Analysis of the Characteristics of the Boundary Layer Jet in the Middle
reaches of the Yangtze River during the Meiyu season
Abstract
The Low-level Jet (LLJ) in the Yangtze River Basin during the Meiyu
season is analyzed and studied mostly as the atmospheric circulation
background of precipitation, which cannot adequately reflect the
characteristics of the jet itself. In this paper a fusion of sounding
observations and precipitation data from Wuhan Station during the Meiyu
season in 2010 are used to analyze the characteristics of the LLJ in the
middle reaches of the Yangtze River. The results show that: the vertical
structure of the LLJ is characterized by the predominance of a
Boundary-layer Jet (BLJ) with an occurrence height concentrated in the
300-1200 m. The BLJ occurs most frequently at 22:00 at night, but most
strongly at 01:00 at night, with resultant wind velocities exceeding 14
m/s. A Synoptic-system-related Low-Level Jet (SLLJ) occurs most
frequently at 07:00 during the day, but most strongly at 10:00, with
resultant wind velocities exceeding 12 m/s. For both the BLJ and SLLJ,
the wind direction is characterized by southwesterly winds. However, the
wind direction of the SLLJ is more westerly relative to the BLJ, and the
northeasterly direction of the SLLJ occurs significantly more
frequently. The analysis of four typical cases of heavy precipitation in
the middle reaches of the Yangtze River shows that before the onset of
heavy precipitation, a LLJ exists in the precipitation center and at its
south side. The SLLJ is dominated by southwesterly winds, and the BLJ
has more southerly wind component with the BLJ developing earlier than
the SLLJ.