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1
Grise, Kevin M., and David W. J. Thompson. "On the Signatures of Equatorial and Extratropical Wave Forcing in Tropical Tropopause Layer Temperatures." Journal of the Atmospheric Sciences 70, no. 4 (April 1, 2013): 1084–102. http://dx.doi.org/10.1175/jas-d-12-0163.1.
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Abstract Temperatures in the tropical tropopause layer (TTL) play an important role in stratosphere–troposphere exchange and in the formation and maintenance of thin cirrus clouds. Many previous studies have examined the contributions of extratropical and equatorial waves to the TTL using coarse-vertical-resolution satellite and reanalysis data. In this study, the authors provide new insight into the role of extratropical and equatorial waves in the TTL using high-vertical-resolution GPS radio occultation data. The results examine the influence of four different wave forcings on the TTL: extratropical waves that propagate vertically into the stratosphere, extratropical waves that propagate meridionally into the subtropical stratosphere, extratropical waves that propagate meridionally into the subtropical troposphere, and the equatorial planetary waves. The vertically and meridionally propagating extratropical stratospheric waves are associated with deep, zonally symmetric temperature anomalies that extend and amplify with height throughout the lower-to-middle tropical stratosphere. In contrast, the extratropical tropospheric waves and the equatorial planetary waves are associated with tropical temperature anomalies that are confined below 20-km altitude. The equatorial planetary waves dominate the zonally asymmetric component of the TTL temperature field, and both the equatorial planetary waves and the extratropical tropospheric waves are linked to large temperature variability in a 1–2-km-deep layer near the tropical tropopause. The fine vertical scale of the TTL temperature features associated with the equatorial planetary waves and the extratropical tropospheric waves is only readily apparent in high-vertical-resolution data.
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Sun, Lantao, Walter A. Robinson, and Gang Chen. "The Role of Planetary Waves in the Downward Influence of Stratospheric Final Warming Events." Journal of the Atmospheric Sciences 68, no. 12 (December 1, 2011): 2826–43. http://dx.doi.org/10.1175/jas-d-11-014.1.
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Abstract Stratospheric final warming events are simulated in an idealized atmospheric model by imposing a winter-to-summer transition in radiative equilibrium temperature only in the stratosphere. Large ensembles of events are simulated with different strengths of topographic forcing. It is found that the dates of final warmings become earlier and their downward influence on the troposphere becomes stronger for greater topographic amplitudes. This result is similar to observed differences between the downward influence of the final warming in the Northern and Southern Hemispheres. The mechanisms through which the final warming exerts its influence on the tropospheric circulation are investigated using a zonally symmetric model. It is found that lower-stratospheric wave driving induces a residual circulation that affects the tropospheric circulation. The stratosphere also affects the propagation of planetary waves in the upper troposphere, resulting in a burst of wave activity and a rapid deceleration of tropospheric zonal winds at the time of the final warming. These results highlight the important roles of planetary waves in the downward influence of the stratospheric final warming events.
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Niranjan Kumar, K., D. V. Phanikumar, T. B. M. J. Ouarda, M. Rajeevan, M. Naja, and K. K. Shukla. "Modulation of surface meteorological parameters by extratropical planetary-scale Rossby waves." Annales Geophysicae 34, no. 1 (January 25, 2016): 123–32. http://dx.doi.org/10.5194/angeo-34-123-2016.
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Abstract. This study examines the link between upper-tropospheric planetary-scale Rossby waves and surface meteorological parameters based on the observations made in association with the Ganges Valley Aerosol Experiment (GVAX) campaign at an extratropical site at Aryabhatta Research Institute of Observational Sciences, Nainital (29.45° N, 79.5° E) during November–December 2011. The spectral analysis of the tropospheric wind field from radiosonde measurements indicates a predominance power of around 8 days in the upper troposphere during the observational period. An analysis of the 200 hPa meridional wind (v200 hPa) anomalies from the Modern-Era Retrospective Analysis for Research and Applications (MERRA) reanalysis shows distinct Rossby-wave-like structures over a high-altitude site in the central Himalayan region. Furthermore, the spectral analysis of global v200 hPa anomalies indicates the Rossby waves are characterized by zonal wave number 6. The amplification of the Rossby wave packets over the site leads to persistent subtropical jet stream (STJ) patterns, which further affects the surface weather conditions. The propagating Rossby waves in the upper troposphere along with the undulations in the STJ create convergence and divergence regions in the mid-troposphere. Therefore, the surface meteorological parameters such as the relative humidity, wind speeds, and temperature are synchronized with the phase of the propagating Rossby waves. Moreover, the present study finds important implications for medium-range forecasting through the upper-level Rossby waves over the study region.
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Nikulin, G., and F. Lott. "On the time-scales of the downward propagation and of the tropospheric planetary wave response to the stratospheric circulation." Annales Geophysicae 28, no. 2 (February 1, 2010): 339–51. http://dx.doi.org/10.5194/angeo-28-339-2010.
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Abstract. Three datasets (the NCEP-NCAR reanalysis, the ERA-40 reanalysis and the LMDz-GCM), are used to analyze the relationships between large-scale dynamics of the stratosphere and the tropospheric planetary waves during the Northern Hemisphere (NH) winter. First, a cross-spectral analysis clarifies the time scales at which downward propagation of stratospheric anomalies occurs in the low-frequency band (that is at periods longer than 50 days). At these periods the strength of the polar vortex, measured by the 20-hPa Northern Annular Mode (NAM) index and the wave activity flux, measured by the vertical component of the Eliassen-Palm flux (EPz) from both the troposphere and the stratosphere, are significantly related with each other and in lead-lag quadrature. While, in the low-frequency band of the downward propagation, the EPz anomalies of the opposite sign around NAM extremes drive the onset and decay of NAM events, we found that the EPz anomalies in the troposphere, are significantly larger after stratospheric vortex anomalies than at any time before. This marked difference in the troposphere is related to planetary waves with zonal wavenumbers 1–3, showing that there is a tropospheric planetary wave response to the earlier state of the stratosphere at low frequencies. We also find that this effect is due to anomalies in the EPz issued from the northern midlatitudes and polar regions.
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Duffy, Dean G. "Transient Stratospheric Planetary Waves Generated by Tropospheric Forcing." Journal of the Atmospheric Sciences 52, no. 17 (September 1995): 3109–28. http://dx.doi.org/10.1175/1520-0469(1995)052<3109:tspwgb>2.0.co;2.
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Chen, Gang, and Lantao Sun. "Mechanisms of the Tropical Upwelling Branch of the Brewer–Dobson Circulation: The Role of Extratropical Waves." Journal of the Atmospheric Sciences 68, no. 12 (December 1, 2011): 2878–92. http://dx.doi.org/10.1175/jas-d-11-044.1.
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Abstract The role of extratropical waves in the tropical upwelling branch of the Brewer–Dobson circulation is investigated in an idealized model of the stratosphere and troposphere. To simulate different stratospheric seasonal cycles of planetary waves in the two hemispheres, seasonally varying radiative heating is imposed only in the stratosphere, and surface topographic forcing is prescribed only in the Northern Hemisphere (NH). A zonally symmetric version of the same model is used to diagnose the effects of different wavenumbers and different regions of the total forcing on tropical stratospheric upwelling. The simple configuration can simulate a reasonable seasonal cycle of the tropical upwelling in the lower stratosphere with a stronger amplitude in January (NH midwinter) than in July (NH midsummer), as in the observations. It is shown that the seasonal cycle of stratospheric planetary waves and tropical upwelling responds nonlinearly to the strength of the tropospheric forcing, with a midwinter maximum under strong NH-like tropospheric forcing and double peaks in the fall and spring under weak Southern Hemisphere (SH)-like forcing. The planetary wave component of the total forcing can approximately reproduce the seasonal cycle of tropical stratospheric upwelling in the zonally symmetric model. The zonally symmetric model further demonstrates that the planetary wave forcing in the winter tropical and subtropical stratosphere contributes most to the seasonal cycle of tropical stratospheric upwelling, rather than the high-latitude wave forcing. This suggests that the planetary wave forcing, prescribed mostly in the extratropics in the model, has to propagate equatorward into the subtropical latitudes to induce sufficient tropical upwelling. Another interesting finding is that the planetary waves in the summer lower stratosphere can drive a shallow residual circulation rising in the subtropics and subsiding in the extratropics.
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Perlwitz, Judith, and Nili Harnik. "Downward Coupling between the Stratosphere and Troposphere: The Relative Roles of Wave and Zonal Mean Processes*." Journal of Climate 17, no. 24 (December 15, 2004): 4902–9. http://dx.doi.org/10.1175/jcli-3247.1.
