卫星观测到的青藏高原雷电活动特征

利用TRMM卫星上携带的闪电探测系统获取的闪电定位资料首次对青藏高原上的闪电活动进行了研究。研究发现,青藏高原上的闪电活动呈现出大陆性气候特征,但是受其特殊地形的热力和动力特征所调制,高于93％的闪电活动发生于5—9月之间,并在夏季出现单一闪电活动峰值。随着地表加热和湿度的增加,闪电活动在5月份开始明显增加。较高的闪电密度发生在高原的中部,揭示了闪电活动与地形特征的相关性。63％的闪电活动发生于14：00—18：00(地方时,下同)之间,而只有＜3％的闪电发生于00：00—l0：00之间。闪电光辐射能的时平均值也呈现出明显的日变化,随着太阳的升起,闪电光辐射能在08：00开始增加,并在l0：00达到稳定的极大值,直到02：00开始明显减小。闪电的光辐射能在高原北部呈现最大值,高原西部呈现最小值。青藏高原上的闪电放电强度比其它地区弱得多,其差别归因于高原上较低的对流不稳定能量。     

Transport-Dissipation Analytical Solutions to the E-∈Turbulence Model and their Role in Predictions of the Neutral ABL

E- turbulence model predictions of the neutralatmospheric boundary layer (NABL) are reinvestigated to determine thecause for turbulence overpredictions found in previous applications. Analytical solutions to the coupled E and equations for the case of steady balance between transport and dissipation terms, the dominant balance just below the NABL top, are derived. It is found that analytical turbulence profiles laminarizeat a finite height only for values of closure parameter ratio c ₂ /_e equal toor slightly greater than one, with laminarization as z for greater . The point = 2 is additionally foundthat where analytical turbulent length scale (l) profilesmade a transition from ones ofdecreasing ( < 2) to increasing ( > 2)values with height. Numerically predicted profiles near the NABL topare consistent with analytical findings. The height-increasingvalues of l predicted throughout the NABL with standard values ofclosure parameters thus appear a consequence of 2.5(> 2), implied by these values (c ₂ = 1.92, _{= 1.3}, _{e = 1}). Comparison of numericalpredictions with DNS data shows that turbulence overpredictions obtained with standard-valued parameters are rectifiedby resetting and _e to 1.1 and 1.6, respectively, giving, with c ₂ = 1.92, 1.3, and laminarization of the NABL's cappingtransport-dissipation region at a finite height.     

MAGE ANALYSIS OF GEOSTATIONARY METEOROLOGICAL SATELLITE FOR MONITORING MOVEMENT OF MESOSCALE CONVECTIVE SYSTEMS OVER TIBETAN PLATEAU

1IN TR O D U C TIO NRecentevidencehasindicatetdhatdisastewreathercon-dition,ssuchasstorms,typhoons,andintensivceonvec-tion,aredirectliynfluencde by MesoscaleConvectiveSystems(MCSs)(JIANG and FAN,2002).Also,theMCSs,whichmove outoftheTibetanPlatea,uarerela-…     

A technique to test finite difference schemes to model some geophysical processes in a geological structure

A preliminary problem to solve in the set-up of a mathematical model simulating a geophysical process is the choice of a suitable discrete scheme to approximate the governing differential equations. This paper presents a simple technique to test finite difference schemes used in the modeling of geophysical processes occurring in a geological structure. This technique consists in generating analytical solutions similar to the ones characterizing a geophysical process, given general information on some relevant parameters. Useful information for the choice of the discrete scheme to employ in the mathematical model simulating the original geophysical process can be obtained from the comparison between the analytical solution and the approximated numerical solutions generated by means of different discrete schemes. Two classes of numerical examples approximating the differential equation that governs the steady state earth's heat flow have been treated using three different finite differences schemes. The first class of examples deals with media whose phenomenological parameters vary as continuous space functions; the second class, instead, deals with media whose phenomenological parameters vary as discontinuous space functions. The finite difference schemes that have been utilized are: Centered Finite Difference Scheme (CDS), Arithmetic Mean Scheme (AMS), and Harmonic Mean Scheme (HMS).The numerical simulations showed that: the CDS may yield physically inconsistent solutions if the lattice internodal distance is too large, but in case of phenomenological parameters varying as a continuous function, this pitfall can be avoided increasing the lattice node refinement. In case of phenomenological parameters varying as a discontinuous function, instead, the CDS may yield physically inconsistent solutions for any lattice-node refinement. The HMS produced good results for both classes of examples showing to be a scheme suitable to model situations like these.     

