Climatic variability in the meridional mode of global atmospheric circulation during recent 60 years
近60年全球大气环流经向模态的气候变化

The climatic variability in the meridional mode of global atmospheric circulation is investigated by using the monthly geopotential height fields at 1000,500,and 100 hPa during 1948 and 2004.The data are taken from the NCEP/NCAR Reanalysis.The leading meridional mode shows opposite characteristics in its spatial and temporal distributions at the high and low latitudes at the three levels.The latitude differences are significantly enlarged in recent 60 years.An abrupt change occurred in the mid-1970s,leading the phases of the first mode reversed at the low and high latitudes in both hemispheres.The variability is generally larger in Southern Hemisphere(SH) at 1000 and 500 hPa,but in Northern Hemisphere(NH) at 100 hPa.In contrast,the second meridional mode shows different features in its spatial and temporal distributions.It mainly manifests as the AAO and AO at 1000 and 100 hPa.The two oscillations have a negative correlation at interannual and interdecadal scales,and show strong anti-phase variations at the SH and NH high latitudes at 100 hPa level,suggesting that the mode could connect the SH and NH circulation at mid-and high latitudes and affect global climate change.