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Abstract Wave and zonal mean features of the downward dynamic coupling between the stratosphere and troposphere are compared by applying a time-lagged singular value decomposition analysis to Northern Hemisphere height fields decomposed into zonal mean and its deviations. It is found that both zonal and wave components contribute to the downward interaction, with zonal wave 1 (due to reflection) dominating on the short time scale (up to 12 days) and the zonal mean (due to wave–mean-flow interaction) dominating on the longer time scale. It is further shown that the two processes dominate during different years, depending on the state of the stratosphere. Winters characterized by a basic state that is reflective for wave 1 show a strong relationship between stratospheric and tropospheric wave-1 fields when the stratosphere is leading and show no significant correlations in the zonal mean fields. On the other hand, winters characterized by a stratospheric state that does not reflect waves show a strong relationship only between stratospheric and tropospheric zonal mean fields. This study suggests that there are two types of stratospheric winter states, characterized by different downward dynamic interaction. In one state, most of the wave activity gets deposited in the stratosphere, resulting in strong wave–mean-flow interaction, while in the other state, wave activity is reflected back down to the troposphere, primarily affecting the structure of tropospheric planetary waves.
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Takaya, Koutarou, and Hisashi Nakamura. "Interannual Variability of the East Asian Winter Monsoon and Related Modulations of the Planetary Waves." Journal of Climate 26, no. 23 (December 2013): 9445–61. http://dx.doi.org/10.1175/jcli-d-12-00842.1.
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Interannual variability of the East Asian winter monsoon is investigated through composite analysis applied to observational data for 50 recent years. Although the monsoon activity itself is confined into the lower troposphere, its midwinter variability tends to accompany upper-tropospheric geopotential height anomalies similar to the Eurasian (EU) and western Pacific (WP) teleconnection patterns. The “EU-like” pattern is characterized by a wavy signature over the Eurasian continent and the North Atlantic, with surface temperature anomalies over the Far East and North America. In the “WP-like” pattern, a meridional dipole of upper-level height anomalies is evident over the Far East. These anomaly patterns related to the anomalous winter monsoon activity are found to accompany marked modulations of the climatological development of the upper-tropospheric planetary waves from late autumn to midwinter. Enhanced monsoon activity in January associated with the WP-like pattern involves anomalous seasonal development of a planetary wave ridge with enhanced positive height tendencies from November to January over eastern Siberia and Alaska, while the corresponding tendencies are anomalously negative under the weakened monsoon activity. The stronger monsoon also accompanies an enhanced seasonal decline of geopotential height over the midlatitude North Pacific, corresponding to the enhanced southeastward development of a planetary wave trough. Similar modulations of the planetary wave evolution are observed with the anomalous monsoon activity associated with the EU-like pattern. In addition, the anomalous midwinter activity of the monsoon is also accompanied by noticeable variability of the seasonal development of the planetary waves over the Euro-Atlantic sector.
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Xie, Jincai, Jinggao Hu, Haiming Xu, Shuai Liu, and Huan He. "Dynamic Diagnosis of Stratospheric Sudden Warming Event in the Boreal Winter of 2018 and Its Possible Impact on Weather over North America." Atmosphere 11, no. 5 (April 26, 2020): 438. http://dx.doi.org/10.3390/atmos11050438.
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In the winter of 2018, a major stratospheric sudden warming (SSW) event occurred in the Northern Hemisphere. This study performs a dynamic diagnosis on this 2018 SSW event and analyzes its possible impact on the weather over North America. The result shows that the ridge over Alaska in the mid-troposphere and the trough over the northeastern North America are the prominent tropospheric precursory signals before the occurrence of this SSW event. The signals appear 10 days before the SSW, which greatly enhances the propagation of the planetary wavenumber 2 from the troposphere to the extratropical stratosphere. The collapse process of stratospheric polar vortex indicates that this SSW is a typical vortex splitting event dominated by planetary wavenumber 2. Additionally, after the SSW onset, no reflection of the stratosphere on the tropospheric planetary waves is observed. Thus, this event can also be classified as an absorbing-type SSW event. A noticeable cold wave occurs in the northwestern North America within 10 days after the 2018 SSW. This cold wave is probably associated with the SSW-related west–east dipole, namely a ridge over Alaska and a trough over the northeastern North America in the mid-troposphere that lasted up to 10 days after the onset date. The composite analysis of the other seven SSW events with an emergence of similar mid-tropospheric circulation pattern after SSW onset date yields coincident 2-meter temperature anomalies in the northwestern North America, which confirms the above conclusion to some extent.
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Chen, Quanliang, Luyang Xu, and Hongke Cai. "Impact of Stratospheric Sudden Warming on East Asian Winter Monsoons." Advances in Meteorology 2015 (2015): 1–10. http://dx.doi.org/10.1155/2015/640912.
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Fifty-two Stratospheric sudden warming (SSW) events that occurred from 1957 to 2002 were analyzed based on the 40-year European Centre for Medium-Range Weather Forecasts Reanalysis dataset. Those that could descent to the troposphere were composited to investigate their impacts on the East Asian winter monsoon (EAWM). It reveals that when the SSW occurs, the Arctic Oscillation (AO) and the North Pacific Oscillation (NPO) are both in the negative phase and that the tropospheric circulation is quite wave-like. The Siberian high and the Aleutian low are both strengthened, leading to an increased gradient between the Asian continent and the North Pacific. Hence, a strong EAWM is observed with widespread cooling over inland and coastal East Asia. After the peak of the SSW, in contrast, the tropospheric circulation is quite zonally symmetric with negative phases of AO and NPO. The mid-tropospheric East Asian trough deepens and shifts eastward. This configuration facilitates warming over the East Asian inland and cooling over the coastal East Asia centered over Japan. The activities of planetary waves during the lifecycle of the SSW were analyzed. The anomalous propagation and the attendant altered amplitude of the planetary waves can well explain the observed circulation and the EAWM.
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White, Ian P., Chaim I. Garfinkel, Edwin P. Gerber, Martin Jucker, Peter Hitchcock, and Jian Rao. "The Generic Nature of the Tropospheric Response to Sudden Stratospheric Warmings." Journal of Climate 33, no. 13 (July 1, 2020): 5589–610. http://dx.doi.org/10.1175/jcli-d-19-0697.1.
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AbstractThe tropospheric response to midwinter sudden stratospheric warmings (SSWs) is examined using an idealized model. SSW events are triggered by imposing high-latitude stratospheric heating perturbations of varying magnitude for only a few days, spun off from a free-running control integration (CTRL). The evolution of the thermally triggered SSWs is then compared with naturally occurring SSWs identified in CTRL. By applying a heating perturbation, with no modification to the momentum budget, it is possible to isolate the tropospheric response directly attributable to a change in the stratospheric polar vortex, independent of any planetary wave momentum torques involved in the initiation of an SSW. Zonal-wind anomalies associated with the thermally triggered SSWs first propagate downward to the high-latitude troposphere after ~2 weeks, before migrating equatorward and stalling at midlatitudes, where they straddle the near-surface jet. After ~3 weeks, the circulation and eddy fluxes associated with thermally triggered SSWs evolve very similarly to SSWs in CTRL, despite the lack of initial planetary wave driving. This suggests that at longer lags, the tropospheric response to SSWs is generic and it is found to be linearly governed by the strength of the lower-stratospheric warming, whereas at shorter lags, the initial formation of the SSW potentially plays a large role in the downward coupling. In agreement with previous studies, synoptic waves are found to play a key role in the persistent tropospheric jet shift at long lags. Synoptic waves appear to respond to the enhanced midlatitude baroclinicity associated with the tropospheric jet shift, and preferentially propagate poleward in an apparent positive feedback with changes in the high-latitude refractive index.
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Sun, Lantao, Walter A. Robinson, and Gang Chen. "The Predictability of Stratospheric Warming Events: More from the Troposphere or the Stratosphere?" Journal of the Atmospheric Sciences 69, no. 2 (February 1, 2012): 768–83. http://dx.doi.org/10.1175/jas-d-11-0144.1.
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Abstract The roles of the stratosphere and the troposphere in determining the predictability of stratospheric final warming and sudden warming events are evaluated in an idealized atmospheric model. For each stratospheric warming event simulated in the model, a number of forecast experiments are performed from 10 or 20 days prior to the warming onset with perturbations in the troposphere and in the stratosphere separately. It is found that the stratosphere affects predictions of warming onset primarily by providing the initial state of the zonal winds, while the tropospheric initial conditions have a large impact through the generation and propagation of planetary waves. These results correspond to the roles played by the initial zonal flow and the evolution of eddy forcings in a zonally symmetric model. The initial stratospheric zonal flow has some influence on stratospheric wave driving, but in most cases this does not significantly affect the timing of the warming, except when the initial condition is close to the onset date. These results highlight the role of the troposphere in determining stratospheric planetary wave driving and support the importance of tropospheric precursors to the stratospheric warming events.
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Luo, Dehai, and Wenqi Zhang. "A Nonlinear Multiscale Theory of Atmospheric Blocking: Eastward and Upward Propagation and Energy Dispersion of Tropospheric Blocking Wave Packets." Journal of the Atmospheric Sciences 77, no. 12 (December 2020): 4025–49. http://dx.doi.org/10.1175/jas-d-20-0153.1.
