Low-Level Jets Over the Bohai Sea and Yellow Sea: Climatology, Variability, and the Relationship With Regional Atmospheric Circulations

Abstract

The present study reveals climate features of low-level jets (LLJs) over the Bohai Sea and Yellow Sea (BYS) based on a 35-year (1979–2013) high-resolution (7 km) atmospheric hindcast. The regional climate model COSMO-CLM driven by the ERA-Interim reanalysis data set was used to obtain the hindcast. Through comparison with observations, the hindcast was proved to robustly reproduce the climatology, the diurnal cycle, the variability of wind profiles, and specific LLJ cases. LLJs over the BYS feature a strong diurnal cycle, intra-annual, and interannual variability but weak decadal variability. LLJs are more frequent in April, May, and June (LLJ season) and less frequent in winter over the Bohai Sea and western coastal areas of the Yellow Sea, which is due to the intra-annual variations of large-scale circulation and local land-sea thermal contrast. In the LLJ season, the heights of jet cores are generally lower than 500 m above sea level. The maximum wind speed of LLJs is mostly in the range of 10–16 m/s, and prevailing wind directions are southerly and southwesterly. The LLJs are of the nocturnal type, with the highest occurrence frequency at approximately 2300 local time. Furthermore, a low-frequency link between anomalies of LLJ occurrence and regional large-scale barotropic circulation was identified using canonical correlation analysis and associated correlation patterns. Pressure systems over the East Asia-northwest Pacific region are significantly correlated with the variations of LLJ occurrence over the BYS in terms of the intra-annual and interannual variability.