To see the other types of publications on this topic, follow the link: Sudden warming; Tropospheric planetary waves.
Journal articles on the topic 'Sudden warming; Tropospheric planetary waves'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 journal articles for your research on the topic 'Sudden warming; Tropospheric planetary waves.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse journal articles on a wide variety of disciplines and organise your bibliography correctly.
1
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.
Full textAbstract:
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.
2
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.
Full textAbstract:
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.
3
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.
Full textAbstract:
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.
4
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.
Full textAbstract:
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.
5
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.
Full textAbstract:
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.
6
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.
Full textAbstract:
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.
7
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.
Full textAbstract:
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.
8
Lindgren, Erik A., and Aditi Sheshadri. "The role of wave–wave interactions in sudden stratospheric warming formation." Weather and Climate Dynamics 1, no. 1 (March 10, 2020): 93–109. http://dx.doi.org/10.5194/wcd-1-93-2020.
Full textAbstract:
Abstract. The effects of wave–wave interactions on sudden stratospheric warming formation are investigated using an idealized atmospheric general circulation model, in which tropospheric heating perturbations of zonal wave numbers 1 and 2 are used to produce planetary-scale wave activity. Zonal wave–wave interactions are removed at different vertical extents of the atmosphere in order to examine the sensitivity of stratospheric circulation to local changes in wave–wave interactions. We show that the effects of wave–wave interactions on sudden warming formation, including sudden warming frequencies, are strongly dependent on the wave number of the tropospheric forcing and the vertical levels where wave–wave interactions are removed. Significant changes in sudden warming frequencies are evident when wave–wave interactions are removed even when the lower-stratospheric wave forcing does not change, highlighting the fact that the upper stratosphere is not a passive recipient of wave forcing from below. We find that while wave–wave interactions are required in the troposphere and lower stratosphere to produce displacements when wave number 2 heating is used, both splits and displacements can be produced without wave–wave interactions in the troposphere and lower stratosphere when the model is forced by wave number 1 heating. We suggest that the relative strengths of wave number 1 and 2 vertical wave flux entering the stratosphere largely determine the split and displacement ratios when wave number 2 forcing is used but not wave number 1.
9
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.
Full textAbstract:
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.
10
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.
Full textAbstract:
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.
11
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.
Full textAbstract:
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.
12
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.
Full textAbstract:
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.
13
Lü, Zhuozhuo, Fei Li, Yvan J. Orsolini, Yongqi Gao, and Shengping He. "Understanding of European Cold Extremes, Sudden Stratospheric Warming, and Siberian Snow Accumulation in the Winter of 2017/18." Journal of Climate 33, no. 2 (January 15, 2020): 527–45. http://dx.doi.org/10.1175/jcli-d-18-0861.1.
Full textAbstract:
AbstractIt is unclear whether the Eurasian snow plays a role in the tropospheric driving of sudden stratospheric warming (SSW). The major SSW event of February 2018 is analyzed using reanalysis datasets. Characterized by predominant planetary waves of zonal wave 2, the SSW developed into a vortex split via wave–mean flow interaction. In the following two weeks, the downward migration of zonal-mean zonal wind anomalies was accompanied by a significant transition to the negative phase of the North Atlantic Oscillation, leading to extensive cold extremes across Europe. Here, we demonstrate that anomalous Siberian snow accumulation could have played an important role in the 2018 SSW occurrence. In the 2017/18 winter, snow depths over Siberia were much higher than normal. A lead–lag correlation analysis shows that the positive fluctuating snow depth anomalies, leading to intensified “cold domes” over eastern Siberia (i.e., in a region where the climatological upward planetary waves maximize), precede enhanced wave-2 pulses of meridional heat fluxes (100 hPa) by 7–8 days. The snow–SSW linkage over 2003–19 is further investigated, and some common traits among three split events are found. These include a time lag of about one week between the maximum anomalies of snow depth and wave-2 pulses (100 hPa), high sea level pressure favored by anomalous snowpack, and a ridge anchoring over Siberia as precursor of the splits. The role of tropospheric ridges over Alaska and the Urals in the wave-2 enhancement and the role of Arctic sea ice loss in Siberian snow accumulation are also discussed.
14
Krüger, Kirstin, Barbara Naujokat, and Karin Labitzke. "The Unusual Midwinter Warming in the Southern Hemisphere Stratosphere 2002: A Comparison to Northern Hemisphere Phenomena." Journal of the Atmospheric Sciences 62, no. 3 (March 1, 2005): 603–13. http://dx.doi.org/10.1175/jas-3316.1.
Full textAbstract:
Abstract A strong midwinter warming occurred in the Southern Hemisphere (SH) stratosphere in September 2002. Based on experiences from the Northern Hemisphere (NH), this event can be defined as a major warming with a breakdown of the polar vortex in midwinter, which has never been detected so far in the SH since observations began at the earliest in the 1940s. Minor midwinter warmings occasionally occurred in the SH, but a strong interannual variability, as is present in winter and spring in the NH, has been explicitly associated with the spring reversals. A detailed analysis of this winter reveals the dominant role of eastward-traveling waves and their interaction with quasi-stationary planetary waves forced in the troposphere. Such wave forcing, finally leading to the sudden breakdown of the vortex, is a familiar feature of the northern winter stratosphere. Therefore, the unusual development of this Antarctic winter is described in the context of more than 50 Arctic winters, concentrating on winters with similar wave perturbations. The relevance of preconditioning of major warmings by traveling and quasi-stationary planetary waves is discussed for both hemispheres.
15
Attard, Hannah E., Rosimar Rios-Berrios, Corey T. Guastini, and Andrea L. Lang. "Tropospheric and Stratospheric Precursors to the January 2013 Sudden Stratospheric Warming." Monthly Weather Review 144, no. 4 (March 23, 2016): 1321–39. http://dx.doi.org/10.1175/mwr-d-15-0175.1.
Full textAbstract:
Abstract This paper investigates the tropospheric and stratospheric precursors to a major sudden stratospheric warming (SSW) that began on 6 January 2013. Using the Climate Forecast System Reanalysis dataset, the analysis identified two distinct decelerations of the 10-hPa zonal mean zonal wind at 65°N in December in addition to the major SSW, which occurred on 6 January 2013 when the 10-hPa zonal mean zonal wind at 65°N reversed from westerly to easterly. The analysis shows that the two precursor events preconditioned the stratosphere for the SSW. Analysis of the tropospheric state in the days leading to the precursor events and the major SSW suggests that high-latitude tropospheric blocks occurred in the days prior to the two December deceleration events, but not in the days prior to the SSW. A detailed wave activity flux (WAF) analysis suggests that the tropospheric blocking prior to the two December deceleration events contributed to an anomalously positive 40-day-average 100-hPa zonal mean meridional eddy heat flux prior to the SSW. Analysis of the stratospheric structure in the days prior to the SSW reveals that the SSW was associated with enhanced WAF in the upper stratosphere, planetary wave breaking, and an upper-stratospheric/lower-mesospheric disturbance. These results suggest that preconditioning of the stratosphere occurred as a result of WAF initiated by tropospheric blocking associated with the two December deceleration events. The two December deceleration events occurred in the 40 days prior to the SSW and led to the amplification of wave activity in the upper stratosphere and wave resonance that caused the January 2013 SSW.
16
Kang, Wanying, and Eli Tziperman. "More Frequent Sudden Stratospheric Warming Events due to Enhanced MJO Forcing Expected in a Warmer Climate." Journal of Climate 30, no. 21 (November 2017): 8727–43. http://dx.doi.org/10.1175/jcli-d-17-0044.1.
