scholarly journals Planetary wave activity in the Arctic and Antarctic lower stratospheres during 2007 and 2008

2009 ◽  
Vol 9 (4) ◽  
pp. 14601-14643
Author(s):  
S. P. Alexander ◽  
M. G. Shepherd
Keyword(s):  
Northern Hemisphere ◽  
Planetary Wave ◽  
Travelling Waves ◽  
Maximum Amplitude ◽  
Wave Activity ◽  
Planetary Waves ◽  
The Arctic ◽  
Stationary Waves ◽  
Wave Amplification ◽  
Zonal Wavenumber

Abstract. Temperature data from the COSMIC GPS-RO satellite constellation are used to study planetary wave activity in both polar stratospheres from September 2006 until November 2008. One major and several minor sudden stratospheric warmings (SSWs) were recorded during the boreal winters of 2006/2007 and 2007/2008. Planetary wave morphology is studied using space-time spectral analysis while individual waves are extracted using a linear least squares fitting technique. Results show the planetary wave frequency and zonal wavenumber distribution varying between hemisphere and altitude. Most of the large Northern Hemisphere wave activity is associated with the winter SSWs, while the largest amplitude waves in the Southern Hemisphere occur during spring. Planetary wave activity during the 2006/2007 and 2007/2008 Arctic SSWs is due largely to travelling waves with zonal wavenumbers |s|=1 and |s|=2 having periods of 12, 16 and 23 days and stationary waves with |s|=1 and |s|=2. The latitudinal variation of wave amplification during the two Northern Hemisphere winters is studied. Most planetary waves show different structure and behaviour during each winter. Abrupt changes in the latitude of maximum amplitude of some planetary waves is observed co-incident in time with some of the SSWs.

scholarly journals Planetary wave activity in the polar lower stratosphere

2010 ◽  
Vol 10 (2) ◽  
pp. 707-718 ◽  
Author(s):  
S. P. Alexander ◽  
M. G. Shepherd
Keyword(s):  
Planetary Wave ◽  
Travelling Waves ◽  
Stationary Wave ◽  
Wave Activity ◽  
The Arctic ◽  
Small Scale ◽  
Stationary Waves ◽  
Significant Activity ◽  
Zonal Wavenumber ◽  
The Times

Abstract. Temperature data from the COSMIC GPS-RO satellite constellation are used to study the distribution and variability of planetary wave activity in the low to mid- stratosphere (15–40 km) of the Arctic and Antarctic from September 2006 until March 2009. Stationary waves are separated from travelling waves and their amplitudes, periods and small-scale vertical distribution then examined. COSMIC observed short lived (less than two weeks and less than 5 km vertically) but large enhancements in planetary wave amplitudes occurring regularly throughout all winters in both hemispheres. In contrast to recent Arctic winters, eastward wave activity during 2008–2009 was significantly reduced during the early part of the winter and immediately prior to the major SSW. The eastward waves which did exist had similar periods to the two preceding winters (~16–20 days). A westward wave with zonal wavenumber two, with distinct peaks at 22 km and 35 km and period around 16–24 days, as well as a stationary wave two were associated with the 2009 major SSW. In the Southern Hemisphere, the height structure of planetary wave amplitudes also exhibited fluctuations on short time and vertical scales superimposed upon the broader seasonal cycle. Significant inter-annual variability in planetary wave amplitude and period are noticed, with the times of cessation of significant activity also varying.

Interdecadal Variations of the East Asian Winter Monsoon and Their Association with Quasi-Stationary Planetary Wave Activity

2009 ◽  
Vol 22 (18) ◽  
pp. 4860-4872 ◽  
Author(s):  
Lin Wang ◽  
Ronghui Huang ◽  
Lei Gu ◽  
Wen Chen ◽  
Lihua Kang
Keyword(s):  
Planetary Wave ◽  
East Asian Winter Monsoon ◽  
East Asian ◽  
Wave Activity ◽  
Winter Monsoon ◽  
Planetary Waves ◽  
Asian Winter Monsoon ◽  
Zonal Wavenumber ◽  
Propagation Of Waves ◽  
Stationary Planetary Wave

