基于COSMIC掩星数据分析中低纬度地区电子密度分布变化

利用COSMIC掩星2009年电子密度剖面数据,筛选数据进行网格划分,网格内数据统计平均,基于球谐函数计算模型值,分析电离层中低纬度地区最大电子密度的地磁季节变化、昼夜测分布相对变化,及地磁活动对电子密度的分布影响.结果表明,最大电子密度昼测值明显高于夜测值,在中纬度部分区域增大明显.电子密度昼测值在地磁活动期间高度150-550 km中低纬度范围为正相扰动,随纬度变化存在区域差异,随高度增加,扰动加强.     

The warm pool in the Indian Ocean

The structure of the warm pool (region with temperature greater than 28°C) in the equatorial Indian Ocean is examined and compared with its counterpart in the Pacific Ocean using the climatology of Levitus. Though the Pacific warm pool is larger and warmer, a peculiarity of the pool in the Indian Ocean is its seasonal variation. The surface area of the pool changes from 24 × 10⁶ km² in April to 8 × 10⁶ km² in September due to interaction with the southwest monsoon. The annual cycles of sea surface temperature at locations covered by the pool during at least a part of the year show the following modes: (i) a cycle with no significant variation (observed in the western equatorial Pacific and central and eastern equatorial Indian Ocean), (ii) a single maximum/minimum (northern and southern part of the Pacific warm pool and the south Indian Ocean), (iii) two maxima/minima (Arabian Sea, western equatorial Indian Ocean and southern Bay of Bengal), and (iv) a rapid rise, a steady phase and a rapid fall (northern Bay of Bengal).     

Effects of meteorological and hydrogeological factors on gross recharge percentage at unconfined sandy aquifers with an equatorial climate

A thorough understanding of rainfall recharge processes and their controlling factors is essential for management of groundwater systems. This study investigates the effects of various meteorological and hydrogeological factors on the gross recharge percentages, the rainfall–recharge relationships and the recharge threshold values for unconfined sandy aquifers under an equatorial climate. Among the meteorological factors investigated, rainfall intensity was found to have the most significant impact on the gross recharge rate. The effects of potential evaporation rate, relative humidity and air temperature on the gross recharge percentage were significant when the vadose zone thickness is larger than 2·5 m. The recharge threshold values were found to depend strongly on the vadose zone thickness. The rainfall–recharge relationships could generally be well defined by a normal–log relationship. The rainfall–recharge relationships derived here are applicable to yield estimates of gross recharge percentages for unconfined sandy aquifers under an equatorial climate, using rainfall intensity and vadose zone thickness as input variables. In this study, a theory was developed and validated to provide physical explanations for the observations, based on the residence time of the percolated rainwater within the vadose zone. Among the soil hydraulic parameters tested, porosity and saturated hydraulic conductivity were found to have the most pronounced effects on the gross recharge percentage. Utilizing the sensitivity results and the theory derived, an approach was developed for extending the application of the derived rainfall–recharge relationships to other sand textures. The approach was found to be capable of producing rough and fast estimations of gross recharge percentage for other sand textures. Copyright © 2007 John Wiley & Sons, Ltd.     

1972年8月事件期间四个耀斑引起的日球层扰动的模拟研究

1972年8月发生的太阳耀斑事件是第20太阳周期内最重大的事件,我们在改进Hakamada-Akasofu方法（以下简称HA方法）的基础上,对事件期间四个较大的耀斑所引起的行星际扰动进行了计算机模拟研究,并取得了令人满意的结果。这些模拟包括赤道平面上一系列二维的激波形状、激波传播以及空间飞船先驱者9号、先驱者10号（以下简称P9、P10）和地球位置上的粒子速度-时间曲线。最后,本文还将该模拟结果与Dryer等人所做的同一事件的一维MHD模拟结果做了比较,并对模拟结果和HA方法本身做了一些讨论。     

与广东持续性干旱事件有关的两类海温异常型

利用1961\_2005年广东省86个常规地面观测站降水资料、 ERSST全球月平均海温资料以及NCEP/NCAR 大气多要素再分析资料, 分析了广东跨季节持续性干旱事件(下称广东干旱)与海温外强迫之间的关系及其物理过程。结果表明, 与广东干旱相关的海温异常有赤道东太平洋海温负异常型（即La Nia型）、 赤道中太平洋海温正异常型两种类型。约在1975年之前, 广东干旱基本上属于La Nia型; 在1975年之后, 除了La Nia型外, 赤道中太平洋海温正异常型干旱出现概率明显增加。可见, 在全球气候变暖的背景下, 广东干旱成因更复杂。近几年来广东干旱频繁发生, 与赤道中太平洋海温正异常型出现概率增加有关。La Nia型、 赤道中太平洋海温正异常型与广东干旱之间都存在物理上的联系, 不同的海温异常型对广东干旱影响的物理过程有所不同, 即使同一种海温异常型对不同季节的影响过程也有所不同, 然而所有物理过程最终都是通过改变和削弱降水所需的动力条件或水汽条件, 从而造成局地干旱的发生。     

