A Major Stratospheric Sudden Warming Event in January 2009

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.

Latitudinal Extension of Cooling and Upwelling Signals Associated with Stratospheric Sudden Warmings

“…The difference in the numbers is due to the data length, as the key days are well matched between the two sets of data in the common period. Defined in a slightly different manner, the key days reasonably agree with the existing studies (Charlton and Polvani 2007;Harada et al 2010). The present definition of the SSW key days is not seriously affected by the discontinuities in the JRA/JCDAS data.…”

Global distribution of vertical wavenumber spectra in the lower stratosphere observed using high-vertical-resolution temperature profiles from COSMIC GPS radio occultation

“…N 2 reached the maximum and minimum values of 6.5 × 10 −4 and 4 × 10 −4 rad s −2 in winter and summer, respectively. A seasonal variation was also evident at high latitudes (50-90 • N) in the NH, but it exhibited considerable year-to-year differences probably due to sudden stratospheric warming events in winter of the NH (Harada et al, 2010). It is expected that the increase in N 2 could be related to an enhancement of GW energy in winter in the polar region, because the model spectrum indicates a proportionality of the spectral density with N 2 as in Eq.…”

The role of convective overshooting clouds in tropical stratosphere–troposphere dynamical coupling

“…Therefore, case studies are made in the present paper on two exceptionally large events focusing on the role of overshooting and deep convective clouds in stratosphere-troposphere dynamical coupling in the tropics. The selected two largest SSW events of January 2009 and January 2010 (Harada et al, 2010;Ayarzagüena et al, 2011) have a large impact on the tropical upwelling in the lower stratosphere as will be shown later. These SSWs are not only large but also localized in time unlike other SSWs.…”