摘要:本文采用1981～2010年夏季5～10月逐日的（10°S～50°N，40°E～160°E）范围内向外长波辐射OLR（Outgoing Longwave Radiation）资料和850 hPa层纬向风速资料（简称U850）作经验EOF（Empirical Orthogonal Function）分解，重新计算北半球夏季大气低频振荡BSISO（Boreal Summer Intraseasonal Oscillation）指数，并分析了其演变特征及其对华北夏季降水的影响规律。结果表明：（1）在北半球夏季印度洋—西北太平洋地区存在两种明显的低频信号，一种是BSISO1，空间分布呈西北—东南倾斜状，从热带印度洋向东北方向传播，振荡周期约为45 d；另一种是BSISO2，空间分布呈西南—东北倾斜状，从西北太平洋向西北方向传播，振荡周期约为20 d。（2）BSISO主要是通过影响大气环流和水汽输送来影响华北夏季降水过程。在500 hPa层，BSISO信号会造成华北地区东部副热带高压位置南北移动和强度发生变化来影响华北夏季降水；在850 hPa层，BSISO信号会通过伴随的气旋性或反气旋性异常环流影响向华北的水汽输送来影响华北夏季降水。（3）虽然热带大气季节内振荡MJO（Madden-Julian Oscillation）信号在全年都存在，但其变化在冬半年尤其冬季振幅最大，在夏季最小。BSISO信号变化在夏半年尤其夏季振幅最大。因此，利用热带大气低频信号开展延伸期降水过程预测，冬半年可以重点考虑MJO的影响，夏半年重点考虑BSISO的影响。
关键词:BSISO/
演变特征/
华北/
夏季降水/
影响机制
Abstract:This paper recalculates the BSISO (boreal summer intraseasonal oscillation) index by making an EOF (empirical orthogonal function) decomposition using the OLR (outgoing longwave radiation) data and 850-hPa zonal wind velocity (U850) data over (10°S–50°N, 40°E–160°E) from May to October in 1981–2010. The evolution characteristics of the BSISO and its influence on the summer precipitation in North China were analyzed. The results are as follows: (1) There are two obvious low-frequency signals in the Indian Ocean–Northwest Pacific region in summer. The first is the BSISO1, which is inclined from northwest to southeast and propagates from the tropical Indian Ocean to the northeast with an oscillation period of approximately 45 days. The second is the BSISO2, which is inclined from southwest to northeast and propagates from the Northwest Pacific to the northwest with an oscillation period of approximately 20 days. (2) The BSISO affects the summer precipitation process in North China mainly by influencing the atmospheric circulation and water vapor transport. At 500 hPa, the BSISO signal will cause the North–South movement and intensity change of the subtropical high in the east of North China to affect the summer precipitation in North China. At 850 hPa, the BSISO signal will affect the water vapor transport to North China through the associated cyclonic or anticyclonic anomalous circulation to influence the summer precipitation in North China. (3) Although the MJO signal exists throughout the year, its amplitude is largest in the winter half-year, especially in winter, and is lowest in summer. However, the amplitude of the BSISO signal is largest in the summer half-year, especially in summer. Therefore, the MJO and BSISO signals can respectively be taken into account in winter and summer when using low-frequency signals of the tropical atmosphere to predict the precipitation process in an extended range.
Key words:Boreal summer intraseasonal oscillation (BSISO)/
Evolution characteristics/
North China/
Summer precipitation/
Influence mechanism
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