层状云人工催化物理效应的数值模拟

对于自然云催化过程的数值模拟可以再现人工催化后云的宏微观物理响应特征,有助于提高对人工催化机理的科学认识、优化人工催化方案。本文在WRF（Weather Research and Forecasting Model）模式Thompson微物理方案中加入碘化银人工催化过程,对2018年河北省一次层状云催化过程开展数值研究。数值模拟结果表明,采用与实际催化过程相似的催化剂量,层状云降水个例催化后冰晶含水量、数浓度及地面降水显著增加。该次降水个例自然云中冰相粒子较少,自然云中冰相过程不活跃,数值模拟结果再现了降水个例催化后从过冷却到冰、雪晶含量明显增加的转变。相同催化剂量下,催化层厚度的减少提高了播撒率,进一步优化了催化效果,可见,应该在云中过冷水含量丰富的云区开展冷云催化作业。人工催化过程增加的冰晶通过凝华过程增长并自动转化为雪晶,雪晶增长下落过程中以凇附过冷云水增长为主。本次催化过程导致地面降雪显著增加。     

碘化银播撒对流云增雨数值模拟

利用中国科学院大气物理研究所建立的完全弹性三维对流云模式,对发生在2008年内蒙古通辽市8月26日的一次对流性降水过程进行催化模拟和分析.结果表明,在本例中,在最大过冷水区播撒,采用合适的剂量进行催化对取得较好的增雨效果非常重要,AgI催化剂浓度过大则会取得负效果.播撒的时间越早,增雨效果越好.     

云微物理方案对一次高原切变线暴雨过程数值模拟的影响

利用中尺度数值模式WRF v3.8.1中的16种云微物理参数化方案,对2014年8月26—27日川渝地区的1次高原切变线主导下的暴雨过程进行了数值模拟对比实验.结果表明:WRF模式能够较好地模拟本次切变线强降水过程,总体来说NSSL 2-moment方案的模拟效果最好.但不同云微物理方案对于不同量级降水的模拟各有优势,NSSL 2-moment方案对大雨及暴雨的模拟效果最好.在主要降水区,各方案模拟的逐小时降水量的峰值均滞后于实况并且突发性更强,NSSL 2-moment+CCN方案在此区域模拟的累积降水量与实况最为接近.云中水成物含量的模拟结果显示,模拟降水较多的方案中其雪粒子含量也较多,而雪粒子不仅在其凝结过程中的潜热释放有利于对流活动发展,并且亦可以通过融化过程促进降水.而对于暖云降水部分,能够到达地面的雨水粒子含量的模拟在各方案中并无显著差异.     

利用三维云模式对一次强暴雨微物理过程的数值模拟

利用三维准弹性中小尺度云模式，对武汉地区1998年7月的一次强降水过程进行了数值模拟，研究了产生强降水云的微物理过程和降水机制，揭示了暴雨云高效率降水的基本原因。结果表明，这次暴雨过程的最大特点是降水持续且降水强度大，云内上升速度的长时间维持和云内较大水凝物含量为特大暴雨的产生提供了条件。这次暴雨过程中，云雨的自动转化碰并过程以及霰的融化致雨过程相对于其它物理过程更为重要。     

自然崩落采矿法的颗粒流数值模拟

以自然崩落采矿法为研究对象,利用二维颗粒流数值模拟(PFC2D)的原理和方法,研究了自然崩落法矿体崩落规律. 以某镍铜矿的地质条件及矿岩物理力学性质为依据,采用数值模拟的方法分析了自然崩落法的崩落规律. 结果表明:PFC2D模型在分析自然崩落过程中力学机理的同时,能有效地模拟自然崩落法采矿过程,并且能直观地给出矿体在崩落过程中各种参数的具体形态变化. 利用PFC2D模型预测该镍铜矿自然崩落法初始崩落拉底半径为10 m,连续崩落的拉底半径为22 m,有效地指导该矿自然崩落法的放矿.     

高速碰撞下二次破片光滑粒子流体力学法数值模拟

采用AUTODYN-2D无网格光滑粒子流体力学方法(SPH)数值技术,对遭遇速度为1.5～2.5 km/s下圆柱钨弹丸垂直碰撞装甲靶板产生的二次破片云分布特征进行了数值模拟,获得了不同碰撞速度下靶板穿孔直径及破片云前端运动速度、侧向膨胀速度和最大飞散角等分布特征.在此基础上,建立了二次破片云质量及空间分布预测模型.结果表明,数值模拟和模型预测均与实验结果相吻合.     