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AbstractIn this paper, a nonlinear multiscale interaction model is used to examine how the planetary waves associated with eddy-driven blocking wave packets propagate through the troposphere in vertically varying weak baroclinic basic westerly winds (BWWs). Using this model, a new one-dimensional finite-amplitude local wave activity flux (WAF) is formulated, which consists of linear WAF related to linear group velocity and local eddy-induced WAF related to the modulus amplitude of blocking envelope amplitude and its zonal nonuniform phase. It is found that the local eddy-induced WAF reduces the divergence (convergence) of linear WAF in the blocking upstream (downstream) side to favor blocking during the blocking growth phase. But during the blocking decay phase, enhanced WAF convergence occurs in the blocking downstream region and in the upper troposphere when BWW is stronger in the upper troposphere than in the lower troposphere, which leads to enhanced upward-propagating tropospheric wave activity, though the linear WAF plays a major role. In contrast, the downward propagation of planetary waves may be seen in the troposphere for vertically decreased BWWs. These are not seen for a zonally uniform eddy forcing. A perturbed inverse scattering transform method is used to solve the blocking envelope amplitude equation. It is found that the finite-amplitude WAF represents a modified group velocity related to the variations of blocking soliton amplitude and zonal wavenumber caused by local eddy forcing. Using this amplitude equation solution, it is revealed that, under local eddy forcing, the blocking wave packet tends to be nearly nondispersive during its growth phase but strongly dispersive during the decay phase for vertically increased BWWs, leading to strong eastward and upward propagation of planetary waves in the downstream troposphere.
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Grise, Kevin M., and David W. J. Thompson. "Equatorial Planetary Waves and Their Signature in Atmospheric Variability." Journal of the Atmospheric Sciences 69, no. 3 (March 1, 2012): 857–74. http://dx.doi.org/10.1175/jas-d-11-0123.1.
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Abstract Equatorial planetary waves are a fundamental component of the tropical climate system. Previous studies have examined their structure in the climatological-mean circulation, their role in the climatological-mean momentum balance of the tropics, and their contribution to the climatological-mean upwelling across the tropical tropopause. In this study, the authors focus on the contribution of the equatorial planetary waves to variability in the tropical circulation about its climatological-mean state. The equatorial planetary waves that dominate the climatological mean exhibit considerable variability on intraseasonal and interannual time scales. Variability in the amplitude of the equatorial planetary waves is associated with a distinct pattern of equatorially symmetric climate variability that also emerges from empirical orthogonal function analysis of various tropical dynamical fields. Variability in the equatorial planetary waves is characterized by variations in 1) convection in the deep tropics, 2) eddy momentum flux convergence and zonal-mean zonal wind in the tropical upper troposphere, 3) the mean meridional circulation of the tropical and subtropical troposphere, 4) temperatures in the tropical lower stratosphere and subtropical troposphere of both hemispheres, and 5) the amplitude of the upper tropospheric anticyclones over the western tropical Pacific Ocean. It is argued that pulsation of the equatorial planetary waves provides an alternative framework for interpreting the response of the tropical circulation to a range of climate phenomena. Pulsation of the equatorial planetary waves is apparent in association with opposing phases of El Niño–Southern Oscillation and select phases of the Madden–Julian oscillation. Pulsation of the equatorial planetary waves also contributes to variability in measures of the width of the tropical belt.
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Magnusdottir, Gudrun, and Peter H. Haynes. "Reflection of Planetary Waves in Three-Dimensional Tropospheric Flows." Journal of the Atmospheric Sciences 56, no. 4 (February 1999): 652–70. http://dx.doi.org/10.1175/1520-0469(1999)056<0652:ropwit>2.0.co;2.
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Mayr, H. G., J. G. Mengel, E. R. Talaat, H. S. Porter, and K. L. Chan. "Modeling study of mesospheric planetary waves: genesis and characteristics." Annales Geophysicae 22, no. 6 (June 14, 2004): 1885–902. http://dx.doi.org/10.5194/angeo-22-1885-2004.
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Abstract. The Numerical Spectral Model (NSM) extends from the ground into the thermosphere and incorporates Hines' Doppler Spread Parameterization for small-scale gravity waves (GWs). In the present version of the model we account for a tropospheric heat source in the zonal mean (m=0), which reproduces qualitatively the observed zonal jets near the tropopause and the accompanying reversal in the latitudinal temperature variations. In the study presented here, we discuss the planetary waves (PWs) that are solely generated internally, i.e. without the explicit excitation sources related to tropospheric convection or topography. Our analysis shows that PWs are not produced when the zonally averaged heat source into the atmosphere is artificially suppressed, and that the PWs are generally weaker when the tropospheric source is not applied. Instabilities associated with the zonal mean temperature, pressure and wind fields, which still need to be explored, are exciting PWs that have amplitudes in the mesosphere comparable to those observed. Three classes of PWs are generated in the NSM. (1) Rossby type PWs, which slowly propagate westward relative to the mean zonal flow, are carried by the winds so that they appear (from the ground) to propagate, respectively, eastward and westward in the winter and summer hemispheres below 80km. Depending on the zonal wave number and magnitudes of the zonal winds, and under the influence of the equatorial oscillations, these PWs typically have periods between 2 and 20 days. Their horizontal wind amplitudes can exceed 40 m/s in the lower mesosphere. (2) Rossby-gravity waves, which propagate westward at low latitudes and have periods around 2 days for zonal wave numbers m=2 to 4. (3) Eastward propagating equatorial Kelvin waves, which are generated in the upper mesosphere with periods between 1 and 3 days depending on m. A survey of the PWs reveals that the largest wind amplitudes tend to occur below 80km in the winter hemisphere; but above that altitude the amplitudes are larger in the summer hemisphere where the winds can approach 50m/s. This pattern in the seasonal variations also appears in the baroclinity of the zonal mean (m=0). The nonmigrating tides in the mesosphere are significantly larger for the model with the tropospheric heat source, in which PWs are apparently generated by the instabilities that arise around the tropopause.
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Lin, Pu, Qiang Fu, and Dennis L. Hartmann. "Impact of Tropical SST on Stratospheric Planetary Waves in the Southern Hemisphere." Journal of Climate 25, no. 14 (July 15, 2012): 5030–46. http://dx.doi.org/10.1175/jcli-d-11-00378.1.
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Abstract The impact of tropical sea surface temperature (SST) on stratospheric planetary waves in the Southern Hemisphere (SH) is investigated in austral spring using observed SST and reanalysis data for the past three decades. Maximum covariance analysis indicates that the tropical SST and the SH stratospheric planetary wave activity are primarily coupled through two modes. The leading two modes show the La Niña–like and the central-Pacific El Niño–like SST anomalies in their positive polarities, respectively, which each are related to enhanced stratospheric planetary wave activity. These two modes also introduce phase shifts to the stratospheric stationary planetary waves: a westward shift is seen for La Niña and an eastward shift for warm SST anomalies is seen in the central Pacific. The Eliassen–Palm fluxes associated with the two modes indicate that the anomalous stratospheric wave activity originates in the troposphere and propagates upward over the mid–high latitudes, so that the linkages between tropical SST and extratropical tropospheric circulation appear to play a key role. Furthermore, the observed circulation anomaly patterns for the two modes change rapidly from spring to summer, consistent with a sharp seasonal transition in the SH basic state. Similar SST and circulation anomaly patterns associated with the two modes are simulated in chemistry–climate models.
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Orr, Andrew, Thomas J. Bracegirdle, J. Scott Hosking, Thomas Jung, Joanna D. Haigh, Tony Phillips, and Wuhu Feng. "Possible Dynamical Mechanisms for Southern Hemisphere Climate Change due to the Ozone Hole." Journal of the Atmospheric Sciences 69, no. 10 (May 10, 2012): 2917–32. http://dx.doi.org/10.1175/jas-d-11-0210.1.
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Abstract The authors report a hypothesis for the dynamical mechanisms responsible for the strengthening of the Southern Hemisphere circumpolar winds from the lower stratosphere to the surface due to the ozone hole. A general circulation model forced by stratospheric ozone depletion representative of the ozone hole period successfully reproduced these observed changes. Investigation of the dynamical characteristics of the model therefore provides some insight into the actual mechanisms. From this the authors suggest the following: 1) An initial (radiative) strengthening of the lower-stratospheric winds as a result of ozone depletion conditions the polar vortex so that fewer planetary waves propagate up from the troposphere, resulting in weaker planetary wave driving. 2) This causes further strengthening of the vortex, which results in an additional reduction in upward-propagating planetary waves and initiates a positive feedback mechanism in which the weaker wave driving and the associated strengthened winds are drawn downward to the tropopause. 3) In the troposphere the midlatitude jet shifts poleward in association with increases in the synoptic wave fluxes of heat and momentum, which are the result of a positive feedback mechanism consisting of two components: 4) increases in low-level baroclinicity, and the subsequent generation of baroclinic activity (associated with a poleward heat flux), are collocated with the jet latitudinal position, and 5) strengthening anticyclonic shear increases the refraction of wave activity equatorward (associated with a poleward momentum flux). Finally, 6) confinement of planetary waves in the high-latitude troposphere is an important step to couple the stratospheric changes to the tropospheric response.
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Newman, Paul A., and Eric R. Nash. "The Unusual Southern Hemisphere Stratosphere Winter of 2002." Journal of the Atmospheric Sciences 62, no. 3 (March 1, 2005): 614–28. http://dx.doi.org/10.1175/jas-3323.1.
