耦合模式对印度洋偶极子的模拟研究

利用一个海洋-大气-陆面系统耦合模式,模拟分析了热带印度洋的季节和年际气候变化特征。该模式很好地模拟出热带印度洋区域的季节变化特征,对热带印度洋强的局地年际耦合信号-偶极子模拟也比较成功,模拟结果与已有的观测分析以及高分辨率耦合模式模拟结果接近。     

印度洋偶极子中的西极子对西藏高原盛夏降水的影响

利用西藏高原地区1987-2016年的逐月夏季降水资料和印度洋偶极子指数资料分析了两者的关系,结果表明：高原地区盛夏降水与表征西印度洋异常海温的西极子指数表现出良好的相关关系,在西极子指数正异常年时高原降水偏多10%~30%,其中高原中部偏多最为显著,而在负异常年时与之相反。分析其机理研究发现,在正西极子异常年,南海和西太暖池区域的深对流加强、西太副高偏西偏南和印度热低压的减弱使得来自热带的水汽更容易深入高原腹地,其次,南亚高压东体异常增强,配合低空异常辐合,都使得高原降水偏多。同时,高原上空局地纬圈环流在高原中部（90 °E附近）上空（400 hPa以上）有异常辐合上升区,使得高原中部更容易发展暖湿切变线、高原低涡等中尺度涡旋低值系统,造成更多的降水。本研究从高原气候变化响应海洋年际变化的角度分析了区域降水的季节差异,可以为高原气候预测提供新的思路。     

非球形冰晶的毫米波k-Ze关系研究

针对毫米波雷达处理数据的实际需要,应用离散偶极子近似法DDA,获得了非球形冰晶的后向散射及衰减截面并进行了参数化,并主要基于细化的冰云模型,假设冰晶粒子谱为Γ分布,通过模拟取样各1330次（代表1330种粒子分布）,分别计算得到了W波段（94 GHz）与Ka波段（35 GHz）毫米波雷达探测的冰云衰减系数k及雷达反射率因子Z_e,而且利用数值模拟的方法,建立了k-Z_e关系的具体表达式。计算表明,非球形和非瑞利散射对W波段毫米波雷达衰减的影响较大,而且在同样滴谱分布条件下,W波段毫米波雷达的衰减比Ka波段毫米波雷达的大几倍,此外细化的冰云模型对k-Z_e关系具有影响。本研究对中纬度非降水性冰云的毫米波雷达的衰减订正具有参考价值,并对中国的毫米波雷达应用具有借鉴作用。     

印度洋地区异常海温的偶极振荡与中国降水及温度的关系

利用1951-1997年近47年的印度洋海温距平场资料以及相应中国160站降水资料，通过相关普查得出，印度洋地区东西海温的偶极振荡与中国6-8月汛期的降水有较好的相关关系，特别是前期3-5月份的印度洋地区东西海温的偶极指数与中国6-8月降水的相关较好。分析1958-1995年NCEP 500hPa北半球高度场资料发现，印度洋偶极指数与欧亚中高纬度地区的高度场异常有密切的联系，其中印度洋偶极指数IODI负位相年有明显的PJ波列存在，印度洋偶极海湿异常很可能是通过PJ波列来影响中国的降水。同时，对印度洋地区海温偶极指数和中国地区温度的相关分析表明，印度洋地区海温偶极指数与冬季中国南部地区的温度也有较好的相关关系。     

Instantaneous power radiated from magnetic dipole moments

We compute the power radiated per unit solid angle of a moving magnetic dipole moment, and its instantaneous radiated power, both non-relativistically and relativistically. This is then applied to various interesting situations: solar neutrons, electron synchrotrons and cosmological Dirac neutrinos. Concerning the latter, we show that hypothesized early-universe Big Bang conditions allow for neutrino radiation cooling and provide an energy loss-mechanism for subsequent neutrino condensation.     

Two modes of dipole events in tropical Indian Ocean

By analyzing the distributions of subsurface temperature and the surface wind stress anomalies in the tropical Pacific and Indian Oceans during the Indian Ocean Dipole (IOD) events, two major modes of the IOD and their formation mechanisms are revealed. (1) The subsurface temperature anomaly (STA) in the tropical Indian Ocean during the IOD events can be described as a “<” -shaped and west-east-oriented dipole pattern; in the east side of the “<” pattern, a notable tongue-like STA extends westward along the equator in the tropical eastern Indian Ocean; while in the west side of the “<” pattern, the STA has opposite sign with two centers (the southern one is stronger than the northern one in intensity) being of rough symmetry about the equator in the tropical mid-western Indian Ocean. (2) The IOD events are composed of two modes, which have similar spatial pattern but different temporal variabilities due to the large scale air-sea interactions within two independent systems. The first mode of the IOD event originates from the air-sea interaction on a scale of the tropical Pacific-Indian Ocean and coexists with ENSO. The second mode originates from the air-sea interaction on a scale of the tropical Indian Ocean and is closely associated with changes in the position and intensity of the Mascarene high pressure. The strong IOD event occurs when the two modes are in phase, and the IOD event weakens or disappears when the two modes are out of phase. Besides, the IOD events are normally strong when either of the two modes is strong. (3) The IOD event is caused by the abnormal wind stress forcing over the tropical Indian Ocean, which results in vertical transports, leading to the upwelling and pileup of seawater. This is the main dynamic processes resulting in the STA. When the anomalous easterly exists over the equatorial Indian Ocean, the cold waters upwell in the tropical eastern Indian Ocean while the warm waters pileup in the tropical western Indian Ocean, hence the thermocline in the tropical Indian Ocean is shallowed in the east and deepened in the west. The off-equator component due to the Coriolis force in the equatorial area causes the upwelling of cold waters and the shallowing of the equatorial India Ocean thermocline. On the other hand, the anomalous anticyclonic circulations and their curl fields located on both sides of the equator, cause the pileup of warm waters in the central area of their curl fields and the deepening of the equatorial Indian Ocean thermocline off the equator. The above three factors lead to the occurrence of positive phase IOD events. When anomalous westerly dominates over the tropical Indian Ocean, the dynamic processes are reversed, and the negative-phase IOD event occurs. Supported by National Natural Science Foundation of China (Grant No. 40776013), National Basic Research Program of China (Grant No. 2006CB403601) and the Knowledge Innovation Project of Chinese Academy of Sciences (Grant No. KZCX-SW-222)     