Full textAbstract:
Sudden stratospheric warming (SSW) events influence the Arctic Oscillation and midlatitude extreme weather. Observations show SSW events to be correlated with certain phases of the Madden–Julian oscillation (MJO), but the effect of the MJO on SSW frequency is unknown, and the teleconnection mechanism, its planetary wave propagation path, and time scale are still not completely understood. The Arctic stratosphere response to increased MJO forcing expected in a warmer climate using two models is studied: the comprehensive Whole Atmosphere Community Climate Model and an idealized dry dynamical core with and without MJO-like forcing. It is shown that the frequency of SSW events increases significantly in response to stronger MJO forcing, also affecting the averaged polar cap temperature. Two teleconnection mechanisms are identified: a direct propagation of MJO-forced transient waves to the Arctic stratosphere and a nonlinear enhancement of stationary waves by the MJO-forced transient waves. The MJO-forced waves propagate poleward in the lower stratosphere and upper troposphere and then upward. The cleaner results of the idealized model allow identifying the propagating signal and suggest a horizontal propagation time scale of 10–20 days, followed by additional time for upward propagation within the Arctic stratosphere, although there are significant uncertainties involved. Given that the MJO is predicted to be stronger in a warmer climate, these results suggest that SSW events may become more frequent, with possible implications on tropospheric high-latitude weather. However, the effect of an actual warming scenario on SSW frequency involves additional effects besides a strengthening of the MJO, requiring further investigation.
17
Coy, Lawrence, Stephen Eckermann, and Karl Hoppel. "Planetary Wave Breaking and Tropospheric Forcing as Seen in the Stratospheric Sudden Warming of 2006." Journal of the Atmospheric Sciences 66, no. 2 (February 1, 2009): 495–507. http://dx.doi.org/10.1175/2008jas2784.1.
Full textAbstract:
Abstract The major stratospheric sudden warming (SSW) of January 2006 is examined using meteorological fields from Goddard Earth Observing System version 4 (GEOS-4) analyses and forecast fields from the Navy Operational Global Atmospheric Prediction System–Advanced Level Physics, High Altitude (NOGAPS-ALPHA). The study focuses on the upper tropospheric forcing that led to the major SSW and the vertical structure of the subtropic wave breaking near 10 hPa that moved low tropical values of potential vorticity (PV) to the pole. Results show that an eastward-propagating upper tropospheric ridge over the North Atlantic with its associated cold temperature perturbations (as manifested by high 360-K potential temperature surface perturbations) and large positive local values of meridional heat flux directly forced a change in the stratospheric polar vortex, leading to the stratospheric subtropical wave breaking and warming. Results also show that the anticyclonic development, initiated by the subtropical wave breaking and associated with the poleward advection of the low PV values, occurred over a limited altitude range of approximately 6–10 km. The authors also show that the poleward advection of this localized low-PV anomaly was associated with changes in the Eliassen–Palm (EP) flux from equatorward to poleward, suggesting an important role for Rossby wave reflection in the SSW of January 2006. Similar upper tropospheric forcing and subtropical wave breaking were found to occur prior to the major SSW of January 2003.
18
Eguchi, N., K. Kodera, and T. Nasuno. "A global non-hydrostatic model study of a downward coupling through the tropical tropopause layer during a stratospheric sudden warming." Atmospheric Chemistry and Physics Discussions 14, no. 5 (March 13, 2014): 6803–20. http://dx.doi.org/10.5194/acpd-14-6803-2014.
Full textAbstract:
Abstract. The dynamical coupling process between the stratosphere and troposphere in the tropical tropopause layer (TTL) during a stratospheric sudden warming (SSW) in boreal winter was investigated using simulation data from a global non-hydrostatic model (NICAM) that does not use cumulus parameterization. The model reproduced well the observed tropical tropospheric changes during the SSW including the enhancement of convective activity following the amplification of planetary waves. Deep convective activity was enhanced in the latitude zone 20–10° S, in particular over the southwest Pacific and southwest Indian Ocean. Although the upwelling in the TTL was correlated with that in the stratosphere, the temperature tendency in the TTL was mainly controlled by diabatic heating originating from cloud formation. This result suggests that the stratospheric meridional circulation affects cloud formation in the TTL.
19
Eguchi, N., K. Kodera, and T. Nasuno. "A global non-hydrostatic model study of a downward coupling through the tropical tropopause layer during a stratospheric sudden warming." Atmospheric Chemistry and Physics 15, no. 1 (January 13, 2015): 297–304. http://dx.doi.org/10.5194/acp-15-297-2015.
Full textAbstract:
Abstract. The dynamical coupling process between the stratosphere and troposphere in the tropical tropopause layer (TTL) during a~stratospheric sudden warming (SSW) in boreal winter was investigated using simulation data from a global non-hydrostatic model (NICAM) that does not use cumulus parameterization. The model reproduced well the observed tropical tropospheric changes during the SSW, including the enhancement of convective activity following the amplification of planetary waves. Deep convective activity was enhanced in the latitude zone 20–10° S, in particular over the southwest Pacific and southwest Indian Ocean. Although the upwelling in the TTL was correlated with that in the stratosphere, the temperature tendency in the TTL changed little due to a compensation by diabatic heating originating from cloud formation. This result suggests that the stratospheric meridional circulation affects cloud formation in the TTL.
20
Kodera, Kunihiko, Nawo Eguchi, Hitoshi Mukougawa, Tomoe Nasuno, and Toshihiko Hirooka. "Stratospheric tropical warming event and its impact on the polar and tropical troposphere." Atmospheric Chemistry and Physics 17, no. 1 (January 12, 2017): 615–25. http://dx.doi.org/10.5194/acp-17-615-2017.
Full textAbstract:
Abstract. Stratosphere–troposphere coupling is investigated in relation to middle atmospheric subtropical jet (MASTJ) variations in boreal winter. An exceptional strengthening of the MASTJ occurred in association with a sudden equatorward shift of the stratospheric polar night jet (PNJ) in early December 2011. This abrupt transformation of the MASTJ and PNJ had no apparent relation to the upward propagation of planetary waves from the troposphere. The impact of this stratospheric event penetrated into the troposphere in two regions: in the northern polar region and the tropics. Due to the strong MASTJ, planetary waves at higher latitudes were deflected and trapped in the northern polar region. Trapping of the planetary waves resulted in amplification of zonal wave number 1 component, which appeared in the troposphere as the development of a trough over the Atlantic sector and a ridge over the Eurasian sector. A strong MASTJ also suppressed the equatorward propagation of planetary waves, which resulted in weaker tropical stratospheric upwelling and produced anomalous warming in the tropical stratosphere. In the tropical tropopause layer (TTL), however, sublimation of ice clouds kept the temperature change minor. In the troposphere, an abrupt termination of a Madden–Julian Oscillation (MJO) event occurred following the static stability increase in the TTL. This termination suggests that the stratospheric event affected the convective episode in the troposphere.
21
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.
Full textAbstract:
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.
22
Statnaia, Irina A., Alexey Y. Karpechko, and Heikki J. Järvinen. "Mechanisms and predictability of sudden stratospheric warming in winter 2018." Weather and Climate Dynamics 1, no. 2 (October 27, 2020): 657–74. http://dx.doi.org/10.5194/wcd-1-657-2020.
