基于VisIt的全球科学数据并行可视化——以大气温度场为例

针对当前大规模全球科学数据可视化中存在的单机可视化数据量有限、从底层开发并行可视化系统难度大等问题,该文基于分布式环境和VisIt,提出了一种简便、开放而又有效的大规模全球科学数据可视化方法。介绍了VisIt的体系结构及运行机制,给出了自定义数据的并行可视化方法;并基于NCEP数据集及全球空间格网,在小规模集群环境下实现了小粒度适应性球体退化八叉树格网(SDOG)下的全球大气温度场的并行可视化。VisIt的并行可视化性能测试结果表明:通过增加计算节点,VisIt能有效摆脱传统单机可视化对数据量的限制,可实现大规模全球科学数据的并行可视化。     

2004年春季中国沙尘天气特征分析

利用全国681个站的沙尘天气观测资料分析得出,2004年春季中国北方的沙尘天气明显偏少、偏弱,主要表现在：（1）2004年春季681个站累计的沙尘天气日数2 080 d,相当于历史平均值的46.9%,是近四十余年中第三个偏少年份。沙尘暴的总面积约190万km2,仅为历史平均值的37.3%。（2）危害性较大的沙尘暴和强沙尘暴过程6次,不足2001年的一半。（3）4月和5月沙尘天气明显偏少导致整个春季显著偏少。沙尘天气出现时,PM10浓度相对增加,空气质量恶化,但与历史上较典型的强沙尘暴个例相比,PM10浓度增加的幅度不大。进一步分析表明,2004年春季沙尘天气偏少、偏弱的主要原因是大气动力条件不足,是比较特殊的一个年份。     

全球重力异常对大气活动中心、气旋多发区的影响

利用卫星观测和地面实测资料统一归算的全球空间重力异常,探讨重力异常对全球冬夏大气活动中心、热带气旋以及温带气旋和高原低涡多发区的影响,并对其物理机理作一简要讨论.认为重力异常是大气运动发生发展不可忽视的因子之一.     

卫星测高逆气压改正及其对海平面变化的影响

研究了全球平均大气压的变化特征,分析了传统卫星测高逆气压改正存在的缺陷,并对以常数大气压为参考值、以全球海洋平均大气压为参考值和顾及高频信号的3种逆气压改正进行了对比。根据T/P卫星测高数据对3种改正方法得到的海面高和海平面变化进行了比较分析,相比于前两种逆气压改正,顾及高频信号的逆气压改正最接近海平面的真实响应,可减少卫星测高海面高交叉点不符值RMS约5.70mm,分别提高海平面变化估计精度约18%和12%。     

Salinity and periodic inundation controls on the soil‐plant‐atmosphere continuum of gray mangroves

Salinity and periodic inundation are both known to have a major role in shaping the ecohydrology of mangroves through their controls on water uptake, photosynthesis, stomatal conductance, gas exchanges, and nutrient availability. Salinity, in particular, can be considered one of the main abiotic regulating factors for halophytes and salt‐tolerant species, due to its influence on water use patterns and growth rate. Ecohydrological literature has rarely focused on the effects of salinity on plant transpiration, based on the fact that the terrestrial plants mostly thrive in low‐saline, unsaturated soils where the role of osmotic potential can be considered negligible. However, the effect of salinity cannot be neglected in the case of tidal species like mangroves, which have to cope with hyperosmotic conditions and waterlogging. We introduce here a first‐order ecohydrological model of the soil/plant‐atmosphere continuum of Avicennia marina—also known as gray mangrove—a highly salt‐tolerant pioneer species able to adapt to hyperarid intertidal zones and characterized by unique morphological and ecophysiological traits. The A. marina's soil‐plant‐atmosphere continuum takes explicitly into account the role of water head, osmotic water potential, and water salinity in governing plant water fluxes. A. marina's transpiration is thus modeled as a function of salinity based on a simple parameterization of salt exclusion mechanisms at the root level and a modified Jarvis' expression accounting for the effects of salinity on stomatal conductance. Consistently with previous studies investigating the physiology of mangroves in response to different environmental drivers, our results highlight the major influence of salinity on mangrove transpiration when contrasted with other potential stressors such as waterlogging and water stress.     

