scholarly journals Eastward-propagating planetary waves in the polar middle atmosphere

2021 ◽  
Vol 21 (23) ◽  
pp. 17495-17512
Author(s):  
Liang Tang ◽  
Sheng-Yang Gu ◽  
Xian-Kang Dou
Keyword(s):  
Middle Atmosphere ◽  
Flow Instability ◽  
Planetary Waves ◽  
Background Wind ◽  
Mean Flow ◽  
Zonal Wavenumber ◽  
Critical Layers ◽  
The Mean ◽  
Modern Era ◽  
Research Analysis

Abstract. According to Modern-Era Retrospective Research Analysis for Research and Applications (MERRA-2) temperature and wind datasets in 2019, this study presents the global variations in the eastward-propagating wavenumber 1 (E1), 2 (E2), 3 (E3) and 4 (E4) planetary waves (PWs) and their diagnostic results in the polar middle atmosphere. We clearly demonstrate the eastward wave modes exist during winter periods with westward background wind in both hemispheres. The maximum wave amplitudes in the Southern Hemisphere (SH) are slightly larger and lie lower than those in the Northern Hemisphere (NH). Moreover, the wave perturbations peak at lower latitudes with smaller amplitudes as the wavenumber increases. The period of the E1 mode varies between 3–5 d in both hemispheres, while the period of the E2 mode is slightly longer in the NH (∼ 48 h) than in the SH (∼ 40 h). The periods of the E3 are ∼ 30 h in both the SH and the NH, and the period of E4 is ∼ 24 h. Despite the shortening of wave periods with the increase in wavenumber, their mean phase speeds are relatively stable, ∼ 53, ∼ 58, ∼ 55 and ∼ 52 m/s at 70∘ latitudes for E1, E2, E3 and E4, respectively. The eastward PWs occur earlier with increasing zonal wavenumber, which agrees well with the seasonal variations in the critical layers generated by the background wind. Our diagnostic analysis also indicates that the mean flow instability in the upper stratosphere and upper mesosphere might contribute to the amplification of the eastward PWs.

scholarly journals Eastward-propagating planetary wave in the polar middle atmosphere

2021 ◽  
Author(s):  
Liang Tang ◽  
Sheng-Yang Gu ◽  
Xian-Kang Dou
Keyword(s):  
Zonal Wind ◽  
Planetary Wave ◽  
Middle Atmosphere ◽  
Flow Instability ◽  
Diagnostic Analysis ◽  
Background Wind ◽  
Mean Flow ◽  
Zonal Wavenumber ◽  
Critical Layers ◽  
The Mean

Abstract. We presented the global variations of the eastward propagating wavenumber 1 (E1), 2 (E2), 3 (E3), and 4 (E4) planetary waves (PWs) and their diagnostic results in the polar middle atmosphere, using MERRA-2 temperature and wind datasets in 2019. It is clearly shown that the eastward wave modes exist during winter periods with westward background wind in both hemispheres. The maximum wave amplitudes in the southern hemisphere (SH) are slightly larger and lie lower than those in the northern hemisphere (NH). It is also found that the wave perturbations peak at lower latitudes with smaller amplitude as the wavenumber increases. The period of the E1 mode varies from 3 to 5 days in both hemispheres, while the period of E2 mode is slightly longer in the NH (48 h) than in the SH (40 h). The periods of the E3 are ~30 h in both SH and NH, and the period of E4 is ~24 h. Though the wave periods become shorter as the wavenumber increases, their mean phase speeds are relatively stable, which are ~53, ~58, ~55, and ~52 m/s at 70° latitudes for W1, W2, W3, and W4, respectively. The eastward PWs occur earlier with increasing zonal wavenumber, which agrees well with the seasonal variations of the background zonal wind through the generation of critical layers. Diagnostic analysis also shows that the mean flow instability in the upper stratosphere and upper mesosphere may both contribute to the amplification of the eastward PWs.

