梅雨准双周振荡的年际变化及其前期强信号分析

利用1954—2005年中国740站逐日降水资料和NCEP/NCAR再分析资料,分析了江淮梅雨准双周振荡的年际变化,并讨论了异常年的海气背景特征。将滤波后的每个降水周期划分为8个位相,其中第3位相对应准双周降水正距平最大,而第7位相对应准双周降水负距平最大,在此基础上的诊断结果表明：1）振荡强弱偏差场,在梅雨降水偏多的第3位相,低层大气中类似Rossby波列从南海经日本海、鄂霍次克海和阿留申群岛延伸至阿拉斯加地区,其中南海上空的反气旋和日本上空的气旋相互配合,造成冷暖空气在江淮地区交汇,有利于准双周降水正距平的产生。在降水偏少的第7位相,波列位相基本反向,传播路径偏南。2）第3位相时高层环流显示,鄂霍次克海地区高度场正异常明显,和我国东北地区的负距平共同作用为梅雨降水提供了足够的干冷空气。第7位相分布相反。3）前期3月至同期的黑潮及其延伸区海表温度和梅雨的准双周振荡强强度之间呈很好的正相关关系。黑潮及其延伸区持续的正海温异常,通过影响西太平洋副热带高压的位置和强度的变化,进而增强梅雨降水的准双周振荡     

人工观测与自动观测地面最低温度的差异分析

分析在地面温度下降到零度以下时,自动站的地面最低温度与人工站的地面最低温度差异明显增大的原因,为两者资料能正确应用提供依据。     

Photochemistry of N2O4 Adsorbed on Ice Surfaces at 193 nm

A multi-layer deposited ice film was prepared through water vapor deposition on a Ni plate in a vacuum chamber at 90 K, and was used as it was or after annealing at 140 K. NO₂ was adsorbed as N₂O₄ approximately 90 K on the ice film prepared as above, and irradiated by 193 nm excimer laser light. The time-of-flight (TOF) spectra of the desorbed species, i.e., NO₂, NO, O₂ and O, were measured by a quadrupole mass spectrometer. The photochemical process obeyed an one-photon process. The relative yields of the products and their TOF spectra were dependent on the preparation condition of the ice film and also varied with the continuation of the laser irradiation. From the ice film annealed at 140 K, NO₂, NO and O₂ were desorbed with an approximate ratio of 1:1:0.01. From the non-annealed film, the relative yield of NO₂ was much smaller than that of NO. The TOF spectrum of NO from the non-annealed ice film consisted of distinctly different two components corresponding to the 1700 and 100 K translational temperature, respectively. The fast component was lost when additional ice was deposited on the adsorbed N₂O₄. NO was supposed to be a predissociation product from the electronically excited NO₂ prepared through the photodissociation of N₂O₄.     

Numerical Simulation of Drag Partition over Rough Surfaces

We present a numerical simulation of drag partition over rough surfaces. A computational fluid dynamics model is applied with high resolution to simulatingturbulent flows over arrays of roughness elements positioned on asmooth surface. The skin drag on the surface and the pressure drag on the roughnesselements are computed. The simulated drag partition compares well with wind-tunnelmeasurements and theoretical estimates for similar rough surfaces. This confirms that the computational approach offers an alternative to wind-tunnel and field experiments in studying drag and drag partition. The model is then applied to studying drag partition over rough surfaces with various roughness configurations. It is shown that drag partition depends not only on the magnitude of the roughness frontal area but also on the sizes and arrangement of roughness elements, because (1) the pressure drag coefficient is sensitive to roughness-element dimensions and (2) the arragement of roughness elements lead to different interferences of turbulent wakes. The impact ofthe latter factor is not insignificant.     

The climatic impacts of land surface change and carbon management, and the implications for climate-change mitigation policy

Strategies to mitigate anthropogenic climate change recognize that carbon sequestration in the terrestrial biosphere can reduce the build-up of carbon dioxide in the Earth’s atmosphere. However, climate mitigation policies do not generally incorporate the effects of these changes in the land surface on the surface albedo, the fluxes of sensible and latent heat to the atmosphere, and the distribution of energy within the climate system. Changes in these components of the surface energy budget can affect the local, regional, and global climate. Given the goal of mitigating climate change, it is important to consider all of the effects of changes in terrestrial vegetation and to work toward a better understanding of the full climate system. Acknowledging the importance of land surface change as a component of climate change makes it more challenging to create a system of credits and debits wherein emission or sequestration of carbon in the biosphere is equated with emission of carbon from fossil fuels. Recognition of the complexity of human-caused changes in climate does not, however, weaken the importance of actions that would seek to minimize our disturbance of the Earth’s environmental system and that would reduce societal and ecological vulnerability to environmental change and variability.     