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Abstract The Southern Hemisphere (SH) stratospheric winter of 2002 was the most unusual winter yet observed in the SH climate record. Temperatures near the edge of the Antarctic polar vortex were considerably warmer than normal over the entire course of the winter. The polar night jet was considerably weaker than normal and was displaced more poleward than has been observed in previous winters. These record high temperatures and weak jet resulted from a series of wave events that took place over the course of the winter. The propagation of these wave events from the troposphere is diagnosed from time series of Eliassen–Palm flux vectors and autoregression time series. Strong levels of planetary waves were observed in the midlatitude lower troposphere. The combinations of strong tropospheric waves with a low index of refraction at the tropopause resulted in the large stratospheric wave forcing. The wave events tended to occur irregularly over the course of the winter, and the cumulative effect of these waves was to precondition the polar night jet for the extremely large wave event of 22 September. This large wave event resulted in the first ever observed major stratospheric warming in the SH and split the Antarctic ozone hole. The combined effect of all of the 2002 winter wave events resulted in the smallest ozone hole observed since 1988. The sequence of stratospheric wave events was also found to be strongly associated with unusually strong levels of wave 1 in the SH tropospheric subtropics.
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Albers, John R., George N. Kiladis, Thomas Birner, and Juliana Dias. "Tropical Upper-Tropospheric Potential Vorticity Intrusions during Sudden Stratospheric Warmings." Journal of the Atmospheric Sciences 73, no. 6 (May 20, 2016): 2361–84. http://dx.doi.org/10.1175/jas-d-15-0238.1.
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Abstract The intrusion of lower-stratospheric extratropical potential vorticity into the tropical upper troposphere in the weeks surrounding the occurrence of sudden stratospheric warmings (SSWs) is examined. The analysis reveals that SSW-related PV intrusions are significantly stronger, penetrate more deeply into the tropics, and exhibit distinct geographic distributions compared to their climatological counterparts. While climatological upper-tropospheric and lower-stratospheric (UTLS) PV intrusions are generally attributed to synoptic-scale Rossby wave breaking, it is found that SSW-related PV intrusions are governed by planetary-scale wave disturbances that deform the extratropical meridional PV gradient maximum equatorward. As these deformations unfold, planetary-scale wave breaking along the edge of the polar vortex extends deeply into the subtropical and tropical UTLS. In addition, the material PV deformations also reorganize the geographic structure of the UTLS waveguide, which alters where synoptic-scale waves break. In combination, these two intrusion mechanisms provide a robust explanation describing why displacement and split SSWs—or, more generally, anomalous stratospheric planetary wave events—produce intrusions with unique geographic distributions: displacement SSWs have a single PV intrusion maximum over the Pacific Ocean, while split SSWs have intrusion maxima over the Pacific and Indian Oceans. It is also shown that the two intrusion mechanisms involve distinct time scales of variability, and it is highlighted that they represent an instantaneous and direct link between the stratosphere and troposphere. This is in contrast to higher-latitude stratosphere–troposphere coupling that occurs indirectly via wave–mean flow feedbacks.
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Boljka, Lina, and Thomas Birner. "Tropopause-level planetary wave source and its role in two-way troposphere–stratosphere coupling." Weather and Climate Dynamics 1, no. 2 (October 17, 2020): 555–75. http://dx.doi.org/10.5194/wcd-1-555-2020.
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Abstract. Atmospheric planetary waves play a fundamental role in driving stratospheric dynamics, including sudden stratospheric warming (SSW) events. It is well established that the bulk of the planetary wave activity originates near the surface. However, recent studies have pointed to a planetary wave source near the tropopause that may play an important role in the development of SSWs. Here we analyze the dynamical origin of this wave source and its impact on stratosphere–troposphere coupling, using an idealized model and a quasi-reanalysis. It is shown that the tropopause-level planetary wave source is associated with nonlinear wave–wave interactions, but it can also manifest as an apparent wave source due to transient wave decay. The resulting planetary waves may then propagate deep into the stratosphere, where they dissipate and may help to force SSWs. Our results indicate that SSWs preceded by both the tropopause and the surface wave-source events tend to be followed by a weakened tropospheric zonal flow several weeks later. However, while in the case of a preceding surface wave-source event this downward impact is found mainly poleward of 60∘ N, it appears to be the strongest between 40 and 60∘ N for SSWs preceded by tropopause wave-source events. This suggests that tropopause wave-source events could potentially serve as an additional predictor of not only SSWs but also their downward impact as well.
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Gavrilov, N. M. "Parametrization of momentum and energy depositions from gravity waves generated by tropospheric hydrodynamic sources." Annales Geophysicae 15, no. 12 (December 31, 1997): 1570–80. http://dx.doi.org/10.1007/s00585-997-1570-4.
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Abstract. The mechanism of generation of internal gravity waves (IGW) by mesoscale turbulence in the troposphere is considered. The equations that describe the generation of waves by hydrodynamic sources of momentum, heat and mass are derived. Calculations of amplitudes, wave energy fluxes, turbulent viscosities, and accelerations of the mean flow caused by IGWs generated in the troposphere are made. A comparison of different mechanisms of turbulence production in the atmosphere by IGWs shows that the nonlinear destruction of a primary IGW into a spectrum of secondary waves may provide additional dissipation of nonsaturated stable waves. The mean wind increases both the effectiveness of generation and dissipation of IGWs propagating in the direction of the wind. Competition of both effects may lead to the dominance of IGWs propagating upstream at long distances from tropospheric wave sources, and to the formation of eastward wave accelerations in summer and westward accelerations in winter near the mesopause.
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Shaman, Jeffrey, and Eli Tziperman. "The Superposition of Eastward and Westward Rossby Waves in Response to Localized Forcing." Journal of Climate 29, no. 20 (October 5, 2016): 7547–57. http://dx.doi.org/10.1175/jcli-d-16-0119.1.
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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.
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Scinocca, J. F., and P. H. Haynes. "Dynamical Forcing of Stratospheric Planetary Waves by Tropospheric Baroclinic Eddies." Journal of the Atmospheric Sciences 55, no. 14 (July 1998): 2361–92. http://dx.doi.org/10.1175/1520-0469(1998)055<2361:dfospw>2.0.co;2.
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Sousasantos, Jonas, José Humberto Andrade Sobral, Esfhan Alam Kherani, Marcelo Magalhães Fares Saba, and Diovane Rodolfo de Campos. "Relationship between ionospheric plasma bubble occurrence and lightning strikes over the Amazon region." Annales Geophysicae 36, no. 2 (March 9, 2018): 349–60. http://dx.doi.org/10.5194/angeo-36-349-2018.
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Abstract. The vertical coupling between the troposphere and the ionosphere presents some remarkable features. Under intense tropospheric convection, gravity waves may be generated, and once they reach the ionosphere, these waves may seed instabilities and spread F and equatorial plasma bubble events may take place. Additionally, there is a close association between severe tropospheric convection and lightning strikes. In this work an investigation covering an equinox period (September–October) during the deep solar minimum (2009) presents the relation between lightning strike activity and spread F (equatorial plasma bubble) detected over a low-latitude Brazilian region. The results show a considerable correlation between these two phenomena. The common element in the center of this conformity seems to be the gravity waves. Once gravity waves and lightning strikes share the same source (intense tropospheric convection) and the effects of such gravity waves in the ionosphere include the seeding of instabilities according to the gravity waves magnitude, the monitoring of the lightning strike activity seems to offer some information about the subsequent development of spread F over the equatorial region. Keywords. Ionosphere (equatorial ionosphere)
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Lubis, Sandro W., Katja Matthes, Nour-Eddine Omrani, Nili Harnik, and Sebastian Wahl. "Influence of the Quasi-Biennial Oscillation and Sea Surface Temperature Variability on Downward Wave Coupling in the Northern Hemisphere." Journal of the Atmospheric Sciences 73, no. 5 (April 19, 2016): 1943–65. http://dx.doi.org/10.1175/jas-d-15-0072.1.
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Abstract Downward wave coupling occurs when an upward-propagating planetary wave from the troposphere decelerates the flow in the upper stratosphere and forms a downward reflecting surface that redirects waves back to the troposphere. To test this mechanism and potential factors influencing the downward wave coupling, three 145-yr sensitivity simulations with NCAR’s Community Earth System Model [CESM1(WACCM)], a state-of-the-art high-top chemistry–climate model, are analyzed. The results show that the quasi-biennial oscillation (QBO) and SST variability significantly impact downward wave coupling. Without the QBO, the occurrence of downward wave coupling is significantly suppressed. In contrast, stronger and more persistent downward wave coupling occurs when SST variability is excluded. The above influence on the occurrence of downward wave coupling is mostly due to a direct influence of the QBO and SST variability on stratospheric planetary wave source and propagation. The strengths of the tropospheric circulation and surface responses to a given downward wave coupling event, however, behave differently. The surface anomaly is significantly weaker (stronger) in the experiment with fixed SSTs (without QBO), even though the statistical signal of downward wave coupling is strongest (weakest) in this experiment. This apparent mismatch is explained by the differences in the strength of the synoptic-scale eddy–mean flow feedback and the possible contribution of SST anomalies in the North Atlantic during the downward wave coupling event. The weaker synoptic-scale eddy–mean flow feedback and the absence of the positive NAO-related SST-tripole pattern in the fixed SST experiment are consistent with a weaker tropospheric response to downward wave coupling. The results highlight the importance of synoptic-scale eddies in setting the tropospheric response to downward wave coupling.
