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.

Characteristics of Coastal Low‐Level Jets in the Bohai Sea, China, During the Early Warm Season

“…By contrast, the proportion of wind from other directions is far smaller than that from the southwest. This consequence is similar to the 35‐year regional climate model analysis in Bohai Sea (Li et al, ). It should be noted that in our analysis, days with background winds from nonsouthwesterly directions are filtered out to avoid confusion among different wind directions.…”

How Will a Warming Climate Affect the Benguela Coastal Low‐Level Wind Jet?

“…In the EBUS regions, the feedbacks between atmosphere, land, and ocean play a crucial role in defining the respective regional climates. However, CLLJs can also be found along the southeast Arabian Peninsula (Ranjha et al, 2015) and over the Bohai Sea and Yellow Sea (D. Li et al, 2018). Along the EBUSs, the sea surface temperature (SST) decreases due to upwelling, which leads to a reduction of the evaporation over the ocean and subsequently to less water vapor content in the marine atmospheric boundary layer (MABL).…”

“…Coastal jets are usually found along the equatorward eastern boundary currents (California, Canary, Humboldt, Benguela, and West Australia), due to a large-scale synoptic forcing Ranjha et al, 2013;Winant et al, 1988). However, CLLJs can also be found along the southeast Arabian Peninsula (Ranjha et al, 2015) and over the Bohai Sea and Yellow Sea (D. Li et al, 2018). The synoptic forcing of the eastern boundary currents CLLJs is characterized by semipermanent high-pressure systems over the ocean and the thermal low over land, resulting in strong coastal parallel winds.…”

State and Perspectives of the Concept of Large‐Scale Conditioning of Regional Climate Modelling

“…Furthermore. Li et al (2018) proved the hindcast can reproduce the climatology, the diurnal cycle, the variability of wind profiles, and specific low level jet (LLJ) cases, which are mesoscale-flow phenomena with horizontal wind maxima within the lowest few kilometers of the troposphere. Long-term statistics of LLJs reveal that they feature a strong diurnal cycle, intraannual, and interannual variability but weak decadal variability.…”

“…A climatology of Polar Lows in the North Atlantic was obtained by implementing this method , and later of Polar Lows in the North Pacific (Chen and von Storch, 2013), of Medicanes in the Mediterranean Sea (Cavicchia et al, 2014a), and of Coastal Low Level Jets in the Bohai / Yellow sea region (Li et al, 2018). The methodology has matured now and is routinely used in many applications -mainly for deriving atmospheric states in the past decades.…”