Wave propagation and transport in the middle atmosphere

1980 ◽  
Vol 296 (1418) ◽  
pp. 73-85 ◽  
Keyword(s):  
Wave Propagation ◽  
Middle Atmosphere ◽  
Transport Processes ◽  
Planetary Waves ◽  
Wave Radiation ◽  
Mean Flow ◽  
Flow Interaction ◽  
Wave Transport ◽  
Equatorial Wave ◽  
The Mean

The dynamics of wave propagation and wave transport are reviewed for vertically propagating, forced, planetary scale waves in the middle atmosphere. Such waves can be divided into two major classes: extratropical planetary waves and equatorial waves. The most important waves of the former class are quasi-stationary Rossby modes of zonal wave numbers 1 and 2 (1 or 2 waves around a latitude circle), which propagate vertically only during the w inter season when the m ean winds are westerly. These modes transport heat and ozone towards the poles, thus maintaining the mean temperature above its radiative equilibrium value in high latitudes and producing the high latitude ozone maximum . It is shown that these wave transport processes depend on wave transience and wave dam ping. The precise form of this dependency is illustrated for transport of a strongly stratified tracer by small amplitude planetary waves. The observed equatorial wave modes are of two types: an eastward propagating Kelvin m ode and a westward propagating mixed Rossby—gravity mode. These modes are therm ally damped in the stratosphere where they interact with the mean flow to produce eastward and westward accelerations, respectively. It is shown tha t in the absence of mechanical dissipation this wave—mean flow interaction is caused by the vertical divergence of a wave ‘radiation stress’. This wave—mean flow interaction process is responsible for producing the well known equatorial quasi-biennial oscillation.

 Generation of planetary waves by gravity-wave drag in the middle atmosphere

2021 ◽  
Author(s):  
Hye-Yeong Chun ◽  
Byeong-Gwon Song ◽  
In-Sun Song
Keyword(s):  
Large Scale ◽  
Middle Atmosphere ◽  
Weather Forecasting ◽  
Wave Theory ◽  
Wave Drag ◽  
Planetary Waves ◽  
Mean Flow ◽  
Long Time ◽  
The Mean

<p>Large-scale atmospheric circulation has been represented mostly by interaction between the mean flow and planetary waves (PWs). Although the importance of gravity waves (GWs) has been recognized for long time, contribution of GWs to the large-scale circulation is receiving more attention recently, with conjunction to GW drag (GWD) parameterizations for climate and global weather forecasting models that extend to the middle atmosphere. As magnitude of GWD increases with height significantly, circulations in the middle atmosphere are determined largely by interactions among the mean flow, PWs and GWs. Classical wave theory in the middle atmosphere has been represented mostly by the Transformed Eulerian Mean (TEM) equation, which include PW and GW forcing separately to the mean flow. Recently, increasing number of studies revealed that forcing by combined PWs and GWs is the same, regardless of different PW and GW forcings, implying a compensation between PWs and GWs forcing. There are two ways for GWs to influence on PWs: (i) changing the mean flow that either influences on waveguide of PWs or induces baroclinic/brotropic instabilities to generate in situ PWs, and (ii) generating PWs as a source of potential vorticity (PV) equation when asymmetric components of GWD exist. The fist mechanism has been studies extensively recently associated with stratospheric sudden warmings (SSWs) that are involved large amplitude PWs and GWD. The second mechanism represents more directly the relationship between PWs and GWs, which is essential to understand the dynamics in the middle atmosphere completely (among the mean flow, PWs and GWs). In this talk, a recently reported result of the generation of PWs by GWs associated with the strongest vortex split-type SSW event occurred in January 2009 (Song et al. 2020, JAS) is presented focusing on the second mechanism.  </p>

Influence of thermospheric effects of solar activity on the middle atmosphere circulation and stationary planetary waves

