The large-scale dynamics of the mesosphere–lower thermosphere during the Southern Hemisphere stratospheric warming of 2002 (original) (raw)
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Annales Geophysicae, 2010
We present kinetic temperatures at ∼87 km and ∼94 km altitudes inferred from OH (6,2) and O 2 At(0,1) airglow observations, respectively, at South Pole (90 • S), Antarctica in the austral winter of 2002. These OH and O 2 rotational temperatures measurements show mesosphere and lower thermosphere (MLT) temperature anomalies prior to the 2002 Southern Hemisphere Sudden Stratospheric Warming (SSW). In this paper we focus on the first of the three minor stratospheric warmings which preceded the major SSW event. Temperature anomalies observed in the MLT region show sudden cooling (T =∼30 K) in OH temperatures accompanied by warming (T =∼15 K) in O 2 temperatures preceding the onset of SSW event by about three to four weeks. This shallow vertical extent of mesospheric cooling is in agreement with the numerical simulation of Coy et al. (2005), however, the model cooling was centered well below the mesopause level. The other observed feature of the South Pole MLT temperature dataset is the intensification of planetary wave activity prior to the onset of SSW event. Fourier analyses of both OH and O 2 temperatures show amplification of planetary wave activity in the 5-10 day range prior to the onset of SSW. The timing of wave amplification seen in the wave spectra coincides with the peak in OH and O 2 temperature anomalies.
Southern Hemisphere Stratospheric Warmings and Coupling to the Mesosphere-Lower Thermosphere
2022
Twenty six years of MF radar wind measurements made from 1994 to 2019 at Davis Station (68.6*S, 77.9*E) are used to study the mean response of the mesosphere-lower thermosphere to stratospheric warmings in the southern hemisphere. Warming events were detected using Modern-Era Retrospective Analysis for Research and Applications (MERRA)-2 data with a systematic search for reductions in the zonal-mean circulation at 60*S and corresponding increases in polar temperatures. Some 38 events were identified, including the major warmings of 2002 and 2019, with an average of 1 to 2 warmings per year. At the 10 hPa level, the polar cap temperature increases ranged from 5 to 30 K, with a mean value of 11 K, while the zonal wind speed reductions varied between-7 to-43 ms-1, with-1 a mean value of-15 ms. Peak values occurred near 40 km. Warmings occurred mainly between August and October, with a small peak in occurrence in April/May. The MF radar data showed an average reduction in the mesospheric eastward winds of about 5-7 ms-1 at heights near 75 km that occurred some 3-4 days prior to the changes in the stratosphere. Warming events were driven by episodic intensifications in planetary waves amplitudes, with quasi-stationary PW 1 being especially important. Planetary wave Eliassen-Palm flux divergences show a systematic behavior with time and height that is consistent with a poleward residual circulation and downwelling over the pole prior to the warming events and an equatorward flow and upwelling after the peak of the events.
