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.

scholarly journals Intensive radiosonde observations of gravity waves in the lower atmosphere over Yichang (111°18´ E, 30°42´ N), China

2008 ◽  
Vol 26 (7) ◽  
pp. 2005-2018 ◽  
Author(s):  
◽  
◽  
◽  
Keyword(s):  
Energy Density ◽  
Gravity Waves ◽  
Lower Stratosphere ◽  
Daily Basis ◽  
Lower Atmosphere ◽  
Wave Number ◽  
Kinetic Energy Density ◽  
Seasonal Differences ◽  
Seasonal Characteristics ◽  
The Mean

Abstract. The characteristics of dynamical and thermal structures and inertial gravity waves (GWs) in the troposphere and lower stratosphere (TLS) over Yichang (111°18´ E, 30°42´ N) were statistically studied by using the data from intensive radiosonde observations in August 2006 (summer month) and January 2007 (winter month) on an eight-times-daily basis. The background atmosphere structures observed in different months exhibit evident seasonal differences, and the zonal wind in winter has a prominent tropospheric jet with a maximum wind speed of about 60 ms−1 occurring at the height of 11.5 km. The statistical results of the inertial GWs in our two-month observations are generally consistent with previous observations in the mid-latitudes. In the summer month, the mean intrinsic frequency and vertical wavelength of the inertial GWs in the troposphere are still larger than those in the lower stratosphere with the absence of intensive tropospheric jets, suggesting that the Doppler shifting due to the tropospheric jets cannot completely account for the differences between the GWs in the troposphere and lower stratosphere. Compared with the observations in the summer month, some interesting seasonal characteristics of the GWs are revealed by the observations in the winter month: 1) more and stronger tropospheric GWs are observed in the winter month; 2) less and weaker GWs are observed in the lower stratosphere in winter; 3) the ratio of the mean GW kinetic energy density to potential energy density is smaller than 1 in winter, which contrasts to that in summer. Most of the seasonal differences can be explained by the intensive tropospheric jets in winter. In both the summer and winter months, the fitted spectral slopes of the vertical wave number spectra for GWs are generally smaller than the canonical spectral slope of −3. Correlation analyses suggest that the tropospheric jet induced wind shear is the dominant source for GWs in both the troposphere and lower stratosphere. Moreover, the tropospheric (lower stratospheric) GWs are found to be modulated by the quasi-7-day (10-day) PW, and the impacts of the diurnal tide on the GWs are relatively weak.

scholarly journals On the climatological probability of the vertical propagation of stationary planetary waves

2016 ◽  
Vol 16 (13) ◽  
pp. 8447-8460 ◽  
Author(s):  
Khalil Karami ◽  
Peter Braesicke ◽  
Miriam Sinnhuber ◽  
Stefan Versick
Keyword(s):  
Wave Propagation ◽  
Climate Model ◽  
Reanalysis Data ◽  
Planetary Waves ◽  
Superior Performance ◽  
Wave Number ◽  
Wave Numbers ◽  
Membership Value ◽  
Environmental Prediction ◽  
Strong Vortex

Abstract. We introduce a diagnostic tool to assess a climatological framework of the optimal propagation conditions for stationary planetary waves. Analyzing 50 winters using NCEP/NCAR (National Center for Environmental Prediction/National Center for Atmospheric Research) reanalysis data we derive probability density functions (PDFs) of positive vertical wave number as a function of zonal and meridional wave numbers. We contrast this quantity with classical climatological means of the vertical wave number. Introducing a membership value function (MVF) based on fuzzy logic, we objectively generate a modified set of PDFs (mPDFs) and demonstrate their superior performance compared to the climatological mean of vertical wave number and the original PDFs. We argue that mPDFs allow an even better understanding of how background conditions impact wave propagation in a climatological sense. As expected, probabilities are decreasing with increasing zonal wave numbers. In addition we discuss the meridional wave number dependency of the PDFs which is usually neglected, highlighting the contribution of meridional wave numbers 2 and 3 in the stratosphere. We also describe how mPDFs change in response to strong vortex regime (SVR) and weak vortex regime (WVR) conditions, with increased probabilities of the wave propagation during WVR than SVR in the stratosphere. We conclude that the mPDFs are a convenient way to summarize climatological information about planetary wave propagation in reanalysis and climate model data.

scholarly journals Kelvin-Helmholtz billows and their effects on mean state during gravity wave propagation

