Westward Acceleration of Tropical Stratopause Zonal Winds During Major Sudden Stratospheric Warming Events

Various criteria exist for determining the occurrence of a major sudden stratospheric warming (SSW), but the most common is based on the reversal of the climatological westerly zonal-mean zonal winds at 60° latitude and 10 hPa in the winter stratosphere. This definition was established at a time when observations of the stratosphere were sparse. Given greater access to data in the satellite era, a systematic analysis of the optimal parameters of latitude, altitude, and threshold for the wind reversal is now possible. Here, the frequency of SSWs, the strength of the wave forcing associated with the events, changes in stratospheric temperature and zonal winds, and surface impacts are examined as a function of the stratospheric wind reversal parameters. The results provide a methodical assessment of how to best define a standard metric for major SSWs. While the continuum nature of stratospheric variability makes it difficult to identify a decisively optimal threshold, there is a relatively narrow envelope of thresholds that work well—and the original focus at 60° latitude and 10 hPa lies within this window.

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Effect of Semidiurnal Lunar Tides Modulated by Quasi-2-Day Wave on Equatorial Electrojet during Three Sudden Stratospheric Warming events

10.5194/egusphere-egu21-6985 ◽

2021 ◽

Author(s):

Yaxian Li ◽

Gang Chen

Keyword(s):

Lower Thermosphere ◽

Equatorial Electrojet ◽

Stratospheric Warming ◽

Sudden Stratospheric Warming ◽

Zonal Winds ◽

Wave Characteristics ◽

Lunar Tides ◽

Time Period ◽

Mesosphere And Lower Thermosphere ◽

Good Agreement

<p>We present an analysis of the perturbations and wave characteristics in equatorial electrojet&#160;(EEJ) and equatorial zonal winds in the mesosphere and lower thermosphere region during three&#160;sudden stratospheric warming (SSW) events, based on the wind observations by two meteor&#160;radars in Indonesia and the geomagnetic field observations in India. During three SSWs, the&#160;shifting semidiurnal perturbations are consistently observed in the EEJ and accompanied with&#160;strong 2-day periodic perturbations simultaneously. The semidiurnal lunar (L2) tidal amplitudes&#160;in the EEJ and zonal winds show the prominent enhancements during the episodes of EEJ perturbations. The time-period spectra of the L2 tidal amplitudes in both the EEJ and zonal&#160;winds present the obvious quasi-2-day wave (QTDW) amplification with good agreement during&#160;these periods. Our results firstly reveal the important contributions of QTDW to EEJ&#160;perturbations during SSWs and the semidiurnal lunar tides modulated by QTDW serve as the&#160;main forcing agent therein</p>

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The sudden stratospheric warming of the Arctic winter 2009/2010: comparison to other recent warm winters

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-12-7243-2012 ◽

2012 ◽

Vol 12 (3) ◽

pp. 7243-7271 ◽

Cited By ~ 10

Author(s):

J. Kuttippurath ◽

G. Nikulin

Keyword(s):

Planetary Wave ◽

Mean Amplitude ◽

The Arctic ◽

Stratospheric Warming ◽

Sudden Stratospheric Warming ◽

Ozone Loss ◽

Zonal Winds ◽

The Past ◽

Large Vortex ◽

A Minor

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.

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A Continuum of Sudden Stratospheric Warmings

Journal of the Atmospheric Sciences ◽

10.1175/2008jas2792.1 ◽

2009 ◽

Vol 66 (2) ◽

pp. 531-540 ◽

Cited By ~ 20

Author(s):

K. Coughlin ◽

L. J. Gray

Keyword(s):

