变分同化方法在Lorenz系统中的简单应用研究

利用Lorenz模式作变分同化数值试验 ,通过对一个简单系统的讨论 ,介绍四维变分同化方法。对初值敏感性和观测点的个数及观测值作了对比试验 ,发现随着模式对初值敏感性的增加 ,同化效果会越来越差 ;观测点越少 ,观测值误差越大 ,这些都会影响同化效果 ,甚至导致同化失败。

奥斯特/GPS掩星与地面雷达联合观测电离层电子密度的初步结果

1999年2月丹麦发射了一颗奥斯特小卫星,它装载了两台GPS接收机,其中一台用于电离层和中性大气掩星测量,另一台用于自主定位。本文给出了1999年10月奥斯特/GPS掩星与日本MU雷达和数字测高仪的联合观测结果。奥斯特掩星反演得到的电子密度剖面与地面雷达观测的进行了比较,结果表明:天基和地基雷达观测的电子密度是一致的。文章还给出利用GPS的单频信号反演电离层电子密度剖面技术和3维射线追踪技术模拟掩星结果。

Altimetric Data Assimilation by EnOI and 3DVAR in a Tropical Pacific Model:Impact on the Simulation of Variability

When altimetric data is assimilated, 3DVAR and Ensemble Optimal Interpolation （EnOI） have different ways of projecting the surface information downward. In 3DVAR, it is achieved by minimizing a cost function relating the temperature, salinity, and sea level. In EnOI, however, the surface information is propagated to other variables via a stationary ensemble. In this study, the differences between the two methods were compared and their impacts on the simulated variability were evaluated in a tropical Pacific model. Sea level anomalies （SLA） from the TOPEX/Poseidon were assimilated using both methods on data from 1997 to 2001 in a coarse resolution model. Results show that the standard deviation of sea level was improved by both methods, but the EnOI was more effective in the central/eastern Pacific. Meanwhile, the SLA evolution was better reproduced with EnOI than with 3DVAR. Correlations of temperature with the reanalysis data increased with EnOI by 0.1 0.2 above 200 m. In the eastern Pacific below 200 m, the correlations also increased by 0.2. However, the correlations decreased with 3DVAR in many areas. Correlations with the independent TAO profiles were also compared at two locations. While the correlations increased by up to 0.2 at some depths with EnOI, 3DVAR generally reduced the correlations by 0.1 0.3. Though both methods were able to reduce the model-data difference in climatological sense, 3DVAR appears to have degraded the simulated variability, especially during E1 Nifio-Southern Oscillation events. For salinity, similar results were found from the correlations. This tendency should be considered in future SLA assimilations, though the comparisons may vary among different model implementations.

Reduced Solar Activity Disguises Global Temperature Rise

The question whether human activities seriously affect climate is asked with increasing voice these days. Quite understandable since the climate appears to be out of control with the significant global temperature increases already seen during the last three decades and with still heavier temperature increases to come in the future according to prognoses, among others, in the recent comprehensive IPCC reports [1]. However, the most recent climate data [2], show global temperature development levelling off or even turning negative since 2001 in contrast to the anticipated course related to the steady increases in the concentration in the atmosphere of green-house gasses, primarily carbon dioxide and methane [1]. The purpose of this communication is to demonstrate that the reduced rate in the global temperature rise complies with expectations related to the decaying level of solar activity according to the relation published in an earlier analysis [3]. Without the reduction in the solar activity-related contributions the global temperatures would have increased steadily from 1980 to present.

Exploring Greenhouse Gases Water and Climate Changes:Scientific Opportunities for the Climate and Atmospheric Composition Exploring Satellites Mission

The Essential Climate Variables(ECVs),such as the atmospheric thermodynamic state variables and greenhouse gases,play an important role in the atmosphere physical processes and global climate change.Given the need of improvements in existing ground-based and satellite observations to successfully deliver atmosphere and climate benchmark data and reduce data ambiguity,the Climate and Atmospheric Composition Exploring Satellites mission(CACES)was proposed and selected as a candidate mission of the Strategic Priority Research Program of Chinese Academy Science(SPRPCAS).This paper presents an overview of the key scientific questions and responses of EC Vs in relation to global change;the principles,algorithms,and payloads of microwave occultation using centimeter and millimeter wave signals between low Earth orbit satellites(LEO-LEO microwave occultation,LMO)as well as of the LEO-LEO infrared-laser occultation(LIO);the CACES mission with its scientific objectives,mission concept,spacecraft and instrumentation.

