共查询到20条相似文献，搜索用时 500 毫秒
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利用一个由表面摩擦和辐射线弛强迫驱动的斜压准地转两层模式作数值试验，来研究斜压大气中的亚临界不稳定现象。试验结果表明，当无量纲量β≥0.25时，斜压两层大气中能够发生亚临界不稳定现象。亚临界不稳定现象的发生与初始扰动的选择有关。科氏参数的经向梯度的大小又是影响斜压稳定性强度的一个重要因素，其值越大，斜压稳定性强度越小。 相似文献
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小尺度对流的发展和环境间相互作用的一个近似分析 总被引：3，自引：0，他引：3
本文应用一个近似的模式,分析了大气中小尺度对流发展时和环境(平均运动)间的非线性相互作用。分析结果指出,对流除在不稳定和中性稳定层结条件下可以发展外,在稳定层结条件下也可以得到发展,并且扰动的振幅最后均趋于有限值。同时,由于扰动的发展,大气的平均状态也要发生改变,不论开始时大气的层结如何,最后均趋向于中性,而大气的平均风速最后一般都要减小。 相似文献
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显著性检验方法筛选了14个在强对流降水前大气垂直层结中有明显指示作用的因子，其中K指数、γ与γm在各层中差值的绝对最大值等7个因子的指示作用最明显。这些因子表示了大气层结的对流不稳定、条件不稳定、水汽含量和整层大气的垂直均匀性，可用于短时强对流降水的分析和预报。 相似文献
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Although the residual layer has already been noted in the classical diurnal cycle of the atmospheric boundary layer,its effect on the development of the convective boundary layer has not been well studied. In this study, based on 3-hourly20 th century reanalysis data, the residual layer is considered as a common layer capping the convective boundary layer. It is identified daily by investigating the development of the convective boundary layer. The region of interest is bounded by(30°–60° N, 80°–120° E), where a residual layer deeper than 2000 m has been reported using radiosondes. The lapse rate and wind shear within the residual layer are compared with the surface sensible heat flux by investigating their climatological means, interannual variations and daily variations. The lapse rate of the residual layer and the convective boundary layer depth correspond well in their seasonal variations and climatological mean patterns. On the interannual scale, the correlation coefficient between their regional averaged(40°–50°N, 90°–110° E) variations is higher than that between the surface sensible heat flux and convective boundary layer depth. On the daily scale, the correlation between the lapse rate and the convective boundary layer depth in most months is still statistically significant during 1970–2012. Therefore, we suggest that the existence of a deep neutral residual layer is crucial to the formation of a deep convective boundary layer near the Mongolian regions. 相似文献
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A Study of the Atmospheric Boundary Layer Structure During a Clear Day in the Arid Region of Northwest China 
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下载免费PDF全文 The local climate and atmospheric circulation pattern exert a clear influence on the atmospheric boundary layer （ABL） formation and development in Northwest China. In this paper, we use field observational data to analyze the distribution and characteristics of the ABL in the extremely arid desert in Dunhuang, Northwest China. These data show that the daytime convective boundary layer and night time stable boundary layer in this area extend to higher altitudes than in other areas. In the night time, the stable boundary layer exceeds 900 m in altitude and can sometimes peak at 1750 m, above which the residual layer may reach up to about 4000 m. The daytime convective boundary layer develops rapidly after entering the residual layer, and exceeds 