基于MERIS数据的永久散射体处理中大气改正方法研究

分析了永久散射体PS(Permanent Scatlerers)处理中进行大气改正的必要性,介绍了大气改正的方法,指出现有方法存在的不足; 结合利用MERIS数据进行大气改正的优势,提出了基于MERIS数据的PS处理中大气改正的模型.采用青藏高原北麓河实验区ASAR数据对该模型进行验证的结果表明,该方法能够有效提高永久散射体处理中大气改正的可信性,从而使得利用相对较少的ASAR数据进行PS分析成为可能.     

The diffusion coefficient of dissolved silica revisited

The diffusion coefficient of dissolved silica was determined for two different salinities, 36 and 0, at temperatures ranging from 2 °C to 30 °C and at an average pH value of 8.1. Our results show limited influence of salinity and a variation by a factor of 2 to 3 of the silica diffusion coefficient within the temperature range considered in this study. The values obtained at 25 °C are in agreement with previous work carried out at room temperature for seawater and freshwater. The dependency on temperature and viscosity of the diffusion coefficient agrees well with the Einstein–Stokes equation. The composition of the solvent appears to be an important factor because it modifies the viscosity and allows for the complexation of the dissolved silica with less mobile ions, while its pH controls the dissolved silica speciation. In seawater, the higher viscosity and the presence of dissociated and polymeric species result in a decrease of the diffusion coefficient compared to freshwater systems.     

Bivariate conditional sampling of buoyancy flux during an intense cold-air outbreak

Buoyancy fluxes in the marine atmospheric boundary layer (MABL) for the cloud street regime, observed during the Genesis of Atlantic Lows Experiment (GALE), have been analyzed using the technique of joint frequency distribution. For the lower half of the MABL, the results suggest that the buoyancy flux is mainly generated by the rising thermals and the sinking compensating ambient air, and is mainly consumed by the entrainment and detrainment of thermals, penetrative convection, and the entrainment from the MABL top.The results are compared to those from previous studies of mesoscale cellular convection (Air-Mass Transformation Experiment, AMTEX), the dry convective boundary layer, and the trade-wind MABL. For the lower MABL, the quadrant buoyancy fluxes, fractional coverages, and flux intensities are in good agreement with those of mesoscale cellular convection (AMTEX) and the dry convective boundary layer. The results suggest that, if the buoyancy flux is primarily driven by the temperature flux, the physical processes for generating buoyancy flux mentioned above are about the same for the lower boundary layers over land and ocean, even with different convective regimes. For the trade-wind MABL, the buoyancy flux is mainly driven by the moisture flux; the quadrant flux intensities are stronger than those of the other three studies except for the buoyant updrafts (thermals). These results suggest that the entrainment and detrainment of thermals are more effective in the trade-wind MABL than in the boundary layers driven by the temperature flux.Scale analysis of the buoyancy flux is in good agreement with that of AMTEX. For the lower half of the MABL, the buoyancy flux is mainly generated by the intermediate scale (200 m to 2 km), which includes the dominant convective thermals in the surface layer and the mixed layer. The scale smaller than 200 m is important only in the surface layer. The scale larger than 2 km, which includes the roll vortices, increases its significance upward. While most of the positive and negative fluxes are associated with the updrafts for the intermediate scale, the downdrafts are as important as updrafts for the larger scale.ST Systems Corporation, Lanham, MD, 20706, U.S.A.     

Seasonal climate hindcasts with Eta model nested in CPTEC coupled ocean–atmosphere general circulation model

This work evaluates the added value of the downscaling technique employed with the Eta model nested in the CPTEC atmospheric general circulation model and in the CPTEC coupled ocean?Catmosphere general circulation model (CGCM). The focus is on the austral summer season, December?CJanuary?CFebruary, with three members each year. Precipitation, latent heat flux, and shortwave radiation flux at the surface hindcast by the models are compared with observational data and model analyses. The global models generally overestimate the precipitation over South America and tropical Atlantic. The CGCM and the nested Eta (Eta + C) both produce a split in the ITCZ precipitation band. The Eta + C produces better precipitation pattern for the studied season. The Eta model reduces the excessive latent heat flux generated by these global models, in particular the Eta + C. Comparison against PIRATA buoys data shows that the Eta + C results in the smallest precipitation and shortwave radiation forecast errors. The Eta + C comparatively best results are though as a consequence of both: the regional model resolution/physics and smaller errors on the lateral boundary conditions provided by the CGCM.     

副热带高压研究进展及展望

介绍了国家自然科学基金委员会九五重点项目"副热带高压形成和变异的机理"的研究成果.该项目的研究纠正了对副热带高压成因的若干传统认识,揭示了副热带高压脊线年际变化的新事实,发展了脊线这一东西风交界面的动力模型,建立了"全型涡度方程"、"热力适应"理论及"两级热力适应"模式,并通过模拟和资料诊断研究了各副热带高压单体的形成机制及其季节和年际变化,在西太平洋副热带高压变化的规律和机制的研究中得到了新的认识.     

THE EFFECTS OF EXTERNAL FORCING,DISSIPATION AND NONLINEARITY ON THE SOLUTIONS OF ATMOSPHERIC EQUATIONS

Based on the primitive equations of the atmosphere,we study the effects of external forcing.dissipation and nonlinearity on the solutions of stationary motion and non-stationary motion.Theresults show that the asymptotic behavior of solutions of the forced dissipative nonlinear system isessentially different from that of the adiabatic non-dissipative system,the adiabatic dissipativesystem,the diabatic non-dissipative system and the diabatic dissipative linear system,and that thejoint action of external forcing,dissipation and nonlinearity is the source of multiple equilibria.From this we can conclude that the important actions of diabatic heating and dissipation must beconsidered in the models of the long-term weather and the climate.     

气候系统可预报性理论研究

介绍了作者近年来关于气候系统可预报性理论研究的一些工作,包括:非线性最快增长扰动理论以及在气候预测的可预报性研究中的应用;从一个新的角度研究了2类可预报性问题,并提出可预报性的3类子问题;根据计算不确定性原理,讨论了模式可预报性与机器精度的关系;探讨了可预报性与时空尺度的关系,建立了可预报性的相对观.     

预报模式识别的扰动方法

本文从数值天气预报模式并不完全准确描述实际大气过程的观点出发,提出利用观测的近期演变资料确定模式中的未知部份(模式识别),以改善预报结果.叙述了一种模式识别的扰动方法,用正压涡度方程模式作了模拟实验,证明方法是有效的.     

长江三角洲汛期预报模式的研究及其初步应用

在短期自忆气候模式的基础上 ,着重考虑了区域性降水特点 ,组合均生函数时序模型 ,构造了区域降水预报模式。以降水预报为实例 ,计算表明 ,它能滚动制作月、季、年降水预报 ,尤其对汛期 (6～ 8月 )降水预报 ,具有相当好的预报能力。