Observations of the Relation Between Upslope Flows and the Convective Boundary Layer in Steep Terrain

Slope flow mechanisms are crucial for the transport of air pollutants in complex terrain. Previous observations in sloping terrain showed upslope flows filling the entire convective boundary layer (CBL) and reducing air pollution concentrations by venting air pollutants out of the CBL into the free atmosphere. During the Pacific 2001 Air Quality Field Study in the Lower Fraser Valley, British Columbia, Canada, we observed slope flows during weak synoptic winds, clear skies, and strong daytime solar heating. With a Doppler sodar we measured the three wind components at the foot of a slope having an average angle of 19° and a ridge height of 780 m. We operated a scanning lidar system and a tethersonde at a nearby site on the adjacent plain to measure backscatter of particulate matter, temperature, wind speed, wind direction, and specific humidity. Strong daytime upslope flows of up to 6 m s⁻¹ through a depth of up to 500 m occurred in the lower CBL, but with often equally strong and deep return flows in the upper part of the CBL. The mass transport of upslope flow and return flow approximately balanced over a 4-h morning period, suggesting a closed slope-flow circulation within the CBL. These observations showed that air pollutants can remain trapped within a CBL rather than being vented from the CBL into the free atmosphere.     

热带西太平洋对流活动与中国夏季降水

利用 1 979～ 2 0 0 3年月平均射出长波辐射 (OLR)资料 ,分析了中国夏季江淮多 (少 )雨年的同期及前期热带太平洋地区OLR场分布特征。通过定义和计算OLR对流强度指数 ,探讨对流活动与中国夏季雨型的关系。结果表明 ,夏季热带西太平洋地区平均对流活动强度与同期江淮地区降水有很好的反相关关系 ,即当热带西太平洋地区对流活动强时 ,江淮地区降水易偏少 ,当对流活动弱时 ,江淮地区降水易偏多。不仅如此 ,前期冬、春季对流活动强度与夏季对流活动强度有明显的正相关关系 ,则可利用前期冬、春季对流活动强度对当年中国夏季降水趋势进行预测和补充订正。因此 ,热带西太平洋地区对流活动强弱对于中国夏季降水预测有一定的指示意义。     

A Numerical Study of Sensitivity of the Physical Dissipative Technique to Precipitation Parameterization in a Mesoscale Model

1. IntroductionRecently, the improvement of accuracy in the out-puts of a numerical mesoscale model by the physi-cal dissipative technique is reached (Liu et al., 2002;Liu and Liu, 2003). The effect of improvement ofthis technique differs not only from model to model,but from scheme to scheme of parameterization em-ployed in the same model. The rapid developmentof the computer technology makes possible the com-plicated numerical experiments by a model with highresolution and multiple domains …     

Chondritic osmium isotopic composition of Archean ophiolitic mantle, North China craton

Podiform chromitites are diagnostic but rare features of Phanerozoic ophiolites, and often contain the most pristine textural, chemical and isotopic record of convective upper mantle conditions extant during ophiolite genesis. Ophiolitic podiform chromitites, owing to their high Os concentrations and low Re/Os ratios provide the best evidence for the Os-isotopic evolution of oceanic mantle, but established records of ophiolitic chromites from bona fide Archean ophiolites are still lacking. We report Re–Os isotopic compositions of the world's oldest known ophiolitic podiform chromites from the 2.5 billion year old Dongwanzi–Zunhua ophiolite, North China. This provides the oldest Os isotope composition for the convective upper mantle yet obtained from ophiolitic podiform chromitites, and reveals a chondritic Os isotopic composition of the Archean convective upper mantle.     

改进AMSR-E雪水当量算法研究

为了发展雪水当量物理反演算法,本文对不同散射阶模型——零阶、一阶、多次散射模型进行敏感性试验与分析,结果表明我们必须在前向理论模型和反演模型中考虑多次散射作用。本文采用的多次散射积雪辐射理论模型——双矩阵法（Matrix Doubling）求解辐射传输方程,用致密介质理论模型（DMRT）模拟积雪发射和消光特性,用AIEM模型模拟地表辐射及作为辐射传输方程的边界条件。由于该多次散射积雪辐射理论模型的复杂性,拟发展出简单且高精度的积雪辐射参数化模型,以发展雪水当量物理反演算法。因此,在包括多次散射的积雪理论模型基础上,本文通过建立针对AMSR-E传感器参数设置的积雪辐射模拟数据库,该数据库包含了各种可能的自然积雪和地表特性参数。从而在模拟数据库基础上,本文发展了针对AMSR-E的积雪参数化模型。     

Ontario’s Environmental Farm Plan: Evaluation and research agenda

This paper analyses the operation of the Environmental Farm Plan (EFP) scheme in Ontario, Canada, a voluntary agri-environment scheme established in 1993. Previously unpublished data and interviews with farmers, leaders of farmers’ organisations and government officials are used to detail participation rates, geographical spread and method of operation. Largely developed by farmers’ organisations, the scheme has focused on soil management, water quality and storage/disposal of agricultural wastes. The environmental actions associated with these activities are discussed, revealing both successes and limitations. Distinctions are drawn with agri-environmental schemes in the European Union, and a broader context for the EFP is provided with respect to the proposed post-productivist transition of agri-food systems and the need to examine the way these systems are regulated. A need for further systematic research is proposed, specifically with respect to barriers to participation, the voluntary nature of the scheme, financial incentives and the resultant environmental impacts.