4000 m in thickness. The results show that the deep convective boundary layer in the daytime is a pre-requisite for maintaining the deep residual mixed layer in the night time. Meanwhile, the deep residual mixed layer in the night time provides favorable thermal conditions for the development of the convective boundary layer in the daytime. The prolonged periods of clear weather that often occurs in this area allow the cumulative effect of the atmospheric residual layer to develop fully, which creates thermal conditions beneficial for the growth of the daytime convective boundary layer. At the same time, the land surface process and atmospheric motion within the surface layer in this area also provide helpful support for forming the particular structure of the thermal ABL. High surface temperature is clearly the powerful external thermal forcing for the deep convective boundary layer. Strong sensible heat flux in the surface layer provides the required energy. Highly convective atmosphere and strong turbulence provide the necessary dynamic conditions, and the accumulative effect of the residual layer provides a favorable thermal environment. 相似文献
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Analytical solutions of convective waves in the convective boundary layer (CBL) were obtained with two-layer linearized atmospheric
equations including Rayleigh friction, which represents the turbulent viscosity in the lower CBL. The analytical model shows
that the interaction between the convection in the lower layer and gravity waves in the upper layer is one of the causes for
the formation of convective bands. The flow and temperature fields obtained by the analytical model present the main characteristics
of convective bands found in field observations. We have also investigated the influences of atmospheric conditions on the
characteristics of the bands. Results accord with previous knowledge about these phenomena. 相似文献
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从深对流发展必须满足的对流层低层有足够强的湿层、层结不稳定和足够强的触发机制出发,对2002年7月11～15日由东北冷涡诱发的一次连续强风暴生成的环境条件进行了诊断分析。结果表明:低层暖湿条件是冷涡强对流预报的关键,强大的冷涡由于冷性层结深厚难以诱发强的对流性天气,而其分裂的次涡度中心或弱的冷性低涡配合低层暖湿气流常常产生突发性强对流性天气;强的风垂直切变引发的斜压不稳定和垂直运动是强对流触发和维持的重要条件,风暴发生前边界层到500 hPa风向随高度顺转超过90°,随着对流性天气的发展,850 hPa以上风垂直切变逐渐减小,而850 hPa以下可能受低层冷丘产生中高压的影响,切变有增大的趋势;冷涡诱发的强对流性天气常常位于高空急流出口区左侧,但在实际预报业务中需要配合散度场来进行综合判断。 相似文献
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利用 1 998年第 2次青藏高原野外试验中的多普勒声雷达探测、低空探测观测以及卫星观测资料对高原大气边界层内的对流现象进行分析研究。声雷达探测到了高原边界层内有强烈的对流活动。这种对流泡中心的垂直速度可超过 1m/s,并存在尺度为 1个多小时的周期性 ,表现为中小尺度的有组织的湍流活动。高原边界层强对流得以发展和维持的物理机制是 :强辐射加热、复杂的地形地貌形成的下垫面不均一性造成边界层斜压性、边界层内的平流活动等 ,这些现象都有利于对流的发展。在这些条件的作用下 ,边界层内可以产生一系列有组织的强湍流大涡旋活动 ,这些大涡旋形成的热泡在向上发展的过程中有的能够发生合并 ,变得更大也更为猛烈 ,达到凝结高度以上可形成对流云 ,并发生充分的对流混合。成云过程凝结潜热释放更有利于对流运动进一步发展 ,使对流云逐步发展成更大的对流云团 ,从而产生卫星云图中显示的云团发展过程。 相似文献
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盛夏渤海湾大气边界层辐合线触发对流风暴对比分析 总被引：2，自引：2，他引：0
本文对渤海湾2008—2009年,由大气边界层辐合线引起的对流风暴进行了分析。结果表明,在高温、高湿不稳定大气层结环境条件下：（1）单一的海风锋在其端点可产生对流性降水。（2）海风锋与弱冷锋相遇,或者两条海风锋相交,或者雷暴单体的出流边界与海风锋相遇均会产生强对流风暴。（3）渤海湾边界层辐合线触发对流风暴大多发生在每年7 8月,且在副热带高压控制渤海湾后东退的过程中,此时大气层结处在高温、高湿不稳定状态。辐合线触发的对流风暴是沿辐合线移动,移动方向取决于辐合线两侧的主导风向。（4）边界层辐合线触发对流风暴,具有突发性强,持续时间短等特点,分析渤海湾边界层辐合线的移动与演变能提高强对流风暴的临近预报、预警,减少突发性天气引起的灾害。 相似文献
