Seasonality of Interannual Inter-hemispheric Oscillations over the Past Five Decades |
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| Authors: | GUAN Zhaoyong LU Chuhan MEI Shilong and CONG Jing |
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| Institution: | Key Laboratory of Meteorological Disaster of Ministry of Education, College of Atmospheric Sciences, Nanjing University of Information Science and Technology, Nanjing 210044,Key Laboratory of Meteorological Disaster of Ministry of Education, College of Atmospheric Sciences, Nanjing University of Information Science and Technology, Nanjing 210044,Weather Service Division of Jiaxing Meteorological Bureau, Jiaxing 314000,Dalian Municipal Meteorological Bureau, Dalian 116001 |
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| Abstract: | Air mass is inter-hemispherically redistributed, leading to an interesting phenomenon
known as the Inter-Hemispheric Oscillation (IHO). In the present article, the seasonality of the
interannual IHO has been examined by employing monthly mean reanalyses from NCEP/NCAR, EAR40, and
JRA25 for the period of 1958--2006. It is found that the IHO indices as calculated from different
reanalyses are generally consistent with each other. A distinct seesaw structure in all four seasons
between the northern and southern hemispheres is observed as the IHO signature in both the surface
air pressure anomalies (SAPAs) and the leading EOF component of the anomalous zonal mean quantities.
When the SAPAs are positive (negative) in the northern hemisphere, they are negative (positive) in
the southern hemisphere. Large values of SAPAs are usually observed in mid- and high-latitude areas
in all but the solstice seasons. In boreal summer and winter, relatively stronger perturbations of
IHO-related SAPA are found in the Asian monsoon region, which shows a large difference from the
status in boreal spring and fall. This suggests that seasonal mean monsoon activity is globally linked
via air mass redistribution globally on interannual timescales, showing a very interesting linkage
between monsoons and the IHO in the global domain. In all seasons, large values of SAPA always exist
over the Antarctic and the surrounding regions, implying a close relation with Antarctic oscillations. |
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| Keywords: | inter-hemispheric oscillation seasonality interannual variability surface air pressure anomaly |
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