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Gerber, Edwin P. "Stratospheric versus Tropospheric Control of the Strength and Structure of the Brewer–Dobson Circulation." Journal of the Atmospheric Sciences 69, no. 9 (September 1, 2012): 2857–77. http://dx.doi.org/10.1175/jas-d-11-0341.1.
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Abstract The strength and structure of the Brewer–Dobson circulation (BDC) are explored in an idealized general circulation model. It is shown that diabatic forcing of the stratosphere and planetary wave forcing by the troposphere can have comparable effects on tracer transport through the stratosphere, as quantified by the mean age of air and age spectrum. Their impact, however, is mediated through different controls on the mass circulation. Planetary waves are modulated by changing surface topography. Increased wave forcing strengthens the circulation, particularly at lower levels. This is primarily a tropospheric control on the BDC, as the wave forcing is set by stationary waves at the base of the stratosphere. Stratospheric control of the circulation is effected indirectly through the strength of the stratospheric polar vortex. A colder vortex creates a waveguide higher into the stratosphere, raising the breaking level of Rossby waves and deepening the circulation. Ventilation of mass in the stratosphere depends critically on the depth of tropical upwelling, and so mass and tracer transport is comparably sensitive to both tropospheric and stratospheric controls. The two controls on the circulation can lead to separate influences on the lower and upper stratosphere, with implications for the seasonal cycle of tropical upwelling. They allow for independent changes in the “shallow” and “deep” branches of the BDC, which may be important for comparing modeled trends with observations. It is also shown that changes in the BDC have a significant impact on the tropical cold point (on the order of degrees) and the equator-to-pole gradient in the tropopause (on the order of a kilometer).
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Peters, D. H. W., P. Vargin, A. Gabriel, N. Tsvetkova, and V. Yushkov. "Tropospheric forcing of the boreal polar vortex splitting in January 2003." Annales Geophysicae 28, no. 11 (November 26, 2010): 2133–48. http://dx.doi.org/10.5194/angeo-28-2133-2010.
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Abstract. The dynamical evolution of the relatively warm stratospheric winter season 2002–2003 in the Northern Hemisphere was studied and compared with the cold winter 2004–2005 based on NCEP-Reanalyses. Record low temperatures were observed in the lower and middle stratosphere over the Arctic region only at the beginning of the 2002–2003 winter. Six sudden stratospheric warming events, including the major warming event with a splitting of the polar vortex in mid-January 2003, have been identified. This led to a very high vacillation of the zonal mean circulation and a weakening of the stratospheric polar vortex over the whole winter season. An estimate of the mean chemical ozone destruction inside the polar vortex showed a total ozone loss of about 45 DU in winter 2002–2003; that is about 2.5 times smaller than in winter 2004–2005. Embedded in a winter with high wave activity, we found two subtropical Rossby wave trains in the troposphere before the major sudden stratospheric warming event in January 2003. These Rossby waves propagated north-eastwards and maintained two upper tropospheric anticyclones. At the same time, the amplification of an upward propagating planetary wave 2 in the upper troposphere and lower stratosphere was observed, which could be caused primarily by those two wave trains. Furthermore, two extratropical Rossby wave trains over the North Pacific Ocean and North America were identified a couple of days later, which contribute mainly to the vertical planetary wave activity flux just before and during the major warming event. It is shown that these different tropospheric forcing processes caused the major warming event and contributed to the splitting of the polar vortex.
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Gavrilov, N. M., and S. Fukao. "Numerical and the MU radar estimations of gravity wave enhancement and turbulent ozone fluxes near the tropopause." Annales Geophysicae 22, no. 11 (November 29, 2004): 3889–98. http://dx.doi.org/10.5194/angeo-22-3889-2004.
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Abstract. It is shown with a numerical simulation that a sharp increase in the vertical temperature gradient and Brunt-Väisälä frequency near the tropopause may produce an increase in the amplitudes of internal gravity waves (IGWs) propagating upward from the troposphere, wave breaking and generation of stronger turbulence. This may enhance the transport of admixtures between the troposphere and stratosphere in the middle latitudes. Turbulent diffusion coefficient calculated numerically and measured with the MU radar are of 1-10m2/s in different seasons in Shigaraki, Japan (35° N, 136° E). These values lead to the estimation of vertical ozone flux from the stratosphere to the troposphere of (1-10)x1014, which may substantially add to the usually supposed ozone downward transport with the general atmospheric circulation. Therefore, local enhancements of IGW intensity and turbulence at tropospheric altitudes over mountains due to their orographic excitation and due to other wave sources may lead to the changes in tropospheric and total ozone over different regions.
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Martineau, Patrick, and Seok-Woo Son. "Onset of Circulation Anomalies during Stratospheric Vortex Weakening Events: The Role of Planetary-Scale Waves." Journal of Climate 28, no. 18 (September 11, 2015): 7347–70. http://dx.doi.org/10.1175/jcli-d-14-00478.1.
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Abstract To highlight the details of stratosphere–troposphere dynamical coupling during the onset of strong polar vortex variability, this study identifies stratospheric vortex weakening (SVW) events by rapid deceleration of the polar vortex and performs composite budget analyses in the transformed Eulerian-mean (TEM) framework on daily time scales. Consistent with previous work, a rapid deceleration of the polar vortex, followed by a rather slow recovery, is largely explained by conservative dynamics with nonnegligible contribution by nonconservative sinks of wave activity. During the onset of such events, stratospheric zonal wind anomalies show a near-instantaneous vertical coupling to the troposphere, which results from an anomalous upward and poleward propagation of planetary-scale waves. In the troposphere, zonal wind anomalies are also influenced by synoptic-scale waves, confirming previous studies. The SVW events driven by wavenumber-1 disturbances show comparable circulation anomalies to those driven by wavenumber-2 disturbances both in the stratosphere and troposphere. The former, however, exhibits more persistent anomalies after the onset than the latter. During both events, tropospheric wavenumber-1 and 2 disturbances project strongly onto the climatological waves, indicating that vertical propagation of planetary-scale waves into the stratosphere is largely caused by constructive linear interference. It is also found that the SVW-related vertical coupling is somewhat sensitive to the stratospheric mean state. Although overall evolution of zonal-mean circulation anomalies are reasonably similar under an initially weak or strong polar vortex, the time-lagged downward coupling is evident only when the polar vortex is decelerated under a weak vortex state. These results are compared with other definitions of weak polar vortex events, such as stratospheric sudden warming events.
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Gisinger, Sonja, Andreas Dörnbrack, Vivien Matthias, James D. Doyle, Stephen D. Eckermann, Benedikt Ehard, Lars Hoffmann, Bernd Kaifler, Christopher G. Kruse, and Markus Rapp. "Atmospheric Conditions during the Deep Propagating Gravity Wave Experiment (DEEPWAVE)." Monthly Weather Review 145, no. 10 (October 2017): 4249–75. http://dx.doi.org/10.1175/mwr-d-16-0435.1.
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This paper describes the results of a comprehensive analysis of the atmospheric conditions during the Deep Propagating Gravity Wave Experiment (DEEPWAVE) campaign in austral winter 2014. Different datasets and diagnostics are combined to characterize the background atmosphere from the troposphere to the upper mesosphere. How weather regimes and the atmospheric state compare to climatological conditions is reported upon and how they relate to the airborne and ground-based gravity wave observations is also explored. Key results of this study are the dominance of tropospheric blocking situations and low-level southwesterly flows over New Zealand during June–August 2014. A varying tropopause inversion layer was found to be connected to varying vertical energy fluxes and is, therefore, an important feature with respect to wave reflection. The subtropical jet was frequently diverted south from its climatological position at 30°S and was most often involved in strong forcing events of mountain waves at the Southern Alps. The polar front jet was typically responsible for moderate and weak tropospheric forcing of mountain waves. The stratospheric planetary wave activity amplified in July leading to a displacement of the Antarctic polar vortex. This reduced the stratospheric wind minimum by about 10 m s−1 above New Zealand making breaking of large-amplitude gravity waves more likely. Satellite observations in the upper stratosphere revealed that orographic gravity wave variances for 2014 were largest in May–July (i.e., the period of the DEEPWAVE field phase).
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Scaife, A. A., and I. N. James. "Response of the stratosphere to interannual variability of tropospheric planetary waves." Quarterly Journal of the Royal Meteorological Society 126, no. 562 (January 2000): 275–97. http://dx.doi.org/10.1002/qj.49712656214.
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Xu, Mian, Wenshou Tian, Jiankai Zhang, Tao Wang, and Kai Qie. "Impact of Sea Ice Reduction in the Barents and Kara Seas on the Variation of the East Asian Trough in Late Winter." Journal of Climate 34, no. 3 (February 2021): 1081–97. http://dx.doi.org/10.1175/jcli-d-20-0205.1.
