Significant relationship between Hadley circulation and North Pacific Oscillation

The present study addresses the variability of Northern Hemispheric Hadley circulation and North Pacific Oscillation (NPO) in winter and their relationship, employing NCEP/NCAR data for the period 1954 similar to 2003. In this research, the index for Hadley circulation intensity is defined as the maximum positive value of the zonal mean streamfunction occurring within the latitudinal zone of 0 degrees similar to 30 degrees N, and index for NPO as normalized sea level pressure (SLP) difference between the region (20 degrees N, 180 degrees similar to 160 degrees W) and the region (60 degrees N, 180 degrees similar to 160 degrees W). Results show that the change of Hadley circulation is similar to that of NPO. They both exhibit apparent interannual and interdecadal variability, with a negative phase before the 1970s and a positive phase after the 1980s. In addition, there exist increasing linear trends for Hadley circulation and NPO. Hadley circulation is significantly and positively correlated to NPO on the interannual and interdecadal timescale. Due to the high comparability, the spatial structures associated with Hadley circulation and NPO are also alike over the Pacific. It is also suggested that the anomaly of the descending branch in 10 degrees similar to 30 degrees N and the ascending branch in 40 degrees similar to 60 degrees N over the Pacific may be responsible for the linkage of Hadley circulation to NPO.