| Abstract: | By adopting characteristic index data for the Western Pacific
Subtropical High (WPSH) from the National Climate Center of China, U.S.
National Centers for Environmental Prediction-National Center for
Atmospheric Research (NCEP/NCAR) reanalysis data, and the National
Oceanic and Atmospheric Administration (NOAA) sea surface temperature
(SST) data, we studied the WPSH variability considering the background
of climate warming by using a Gaussian filter, moving averages,
correlation analysis, and synthetic analysis. Our results show that
with climate warming over the past 60 years, significant changes in the
WPSH include its enlarged area, strengthened intensity, westward
extended ridge point and southward expanded southern boundary, as well
as enhanced interannual fluctuations in all these indices. The western
ridge point of the WPSH consistently varies with temperature changes in
the Northern Hemisphere, but the location of the ridgeline varies
independently. The intensity and area of the WPSH were both
significantly increased in the late 1980s. Specifically, the western
ridge point started to significantly extend westward in the early
1990s, and the associated interannual variability had a significant
increase in the late 1990s; in addition, the ridgeline was swaying
along the north-south-north direction, and the corresponding
variability was also greatly enhanced in the late 1990s. With climate
warming, the SST increase becomes more weakly correlated with the WPSH
intensity enhancement but more strongly correlated with the westward
extension of the ridge point in the equatorial central and eastern
Pacific Ocean in winter, corresponding to an expanding WPSH in space.
In the northern Pacific in winter, the SST decrease has a weaker
correlation with the southerly location of the ridgeline but also a
stronger correlation with the westward extension of the ridge point. In
the tropical western Pacific in winter, the correlations of the SST
decrease with the WPSH intensity enhancement, and the westward
extension of the ridge point is strengthened. These observations can be
explained by strengthened Hadley circulations, the dominant effects of
the southward shift, and additional effects of the weakened ascending
branch of the Walker circulation during warm climatological periods,
which consequently lead to strengthened intensities, increased areas,
and southward expansions of the WPSH in summer. |