Environmental Science and Pollution Research, 2004
Goal, Scope and Background. Great interest in the unprecedented events of the major, sudden stratospheric warming and the ozone hole split over Antarctica in September 25, 2002 motivates a necessity to analyze the current understanding on the dynamics, chemistry and climate impacts that are associated with both events. Methods. Significant progress in the analysis of the observational data obtained, as well as successful development and application of dynamical modeling, which have been achieved very recently, create a basis for the first survey on the role of the major, sudden stratospheric warming observed in the southern hemisphere and its relationship to the diminutive Antarctic ozone hole and its break up into two parts. Results and Discussion. Special attention has been paid to assessments of the causes of the major warming event and the future expectations concerning the stratospheric ozone depletion effect. Among the principal results is the fact that, as the polar vortex elongated, it became hydrodynamically unstable, and this instability affected the upper troposphere and stratosphere. During the major, sudden stratospheric warming, the middle stratospheric vortex split into two pieces; one piece rapidly mixed with extra vortex air, while the other returned to the pole as a much weaker and smaller vortex. The polar night jet was considerably weaker than normal, and was displaced more poleward than has been observed in previous winters, resulting from a series of wave events (propagated from the troposphere) that took place over the course of the winter-Finally, the relative ozone decrease (increase) in the eastern Antarctic is tightly associated with westerly (easterly) zonal wind anomalies near the southern tip of South America, and the unusual behavior of the ozone hole in 2002 therefore appears to be caused by great easterlies in this region. Conclusions. The main conclusion is that the southern polar vortex and the diminutive ozone hole split into two parts in September 2002, due to the prevalence of very strong planetary waves, led to the appearance of a major, sudden stratospheric warming. Although there is evidence that sea surface temperature anomalies contributed to the excitation of the quite strong planetary waves over Antarctica in 2002, there is not yet a widely approved mechanism supporting that. Recommendations and Oudook. The appearance of the near-record size of the 2003 ozone hole confirmed that the 'no-ozone-hole' episode observed in the year 2002 does not denote a recovery of the ozone layer. Despite the current successful attempts to get a su~cient understanding for the genesis of both extraordinary events, more observations and fuxther modeling efforts are necessary to more reliably assess the contribution of various dynalniC mechanisms to the recently observed tropo-stratospheric surprises.
Atmosphere
Processes behind Sudden Stratospheric Warming (SSW), which occurs more frequently in the northern hemispheric polar latitudes and its influence from the stratosphere to the upper atmosphere are well documented. However, physical processes associated with SSW, although it ensues rarely in the southern hemisphere (SH), have a strong influence on the background atmosphere from the stratosphere to the mesosphere and are poorly understood. Using a ground-based meteor radar, satellite-borne Microwave-Limb sounder, and Modern-Era Retrospective Analysis for Research and Applications observations, we identified cooling of Antarctic mesopause by 26 K in response to a 66 K warming in the polar stratosphere during the 2019 minor SSW in the SH. The observed cooling is attributed to the interplay between planetary waves, CO2 infrared cooling, and O3 depletion, rather than adiabatic cooling due to gravity waves alone during SSW. It is proposed that anthropogenic and other sources generating chemic...
A unique stratospheric warming event in November 2000
Geophysical Research Letters, 2001
Stratospheric sudden warmings frequently influence temperatures and circulation in the Arctic winter stratosphere. A unique stratospheric warming in Nov 2000 was characterized by wave 1 amplification with little phase tilt with height, a large displacement of the vortex off the pole, a warm pool at high latitudes, and a modest polar temperature increase, all of which are characteristic of early winter "Canadian" warmings. Unlike most Canadian warmings, the Nov 2000 event led to a strong zonal mean wind reversal for •9 days in the mid and lower stratosphere. Wind reversals during Canadian warmings occurred only three times before in the last 23 years. Midstratospheric minimum temperatures continued to decrease during the warming, but lower stratospheric temperatures increased substantially. The Nov 2000 warming was unique in its timing, intensity and duration, and in its impact on the development of the polar vortex, especially in the lower stratosphere.
Geophysical Research Letters, 2005
We have examined the Michelson Interferometer (MI) OH airglow measurements at the South Pole Station and the National Center for Environment Prediction (NCEP) temperatures to investigate the dynamical effects of sudden stratospheric warming (SSW) events on the Antarctic mesosphere and stratosphere. Comparisons of stratospheric and mesospheric temperatures at the South Pole during the 1995 and 2002 observing seasons show evidence of mesospheric cooling preceding the SSW events. Spectral analyses of South Pole OH air glow brightness measurements from the 1995 and 2002 observing season and NCEP stratospheric temperatures show amplification of the 4-day wave planetary wave before the start of the mesospheric cooling trend, the latter preceding the onset of SSW event. A similar behavior of planetary wave is also seen in the stratosphere where the 4-day wave is seen to grow in amplitude just before the peak of the sudden increase in temperatures.