Northern Hemisphere ◽

Threshold Value ◽

Stratospheric Warming ◽

Sudden Stratospheric Warming ◽

Cluster Technique ◽

Annular Mode ◽

Northern Annular Mode ◽

Zonal Winds ◽

Warm State

Abstract The k-means cluster technique is used to examine 43 yr of daily winter Northern Hemisphere (NH) polar stratospheric data from the 40-yr ECMWF Re-Analysis (ERA-40). The results show that the NH winter stratosphere exists in two natural well-separated states. In total, 10% of the analyzed days exhibit a warm disturbed state that is typical of sudden stratospheric warming events. The remaining 90% of the days are in a state typical of a colder undisturbed vortex. These states are determined objectively, with no preconceived notion of the groups. The two stratospheric states are described and compared with alternative indicators of the polar winter flow, such as the northern annular mode. It is shown that the zonally averaged zonal winds in the polar upper stratosphere at ∼7 hPa can best distinguish between the two states, using a threshold value of ∼4 m s−1, which is remarkably close to the standard WMO criterion for major warming events. The analysis also determines that there are no further divisions within the warm state, indicating that there is no well-designated threshold between major and minor warmings, nor between split and displaced vortex events. These different manifestations are simply members of a continuum of warming events.

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Features of the stratospheric circulation dynamics due to the January 2009 sudden stratospheric warming

Оптика атмосферы и океана ◽

10.15372/aoo20170408 ◽

2017 ◽

Keyword(s):

Stratospheric Warming ◽

Sudden Stratospheric Warming ◽

Stratospheric Circulation ◽

Circulation Dynamics

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Identification of the mechanisms responsible for anomalies in the tropical lower thermosphere/ionosphere caused by the January 2009 sudden stratospheric warming

Journal of Space Weather and Space Climate ◽

10.1051/swsc/2019037 ◽

2019 ◽

Vol 9 ◽

pp. A39 ◽

Cited By ~ 1

Author(s):

Maxim V. Klimenko ◽

Vladimir V. Klimenko ◽

Fedor S. Bessarab ◽

Timofei V. Sukhodolov ◽

Pavel A. Vasilev ◽

...

Keyword(s):

Electric Field ◽

Phase Change ◽

Lower Thermosphere ◽

Upper Atmosphere ◽

Electron Content ◽

Stratospheric Warming ◽

Sudden Stratospheric Warming ◽

Low Latitude ◽

Plasma Drift ◽

Solar Tide

We apply the Entire Atmosphere GLobal (EAGLE) model to investigate the upper atmosphere response to the January 2009 sudden stratospheric warming (SSW) event. The model successfully reproduces neutral temperature and total electron content (TEC) observations. Using both model and observational data, we identify a cooling in the tropical lower thermosphere caused by the SSW. This cooling affects the zonal electric field close to the equator, leading to an enhanced vertical plasma drift. We demonstrate that along with a SSW-related wind disturbance, which is the main source to form a dynamo electric field in the ionosphere, perturbations of the ionospheric conductivity also make a significant contribution to the formation of the electric field response to SSW. The post-sunset TEC enhancement and pre-sunrise electron content reduction are revealed as a response to the 2009 SSW. We show that at post-sunset hours the SSW affects low-latitude TEC via a disturbance of the meridional electric field. We also show that the phase change of the semidiurnal migrating solar tide (SW2) in the neutral wind caused by the 2009 SSW at the altitude of the dynamo electric field generation has a crucial importance for the SW2 phase change in the zonal electric field. Such changes lead to the appearance of anomalous diurnal variability of the equatorial electromagnetic plasma drift and subsequent low-latitudinal TEC disturbances in agreement with available observations. Plain Language Summary – Entire Atmosphere GLobal model (EAGLE) interactively calculates the troposphere, stratosphere, mesosphere, thermosphere, and plasmasphere–ionosphere system states and their response to various natural and anthropogenic forcing. In this paper, we study the upper atmosphere response to the major sudden stratospheric warming that occurred in January 2009. Our results agree well with the observed evolution of the neutral temperature in the upper atmosphere and with low-latitude ionospheric disturbances over America. For the first time, we identify an SSW-related cooling in the tropical lower thermosphere that, in turn, could provide additional information for understanding the mechanisms for the generation of electric field disturbances observed at low latitudes. We show that the SSW-related vertical electromagnetic drift due to electric field disturbances is a key mechanism for interpretation of an observed anomalous diurnal development of the equatorial ionization anomaly during the 2009 SSW event. We demonstrate that the link between thermospheric winds and the ionospheric dynamo electric field during the SSW is attained through the modulation of the semidiurnal migrating solar tide.

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