2008年初云南低温雨雪冰冻天气的气候成因分析

2008年1月下旬~3月上旬云南出现了一次持续性的低温雨雪冰冻天气, 给交通、 电力、 通讯以及人民的生产、 生活带来了极大危害。本文首先对云南高低层大气的异常状况及大尺度环流背景场特征对这次天气过程的影响进行诊断分析, 然后进一步探讨了赤道东太平洋海温异常对东亚冬季风活动和云南天气气候异常的影响。结果表明, 这次低温冷害过程主要发生在冷空气由北至南逐渐加强南压, 南支西风波动配合, 以及西太平洋副热带高压减弱东退的大尺度环流背景之下。同时, 云南区域的大气异常状态表现出了明显的高湿、 强上升运动以及对流层中高层温度升高而低层温度降低。另外, 本文分析还进一步表明了2008年赤道东太平洋地区的冷海水异常对这次云南低温冷害天气过程的重要作用。     

Simulation of equatorial wind field patterns with TAPM during the 1997 haze episode in Peninsular Malaysia

The large‐scale forest fires that occurred during the major El Niño event in 1997 can be counted among the worst environmental disasters in Southeast Asia. This study investigates atmospheric mesoscale features over Sumatra and the Klang Valley in Peninsular Malaysia during the resultant haze episode of September 1997 utilizing a limited area mesoscale three‐dimensional meteorological and dispersion model, The Air Pollution Model (TAPM). Mesoscale features that would not be highlighted by global numerical prediction models, such as the daily land and sea breeze conditions at the selected air pollution stations located near the west coast of Peninsular Malaysia, were predicted with an Index of Agreement of 0.3, which implied a moderate conformity between the predicted and observed values. Tracer analysis of air particles at a selected location in the Straits of Malacca verified the existence of the landward and shoreward movement of the air during the simulation of the low‐level wind field. Air pollutants from the burning areas of neighbouring Sumatra just across the straits were transported towards the Klang valley during the daytime and seawards during the nighttime, highlighting the recirculation features of aged and newer air particles over the seven days (13–18 September) of the model simulation. The presence of the central Main Range east of the Klang valley to a certain extent limited further eastward movement of the air particles. Near calm conditions at low levels were simulated from midnight to midday on 14 September, where the movement of the polluted air particles from the uncontrolled burning in Sumatra was confined within the Straits of Malacca. Turbulence within the planetary boundary layer in terms of the total kinetic energy was found to be weak from 14 to 15 September, congruent with the weak strength of low level winds that reduced the ability of the air to transport the pollutants during the period of severe smoke haze. Statistical evaluation showed that parameters such as the systematic RMSE (root mean square error) and unsystematic RMSE for the zonal wind component were slightly higher than for the meridional one, indicating higher errors between the observed and simulated zonal values. Otherwise, the equatorial meteorological parameters such as wind speed and temperature were successfully simulated by the model with comparatively high correlation coefficients, lower RMSEs and moderately high indices of agreement with observed values.     

Global distributions of storm-time ionospheric currents as seen in geomagnetic field variations

To investigate temporal and spatial evolution of global geomagnetic field variations from high-latitude to the equator during geomagnetic storms, we analyzed ground geomagnetic field disturbances from high latitudes to the magnetic equator. The daytime ionospheric equivalent current during the storm main phase showed that twin-vortex ionospheric currents driven by the Region 1 field-aligned currents （R1 FACs） are intensified significantly and expand to the low-latitude region of-30~ magnetic latitude. Centers of the currents were located around 70~ and 65~ in the morning and afternoon, respectively. Corresponding to intensification of the R1 FACs, an enhancement of the eastward/westward equatorial electrojet occurred at the daytime/nighttime dip equator. This signature suggests that the enhanced convection electric field penetrates to both the daytime and nighttime equa- tor. During the recovery phase, the daytime equivalent current showed that two new pairs of twin vortices, which are different from two-cell ionospheric currents driven by the R1 FACs, appear in the polar cap and mid latitude. The former led to enhanced north- ward Bz （NBZ） FACs driven by lobe reconnection tailward of the cusps, owing to the northward interplanetary magnetic field （IMF）. The latter was generated by enhanced Region 2 field-aligned currents （R2 FACs）. Associated with these magnetic field variations in the mid-latitudes and polar cap, the equatorial magnetic field variation showed a strongly negative signature, produced by the westward equatorial electrojet current caused by the dusk-to-dawn electric field.     

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Reflection of equatorial Kelvin waves at eastern ocean boundaries Part I: hypothetical boundaries

A baroclinic shallow-water model is developed to investigate the effect of the orientation of the eastern ocean boundary on the behavior of equatorial Kelvin waves. The model is formulated in a spherical polar coordinate system and includes dissipation and non-linear terms, effects which have not been previously included in analytical approaches to the problem. Both equatorial and middle latitude response are considered given the large latitudinal extent used in the model. Baroclinic equatorial Kelvin waves of intraseasonal, seasonal and annual periods are introduced into the domain as pulses of finite width. Their subsequent reflection, transmission and dissipation are investigated. It is found that dissipation is very important for the transmission of wave energy along the boundary and for reflections from the boundary. The dissipation was found to be dependent not only on the presence of the coastal Kelvin waves in the domain, but also on the period of these coastal waves. In particular the dissipation increases with wave period. It is also shown that the equatorial β-plane approximation can allow an anomalous generation of Rossby waves at higher latitudes. Nonlinearities generally have a small effect on the solutions, within the confines of this model.