EFFECTS OF ENSO ON THE RELATIONSHIP BETWEEN IOD AND SUMMER RAINFALL IN CHINA

Based on the data of 1950 – 1999 monthly global SST from Hadley Center, NCAR/NCEP reanalysis data and rainfall over 160 weather stations in China, investigation is conducted into the difference of summer rainfall in China (hereafter referred to as the “CS rainfall”) between the years with the Indian Ocean Dipole (IOD) occurring independently and those with IOD occurring along with ENSO so as to study the effects of El Ni?o - Southern Oscillation (ENSO) on the relationship between IOD and the CS rainfall. It is shown that CS rainfall will be more than normal in South China (centered in Hunan province) in the years of positive IOD occurring independently; the CS rainfall will be less (more) than normal in North China (Southeast China) in the years of positive IOD occurring together with ENSO. The effect of ENSO is offsetting (enhancing) the relationship between IOD and summer rainfall in Southwest China, the region joining the Yangtze River basin with the Huaihe River basin (hereafter referred to as the “Yangtze-Huaihe basin”) and North China (Southeast China). The circulation field is also examined for preliminary causes of such an influence.     

热带太平洋与印度洋相互作用的年代际变化

利用全球海表海温资料（GISST）和NCEP／NCAR再分析资料,研究了热带太平洋与印度洋之间的相互作用及其在不同年代二者作用关系的变化。结果表明：热带印度洋偶板子指数超前热带太平洋Nin03指数2月时相关最大,印度洋单板子指数滞后Nin03指数3～4月时相关最大。印度洋偶板子在一定程度上影响E1 Nino事件的发生,而E1 Nino事件的发生、发展会影响印度洋单板子事件的发生。热带印度洋偶板子事件与热带太平洋ENSO事件的相互作用在1961年发生了明显跃变,其原因可能是1961年之前热带印度洋偶板子对热带太平洋上空的纬向风影响很小,而1961年以后其影响明显加强。热带印度洋单板子事件与热带太平洋ENSO事件的相关一直显著,没有明显跃变。     

Effects of dipole tilt angle on geomagnetic activity

The relationship between the orientation of the interplanetary magnetic field (IMF), represented by the clock angle which is the angle defined by IMF-B_y and -B_z components, and the AL and AU indices is examined at various dipole tilt angles for the period of 1978-1988. We use the IMF data obtained from the IMP 8 satellite, AL and AU indices with corrected seasonal variations, and the dipole tilt angle, which is the dipole magnetic latitude of the subsolar point calculated as a function of the day of year and universal time. For both positive (dipole tilted to the Sun) and negative dipole tilt angles, the values of |AL| and AU decrease as the IMF clock angle moves away from 180^°, becoming more northward. The indices also tend to become smaller for larger dipole tilt angle, either toward or away from the Sun. This dependence on dipole tilt angle enhances the semiannual variation of geomagnetic activity.     

我国西北和华北夏季降水的偶极子关系及其环流特征

用全国35年以上资料的672个站,讨论了华北和西北夏季降水关系及其环流特征,结果表明:(1)华北和西北夏季降水存在跷跷板式的偶极子关系,当华北夏季降水偏多时,西北降水偏少,反之亦然。华北夏季降水指数与西北夏季降水指数之间的相关系数为-0.28,超过了0.05显著性水平检验。这两条曲线的10年滑动平均的相关系数达到-0.61;而滤去年代际振荡后,它们的相关系数为-0.23,显著性水平接近0.05。这表明华北与西北夏季降水的偶极子关系主要是由年代际振荡引起的,但年际变化也是一个不可忽略的因素。(2)环流分析表明:华北与西北地区夏季降水的偶极子关系与贝加尔湖南部地区(45°~55°N,80°~110°E之间的8个格点)和西部巴尔喀什湖地区(35°~40°N,70°~90°E之间的5个格点)500 hPa高度距平符号相反有关,由它们之差(G-D)组成的华北和西北夏季降水的偶极子关系的环流指数,能很好地解释华北和西北夏季降水的偶极子关系。