热带气旋重力波的激发和传播机制研究

发布时间：2018-09-01 18:21

【摘要】：大气重力波在向上传播过程中能够不断向背景大气传递动量和能量,被认为是中低层大气耦合过程中最重要的物理过程。强对流又是激发大气重力波的最重要的波源之一,特别是在热带地区。最近的研究表明,强对流系统中的非绝热力和对流过冲过程能够在大的时间和空间尺度上激发广谱重力波。在西北太平洋区域形成的台风(或者说南太平洋区域的热带气旋)是一种大尺度强对流系统,能够激发出波长达几百公里、周期达数小时的对流重力波。台风重力波(热带气旋重力波)形成于台风路径周围对流层区域,并且能够在水平和垂直方向上传播。台风重力波在中高层大气动量传输中有着重要作用,并且影响着全球大气环流。近几十年来,研究者们一直不遗余力的利用观测和数值模拟的方式探索重力波活动,包括激发波源、波动特性和物理过程等。尽管台风重力波对全球大气环流非常重要,但目前观测仪器并不能在足够的时间和空间分辨率上量化台风重力波。由于台风期间恶劣的气象环境和观测设备自身的限制等因素,现有观测设备(比如激光雷达、气辉成像仪和卫星等)并不能精确测量台风重力波的特性。本文通过AIRS (Atmospheric Infrared Sounder)探测器和WRF (Weather Re-search and Forecasting)模式研究了2004年台风“蒲公英”激发的重力波,该台风于2004年6月下旬在关岛附近海域(13°N,144°E)形成。AIRS探测器在台风“蒲公英”周期内探测到了台风激发的平流层重力波现象。我们通过分析AIRS探测器的4.3μm波段亮温,发现台湾上空存在水平范围100-400千米的半环状重力波结构。为了进一步探索台风重力波的特性,我们分析了同一时期的WRF模式模拟结果,模式的初始数据和边界条件使用了ECMWF的高精度再分析数据。模式重现了台风和重力波的主要特点。与AIRS观测结果一致,模式中的台风重力波的水平波长也位于10(0-400千米范围内。通过分析重力波的垂直传播过程发现：重力波在平流层中主要向上和向东传播,而大部分西向传播的重力波都被背景风场过滤掉了。另外,我们还关注了地形重力波能够向上传播的条件。大量的观测和模拟结果显示山地波的发生随着季节和纬度的变化而显著变化。由于盛行风阻止了山地波的向上传播,所以低纬地区夏季很少有探测和研究山地波的例子。本文将研究2004年台风“蒲公英”经过台湾岛期间(2004年7月1号到3号)产生的山地波的向上传播过程。通过比较WRF模式和没有地形信息的模式(WRF-FLAT)模拟的重力波信息,我们发现台风经过台湾中央山脉时所激发的山地波的动量通量占了对流层重力波总动量通量的50%左右,并且山地波的主导方向与中央山脉垂直。模式中,台风中心相对中央山脉的位置决定了山地波是否能够向上传播到平流层。我们发现在台风登陆前后都能激发山地波,但是只有在台风登陆前激发的山地波能够向上传播到平流层,因为台风登陆前从对流层到平流层都是向西的背景风场,不能形成阻碍山地波传播的零风层。由于每年有几十个台风或者热带气旋在太平洋区域登陆,那么研究这些热带气旋相关的山地波的传播就非常重要。随着超级计算机计算能力的增加,Liu, et al. (2014)以美国国家大气研究中心(NCAR)的WACCM (Whole Atmosphere Community Climate Model)模式为基础开发出了一个高精度的全大气环流模式(模式精度～0.25°),用以解析大气中尺度活动。模式捕捉到了中尺度活动,比如在澳大利亚以东海域(167°E,20°S)解析出了热带气旋事件,并在其上空发现了半环状重力波结构。为了探索全球模式和局地模式之间的耦合作用,检验更高精度大气环流模式解析重力波的必要性,我们设计了一种降尺度方法即用高精度WACCM模式输出数据来驱动WRF模式模拟热带气旋重力波的激发过程。降尺度方法是一种获取更小尺度气候产品的高效可行方法。本文使用的局地气候模式是NCAR开发的WRF3.6.1模式。通过比较高精度WACCM模式和相同水平分辨率(25千米)的WRF模式结果,我们发现两种模式在相似位置都产生了近似结构的半环状热带气旋重力波。为了验证全球模式中更高精度解析重力波的必要性和可行性,我们设计了一组不同分辨率的WRF模式(25千米、15千米、10千米和4千米)来检验热带气旋重力波对模式水平分辨率的敏感性。虽然所有分辨率的模式都能解析出半环状重力波结构,但是分辨率越高的模式激发的重力波振幅越大并且主导水平波长也越短。同时还探索了模式中对流参数化和对流解析对热带气旋重力波激发的影响,发现在4千米分辨率下,解析对流方法激发的重力波和对流参数化方法激发的重力波差别不大。据我们所知,这是第一次用降尺度方法处理中尺度全大气环流模式结果来研究热带气旋重力波。
[Abstract]:Atmospheric gravity waves, which can transmit momentum and energy to the background atmosphere continuously during their upward propagation, are considered to be the most important physical processes in the coupling process between the lower and middle atmosphere. Strong convection is also one of the most important wave sources to excite atmospheric gravity waves, especially in the tropics. Typhoons (or tropical cyclones in the South Pacific region) formed in the Northwest Pacific region are large-scale strong convective systems capable of generating convective gravity waves with wavelengths of several hundred kilometers and periods of several hours. Typhoon gravity waves form in the troposphere around the typhoon track and can propagate horizontally and vertically. Typhoon gravity waves play an important role in momentum transmission in the upper and middle atmosphere and affect global atmospheric circulation. In recent decades, researchers have spared no effort to explore the use of observation and numerical simulation methods. Force wave activities, including excitation sources, wave characteristics, and physical processes. Although typhoon gravity waves are very important to global atmospheric circulation, current observational instruments are not able to quantify typhoon gravity waves at sufficient time and spatial resolution. Due to the adverse weather conditions during typhoons and the limitations of observational equipment, existing views are available. The characteristics of typhoon gravity waves can not be accurately measured by measuring equipment such as lidar, airglow imager and satellite. The gravity waves excited by typhoon "dandelion" in 2004 were studied by using the AIRS (Atmospheric Infrared Sounder) detector and the Weather Re-search and Forecasting (WRF) model. The typhoon was closed in late June 2004. In order to further explore the typhoon gravity, we analyzed the brightness temperature of the 4.3 micron band of the AIRS detector and found that there is a semi-circular gravity wave structure over Taiwan with a horizontal range of 100-400 kilometers. The model reproduces the main features of typhoon and gravity waves. The horizontal wavelengths of typhoon gravity waves in the model are also in the range of 10 (0-400 km). Analyzing the vertical propagation of gravity waves, it is found that gravity waves propagate mainly upward and eastward in the stratosphere, while most westward propagating gravity waves are filtered out by the background wind field. Because prevailing winds prevent the upward propagation of mountain waves, there are few examples of detecting and studying mountain waves in summer in low latitudes. This paper will study the upward propagation of mountain waves produced by typhoon "dandelion" in 2004 over Taiwan Island (July 1-3, 2004). With the gravity wave information simulated by the WRF-FLAT model, we find that the momentum flux of the mountain wave excited by a typhoon passing through the Central Mountains of Taiwan accounts for about 50% of the total momentum flux of the tropospheric gravity wave, and the dominant direction of the mountain wave is perpendicular to the Central Mountains. It is found that mountain waves can be excited both before and after typhoon landfall, but only before typhoon landfall can mountain waves propagate upward to the stratosphere, because before typhoon landfall, both the troposphere and stratosphere are westward background wind fields, which can not form a barrier to mountain wave propagation. Zero Wind Layer. Since dozens of typhoons or tropical cyclones land in the Pacific each year, it is important to study the propagation of these tropical Cyclone-Related mountain waves. Based on the e-Model, a high-precision global atmospheric circulation model (model accuracy ~0.25 degrees) has been developed to analyze mesoscale atmospheric activities. The model captures mesoscale activities, such as tropical cyclone events in the eastern Australian sea area (167 degrees E, 20 degrees S), and a semi-circular gravity wave structure has been found above. To explore the coupling between global and local models, and to test the necessity of analysing gravity waves with more accurate atmospheric circulation models, we designed a scaling method, which uses the output data of WACCM model to drive the WRF model to simulate the excitation process of tropical cyclone gravity waves. The local climate model used in this paper is the WRF 3.6.1 model developed by NCAR. By comparing the results of the WACCM model with high accuracy and the WRF model with the same horizontal resolution (25 km), we found that the two models both produced approximately structured semi-circular tropical cyclone gravity waves at similar locations. A set of WRF models with different resolutions (25 km, 15 km, 10 km and 4 km) were designed to test the sensitivity of tropical cyclone gravity waves to the horizontal resolution of the model. Although all resolution models can resolve the structure of semi-circular gravity waves, the resolution is higher. At the same time, the effects of convection parameterization and convection analysis on the excitation of tropical cyclone gravity waves are also explored. It is found that the gravity waves excited by analytical convection method and convection parameterization method have little difference at the resolution of 4 km. As we all know, this is the first time that a mesoscale global circulation model is used to study tropical cyclone gravity waves.
【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：P444

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