碰撞倾角对碎片云分布影响的数值模拟

研究超高速斜碰撞所形成的二次碎片云的分布特性. 采用SPH与Lagrange耦合的方法计算了靶板上的穿孔尺寸随碰撞倾角的变化,并在此基础上模拟了碰撞倾角对二次碎片云分布的影响. 计算结果与实验拟合结果表明,所采用的耦合方法可以很好地模拟穿孔尺寸和二次碎片云分布;当碰撞倾角增大到60°时,法线碎片云的质心轨迹与直线碎片云的质心轨迹明显分离,并且反跳碎片云中弹丸材料的粒子数目将显著增加.     

甲基叔丁基醚催化精馏塔模拟研究

该文应用PROII软件对甲基叔丁基醚(MTBE)生产过程中的催化精馏塔进行了模拟研究。首先对年产15万吨MTBE生产过程催化精馏塔中的参数进行分析并确定影响因素。其次通过改变参数后比较模拟结果对塔内催化剂用量、催化剂分布和装填位置进行分析,得到相应的合理值。     

基于倾斜影像颜色信息的建筑物点云提取

针对建筑物点云提取不完整问题,笔者采用一种组合方法从影像密集匹配获得的多视图像(MVS)点云中提取建筑物点云.首先运用布料模拟滤波(CSF)算法进行地面点滤波,去除MVS点云中的地面点;然后根据MVS点云的颜色信息,利用过绿指数(EXG)和植被密集成块特性将植被点云剔除;最后使用密度聚类从剩余的点云中分割出建筑物点云....     

用于RFID网络规划的含Expansion关系的多目标云优化算法（英文）

给出了一个含有Expansion关系的多目标云优化算法,并用于求解RFID网络规划问题.该算法的思想源自于云模型,利用云模型理论估计优化过程的优势解区域和生成新解.在优化过程中,算法利用获得的信息建立优势解区域的云模型,并用反向云生成算法计算该云模型的3个数字特征.在此基础上,依据这3个数字特征,用正向云生成算法产生当前代的子代种群.为了引导寻优过程,Expansion关系被用于比较最好的一些个体,并对当前代种群和当前代子种群的并集用Expansion关系进行排序;之后,依据这个排序结果从中选择一些最好的个体组成下一代种群.该算法与其它一些算法就一组基准函数进行了模拟测试比较,并用于求解一个模拟RFID网络规划问题,代距准则(GD)和多样性(Δ)用于评价算法的性能,模拟结果显示该算法是有效的.     

Methane drizzle on Titan

Saturn's moon Titan shows landscapes with fluvial features suggestive of hydrology based on liquid methane. Recent efforts in understanding Titan's methane hydrological cycle have focused on occasional cloud outbursts near the south pole or cloud streaks at southern mid-latitudes and the mechanisms of their formation. It is not known, however, if the clouds produce rain or if there are also non-convective clouds, as predicted by several models. Here we show that the in situ data on the methane concentration and temperature profile in Titan's troposphere point to the presence of layered optically thin stratiform clouds. The data indicate an upper methane ice cloud and a lower, barely visible, liquid methane-nitrogen cloud, with a gap in between. The lower, liquid, cloud produces drizzle that reaches the surface. These non-convective methane clouds are quasi-permanent features supported by the global atmospheric circulation, indicating that methane precipitation occurs wherever there is slow upward motion. This drizzle is a persistent component of Titan's methane hydrological cycle and, by wetting the surface on a global scale, plays an active role in the surface geology of Titan.     

The formation of cubic ice under conditions relevant to Earth's atmosphere

An important mechanism for ice cloud formation in the Earth's atmosphere is homogeneous nucleation of ice in aqueous droplets, and this process is generally assumed to produce hexagonal ice. However, there are some reports that the metastable crystalline phase of ice, cubic ice, may form in the Earth's atmosphere. Here we present laboratory experiments demonstrating that cubic ice forms when micrometre-sized droplets of pure water and aqueous solutions freeze homogeneously at cooling rates approaching those found in the atmosphere. We find that the formation of cubic ice is dominant when droplets freeze at temperatures below 190 K, which is in the temperature range relevant for polar stratospheric clouds and clouds in the tropical tropopause region. These results, together with heat transfer calculations, suggest that cubic ice will form in the Earth's atmosphere. If there were a significant fraction of cubic ice in some cold clouds this could increase their water vapour pressure, and modify their microphysics and ice particle size distributions. Under specific conditions this may lead to enhanced dehydration of the tropopause region.     