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AbstractUsing the European Centre for Medium-Range Weather Forecasts (ECMWF) interim reanalysis (ERA-Interim) dataset and the Specified Chemistry Whole Atmosphere Community Climate Model (WACCM-SC), the impacts of sea ice reduction in the Barents–Kara Seas (BKS) on the East Asian trough (EAT) in late winter are investigated. Results from both reanalysis data and simulations show that the BKS sea ice reduction leads to a deepened EAT in late winter, especially in February, while the EAT axis tilt is not sensitive to the BKS sea ice reduction. Further analysis shows that the BKS sea ice reduction influences the EAT through the tropospheric and stratospheric pathways. For the tropospheric pathway, the results from a linearized barotropic model and Rossby wave ray tracing model reveal that long Rossby wave trains stimulated by the BKS sea ice loss propagate downstream to the North Pacific, strengthening the EAT. For the stratospheric pathway, the upward planetary waves enhanced by the BKS sea ice reduction shift the subpolar westerlies near the tropopause southward. With the critical lines displaced equatorward, the poleward transient eddies break at lower latitudes, shifting the eddy momentum deposit throughout the troposphere equatorward. Tropospheric westerlies maintained by eddy momentum deposit are also shifted southward, inducing the cyclonic anomalies over the North Pacific and deepening the EAT in late winter. Nudging experiments show that the tropospheric pathway only contributes to around 29.7% of the deepening of the EAT in February induced by the BKS sea ice loss, while the remaining 70.3% is caused by stratosphere–troposphere coupling.
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Wrasse, C. M., T. Nakamura, H. Takahashi, A. F. Medeiros, M. J. Taylor, D. Gobbi, C. M. Denardini, et al. "Mesospheric gravity waves observed near equatorial and low–middle latitude stations: wave characteristics and reverse ray tracing results." Annales Geophysicae 24, no. 12 (December 21, 2006): 3229–40. http://dx.doi.org/10.5194/angeo-24-3229-2006.
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Abstract. Gravity wave signatures were extracted from OH airglow observations using all-sky CCD imagers at four different stations: Cachoeira Paulista (CP) (22.7° S, 45° W) and São João do Cariri (7.4° S, 36.5° W), Brazil; Tanjungsari (TJS) (6.9° S, 107.9° E), Indonesia and Shigaraki (34.9° N, 136° E), Japan. The gravity wave parameters are used as an input in a reverse ray tracing model to study the gravity wave vertical propagation trajectory and to estimate the wave source region. Gravity waves observed near the equator showed a shorter period and a larger phase velocity than those waves observed at low-middle latitudes. The waves ray traced down into the troposphere showed the largest horizontal wavelength and phase speed. The ray tracing results also showed that at CP, Cariri and Shigaraki the majority of the ray paths stopped in the mesosphere due to the condition of m2<0, while at TJS most of the waves are traced back into the troposphere. In summer time, most of the back traced waves have their final position stopped in the mesosphere due to m2<0 or critical level interactions (|m|→∞), which suggests the presence of ducting waves and/or waves generated in-situ. In the troposphere, the possible gravity wave sources are related to meteorological front activities and cloud convections at CP, while at Cariri and TJS tropical cloud convections near the equator are the most probable gravity wave sources. The tropospheric jet stream and the orography are thought to be the major responsible sources for the waves observed at Shigaraki.
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Lenouo, A., F. Nkankam Kamga, and E. Yepdjuo. "Weak interaction in the African Easterly Jet." Annales Geophysicae 23, no. 5 (July 28, 2005): 1637–43. http://dx.doi.org/10.5194/angeo-23-1637-2005.
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Abstract. Low-frequency, African Easterlies Waves (AEW) are examined as disturbances embedded in the mid-tropospheric easterly jet of the African low troposphere. The solution to the nonlinear vorticity equation relevant to the description of waves is sought in the form of triplet waves. The latest suggest a unified method to determine their kinetics characteristic and to explain the mechanism of energy exchange between their different modes. The period of energy interaction between different modes of the global wave is equal to 3.5 days when the wave packet is moving with a group velocity dependent on the mean basic flow. The effects of nonlinearity are also identified, and it is noted that the horizontal shears of mean flow, as well as the temporal variation of the amplitude wave functions, are the controlling factors. Keywords. Meteorology and atmospheric dynamics (Synoptic-scale meteorology; Tropical meteorology; Waves and tides)
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Roundy, Paul E. "Observed Structure of Convectively Coupled Waves as a Function of Equivalent Depth: Kelvin Waves and the Madden–Julian Oscillation." Journal of the Atmospheric Sciences 69, no. 7 (July 1, 2012): 2097–106. http://dx.doi.org/10.1175/jas-d-12-03.1.
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Abstract The view that convectively coupled Kelvin waves and the Madden–Julian oscillation (MJO) are distinct modes is tested by regressing data from the Climate Forecast System Reanalysis against satellite outgoing longwave radiation data filtered for particular zonal wavenumbers and frequencies by wavelet analysis. Results confirm that nearly dry Kelvin waves have horizontal structures consistent with their equatorial beta-plane shallow-water-theory counterparts, with westerly winds collocated with the lower-tropospheric ridge, while the MJO and signals along Kelvin wave dispersion curves at low shallow-water-model equivalent depths are characterized by geopotential troughs extending westward from the region of lower-tropospheric easterly wind anomalies through the region of lower-tropospheric westerly winds collocated with deep convection. Results show that as equivalent depth decreases from that of the dry waves (concomitant with intensification of the associated convection), the ridge in the westerlies and the trough in the easterlies shift westward. The analysis therefore demonstrates a continuous field of intermediate structures between the two extremes, suggesting that Kelvin waves and the MJO are not dynamically distinct modes. Instead, signals consistent with Kelvin waves become more consistent with the MJO as the associated convection intensifies. This result depends little on zonal scale. Further analysis also shows how activity in synoptic-scale Kelvin waves characterized by particular phase speeds evolves with the planetary-scale MJO.
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Liu, Y., C. X. Liu, H. P. Wang, X. Tie, S. T. Gao, D. Kinnison, and G. Brasseur. "Atmospheric tracers during the 2003–2004 stratospheric warming event and impact of ozone intrusions in the troposphere." Atmospheric Chemistry and Physics Discussions 8, no. 4 (July 17, 2008): 13633–66. http://dx.doi.org/10.5194/acpd-8-13633-2008.
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Abstract. We use the stratospheric/tropospheric chemical transport model MOZART-3 to study the distribution and transport of stratospheric O3 during the exceptionally intense stratospheric sudden warming event observed in January 2004 in the Northern polar region. A comparison between observations by the MIPAS instrument on board the ENVISAT spacecraft and model simulations shows that the evolution of the polar vortex and of planetary waves during the warming event plays an important role in controlling the spatial distribution of stratospheric ozone and the downward ozone flux in the lower stratospheric and upper tropospheric regions. Compared to the situation during the winter of 2002–2003, lower ozone concentrations were transported from the polar regions (polar vortex) to mid-latitudes, leading to exceptional large areas of low ozone concentrations outside the polar vortex and "low-ozone pockets" in the middle stratosphere. The unusually long-lasting stratospheric westward winds (easterlies) during the 2003–2004 event greatly restricted the upward propagation of planetary waves, causing the weak transport of ozone-rich air originated from low latitudes to the middle polar stratosphere (10 hPa). The restricted wave activities led to a reduced downward ozone flux from the lower stratosphere (LS) to the upper troposphere (UT), especially in East Asia. Consequently, in this region during wintertime (December and January), the column ozone between 100 and 300 hPa was about 10% lower during the 2003–2004 event compared to the situation in 2002–2003.
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Hitchcock, Peter, Theodore G. Shepherd, Masakazu Taguchi, Shigeo Yoden, and Shunsuke Noguchi. "Lower-Stratospheric Radiative Damping and Polar-Night Jet Oscillation Events." Journal of the Atmospheric Sciences 70, no. 5 (April 23, 2013): 1391–408. http://dx.doi.org/10.1175/jas-d-12-0193.1.
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Abstract The effect of stratospheric radiative damping time scales on stratospheric variability and on stratosphere–troposphere coupling is investigated in a simplified global circulation model by modifying the vertical profile of radiative damping in the stratosphere while holding it fixed in the troposphere. Perpetual-January conditions are imposed, with sinusoidal topography of zonal wavenumber 1 or 2. The depth and duration of the simulated sudden stratospheric warmings closely track the lower-stratospheric radiative time scales. Simulations with the most realistic profiles of radiative damping exhibit extended time-scale recoveries analogous to polar-night jet oscillation (PJO) events, which are observed to follow sufficiently deep stratospheric warmings. These events are characterized by weak lower-stratospheric winds and enhanced stability near the tropopause, which persist for up to 3 months following the initial warming. They are obtained with both wave-1 and wave-2 topography. Planetary-scale Eliassen–Palm (EP) fluxes entering the vortex are also suppressed, which is in agreement with observed PJO events. Consistent with previous studies, the tropospheric jets shift equatorward in response to the warmings. The duration of the shift is closely correlated with the period of enhanced stability. The magnitude of the shift in these runs, however, is sensitive only to the zonal wavenumber of the topography. Although the shift is sustained primarily by synoptic-scale eddies, the net effect of the topographic form drag and the planetary-scale fluxes is not negligible; they damp the surface wind response but enhance the vertical shear. The tropospheric response may also reduce the generation of planetary waves, further extending the stratospheric dynamical time scales.
