利用位场连续复小波变换识辨磁场源(下)

基于齐次位场源的位场柯西小波变换，等效于位场向上延拓和求导两种运算相结合原理，建立了不同的理论模型，并编写了所有程序，通过合成资料的大量计算，对所有结果进行了验证与讨论。利用小波变换系数模沿极值轴线的变化特征，可以同时反演位场源的几何形状、埋深、倾角。实用于重磁资料自动化处理与解释，为磁场反演提供了一条新的途径。     

欧亚大气环流对中国北方春季沙尘天气的影响

根据1960-2010年全国701个地面站沙尘观测资料分析了中国春季沙尘天气的空间分布和年际变化,发现南疆和内蒙古两个沙尘源区的沙尘指数51年来都呈现出减小的趋势,其中内蒙古沙尘指数总体较小、年际变化较大,而南疆沙尘指数的波动较小。通过分析南疆和内蒙古沙尘指数典型高、低值年春季环流场发现,控制两个沙尘源区的环流场存在明显差异:南疆沙尘指数低值年时,西路入侵的冷空气减少,受此影响蒙古气旋和南疆热低压减弱,导致南疆地区近地面西风减弱,最终导致南疆沙尘天气减少;内蒙古沙尘指数低值年时,西北路和北路冷空气入侵次数减少,地面场上西伯利亚冷高压和蒙古高压减弱,并且蒙古气旋的发生发展受到限制,导致内蒙古西部近地面西北风和偏西风减小,最终导致内蒙古地区沙尘天气减少。     

Estimating the Isoneutral Slope and Tracer Diffusion from Argo Observations

Tracer diffusion is an important issue in ocean modeling, and isoneutral slope is key to parameterization of tracer diffusion in the ocean interior when using the isoneutral/dianeutral scheme. In this study, multiyear mean temperature, salinity, and pressure-gridded products that cover the upper 2000 m of the global ocean are created by employing all the Argo float observations up to date. Comparison with WOA09 data indicates that Argo temperature and salinity depict the reality well. Based on the reliable Argo gridded products, the in situ density fields are calculated. Then isoneutral slope in the ocean interior deep to 2000 m was determined by using the Argo-derived density. Taking advantage of isoneutral slope, therefore, diffusion tensor as well as isoneutral tracer diffusion flux can be obtained in combination of the tracer diffusion coefficient. The aim of this work is to propose a procedure to estimate the isoneutral slope using Argo observations and to offer new isoneutral slope-gridded products in the hope of further facilitating the parameterization of isoneutral tracer diffusion in geopotential (Z-coordinate) ocean models.     

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A timewise kinematic method for satellite gradiometry: GOCE simulations

We have defined new algorithms for the data processing of a satellite geodesy mission with gradiometer (such as the next European mission GOCE) to extract the information on the gravity field coefficients with a realistic estimate of their accuracy. The large scale data processing can be managed by a multistage decomposition. First the spacecraft position is determined, i.e., a kinematic method is normally used. Second we use a new method to perform the necessary digital calibration of the gradiometer. Third we use a multiarc approach to separately solve for the global gravity field parameters. Fourth we use an approximate resonant decomposition, that is we partition in a new way the harmonic coefficients of the gravity field. Thus the normal system is reduced to blocks of manageable size without neglecting significant correlations. Still the normal system is badly conditioned because of the polar gaps in the spatial distribution of the data. We have shown that the principal components of the uncertainty correspond to harmonic anomalies with very small signal in the region where GOCE is flying; these uncertainties cannot be removed by any data processing method. This allows a complete simulation of the GOCE mission with affordable computer resources. We show that it is possible to solve for the harmonic coefficients up to degree 200–220 with signal to error ratio ≥1, taking into account systematic measurement errors. Errors in the spacecraft orbit, as expected from state of the art satellite navigation, do not degrade the solution. Gradiometer calibration is the main problem. By including a systematic error model, we have shown that the results are sensitive to spurious gradiometer signals at frequencies close to the lower limit of the measurement band. If these spurious effects grow as the inverse of the frequency, then the actual error is larger than the formal error only by a factor ≃2, that is the results are not compromised.     

