The Patterns of Anomalous Climate and Their Pre-circulation Signals in November

Based on the stationery data of temperature and precipitation of 160 stations in China in November, the reanalysis data of 500 hPa geopotential height (GPH) of NCEP/NCAR, the four circulation patterns corresponding to the warm and wet, warm and dry, cold and wet, cold and dry in the monsoon regions over eastern China are analysed, and the previous and corresponding circulations are inspected with t-test method. The time series of positive station numbers about the temperature and precipitation are labeled as S₁ and S₂ respectively after removing long-term trend more than 9 years. Then the typical years according to the cold, warm, dry and wet patterns could be acquired by using the values of S₁+S₂ and S₁-S₂. In detail, the larger values of S₁+S₂ are defined as the warm and wet years, and the smaller values are defined as the cold and dry years. Meanwhile, the larger values of S₁-S₂ are represented as the warm and dry years, and the smaller values are represented as the cold and wet years. The results are as follows: The warm (cold) pattern takes on the inactive (active) blocking high over Ural Mountain and zonal (meridional) circulation prevails at middle and high latitudes. The dry (wet) type is corresponding to the weak (strong) and eastward (westward) of subtropical high in western North Pacific. The circulation difference of warm and dry pattern minus cold and wet pattern in t-test is in meridional direction, similar to the EU pattern. The circulation difference of warm and wet pattern minus cold and dry pattern in t-test is in zonal direction, similar to the anti-PNA pattern. The pentad running-mean of monthly circulation has significant differences for the warm and dry (cold and wet) type in the beginning time on 6, 11, 16 September and warm and wet (cold and dry) type in the beginning time on 11, 16 and 21 September which indicate that the previous circulation has significant implication for climate prediction. The characteristics of cold and wet (warm and dry) type are as below: On one hand, the GPH is high (low) at high latitude and low (high) at middle and low latitudes, and meanwhile AO is negative (positive), leading to low (high) temperature over northern China; on the other hand, the GPH is low (high) at the Qinghai-Tibet Plateau, and the active (inactive) southern branch trough induces the more (less) precipitation.