Full textAbstract:
Abstract. In the beginning of February 2018 a rapid deceleration of the westerly circulation in the polar Northern Hemisphere stratosphere took place, and on 12 February the zonal-mean zonal wind at 60∘ N and 10 hPa reversed to easterly in a sudden stratospheric warming (SSW) event. We investigate the role of the tropospheric forcing in the occurrence of the SSW, its predictability and teleconnection with the Madden–Julian oscillation (MJO) by analysing the European Centre for Medium-Range Weather Forecasts (ECMWF) ensemble forecast. The SSW was preceded by significant synoptic wave activity over the Pacific and Atlantic basins, which led to the upward propagation of wave packets and resulted in the amplification of a stratospheric wavenumber 2 planetary wave. The dynamical and statistical analyses indicate that the main tropospheric forcing resulted from an anticyclonic Rossby wave breaking, subsequent blocking and upward wave propagation in the Ural Mountains region, in agreement with some previous studies. The ensemble members which predicted the wind reversal also reasonably reproduced this chain of events, from the horizontal propagation of individual wave packets to upward wave-activity fluxes and the amplification of wavenumber 2. On the other hand, the ensemble members which failed to predict the wind reversal also failed to properly capture the blocking event in the key region of the Urals and the associated intensification of upward-propagating wave activity. Finally, a composite analysis suggests that teleconnections associated with the record-breaking MJO phase 6 observed in late January 2018 likely played a role in triggering this SSW event.
23
Butler, Amy H., and Daniela I. V. Domeisen. "The wave geometry of final stratospheric warming events." Weather and Climate Dynamics 2, no. 2 (May 27, 2021): 453–74. http://dx.doi.org/10.5194/wcd-2-453-2021.
Full textAbstract:
Abstract. Every spring, the stratospheric polar vortex transitions from its westerly wintertime state to its easterly summertime state due to seasonal changes in incoming solar radiation, an event known as the “final stratospheric warming” (FSW). While FSWs tend to be less abrupt than reversals of the boreal polar vortex in midwinter, known as sudden stratospheric warming (SSW) events, their timing and characteristics can be significantly modulated by atmospheric planetary-scale waves. While SSWs are commonly classified according to their wave geometry, either by how the vortex evolves (whether the vortex displaces off the pole or splits into two vortices) or by the dominant wavenumber of the vortex just prior to the SSW (wave-1 vs. wave-2), little is known about the wave geometry of FSW events. We here show that FSW events for both hemispheres in most cases exhibit a clear wave geometry. Most FSWs can be classified into wave-1 or wave-2 events, but wave-3 also plays a significant role in both hemispheres. The timing and classification of the FSW are sensitive to which pressure level the FSW central date is defined, particularly in the Southern Hemisphere (SH) where trends in the FSW dates associated with ozone depletion and recovery are more evident at 50 than 10 hPa. However, regardless of which FSW definition is selected, we find the wave geometry of the FSW affects total column ozone anomalies in both hemispheres and tropospheric circulation over North America. In the Southern Hemisphere, the timing of the FSW is strongly linked to both total column ozone before the event and the tropospheric circulation after the event.
24
Tripathi, Om P., Mark Baldwin, Andrew Charlton-Perez, Martin Charron, Jacob C. H. Cheung, Stephen D. Eckermann, Edwin Gerber, et al. "Examining the Predictability of the Stratospheric Sudden Warming of January 2013 Using Multiple NWP Systems." Monthly Weather Review 144, no. 5 (May 2016): 1935–60. http://dx.doi.org/10.1175/mwr-d-15-0010.1.
Full textAbstract:
The first multimodel study to estimate the predictability of a boreal sudden stratospheric warming (SSW) is performed using five NWP systems. During the 2012/13 boreal winter, anomalous upward propagating planetary wave activity was observed toward the end of December, which was followed by a rapid deceleration of the westerly circulation around 2 January 2013, and on 7 January 2013 the zonal-mean zonal wind at 60°N and 10 hPa reversed to easterly. This stratospheric dynamical activity was followed by an equatorward shift of the tropospheric jet stream and by a high pressure anomaly over the North Atlantic, which resulted in severe cold conditions in the United Kingdom and northern Europe. In most of the five models, the SSW event was predicted 10 days in advance. However, only some ensemble members in most of the models predicted weakening of westerly wind when the models were initialized 15 days in advance of the SSW. Further dynamical analysis of the SSW shows that this event was characterized by the anomalous planetary wavenumber-1 amplification followed by the anomalous wavenumber-2 amplification in the stratosphere, which resulted in a split vortex occurring between 6 and 8 January 2013. The models have some success in reproducing wavenumber-1 activity when initialized 15 days in advance, but they generally failed to produce the wavenumber-2 activity during the final days of the event. Detailed analysis shows that models have reasonably good skill in forecasting tropospheric blocking features that stimulate wavenumber-2 amplification in the troposphere, but they have limited skill in reproducing wavenumber-2 amplification in the stratosphere.
25
Kushner, Paul J., and Lorenzo M. Polvani. "A Very Large, Spontaneous Stratospheric Sudden Warming in a Simple AGCM: A Prototype for the Southern Hemisphere Warming of 2002?" Journal of the Atmospheric Sciences 62, no. 3 (March 1, 2005): 890–97. http://dx.doi.org/10.1175/jas-3314.1.
Full textAbstract:
Abstract An exceptionally strong stratospheric sudden warming (SSW) that spontaneously occurs in a very simple stratosphere–troposphere AGCM is discussed. The model is a dry, hydrostatic, primitive equation model without planetary stationary waves. Transient baroclinic wave–wave interaction in the troposphere thus provides the only source of upward-propagating wave activity into the stratosphere. The model’s SSW is grossly similar to the Southern Hemisphere major SSW of 2002: it occurs after weaker warmings “precondition” the polar vortex for breaking, it involves a split of the polar vortex, and it has a downward-propagating signature. These similarities suggest that the Southern Hemisphere SSW of 2002 might itself have been caused by transient baroclinic wave–wave interaction. The simple model used for this study also provides some insight into how often such extreme events might occur. The frequency distribution of SSWs in the model has exponential, as opposed to Gaussian, tails. This suggests that very large amplitude SSWs, though rare, might occur with higher frequency than might be naively expected.
26
Liu, Y., C. X. Liu, H. P. Wang, X. 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 9, no. 6 (March 24, 2009): 2157–70. http://dx.doi.org/10.5194/acp-9-2157-2009.
Full textAbstract:
Abstract. We use the stratospheric/tropospheric chemical transport model MOZART-3 to study the distribution and transport of stratospheric O3 during the remarkable 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 stratosphere and upper troposphere (UTLS) region. Compared to the situation during the winter of 2002–2003, lower ozone concentrations were transported from the polar region 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 (30 km). The restricted wave activities led to a reduced extratropical downward ozone flux from the lower stratosphere to the lowermost stratosphere (or from the "overworld" into the "middleworld"), especially over East Asia. Consequently, during wintertime (15 December~15 February), the total downward ozone transport on 100 hPa surface by the descending branches of Brewer-Dobson circulation over this region was about 10% lower during the 2003–2004 event. Meanwhile, the extratropical total cross-tropopause ozone flux (CTOF) was also reduced by ~25%. Compared to the cold 1999–2000 winter, the vertical CTOF in high latitudes (60°~90° N) increased more than 10 times during the two warming winters, while the vertical CTOF in mid-latitudes (30°~60° N) decreased by 20~40%. Moreover, during the two warming winters, the meridional CTOF caused by the isentropic transport associating with the enhanced wave activity also increased and played an important role in the total extratropical CTOF budget.
27
Kishore, P., I. Velicogna, M. Venkat Ratnam, J. H. Jiang, and G. N. Madhavi. "Planetary waves in the upper stratosphere and lower mesosphere during 2009 Arctic major stratospheric warming." Annales Geophysicae 30, no. 10 (October 10, 2012): 1529–38. http://dx.doi.org/10.5194/angeo-30-1529-2012.
