大气科学  2017, Vol. 41 Issue (5): 1101-1112 PDF
Chanchu台风(0601) 流出层的低理查森数特征分析

1 南京信息工程大学气象灾害教育部重点实验室太平洋台风研究中心/气候与环境变化国际合作联合实验室/气象灾害预报预警与评估协同创新中心, 南京 210044
2 中国气象科学研究院灾害天气国家重点实验室(LaSW), 北京 100081
3 中国科学院大气物理研究所云降水物理与强风暴重点实验室(LACS), 北京 100029
4 中国科学院大学地球科学学院, 北京 100049

Characteristic Analysis of Low Richardson Number in the Outflow Layer of Typhoon Chanchu (2006)
WU Tianyi1, WANG Yongqing1,2, ZHOU Yushu3,4
1 Pacific Typhoon Research Center, Key Laboratory of Meteorological Disaster of Ministry Education/Joint International Research Laboratory of Climate and Environment Change/Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters, Nanjing University of Information Science and Technology, Nanjing 210044
2 State Key Laboratory of Severe Weathers(LaSW), Chinese Academy of Meteorological Science, Beijing 10081
3 Key Laboratory of Cloud-Precipitation Physics and Severe Storms(LACS), Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029
4 College of Earth Sciences, University of Chinese Academy of Sciences, Beijing 100049
Abstract: One typical structure of typhoon is the outflow layer in the upper troposphere. However, there were relatively few studies on the outflow layer. In terms of criterion Richardson number, the data from numerical simulations of the non-hydrostatic mesoscale model WRF on typhoon Chanchu (2006) was used to investigate low Richardson number in the upper troposphere, as well as the structure and causes of the low Richardson layer. Results demonstrate that the prominent frequency of low Richardson number that even reached the turbulence criticality existed in the altitudes ranging from 10 km to 16 km, supporting the assumption of Richardson number criticality in tropical cyclone by Emanuel (2011). By comparing differences in the low Richardson number layer during the newly-born stage, developing stage, mature stage and decaying stage of the tropical cyclone, a correlation was found between the frequency of low Richardson number and the strength of the tropical cyclone, namely, the low Richardson number layer was found to be more common and broader in the stronger phase of the tropical cyclone. The presence and distribution of low Richardson number in the outflow layer was characterized by vertical wind shear and static stability. Along with the process of slowly changing of typhoon intensity, the frequency and distribution of low Richardson number exhibited a diurnal variation, which was associated with the change in static stability caused by diurnal variation of solar radiation. This study revealed the existence of upper-tropospheric low Richardson layer in tropical cyclones, and verified the sensitivity of Richardson number to cyclone intensity and the radiation diurnal cycle.
Key words: Typhoon      Richardson number      Outflow layer      Static stability
1 引言

Chanchu台风是2006年我国编号的首个热带气旋，于2006年5月9日04:00(协调世界时，下同)在菲律宾以东的太平洋海面上生成，向西北方向移动，在12日16:00到达南海。在14日16:00，台风路径发生偏折，开始向北移动，此时台风还未登陆，之后一直向北移动，至17日18:00左右在汕头澄海和潮州饶平之间登陆。登陆之后，向北偏东方向移动。其详细的移动路径如图 1所示。Chanchu台风作为2006年最早登陆我国的台风，具有登陆时间早、台风强度强、影响范围大、移动路径多变而难以预测等特点。本文将通过对西北太平洋Chanchu台风个例使用高分辨率的模式模拟资料分析流出层低理查森数层的存在及其分布特征，低理查森数层与台风强度的关系，以及低理查森数层对昼夜变化的敏感性。本文的研究，可揭示西太平洋上Chanchu台风流出层上低理查森数层的分布特征，其与Chanchu台风强度变化的联系，以及低理查森数层的昼夜变化特征，有利于加深我们对西太平洋上台风流出层结构的认识。

 图 1 Chanchu台风(2006) 数值模拟范围，2006年5月10日00:00时刻模式初始700 hPa风矢量场(单位：m s-1；NCEP/FNL再分析资料)。A区、B区和C区保持不变，D区随着台风移动沿虚线移动(D1至DN)。台风符号表示初始时刻Chanchu台风(2006) 的位置 Figure 1 Domain configuration for the WRF numerical simulation of Chanchu. 700 hPa wind vectors from the model initial condition (units: m s-1; NCEP Final Analysis, FNL) at 0000 UTC 10 May 2006 are shown. Domains A, B, and C remain fixed and the innermost domain D moves with the storm as shown with the dashed line (from D1 to DN). The TC symbol denotes the location of Chanchu at the initial time
2 资料与方法

① Cai Minmin, Wang Yongqing, 2016: A numerical study of spiral rainbands in typhoon Chanchu (2006): Model verification and fine rainband structures, Advances in Atmospheric Sciences, in reviewing

 图 2 (a)台风路径(实线：观测路径；虚线：模拟路径)及(b)台风强度(黑色实线：观测最低中心气压和最大风速；虚线：模拟最低中心气压和最大风速) Figure 2 (a) The track (black solid line: track of the observed Chanchu, black dashed line: track of the WRF-simulated Chanchu) and (b) strength of typhoon Chanchu (2006). In (b), black solid line: observed maximum surface winds and minimum sea level pressure; black dashed line: WRF-simulated maximum surface winds and minimum sea level pressure

