽  
Vol 71 (11) ◽  
pp. 4028-4054 ◽  
Author(s):  
John R. Albers ◽  
Thomas Birner
Keyword(s):  
Gravity Wave ◽  
Gravity Waves ◽  
Planetary Wave ◽  
Surf Zone ◽  
Polar Vortex ◽  
Wave Drag ◽  
Reanalysis Data ◽  
Composite Analysis ◽  
Large Wave ◽  
Wave Forcing

Abstract Reanalysis data are used to evaluate the evolution of polar vortex geometry, planetary wave drag, and gravity wave drag prior to split versus displacement sudden stratospheric warmings (SSWs). A composite analysis that extends upward to the lower mesosphere reveals that split SSWs are characterized by a transition from a wide, funnel-shaped vortex that is anomalously strong to a vortex that is constrained about the pole and has little vertical tilt. In contrast, displacement SSWs are characterized by a wide, funnel-shaped vortex that is anomalously weak throughout the prewarming period. Moreover, during split SSWs, gravity wave drag is enhanced in the polar night jet, while planetary wave drag is enhanced within the extratropical surf zone. During displacement SSWs, gravity wave drag is anomalously weak throughout the extratropical stratosphere. Using the composite analysis as a guide, a case study of the 2009 SSW is conducted in order to evaluate the roles of planetary and gravity waves for preconditioning the polar vortex in terms of two SSW-triggering scenarios: anomalous planetary wave forcing from the troposphere and resonance due to either internal or external Rossby waves. The results support the view that split SSWs are caused by resonance rather than anomalously large wave forcing. Given these findings, it is suggested that vortex preconditioning, which is traditionally defined in terms of vortex geometries that increase poleward wave focusing, may be better described by wave events (planetary and/or gravity) that “tune” the geometry of the vortex toward its resonant excitation points.

scholarly journals Dynamical Control of the Mesosphere by Orographic and Nonorographic Gravity Wave Drag during the Extended Northern Winters of 2006 and 2009

2013 ◽  
Vol 70 (7) ◽  
pp. 2152-2169 ◽  
Author(s):  
Charles McLandress ◽  
John F. Scinocca ◽  
Theodore G. Shepherd ◽  
M. Catherine Reader ◽  
Gloria L. Manney
Keyword(s):  
Gravity Wave ◽  
Gravity Waves ◽  
Middle Atmosphere ◽  
Wave Drag ◽  
Reanalysis Data ◽  
Zonal Winds ◽  
Mesospheric Temperature ◽  
Mean Circulation ◽  
Dynamical Control ◽  
Good Agreement

Abstract A version of the Canadian Middle Atmosphere Model (CMAM) that is nudged toward reanalysis data up to 1 hPa is used to examine the impacts of parameterized orographic and nonorographic gravity wave drag (OGWD and NGWD) on the zonal-mean circulation of the mesosphere during the extended northern winters of 2006 and 2009 when there were two large stratospheric sudden warmings. The simulations are compared to Aura Microwave Limb Sounder (MLS) observations of mesospheric temperature and carbon monoxide (CO) and derived zonal winds. The control simulation, which uses both OGWD and NGWD, is shown to be in good agreement with MLS. The impacts of OGWD and NGWD are assessed using simulations in which those sources of wave drag are removed. In the absence of OGWD the mesospheric zonal winds in the months preceding the warmings are too strong, causing increased mesospheric NGWD, which drives excessive downwelling, resulting in overly large lower-mesospheric values of CO prior to the warming. NGWD is found to be most important following the warmings when the underlying westerlies are too weak to allow much vertical propagation of the orographic gravity waves to the mesosphere. NGWD is primarily responsible for driving the circulation that results in the descent of CO from the thermosphere following the warmings. Zonal-mean mesospheric winds and temperatures in all simulations are shown to be strongly constrained by (i.e., slaved to) the stratosphere. Finally, it is demonstrated that the responses to OGWD and NGWD are nonadditive because of their dependence and influence on the background winds and temperatures.

scholarly journals The Relationship between Equatorial Mixed Rossby–Gravity and Eastward Inertio-Gravity Waves. Part I

