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HOME > Climate System Monitoring > Stratospheric circulation > Explanation

Explanation on the Monitoring of Stratospheric Circulation

   JMA monitors the stratospheric circulation, focusing especially on stratospheric sudden warmings (SSW).

Data

   The atmospheric circulation data are Japanese 55-year Reanalysis (JRA-55) (Ebita et al. 2011). The base period for normal is 1981 - 2010.


Stratospheric Warming

   The Stratospheric Sudden Warming (SSW) is a phenomenon characterized by a rapid increase in polar temperatures in the stratosphere. The temperature increases more than a few dozen degrees in a few days in the boreal winter. In some cases the westerly polar night jet disappears and easterly winds appear during the warming. JMA is monitoring SSWs as one of the Regional Warming Centers. The warming is called a "Minor Warming", when the polar temperature increases more than 25 degrees in a period of a week or less at any stratospheric level. If the zonal mean temperature increases poleward from 60 degrees latitude and the net zonal mean zonal winds become easterly at 60 degrees latitude at 10 hPa (32 km) or below, it is classified as a "Major Warming".
   The SSW was discovered in 1952 by Scherhag (1952), but it took some time before the mechanism was theoretically identified by Matsuno (1971). The SSW is caused by a rapid amplification of planetary waves propagating upward from the troposphere. Planetary waves deposit westward momentum and create a strong meridional circulation which produces a large warming in the polar stratosphere due to adiabatic heating (e.g., McIntyre 1982).


Interaction between Stratosphere and Troposphere

   The relationship between the stratosphere and the troposphere has widely been recognized. During winter, tropospheric planetary waves propagate into the stratosphere along the westerly jet (e.g., Charney and Drazin 1961). More recently, the converse relationship that the zonal mean zonal wind anomalies slowly propagate from the subtropical upper stratosphere to the polar region of the lower stratosphere and the troposphere during the boreal winter, is also noted (Kodera et al. 1990). It has been shown that SSWs occur in association with slowly propagating zonal mean zonal wind anomalies, and the related changes in the troposphere exhibits the Annular Mode (AO) (Thompson and Wallace 1998) like structure (Kodera et al. 2000). Baldwin and Dunkerton (1999) also showed that the downward propagation of the AO from the stratosphere to the troposphere occurs in association with SSWs.


E-P Flux Analysis

   As mentioned above, the stratospheric and the tropospheric circulation are connected with each other through wave mean flow interactions. The Eliassen-Palm (E-P) flux (Eliassen and Palm 1961) is widely used to characterize the wave activity. The direction of the E-P flux is proportional to the group velocity and indicates the direction of the propagation of the waves. Approximately, the vertical and horizontal components of the E-P flux are proportional to the eddy heat and momentum flux, respectively. The divergence of E-P flux is proportional to the northward flux of quasi-geostrophic potential vorticity, so that it is a direct measure of the total forcing of the zonal mean flow by eddies. Therefore, the E-P flux and its divergence are important and useful to diagnose planetary waves propagation as well as the effective mean zonal force induced by the waves. Some figures on this web page display E-P fluxes under different forms, such as meridional cross sections and time series, for monitoring the stratospheric circulation.


References

  • Baldwin, M. P., T. J. Dunkerton, 1999: Propagation of the Arctic Oscillation from the stratosphere to the troposphere, J. Geophys. Res., 104, 30937-30946.
  • Charney, J. and P. Drazin, 1961: Propagation of planetary scale disturbances from the lower into the upper atmosphere. J. Geophys. Res., 66, 83-109.
  • Ebita, A., S. Kobayashi, Y. Ota, M. Moriya, R. Kumabe, K. Onogi, Y. Harada, S. Yasui, K. Miyaoka, K. Takahashi, H. Kamahori, C. Kobayashi, H. Endo, M. Soma, Y. Oikawa and T. Ishimizu, 2011: The Japanese 55-year Reanalysis "JRA-55": an interim report, SOLA, 7, 149-152.
  • Scherhag, R., 1952: Die explosionsartige Stratospharenerwarmung des Spatwinters 1951/52, Ber. Deut. Wetterdienst 38, 51-63.
  • Eliassen, A. and E. Palm, 1961: On the transfer of energy in stationary mountain waves. Geofys. Publ., 22, No. 3, 1-23.
  • Kodera, K., and K. Yamazaki, M.Chiba, and K.Shibata, 1990: Downward propagation of upper stratospheric mean zonal wind perturbation to the troposphere, Geophys. Res. Lett., 17, 1263-1266.
  • Kodera, K., and Y. Kuroda, S. Pawson, 2000: Stratospheric sudden warming and slowly propagating zonal-mean zonal wind anomalies, J. Geophys. Res., 105, 12351-12359.
  • Matsuno, T., 1971: A dynamical model of the stratospheric sudden warming. J. Atmos. Sci., 28, 1479-1494.
  • McIntyre, M. E., 1982: How well do we understand the dynamics of stratospheric warming? J. Meteor. Soc. Japan, 60, 37-65.
  • Thompson, D.W.J., J. M. Wallace, 1998: The Arctic Oscillation signature in the winter geopotential height and temperature fields, Geophys. Res. Lett., 25, 1297-1300.