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为了弥补青藏高原雷暴观测个例的不足,从动力、微物理和起电过程之间的密切联系来解释青藏高原雷暴云底部较大的次正电荷区（LPCC）和暖云区厚度（WCD）之间的关系,本文设置敏感性试验组,通过三种途径,改变了青藏高原那曲地区一次LPCC明显且对流较强的雷暴过程的探空初始场,得到10组具有不同WCD值的初始场算例,利用三维雷暴云动力-电耦合数值模式,模拟分析了WCD和LPCC之间的可能关系。结果表明,在青藏高原WCD并不是决定LPCC大小的唯一因素,明显的LPCC的形成需要较薄的WCD配合较强但不能太强的上升速度,即使WCD很薄,太强的上升气流也仅容易形成主正和主负电荷区非常强的一般型雷暴,太弱的上升气流,也仅能形成主正和主负电荷区很弱的一般型雷暴。雨滴的两个主要源项,即雨滴通过重力碰并收集云水和霰融化形成雨水,及霰的主要源项霰撞冻云水,这三个微物理过程的效率主要取决于对流强度。薄的WCD对暖云降水过程的抑制作用不及强的上升速度对暖云降水过程的增强作用。在对流强度变化不大的情况下,WCD主要影响着冰粒子的分布高度,WCD越薄,向0℃层以上输送的云滴尺寸越小,数目越多,越利于低层冰粒子的生长,L... 相似文献
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外部知识环境与内资企业新出口市场开拓 总被引：1，自引：0，他引：1
自中国加入WTO以来,出口贸易发展迅速。从出口主体来看,内资企业的出口行为对区域经济增长和中国自身实力的提升尤为重要。建立对外联系、利用外部资源能够有效地促进内资企业拓展海外市场。论文使用中国海关库2001—2011年企业层面的进出口数据,借助条件逻辑回归模型研究地级市尺度上外部知识环境对内资企业开拓新出口市场产生的溢出效应。研究区分了影响内资企业海外市场拓展的3种外部知识环境,内资企业可以：从同一区域的外资企业处获得外部知识;与邻近区域企业形成跨区域联系,获取外部知识;从国外进口获取外部知识。通过对比3种外部知识环境对于地级市尺度内资企业开拓新出口市场的影响,发现：① 3种外部知识环境对内资企业开拓新出口市场均表现出积极作用;本地外资企业出口的溢出效应最大,本地企业进口的溢出效应次之,邻近城市企业出口溢出效应最小;② 中西部地区与东北地区的邻近城市企业出口溢出贡献最大,且3种外部知识环境带来的溢出效应均明显强于东部地区;③ 本地外资企业与邻近城市企业出口溢出对高技术产品的影响明显强于低技术产品。 相似文献
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Based on LIS/OTD gridded lightning climatology data, ERA5 reanalysis data, and MODIS atmosphere monthly global products, we examined latitudinal and daily variations of lightning activity over land, offshore areas, open sea, and all marine areas (i.e., the aggregate of open sea and offshore areas) for different seasons over the Pacific Ocean and the adjacent land areas at 65°N-50°S, 99°E-78°W, and analysed the relationships of lightning activity with CAPE (Convective Available Potential Energy) and AOD (Aerosol Optical Depth). At any given latitude, the lightning density is the highest over land, followed by offshore areas, all marine areas and the open sea in sequence. The lightning density over land is approximately an order of magnitude greater than that over all marine areas. Lightning activity over land, offshore areas, open sea, and all marine areas varies with season. The diurnal variation of lightning density over land has a single-peak pattern. Over the offshore area, open sea, and all marine areas, lightning densities have two maxima per day. The magnitude of the daily variation in mean lightning density is the largest over land and the smallest over the open sea. The lightning density over the Pacific Ocean and adjacent land areas is significantly and positively correlated with CAPE. The correlation is the strongest over land and the weakest over the open sea. Cloud Base Height (CBH) may affect the efficiency of CAPE conversion to updraft. CAPE has a positive effect on lightning activity and has a greater impact on land than on the ocean. Over the sea, both CAPE and AOD can contribute to lightning activity, but the magnitudes of the influence of CAPE and AOD on lightning activity remain to be determined. Lightning activity over land and sea is a result of the combined action of AOD and CAPE. 相似文献
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