Abstract Interdecadal variations of the East Asian winter monsoon (EAWM) and their association with the quasi-stationary planetary wave activity are analyzed by using the 40-yr European Centre for Medium-Range Weather Forecasts Re-Analysis dataset and the National Centers for Environmental Prediction–National Center for Atmospheric Research reanalysis dataset. It is found that the EAWM experienced a significant weakening around the late 1980s; that is, the EAWM was strong during 1976–87 and became weak after 1988. This leads to an obvious increase in the wintertime surface air temperature as well as a decrease in the frequency of occurrence of cold waves over East Asia. The dynamical process through which the EAWM is weakened is investigated from the perspective of quasi-stationary planetary waves. It is found that both the propagation and amplitude of quasi-stationary planetary waves have experienced obvious interdecadal variations, which are well related to those of the EAWM. Compared to the period 1976–87, the horizontal propagation of quasi-stationary planetary waves after 1988 is enhanced along the low-latitude waveguide in the troposphere, and the upward propagation of waves into the stratosphere is reduced along the polar waveguide. This results in a weakened subtropical jet around 40°N due to the convergence of the Eliassen–Palm flux. The East Asian jet stream is then weakened, leading to the weakening of the EAWM since 1988. In addition, the amplitude of quasi-stationary planetary waves is significantly weakened around 45°N, which is related to the reduced upward propagation of waves from the lower boundary after 1988. This reduced amplitude may weaken both the Siberian high and the Aleutian low, reduce the pressure gradient in between, and then weaken the EAWM. Further analyses indicate that zonal wavenumber 2 plays the dominant role in this process.

scholarly journals A Short-Term Negative Eddy Feedback on Midlatitude Jet Variability due to Planetary Wave Reflection

2016 ◽  
Vol 73 (11) ◽  
pp. 4311-4328 ◽  
Author(s):  
Gwendal Rivière ◽  
Loïc Robert ◽  
Francis Codron
Keyword(s):  
Planetary Wave ◽  
Physical Nature ◽  
Planetary Waves ◽  
Critical Layer ◽  
Zonal Wavenumber ◽  
Acceleration And Deceleration ◽  
Poleward Shift ◽  
Jet Variability ◽  
Quasigeostrophic Model

Abstract A three-level quasigeostrophic model on the sphere is used to identify the physical nature of the negative planetary wave feedback on midlatitude jet variability. A first approach consists of studying the nonlinear evolution of normal-mode disturbances in a baroclinic westerly zonal jet. For a low-zonal-wavenumber disturbance, successive acceleration and deceleration of the jet occur as a result of reflection of the wave on either side of the jet. The planetary wave deposits momentum in opposite ways during its poleward or equatorward propagation. In contrast, a high-zonal-wavenumber disturbance is not reflected but absorbed within the subtropical critical layer. It thus only induces poleward momentum fluxes, which accelerate the jet and shift it slightly poleward. A long-term simulation forced by a relaxation toward a zonally symmetric temperature profile is then analyzed. Planetary waves are shown to be baroclinically excited. When they propagate equatorward, they induce an acceleration of the jet together with a slight poleward shift. About two-thirds of the planetary waves are absorbed by the subtropical critical layer, which allows the accelerated poleward-shifted jet to persist for a while. For the remaining third, the potential vorticity equatorward of the jet is so well homogenized that a reflection occurs. It is followed by an abrupt jet deceleration during the subsequent poleward propagation. The reflection of planetary waves on the poleward side of the jet is more systematic because of the quasi-permanent presence of a turning latitude there. This negative planetary wave feedback is shown to act more on pulses of the jet than on its latitudinal shifts.

scholarly journals Rayleigh lidar observations of enhanced stratopause temperature over Gadanki (13.5° N, 79.2° E) during major stratospheric warming in 2006

2009 ◽  
Vol 27 (1) ◽  
pp. 373-379 ◽  
Author(s):  
S. Sridharan ◽  
S. Sathishkumar ◽  
K. Raghunath
Keyword(s):  
Gravity Wave ◽  
High Latitude ◽  
Planetary Wave ◽  
Planetary Waves ◽  
Stratospheric Warming ◽  
Linear Interaction ◽  
Zonal Wavenumber ◽  
Low Latitudes ◽  
Rayleigh Lidar ◽  
Lidar Observations

