东北地区冬季降雪的集中度和集中期变化特征

应用1961-2005 年东北地区冬季的台站降水资料,计算并分析了东北地区降雪集中度和集中期的时空变化特征和集中度偏高时的环流特征.结果表明,东北地区降雪集中度呈逐年上升趋势,集中期呈明显下降趋势。从年代际变化上来看,集中期存在着12 年的长周期,在1970 年代中期之后存在8 年左右的短周期。从空间变化的情况来看,东北地区冬季降雪集中度由东向西依次增加,吉林的东部地区出现集中度最低值,辽宁中部、吉林中部存在着集中期的高值中心。对于东北不同区域,东北东部和中部变化趋势一致,集中度呈上升趋势,集中期呈下降趋势。东北西南部和东北北部降水集中度均呈微弱的上升趋势,其中东北西南部地区降雪的集中度上升趋势最弱。东北北部降水集中期的下降趋势最弱。在影响东北降雪集中度偏高时,在高空500 hPa 东北地区均处于东亚大槽控制,东亚大槽在东北西部加深,而在东北东部有高压易于形成并加强,导致东亚大槽东移缓慢。高、低空急流均明显存在,与低空急流相比,高空急流更强,位置偏西南。在太平洋上水汽输送的高值区明显增强,范围也增大,东北地区受沿高值中心北侧向西北向输送的水汽影响。

Variations of Winter Snow Concentration Degree and Snow Concentration Period in Northeast China

Based on 1961-2005 observed winter precipitation data in Northeast China, the temporal and spatial variations of precipitation concentration degree (PCD) and precipitation concentration period (PCP) are computed and analyzed, together with the circulation characteristics when there is a higher PCD. Results show that the PCD in Northeast China presents a yearly rising tendency and the PCP decreases obviously. In terms of decadal variation, there is a 12-year periodic variation in PCP, and since the mid-1970s there has been an 8-year short periodic variation. As to spatial variation, the PCD in winter of Northeast China has increased gradually from the eastern to western part, and the minimum value of PCD occurs in the east of Jilin Province, while the high value center is observed in the central part of the province. For the whole Northeast China, the variation tendencies are consistent in the eastern and central parts. The PCD presents a rising tendency and the PCP shows a decreasing tendency. The PCD in the southwestern and northern parts has a slight rising tendency, with the PCD in the southwestern part having the slightest increasing tendency, and the PCP in the northern part showing the slightest decreasing tendency. When a high PCD value is observed, the areas are controlled by the East Asian deep trough at 500 hPa, and the trough becomes deeper in the western part, while a high pressure, which is easily formed and intensified in the eastern part, makes the East Asia deep trough move eastward slowly. Upper-level jet stream and low-level jet stream co-exist, and the former is stronger and takes more of a southwestward position than the latter. Over the Pacific the high value extent of water vapor transport is intensified obviously, and the extent also increases. Northeast China is influenced by the water vapor transported to the northwest along the north of the high value center.