Full textAbstract:
Abstract. The AURA-MLS daily mean temperatures and zonal wind from NASA-MERRA reanalysis for latitudes between 60° N and 80° N are used to investigate the planetary wave (PW) characteristics in the stratosphere and lower mesosphere during sudden stratospheric warming (SSW) (November 2008 to March 2009). Here, we used a novel method called empirical mode decomposition (EMD) to extract the PWs from the temperature data. The EMD is an interesting approach to decompose signals into locally periodic components, the intrinsic mode functions (IMFs), and will easily identify the embedded structures, even those with small amplitudes. The spectral analysis reveals prevailing planetary wave periods of ~6-day, ~8-day, ~15-day, and ~21–23-day in IMFs 1, 2, 3, and 4, respectively. Clear upward propagation of these waves (20–30 days) is observed, suggesting that sources for these oscillations are in the troposphere.
28
Hu, Jinggao, Rongcai Ren, and Haiming Xu. "Occurrence of Winter Stratospheric Sudden Warming Events and the Seasonal Timing of Spring Stratospheric Final Warming." Journal of the Atmospheric Sciences 71, no. 7 (June 20, 2014): 2319–34. http://dx.doi.org/10.1175/jas-d-13-0349.1.
Full textAbstract:
Abstract Based on the NCEP–NCAR reanalysis dataset covering 1958–2012, this paper demonstrates a statistically significant relationship between the occurrence of major stratospheric sudden warming events (SSWs) in midwinter and the seasonal timing of stratospheric final warming events (SFWs) in spring. Specifically, early spring SFWs that on average occur in early March tend to be preceded by non-SSW winters, while late spring SFWs that on average take place up until early May are mostly preceded by SSW events in midwinter. Though the occurrence (absence) of SSW events in midwinter may not always be followed by late (early) SFWs in spring, there is a much higher (lower) probability of late SFWs than early SFWs in spring after SSW (non-SSW) winters, particularly when the winter SSWs occur no earlier than early January or in the period from late January to early February. Diagnosis shows that, corresponding to an SSW (non-SSW) winter and the following late (early)-SFW spring, intensity of planetary wave activity in the stratosphere tends to evolve out of phase from midwinter to the following spring, being anomalously stronger (weaker) in winter and anomalously weaker (stronger) in spring. Furthermore, the strengthening of the western Eurasian high, which appears during early to mid-January in late-SFW years but does not appear until late February to mid-March in early-SFW years, always precedes the strengthening of planetary wave activity in the stratosphere and thus acts as a tropospheric precursor to the seasonal timing of SFWs.
29
Kodera, K., B. M. Funatsu, C. Claud, and N. Eguchi. "The role of convective overshooting clouds in tropical stratosphere–troposphere dynamical coupling." Atmospheric Chemistry and Physics Discussions 14, no. 16 (September 15, 2014): 23745–61. http://dx.doi.org/10.5194/acpd-14-23745-2014.
Full textAbstract:
Abstract. This paper investigates the role of deep convection and overshooting convective clouds in stratosphere–troposphere dynamical coupling in the tropics during two large major stratospheric sudden warming events in January 2009 and January 2010. During both events, convective activity and precipitation increased in the equatorial Southern Hemisphere as a result of a strengthening of the Brewer–Dobson circulation induced by enhanced stratospheric planetary wave activity. Correlation coefficients between variables related to the convective activity and the vertical velocity were calculated to identify the processes connecting stratospheric variability to the troposphere. Convective overshooting clouds showed a direct relationship to lower stratospheric upwelling at around 70–50 hPa. As the tropospheric circulation change lags behind that of the stratosphere, outgoing longwave radiation shows almost no simultaneous correlation with the stratospheric upwelling. This result suggests that the stratospheric circulation change first penetrates into the troposphere through the modulation of deep convective activity.
30
Kodera, K., B. M. Funatsu, C. Claud, and N. Eguchi. "The role of convective overshooting clouds in tropical stratosphere–troposphere dynamical coupling." Atmospheric Chemistry and Physics 15, no. 12 (June 18, 2015): 6767–74. http://dx.doi.org/10.5194/acp-15-6767-2015.
Full textAbstract:
Abstract. This paper investigates the role of deep convection and overshooting convective clouds in stratosphere–troposphere dynamical coupling in the tropics during two large major stratospheric sudden warming events in January 2009 and January 2010. During both events, convective activity and precipitation increased in the equatorial Southern Hemisphere as a result of a strengthening of the Brewer–Dobson circulation induced by enhanced stratospheric planetary wave activity. Correlation coefficients between variables related to the convective activity and the vertical velocity were calculated to identify the processes connecting stratospheric variability to the troposphere. Convective overshooting clouds showed a direct relationship to lower stratospheric upwelling at around 70–50 hPa. As the tropospheric circulation change lags behind that of the stratosphere, outgoing longwave radiation shows almost no simultaneous correlation with the stratospheric upwelling. This result suggests that the stratospheric circulation change first penetrates into the troposphere through the modulation of deep convective activity.
31
Nishii, Kazuaki, Hisashi Nakamura, and Yvan J. Orsolini. "Geographical Dependence Observed in Blocking High Influence on the Stratospheric Variability through Enhancement and Suppression of Upward Planetary-Wave Propagation." Journal of Climate 24, no. 24 (December 15, 2011): 6408–23. http://dx.doi.org/10.1175/jcli-d-10-05021.1.
Full textAbstract:
Abstract Previous studies have suggested the importance of blocking high (BH) development for the occurrence of stratospheric sudden warming (SSW), while there is a recent study that failed to identify their statistical linkage. Through composite analysis applied to high-amplitude anticyclonic anomaly events observed around every grid point over the extratropical Northern Hemisphere, the present study reveals a distinct geographical dependence of BH influence on the upward propagation of planetary waves (PWs) into the stratosphere. Tropospheric BHs that develop over the Euro-Atlantic sector tend to enhance upward PW propagation, leading to the warming in the polar stratosphere and, in some cases, to major SSW events. In contrast, the upward PW propagation tends to be suppressed by BHs developing over the western Pacific and the Far East, resulting in the polar stratospheric cooling. This dependence is found to arise mainly from the sensitivity of the interference between the climatological PWs and upward-propagating Rossby wave packets emanating from BHs to their geographical locations. This study also reveals that whether a BH over the eastern Pacific and Alaska can enhance or reduce the upward PW propagation is case dependent. It is suggested that BHs that induce the stratospheric cooling can weaken the statistical relationship between BHs and SSWs.
32
Naito, Yoko, and Shigeo Yoden. "Behavior of Planetary Waves before and after Stratospheric Sudden Warming Events in Several Phases of the Equatorial QBO." Journal of the Atmospheric Sciences 63, no. 6 (June 1, 2006): 1637–49. http://dx.doi.org/10.1175/jas3702.1.
Full textAbstract:
Abstract Almost a thousand stratospheric sudden warming (SSW) events are obtained through long time integrations with a simple global circulation model, and a statistical analysis based on such a large number of samples is made to investigate behavior of planetary waves before and after SSW events depending on the phase of the equatorial quasi-biennial oscillation (QBO). An idealized zonal momentum forcing to mimic a phase of the QBO is imposed under a perpetual winter condition, and eight phases of the QBO-wind forcing are examined for 8 × 10 800-day datasets. Some systematic dependence on the phase of the QBO-wind forcing is seen in the anomaly of the Eliassen–Palm (EP) flux in the winter hemisphere, both in the 10 800-day average and in the composites for SSW events. The composite analysis shows that before SSW events, the upward EP flux in the troposphere and midlatitude lower stratosphere as well as the equatorward flux above the tropopause is larger in the westerly forcing runs than in the easterly forcing runs. After SSW events, the upward EP flux in the troposphere is still larger in the westerly forcing runs. Correlation associated with the differences among SSW events that occurred in each run is significantly positive between the magnitude of the warming and the planetary wave activity flux before all the events in QBO-wind forcing in the stratosphere, but only in the easterly forcing runs in the troposphere.