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TRMM测雨雷达和微波成像仪对两个中尺度特大暴雨降水结构的观测分析研究 总被引：40，自引：16，他引：40
文中利用TRMM卫星的测雨雷达和微波成像仪探测结果,研究了1998年7月20日21时(世界时)和1999年6月9日21时发生在武汉地区附近和皖南地区的两个中尺度强降水系统的水平结构和垂直结构,以及TMI微波亮温对降水强弱和分布的响应。研究结果表明:这两个中尺度强降水系统中对流降水所占面积比层云降水面积小,但对流降水具有很强的降水率,它对总降水量的贡献超过了层云降水。降水水平结构表明,两个中尺度强降水系统由多个强雨团或雨带组成,它们均属于对流性降水;降水垂直结构分析表明,强对流降水的雨顶高度可达15km,强对流降水主体中存在垂直方向和水平方向非均匀降水率分布区,层云降水有清晰的亮度带,层云降水的上方存在多层云系结构。降水廓线分布表明:对流降水廓线与层云降水廓线有明显的区别,并且降水廓线清晰地反映了降水微物理过程的垂直分布。整个中尺度强降水系统中对流降水与层云降水的区别还反映在标准化的总降水率随高度的分布。微波信号分析表明:TMI85 GHz极化修正亮温,19.4与37.0,19.4与85.5,37.0与85.5 GHz的垂直极化亮温差均能较好地指示陆面附近的降水分布。 相似文献
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一次弱对流天气降雹成灾的雷达回波特征分析 总被引：2，自引：0，他引：2
通过对新疆玛河流域一次冰雹天气雷达资料及地面实况资料的分析,研究弱对流云降雹的雷达反射率因子与径向速度场的回波特征,进一步探讨弱对流云降雹与0℃层高度较低及垂直风切变的关系：弱对流天气当日零度层高度值可作为分析弱冰雹云的依据;高低空风速的差异形成的风切变造成的动压力产生垂直加速度,使对流运动得到加强和维持,也是此次降雹的动力机制。分析此次天气,揭示了新疆玛河流域弱对流云降雹天气过程生消的一些重要特征和变化,对雹云的识别和分析具有一定的指导意义。 相似文献
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On formation of convective roll vortices by internal gravity waves: A theoretical study 总被引：3，自引：0，他引：3
Dr. J. G. Sang 《Meteorology and Atmospheric Physics》1991,46(1-2):15-28
Summary The linearized atmospheric equations system is solved analytically in a two layer model. The solutions show that the thermal disturbance located at the interface can induce internal gravity wave, which propagates downstream in the stable layer and brings about flow disturbances in the lower unstable layer. Motion of roll vortices with flow pattern similar to that found in the convective cloud street forms in the lower part of the upper layer and the upper part of the lower layer. If proper content of water vapor exists the cloud lines presenting small angle with the mean wind appear at the top of the lower layer. The effects of the wind speed and the temperature structures of the atmosphere in the lower convective layer and the overlying stable layer on the characteristics of the roll vortices are also discussed in this study.With 7 Figures 相似文献
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Applied model for the growth of the daytime mixed layer 总被引：5，自引：2，他引：5
A slab model is proposed for developing the height of the mixed layer capped by stable air aloft. The model equations are closed by relating the consumption of energy (potential and kinetic) at the top of the mixed layer to the production of convective and mechanical turbulent kinetic energy within the mixed layer. By assuming that the temperature difference at the top of the mixed layer instantaneously adjusts to the actual meteorological conditions without regard to the initial temperature difference that prevailed, the model is reduced to a single differential equation which easily can be solved numerically. When the mixed layer is shallow or the atmosphere nearly neutrally stratified, the growth is controlled mainly by mechanical turbulence. When the layer is deep, its growth is controlled mainly by convective turbulence. The model is applied on a data set of the evolution of the height of the mixed layer in the morning hours, when both mechanical and convective turbulence contribute to the growth process. Realistic mixed-layer developments are obtained. 相似文献