2016 ◽  
Vol 73 (5) ◽  
pp. 2123-2145 ◽  
Author(s):  
George N. Kiladis ◽  
Juliana Dias ◽  
Maria Gehne
Keyword(s):  
Spectral Analysis ◽  
Gravity Waves ◽  
Empirical Orthogonal Function ◽  
Equatorial Waves ◽  
Synoptic Scale ◽  
Shallow Water Theory ◽  
Orthogonal Function ◽  
Convectively Coupled Equatorial Waves ◽  
Beta Plane ◽  
The Relationship

Abstract The relationship between n = 0 mixed Rossby–gravity waves (MRGs) and eastward inertio-gravity waves (EIGs) from Matsuno’s shallow-water theory on an equatorial beta plane is studied using statistics of satellite brightness temperature Tb and dynamical fields from ERA-Interim data. Unlike other observed convectively coupled equatorial waves, which have spectral signals well separated into eastward and westward modes, there is a continuum of MRG–EIG power standing above the background that peaks near wavenumber 0. This continuum is also present in the signals of dry stratospheric MRGs. While hundreds of papers have been written on MRGs, very little work on EIGs has appeared in the literature to date. The authors attribute this to the fact that EIG circulations are much weaker than those of MRGs for a given amount of divergence, making them more difficult to observe even though they strongly modulate convection. Empirical orthogonal function (EOF) and cross-spectral analysis of 2–6-day-filtered Tb isolate zonally standing modes of synoptic-scale convection originally identified by Wallace in 1971. These display antisymmetric Tb signals about the equator that propagate poleward with a period of around 4 days, along with westward-propagating MRG-like circulations that move through the Tb patterns. Further analysis here and in Part II shows that these signatures are not artifacts of the EOF approach but result from a mixture of MRG or EIG modes occurring either in isolation or at the same time.

scholarly journals Gravity Wave Diagnostics and Characteristics in Mesoscale Fields

2015 ◽  
Vol 72 (11) ◽  
pp. 4372-4392 ◽  
Author(s):  
Christopher G. Kruse ◽  
Ronald B. Smith
Keyword(s):  
Gravity Wave ◽  
Energy Flux ◽  
Gravity Waves ◽  
Numerical Models ◽  
Mountain Wave ◽  
Atmospheric Flows ◽  
Vertical Propagation ◽  
The Relationship ◽  
Zonal Momentum ◽  
Selection Of

Abstract As numerical models of complex atmospheric flows increase their quality and resolution, it becomes valuable to isolate and quantify the embedded resolved gravity waves. The authors propose a spatial filtering method combined with a selection of quadratic diagnostic quantities such as heat, momentum, and energy fluxes to do this. These covariant quantities were found to be insensitive to filter cutoff length scales between 300 and 700 km, suggesting the existence of a “cospectral gap.” The gravity waves identified with the proposed method display known properties from idealized studies, including vertical propagation, upwind propagation, the relationship between momentum and energy flux, and agreement with fluxes derived from an alternative method involving simulations with and without terrain. The proposed method is applied to 2- and 6-km-resolution realistic WRF simulations of orographic and nonorographic gravity waves over and around New Zealand within complex frontal cyclones. Deep mountain wave, shallow mountain wave, jet-generated gravity wave, and convection-generated gravity wave events were chosen for analysis. The four wave events shared the characteristics of positive vertical energy flux, negative zonal momentum flux, and upwind horizontal energy flux. Two of the gravity wave events were dissipated nonlinearly.

scholarly journals Probing the Analytical Cancelation Factor of Short Scale Gravity Waves Using Na Lidar and Nightglow Data from the Andes Lidar Observatory

2020 ◽  
Author(s):  
Fabio Vargas ◽  
Javier Fuentes ◽  
Pedro Vega ◽  
Luis Navarro ◽  
Gary Swenson
Keyword(s):  
Gravity Wave ◽  
Gravity Waves ◽  
Wave Amplitude ◽  
Lower Thermosphere ◽  
Empirical Method ◽  
Analytical Relationship ◽  
The Andes ◽  
Propagating Waves ◽  
Vertically Propagating ◽  
Airglow Intensity