33
Kang, Wanying, and Eli Tziperman. "The Role of Zonal Asymmetry in the Enhancement and Suppression of Sudden Stratospheric Warming Variability by the Madden–Julian Oscillation." Journal of Climate 31, no. 6 (March 2018): 2399–415. http://dx.doi.org/10.1175/jcli-d-17-0489.1.
Full textAbstract:
Sudden stratospheric warming (SSW) events influence the Arctic Oscillation and midlatitude extreme weather. Previous work showed the Arctic stratosphere to be influenced by the Madden–Julian oscillation (MJO) and that the SSW frequency increases with an increase of the MJO amplitude, expected in a warmer climate. It is shown here that the zonal asymmetry in both the background state and forcing plays a dominant role, leading to either enhancement or suppression of SSW events by MJO-like forcing. When applying a circumglobal MJO-like forcing in a dry dynamic core model, the MJO-forced waves can change the general circulation in three ways that affect the total vertical Eliassen–Palm flux in the Arctic stratosphere. First, weakening the zonal asymmetry of the tropospheric midlatitude jet, and therefore preventing the MJO-forced waves from propagating past the jet. Second, weakening the jet amplitude, reducing the waves generated in the midlatitudes, especially stationary waves, and therefore the upward-propagating planetary waves. Third, reducing the Arctic lower-stratospheric refractory index, which prevents waves from upward propagation. These effects stabilize the Arctic vortex and lower the SSW frequency. The longitudinal range to which the MJO-like forcing is limited plays an important role as well, and the strongest SSW frequency increase is seen when the MJO is located where it is observed in current climate. The SSW suppression effects are active when the MJO-like forcing is placed at different longitudinal locations. This study suggests that future trends in both the MJO amplitude and its longitudinal extent are important for predicting the Arctic stratosphere response.
34
Chandran, A., and R. L. Collins. "Stratospheric sudden warming effects on winds and temperature in the middle atmosphere at middle and low latitudes: a study using WACCM." Annales Geophysicae 32, no. 7 (July 28, 2014): 859–74. http://dx.doi.org/10.5194/angeo-32-859-2014.
Full textAbstract:
Abstract. A stratospheric sudden warming (SSW) is a dynamical phenomenon of the wintertime stratosphere caused by the interaction between planetary Rossby waves propagating from the troposphere and the stratospheric zonal-mean flow. While the effects of SSW events are seen predominantly in high latitudes, they can also produce significant changes in middle and low latitude temperature and winds. In this study we quantify the middle and low latitude effects of SSW events on temperature and zonal-mean winds using a composite of SSW events between 1988 and 2010 simulated with the specified dynamics version of the Whole Atmosphere Community Climate Model (WACCM). The temperature and wind responses seen in the tropics also extend into the low latitudes in the other hemisphere. There is variability in observed zonal-mean winds and temperature depending on the observing location within the displaced or split polar vortex and propagation direction of the planetary waves. The propagation of planetary waves show that they originate in mid–high latitudes and propagate upward and equatorward into the mid-latitude middle atmosphere where they produce westward forcing reaching peak values of ~ 60–70 m s−1 day−1. These propagation paths in the lower latitude stratosphere appear to depend on the phase of the quasi-biennial oscillation (QBO). During the easterly phase of the QBO, waves originating at high latitudes propagate across the equator, while in the westerly phase of the QBO, the planetary waves break at ~ 20–25° N and there is no propagation across the equator. The propagation of planetary waves across the equator during the easterly phase of the QBO reduces the tropical upwelling and poleward flow in the upper stratosphere.
35
Schneidereit, Andrea, Dieter H. W. Peters, Christian M. Grams, Julian F. Quinting, Julia H. Keller, Gabriel Wolf, Franziska Teubler, Michael Riemer, and Olivia Martius. "Enhanced Tropospheric Wave Forcing of Two Anticyclones in the Prephase of the January 2009 Major Stratospheric Sudden Warming Event." Monthly Weather Review 145, no. 5 (April 19, 2017): 1797–815. http://dx.doi.org/10.1175/mwr-d-16-0242.1.
Full textAbstract:
Abstract Tropospheric forcing of planetary wavenumber 2 is examined in the prephase of the major stratospheric sudden warming event in January 2009 (MSSW 2009). Because of a huge increase in Eliassen–Palm fluxes induced mainly by wavenumber 2, easterly angular momentum is transported into the Arctic stratosphere, deposited, and then decelerates the polar night jet. In agreement with earlier studies, the results reveal that the strongest eddy heat fluxes, associated with wavenumber 2, occur at 100 hPa during the prephase of MSSW 2009 in ERA-Interim. In addition, moderate conditions of the cold phase of ENSO (La Niña) contribute to the eddy heat flux anomaly. It is shown that enhanced tropospheric wave forcing over Alaska and Scandinavia is caused by tropical processes in two ways. First, in a climatological sense, La Niña contributes to an enhanced anticyclonic flow over both regions. Second, the Madden–Julian oscillation (MJO) has an indirect influence on the Alaskan ridge by enhancing eddy activity over the North Pacific. This is manifested in an increase in cyclone frequency and associated warm conveyor belt outflow, which contribute to the maintenance and amplification of the Alaskan anticyclone. The Scandinavian ridge is maintained by wave trains emanating from the Alaskan ridge propagating eastward, including an enhanced transport of eddy kinetic energy. The MSSW 2009 is an extraordinary case of how a beneficial phasing of La Niña and MJO conditions together with multiscale interactions enhances tropospheric forcing for wavenumber 2–induced zonal mean eddy heat flux in the lower stratosphere.
36
Shaw, Tiffany A., and Judith Perlwitz. "The Impact of Stratospheric Model Configuration on Planetary-Scale Waves in Northern Hemisphere Winter." Journal of Climate 23, no. 12 (June 15, 2010): 3369–89. http://dx.doi.org/10.1175/2010jcli3438.1.
Full textAbstract:
Abstract The impact of stratospheric model configuration on modeled planetary-scale waves in Northern Hemisphere winter is examined using the Canadian Middle Atmosphere Model (CMAM). The CMAM configurations include a high-lid (0.001 hPa) and a low-lid (10 hPa) configuration, which were each run with and without conservation of parameterized gravity wave momentum flux. The planetary wave structure, vertical propagation, and the basic state are found to be in good agreement with reanalysis data for the high-lid conservative configuration with the exception of the downward-propagating wave 1 signal. When the lid is lowered and momentum is conserved, the wave characteristics and basic state are not significantly altered, with the exception of the downward-propagating wave 1 signal, which is damped by the act of conservation. When momentum is not conserved, however, the wave amplitude increases significantly near the lid, and there is a large increase in both the upward- and downward-propagating wave 1 signals and a significant increase in the strength of the basic state. The impact of conserving parameterized gravity wave momentum flux is found to be much larger than that of the model lid height. The changes to the planetary waves and basic state significantly impact the stratosphere–troposphere coupling in the different configurations. In the low-lid configuration, there is an increase in wave-reflection-type coupling over zonal-mean-type coupling, a reduction in stratospheric sudden warming events, and an increase in the northern annular mode time scale. Conserving gravity wave momentum flux in the low-lid configuration significantly reduces these biases.
37
Martineau, Patrick, Seok-Woo Son, Masakazu Taguchi, and Amy H. Butler. "A comparison of the momentum budget in reanalysis datasets during sudden stratospheric warming events." Atmospheric Chemistry and Physics 18, no. 10 (May 24, 2018): 7169–87. http://dx.doi.org/10.5194/acp-18-7169-2018.
