利用华北地区夏季日降水资料和NCEP/NCAR再分析环流资料, 采用功率谱分析、Butterworth带通滤波等方法, 对华北地区夏季降水低频特征与大气低频环流演变进行了综合分析。结果表明: (1)华北地区夏季降水存在低频特征, 主要以准双周振荡为主.(2)500 hPa高度场大气低频环流表现为闭合的高、低压系统; 850 hPa低频流场演变要复杂一些, 但它们伴随高层低频系统移动会发生有规律的变化。500 hPa高度场上, 在35°N以北, 低频系统向东移动, 有时也从鄂霍次克海附近向西的扩展; 在35°N以南, 低频系统表现为由西北太平洋向西北移动, 然后再向西移动。华北夏季降水主要是直接受中高纬度低频系统影响, 低纬度低频系统很难直接影响华北地区, 但它们可以通过偏南偏北气流的变化影响向华北地区的水汽输送或冷空气活动, 进而加强或减弱华北地区的降水强度。(3)当500 hPa 40°N60°N范围内有低频低压从西向东移近华北地区, 并诱发850 hPa气旋或切变线生成, 从而在华北地区出现明显的降水过程; 当500 hPa低频低压向东移出而后部低频高压移来时, 华北地区低层850 hPa流场就会转为辐散气流或为一致的偏北气流, 降水过程结束。(4)华北地区降水发生时, 高、低空低频环流有较好的配合。
Based on daily precipitation data over North China in summer and the NCEP/NCAR reanalysis atmospheric circulation data, by using of power spectral analysis, Butterworth band-pass filter and other related methods, the low-frequency characteristics of daily precipitation over North China in summer and the features of atmospheric low-frequency circulation evolutions are investigated. The results indicated that low-frequency characteristics of summer rainfall in North China is mainly quasi-biweekly oscillation. In making extended-range forecasts, in addition to focusing on 30-60 day atmospheric oscillation signal, we also should pay attention to quasi-biweekly atmospheric oscillation signal. On 500 hPa height field, atmospheric low-frequency circulation are closed high and low pressure systems, simple and easy to identify. On 850 hPa, low frequency current field changes are a bit more complicated, but they regularly change along with the high level low-frequency systems moving. On 500 hPa height field, north of 35°N, the low-frequency system moves eastward, sometimes extended from Okhotsk Sea to the west. However those south of 35°N appears to be from the Northwestern Pacific to northwest, and then moved to west. In North China, the summer precipitation is mainly directly affected by the low-frequency system from high latitudes, and those from low latitudes is difficult to directly affect the North China, but through changes of the southerly or northerly airstream they can effects water vapor transport or cold air activities to North China, thereby increasing or decreasing precipitation intensity in North China. When the low-frequency low pressure on 500 hPa within 40°N-60°N moving from the west to the east near North China, it will induce cyclone or shear line build on 850 hPa flow field, so obvious precipitation appears in North China. When the low frequency low pressure on 500 hPa moves eastward out of North China, on 850 hPa the low level flow field will switch to divergence field or a consistent northerly wind, precipitation process is finished. Precipitation occurs, the low-frequency circulation of high level and low level has a good matching, these can be applied to extended-range forecasts of summer rainfall over North China.
[1]郑志海. 月动力延伸预报研究进展回顾[J]. 气象科技进展, 2013, 3(1): 25-30.
[2]李泽椿, 毕宝贵, 朱彤, 等. 近30年中国天气预报业务进展[J]. 气象, 2004, 30(12): 4-10.
[3]康志明, 鲍媛媛, 周宁芳. 我国中期和延伸期预报业务现状以及发展趋势[J]. 气象科技进展, 2013, 3(3): 18-24.
[4]肖子牛. 我国短期气候监测预测业务进展[J]. 气象, 2010, 36(7): 21-25.
[5]丁一汇. 季节气候预测的进展和前景[J]. 气象科技进展, 2011, 1(3): 14-27.
[6]Miyakoda K, Hembree G D, Strickler R F, et al. Cumulative results of extended forecast experiments I. Model performance for winter cases[J]. Mon Wea Rev, 1972, 100(12): 836-855.