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Pogoreltsev, A. I., O. G. Aniskina, A. Y. Kanukhina, T. S. Ermakova, A. I. Ugryumov, and Y. V. Efimova. "Tropospheric circulation response to sudden stratospheric warming observed in January 2013." HYDROMETEOROLOGY AND ECOLOGY. PROCEEDINGS OF THE RUSSIAN STATE HYDROMETEOROLOGICAL UNIVERSITY, no. 60 (2020): 241–54. http://dx.doi.org/10.33933/2074-2762-2020-60-241-254.
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Analysis of the dynamical regime changes in the stratosphere during different phases of the Sudden Stratospheric Warming (SSW) that has been observed in January 2013 is presented. The different mechanisms of SSW influence on the tropospheric circulation through the stationary planetary waves (SPWs) reflection and/or increase in SPWs activity due to nonlinear interaction with the mean flow and their subsequent propagation into the troposphere are discussed. Three-dimensional wave activity flux and its divergence are determined using the UK Met Office data; the synoptic situation and its changes during the SSW events are analyzed. The wave activity penetrates downward from stratosphere into the troposphere and can affect weather processes during the SSW and right afterwards. It is this time that polar anticyclones can be formed at high latitudes, which quickly go southward along meridional directions and then deviate to the East at middle latitudes. Interestingly, the locations of polar anticyclone formations and subsequent displacements correspond to the regions of maximal horizontal wave activity fluxes connected with stratospheric processes. The results obtained allow us to suggest that accounting of stratospheric processes and their influence on the troposphere in winter season can improve the middle-range forecast of anticyclone formation and cold weather events at middle latitudes.
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Kennel, Charles F., and Elena Yulaeva. "Influence of Arctic sea-ice variability on Pacific trade winds." Proceedings of the National Academy of Sciences 117, no. 6 (January 27, 2020): 2824–34. http://dx.doi.org/10.1073/pnas.1717707117.
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A conceptual model connecting seasonal loss of Arctic sea ice to midlatitude extreme weather events is applied to the 21st-century intensification of Central Pacific trade winds, emergence of Central Pacific El Nino events, and weakening of the North Pacific Aleutian Low Circulation. According to the model, Arctic Ocean warming following the summer sea-ice melt drives vertical convection that perturbs the upper troposphere. Static stability calculations show that upward convection occurs in annual 40- to 45-d episodes over the seasonally ice-free areas of the Beaufort-to-Kara Sea arc. The episodes generate planetary waves and higher-frequency wave trains that transport momentum and heat southward in the upper troposphere. Regression of upper tropospheric circulation data on September sea-ice area indicates that convection episodes produce wave-mediated teleconnections between the maximum ice-loss region north of the Siberian Arctic coast and the Intertropical Convergence Zone (ITCZ). These teleconnections generate oppositely directed trade-wind anomalies in the Central and Eastern Pacific during boreal winter. The interaction of upper troposphere waves with the ITCZ air–sea column may also trigger Central Pacific El Nino events. Finally, waves reflected northward from the ITCZ air column and/or generated by triggered El Nino events may be responsible for the late winter weakening of the Aleutian Low Circulation in recent years.
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Li, Ying, and Ngar-Cheung Lau. "Influences of ENSO on Stratospheric Variability, and the Descent of Stratospheric Perturbations into the Lower Troposphere." Journal of Climate 26, no. 13 (July 1, 2013): 4725–48. http://dx.doi.org/10.1175/jcli-d-12-00581.1.
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Abstract The linkage between El Niño–Southern Oscillation (ENSO) and North Atlantic Oscillation (NAO) through the stratospheric pathway is examined using a global coupled climate model [GFDL Climate Model version 3 (CM3)], with increased vertical resolution and extent in the stratosphere as compared to an earlier model [GFDL Climate Model version 2 (CM2)]. It is demonstrated that the relationship between ENSO and NAO is stronger in CM3 than in CM2. It is found that ENSO plays an important role in modulating the frequency of occurrence of the stratospheric polar vortex anomalies through enhancement/attenuation of the amplitudes of zonal wavenumbers 1 and 2, especially in late winter. A higher frequency of weak (strong) stratospheric vortex events is simulated in CM3 during El Niño (La Niña) episodes. The weak vortex events during El Niño winters are preceded by enhancement of the zonal wave-1 pattern and weakening of zonal wave-2 pattern. These modified tropospheric planetary waves propagate upward and then weaken the stratospheric polar vortex through eddy–mean flow interaction. The zonal-mean geopotential response in the stratosphere propagates downward and weakens the polar vortex throughout the troposphere. The effects of planetary wave refraction in the upper troposphere on the zonally averaged circulation cells in the tropospheric meridional plane, and the linkage between the lower branches of these cells and the near-surface wind patterns, play an important role in the flow pattern over the region corresponding to the southern lobe of the NAO. Specifically, a negative annular mode and NAO response is discernible in weak stratospheric vortex events during El Niño. Conversely, the positive annular mode and NAO is evident in strong vortex events during La Niña.
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Adames, Ángel F., and John M. Wallace. "On the Tropical Atmospheric Signature of El Niño." Journal of the Atmospheric Sciences 74, no. 6 (May 24, 2017): 1923–39. http://dx.doi.org/10.1175/jas-d-16-0309.1.
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Abstract The linear atmospheric signature of ENSO, obtained by regressing fields of geopotential height Z, wind, vertical velocity, and rainfall upon the Niño-3.4 sea surface temperature (SST) index, is partitioned into zonally symmetric and eddy components. The zonally symmetric component is thermally forced by the narrowing and intensification of the zonally averaged equatorial rain belt during El Niño and mechanically forced by the weakening of the upper-tropospheric equatorial stationary waves and their associated flux of wave activity. The eddy component of the ENSO signature is decomposed into barotropic (BT) and baroclinic (BC) contributions, the latter into first and second modal structures BC1 and BC2, separable functions of space (x, y), and pressure p, using eigenvector analysis. BC1 exhibits a nearly equatorially symmetric planetary wave structure comprising three dumbbell-shaped features suggestive of equatorial Rossby waves, with out-of-phase wind and geopotential height perturbations in the upper and lower troposphere. BC1 and BT exhibit coincident centers of action. In regions of the tropics where the flow in the climatological-mean stationary waves is cyclonic, BT reinforces BC1, and vice versa, in accordance with vorticity balance considerations. BC1 and BT dominate the eddy ENSO signature in the free atmosphere. Most of the residual is captured by BC2, which exhibits a shallow, convergent boundary layer signature forced by the weakening of the equatorial cold tongue in SST. The anomalous boundary layer convergence drives a deep convection signature whose upper-tropospheric outflow is an integral part of the BC1 contribution to the ENSO signature.
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Nicholson, S. E., A. I. Barcilon, and M. Challa. "An Analysis of West African Dynamics Using a Linearized GCM*." Journal of the Atmospheric Sciences 65, no. 4 (April 1, 2008): 1182–203. http://dx.doi.org/10.1175/2007jas2194.1.
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Abstract This study utilizes a linear, primitive equation spherical model to study the development and propagation of easterly wave disturbances over West Africa. Perturbations are started from an initial disturbance consisting of a barotropic vortex and the governing equations are integrated forward in time. The perturbations are introduced into basic states corresponding to the observed dynamical and thermodynamical characteristics of two wet years in the Sahel and two dry years. The model simulations show consistent contrasts in wave activity between the wet and dry years. The waves are markedly stronger in the wet years and show a barotropic structure throughout the troposphere. The waves tend to extend throughout the troposphere to the level of the tropical easterly jet (TEJ) in the wet years, but not in the dry years. The upper-tropospheric shear, which is stronger in wet years, appears to be a key factor in wave development. This shear is dependent on the intensity of the TEJ, suggesting that the TEJ is an important factor in interannual variability in the Sahel. When the overall shear is weak, vertical development is suppressed. Another contrast is that in the dry years the growth rates show a single maximum around 3000–4000 km, but in the wet years there is a second, around 6000–7000 km. This suggests that both synoptic-scale and planetary-scale waves are active in the rainy season of some wet years. Imposing considerations of potential vorticity, the generation of planetary-scale waves implies a strong link between the surface and the TEJ in wet years. Such a link is absent in the dry years. This is likely a major factor in the interannual variability of rainfall in the Sahel.
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Sjoberg, Jeremiah P., and Thomas Birner. "Transient Tropospheric Forcing of Sudden Stratospheric Warmings." Journal of the Atmospheric Sciences 69, no. 11 (November 1, 2012): 3420–32. http://dx.doi.org/10.1175/jas-d-11-0195.1.
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Abstract The amplitude of upward-propagating tropospherically forced planetary waves is known to be of first-order importance in producing sudden stratospheric warmings (SSWs). This forcing amplitude is observed to undergo strong temporal fluctuations. Characteristics of the resulting transient forcing leading to SSWs are studied in reanalysis data and in highly truncated simple models of stratospheric wave–mean flow interaction. It is found in both the reanalysis data and the simple models that SSWs are preferentially generated by transient forcing of sufficiently long time scales (on the order of 1 week or longer). The time scale of the transient forcing is found to play a stronger role in producing SSWs than the strength of the forcing. In the simple models it is possible to fix the amplitude of the tropospheric forcing but to vary the time scale of the forcing. The resulting frequency of occurrence of SSWs shows dramatic reductions for decreasing forcing time scales.