Full textAbstract:
Abstract. The agreement between reanalysis datasets, in terms of the zonal-mean momentum budget, is evaluated during sudden stratospheric warming (SSW) events. It is revealed that there is a good agreement among datasets in the lower stratosphere and troposphere concerning zonal-mean zonal wind, but less so in the upper stratosphere. Forcing terms of the momentum equation are also relatively similar in the lower atmosphere, but their uncertainties are typically larger than uncertainties of the zonal-wind tendency. Similar to zonal-wind tendency, the agreement among forcing terms is degraded in the upper stratosphere. Discrepancies among reanalyses increase during the onset of SSW events, a period characterized by unusually large fluxes of planetary-scale waves from the troposphere to the stratosphere, and decrease substantially after the onset. While the largest uncertainties in the resolved terms of the momentum budget are found in the Coriolis torque, momentum flux convergence also presents a non-negligible spread among the reanalyses. Such a spread is reduced in the latest reanalysis products, decreasing the uncertainty of the momentum budget. It is also found that the uncertainties in the Coriolis torque depend on the strength of SSW events: the SSW events that exhibit the most intense deceleration of zonal-mean zonal wind are subject to larger discrepancies among reanalyses. These uncertainties in stratospheric circulation, however, are not communicated to the troposphere.
38
Zuev, V. V., E. S. Savelieva, and A. V. Pavlinsky. "Analysis of the Arctic polar vortex dynamics during the sudden stratospheric warming in January 2009." Arctic and Antarctic Research 67, no. 2 (July 11, 2021): 134–46. http://dx.doi.org/10.30758/0555-2648-2021-67-2-134-146.
Full textAbstract:
The Arctic polar vortex is often affected by wave activity during its life cycle. The planetary Rossby waves propagating from the troposphere to the stratosphere occasionally lead to the displacement or splitting of the polar vortex, accompanied by sudden stratospheric warming (SSW). In January 2009, one of the largest SSWs was observed in the Arctic. In this work, the dynamics of the polar vortex during the 2009 SSW is considered using a new method that allows one to estimate the vortex area, the wind speed at the vortex edge, the mean temperature and ozone mass mixing ratio inside the vortex, based on the fact that the Arctic vortex edge at the 50 and 10 hPa pressure levels is determined by the geopotential values, respectively, 19.5. 104 and 29.5. 104 m2 /s2 , using the ERA5 reanalysis data. The application of this method is justified for the Arctic polar vortex, which is characterized by significant variability, especially during the period of its splitting. The splitting of the polar vortex in 2009 was observed on January 24 and 28, respectively, in the middle and lower stratosphere. About a week after the splitting, the vortices became closer in characteristics to small cyclones, which completely collapsed within 1–3 weeks. The influence of planetary wave activity on the polar vortex does not always lead to its breakdown. Short-term splitting of the polar vortex is sometimes observed for several days after which the polar vortex strengthens again and PSCs form inside the vortex. Such a recovery of the polar vortex is most likely to occur in the winter. Based on the analysis of the dynamics of the Arctic polar vortex for 1979–2020 and using the example of the 2009 SSW, we showed that when the vortex area decreases to less than 10 million km2 and the mean wind speed at the vortex edge decreases below 30 and 45 m/s, respectively, in the lower and middle stratosphere, the polar vortex becomes a small cyclone (with significantly higher temperatures within it), which usually collapses within 3 weeks.
39
Matthewman, N. Joss, and J. G. Esler. "Stratospheric Sudden Warmings as Self-Tuning Resonances. Part I: Vortex Splitting Events." Journal of the Atmospheric Sciences 68, no. 11 (November 1, 2011): 2481–504. http://dx.doi.org/10.1175/jas-d-11-07.1.
Full textAbstract:
Abstract The fundamental dynamics of “vortex splitting” stratospheric sudden warmings (SSWs), which are known to be predominantly barotropic in nature, are reexamined using an idealized single-layer f-plane model of the polar vortex. The aim is to elucidate the conditions under which a stationary topographic forcing causes the model vortex to split, and to express the splitting condition as a function of the model parameters determining the topography and circulation. For a specified topographic forcing profile the model behavior is governed by two nondimensional parameters: the topographic forcing height M and a surf-zone potential vorticity parameter Ω. For relatively low M, vortex splits similar to observed SSWs occur only for a narrow range of Ω values. Further, a bifurcation in parameter space is observed: a small change in Ω (or M) beyond a critical value can lead to an abrupt transition between a state with low-amplitude vortex Rossby waves and a sudden vortex split. The model behavior can be fully understood using two nonlinear analytical reductions: the Kida model of elliptical vortex motion in a uniform strain flow and a forced nonlinear oscillator equation. The abrupt transition in behavior is a feature of both reductions and corresponds to the onset of a nonlinear (self-tuning) resonance. The results add an important new aspect to the “resonant excitation” theory of SSWs. Under this paradigm, it is not necessary to invoke an anomalous tropospheric planetary wave source, or unusually favorable conditions for upward wave propagation, in order to explain the occurrence of SSWs.
40
Richter, Jadwiga H., Fabrizio Sassi, and Rolando R. Garcia. "Toward a Physically Based Gravity Wave Source Parameterization in a General Circulation Model." Journal of the Atmospheric Sciences 67, no. 1 (January 1, 2010): 136–56. http://dx.doi.org/10.1175/2009jas3112.1.
Full textAbstract:
Abstract Middle atmospheric general circulation models (GCMs) must employ a parameterization for small-scale gravity waves (GWs). Such parameterizations typically make very simple assumptions about gravity wave sources, such as uniform distribution in space and time or an arbitrarily specified GW source function. The authors present a configuration of the Whole Atmosphere Community Climate Model (WACCM) that replaces the arbitrarily specified GW source spectrum with GW source parameterizations. For the nonorographic wave sources, a frontal system and convective GW source parameterization are used. These parameterizations link GW generation to tropospheric quantities calculated by the GCM and provide a model-consistent GW representation. With the new GW source parameterization, a reasonable middle atmospheric circulation can be obtained and the middle atmospheric circulation is better in several respects than that generated by a typical GW source specification. In particular, the interannual NH stratospheric variability is significantly improved as a result of the source-oriented GW parameterization. It is also shown that the addition of a parameterization to estimate mountain stress due to unresolved orography has a large effect on the frequency of stratospheric sudden warmings in the NH stratosphere by changing the propagation of stationary planetary waves into the polar vortex.
41
Kuttippurath, J., and G. Nikulin. "The sudden stratospheric warming of the Arctic winter 2009/2010: comparison to other recent warm winters." Atmospheric Chemistry and Physics Discussions 12, no. 3 (March 12, 2012): 7243–71. http://dx.doi.org/10.5194/acpd-12-7243-2012.