Space Weather Parameters Computed on the Basis of the Magnetogram Inversion Technique

In this paper is given short description of the magnetogram inversion technique, MIT2, and of methods of calculation of some parameters of space weather. Are given also examples of new results, obtained using the MIT2 and solar wind data.

Atmospheric Trajectory and Chemical Transport Modelling for Elevated Ozone Events in Denmark

In this study, three Danish sites having the longest (1990-2004) time-series of ozone measurements were analysed on inter-annual, monthly and diurnal cycle variability as well as elevated and lowered ozone concentration events were identified. The atmospheric trajectory (HYSPLIT) and dispersion (HIRLAM + CAMx) models were employed to study dominating atmospheric transport patterns associated with elevated events and to evaluate spatio-temporal variability of ozone specific episode and typical seasonal patterns for Denmark. It was found that generally inter-annual variability has a positive trend, and events with low ozone concentration (≤10 μg/m3) continued to diminish. On a monthly scale, the highest and lowest mean concentrations are observed in May and November-December, respectively. The elevated concentrations (≥120 μg/m3) are observed during March-September. On a diurnal cycle, it is observed mostly during 13-16 of local time, and more frequent (ten-fold) compared with nighttime-early morning hours. For ozone elevated events, several sectors (or pathways of atmospheric transport) were identified depending on the sites’ positions, showing the largest (39%) number of such events associated with the north-western sector, and lowest (13% each)—southwestern and northern sectors. For each site, less than 60 events showed very high concentrations (≥180 μg/m3). Among 12 episodes, one longest elevated episode (19-21 Jun 2000) simultaneously registered at all sites and characterized by dominating transport from the south-southwestern sector, low wind speed, clear-sky, and multiple inversions was studied using modelling tools. For this episode, both measurements and modeling (trajectory and dispersion) results showed a relatively good agreement.

Effects of Changed Climate Conditions on Tropospheric Ozone over Three Centuries

The ozone chemistry in four decades (1890s, 1990s, 2090s and 2190s) representing the changes over three centuries has been simulated using the chemistry version of the atmospheric long-range transport model: the Danish Eulerian Hemispheric Model (DEHM) forced with meteorology projected by theECHAM5/MPI-OM coupled Atmosphere-Ocean General Circulation Model. The largest changes in meteorology, ozone and its precursors are found in the 21st century, however, also significant changes are found in the 22nd century. At surface level the ozone concentration is projected to increase due to climate change in the areas where substantial amounts of ozone precursors are emitted. Elsewhere a significant decrease is projected at the surface. In the free troposphere a general increase is found in the entire Northern Hemisphere except in the tropics, where the ozone concentration is decreasing. In the Arctic the ozone concentration will increase in the entire air column, which most likely is due to changes in atmospheric transport. Changes in temperature, humidity and the naturally emitted Volatile Organic Compounds (VOCs) are governing the changes in ozone both in the past, present and future century.

ON THE SENSITIVITY OF PRECIPITATION FORECASTS TO THE MOIST PHYSICS AND THE HORIZONTAL RESOLUTION OF NUMERICAL MODEL

The impacts of the enhanced model's moist physics and horizontal resolution upon the QPFs (quantitative precipitation forecasts)are investigated by applying the HIRLAM(high resolution limited area model)to the summer heavy-rain cases in China.The performance of the control run, for which a 0.5°×0.5°grid spacing and a traditional“grid-box supersaturation removal+Kuo type convective paramerization”are used as the moist physics,is compared with that of the sensitivity runs with an enhanced model's moist physics(Sundqvist scheme)and an increased horizontal resolution(0.25°×0.25°),respectively.The results show: (1)The enhanced moist physics scheme(Sundqvist scheme),by introducing the cloud water content as an additional prognostic variable and taking into account briefly of the microphysics involved in the cloud-rain conversion,does bring improvements in the model's QPFs.Although the deteriorated QPFs also occur occasionally,the improvements are found in the majority of the cases,indicating the great potential for the improvement of QPFs by enhancing the model's moist physics. (2)By increasing the model's horizontal resolution from 0.5°×0.5°,which is already quite high compared with that of the conventional atmospheric soundings,to 0.25°×0.25°without the simultaneous enhancement in model physics and objective analysis,the improvements in QPFs are very limited.With higher resolution,although slight amelioration in locating the rainfall centers and in resolving some finer structures of precipitation pattern are made,the number of the mis- predicted fine structures in rainfall field increases with the enhanced model resolution as well.