2020 ◽  
Author(s):  
Andrey Koval ◽  
Nikolai Gavrilov ◽  
Alexander Pogoreltsev ◽  
Nikita Shevchuk
Keyword(s):  
Solar Activity ◽  
Atmospheric Circulation ◽  
General Circulation ◽  
Large Scale ◽  
Middle Atmosphere ◽  
Thermal Structure ◽  
Planetary Waves ◽  
Boreal Winter ◽  
Zonal Wavenumber ◽  
The Mean

<p>Atmospheric large-scale disturbances, for instance planetary waves, play a significant role in atmospheric general circulation, influencing its dynamical and thermal conditions. Solar activity may influence the mean temperature at altitudes above 100 km and alter conditions of wave propagation and reflection in the thermosphere. Using numerical simulations of the general atmospheric circulation during boreal winter, statistically confident evidences are obtained for the first time, demonstrating that changes in the solar activity (SA) in the thermosphere at heights above 100 km can influence propagation and reflection conditions for stationary planetary waves (SPWs) and can modify the middle atmosphere circulation below 100 km. A numerical mechanistic model simulating  atmospheric circulation and SPWs at heights 0 – 300 km is used. To achieve sufficient statistical confidence, 80 pairs of 15-day intervals were extracted from an ensemble of 16 pairs of model runs corresponding to low and high SA. Results averaged over these intervals show that impacts of SA above 100 km change the mean zonal wind and temperature up to 10% at altitudes below 100 km. The statistically confident changes in SPW amplitudes due to SA impacts above 100 km reach up to 50% in the thermosphere and 10 – 15% in the middle atmosphere depending on zonal wavenumber. Changes in wave amplitudes correspond to variations of the EP-flux and may alter dynamical and thermal SPW impacts on the mean wind and temperature. Thus, variable conditions of SPW propagation and reflection at thermospheric altitudes may influence the middle atmosphere circulation, thermal structure and planetary waves at different altitudes.</p>

scholarly journals Investigation of dominant traveling 10-day wave components using long-term MERRA-2 database

2021 ◽  
Vol 73 (1) ◽  
Author(s):  
Chunming Huang ◽  
Wei Li ◽  
Shaodong Zhang ◽  
Gang Chen ◽  
Kaiming Huang ◽  
...  
Keyword(s):  
Flow Instability ◽  
Transmission Condition ◽  
Wave Number ◽  
Mean Flow ◽  
Excited Wave ◽  
Propagating Waves ◽  
Zonal Wave Number ◽  
The Mean

AbstractThe eastward- and westward-traveling 10-day waves with zonal wavenumbers up to 6 from surface to the middle mesosphere during the recent 12 years from 2007 to 2018 are deduced from MERRA-2 data. On the basis of climatology study, the westward-propagating wave with zonal wave number 1 (W1) and eastward-propagating waves with zonal wave numbers 1 (E1) and 2 (E2) are identified as the dominant traveling ones. They are all active at mid- and high-latitudes above the troposphere and display notable month-to-month variations. The W1 and E2 waves are strong in the NH from December to March and in the SH from June to October, respectively, while the E1 wave is active in the SH from August to October and also in the NH from December to February. Further case study on E1 and E2 waves shows that their latitude–altitude structures are dependent on the transmission condition of the background atmosphere. The presence of these two waves in the stratosphere and mesosphere might have originated from the downward-propagating wave excited in the mesosphere by the mean flow instability, the upward-propagating wave from the troposphere, and/or in situ excited wave in the stratosphere. The two eastward waves can exert strong zonal forcing on the mean flow in the stratosphere and mesosphere in specific periods. Compared with E2 wave, the dramatic forcing from the E1 waves is located in the poleward regions.

scholarly journals On the Wave Spectrum Generated by Tropical Heating

2011 ◽  
Vol 68 (9) ◽  
pp. 2042-2060 ◽  
Author(s):  
David A. Ortland ◽  
M. Joan Alexander ◽  
Alison W. Grimsdell
Keyword(s):  
Linear Models ◽  
Nonlinear Models ◽  
Wave Spectrum ◽  
Convective Heating ◽  
Temperature Structure ◽  
Mean Flow ◽  
Quasi Biennial Oscillation ◽  
Wave Response ◽  
Zonal Wavenumber ◽  
The Mean