Full textAbstract:
Abstract. The Arctic winter 2009/10 was moderately cold in December. A minor warming occurred around mid-December due to a wave 2 amplification split the lower stratospheric vortex into two lobes. The vortices merged again and formed a relatively large vortex in a few days. The temperatures began to rise by mid-January and triggered a major sudden stratospheric warming (SSW) by the reversal of westerlies in late (24–26) January, driven by a planetary wave 1 with a peak amplitude of about 100 m2 s−2 at 60° N/10 hPa. The momentum flux associated with this warming showed the largest value in the recent winters, about 450 m2 s−2 at 60° N/10 hPa. The associated vortex split confined to altitudes below 10 hPa and hence, the major warming (MW) was a vortex displacement event. Large amounts of Eliassen-Palm (EP) and wave 2 EP fluxes (3.9 ×105 kg s−2) are found shortly before the MW event at 100 hPa over 45–75° N, suggesting a tropospheric preconditioning of the MW event. We observe an increase in SSWs in the Arctic in recent years, as there were 6 MWs in 6 out of the 7 winters of 2003/04–2009/10, which confirms the conclusions of previous studies on the SSWs in winters prior to 2003/04. Each MW event was unique as far as its evolution and related polar processes were concerned. As compared to the MWs in the recent Arctic winters, the strongest MW was observed in 2008/09 and was initiated by a wave 2 event. A detailed diagnosis of ozone loss during the past fifteen years shows that the loss is inversely proportional to the intensity and timing of SSWs in each winter, where early MWs lead to minimal loss. The ozone loss shows a good correlation with the zonal mean amplitude of zonal winds in January over 60–90° N, suggesting a proxy for MWs in the Arctic winters.
42
Scott, R. K., and L. M. Polvani. "Internal Variability of the Winter Stratosphere. Part I: Time-Independent Forcing." Journal of the Atmospheric Sciences 63, no. 11 (November 1, 2006): 2758–76. http://dx.doi.org/10.1175/jas3797.1.
Full textAbstract:
Abstract This paper examines the nature and robustness of internal stratospheric variability, namely the variability resulting from the internal dynamics of the stratosphere itself, as opposed to that forced by external sources such as the natural variability of the free troposphere. Internal stratospheric variability arises from the competing actions of radiative forcing, which under perpetual winter conditions strengthens the polar vortex, and planetary wave breaking, which weakens it. The results from a stratosphere-only model demonstrate that strong internal stratospheric variability, consisting of repeated sudden warming-type events, exists over a wide range of realistic radiative and wave forcing conditions, and is largely independent of other physical and numerical parameters. In particular, the coherent form of the variability persists as the number of degrees of freedom is increased, and is therefore not an artifact of severe model truncation. Various diagnostics, including three-dimensional representations of the potential vorticity, illustrate that the variability is determined by the vertical structure of the vortex and the extent to which upward wave propagation is favored or inhibited. In this paper, the variability arising from purely internal stratosphere dynamics is isolated by specifying thermal and wave forcings that are completely time independent. In a second paper, the authors investigate the relative importance of internal and external variability by considering time-dependent wave forcing as a simple representation of tropospheric variability.
43
Kim, Young-Joon, and Maria Flatau. "Hindcasting the January 2009 Arctic Sudden Stratospheric Warming and Its Influence on the Arctic Oscillation with Unified Parameterization of Orographic Drag in NOGAPS. Part I: Extended-Range Stand-Alone Forecast." Weather and Forecasting 25, no. 6 (December 1, 2010): 1628–44. http://dx.doi.org/10.1175/2010waf2222421.1.
Full textAbstract:
Abstract A very strong Arctic major sudden stratospheric warming (SSW) event occurred in late January 2009. The stratospheric temperature climbed abruptly and the zonal winds reversed direction, completely splitting the polar stratospheric vortex. A hindcast of this event is attempted by using the Navy Operational Global Atmospheric Prediction System (NOGAPS), which includes the full stratosphere with its top at around 65 km. As Part I of this study, extended-range (3 week) forecast experiments are performed using NOGAPS without the aid of data assimilation. A unified parameterization of orographic drag is designed by combining two parameterization schemes; one by Webster et al., and the other by Kim and Arakawa and Kim and Doyle. With the new unified orographic drag scheme implemented, NOGAPS is able to reproduce the salient features of this Arctic SSW event owing to enhanced planetary wave activity induced by more comprehensive subgrid-scale orographic drag processes. The impact of the SSW on the tropospheric circulation is also investigated in view of the Arctic Oscillation (AO) index, which calculated using 1000-hPa geopotential height. The NOGAPS with upgraded orographic drag physics better simulates the trend of the AO index as verified by the Met Office analysis, demonstrating its improved stratosphere–troposphere coupling. It is argued that the new model is more suitable for forecasting SSW events in the future and can serve as a tool for studying various stratospheric phenomena.
44
Harada, Yayoi, Atsushi Goto, Hiroshi Hasegawa, Norihisa Fujikawa, Hiroaki Naoe, and Toshihiko Hirooka. "A Major Stratospheric Sudden Warming Event in January 2009." Journal of the Atmospheric Sciences 67, no. 6 (June 1, 2010): 2052–69. http://dx.doi.org/10.1175/2009jas3320.1.
Full textAbstract:
Abstract The major stratospheric sudden warming (SSW) event of January 2009 is analyzed using the Japan Meteorological Agency (JMA) Climate Data Assimilation System (JCDAS). This SSW event is characterized by the extraordinary predominance of the planetary-scale wave of zonal wavenumber 2 (wave 2). The total amount of the upward Eliassen–Palm (EP) flux for wave 2 was the strongest since the winter of 1978/79. It is found that the remarkable development of the upper troposphere ridge over Alaska played important roles in the SSW in January 2009. During the first development stage, the ridge excited wave packets upward as well as eastward over around Alaska. The eastward-propagating packets intensified a trough over eastern Siberia, which led to the development of the planetary wave over eastern Siberia during the second development stage. The results of this study indicate that the pronounced wave-2 pattern observed in the stratosphere was brought about by accumulative effects of rather localized propagation of wave packets from the troposphere during the course of this SSW event rather than by the ubiquitous propagation of planetary-scale disturbances in the troposphere. The features of the SSW in January 2009 are quite similar to those during the major stratospheric warming event in February 1989: both SSWs are characterized by the predominance of wave 2, the remarkable development of the upper troposphere ridge over around Alaska, and positive SSTs in the eastern part of the North Pacific corresponding to a La Niña condition.
45
Albers, John R., and Thomas Birner. "Vortex Preconditioning due to Planetary and Gravity Waves prior to Sudden Stratospheric Warmings." Journal of the Atmospheric Sciences 71, no. 11 (October 29, 2014): 4028–54. http://dx.doi.org/10.1175/jas-d-14-0026.1.
Full textAbstract:
Abstract Reanalysis data are used to evaluate the evolution of polar vortex geometry, planetary wave drag, and gravity wave drag prior to split versus displacement sudden stratospheric warmings (SSWs). A composite analysis that extends upward to the lower mesosphere reveals that split SSWs are characterized by a transition from a wide, funnel-shaped vortex that is anomalously strong to a vortex that is constrained about the pole and has little vertical tilt. In contrast, displacement SSWs are characterized by a wide, funnel-shaped vortex that is anomalously weak throughout the prewarming period. Moreover, during split SSWs, gravity wave drag is enhanced in the polar night jet, while planetary wave drag is enhanced within the extratropical surf zone. During displacement SSWs, gravity wave drag is anomalously weak throughout the extratropical stratosphere. Using the composite analysis as a guide, a case study of the 2009 SSW is conducted in order to evaluate the roles of planetary and gravity waves for preconditioning the polar vortex in terms of two SSW-triggering scenarios: anomalous planetary wave forcing from the troposphere and resonance due to either internal or external Rossby waves. The results support the view that split SSWs are caused by resonance rather than anomalously large wave forcing. Given these findings, it is suggested that vortex preconditioning, which is traditionally defined in terms of vortex geometries that increase poleward wave focusing, may be better described by wave events (planetary and/or gravity) that “tune” the geometry of the vortex toward its resonant excitation points.
46
Gray, Lesley, Warwick Norton, Charlotte Pascoe, and Andrew Charlton. "A Possible Influence of Equatorial Winds on the September 2002 Southern Hemisphere Sudden Warming Event." Journal of the Atmospheric Sciences 62, no. 3 (March 1, 2005): 651–67. http://dx.doi.org/10.1175/jas-3339.1.
