Multi-decadal Variability of Precipitation in Arid and Semi-Arid Region of Northern China and Its Relationship with Pacific Decadal Oscillation Index

Based on GPCC_V7 (Global Precipitation Climatology Centre Version 7) and ERA-20C (European Centre for Medium-Range Weather Forecasts atmospheric reanalysis of the 20th century) monthly precipitation data, multi-decadal variability (MDV) of precipitation in arid and semi-arid region of northern China and the relationship between MDV and Pacific Decade Oscillation (PDO) are analyzed using ensemble empirical mode decomposition (EEMD) and composition analysis methods. The result shows that precipitation in arid and semi-arid region of northern China has a multi-decadal variability with an average period of about 50-60 years, which may be modulated by PDO. Precipitation in northern Xinjiang and the Inner Mongolia are significantly positively correlated with PDO, while that in eastern and western Ordos Loop region is significantly negatively correlated with PDO. Further study shows that meridional circulation intensifies during positive PDO phase, leading to more southward water vapor transport from the Arctic Ocean. As a result, precipitation in Xinjiang increases due to the convergence of cold, moist northwesterly flow from the Arctic Ocean and warm, moust southwesterly flow from Arabian Sea in southern Xinjiang. On the other hand, convective heating over the equatorial western Pacific Ocean and Indian Ocean leads to the Pacific Japan/East Asia-Pacific(PJ/EAP) pattern of teleconnection. It is favorable for the transport of moist airmass from Bohai Sea to its northern area and increases precipitation there during positive PDO phrase. Besides, the moist northerly flow from Bohai and westerly flow converges in the northern Ordos Loop area, where a maximum precipitation center forms. The situation is opposite during negative PDO phrase.