Abstract. Rayleigh lidar observations of temperature structure and gravity wave activity were carried out at Gadanki (13.5° N, 79.2° E) during January–February 2006. A major stratospheric warming event occurred at high latitude during the end of January and early February. There was a sudden enhancement in the stratopause temperature over Gadanki coinciding with the date of onset of the major stratospheric warming event which occurred at high latitudes. The temperature enhancement persisted even after the end of the high latitude major warming event. During the same time, the UKMO (United Kingdom Meteorological Office) zonal mean temperature showed a similar warming episode at 10° N and cooling episode at 60° N around the region of stratopause. This could be due to ascending (descending) motions at high (low) latitudes above the critical level of planetary waves, where there was no planetary wave flux. The time variation of the gravity wave potential energy computed from the temperature perturbations over Gadanki shows variabilities at planetary wave periods, suggesting a non-linear interaction between gravity waves and planetary waves. The space-time analysis of UKMO temperature data at high and low latitudes shows the presence of similar periodicities of planetary wave of zonal wavenumber 1.

scholarly journals The Superposition of Eastward and Westward Rossby Waves in Response to Localized Forcing

2016 ◽  
Vol 29 (20) ◽  
pp. 7547-7557 ◽  
Author(s):  
Jeffrey Shaman ◽  
Eli Tziperman
Keyword(s):  
El Niño ◽  
Rossby Waves ◽  
El Nino ◽  
Phase Speed ◽  
Planetary Waves ◽  
Stationary Waves ◽  
Zonal Wavenumber ◽  
Wide Range ◽  
Localized Forcing ◽  
Diabatic Forcing

Abstract Rossby waves are a principal form of atmospheric communication between disparate parts of the climate system. These planetary waves are typically excited by diabatic or orographic forcing and can be subject to considerable downstream modification. Because of differences in wave properties, including vertical structure, phase speed, and group velocity, Rossby waves exhibit a wide range of behaviors. This study demonstrates the combined effects of eastward-propagating stationary barotropic Rossby waves and westward-propagating very-low-zonal-wavenumber stationary barotropic Rossby waves on the atmospheric response to wintertime El Niño convective forcing over the tropical Pacific. Experiments are conducted using the Community Atmosphere Model, version 4.0, in which both diabatic forcing over the Pacific and localized relaxation outside the forcing region are applied. The localized relaxation is used to dampen Rossby wave propagation to either the west or east of the forcing region and isolate the alternate direction signal. The experiments reveal that El Niño forcing produces both eastward- and westward-propagating stationary waves in the upper troposphere. Over North Africa and Asia the aggregate undamped upper-tropospheric response is due to the superposition and interaction of these oppositely directed planetary waves that emanate from the forcing region and encircle the planet.

scholarly journals Evaluation of Northern Hemisphere Blocking Climatology in the Global Environment Multiscale Model

2013 ◽  
Vol 141 (2) ◽  
pp. 707-727 ◽  
Author(s):  
Etienne Dunn-Sigouin ◽  
Seok-Woo Son ◽  
Hai Lin
Keyword(s):  
Northern Hemisphere ◽  
North Atlantic ◽  
North Pacific ◽  
Detection Algorithm ◽  
Late Winter ◽  
Stationary Waves ◽  
The North ◽  
Zonal Wavenumber ◽  
The North Atlantic ◽  
The North Pacific

Abstract The performance of the Global Environmental Multiscale (GEM) model, the Canadian operational numerical model, in reproducing atmospheric low-frequency variability is evaluated in the context of Northern Hemisphere blocking climatology. The validation is conducted by applying a comprehensive but relatively simple blocking detection algorithm to a 20-yr (1987–2006) integration of the GEM model in climate mode. The comparison to reanalysis reveals that, although the model can reproduce Northern Hemisphere blocking climatology reasonably well, the maximum blocking frequency over the North Atlantic and western Europe is generally underestimated and its peak season is delayed from late winter to spring. This contrasts with the blocking frequency over the North Pacific, which is generally overestimated during all seasons. These misrepresentations of blocking climatology are found to be largely associated with the biases in climatological background flow. The modeled stationary waves show a seasonal delay in zonal wavenumber 1 and an eastward extension in zonal wavenumber-2 components consistent with blocking frequency biases. High-frequency eddies are, however, consistently underestimated both in the North Atlantic and Pacific, indicating that the biases in eddy fields might not be the main reason for the blocking biases in the North Pacific.

