Potential links between tropospheric and stratospheric circulation extremes during early 2020

Abstract. Constituent evolution for 1990–2015 simulated using the Global Modeling Initiative Chemistry and Transport Model driven by meteorological fields from the Modern Era Retrospective analysis for Research and Applications Version 2 (MERRA-2) is compared with three sources of observations: ground based column measurements of HNO3 and HCl from two stations in the Network for Detection of Atmospheric Composition Change (NDACCC, ~ 1990–ongoing); profiles of CH4 from the HALogen Occultation Experiment (HALOE) on the Upper Atmosphere Research Satellite (UARS, 1992–2005); profiles of N2O from the Microwave Limb Sounder on the Earth Observing System satellite Aura (2015–ongoing). The differences between observed and simulated values are shown to be time dependent, with better agreement after ~2000 compared with the prior decade. Furthermore, the differences between observed and simulated HNO3 and HCl columns are shown to be correlated with each other, suggesting that issues with the simulated transport and mixing cause the differences during the 1990s and these issues are less important during the later years. Because the simulated fields are related to mean age in the lower stratosphere, we use these comparisons to evaluate the time dependence of mean age. We use these relationships to account for dynamical variability when determining decadal scale trends in constituents and mean age. The ongoing NDACC column observations provide critical information necessary to substantiate trends in mean age obtained using fields from MERRA-2 or any other reanalysis products.

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On the values of stratospheric circulation index over Natal, Brasil

Pure and Applied Geophysics ◽

10.1007/bf00875905 ◽

1973 ◽

Vol 104 (1) ◽

pp. 608-613

Author(s):

N. Jagan Mohana Rao ◽

P. Sathyamurthi ◽

T. V. Ramana Rao

Keyword(s):

Circulation Index ◽

Stratospheric Circulation

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Final Sudden Stratospheric Warmings and the memory of the stratosphere

10.5194/egusphere-egu21-9970 ◽

2021 ◽

Author(s):

Alain Hauchecorne ◽

Chantal Claud ◽

Philippe Keckhut

Keyword(s):

Zonal Wind ◽

Planetary Wave ◽

Middle Atmosphere ◽

Temperature Anomaly ◽

Polar Vortex ◽

Wave Activity ◽

Late Winter ◽

Easterly Wind ◽

Weather Forecasts ◽

Stratospheric Circulation

Sudden Stratospheric Warming (SSW) is the most spectacular dynamic event occurring in the middle atmosphere. It can lead to a warming of the winter polar stratosphere by a few tens of K in one to two weeks and a reversal of the stratospheric circulation from wintertime prevailing westerly winds to easterly winds similar to summer conditions. This strong modification of the stratospheric circulation has consequences for several applications, including the modification of the stratospheric infrasound guide. Depending on the date of the SSW, the westerly circulation can be re-established if the SSW occurs in mid-winter or the summer easterly circulation can be definitively established if the SSW occurs in late winter. In the latter case it is called Final Warming (FW). Each year, it is possible to define the date of the FW as the date of the final inversion of the zonal wind at 60&#176;N - 10 hPa . If the FW is associated with a strong peak of planetary wave activity and a rapid increase in polar temperature, it is classified as dynamic FW. If the transition to the easterly wind is smooth without planetary wave activity, the FW is classified as radiative.The analysis of the ERA5 database, which has recently been extended to 1950 (71 years of data), allowed a statistical analysis of the evolution of the stratosphere in winter. The main conclusions of this study will be presented :- the state of the polar vortex in a given month is anticorrelated with its state 2 to 3 months earlier. The beginning of winter is anticorrelated with mid-winter and mid-winter is anticorrelated with the end of winter;- dynamic FWs occur early in the season (March - early April) and are associated with a strong positive polar temperature anomaly, while radiative FWs occur later (late April - early May) without a polar temperature anomaly;- the summer stratosphere (polar temperature and zonal wind) keeps the memory of its state in April-May at the time of FW at least until July .These results could help to improve medium-range weather forecasts in the Northern Hemisphere due to the strong dynamic coupling between the troposphere and stratosphere during SSW events.

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