Variability of seasonal-mean fields arising from intraseasonal variability. Part 3: Application to SH winter and summer circulations |
| |
Authors: | Carsten S Frederiksen Xiaogu Zheng |
| |
Institution: | (1) Bureau of Meteorology Research Centre, GPO Box 1289, Melbourne, 3001, VIC, Australia;(2) National Institute of Water and Atmospheric Research, Wellington, New Zealand |
| |
Abstract: | A study has been made, using the National Centers for Environmental Prediction and National Center for Atmospheric Research
re-analysis 500 hPa geopotential height data, to determine how intraseasonal variability influences, or can generate, coherent
patterns of interannual variability in the extratropical summer and winter Southern Hemisphere atmospheric circulation. In
addition, by separating this intraseasonal component of interannual variability, we also consider how slowly varying external
forcings and slowly varying (interannual and longer) internal dynamics might influence the interannual variability of the
Southern Hemisphere circulation. This slow component of interannual variation is more likely to be potentially predictable.
How sea surface temperatures are related to the slow components is also considered. The four dominant intraseasonal modes
of interannual variability have horizontal structures similar to those seen in both well-known intraseasonal dynamical modes
and statistical modes of intraseasonal variability. In particular, they reflect intraseasonal variability in the high latitudes
associated with the Southern Annular Mode, and wavenumber 4 (summer) and wavenumber 3 (winter) patterns associated with south
Pacific regions of persistent anomalies and blocking, and possibly variability related to the Madden-Julian Oscillation (MJO).
The four dominant slow components of interannual variability, in both seasons, are related to high latitude variability associated
with the Southern Annular Mode, El Nino Southern Oscillation (ENSO) variability, and South Pacific Wave variability associated
with Indian Ocean SSTs. In both seasons, there are strong linear trends in the first slow mode of high latitude variability
and these are shown to be related to similar trends in the Indian Ocean. Once these are taken into account there is no significant
sea surface temperature forcing of these high latitude modes. The second and third ENSO related slow modes, in each season,
have high correlations with tropical sea surface temperature variability in the Pacific and Indian Oceans, both contemporaneously
and at one season lag. The fourth slow mode has a characteristic South Pacific wave structure of either a wavenumber 4 (summer)
or wavenumber 3 (winter) pattern, with strongest loadings in the South Pacific sector, and an association simultaneously with
a dipole SST temperature gradient in the subtropical Indian Ocean. |
| |
Keywords: | |
本文献已被 SpringerLink 等数据库收录! |
|