INTERACTION BETWEEN TROPICAL CYCLONE AND MEIYU FRONT*

Generally speaking,the convection activities are inactive over western Pacific warm pool and tropical cyclone (TC) activity seldom occurs over the offshore of East Asia during the period of Meiyu rainfall.However,if a TC is active in this area,the Meiyu rainfall will often weaken or end up.Based on a statistical study with the data from 1980 to 1995,it is found that about 91% of 23 TC activities affected the intensity of Meiyu rainfall,and 50% of the end-up of Meiyu events were related to the active TCs and the change of subtropical high.The present paper simulates the effect of TC on Meiyu circulation by using MM4 model,and the results agree with the observations.From the point of view of vapor and energy transport,the landing of TC cuts not only the transport of the water vapor to Changjiang-Huaihe River basin from the Bay of Bengal but also the conversion of the mean flow energy to the Meiyu circulation because of the TC forcing to the zonal circulation.These two effects make the convection and perturbation existing in Meiyu region lack the supply of the vapor and energy for their maintenance and lead to the end of Meiyu rainfall.     

澳大利亚植被覆盖对亚澳季风影响的数值模拟(Ⅱ): 对东亚夏季风环流的影响

在文献[1]的基础上,对澳大利亚大陆植被覆盖变化对北半球夏季越赤道气流和东亚季风环流季节变化的影响进行了研究.结果表明,植被覆盖变化对东亚季风建立前后南风越赤道气流建立时间、强弱和南半球主要环流系统都有显著的影响.绿化导致了索马里越赤道气流的建立提前,增强了不同时期南风越赤道气流的强度,但对90°E以东来自澳大利亚高压的几支越赤道气流影响不大.同时,绿化促使南半球澳大利亚高压和马斯克林高压提前建立,西太平洋副热带高压北进提前,且强度减弱,导致西南气流更容易深入东亚内陆和西太平洋.这些影响促使盛夏期西南亚季风的影响区域和强度都有所扩展,对东南季风则影响不大.沙漠化则使索马里气流略微减弱,西太平洋副热带高压在春夏季节则一直偏强,至7月中旬,才有明显东撤,阻碍了越赤道气流的北上,西南季风在此影响下强度和影响范围均有所缩减.     

海洋风暴形成的一种动力学机制

文中从观测统计学、瞬变涡动能量学和 MM5中尺度数值模拟角度 ,研究了海洋风暴 (爆发性气旋 )形成的气候特征及其可能的动力学机制 ,揭示了一幅爆发性发展的物理图像。结果表明 ,在冷季大气特别是日本以东洋面上大气特有的热力气候背景下 ,通过同海洋风暴过程相联系的涡动热通量 vθ的向极地输送 (- vθ· θm>0 ) ,将季节尺度的时间平均有效位能向瞬变涡旋时间尺度的涡动有效位能转换 ,是海洋风暴形成的主要动力机制。在该过程中转换来的具有最大贡献的涡动有效位能 ,连同具有次大贡献的积云加热制造的涡动有效位能(q3 )一起 ,通过暖异常区 (α >0 )暖湿空气上升运动 (-ω >0 )的斜压转换 (-ωα) ,促使涡动动能增长。同时 ,补充的涡动有效位能又加强了暖异常区的暖湿空气上升运动 ,进而产生积云对流活动及其潜热释放的正反馈过程 ,最终导致涡动动能急剧增长和海洋风暴的形成。海-气潜热输送的作用是在风暴形成初期提供后来积云尺度对流活动及潜热释放的水汽潜力。研究还表明 ,海洋风暴主要发生在冷季月份 1 3 0°E以东的中高纬洋面上 ,这种对特定季节和特定海域的依赖性是大气和海洋气候背景的动力 /热力共同作用的结果     

Conversion of kinetic energy from synoptic scale disturbance to low-frequency fluctuation over the Yangtze River valley in the summers of 1997 and 1999

In order to investigate the conversion of kinetic energy from a synoptic scale disturbance （SSD; period≤seven days） to a low-frequency fluctuation （LFF; period〉seven days）, the budget equation of the LFF kinetic energy is derived. The energy conversion is then calculated and analyzed for the summers of 1997 and 1999. The results show that the energy conversion from the SSD to the LFF is obviously enhanced in the middle and lower troposphere during the heavy rainfall, suggesting this to be one of mechanisms inducing the heavy rainfall, although the local LFF kinetic energy may not be enhanced.     

非均匀下垫面陆面过程参数化问题研究进展

非均匀下垫面对陆面过程模式应用有着重要影响。若将下垫面一概视为均一,在很多情况下会影响模式模拟的准确性。本文详细介绍了目前非均匀地表陆面过程参数化的方法(Mosaic法、统计—动力法和其它方法),初步分析了这些参数化方法的缺陷,并简单探讨了陆面参数尺度转换问题,最后对今后研究的问题给出了建议,其中特别提出要寻找适当方法实现陆面物理量不同尺度间的转换。     

华北平原回流天气综合形势特征分析

随着探测手段的发展,越来越多的探测资料可以提供给数值天气预报.为了更有效地将这些不同格式的探测资料融合同化为常规物理量,为预报员提供更加直观的中尺度分析场以及为数值模式提供包含丰富中尺度信息的初始场,引进美国的局地分析预报系统LAPS(Local Analysis and Prediction System).介绍了该系统处理资料的原理、方法.初步试验结果表明,对LAPS系统的局地化比较成功,可以融合T213或NCEP、多普勒雷达、云导风、探空及自动站等多种资料,为预报员提供更好的预报依据.     

