乌拉特中旗一次寒潮天气过程分析

通过对乌拉特中旗2010年3月13—15日的寒潮天气过程,应用天气学原理和方法进行诊断分析,总结出阻高崩溃型寒潮天气过程形成发展的特点以及预报着眼点。     

High-resolution climate simulation of the last glacial maximum

The climate of the last glacial maximum (LGM) is simulated with a high-resolution atmospheric general circulation model, the NCAR CCM3 at spectral truncation of T170, corresponding to a grid cell size of roughly 75 km. The purpose of the study is to assess whether there are significant benefits from the higher resolution simulation compared to the lower resolution simulation associated with the role of topography. The LGM simulations were forced with modified CLIMAP sea ice distribution and sea surface temperatures (SST) reduced by 1°C, ice sheet topography, reduced CO₂, and 21,000 BP orbital parameters. The high-resolution model captures modern climate reasonably well, in particular the distribution of heavy precipitation in the tropical Pacific. For the ice age case, surface temperature simulated by the high-resolution model agrees better with those of proxy estimates than does the low-resolution model. Despite the fact that tropical SSTs were only 2.1°C less than the control run, there are many lowland tropical land areas 4–6°C colder than present. Comparison of T170 model results with the best constrained proxy temperature estimates (noble gas concentrations in groundwater) now yield no significant differences between model and observations. There are also significant upland temperature changes in the best resolved tropical mountain belt (the Andes). We provisionally attribute this result in part as resulting from decreased lateral mixing between ocean and land in a model with more model grid cells. A longstanding model-data discrepancy therefore appears to be resolved without invoking any unusual model physics. The response of the Asian summer monsoon can also be more clearly linked to local geography in the high-resolution model than in the low-resolution model; this distinction should enable more confident validation of climate proxy data with the high-resolution model. Elsewhere, an inferred salinity increase in the subtropical North Atlantic may have significant implications for ocean circulation changes during the LGM. A large part of the Amazon and Congo Basins are simulated to be substantially drier in the ice age—consistent with many (but not all) paleo data. These results suggest that there are considerable benefits derived from high-resolution model regarding regional climate responses, and that observationalists can now compare their results with models that resolve geography at a resolution comparable to that which the proxy data represent.     

Some Insights into Topographic,Elastic and Self-gravitation Interaction in Modelling Ground Deformation and Gravity Changes in Active Volcanic Areas

Surface displacements and gravity changes due to volcanic sources are influenced by medium properties. We investigate topographic, elastic and self-gravitation interaction in order to outline the major factors that are significant in data modelling. While elastic-gravitational models can provide a suitable approximation to problems of volcanic loading in areas where topographic relief is negligible, for prominent volcanoes the rough topography could affect deformation and gravity changes to a greater extent than self-gravitation. This fact requires the selection, depending on local relief, of a suitable model for use in the interpretation of surface precursors of volcanic activity. We use the three-dimensional Indirect Boundary Element Method to examine the effects of topography on deformation and gravity changes in models of magma chamber inflation/deflation. Topography has a significant effect on predicted surface deformation and gravity changes. Both the magnitude and pattern of the geodetic signals are significantly different compared to half-space solutions. Thus, failure to account for topographic effects in areas of prominent relief can bias the estimate of volcanic source parameters, since the magnitude and pattern of deformation and gravity changes depend on such effects.     

高精度温度采集系统设计

针对高精度温度采集的需求,设计了一个以低功耗单片机MSP430F149作为核心处理器,以PT100铂电阻为传感器的温度采集系统。为了提高系统的复用性,采用精密电阻法,从硬件设计上消除了恒流源电流漂移以及A/D转换电路参考电压精度对温度测量数据的影响。重点描述了系统设计方案,详细说明了恒流源选择的原则、电流偏差的消除以及AD7792转换器的操作步骤。实验结果表明,温度测量精度优于0.1 ℃。对比试验表明,系统稳定性良好,已应用于业务产品中。     

雷达VIL在局地强对流天气应用中应注意的几个问题

结合兰州新一代天气雷达的使用情况,介绍了其物理量产品中垂直积分液态含水量(Verti-cally Integrated L iqu id W ater Content,)的理论计算模式,从雷达观测距离对VIL计算的影响、VIL理论模式中的反射率强度和探测高度对VIL计算的影响及VIL在强对流天气识别中受季节变化的影响3方面提出了思考,以期为今后应用VIL识别强对流天气提供参考。     

UV attenuation in the cloudy atmosphere

Ultraviolet (UV) energy absorption plays a very important role in the Earth–atmosphere system. Based on observational data for Beijing, we suggest that some atmospheric constituents utilize or transfer UV energy in chemical and photochemical (C&P) reactions, in addition to those which absorb UV energy directly. These constituents are primarily volatile organic compounds (VOCs) emitted from both vegetative and anthropogenic sources. The total UV energy loss in the cloudy atmosphere for Beijing in 1990 was 78.9 Wm⁻². This attenuation was caused by ozone (48.3 Wm⁻²), other compounds in the atmosphere (26.6 Wm⁻²) and a scattering factor (4.0 Wm⁻²). Our results for a cloudy atmosphere in the Beijing area show that the absorption due to these other compounds occurs largely through the mediation of water vapor. This fraction of energy loss has not been fully accounted for in previous models. Observations and previous models results suggest that 1) a cloudy atmosphere absorbs 25∼30 Wm⁻² more solar shortwave radiation than models predict; and 2) aerosols can significantly decrease the downward mean UV-visible radiation and the absorbed solar radiation at the surface by up to 28 and 23 Wm⁻², respectively. Thus, quantitative study of UV and visible absorption by atmospheric constituents involved in homogeneous and heterogeneous C&P reactions is important for atmospheric models.     