[7]Miyakoda K, Gordon T, Carerly R, et al. Simulation of a blocking event in January 1977[J]. Mon Wea Rev, 1983, 111(4): 846-849.
[8]张培群, 丑纪范. 改进月延伸预报的一种方法[J]. 高原气象, 1997, 16(4): 376-388.
[9]陈丽娟, 李维京. 月动力延伸期预报产品的评估和解释应用[J]. 应用气象学报, 1999, 10(4): 486-490.
[10]李维京, 陈丽娟. 动力延伸预报产品释用方法的研究[J]. 气象学报, 1999, 57(3): 338-345.
[11]陈伯民, 纪立人, 杨培才, 等. 改善月动力延伸预报水平的一种新途径[J]. 科学通报, 2003, 48(5): 513-520.
[12]何金海, 梁萍, 孙国武. 延伸期预报的思考及其应用研究进展[J]. 气象科技进展, 2013, 3(1): 11-17.
[13]Wheel M C, Hendon H H. An all-season real time multivariate MJO index: Development of an index for monitoring and prediction[J]. Mon Wea Rev, 2004, 132(8): 1917-1932.
[14]Jones C, Carvalho M V, Higgins R W, et al. A statistical forecast model of tropical intraseasonal convective anomalies[J]. J Climate, 2004, 17(11): 2078-2094.
[15]Galin M B. Study of the low-frequency variability of the atmospheric general circulation with the use of time dependent empirical orthogonal functions[J]. Atmos Oceanic Phys, 2007, 43(1): 15-23.
[16]杨玮, 何金海, 孙国武, 等. 低频环流系统的一种统计预报方法[J]. 气象与环境学报, 2011, 27(3): 1-5.
[17]信飞, 孙国武, 陈伯民. 自回归统计模型在延伸期预报中的应用[J]. 高原气象, 2008, 27(增刊1): 69-75.
[18]孙国武, 陈葆德. 青藏高原上空大气低频波的振荡及其经向传播[J]. 大气科学, 1988, 12(3): 250-256.
[19]孙国武, 信飞, 孔春燕, 等. 大气低频振荡与延伸期预报[J]. 高原气象, 2010, 29(5): 1142-1147.
[20]孙国武, 孔春燕, 信飞, 等. 天气关键区大气低频波延伸期预报方法[J]. 高原气象, 2011, 30(3): 594-599.
[21]孙国武, 冯建英, 陈伯民, 等. 大气低频振荡在延伸期预报中的应用进展[J]. 气象科技进展, 2012, 2(1): 12-18.
[22]丁一汇, 梁萍. 基于MJO的延伸预报[J]. 气象, 2011, 36(7): 111-122.
[23]梁萍, 丁一汇. 基于季节内振荡的延伸预报试验[J]. 大气科学, 2012, 36(1): 102-116.
[24]梁萍, 丁一汇. 强降水过程气候态季节内振荡及其在延伸期预报中的应用[J]. 高原气象, 2013, 32(5): 1329-1338, doi: 10.7522/j.issn.1000-0534.2012.00125.
[25]孙国武, 信飞, 陈伯民, 等. 低频天气图预报方法[J]. 高原气象, 2008, 27(增刊1): 64-68.
[26]孙国武, 李震坤, 信飞, 等. 延伸期天气过程预报的一种新方法——低频天气图[J]. 大气科学, 2013, 37 (4): 945-954.
[27]Kalnay E, Kanamitsu M, Kistler R, et al. The NCEP/NCAR 40–year reanalysis project [J]. Bull Amer Meteor Soc, 1996, 77(3): 437-472.
[28]魏凤英. 现代气候统计诊断与预测技术[M]. 北京: 气象出版社, 2007: 71-76.
[29]李崇银. 大气低频振荡[M]. 北京: 气象出版社, 1993: 12-18.
[30]温克刚, 臧建升. 中国气象灾害大典(河北卷)[M]. 北京: 气象出版社, 2008: 76-197.
[31]陈伯民, 信飞, 沈愈, 等. 月内重要天气过程与气候趋势预测系统及应用进展[J]. 气象科技进展, 2013, 3(1): 46-51.
[32]琚建华, 刘一伶, 李汀, 等. 预测夏季南海季节内振荡的一种新方法[J]. 热带气象学报, 2010, 26(5): 521-525.