Abstract Convective heating profiles are computed from one month of rainfall rate and cloud-top height measurements using global Tropical Rainfall Measuring Mission and infrared cloud-top products. Estimates of the tropical wave response to this heating and the mean flow forcing by the waves are calculated using linear and nonlinear models. With a spectral resolution up to zonal wavenumber 80 and frequency up to 4 cpd, the model produces 50%–70% of the zonal wind acceleration required to drive a quasi-biennial oscillation (QBO). The sensitivity of the wave spectrum to the assumed shape of the heating profile, to the mean wind and temperature structure of the tropical troposphere, and to the type of model used is also examined. The redness of the heating spectrum implies that the heating strongly projects onto Hough modes with small equivalent depth. Nonlinear models produce wave flux significantly smaller than linear models due to what appear to be dynamical processes that limit the wave amplitude. Both nonlinearity and mean winds in the lower stratosphere are effective in reducing the Rossby wave response to heating relative to the response in a linear model for a mean state at rest.

Critical layers in accelerating two-layer flows

1988 ◽  
Vol 197 ◽  
pp. 429-451 ◽  
Author(s):  
Donald B. Altman
Keyword(s):  
Laboratory Experiments ◽  
Single Mode ◽  
Shear Instability ◽  
Mean Flow ◽  
Velocity Measurements ◽  
Interfacial Wave ◽  
Flow Acceleration ◽  
Critical Layers ◽  
The Mean ◽  
Processing Software

A series of laboratory experiments on accelerating two-layer shear flows over topography is described. The mean flow reverses at the interface of the layers, forcing a critical layer to occur there. It is found that for a sufficiently thin interface, a slowly growing recirculating region, the ‘acceleration rotor’, develops on the interfacial wave at mean-flow Richardson numbers of O(0.5). This, in turn, can induce a secondary dynamical shear instability on the trailing edge of the wave. A single-mode, linear, two-layer numerical model reproduces many features of the acceleration rotor if mean-flow acceleration and bottom forcing are included. Velocity measurements are obtained from photographs using image processing software developed for the automated reading of particle-streak photographs. Typical results are shown.

scholarly journals Climatic variability of the mean flow and stationary planetary waves in the NCEP/NCAR reanalysis data

2008 ◽  
Vol 26 (5) ◽  
pp. 1233-1241 ◽  
Author(s):  
A. Yu. Kanukhina ◽  
E. V. Suvorova ◽  
L. A. Nechaeva ◽  
E. K. Skrygina ◽  
A. I. Pogoreltsev
Keyword(s):  
Lower Stratosphere ◽  
Climatic Variability ◽  
Reanalysis Data ◽  
Planetary Waves ◽  
Lower Atmosphere ◽  
Wave Number ◽  
Mean Flow ◽  
The Mean ◽  
The 1960S ◽  
Environmental Prediction

Abstract. NCEP/NCAR (National Center for Environmental Prediction – National Center for Atmospheric Research) data have been used to estimate the long-term variability of the mean flow, temperature, and Stationary Planetary Waves (SPW) in the troposphere and lower stratosphere. The results obtained show noticeable climatic variabilities in the intensity and position of the tropospheric jets that are caused by temperature changes in the lower atmosphere. As a result, we can expect that this variability of the mean flow will cause the changes in the SPW propagation conditions. The simulation of the SPW with zonal wave number m=1 (SPW1), performed with a linearized model using the mean flow distributions typical for the 1960s and for the beginning of 21st century, supports this assumption and shows that during the last 40 years the amplitude of the SPW1 in the stratosphere and mesosphere increased substantially. The analysis of the SPW amplitudes extracted from the geopotential height and zonal wind NCEP/NCAR data supports the results of simulation and shows that during the last years there exists an increase in the SPW1 activity in the lower stratosphere. These changes in the amplitudes are accompanied by increased interannual variability of the SPW1, as well. Analysis of the SPW2 activity shows that changes in its amplitude have a different sign in the northern winter hemisphere and at low latitudes in the southern summer hemisphere. The value of the SPW2 variability differs latitudinally and can be explained by nonlinear interference of the primary wave propagation from below and from secondary SPW2.