2009 ◽  
Vol 27 (7) ◽  
pp. 2789-2798 ◽  
Author(s):  
X. Liu ◽  
J. Xu ◽  
H. Gao ◽  
G. Chen
Keyword(s):  
Gravity Wave ◽  
Lower Thermosphere ◽  
Dominant Mode ◽  
Lower Atmosphere ◽  
Wave Number ◽  
Small Scale ◽  
Mean Flow ◽  
Triggering Mechanism ◽  
The Mean ◽  
Mlt Region

Abstract. The Kelvin-Helmholtz (KH) billows which appear in the process of gravity wave (GW) propagation are simulated directly by using a compressible nonlinear two-dimensional gravity wave model. The differences between our model and others include: the background field has no special initial configuration and there is no initial triggering mechanism needed in the mesosphere and lower thermosphere (MLT) region to excite the KH billows. However, the initial triggering mechanism is performed in the lower atmosphere through GW, which then propagate into the MLT region and form billows. The braid structures and overturning of KH billows, caused by nonlinear interactions between GWs and mean flow, can be resolved precisely by the model. These results support the findings in airglow studies that GWs propagating from below into the MLT region are important sources of KH billows. The onset of small scale waves and the wave energy transfer induce the shallower vertical wave number power spectral densities (PSD). However, most of the slopes are steeper than the expected kz−3 power law, which indicates that GWs with 10 km vertical wavelength are still a dominant mode. The results also show that the evolution of mean wind vary substantially between the different processes of GWs propagation. Before the KH billows evolve, the mean wind is accelerated greatly by GWs. By contrast, as the KH billows evolve and mix with mean flow, the mean wind and its peak value decrease.

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.

On the mean motion induced by internal gravity waves

1969 ◽  
Vol 36 (4) ◽  
pp. 785-803 ◽  
Author(s):  
Francis P. Bretherton
Keyword(s):  
Gravity Waves ◽  
Wave Energy ◽  
Wave Train ◽  
Three Dimensional ◽  
Internal Gravity Waves ◽  
Wave Number ◽  
Mean Flow ◽  
Mean Velocity ◽  
Mean Motion ◽  
The Mean

A train of internal gravity waves in a stratified liquid exerts a stress on the liquid and induces changes in the mean motion of second order in the wave amplitude. In those circumstances in which the concept of a slowly varying quasi-sinusoidal wave train is consistent, the mean velocity is almost horizontal and is determined to a first approximation irrespective of the vertical forces exerted by the waves. The sum of the mean flow kinetic energy and the wave energy is then conserved. The circulation around a horizontal circuit moving with the mean velocity is increased in the presence of waves according to a simple formula. The flow pattern is obtained around two- and three-dimensional wave packets propagating into a liquid at rest and the results are generalized for any basic state of motion in which the internal Froude number is small. Momentum can be associated with a wave packet equal to the horizontal wave-number times the wave energy divided by the intrinsic frequency.

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.

The propagation of atmospheric Rossby gravity waves in latitudinally sheared zonal flows

1977 ◽  
Vol 287 (1340) ◽  
pp. 115-143 ◽  
Keyword(s):  
Gravity Waves ◽  
Rossby Waves ◽  
Zonal Flow ◽  
Flow Speed ◽  
Wave Number ◽  
Mean Flow ◽  
Zonal Flows ◽  
Planetary Scale ◽  
The Mean ◽  
Critical Latitude