论大地水准面

经典大地水准面被定义为等重力位水准面,它在海洋中重合于假想的静止海水面,而后者通常又由平均海水面来代替。然而,平均海水面并非重力等位面,如果精度要求高于1m,则上述经典定义不再适用。近代大地水准面被定义为最接近于平均海水面的重力等位面,但关键问题是如何确定这种大地水准面。为实现这一目标,不仅需要确定大地水准面的形状,而且需要确定大地位常数W₀。探讨了几种主要的大地水准面的定义及其相关的确定大地水准面的问题,并建议了一种新的大地水准面的定义。     

陕西盛夏多雨年与少雨年的大气环流特征分析

应用NCEP/NCAR 1979—2004年再分析资料,针对陕西盛夏（7—8月）降水的情况,分析了汛期降水异常的大气环流特征。结果表明:陕西汛期多雨年,影响降水的主要天气系统表现为“三强一弱”,即西太平洋副热带高压、西风带蒙古低槽、乌拉尔山阻塞高压强,青藏高压弱;少雨年天气系统表现为“三弱一强”,即西太平洋副热带高压、西风带蒙古低槽、乌拉尔山阻塞高压弱,青藏高压强。另外,在多雨年,500 hPa流场,在陕西中部有一条东西向的切变线或风向辐合区;850 hPa形成了孟加拉湾经四川盆地到陕西和南海经鄂西北到陕西的水汽通道;少雨年500 hPa河套中部为西北气流控制,850 hPa水汽通道不明显或水汽输送中途减弱。     

Efficient Determination of Global Gravity Field from Satellite-to-satellite Tracking Mission

The gravity field dedicated satellite missions like CHAMP, GRACE, and GOCE are supposed to map the Earth's global gravity field with unprecedented accuracy and resolution. New models of the Earth's static and time-variable gravity fields will be available every month as one of the science products from GRACE. A method for the efficient gravity field recovery is presented using in situ satellite-to-satellite observations at altitude and results on static as well as temporal gravity field recovery are shown. Considering the energy relationship between the kinetic energy of the satellite and the gravitational potential, the disturbing potential observations can be computed from the orbital state vector, using high-low GPS tracking data, low–low satellite-to-satellite GRACE measurements, and data from 3-axis accelerometers. The solution method is based on the conjugate gradient iterative approach to efficiently recover the gravity field coefficients and approximate error covariance up to degree and order 120 every month. Based on the monthly GRACE noise-only simulation, the geoid was obtained with an accuracy of a few cm and with a resolution (half wavelength) of 160 km. However, the geoid accuracy can become worse by a factor of 6–7 because of spatial aliasing. The approximate error covariance was found to be a very good accuracy measure of the estimated coefficients, geoid, and gravity anomaly. The temporal gravity field, representing the monthly mean continental water mass redistribution, was recovered in the presence of measurement noise and high frequency temporal variation. The resulting recovered temporal gravity fields have about 0.3 mm errors in terms of geoid height with a resolution of 670 km.     

华东高温期的大气环流特征分析

利用NCEP/NCAR再分析资料和地面气象站点资料,对1951—2005年华东高温日数较多（少）月和高温过程各阶段的500 hPa位势高度、850 hPa温度和相对湿度及700 hPa垂直速度的环流特征进行对比分析。结果表明：在高温日数较多月,副高西伸,850 hPa温度较高而相对湿度较低,华东中南部下沉气流明显,华东多为位势高度、温度和垂直速度正距平及相对湿度负距平;而在高温日数较少月,副高东退,850 hPa温度较低而相对湿度较高,整个华东为上升气流,并为位势高度、温度和垂直速度负距平及相对湿度正距平。与高温前期和衰退期相比,高温盛期副高北抬西进,华东850 hPa温度较高而相对湿度较低,华东南部下沉气流强盛,各要素距平值增加,多数要素距平中心移向华东或其周边。高温间断期则比盛期各要素距平减弱。大气环流要素场及其距平场的变动可以作为预报华东7—8月高温日数多寡和高温进程的参考依据。