基于NCEP FNL资料的环渤海地区低空急流的时空分布特征

Spatial and temporal characteristics of low-level jet over the Bohai rim from the NCEP FNL global analysis data

利用2008年NCEP FNL全球分析资料,研究了环渤海地区低空急流的时空特征,并与探空资料结果进行对比。结果表明：环渤海地区低空急流的日变化特征明显,18时（世界时）达到最大;季节变化非常明显,春季出现的次数最多;它的风速范围为12-14 m/s,风向以SW为主,主要出现在925 h Pa上;环渤海地区低空急流在西北部以高层（700和850 h Pa）为主,在东北部和南部以低层（925 h Pa）为主;在700 h Pa上,各时次出现低空急流的个数差异不大,在850 h Pa上出现低空急流最多的时次主要是12时,在925 h Pa和1 000 h Pa上出现低空急流最多的时次是18时;由高层到低层,低空急流的中心由西北部逐渐向东北部移动,低空急流的强度在春季逐渐增强,在秋冬季逐渐减弱。NCEP FNL分析资料能够捕捉到更多的低空急流。

Spatial and temporal characteristics of low-level jet（ LLJ） are derived from four times per day NCEP FNL operational global analysis data in 2008 over the Bohai rim. Comparison between the conclusion and the analysis results obtained from twice-daily radiosonde data indicates that NCEP FNL analysis data are able to capture more LLJs. The results show that the frequency of LLJ over the Bohai rim has evident diurnal and seasonal variations reflected in that the LLJ occurred more frequently at 1800 UTC and in spring,respectively. The wind speed of LLJ is mainly around 12—14 m / s,the wind direction of LLJ is predominately from SW,and the height of LLJ mostly occurs at 925 h Pa. The LLJ in the northwest of Bohai rim are usually found at high level（ 700 h Pa and 850 h Pa）,while in the northeast and south of Bohai rim,it typically occurs at the lower level（ 925 h Pa）. Small differences in the number of LLJ occues at each times at 700 h Pa. LLJ frequently happens at 850 h Pa at 1200 UTC,but at 925 h Pa and 1 000 h Pa at1800 UTC. From the high level to the low level,the center of LLJ over the Bohai rim gradually moves toward northeast from northwest,and LLJ＇s intensity gradually increases in spring and decreases in autumn and winter.