Estimation of Surface-Layer Scaling Parameters in the Unstable Boundary Layer: Implications for Orographic Flow Speed-Up

A method is proposed for estimating the surface-layer depth \((z_s)\) and the friction velocity \((u_*)\) as a function of stability (here quantified by the Obukhov length, L) over the complete range of unstable flow regimes. This method extends that developed previously for stable conditions by Argaín et al. (Boundary-Layer Meteorol 130:15–28, 2009), but uses a qualitatively different approach. The method is specifically used to calculate the fractional speed-up \((\varDelta S)\) in flow over a ridge, although it is suitable for more general boundary-layer applications. The behaviour of \(z_s \left( L\right) \) and \(u_*\left( L\right) \) as a function of L is indirectly assessed via calculation of \(\varDelta S\left( L\right) \) using the linear model of Hunt et al. (Q J R Meteorol Soc 29:16–26, 1988) and its comparison with the field measurements reported in Coppin et al. (Boundary-Layer Meteorol 69:173–199, 1994) and with numerical simulations carried out using a non-linear numerical model, FLEX. The behaviour of \(\varDelta S\) estimated from the linear model is clearly improved when \(u_*\) is calculated using the method proposed here, confirming the importance of accounting for the dependences of \(z_s\left( L \right) \) and \(u_*\left( L \right) \) on L to better represent processes in the unstable boundary layer.     

Characteristics of carbonyl compounds in ambient air of Shanghai,China

The levels of carbonyl compounds in Shanghai ambient air were measured in five periods from January 2007 to October 2007 (covering winter, high-air-pollution days, spring, summer and autumn). A total of 114 samples were collected and eighteen carbonyls were identified. Formaldehyde, acetaldehyde and acetone were the most abundant carbonyls and their mean concentrations of 19.40 ± 12.00, 15.92 ± 12.07 and 11.86 ± 7.04 μg m⁻³ respectively, in the daytime for five sampling periods. Formaldehyde and acetaldehyde showed similar diurnal profiles with peak mixing ratios in the morning and early afternoon during the daytime. Their mean concentrations were highest in summer and lowest in winter. Acetone showed reversed seasonal variation. The high molecular weight (HMW, ≥C5) carbonyls also showed obvious diurnal variations with higher concentrations in the daytime in summer and autumn, while they were all not detected in winter. Formaldehyde and acetaldehyde played an important role in removing OH radicals in the atmosphere, but the contribution of acetone was below 1%. The carbonyls levels in high-air-pollution days were reported. More carbonyl species with higher concentrations were found in high-air-pollution days than in spring. These carbonyls were transported with other pollutants from north and northwest in March 27 to April 2, 2007 and then mixed with local sources. Comparing with Beijing and Guangzhou, the concentrations of formaldehyde and acetaldehyde in Shanghai were the highest, which indicated that the air pollution in Shanghai was even worse than expected.     

Adaptation of Pressure Based CFD Solvers for Mesoscale Atmospheric Problems

General purpose Computational Fluid Dynamics (CFD) solvers are frequently used in small-scale urban pollution dispersion simulations without a large extent of ver- tical flow. Vertical flow, however, plays an important role in the formation of local breezes, such as urban heat island induced breezes that have great significance in the ventilation of large cities. The effects of atmospheric stratification, anelasticity and Coriolis force must be taken into account in such simulations. We introduce a general method for adapting pressure based CFD solvers to atmospheric flow simulations in order to take advantage of their high flexibility in geometrical modelling and meshing. Compressibility and thermal stratification effects are taken into account by utilizing a novel system of transformations of the field variables and by adding consequential source terms to the model equations of incompressible flow. Phenomena involving mesoscale to microscale coupled effects can be analyzed without model nesting, applying only local grid refinement of an arbitrary level. Elements of the method are validated against an analytical solution, results of a reference calculation, and a laboratory scale urban heat island circulation experiment. The new approach can be applied with benefits to several areas of application. Inclusion of the moisture transport phenomena and the surface energy balance are important further steps towards the practical application of the method.     

Geochronology and geochemistry of the Hekoulinchang Sn-Pb-Zn-Ag polymetallic deposit (73240 t) in Heilongjiang Province,China

The Hekoulinchang Sn-Pb-Zn-Ag polymetallic deposit(20000 t Sn at 0.27%,236 t Ag at 122.89 g/t,15000 t Pb at 0.84%,and 38000 t Zn at 1.43%)is located in the Wandashan Terrane of the easternmost segment of the Central Asian Orogenic Belt.The timing of Sn-Pb-Zn-Ag polymetallic mineralization remains unclear due to a lack of precise isotope dating directly conducted on ore minerals.The authors herein report that the LA-ICP-MS U-Pb ages of cassiterite and zircon from the granite porphyry in the Hekoulinchang Sn-Pb-Zn-Ag polymetallic deposit are 101.4±7.9 Ma and 115.4±1.0 Ma,respectively,indicating that Sn mineralization and magmatism occurred during the Early Cretaceous.The granite porphyry belongs to the subalkaline series peraluminous I-type granites that are depleted in Nb,Ta,and Ti and enriched in Rb,Th,U,and Pb.TheεHf(t)values of the granite porphyry range from 0.9 to 7.4,with an average of about 5.6 and two-stage model ages(T_DM2)of 705–1116 Ma,with an average age of 819 Ma.The ε_Nd(t)values of the apatites are–1.60–0.45,with an average of–0.9,and two-stage model ages(T_DM2)of 872–1040 Ma,with an average age of 983 Ma.The Nd-Hf isotope data indicate that the magma may have been derived from the partial melting of juvenile crustal material.