The Fluxes and Behaviour of Plumes Inferred from Measurements of Coherent Structures within Images of the Bulk Flow

This paper describes how measurements of the movement of identifiable features at the edge of a turbulent plume can be interpreted to determine the properties of the mean flow and consequently, using plume theory, can be used to make estimates of the fluxes of volume (mass), momentum, and buoyancy in a plume. This means that video recordings of smoke rising from a chimney or buoyant material from a source on the sea bed can be used to make accurate estimates of the source conditions for the plume. At best we can estimate the volume flux and buoyancy flux to within about 5% and 15% of the actual values, respectively. Although this is restricted to the case of a plume rising in a stationary and unstratified environment, we show that the results may be of practical use in other more complex situations. In addition, we demonstrate that large-scale (turbulent) coherent structures at the plume edge form on a scale approximately 40% of the local (mean) plume half-width and travel at almost 60% of the average local (mean) velocity in the plume.     

高层大气密度的午夜极大值特征分析与建模

利用CHAMP (CHAllenging Minisatellite Payload)、GRACE-A (Gravity Recovery and Climate Experiment-A)、SWARM-C (The Earth''s Magnetic Field and Environment Explorers-C)等3颗极轨卫星的资料, 研究360—480km高层大气密度在低纬度区域的午夜极大值(Midnight Density Maximum, MDM)现象. MDM一般出现在23:00- 02:00 LT (Local Time)之间,峰值位置在低纬度15°以内,谷值位置在中纬度35°-45°附近,整体略偏向南半球,振幅约为平均密度的26%.随着高度增大以及太阳辐射水平的增强,MDM振幅呈减小趋势;冬至和夏至日附近的季节效应会减弱MDM振幅,在春秋分日的振幅最大.用3个主流大气模型DTM2000 (Drag Temperature Model 2000), NRLMSISE00 (US Naval Research Laboratory, Mass Spectrom-eter and Incoherent Scatter radar)和JB2008 (Jacchia- Bowman 2008 model)对MDM进行模拟,JB2008没有刻画出MDM现象;另两个模型低估了MDM效应,在360km和480km两个高度DTM2000模型的振幅仅为观测的46%和53%, NRLMSISE00模型仅为观测的33%和26%;模型没有准确刻画出MDM与高度、辐射水平和季节的关系.联合3颗卫星的资料,研究了-种基于地理纬度的6阶勒让德多项式,同时融合地方时和高度因素的经验函数,在振幅和相位上可以较好地刻画MDM特征,相关系数达到0.923,可为大气密度模型的修正提供借鉴,服务于低轨道航天器高精度轨道预报.     

鲅鱼圈地区污染气象特征分析

利用近3a的鲅鱼圈地区地面常规气象资料和2005年3～4月鲅鱼圈地区低空污染气象探测资料,分析了鲅鱼圈地区低空污染气象特征。结果表明:鲅鱼圈地区各类型风速廓线出现频率比较均匀,而且由于地面粗糙度较大,因此风速廓线指数比平原地区稍大。     

Temperature and heat flux spectra in the turbulent buoyancy subrange

The physical nature of motions with scales intermediate between approximately isotropic turbulence and quasi-linear internal gravity waves is not understood at the present time. Such motions play an important role in the energetics of small scales processes, both in the ocean and in the atmosphere, and in vertical transport of heat and constituents. This scale range is currently interpreted either as a saturated gravity waves field or as a buoyancy range of turbulence.We first discuss some distinctive predictions of the classical (Lumley, Phillips) buoyancy range theory, recently improved (Weinstock, Dalaudier and Sidi) to describe potential energy associated with temperature fluctuations. This theory predicts the existence of a spectral gap in the temperature spectra and of an upward mass flux (downward buoyancy and heat fluxes), strongly increasing towards large scales. These predictions are contrasted with an alternate theory, assuming energetically insignificant buoyancy flux, proposed by Holloway.Then we present experimental evidences of such characteristic features obtained in the lower stratosphere with an instrumented balloon. Spectra of temperature, vertical velocity, and cospectra of both, obtained in homogeneous, weakly turbulent regions, are compared with theoretical predictions. These results are strongly consistent with the improved classical buoyancy range theory and support the existence of a significant downward heat flux in the buoyancy range.The theoretical implications of the understanding of this scale range are discussed. Many experimental evidences consistently show the need for an anisotropic theory of the buoyancy range of turbulence.