利用MERRA再分析资料,选取2007年江淮梅雨作为研究个例,通过对上对流层、下平流层(UTLS)区域3种化学示踪物(臭氧、一氧化碳和水汽)及位涡的水平与垂直分布变化的分析,探讨梅雨发生前后梅雨区上空的平流层-对流层物质交换(STE)特征.研究表明,梅雨期存在由对流层顶折卷造成的跨越对流层顶向下的物质传输和对流活动引起的物质向上传输.入梅前,主要是由对流层顶折卷造成的物质向下传输(至少能达到300hPa),这一过程导致对流层中上层存在高浓度臭氧及一个干层;随后,伴随梅雨的发生,对流活动频繁出现,对流层顶开始抬升,在入梅第二天已经恢复到对流层顶折卷过程发生之前的高度,对流层内的高浓度臭氧和干层也随对流层顶折卷的东移而移出梅雨区.还通过分析梅雨区臭氧和整个亚洲夏季风区臭氧的相对变化量发现,整个梅雨期的STE为物质的向下传输,在UTLS区,梅雨区对亚洲夏季风区的STE贡献为跨越对流层顶向下传输.
Using the MERRA reanalysis data,the details of the Stratosphere-Troposphere Exchange (STE) during Meiyu season was analyzed by investigating variations of O3,CO,H2O,and tropopause height.The results show that there were both downward transport from stratosphere to troposphere because of tropopause folding event and upward transport due to convections over Meiyu region during the Meiyu season.Before Meiyu onset,the main transport over this region was downward which is attributed by tropopause fold.It contributed relative high ozone and a dry layer in middle and upper troposphere.The downward transport could reach at least 300 hPa.When Meiyu was onset,the tropopasue lifted because of frequent convections.On the second day after Meiyu onset,the tropopause height was approximately that at six days before the Meiyu onset.Stratospheric air with high ozone concentration and low water vapor moved easterly with the tropopause fold gradually.We further studied the relative variation of STE between Meiyu region and Asian monsoon region to diagnose the impact of STE during Meiyu season on that of the whole Asian summer monsoon season.It is found that the STE of Meiyu region over Meiyu season was downward mass flux by comparing the concentration of ozone in Meiyu region and Asian monsoon region.