FY-2G地表温度反演产品改变模式初值对一次台风暴雨模拟的影响

为探讨地表温度初始场在台风暴雨模拟中的重要性,以2015年第13号台风"苏迪罗"为例,分别用FY-2G卫星反演的陆表温度、海表温度产品替换NCEP资料初始场,进行数值模拟试验。对模拟结果进行分量级降水TS评分和预报正确率检验,并对比分析了各试验方案2 m温度场、感热通量和潜热通量场、900 h Pa流场和850 h Pa垂直速度场间的差异。结果表明:使用FY-2G卫星反演的陆、海表温度产品作模式初始场均能不同程度地改善降水模拟效果,但改善程度随时间降低,24 h后其改善作用已较小;陆表温度试验对小雨和中雨量级的预报质量均有提高,而海表温度试验仅提高了小雨量级的预报质量。进一步分析表明,陆表温度试验主要通过改善陆表温度初始场影响感热通量和潜热通量的分布,进而减小台风东北部低层温度正异常,使该区域气旋性环流减弱、垂直速度减小,有效抑制了虚假对流出现,最终达到改善降水预报质量的效果;海表温度试验原理与陆表温度试验类似,但对降水预报质量改善不明显,仅在广东南部沿海地区降水模拟效果较好。     

Climatology of Lightning Activity over the Indian Seas

The climatology of lightning activity over the Indian seas (Arabian Sea (AS) and Bay of Bengal (BoB)) has been studied using monthly satellite-based lightning flash count grid (0.5°?×?0.5°) data from 1998 to 2007. These data have been used to investigate the annual and seasonal variations in lightning activity over the Indian seas. It was found that annual variations in flash rate density and sea surface temperature (SST) show a bimodal pattern with the first peak occurring in May and the second in October. The correlation coefficients between flash rate density and SSTs are 0.76 and 0.65 for the AS and BoB, respectively. Further, the relationship between flash rate density and a low pressure system (LPS) over the BoB shows that the formation of severe tropical cyclonic storms starts during April with the maximum number of storms forming during August. The performance of monsoon on a seasonal and monthly basis depends on the total number of lows, the formation of a depression in the monsoon trough, and the number of days with an LPS. Secular decreases in the number of lows and monsoon depressions were observed in 2000, 2002, and 2004. Overall, results indicate that the peaks in SST during April and September/October over the AS and the BoB may be responsible for advancing the onset of the southwest and northeast monsoon by 30–40 days.     

冬季审核地面气象资料的一些注意事项

对冬季较少出现的天气现象及其引伸的现象的资料处理情况进行概括,有助于台站处理审核原始资料。     

First-Order Chemistry in the Surface-Flux Layer

We have discussed the behavior of a non-conserved scalar in the stationary, horizontally homogeneous, neutral surface-flux layer and, on the basis of conventional second-order closure, derived analytic expressions for flux and for mean concentration of a gas, subjected to a first-order removal process. The analytic flux solution showed a clear deviation from the constant flux, characterizing a conserved scalar in the surface-flux layer. It decreases with height and is reduced by an order of magnitude of the surface flux at a height equal to about the typical mean distance a molecule can travel before destruction. The predicted mean concentration profile, however, shows only a small deviation from the logarithmic behavior of a conserved scalar. The solution is consistent with assuming a flux-gradient relationship with a turbulent diffusivity corrected by the Damköhler ratio, the ratio of a characteristic turbulent time scale and the scalar mean lifetime. We show that if we use only first-order closure and neglect the effect of the Damköhler ratio on the turbulent diffusivity we obtain another analytic solution for the profiles of the flux and the mean concentration which, from an experimental point of view, is indistinguishable from the first analytic solution. We have discussed two cases where the model should apply, namely NO which, by night, is irreversibly destroyed by interaction with mainly O₃ and the radioactive ²²⁰Rn. Only in the last case was it possible to find data to shed light on the validity of our predictions. The agreement seemed such that a falsification of our model was impossible. It is shown how the model can be used to predict the surface flux of ²²⁰Rn from measured concentration profiles.     

利用MODIS反演四川盆地地表温度与地面 同步气温、地温观测值的相关性试验

通过对MODIS反演的地表温度与四川盆地自动气象站观测的准同步地面空气温度Ta和0 cm地温Ts的相关分析,结果表明：对于非均匀下垫面,卫星反演地表温度TLS分别与Ta和Ts的相关系数稳定性都不好,不同卫星过境时间的相关系数差异很大。但（Ts-TLS）与（Ts-Ta）却有着既显著又稳定的线性相关,不同卫星过境时间的相关系数都达到0.8以上,具有良好的相关性。基于卫星反演地表温度和空气温度的地温统计模型,其标准误差为4.85 ℃。