ENSO Impact On The Winter Synoptic-scale Air Temperature Variability Over China And Its Possible Mechanism

Based on the daily average temperature data of 753 stations,the NOAA rebuilds monthly sea surface temperature data,the NCEP/NCAR reanalysis data and the atmospheric circulation model tests from 1960 to 2017.The present study analysis the spatiotemporal characteristics of the winter synoptic-scale air temperature variability over China and its relationship with ENSO events.The different effects of two types of ENSO events on the winter synoptic-scale air temperature variability over China are explored,And analyze the characteristics of the interdecadal variation and possible causes of the influence of ENSO on the winter synopticscale air temperature variability.The main conclusions are as follows:(1)ENSO has a significantly positive correlation with the winter synoptic-scale air temperature variability in a large area of eastern China.The fluctuation of temperature and the synoptic-scale air temperature variability is usually stronger than normal during El Ni?o winters.In contrast,the synoptic-scale air temperature variability is weakened during La Ni?a winters.Further research found that during the El Ni?o winters,the meridional temperature gradient in the middle and high latitudes of Eurasia is strengthened,leads to the enhanced local atmospheric baroclinicity according to the thermal wind relationship thus further increase the storm activity in the Siberian region and the synoptic-scale variation of the atmospheric circulation in the East Asia region.Correspondingly,the synoptic-scale air temperature variability is enhanced in most of China.Roughly opposite mechanisms also apply during the La Ni?a winters.The sensitivity test verified the modulation of ENSO on the winter synoptic-scale air temperature variability over China.(2)Two types of ENSO events have different effects on the winter synoptic-scale air temperature variability over China.During the EP ENSO years,the two show a significant positive correlation;conversely,in the CP ENSO winter,the response is weak,with only a few sites passing the significance test.Further analysis found that,during the EP ENSO years,the synoptic-scale transient vortex activity in the Siberian region has significantly strengthened,and the synoptic-scale variability of the atmospheric circulation in the downstream East Asia region has also increased,which in turn led to an increase in the synoptic-scale temperature variability over China.However,in CP ENSO years,due to the weak and north-centered anomalous activities of the transient vorticity,the response of the synoptic-scale air temperature variability over China is weak.(3)The relationship between ENSO and synoptic-scale air temperature variability has obvious interdecadal characteristics.Before the 1990 s,there was a significant positive correlation between the two,but this positive correlation has weakened significantly since 1990,and it is not statistically significant.The study found that is closely related to the change of ENSO type after the 1990 s,The effects of different types of ENSO events on the temperature variability are significantly different,CP ENSO have increased significantly since the 1990 s,which is an important reason for the interdecadal weakening of the relationship between ENSO and the winter synoptic-scale air temperature variability.