The cancelation factor (CF) is a model for the ratio between gravity wave perturbations in the airglow intensity to that in the ambient temperature. The CF model allows to estimate the momentum and energy flux of gravity waves seen in nightglow images as well as the divergence of these fluxes due to waves propagating through the mesosphere and lower thermosphere region, where the nightglow and the Na layers are located. This study uses a set of T/W Na Lidar data and zenith nightglow image observations of the OH and O(1S) emissions to test and validate the CF model from the experimental perspective. The dataset analyzed was obtained during campaigns carried out at the Andes Lidar Observatory (ALO), Chile in 2015, 2016, and 2017. The CF modeled function was compared with observed points from an empirical method for vertically propagating waves that calculates directly the ratio of the gravity wave amplitude seen in nightglow images to the wave amplitude seen in lidar temperatures. We show that the CF analytical relationship underestimates the observed results generally. However, the O(1S) emission line has better agreement respect to the theoretical value due to simpler nightglow photochemistry. In contrast, the observed CF ratio from the OH emission deviates by a factor of two from the modeled asymptotic value.

scholarly journals Growth Rate of Gravity Wave Amplitudes Observed in Sodium Lidar Density Profiles and Nightglow Image Data

Atmosphere ◽  
2019 ◽  
Vol 10 (12) ◽  
pp. 750
Author(s):  
Fabio Vargas ◽  
Guotao Yang ◽  
Paulo Batista ◽  
Delano Gobbi
Keyword(s):  
Growth Rate ◽  
Gravity Wave ◽  
Gravity Waves ◽  
Growth Rates ◽  
Lower Thermosphere ◽  
Image Data ◽  
Density Profiles ◽  
Propagating Waves ◽  
Airglow Image ◽  
Amplitude Growth

Amplitude growth rates of quasi-monochromatic gravity waves were estimated and compared from multiple instrument measurements carried out in Brazil. Gravity wave parameters, such as the wave amplitude and growth rate in distinct altitudes, were derived from sodium lidar density and nightglow all-sky images. Lidar observations were carried out in São Jose dos Campos (23 ∘ S, 46 ∘ W) from 1994 to 2004, while all-sky imagery of multiple airglow layers was conducted in Cachoeira Paulista (23 ∘ S, 45 ∘ W) from 1999–2000 and 2004–2005. We have found that most of the measured amplitude growth rates indicate dissipative behavior for gravity waves identified in both lidar profiles and airglow image datasets. Only a small fraction of the observed wave events (4% imager; 9% lidar) are nondissipative (freely propagating waves). Our findings also show that imager waves are strongly dissipated within the mesosphere and lower thermosphere region (MLT), decaying in amplitude in short distances (<12 km), while lidar waves tend to maintain a constant amplitude within that region. Part of the observed waves (16% imager; 36% lidar) showed unchanging amplitude with altitude (saturated waves). About 51.6% of the imager waves present strong attenuation (overdamped waves) in contrast with 9% of lidar waves. The general saturated or damped behavior is consistent with diffusive filtering processes imposing limits to amplitude growth rates of the observed gravity waves.

scholarly journals Modulation of Seasonal Precipitation over the Tropical Western/Central Pacific by Convectively Coupled Mixed Rossby–Gravity Waves

2013 ◽  
Vol 70 (2) ◽  
pp. 600-606 ◽  
Author(s):  
Takeshi Horinouchi
Keyword(s):  
Gravity Waves ◽  
Sea Surface ◽  
Boreal Summer ◽  
Seasonal Precipitation ◽  
Equatorial Waves ◽  
Central Pacific ◽  
Central Pacific Ocean ◽  
Convectively Coupled Equatorial Waves ◽  
Similar Relation ◽  
The Relationship

Abstract The relationship between the interannual variations of the activity of convectively coupled equatorial waves and seasonal mean precipitation in the tropical western to central Pacific Ocean is investigated. It is found that the convectively coupled mixed Rossby–gravity (MRG) waves are highly and negatively correlated with the seasonal precipitation near the equator in boreal summer. It is suggested that the MRG waves, which have convection centers off the equator, suppress the equatorial precipitation. The relation is insignificant in the other seasons, when the interannual variation of sea surface temperature near the equator is greater than in boreal summer. Also, a similar relation is not found in the eastern Pacific in any season.

scholarly journals Influence of the cloud-level neutral layer on the vertical propagation of topographically generated gravity waves on Venus

2019 ◽  
Vol 71 (1) ◽  
Author(s):  
Takeru Yamada ◽  
Takeshi Imamura ◽  
Tetsuya Fukuhara ◽  
Makoto Taguchi
Keyword(s):  
Layer Thickness ◽  
Gravity Wave ◽  
Local Time ◽  
Gravity Waves ◽  
Analytical Approach ◽  
Wave Activity ◽  
Neutral Layer ◽  
Low Latitudes ◽  
Vertical Propagation ◽  
The Waves