Using the B-plane approximation we formulate the equations which govern small perturbations in a rotating atmosphere and describe a wide class of possible wave motions, in the presence of a background zonal flow, ranging from ‘moderately high’ frequency acoustic-gravity-inertial waves to ‘low’ frequency planetary-scale (Rossby) waves. The discussion concentrates mainly on the propagation properties of Rossby waves in various types of latitudinally sheared zonal flows which occur at different heights and seasons in the earth’s atmosphere. However, it is first shown that gravity waves in a latitudinally sheared zonal flow exhibit critical latitude behaviour where the ‘intrinsic ’ wave frequency matches the Brunt-Vaisala frequency (in contrast to the case of gravity waves in a vertically sheared flow where a critical layer exists where the horizontal wave phase speed equals the flow speed) and that the wave behaviour near such a latitude is similar to that of Rossby waves in the vicinity of their critical latitudes which occur where the ‘intrinsic’ wave frequency approaches zero. In the absence of zonal flow in the atmosphere the geometry of the planetary wave dispersion equation (which is described by a highly elongated ellipsoid in wave-number vector space) implies that energy propagates almost parallel to the /--planes. This feature may provide a reason why there seems to be so little coupling between planetary scale motions in the lower and upper atmosphere. Planetary waves can be made to propagate eastward, as well as westward, if they are evanescent in the vertical direction. The W.K.B. approximation, which provides an approximate description of wave propagation in slowly varying zonal wind shears, shows that the distortion of the wave-number surface caused by the zonal flow controls the dependence of the wave amplitude on the zonal flow speed. In particular it follows that Rossby waves propagating into regions of strengthening westerlies are intensified in amplitude whereas those waves propagating into strengthening easterlies are diminished in amplitude. A classification of the various types of ray trajectories that arise in zonal flow profiles occurring in the Earth’s atmosphere, such as jet-like variations of westerly or easterly zonal flow or a belt of westerlies bounded by a belt of easterlies, is given, and provides the conditions giving rise to such phenomena as critical latitude behaviour and wave trapping. In a westerly flow there is a tendency for the combined effects on wave propagation of jet-like variations of B and zonal flow speed to counteract each other, whereas in an easterly flow such variations tend to reinforce each other. An examination of the reflexion and refraction of Rossby waves at a sharp jump in the zonal flow speed shows that under certain conditions wave amplification, or over-reflexion, can arise with the implication that the reflected wave can extract energy from the background streaming motion. On the other hand the wave behaviour near critical latitudes, which can be described in terms of a discontinuous jump in the ‘wave invariant’, shows that such latitudes can act as either wave absorbers (in which case the mean flow is accelerated there) or wave emitters (in which case the mean flow is decelerated there).

scholarly journals A global ozone climatology from ozone soundings via trajectory mapping: a stratospheric perspective

2013 ◽  
Vol 13 (22) ◽  
pp. 11441-11464 ◽  
Author(s):  
J. Liu ◽  
D. W. Tarasick ◽  
V. E. Fioletov ◽  
C. McLinden ◽  
T. Zhao ◽  
...  
Keyword(s):  
Satellite Data ◽  
Lower Stratosphere ◽  
Stratospheric Ozone ◽  
A Priori ◽  
Forecast Model ◽  
Reanalysis Data ◽  
Trajectory Mapping ◽  
Decadal Variations ◽  
Mean Differences ◽  
The 1960S

Abstract. This study explores a domain-filling trajectory approach to generate a global ozone climatology from relatively sparse ozonesonde data. Global ozone soundings comprising 51 898 profiles at 116 stations over 44 yr (1965–2008) are used, from which forward and backward trajectories are calculated from meteorological reanalysis data to map ozone measurements to other locations and so fill in the spatial domain. The resulting global ozone climatology is archived monthly for five decades from the 1960s to the 2000s on a grid of 5° × 5° × 1 km (latitude, longitude, and altitude), from the surface to 26 km altitude. It is also archived yearly for the same period. The climatology is validated at 20 selected ozonesonde stations by comparing the actual ozone sounding profile with that derived through trajectory mapping of ozone sounding data from all stations except the one being compared. The two sets of profiles are in good agreement, both overall with correlation coefficient r = 0.991 and root mean square (RMS) of 224 ppbv and individually with r from 0.975 to 0.998 and RMS from 87 to 482 ppbv. The ozone climatology is also compared with two sets of satellite data from the Satellite Aerosol and Gas Experiment (SAGE) and the Optical Spectrography and InfraRed Imager System (OSIRIS). The ozone climatology compares well with SAGE and OSIRIS data in both seasonal and zonal means. The mean differences are generally quite small, with maximum differences of 20% above 15 km. The agreement is better in the Northern Hemisphere, where there are more ozonesonde stations, than in the Southern Hemisphere; it is also better in the middle and high latitudes than in the tropics where reanalysis winds are less accurate. This ozone climatology captures known features in the stratosphere as well as seasonal and decadal variations of these features. The climatology clearly shows the depletion of ozone from the 1970s to the mid 1990s and ozone increases in the 2000s in the lower stratosphere. When this climatology is used as the upper boundary condition in an Environment Canada operational chemical forecast model, the forecast is improved in the vicinity of the upper troposphere-lower stratosphere (UTLS) region. This ozone climatology is latitudinally, longitudinally, and vertically resolved and it offers more complete high latitude coverage as well as a much longer record than current satellite data. As the climatology depends on neither a priori data nor photochemical modeling, it provides independent information and insight that can supplement satellite data and model simulations of stratospheric ozone.

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.

 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>

Sign in / Sign up

Export Citation Format

Share Document