Characteristics of Change in the Onset Dates of Spring and Its Early Signals in Northeast China

Using CN05.1 daily mean temperature data with a horizontal resolution of 0.25°×0.25° for the period 1961–2020, daily NCEP/NCAR reanalysis data, and daily sea surface temperature (SST) data from NOAA, this paper explored the variation characteristics of the onset dates of spring and their early signals over Northeast China (NEC). It was revealed that (1) the spatial distribution characteristics of the onset dates of spring over NEC showed a progressively later pattern from south to north. The maximum spring area was primarily concentrated in the 26th and 27th pentads, and the advanced trend was evident in the recent 60 years. (2) In the years with early-starting spring, positive temperature and precipitation anomalies emerged in March over NEC and an “Ω” circulation pattern at 500 hPa was observed over the West Siberian Plain, Baikal, and Kamchatka Peninsula. Meanwhile, in the years with late-starting spring, negative temperature and precipitation anomalies were found in March over NEC, and a high-pressure ridge in the Ural Mountains was observed, with a large-scale tilted ridge on the east side, which lasted from the 22nd pentad to the 26th pentad. (3) La Niña-related SST anomalies were found over the equatorial central eastern Pacific, while positive ones were observed in the ocean south of Greenland and east of the Philippines in the years of early-starting spring, which was opposite in the years of late-starting spring. In addition, by correlation analysis, SST anomalies during the preceding winter (i.e., December–January–February, referred to as DJF) in the ocean south of Greenland and east of the Philippines had a better indication for the onset dates of spring.