TITLE:
What Controls Recent Changes in the Circulation of the Southern Hemisphere: Polar Stratospheric or Equatorial Surface Temperatures?
AUTHORS:
Isidoro Orlanski
KEYWORDS:
Southern Hemisphere Changes; Ozone Depletion; Ocean Warming; Poleward Stormtrack
JOURNAL NAME:
Atmospheric and Climate Sciences,
Vol.3 No.4,
September
11,
2013
ABSTRACT: Recent research suggests that both tropical ocean warming and
stratospheric temperature anomalies due to ozone depletion have led to a
poleward displacement of the midand high-latitude circulation of the Southern
Hemisphere over the past century. In this study, we attempt to distinguish the
influences of ocean warming and stratospheric cooling trends on seasonal
changes of both the zonally symmetric and asymmetric components of the southern
hemisphere circulation. Our analysis makes use of three data sets-the ERA40
reanalysis and results from two different runs of the GFDL global atmosphere
and land model (AM2.1) for the period 1870 to 2004. A regression analysis was
applied to two variables in each of the three data sets-the zonal component of
the surface wind U(10 m)
and the height at 300 hPa—to determine their correlation with zonally
averaged polar stratospheric temperatures (T_polar—at 150 hPa, averaged
over a band from 70S - 80S) and low-level equatorial temperatures (T_equator—at 850
hPa averaged over a band at 5S - 5N). Our analysis shows that the zonally symmetric surface winds have a
considerably enhanced intensity in high latitudes of the southern hemisphere
over the summer period, and that the stratospheric temperature trend, and thus
ozone depletion, is the dominant contributor to that change. However, the
climatic change of the asymmetric component of zonal wind component at z = 10 m (U10) as well as of 300hPa heights has been found to be large for
both summer and winter periods. Our regression results show that correlation
with T_equator (our proxy for global warming) explains most of the climatic
changes for the asymmetric component of U10 and 300 hPa heights for
summer and winter periods, suggesting the influence of warming of the global
oceans on anticyclones south of the Indian Ocean and south-eastern Pacific
Ocean.