Application of the IDEMIX Concept for Internal Gravity Waves in the Atmosphere

2020 ◽  
Vol 77 (10) ◽  
pp. 3601-3618
Author(s):  
B. Quinn ◽  
C. Eden ◽  
D. Olbers
Keyword(s):  
Energy Balance ◽  
Wave Field ◽  
Gravity Wave ◽  
Gravity Waves ◽  
Momentum Flux ◽  
Middle Atmosphere ◽  
Internal Gravity Waves ◽  
Wave Drag ◽  
Mean Flow ◽  
The Mean

AbstractThe model Internal Wave Dissipation, Energy and Mixing (IDEMIX) presents a novel way of parameterizing internal gravity waves in the atmosphere. IDEMIX is based on the spectral energy balance of the wave field and has previously been successfully developed as a model for diapycnal diffusivity, induced by internal gravity wave breaking in oceans. Applied here for the first time to atmospheric gravity waves, integration of the energy balance equation for a continuous wave field of a given spectrum, results in prognostic equations for the energy density of eastward and westward gravity waves. It includes their interaction with the mean flow, allowing for an evolving and local description of momentum flux and gravity wave drag. A saturation mechanism maintains the wave field within convective stability limits, and a closure for critical-layer effects controls how much wave flux propagates from the troposphere into the middle atmosphere. Offline comparisons to a traditional parameterization reveal increases in the wave momentum flux in the middle atmosphere due to the mean-flow interaction, resulting in a greater gravity wave drag at lower altitudes. Preliminary validation against observational data show good agreement with momentum fluxes.

On the non-separable baroclinic parallel flow instability problem

1970 ◽  
Vol 40 (2) ◽  
pp. 273-306 ◽  
Author(s):  
Michael E. McIntyre
Keyword(s):  
Flow Instability ◽  
Baroclinic Instability ◽  
Short Wave ◽  
Perturbation Series ◽  
Rate Of Change ◽  
Horizontal Shear ◽  
Mean Flow ◽  
Wave Regime ◽  
Parallel Flows ◽  
The Mean

Perturbation series are developed and mathematically justified, using a straightforward perturbation formalism (that is more widely applicable than those given in standard textbooks), for the case of the two-dimensional inviscid Orr-Sommerfeld-like eigenvalue problem describing quasi-geostrophic wave instabilities of parallel flows in rotating stratified fluids.The results are first used to examine the instability properties of the perturbed Eady problem, in which the zonal velocity profile has the formu=z+ μu1(y,z) where, formally, μ [Lt ] 1. The connexion between baroclinic instability theories with and without short wave cutoffs is clarified. In particular, it is established rigorously that there is instability at short wavelengths in all cases for which such instability would be expected from the ‘critical layer’ argument of Bretherton. (Therefore the apparently conflicting results obtained earlier by Pedlosky are in error.)For the class of profiles of formu=z+ μu1(y) it is then shown from an examination of theO(μ) eigenfunction correction why, under certain conditions, growing baroclinic waves will always produce a counter-gradient horizontal eddy flux of zonal momentum tending to reinforce the horizontal shear of such profiles. Finally, by computing a sufficient number of the higher corrections, this first-order result is shown to remain true, and its relationship to the actual rate of change of the mean flow is also displayed, for a particular jet-like form of profile withfinitehorizontal shear. The latter detailed results may help to explain at least one interesting feature of the mean flow found in a recent numerical solution for the wave régime in a heated rotating annulus.

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