Abstract
The Northeastern China Cold Vortex (NCCV) processes during the early summer periods (June) from 1979 to 2018 were objectively identified in this study by using the daily precipitation data in Northeastern China (NEC), along with the six-hourly atmospheric circulation fields of ERA Interim/ECMWF, and the temperature field data and monthly mean sea surface temperature field data reconstructed by NOAA. Then, the NCCV processes from the objective identifications were divided into the Southern Cold Vortex (SCV) and the Northern Cold Vortex (NCV) according to the positions of their activity trajectories in the NEC geographical range. Next, an index was defined which could better represent the frequencies and intensities of the SCV and NCV. Relationships between the indices of the SCV and NCV and atmospheric circulation fields during the early summer months and the early SST fields were analyzed. Finally, the results of the sensitivity test of the AM2.1 model were used to verify the statistical analysis results. It was found that the SST factor impacting the intensity of the SCV was the North Atlantic Tripole (NAT) in early April. The anomalies of the NAT in April forced the formation of the “high-low pressure cooperation types” in early summer, which resulted in the intensity anomalies of the SCV. The SST factors impacting the intensity of the NCV were the south-north inverse SSTs of the Northwest Pacific (March) and the SSTs of the tropical Southeast Pacific (May). During the two examined periods of 1979 to 1999 and 2000 to 2018, the south-north inverse SST anomalies in the Northwest Pacific in March, as well as the SST anomalies in the tropical Southeast Pacific in May, were observed to have forced the formations of “double blocking low vortex types” and EAP teleconnection types during the early summer months, which resulted in anomalies in the NCV intensities. AM2.1 model was found to have good simulation effects regarding the observed impact results of the SSTs on the early circulation types during the early summer months, which further supported the conclusions achieved from the statistical analysis results.
Highlights
The Northeastern China (NEC) region is the largest commodity grain base in China, and early summer is the growing season of the crops
The Northeastern China Cold Vortex (NCCV) processes were objectively identified by an improved objective identification method, and divided into Southern Cold Vortex (SCV) and Northern Cold Vortex (NCV)
This study adopted statistical analysis and numerical simulation methods in order to examine the mechanisms of the influences of the Sea surface temperature (SST) in the early stage, as well as the atmospheric circulation fields during the early summer months, on the intensities of the SCV and NCV
Summary
The Northeastern China (NEC) region is the largest commodity grain base in China, and early summer is the growing season of the crops. Wang et al (2018) and Chen et al (2018), respectively, revealed the relationships between the surface thermal factors of Western Asia during the spring months and the downstream atmospheric circulation activities, and investigated their impacts on the NCCV activities and precipitation values in the NEC region in early summer. Fang et al (2018) carried out diagnostic analyses and numerical simulations of the causes of precipitation anomalies in the NEC region in early summer It was pointed out in the aforementioned study that the anomalies of the North Atlantic Tripole (NAT) and the SSTs of the Kuroshio area were the possible factors causing the anomalies of circulation systems, such as the NCCV activities during the early summer months, as well as the high blocking pressure in the upper and lower reaches, and so on.
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