摘要
利用1948 2011年NCEP/NCAR逐月再分析海平面气压场资料计算了北太平洋涛动指数NPOI,研究NPOI与华北地区夏季(6 8月平均)帕默尔干旱指数PDSI的关系。结果表明,5月北太平洋涛动与华北夏季旱涝有较好的正相关关系。NPOI正(负)位相异常年,PDSI偏大(小),华北地区夏季偏涝(旱)。可能的环流机制分析表明,NPOI正(负)位相异常年,850 hPa风矢量距平场上乌拉尔山、贝加尔湖及西太平洋附近地区分别为反气旋(气旋)、气旋(反气旋)、反气旋(气旋)距平环流,共同加强了低层西南暖湿气流在华北地区的辐合(辐散);欧亚500 hPa位势高度距平场上分别呈现"+-+"("-+-")波列分布,西太平洋副热带高压强度偏强(弱),位置偏西(东)偏北(南),冷暖气流活动使华北多(少)雨。整层水汽输送来自阿拉伯海和孟加拉湾及西太平洋上空,使华北为水汽输送正距平中心,降水偏多;华北水汽通量散度为负值,为水汽汇区,易于降水,阿拉伯海、孟加拉湾、中南半岛南部至南海及西太平洋地区为强水汽辐散中心,是影响华北地区重要的水汽来源。前冬太平洋海温异常对5月北太平洋涛动有强迫作用,继而影响华北地区夏季旱涝。
The relationship between the North Pacific Oscillation( NPO) in May and the summer drought /flood in North China was analysed using the NCEP /NCAR month by month reanalysis data from 1948 to 2011 including sea level pressure,500 hPa geopotential height,specific humidity( 8 layers) and wind field( 8 layers). The North Pacific Oscillation Index( NPOI) which reflects the changes of the sea level pressure in North Pacific was calculated firstly. Then the correlation coefficient between NPOI and Palmer Drought Severity Index( PDSI)which represents the situation of summer drought /flood in North China from 1960 to 2011 was also calculated.The results show that there is a positive correlation between NPO and summer drought /flood in North China.When in positive NPOI years,PDSI in summer is higher than normal,and North China has more summer floods; otherwise,in negative NPOI years,PDSI in summer is lower than normal,and North China has more summer droughts. In order to explain the positive correlation between NPO and summer drought /flood in North China,wind vector field on 850 hPa and geopotential height field on 500 hPa were composite analysed,respectively,and compare the different intensity,area and position of western boundary of Western Pacific Subtropical High( WPSH) when NPO is in different strength( weak and strong). The possible circulation mechanism is that when in positive( negative) NPOI years,on lower layer( 850 hPa wind field),the common action of anti-cyclonic( cyclonic) in Ural Mountains,the cyclone( anti-cyclonic) of Lake Baikal,and the anti-cyclonic( cyclonic) anomaly circulation in West Pacific have strengthened( weakened) the convergence of south-west warm and humid air flows of low layer in North China region. And also,when in positive( negative) NPOI years,500 hPa geopotential height anomaly shows ‘+-+'( ‘-+-') wave train,and WPSH is stronger( weaker) shifting northwest( southeast) than normal years,cold and warm air activities make more( less) rainfall in North China.Vertically intergraded moisture fluxes was calculated,in order to show water transportation of summer drought /flood in North China and study the relationship between NPO in May and sea surface temperature in winter by using composition method. In the difference of vertically intergraded moisture fluxes field in summer,the moisture transport from the Arabian Sea and Bay of Bengal and the West Pacific make North China the positive anomaly of water vapor moisture,so there is more rainfall in North China; In divergence field,the water vapor divergence is negative in North China,so it is moisture sink and there is more rain. And also the Arabian Sea,Bay of Bengal,the south of Indo-China Peninsula to the South China Sea and the Western Pacific are the water vapor divergence centers,which are important vapor source for North China. The SST in winter in Pacific Ocean has forcing role on NPO in May,which influences summer drought /flood in North China.
出处
《高原气象》
CSCD
北大核心
2014年第3期775-785,共11页
Plateau Meteorology
基金
全球变化重大研究计划(2012CB955902)
国家自然科学基金项目(41175067
41175083
41205040)
关键词
北太平洋涛动
帕默尔干旱指数
华北夏季旱涝
North Pacific Oscillation
Palmer Drought Severity Index
Drought /Flood in North China
