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Using the 1979-2009 NCEP/NACR reanalysis data and precipitation records in East China, research is performed of the climatological features of low-frequency oscillation (LFO) in OLR over the Maritime Continent (MC) as well as their associations with precipitation disturbance in the eastern part of China. Results suggest that in the MC there is significant climatological low-frequency oscillation (CLFO) in outgoing long-wave radiation (OLR), with the intraseasonal oscillation (30-60 days) being the strongest for April-September, and the MC acting as a high-value region of percentage contributions of low-frequency OLR variance. On the low-frequency time scale there occur four events of more intense active OLR during this time interval. In the January-April (May-August) phase, MC convection is relatively weak (vigorous). The CLFO makes pronounced eastward displacement at tropics, with phase propagation seen longitudinally, too. There occur low-frequency disturbance circulations similar to the EAP wavetrain or P-J teleconnection, starting from the MC via the South China Sea and the Philippines to the Yangtze valley of China. At different phases, the variation in the low-frequency circulations and heating fields shows that the rainfall disturbance in eastern China is likely to be under possible effects of the CLFO from the MC in April-September, and the low-frequency heating variation exhibits a meridional pattern as an EAP wavetrain or P-J teleconnection. As the OLR CLFO is in a peak (valley) phase the low-level divergence or convergence with the reversal at high levels over the MC is related to relatively feeble (robust) low frequency convection, thereby exciting an EAP or P-J wavetrain from the MC to the Sea of Japan. At the higher levels, the South-Asian high is eastward (westward) of normal due to effects of low-frequency cyclones (anticyclones), resulting in less (more) rainfall in the Jiangnan (areas in the middle and lower reaches of Yangtze and to the south of the river) and Hetao (the Great Bend of Yellow River) areas, and increased (decreased) rainfall in SW China, Qinghai Plateau and Gansu. At the conversion phases, low-frequency convection becomes more active in parts of the MC, consequently exciting low-frequency wavetrain of cyclones-anticyclones-cyclones at low levels, making the South-Asian high southward of the mean, so that strong convergent zones emerge in the upper and middle Yangtze basins and Jilin of NE China, responsible for plentiful precipitation there in sharp contrast to the rainfall over the band between the Yellow and Huaihe Rivers and the Yunnan-Guizhou Plateau. These results help understand in depth the climatological LFO characteristics and the phase-locked feature, thereby further improving our understanding of the causes of rainfall disturbances in different parts of the country. 相似文献
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利用风廓线雷达、微波辐射计、FY卫星亮温(TBB)及多普勒天气雷达探测等非常规资料,对2012年7月25日发生在天津沿海的一次特大暴雨过程进行分析和研究。结果表明:1)中尺度对流系统是造成暴雨的主要影响系统,地面中尺度辐合导致雷达回波列车效应从而产生区域性特大暴雨,强降水过程中50～55 dBZ强回波超过0℃层到达6.5 km高度,表现出高质心结构,雷达回波多仰角出现逆风区,持续时间近3 h,气旋式辐合增强,使对流有很强的组织性;2)暴雨过程伴随多个中尺度对流云团的强烈发展,成熟的对流云团冷中心温度达-63℃,云团后部温度等值线梯度大,对流旺盛,是引发强降水的关键;3)云液态水含量跃增与地面降水增强有直接关系,高液态水含量集中在0.8～1.6 km高度,强降水前湿层深厚,降水发生后湿层厚度迅速减小;4)风廓线雷达有能力捕捉到对暴雨预报有指示意义的信号,暴雨开始前约1～2 h边界层急流和低空急流建立,且低空急流在强降水发生前达到最强,暴雨开始前约1 h有中层弱冷空气侵入,暴雨开始前10～20 min急流可触发边界层扰动和低空扰动。 相似文献
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海洋性大陆区域OLR的气候低频振荡及其与中国降水的可能联系 总被引：1，自引：0，他引：1
利用1979—2009年NCEP/NCAR再分析资料和地面观测站降水资料,研究了海洋性大陆（Maritime Continent,MC）区域的低频振荡气候学特征及其与中国东部降水扰动的关系。结果表明:气候平均状况下MC区域存在显著的低频振荡（CLFO）,30～60 d季节内振荡在4—9月强度最大,且MC区域为低频OLR方差贡献率大值区。低频时间尺度上,MC区域OLR在4—9月有4次比较明显的活跃过程,在1～4（5～8）位相,对流相对较弱（活跃）。OLR的CLFO在热带地区显著东传,在南北方向亦存在位相的传播。从MC区域经南海、菲律宾群岛至中国长江流域存在类似于EAP波列（或P-J型遥相关）的扰动环流分布。不同位相上,低频环流及加热场的变化表明,中国降水的扰动在4—9月间受到MC区域CLFO的可能影响。低频热力场在南北方向上呈现EAP波列状或P-J型遥相关状分布。在OLR的CLFO的峰（谷）位相时,MC区域低层辐散（辐合）,高层辐合（辐散）,低频对流相对较弱（较强）,在MC区域至日本海激发EAP波列（或P-J型遥相关）;在对流层上层南亚高压因低频气旋（反气旋）而位置偏东（偏西）;中国的江南及河套地区降水偏少（偏多）,西南及青海、甘肃等地降水增加（减少）。在转换位相时,MC区域低频对流在部分地区更为活跃,在对流层低层激发低频的气旋-反气旋-气旋的波列,南亚高压偏南,长江中上游、吉林地区出现明显的辐合区,降水偏多,黄淮之间及云贵地区降水偏少。这些结果有助于人们深刻认识气候学意义上的低频振荡特征及LFO的季节锁相问题,有利于进一步认识中国不同地区降水扰动的成因。 相似文献
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2016年7月24日下午,天津大港地区出现极端强降水,最大雨强为95.0 mm·h~(-1),突破了当地近10 a以来的极值。利用逐分钟加密自动站、探空、雷达、微波辐射计等多种观测资料,对造成此次短时强降水超级单体雷暴的生成环境及结构进行了定性和定量分析,结果表明:(1)超级单体的演变过程为,地面辐合线触发了雷暴生成,雷暴形成的冷池出流边界触发新雷暴生成,新雷暴不断合并、发展、加强为超级单体。(2)极端强降水发生之前3 h,来自渤海的海风具有冷湿性质,它起到"冷垫"和输送水汽的作用。(3)超级单体表现为高质心发展,其强回波核由低到高向右侧偏移,有界弱回波区、后侧入流缺口及悬垂结构明显,弱中气旋维持4个体扫,且旋转速度为16 m·s~(-1),核区直径为40 km,伸展高度为13 km,始终处在强降水的包裹中。雷达回波参数V50(反射率大于等于50 dBz的体积)达到最大值之前,回波变率参数FV50(50 dBz回波体积6 min的变化)出现了"突降",这对单体即将发展有预警意义。(4) 6 min内强降水量与低层水汽密度垂直递减率、单体有效厚度和有效面积有较好的对应。 相似文献
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