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Yamazaki, Koji, Tetsu Nakamura, Jinro Ukita, and Kazuhira Hoshi. "A tropospheric pathway of the stratospheric quasi-biennial oscillation (QBO) impact on the boreal winter polar vortex." Atmospheric Chemistry and Physics 20, no. 8 (April 30, 2020): 5111–27. http://dx.doi.org/10.5194/acp-20-5111-2020.
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Abstract. The quasi-biennial oscillation (QBO) is quasi-periodic oscillation of the tropical zonal wind in the stratosphere. When the tropical lower stratospheric wind is easterly (westerly), the winter Northern Hemisphere (NH) stratospheric polar vortex tends to be weak (strong). This relation is known as the Holton–Tan relationship. Several mechanisms for this relationship have been proposed, especially linking the tropics with high latitudes through stratospheric pathway. Although QBO impacts on the troposphere have been extensively discussed, a tropospheric pathway of the Holton–Tan relationship has not been explored previously. Here, we propose a tropospheric pathway of the QBO impact, which may partly account for the Holton–Tan relationship in early winter, especially in the November–December period. The study is based on analyses of observational data and results from a simple linear model and atmospheric general circulation model (AGCM) simulations. The mechanism is summarized as follows: the easterly phase of the QBO is accompanied with colder temperature in the tropical tropopause layer, which enhances convective activity over the tropical western Pacific and suppresses it over the Indian Ocean, thus enhancing the Walker circulation. This convection anomaly generates a Rossby wave train, propagating into the midlatitude troposphere, which constructively interferences with the climatological stationary waves, especially in wavenumber 1, resulting in enhanced upward propagation of the planetary wave and a weakened polar vortex.
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Huang, C. M., S. D. Zhang, and F. Yi. "Intensive radiosonde observations of the diurnal tide and planetary waves in the lower atmosphere over Yichang (111°18' E, 30°42' N), China." Annales Geophysicae 27, no. 3 (March 4, 2009): 1079–95. http://dx.doi.org/10.5194/angeo-27-1079-2009.
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Abstract. The characteristics of diurnal tide and planetary waves (PWs) in the troposphere and lower stratosphere (TLS) over Yichang (111°18' E, 30°42' N) were 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 radiosonde observations of the diurnal tide and PWs in the TLS in the mid-latitudes have seldom been reported. We find that there exists dominant diurnal oscillations in the TLS over Yichang. The observed diurnal tide consists of significant nonmigrating components, which may be owning to the local latent heat release. Since the nonmigrating tides are usually composed of high order modes with smaller vertical wavelengths, which are prone to dissipation in comparison with the low order modes, the observational tidal amplitudes decrease sharply at several heights. Some evident discrepancies between the observations and the GSWM-02 are found, which may result mainly from the inaccurate prediction of the nonmigrating tidal components by the GSWM-02. And, due to the evident seasonal differences of the water vapor mixing ratio disturbance and the tropospheric jet induced turbulence in winter, the diurnal tides in the summer and winter months have some different characteristics. Besides the diurnal tide, obvious quasi 7-day PW (QSDPW) and quasi 10-day PW (QTDPW) are also recognized from our observations in both the summer and winter months. The QSDPWs in the troposphere in both the summer and winter months show a standing wave structure, while the QTDPWs generally exhibit traveling wave characteristics. Spectral analyses reveal that some waves with periods around that of the diurnal tide are generated due to the interactions of the diurnal tide and PWs and the tidal amplitudes are modulated by the PWs, indicating the extensive coupling between the diurnal tide and PWs. Moreover, our observations manifest that the PWs can exert great impacts on the tropospheric jet in winter and the tropopause in both the summer and winter months.
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Ando, Yuta, Koji Yamazaki, Yoshihiro Tachibana, Masayo Ogi, and Jinro Ukita. "Detection of a climatological short break in the polar night jet in early winter and its relation to cooling over Siberia." Atmospheric Chemistry and Physics 18, no. 17 (August 31, 2018): 12639–61. http://dx.doi.org/10.5194/acp-18-12639-2018.
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Abstract. The polar night jet (PNJ) is a strong stratospheric westerly circumpolar wind at around 65∘ N in winter, and the strength of the climatological PNJ is widely recognized to increase from October through late December. Remarkably, the climatological PNJ temporarily stops increasing during late November. We examined this “short break” in terms of the atmospheric dynamical balance and the climatological seasonal march. We found that it results from an increase in the upward propagation of climatological planetary waves from the troposphere to the stratosphere in late November, which coincides with a maximum of the climatological Eliassen–Palm (EP) flux convergence in the lower stratosphere. The upward propagation of planetary waves at 100 hPa, which is strongest over Siberia, is related to the climatological strengthening of the tropospheric trough over Siberia. We suggest that longitudinally asymmetric forcing by land–sea heating contrasts caused by their different heat capacities can account for the strengthening of the trough.
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Thomas, L., R. M. Worthington, and A. J. McDonald. "Inertia-gravity waves in the troposphere and lower stratosphere associated with a jet stream exit region." Annales Geophysicae 17, no. 1 (January 31, 1999): 115–21. http://dx.doi.org/10.1007/s00585-999-0115-4.
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Abstract. Radar measurements at Aberystwyth (52.4° N, 4.1° W) of winds at tropospheric and lower stratospheric heights are shown for 12-13 March 1994 in a region of highly curved flow, downstream of the jet maximum. The perturbations of horizontal velocity have comparable amplitudes in the troposphere and lower stratosphere with downward and upward phase propagation, respectively, in these two height regions. The sense of rotation with increasing height in hodographs of horizontal perturbation velocity derived for hourly intervals show downwards propagation of energy in the troposphere and upward propagation in the lower stratosphere with vertical wavelengths of 1.7 to 2.3 km. The results indicate inertia-gravity waves propagating in a direction similar to that of the jet stream but at smaller velocities. Some of the features observed contrast with those of previous observations of inertia-gravity waves propagating transverse to the jet stream. The interpretation of the hodographs to derive wave parameters has taken account of the vertical shear of the background wind transverse to the direction of wave propagation.Key words. Meteorology and atmospheric dynamics (mesoscale meteorology; middle atmosphere dynamics; waves and tides)
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Harnik, Nili, Judith Perlwitz, and Tiffany A. Shaw. "Observed Decadal Changes in Downward Wave Coupling between the Stratosphere and Troposphere in the Southern Hemisphere." Journal of Climate 24, no. 17 (September 2011): 4558–69. http://dx.doi.org/10.1175/2011jcli4118.1.
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Downward wave coupling dominates the intraseasonal dynamical coupling between the stratosphere and troposphere in the Southern Hemisphere. The coupling occurs during late winter and spring when the stratospheric basic state forms a well-defined meridional waveguide, which is bounded above by a reflecting surface. This basic-state configuration is favorable for planetary wave reflection and guides the reflected waves back down to the troposphere, where they impact wave structures. In this study decadal changes in downward wave coupling are analyzed using the Modern Era Retrospective-Analysis for Research and Applications (MERRA) dataset. A cross-spectral correlation analysis, applied to geopotential height fields, and a wave geometry diagnostic, applied to zonal-mean zonal wind and temperature data, are used to understand decadal changes in planetary wave propagation. It is found that downward wave 1 coupling from September to December has increased over the last three decades, owing to significant increases at the beginning and end of this 4-month period. The increased downward wave coupling is caused by both an earlier onset of the vertically bounded meridional waveguide configuration and a persistence of this configuration into December. The latter is associated with the observed delay in vortex breakup. The results point to an additional dynamical mechanism whereby the stratosphere has influenced the tropospheric climate in the Southern Hemisphere.
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Son, Seok-Woo, Sukyoung Lee, and Steven B. Feldstein. "Intraseasonal Variability of the Zonal-Mean Extratropical Tropopause Height." Journal of the Atmospheric Sciences 64, no. 2 (February 1, 2007): 608–20. http://dx.doi.org/10.1175/jas3855.1.
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Abstract The physical processes that drive the fluctuations of the extratropical tropopause height are examined with the National Centers for Environmental Prediction–National Center for Atmospheric Research (NCEP–NCAR) reanalysis data. A composite zonal-mean heat budget analysis for the Northern Hemisphere winter shows that fluctuations in the extratropical tropopause height result not only from a warming of the troposphere but also from an even stronger cooling of the lower stratosphere. While the tropospheric warming is caused by a poleward eddy heat transport associated with baroclinic eddies, the stratospheric cooling is driven primarily by planetary-scale waves. The results from analyses of synoptic- and planetary-scale eddy kinetic energy and Eliassen–Palm fluxes are consistent with the planetary waves first gaining their energy within the troposphere, and then propagating vertically into the stratosphere. For the Southern Hemisphere, while lower-stratospheric temperature anomalies still play an important role for the fluctuations in the tropopause height, the temperature anomalies are accounted for primarily by a poleward eddy heat transport associated with synoptic-scale eddies, and by diabatic heating. These results indicate that, although the height of the extratropical tropopause is modulated by baroclinic eddies, which is consistent with existing theories, the amount of the modulation is highly influenced by stratospheric processes.