 $Ri = \frac{{\frac{g}{{{{\bar \theta }_v}}}\frac{{\Delta {\theta _v}}}{{\Delta z}}}}{{\frac{{{{\left( {\Delta u} \right)}^2} + {{\left( {\Delta v} \right)}^2}}}{{{{\left( {\Delta z} \right)}^2}}}}},$ (1)

3 低理查森数分布 3.1 低理查森数分布随台风强度变化

 图 3 Chanchu台风5月11日00:00至5月17日00:00 10 m最大风速(黑色虚线，单位：m s-1)和600 km半径范围内Ri＜1出现频率大于30%的格点数(黑色实线) Figure 3 Maximum wind speed at 10 m of typhoon Chanchu (black dashed line, units: m s-1) and the number of grid points where the frequency of Ri < 1 within a radius of 600 km was greater than 30% (black solid line) from 0000 UTC 11 May to 0000 UTC 17 May

 图 4 Chanchu台风四个阶段Ri＜1频率的半径—高度轴对称平均图，阴影区为低理查森数出现频率大于20%的区域：(a)发生阶段；(b)发展阶段；(c)成熟阶段；(d)消亡阶段 Figure 4 Radius–height azimuthally-averaged section of the frequency for Ri < 1 in the (a) newly-born stage, (b) developing stage, (c) mature stage, and (d) decaying stage. The shaded area represents the region where the frequency of low-Ri number is greater than 20%

 图 5 Chanchu台风(a)5月12日21:00较弱时次和(b)5月14日15:00较强时次Ri＜1出现频率的半径-高度轴对称平均图，阴影区为低理查森数出现频率大于20%的区域 Figure 5 Radius–height azimuthally-averaged section of the frequency for Ri < 1 at (a) 2100 UTC 12 May in the weak phase and(b) 1500 UTC 14 May in the strong phase for typhoon Chanchu (2006). The shaded area represents the region where the frequency of low-Ri number is greater than 20%

 图 6 Chanchu台风在(a、c、e)5月12日21:00较弱时次和(b、d、f)5月14日15:00较强时次不同高度Ri平面图：(a、b)12 km；(c、d)14 km；(e、f)15 km。以向北和向东为正方向，坐标单位为km，台风标志表示台风中心位置，阴影区为低理查森数小于1的区域 Figure 6 Horizontal diagrams of Ri at 2100 UTC 12 May (left column) in the weak phase and (b) at 1500 UTC 14 May (right column) in the strong phase at elevations of (a, b) 12 km, (c, d) 14 km, and (e, f) 15 km. The northward and eastward are set as positive directions; the units of the coordinate are km; the symbols of typhoon show the center of typhoon; shaded areas represent the region where the Ri number is smaller than 1

 图 7 Chanchu台风5月12日21:00较弱时次和14日15:00较强时次的(a)静力稳定度之差和(b)水平风的垂直切变之差的半径—高度轴对称平均图，单位：10-5 s2。深色阴影区表示正值区，浅色阴影区表示负值区，黑色实线与虚线分别代表 14日15:00和12日21:00的对流层顶 Figure 7 Radius–height sections of differences in (a) static stability and (b) vertical wind shear between 2100 UTC 12 May in the weak phase and 1500 UTC 14 May in the strong phase (units: 10-5 s2) for typhoon Chanchu (2006). The deep shadow indicates positive region, the shallow shadow represents negative region, black solid line and dashed line represent tropopauses at 1500 UTC 14 May and 2100 UTC 12 May, respectively

 图 8 Chanchu台风5月12日21:00较弱时次和5月14日15:00较强时次的温度之差的半径—高度轴对称平均图，单位：K。深色阴影表示正值区，浅色阴影表示负值区 Figure 8 Radius–height azimuthally-averaged section of the difference (units: K) in temperature between 2100 UTC 12 May in the weak phase and 1500 UTC 14 May in the strong phase for typhoon Chanchu (2006). Deep shadow indicates positive region; shallow shadow indicates negative region

3.2 低理查森数分布的日变化

 图 9 (a、b)12日、(c、d)13日、(e、f)14日和(g、h)15日00:00(左列)和12:00(右列)台风Chanchu Ri < 1出现频率平均的半径—高度轴对称平均图，阴影区为频率大于20%的区域 Figure 9 Radius–height azimuthally-averaged sections of the frequency for Ri < 1 at 0000 UTC (left column) and 1200 UTC (right column) on (a, b) 12th, (c, d) 13th, (e, f) 14th, and (g, h) 15th for typhoon Chanchu (2006). The shadow represents the region where the frequency of low-Ri number is greater than 20%

 图 10 15日12:00(日落)和00:00(日出)Chanchu台风(a)稳定度之差(填色，单位：10-5 s2)和(b)温度之差(填色，单位：K)的半径—高度轴对称平均图，深色阴影表示正值区，浅色阴影表示负值区 Figure 10 Radius–height azimuthally-averaged sections of (b) differences in static stability (shaded, units: 10-5 s2) and (b) temperature (units: K) between1200 UTC 15 May (sunset) and 0000 UTC 15 May (sunrise) for typhoon Chanchu (2006). The deep shadow indicates positive region, and the shallow shadow indicates negative region
4 总结与讨论

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