CHARACTERISTICS OF GRAVITY WAVE PROPAGATION AND ENERGY CONVERSION IN A SUDDEN HEAVY RAINFALL EVENT

In this paper, a sudden heavy rainfall event is analyzed, which occurred over the Yellow River midstream during 5–6 August 2014. We used observational, NCEP/NCAR reanalysis, high-resolution satellite, and numerical simulation data. The main results are as follows. Under an unfavorable environmental circulation, inadequate water vapor and unfavorable dynamic conditions but sufficient energy, a local sudden heavy rainfall was caused by the release of strong unstable energy that was triggered by cold air transport into middle and lower layers and the propagation of gravity waves. The distributions of rain area, rain clusters, and 10-minute rainfall showed typical mesoscale and microscale fluctuation characteristics. In the mesoscale rain area or upstream, there was a quasi-stationary wave of mesoscale gravity waves with their propagation downstream. In the course of propagation from southwest to northeast, the wavelength became longer and the amplitude attenuated. In the various phases of gravity wave development, there were evident differences in the direction of the wave front. Wave energy was mainly in the lower layers. Unstable vertical wind shear at heights of 1–6 km provided fluctuation energy for the gravity waves. The mechanisms of heavy rainfall formation were different at Linyou and Hancheng stations. Diabatic heating was the main source of disturbed effective potential energy at Linyou. The explosive short-period strong precipitation was caused by the release of strong effective potential energy triggered by the gravity waves, and its development and propagation after that energy maximized. In contrast, the latent heat release of upstream precipitation was the main source of disturbed effective potential energy at Hancheng. This formed a positive feedback mechanism that produced continuous precipitation. In the studied event, the development of westerly belt systems had disturbed the wind field. The contribution of kinetic energy generated by this disturbance could not be ignored. The Froude number, mountain shape parameter, and ratio between mountain height and temperature inversion layer thickness had various effects of atmosphere and terrain on mesoscale and microscale mountain waves. In upper and lower layers, there were five airflows that were strengthened by the terrain. All these had important influences on local heavy rainfall at Linyou and Hancheng stations.     

北大西洋风暴轴高低空分布及其能量诊断

利用1979~2013年NCEP再分析数据,通过经验正交分解对比了前冬时期北大西洋风暴轴的高低空分布,并用涡动动能(Eddy Kinetic Energy,EKE)方程对风暴轴高低空分布型差异进行了诊断。研究结果表明:上层和下层第一空间分布型差异巨大,对流层下层风暴轴中心偏北,靠近极地,而上层风暴轴中心偏西南,靠近北美沿岸。EKE方程诊断结果表明:正压转换项在高低空符号相反,导致了EKE在上、下层分布出现显著差异,即上层正压转换项为负,在扰动发展中起能量耗散作用,而下层正压转换项为正,且极大值区域对应下层EKE极大值区域,为风暴轴下层向极区域增强的主要原因。而斜压转换和非地转位势通量散度在上层均为正,且远大于下层,为风暴轴上层涡动能量维持的原因,也从涡动能量收支上解释了风暴轴的主体出现在上层。     

环境WiFi能量采集系统的匹配网络与整流电路设计

设计了一款针对WiFi信号的环境能量采集系统,工作频率范围从2.4 GHz到2.485 GHz.该系统采用了4倍压整流电路,并设计了从天线到整流电路的宽带匹配电路,提升了能量采集的效率.设计的宽带匹配电路在WiFi工作频率范围内,S₁₁均小于-10 dB.整流电路可将采集信号增加4倍,能有效提高RF-DC转换效率.测试结果表明,所设计的电路达到了设计要求,在-10 dBm的输入功率下,达到了40%的RF-DC转换效率,并使超级电容在30 min内采集到了257 mV的电压.     

东亚-太平洋型季节内演变和维持机理研究

利用850hPa的纬向风异常建立一个逐候东亚-太平洋(East Asian Pacific,EAP)型指数,研究其季节内演变特征,发现东亚-太平洋型经向波列是东亚夏季风季节内变化的主要模态.其演变过程为:扰动首先出现在北太平洋中部,并通过正压不稳定过程从基本气流中获得能量而发展,在高层罗斯贝波能量向南频散,激发热带对流异常和赤道罗斯贝波,并相互锁相,因赤道罗斯贝波受β效应影响而共同向西移动.热带对流和环流异常在菲律宾附近达到最强,此时在东亚沿岸出现经向三极型波列,此后中低纬度异常继续向西北方向移动,使降水异常在长江流域能维持较长时间.东亚-太平洋型在东亚发展和维持有以下原因:首先,菲律宾暖水上空的对流和低层环流之间存在正反馈;其次,由于海陆热力差异导致暖大陆和冷海洋之间存在特殊的纬向温度梯度和北风垂直切变,东亚-太平洋型在经向上有向北倾斜的斜压结构,能通过斜压能量转换从平均有效位能中获得能量,同时,也能从经向温度梯度的平均有效位能中获得能量.