分层气流条件下地形降水的二维理想数值试验

利用WRF v3.5中尺度数值模式,在条件不稳定层结下,针对分层气流(基本气流风速和大气湿浮力频率呈二层均匀分布)过山时,地形对降水的影响进行了多组二维理想数值试验,以研究不同高度、尺度山脉和不同方向基本气流对降水形态和分布的影响。模拟结果表明,地形重力波触发对流是地形降水的主要机制之一,地形波的特征(波长、振幅)和传播均受到地形和基本气流的影响,其中,强基本气流流经高而陡峭的山脉时,更容易在其背风坡捕捉到重力波,地形降水呈现多种模态,反之亦然;当改变基本气流与山脉交角时,主要通过影响地形强迫抬升速度、基流对波动稳定性发展来进一步影响地形降水的强度和分布。     

Sediment Movement in Periodic Alternating Current

The present paper summarizes the results of previous studies, including the structure and principle of the rotary ring flume for researching the fine sediment movement, the mechanism of the flume, method of eliminating the influence of the centrifugal force and sediment movement experiments with periodic alternating current. Also included are the experiment-based relationship among sediment concentration, bed shear stress and silt carrying capacity, a proposed erosion-deposition function and bed erosion-deposition calculation together with the results of verification.     

Variabilities of Surface Current in the Tropical Pacific Ocean

The Simple Ocean Data Assimilation (SODA) package is used to better understand the variabilities of surface current transport in the Tropical Pacific Ocean from 1950 to 1999. Seasonal variation, interannual and decadal variability analyses are conducted on the three major surface currents of the Tropical Pacific Ocean: the North Equatorial Current (NEC), the North Equatorial Countercurrent (NECC), and the South Equatorial Current (SEC). The transport of SEC is quite larger than those of NEC and NECC. The SEC has two maximums in February and August. The NEC has a small annual variation. The NECC has a maximum in October and is very weak in March and April. All currents have remarkable interannual and decadal variabilities. The variabilities of the NEC and the SEC relate to the winds over them well, but the relationship between the NECC and the wind over it is not close. Analysis related to El Nin^-o-Southern Oscillation (ENSO) suggests that before El Nifio (La Nin^-a) the SEC is weaker (stronger) and the NECC is stronger (weaker), after El Nifio (La Nifia) the SEC is stronger (weaker) and the SEC is weaker (stronger). There is no notable relationship between the NEC and ENSO.     

山东半岛三次冷流暴雪气流结构差异性分析北大核心CSCD

利用烟台多普勒天气雷达探测资料和常规观测资料,对2005年12月3-4日、2008年12月4-5日和2010年1月3-4日山东半岛3次冷流暴雪过程的海岸锋气流结构进行了分析。结果表明,海岸锋是西北气流和北东北气流相互作用的结果,但气流强度有明显差异:一是西北气流明显强于北东北气流(类型Ⅰ),降雪回波源地在渤海东部区域,东南方向移动过程中逐渐发展,回波带的右侧进入陆地后减弱,左侧在海岸锋的作用下沿海岸锋发展,形成"列车"效应,产生强降雪;二是西北气流明显弱于北东北气流(类型Ⅱ),降雪回波源地在渤海海峡中部区域,东南方向移动过程中逐渐发展,右侧在海岸锋的作用下沿海岸锋发展,形成带状回波,产生强降雪,而回波带的左侧减弱。东部海区气旋的存在,决定了海岸锋北东北气流和西北气流强度结构的差异性。     

