摘要
This study investigates the variations in the tropical ascending branches （TABs） of Hadley circulations （HCs） during past decades, using a variety of reanalysis datasets. The northern tropical ascending branch （NTAB） and the southern tropical ascending branch （STAB）, which are defined as the ascending branches of the Northern Hemisphere HC and Southern Hemi- sphere HC, respectively, are identified and analyzed regarding their trends and variability. The reanalysis 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 are attributed to asymmetric trends in the tropical SSTs. The relationship between STAB/NTAB and tropical SSTs is further examined regarding their interannual and decadal- to multidecadal variability. On the interannual time scale, the STAB and NTAB are essentially modulated by the eastern-Pacific type of ENSO, with a strengthened （weakened） STAB （NTAB） under an E1 Nifio condition. 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. The tropical eastern Pacific SSTs （southern tropical SSTs） dominate the tropical SST-NTAB/STAB relationship on the interannual （decadal- to multidecadal） scale, whereas the NTAB is a passive factor in this relationship. Moreover, a cross-hemispheric relationship between the NTAB/STAB and the HC upper-level meridional winds is revealed.
This study investigates the variations in the tropical ascending branches （TABs） of Hadley circulations （HCs） during past decades, using a variety of reanalysis datasets. The northern tropical ascending branch （NTAB） and the southern tropical ascending branch （STAB）, which are defined as the ascending branches of the Northern Hemisphere HC and Southern Hemi- sphere HC, respectively, are identified and analyzed regarding their trends and variability. The reanalysis 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 are attributed to asymmetric trends in the tropical SSTs. The relationship between STAB/NTAB and tropical SSTs is further examined regarding their interannual and decadal- to multidecadal variability. On the interannual time scale, the STAB and NTAB are essentially modulated by the eastern-Pacific type of ENSO, with a strengthened （weakened） STAB （NTAB） under an E1 Nifio condition. 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. The tropical eastern Pacific SSTs （southern tropical SSTs） dominate the tropical SST-NTAB/STAB relationship on the interannual （decadal- to multidecadal） scale, whereas the NTAB is a passive factor in this relationship. Moreover, a cross-hemispheric relationship between the NTAB/STAB and the HC upper-level meridional winds is revealed.
基金
supported by the National Natural Science Foundation of China (Grant Nos. 41421004 and 41210007)
the Atmosphere–Ocean Research Center (AORC) and International Pacific Research Center (IPRC) at the University of Hawaii
the General Program of Natural Science Foundation of Higher Education of Jiangsu Province (Grant No. 3KJB170012)