The impact of humidity above stratiform clouds on indirect aerosol climate forcing

Some of the global warming from anthropogenic greenhouse gases is offset by increased reflection of solar radiation by clouds with smaller droplets that form in air polluted with aerosol particles that serve as cloud condensation nuclei. The resulting cooling tendency, termed the indirect aerosol forcing, is thought to be comparable in magnitude to the forcing by anthropogenic CO2, but it is difficult to estimate because the physical processes that determine global aerosol and cloud populations are poorly understood. Smaller cloud droplets not only reflect sunlight more effectively, but also inhibit precipitation, which is expected to result in increased cloud water. Such an increase in cloud water would result in even more reflective clouds, further increasing the indirect forcing. Marine boundary-layer clouds polluted by aerosol particles, however, are not generally observed to hold more water. Here we simulate stratocumulus clouds with a fluid dynamics model that includes detailed treatments of cloud microphysics and radiative transfer. Our simulations show that the response of cloud water to suppression of precipitation from increased droplet concentrations is determined by a competition between moistening from decreased surface precipitation and drying from increased entrainment of overlying air. Only when the overlying air is humid or droplet concentrations are very low does sufficient precipitation reach the surface to allow cloud water to increase with droplet concentrations. Otherwise, the response of cloud water to aerosol-induced suppression of precipitation is dominated by enhanced entrainment of overlying dry air. In this scenario, cloud water is reduced as droplet concentrations increase, which diminishes the indirect climate forcing.     

Polar methane accumulation and rainstorms on Titan from simulations of the methane cycle

Titan has a methane cycle akin to Earth's water cycle. It has lakes in polar regions, preferentially in the north; dry low latitudes with fluvial features and occasional rainstorms; and tropospheric clouds mainly (so far) in southern middle latitudes and polar regions. Previous models have explained the low-latitude dryness as a result of atmospheric methane transport into middle and high latitudes. Hitherto, no model has explained why lakes are found only in polar regions and preferentially in the north; how low-latitude rainstorms arise; or why clouds cluster in southern middle and high latitudes. Here we report simulations with a three-dimensional atmospheric model coupled to a dynamic surface reservoir of methane. We find that methane is cold-trapped and accumulates in polar regions, preferentially in the north because the northern summer, at aphelion, is longer and has greater net precipitation than the southern summer. The net precipitation in polar regions is balanced in the annual mean by slow along-surface methane transport towards mid-latitudes, and subsequent evaporation. In low latitudes, rare but intense storms occur around the equinoxes, producing enough precipitation to carve surface features. Tropospheric clouds form primarily in middle and high latitudes of the summer hemisphere, which until recently has been the southern hemisphere. We predict that in the northern polar region, prominent clouds will form within about two (Earth) years and lake levels will rise over the next fifteen years.     

利用微脉冲激光雷达识别过冷水云层

在已有的云识别算法基础上, 利用微脉冲激光雷达后向散射信号区分云和气溶胶。按照云粒子的退偏振比, 区分冰云、水云、混合云以及水平导向的冰晶云。结合大气温度廓线, 对过冷水云层进行有效的识别。利用观测点上空持续一年的观测资料, 统计各种云出现的高度及比例的逐月变化, 结果显示, 过冷水云出现的时间占有云时间的9.84%, 对于0~−40℃的云层, 过冷水云出现的时间占11.99%。     

Characteristics of clouds,precipitation, and latent heat in midlatitude frontal system mixed with dust storm from GPM satellite observations and WRF simulations

A heavy dust storm originating in Mongolia and Inner Mongolia traveled to Northeast China and met a midlatitude frontal system on May 3, 2017. The potential ice nuclei (IN) effects of mineral dust aerosols on the vertical structure of clouds, precipitation, and latent heat (LH) were studied using Global Precipitation Mission (GPM) satellite observations and Weather Research and Forecasting (WRF) model simulations. The WRF simulations correctly captured the main features of the system, and the surface rain rate distribution was positively correlated with data retrieved from the GPM Microwave Imager. Moreover, the correlation coefficient increased from 0.31 to 0.54 with increasing moving average window size. The WRF-simulated rainfall vertical profiles are generally comparable to the GPM Dual-Frequency Precipitation Radar (DPR) observations, particularly in low layers. The joint probability distribution functions of the rain rate at different altitudes from the WRF simulation and GPM observations show high positive correlation coefficients of ~0.80, indicating that the assumptions regarding the raindrop size distribution in the WRF model and DPR retrieval were consistent. Atmospheric circulation analysis and aerosol optical depth observations from the Himawari-8 satellite indicated that the dust storm entered only a narrow strip of the northwest edge of the frontal precipitation system. The WRF simulations showed that in carefully selected areas of heavy dust, dust can enhance the heterogeneous ice nucleation process and increase the cloud ice, snowfall, high-altitude precipitation rate, and LH rate in the upper layers. This effect is significant at temperatures of ?15 °C to ?38 °C and requires dust number concentrations exceeding 106 m?3. It is important to accurately classify the dusty region in this type of case study. In the selected vertical cross section, the WRF-simulated and DPR-retrieved LH have comparable vertical shapes and amplitudes. Both results reflect the structure of the tilted frontal surface, with positive LH above it and negative LH below it. The simulated area-averaged LH profiles show positive heating in the entire column, which is a convective-dominated region, and this feature is not significantly affected by dust. DPR-based LH profiles show stratiform-dominated or convective-dominated shapes, depending on the DPR retrieval product.     