AbstractThe reason for stationary gravity waves at Venus’ cloud top to appear mostly at low latitudes in the afternoon is not understood. Since a neutral layer exists in the lower part of the cloud layer, the waves should be affected by the neutral layer before reaching the cloud top. To what extent gravity waves can propagate vertically through the neutral layer has been unclear. To examine the possibility that the variation of the neutral layer thickness is responsible for the dependence of the gravity wave activity on the latitude and the local time, we investigated the sensitivity of the vertical propagation of gravity waves on the neutral layer thickness using a numerical model. The results showed that stationary gravity waves with zonal wavelengths longer than 1000 km can propagate to the cloud-top level without notable attenuation in the neutral layer with realistic thicknesses of 5–15 km. This suggests that the observed latitudinal and local time variation of the gravity wave activity should be attributed to processes below the cloud. An analytical approach also showed that gravity waves with horizontal wavelengths shorter than tens of kilometers would be strongly attenuated in the neutral layer; such waves should originate in the altitude region above the neutral layer.

Self-Acceleration in the Parameterization of Orographic Gravity Wave Drag

2010 ◽  
Vol 67 (8) ◽  
pp. 2537-2546 ◽  
Author(s):  
John F. Scinocca ◽  
Bruce R. Sutherland
Keyword(s):  
Gravity Wave ◽  
Middle Atmosphere ◽  
Wave Train ◽  
Leading Edge ◽  
Wave Theory ◽  
Wave Drag ◽  
Tuning Parameter ◽  
Mean Flow ◽  
Propagating Waves ◽  
The Impact

Abstract A new effect related to the evaluation of momentum deposition in conventional parameterizations of orographic gravity wave drag (GWD) is considered. The effect takes the form of an adjustment to the basic-state wind about which steady-state wave solutions are constructed. The adjustment is conservative and follows from wave–mean flow theory associated with wave transience at the leading edge of the wave train, which sets up the steady solution assumed in such parameterizations. This has been referred to as “self-acceleration” and it is shown to induce a systematic lowering of the elevation of momentum deposition, which depends quadratically on the amplitude of the wave. An expression for the leading-order impact of self-acceleration is derived in terms of a reduction of the critical inverse Froude number Fc, which determines the onset of wave breaking for upwardly propagating waves in orographic GWD schemes. In such schemes Fc is a central tuning parameter and typical values are generally smaller than anticipated from conventional wave theory. Here it is suggested that self-acceleration may provide some of the explanation for why such small values of Fc are required. The impact of Fc on present-day climate is illustrated by simulations of the Canadian Middle Atmosphere Model.

Sleep Phenomena from the Perspectives of Islam and Science

2014 ◽  
Vol 67 (1) ◽  
Author(s):  
Farahwahida Mohd Yusof ◽  
Siti Norlina Muhamad ◽  
Arieff Salleh Rosman ◽  
Sarimah Noor Ahmad ◽  
Nor Farhah Razak ◽  
...  
Keyword(s):  
20Th Century ◽  
Advanced Technology ◽  
Complex Phenomena ◽  
Scientific Facts ◽  
The Relationship ◽  
The Brain ◽  
Taking Care

This article discusses the phenomenon of sleep, with emphasized to its importance, sleeping times, sleeping positions and even the etiquette of sleeping, from the views of Islam and Science. The Quran and Science are inseparable and the relationship between the two is highly balanced. Scientists have said that the phenomena of sleep is a miracle that deserves to be analysed and studied in depth, as it is a complex phenomena. Glory and Praise to be Allah Almighty has decreed in the Quran of the importance of sleep in the day and night, and that sleep is one of the signs of Allah’s Almighty power and is a miracle to be studied by each individual. Islam places great importance on taking care of one’s body and sleep is one need that has to be fulfilled. Scientists have stressed that sleep is needed to rest the brain, improve memory, and increase one’s energy. This shows that Islam places great importance on having productivity and alertness in each individual’s deed. Many scientific facts that had been clearly stated in a fundamental manner in the Quran could only be analysed with the advanced technology of the 20th century. These facts were not known when they were first revealed and are proof that the Quran is the book of Allah Almighty. The view of Islam on the sleep phenomenon is in line with and is according to the findings of contemporary scien

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