In a recent study
published in Advances in Atmospheric
Sciences, scientists from the CAS Institute of Atmospheric Physics investigate
the variations in the tropical ascending branches (TABs) of Hadley circulations
(HCs) during past decades, using NCEP, ERA-40 and JRA-55 reanalysis data. They
identified and analyzed trends and variability of the northern tropical
ascending branch (NTAB; range: 5°–15°N)
and the southern tropical ascending branch (STAB; range: 10°S–5°N),
which are defined as the ascending branches of the Northern Hemisphere HC and
Southern Hemisphere HC, respectively.
datasets consistently show a persistent increase in STAB during past decades,
whereas they show less consistency in NTAB regarding its decadal- to
multidecadal variability, which generally features a decreasing trend. These
asymmetric trends in STAB and NTAB can be attributed to asymmetric trends in
the tropical SSTs.
between STAB/NTAB and tropical SSTs was further examined regarding their
interannual and decadal- to multidecadal variability. On the interannual time
scale, STAB and NTAB are essentially modulated by the eastern-Pacific type of
ENSO, with a strengthened (weakened) STAB (NTAB) under El Ni?o conditions. On
the decadal- to multidecadal time scale, the variability of STAB and NTAB is
closely related to the southern tropical SSTs and the meridional asymmetry of
global tropical SSTs, respectively.
indicate that the tropical eastern Pacific SSTs (southern tropical SSTs)
dominate the tropical SST–NTAB/STAB relationship on the interannual (decadal-
to multidecadal) scale, whereas NTAB is a passive factor in this relationship.
Moreover, a cross-hemispheric relationship between NTAB/STAB and the HC
upper-level meridional winds is revealed.
diagram of asymmetric changes in STAB and NTAB due to asymmetric warming of
Sun, B., 2018: Asymmetric variations in the tropical ascending branches of Hadley circulations
and the associated mechanisms and effects. Adv.
Atmos. Sci., 35(3), doi:
10.1007/s00376-017-7089-z. (in press)