Deep convective clouds with sustained supercooled liquid water down to -37.5 degrees C

In cirrus and orographic wave clouds, highly supercooled water has been observed in small quantities (less than 0.15 g m(-3)). This high degree of supercooling was attributed to the small droplet size and the lack of ice nuclei at the heights of these clouds. For deep convective clouds, which have much larger droplets near their tops and which take in aerosols from near the ground, no such measurements have hitherto been reported. However, satellite data suggest that highly supercooled water (down to -38 degrees C) frequently occurs in vigorous continental convective storms. Here we report in situ measurements in deep convective clouds from an aircraft, showing that most of the condensed water remains liquid down to -37.5 degrees C. The droplets reach a median volume diameter of 17 microm and amount to 1.8 gm(-3), one order of magnitude more than previously reported. At slightly colder temperatures only ice was found, suggesting homogeneous freezing. Because of the poor knowledge of mixed-phase cloud processes, the simulation of clouds using numerical models is difficult at present. Our observations will help to understand these cloud processes, such as rainfall, hail, and cloud electrification, together with their implications for the climate system.     

Precipitation variations recorded in Guliya ice core in the past 400 years

Based on the Guliya ice core records, the precipitation in the past 400 years was retrieved. Its rela tions with other regions were also analyzed. The results demonstrated that there were two high-precipitation periods and two low-precipitation periods in Guliya ice core since 1571 AD. The average precipitation in the two high-precipitation periods was 42 mm (21%) higher than that in the two low-precipitation periods. The precipitation recorded in the Guliya ice core was consistent with that in Dunde ice core. The variation trends of precipitation in the Guliya ice core and the northern hemisphere are similar. During the extremely wet years in the northern hemisphere, the precipitation recorded in the Guliya ice core was two times the long-term average. However, the annual precipitation was 38% less than that of the long-term average in extremely dry years.     

Precipitation variations recorded in Guliya ice core in the past 400 years

Based on the Guliya ice core records, the precipitation in the past 400 years was retrieved. Its rela tions with other regions were also analyzed. The results demonstrated that there were two high-precipitation periods and two low-precipitation periods in Guliya ice core since 1571 AD. The average precipitation in the two high-precipitation periods was 42 mm (21%) higher than that in the two low-precipitation periods. The precipitation recorded in the Guliya ice core was consistent with that in Dunde ice core. The variation trends of precipitation in the Guliya ice core and the northern hemisphere are similar. During the extremely wet years in the northern hemisphere, the precipitation recorded in the Guliya ice core was two times the long-term average. However, the annual precipitation was 38% less than that of the long-term average in extremely dry years.     

Westerly moisture transport to the middle of Himalayas revealed from the high deuterium excess

Previous studies found extremely high d-excess in both ice core and glacial melt water in Dasuopu glacier, Xixiabangma, middle of Himalayas. These values are much higher than the global average and those measured in southwest monsoon precipitation. The d-excess variation in over one year at Nyalam station will clarify this phenomenon. Studies show that the high d-excess is related to the seasonal variation of moisture transport to this region. The d-excess values are low during the southwest monsoon active periods, when moisture originated from the humid ocean surface. The d-excess values are higher in non-monsoon months, when moisture is derived from westerly transport. Winter and spring precipitation accounts for a substantial portion of the annual precipitation, resulting in higher d-excess in the yearly precipitation in the middle of Himalayas than other parts of the southern Tibetan Plateau. This finding reveals that the precipitation in the middle of Himalayas is not purely from southwest monsoon, but a large portion from the westerly transport, which is very important for ice core study in this area.