A Zonal Wavenumber 3 Pattern of Northern Hemisphere Wintertime Planetary Wave Variability at High Latitudes

2012 ◽  
Vol 25 (19) ◽  
pp. 6756-6769 ◽  
Author(s):  
Haiyan Teng ◽  
Grant Branstator
Keyword(s):  
Northern Hemisphere ◽  
Climate Models ◽  
Linear Trend ◽  
Coupled Model ◽  
Meridional Wind ◽  
Planetary Waves ◽  
Climate System Model ◽  
Past Half Century ◽  
The Pacific ◽  
Zonal Wavenumber

Abstract A prominent pattern of variability of the Northern Hemisphere wintertime tropospheric planetary waves, referred to here as the Wave3 pattern, is identified from the NCEP–NCAR reanalysis. It is worthy of attention because its structure is similar to the linear trend pattern as well as the leading pattern of multidecadal variability of the planetary waves during the past half century. The Wave3 pattern is defined as the second empirical orthogonal function (EOF) of detrended December–February mean 300-hPa meridional wind V300 and denotes a zonal shift of the ridges and troughs of the climatological flow. Although its interannual variance is roughly comparable to that of EOF1 of V300, which represents the Pacific–North America (PNA) pattern, its multidecadal variance is nearly twice as large as that of the PNA. Wave3 is not completely structurally or temporally distinct from the northern annular mode (NAM) but, for some attributes, the linkage of the observed trend to Wave3 is clearer than to NAM. The prominence of the Wave3 pattern is further supported by attributes of many climate models that participated in phase 3 of the Coupled Model Intercomparison Project (CMIP3). In particular, in the Community Climate System Model, version 3 (CCSM3), the Wave3 pattern is present as EOF3 of V300 in both a fully coupled integration and a stand-alone atmospheric integration forced by climatological sea surface temperatures. Its existence in the latter experiment indicates that the pattern can be produced by atmospheric processes alone.

scholarly journals Stationary planetary wave propagation in Northern Hemisphere winter – climatological analysis of the refractive index

2007 ◽  
Vol 7 (1) ◽  
pp. 183-200 ◽  
Author(s):  
Q. Li ◽  
H.-F. Graf ◽  
M. A. Giorgetta
Keyword(s):  
Refractive Index ◽  
Wave Propagation ◽  
Northern Hemisphere ◽  
Planetary Wave ◽  
Planetary Waves ◽  
Mean Flow ◽  
Stratospheric Circulation ◽  
Hemisphere Winter ◽  
Planetary Wave Propagation ◽  
Northern Hemisphere Winter

Abstract. The probability density on a height-meridional plane of negative refractive index squared f(nk2<0) is introduced as a new analysis tool to investigate the climatology of the propagation conditions of stationary planetary waves based on NCEP/NCAR reanalysis data for 44 Northern Hemisphere boreal winters (1958–2002). This analysis addresses the control of the atmospheric state on planetary wave propagation. It is found that not only the variability of atmospheric stability with altitudes, but also the variability with latitudes has significant influence on planetary wave propagation. Eliassen-Palm flux and divergence are also analyzed to investigate the eddy activities and forcing on zonal mean flow. Only the ultra-long planetary waves with zonal wave number 1, 2 and 3 are investigated. In Northern Hemisphere winter the atmosphere shows a large possibility for stationary planetary waves to propagate from the troposphere to the stratosphere. On the other hand, waves induce eddy momentum flux in the subtropical troposphere and eddy heat flux in the subpolar stratosphere. Waves also exert eddy momentum forcing on the mean flow in the troposphere and stratosphere at middle and high latitudes. A similar analysis is also performed for stratospheric strong and weak polar vortex regimes, respectively. Anomalies of stratospheric circulation affect planetary wave propagation and waves also play an important role in constructing and maintaining of interannual variations of stratospheric circulation.

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