青海高原短时强降水天气的葵花-8卫星监测预警特征对比分析

为获得青海高原（以下简称高原）对流云团的强降水监测预警特征和预警方法,使用葵花-8卫星数据跟踪识别高原典型强降水天气过程的对流云团,计算并分析具有提前预警意义的云团特征参数。结果表明：（1）本文提出的对流云团识别的改进多通道法,经与传统多通道法对比检验,证明所得云团更接近对流主体,该方法适用于高原对流云团识别。（2）对流形成到成熟阶段,特征参数起伏变化,但红外与水汽通道亮温差（DTB13）和云顶亮温（Tmin）整体下降,云顶亮温梯度（GTmax）整体上升;在对流发展阶段仅红外1和2通道亮温差（DTB12）平均可达预警极值,在成熟阶段则是Tmin、DTB13、GTmax、深对流指数（DCI）等平均可达预警极值。高原上强降水天气的对流云多发展成深对流,降水发生在云团特征参数极值附近,短时强降水发生在深对流云区内特定云顶（上冲云顶或近似上冲云顶）所在特征参数极值区内或边缘附近。（3）特征参数极值对一般降水和强降水的开始时间分别提前0～1 h和0.5～4.5 h出现,在西风型流场下对强降水开始的提前时间相对较长。降水开始前,副高型流场下对流云团向深对流发展变化最剧烈,表现为DCI和GTmax平...     

Influence of Topography and Large-scale Forcing on the Occurrence of Katabatic Flow Jumps in Antarctica： Idealized Simulations

The Regional Atmospheric Modeling System （RAMS）, which is a non-hydrostatic numerical model, has been used to investigate the impact of terrain shape and large-scale forcing on the Antarctic surface-wind regime, focusing on their roles in establishing favorable flow conditions for the formation of katabatic flow jumps. A series of quasi-2D numerical simulations were conducted over idealized slopes representing the slopes of Antarctica during austral winter conditions. Results indicate that the steepness and variations of the underlying slope play a role in the evolution of near-surface flows and thus the formation of katabatic flow jumps. However, large-scale forcing has a more noticeable effect on the occurrence of this small-scale phenomenon by establishing essential upstream and downstream flow conditions, including the upstream supercritical flow, the less stably stratified or unstable layer above the cold katabatic layer, as well as the cold-air pool located near the foot of the slope through an interaction with the underlying topography. Thus, the areas with steep and abrupt change in slopes, e.g. near the coastal areas of the eastern Antarctic, are preferred locations for the occurrence of katabatic flow jumps, especially under supporting synoptic conditions.     

利用多普勒天气雷达分析凉山州"5.4～5.10 "区域性雷雨天气过程

利用凉山州气象局多普勒雷达资料,分析了2005年5月4日影响凉山州北部、西部雷暴天气过程的雷达回波强度、多普勒雷达速度特征.结果表明:雷暴云团在生成发展过程中,经历了生成、消散、再生成并不断移动.回波柱状结构清晰,零速度线不明显,谱宽值不高的特征.     

脉动气流对沸腾表面水分蒸发影响的数值模拟

【目的】考察脉动气流掠过沸腾水面时,流动参数对水分蒸发效果的影响,探究脉动气流强化蒸发过程的机理。【方法】建立二维物理与数学模型,采用商用软件ANSYS FLUENT 14.5进行数值模拟,研究正弦脉动气流掠过沸腾水面时水分的蒸发情况,分析一定蒸发时间内脉动气流的振幅、频率、气流速度以及温度对水分蒸发的影响。【结果】相比于匀速气流,气流脉动时沸腾表面水分的相对蒸发量提高了约50%;脉动气流的相对振幅从0增加至1.0时,沸腾表面水分的相对蒸发量提高了约1.8倍;脉动气流的频率从0 Hz增加至110 Hz时,沸腾表面水分的相对蒸发量呈现出先增加后减小的变化;气流速度从4 m/s增加至10 m/s时,沸腾表面水分的相对蒸发量提高了约15.3倍;脉动气流的温度对沸腾表面水分蒸发的影响不明显;气流脉动时,水分蒸发速率呈周期性变化。【结论】脉动气流周期性地对水面水蒸气浓度边界层进行扰动,强化了水面的对流传质,从而促进了水分蒸发。