Full textAbstract:
Abstract The stratospheric sudden warming in the Southern Hemisphere (SH) in September 2002 was unexpected for two reasons. First, planetary wave activity in the Southern Hemisphere is very weak, and midwinter warmings have never been observed, at least not since observations of the upper stratosphere became regularly available. Second, the warming occurred in a west phase of the quasi-biennial oscillation (QBO) in the lower stratosphere. This is unexpected because warmings are usually considered to be more likely in the east phase of the QBO, when a zero wind line is present in the winter subtropics and hence confines planetary wave propagation to higher latitudes closer to the polar vortex. At first, this evidence suggests that the sudden warming must therefore be simply a result of anomalously strong planetary wave forcing from the troposphere. However, recent model studies have suggested that the midwinter polar vortex may also be sensitive to the equatorial winds in the upper stratosphere, the region dominated by the semiannual oscillation. In this paper, the time series of equatorial zonal winds from two different data sources, the 40-yr ECMWF Re-Analysis (ERA) and the Met Office assimilated dataset, are reviewed. Both suggest that the equatorial winds in the upper stratosphere above 10 hPa were anomalously easterly in 2002. Idealized model experiments are described in which the modeled equatorial winds were relaxed toward these observations for various years to examine whether the anomalous easterlies in 2002 could influence the timing of a warming event. It is found that the 2002 equatorial winds speed up the evolution of a warming event in the model. Therefore, this study suggests that the anomalous easterlies in the 1–10-hPa region may have been a contributory factor in the development of the observed SH warming. However, it is concluded that it is unlikely that the anomalous equatorial winds alone can explain the 2002 warming event.
47
Erlebach, P., U. Langematz, and S. Pawson. "Simulations of stratospheric sudden warmings in the Berlin troposphere-stratosphere-mesosphere GCM." Annales Geophysicae 14, no. 4 (April 30, 1996): 443–63. http://dx.doi.org/10.1007/s00585-996-0443-6.
Full textAbstract:
Abstract. Stratospheric sudden warming events in the Northern Hemisphere of the Berlin TSM GCM are investigated. In about 50% of the simulated years (13 out of 28), major midwinter warmings occur. This agrees well with observations but, whereas real events tend to occur approximately every second season, those in the model are clustered, most of them occur in the period between years 15/16 and years 24/25. In most other years, minor warming events take place. The warming events are found earlier in the winter than in reality. Many of the observed characteristics of warming events are well captured by the model: pulses of wave activity propagate out of the troposphere; these transient events force the zonal-mean zonal wind in the stratosphere and coincide with increases of the temperature at the North Pole and cooling at low levels in the tropics; temperature changes of opposite sign are modelled at higher levels. Synoptically, the modelled stratosphere evolves quite realistically before the warmings: the cyclonic vortex is displaced from the Pole by an amplifying anticyclone. After minor warmings, the stratosphere remains too disturbed as the cyclonic centre does not return to the North Pole as quickly as in reality. In the aftermath of major warmings the cyclonic vortex is not fully eroded and the anticyclonic circulation does not develop properly over the Pole; furthermore, the wintertime circulation is not properly restored after the event.
48
Tomikawa, Yoshihiro. "Persistence of Easterly Wind during Major Stratospheric Sudden Warmings." Journal of Climate 23, no. 19 (October 1, 2010): 5258–67. http://dx.doi.org/10.1175/2010jcli3507.1.
Full textAbstract:
Abstract This study examines why the persistence of easterly wind during major stratospheric sudden warmings (SSWs) varies from one SSW to another. From the 22 SSWs identified between 1979 and 2009, six long and six short SSWs of easterly wind periods longer than 20 days and shorter than 10 days, respectively, are chosen and their composites are compared. While the polar-night jet is stronger than the climatological jet before long SSWs, the preconditioning of the polar-night jet tends to occur before short SSWs. After the occurrence of SSWs, the easterly wind of short SSWs quickly returns to a westerly wind due to large positive Eliassen–Palm (E–P) flux divergence in the winter polar stratosphere. The easterly wind of long SSWs lasts for 20–40 days because the E–P flux divergence is small whether it is positive or negative. Such a difference in the E–P flux divergence originates from the difference in the upward E–P flux from the troposphere. On the other hand, the positive E–P flux divergence during short SSWs is not caused by the variation of upward E–P flux from the troposphere but could be due to the shear instability caused by the overreflection of zonal wavenumber 1 planetary waves at the critical surface. The difference in the persistence of easterly wind between long and short SSWs also has a large impact on the planetary wave activity in the winter stratosphere.
49
Taguchi, Masakazu, and Dennis L. Hartmann. "Increased Occurrence of Stratospheric Sudden Warmings during El Niño as Simulated by WACCM." Journal of Climate 19, no. 3 (February 1, 2006): 324–32. http://dx.doi.org/10.1175/jcli3655.1.
Full textAbstract:
Abstract Experiments with Whole Atmosphere Community Climate Model (WACCM) under perpetual January conditions indicate that stratospheric sudden warmings (SSWs) are twice as likely to occur in El Niño winters than in La Niña winters, in basic agreement with the limited observational dataset. Tropical SST anomalies that mimic El Niño and La Niña lead to changes in the shape of probability distribution functions (PDFs) of stratospheric day-to-day variability, resulting in a warmer pole and weaker vortex on average for El Niño conditions. The tropical SST forcing induces a response similar to the observed response in the enhancement of the planetary wave of zonal wavenumber 1 (wave 1) and the weakening of wave 2 in the upper troposphere and stratosphere of high latitudes. The enhanced wave 1 contributes to a shift of the PDFs of poleward eddy heat flux in the lower stratosphere, or wave forcing entering the stratosphere. The shift of the PDFs includes an increase of strong wave events that induce more frequent SSWs.
50
Lubis, Sandro W., Katja Matthes, Nili Harnik, Nour-Eddine Omrani, and Sebastian Wahl. "Downward Wave Coupling between the Stratosphere and Troposphere under Future Anthropogenic Climate Change." Journal of Climate 31, no. 10 (April 30, 2018): 4135–55. http://dx.doi.org/10.1175/jcli-d-17-0382.1.
Full textAbstract:
Abstract Downward wave coupling (DWC) is an important process that characterizes the dynamical coupling between the stratosphere and troposphere via planetary wave reflection. A recent modeling study has indicated that natural forcing factors, including sea surface temperature (SST) variability and the quasi-biennial oscillation (QBO), influence DWC and the associated surface impact in the Northern Hemisphere (NH). In light of this, the authors further investigate how DWC in the NH is affected by anthropogenic forcings, using a fully coupled chemistry–climate model CESM1(WACCM). The results indicate that the occurrence of DWC is significantly suppressed in the future, starting later in the seasonal cycle, with more events concentrated in late winter (February and March). The future decrease in DWC events is associated with enhanced wave absorption in the stratosphere due to increased greenhouse gases (GHGs), which is manifest as more absorbing types of stratospheric sudden warmings (SSWs) in early winter. This early winter condition leads to a delay in the development of the upper-stratospheric reflecting surface, resulting in a shift in the seasonal cycle of DWC toward late winter in the future. The tropospheric responses to DWC events in the future exhibit different spatial patterns, compared to those of the past. In the North Atlantic sector, DWC-induced circulation changes are characterized by a poleward shift and an eastward extension of the tropospheric jet, while in the North Pacific sector, the circulation changes are characterized by a weakening of the tropospheric jet. These responses are consistent with a change in the pattern of DWC-induced synoptic-scale eddy–mean flow interaction in the future.