Impacts of vortex structure and environment on the intensity of typhoon Hagupit (2020)
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摘要: 为进一步认识影响台风强度预报的因素,提升对台风最大强度预报的能力,利用高精度集合模拟试验对2020年第4号台风“黑格比”的发展增强过程进行了分析,探讨了初期涡旋和大尺度环境背景对台风最大强度的影响。结果表明:描述初期台风涡旋特征的10 m最大轴对称切向风、最大风速半径附近及其外侧低层的轴对称切向风和入流以及涡旋的丰满度均与台风最大强度有较好的相关:最大轴对称切向风能够更早且更准确地指示台风最大强度;最大风速半径附近及其外侧低层的轴对称切向风和入流越强,其伴随的向台风内核区输入的角动量越大,台风的最大强度也越强;初期台风涡旋的丰满度与最大强度的相关远高于外围风圈和最大风速半径与最大强度的相关,意味着对于小台风“黑格比”而言,只要初期涡旋丰满度大,其最大强度也会很强。对于这类台风而言,初始涡旋结构和邻近台风及副热带高压的准确描述是提高台风最大强度预报能力的重要前提。Abstract: To improve understanding of essential aspects that influence forecasting of tropical cyclones, through an ensemble simulation of typhoon Hagupit (2020), this study investigates the impact of the initial vortex and environmental factors on the peak intensity of Hagupit. It is found that there is a stronger correlation between the peak intensity and the maximum azimuthal mean 10 m tangential wind speed than the peak intensity and the maximum 10 m wind speed. This is ascribed to the prominent asymmetry of Hagupit at the early developing stage. Due to the asymmetry, the maximum 10 m wind speed cannot represent the entire wind speed of the vortex. In contrast, the maximum azimuthal mean 10 m tangential wind speed reflects the storm entire wind speed properly and thus is a better predictor for the peak intensity. A stronger correlation exists between the outer-core size and the peak intensity than the inner-core size and the peak intensity. Comparing to the size of the outer-core and the inner-core, the fullness of the typhoon has the strongest and significant correlation with peak intensity, the larger the fullness, the stronger peak intensity. The environmental flow is also found to affect the peak intensity of Hagupit substantially. In the ensemble members with stronger typhoon Sinlaku (2020) and subtropical high respectively to the west and east of Hagupit, the storm usually moves northwards faster under the effect of the steering flow with larger northward component. As a result, the intensification of Hagupit is inhibited by the earlier intrusion of dry air from the north and larger vertical wind shear. These findings mean that for typhoons such as Hagupit, a precise description of the initial vortex structure, nearby typhoon, and subtropical high are crucial for improving the prediction of the maximum intensity.
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Key words:
- Typhoon /
- Peak intensity /
- Maximum wind speed /
- Ensemble simulation /
- Environmental flow
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图 1 “黑格比”台风 (a) 路径、(b) 最低海平面气压和 (c) 最大风速 (黑色粗线为观测 (来自最佳路径数据集),橙色粗线为60个集合成员模拟的平均,红、蓝色细线分别为依据42 h预报最低海平面气压选出的各10个强和弱成员,灰色细线为其余集合成员,红、蓝、灰色粗线分别代表各组的平均;b和c中的垂直灰色虚线表示模式模拟42 h的位置)
Figure 1. 60-member ensemble simulation of (a) the track,(b) the minimum SLP,and (c) the maximum wind speeds (the black line (thick) is the best track from JMA and the orange line (thick) is the ensemble mean,members are grouped by the minimum SLP at 42 h simulation,the strongest and weakest 10 members are colored in red (thin) and blue (thin),and the 40 members in-between are colored in gray (thin),and the thick line represents the mean of each group;the vertical grey dashed lines in (b) and (c) characterize the simulation at 42 h)
图 2 10 m风速与最大强度的相关系数 (蓝、绿、红、粉色曲线分别为轴对称全风速、径向风、切向风最大值和最大风速与最大强度的皮尔逊相关系数,黑色虚线代表通过99%显著性检验)
Figure 2. Correlation coefficients of the peak intensity with the maximum 10 m axisymmetric full wind speed (blue),the maximum 10 m axisymmetric radial wind speed(green),the maximum 10 m axisymmetric tangential wind speed (red),the maximum 10 m wind speed (pink) (black dashed lines denote correlation coefficients statistically significant at/above the 99% confidence interval)
图 3 集合成员模拟的距台风中心半径150 km平均轴对称参数 (黑色曲线为所有集合成员的平均,灰色曲线从浅到深为最大强度由弱至强)
Figure 3. Average axisymmetric parameters of the ensemble members within a 150 km radius from the typhoon center (the black thick line is the average of all members,the shades of the thin gray lines are graded according to maximum intensity,from light to dark means that the peak intensity goes from weak to strong)
图 6 初始轴对称 (a) 切向风和 (b) 径向风与台风最大强度的偏相关系数随半径和高度的变化 (黑色圆点表示通过99%信度显著性检验,交叉线表示通过95%信度显著性检验,蓝色圆点表示集合成员中平均最大风速半径)
Figure 6. Ensemble radius-height correlations between initial (a) azimuthal mean tangential wind speed and (b) azimuthal mean radial wind speed and the peak intensity (stippling denotes regions where the statistical significance exceeds the 99% confidence interval,and the black diagonal crosshatched line denotes the 95% confidence interval;blue dots represent the RMW)
图 8 集合成员的 (a) 12 m/s风圈半径、(b) 最大风速半径和 (c) 丰满度与最大强度的相关系数随时间变化 (浅灰 (深灰) 代表t = 42 h时最大风速 (最低海平面气压) 为最大强度,黑色虚线为通过99%显著性检验)
Figure 8. Correlation coefficient between the peak intensity and R12 (a),RMW (b),TCF (c) (the light gray and dark gray represent the maximum intensity with 42 h minimum sea level pressure and 10 m maximum wind speed respectively,black dash lines denote the correlation coefficient which the statistical significance exceeds the 99% confidence interval)
图 10 强、弱成员引导气流在 (a) 东西和 (b) 南北方向上的分量随时间的变化 (黑色细线为强成员、黑色粗线为强成员平均,灰色细线为弱成员、灰色粗线为弱成员平均)
Figure 10. The component of the steering flow in the strong and weak members in the (a) east-west and (b) north-south directions (the thin black (gray) lines are the strong (weak),and the thick black (gray) line is their mean)
图 11 模式积分6 (a、e)、18 (b、f)、30 (c,g) 和42 (d、h) h强 (a—d)、弱 (e—h)成员大于700 hPa的合成位势高度场(色阶;单位:dgpm) 叠加风场 (矢量) 及其差值 (i—l) (图a中圆圈表示中心在台风中心半径为300 km的主要环流区域,东西两侧矩形长和宽分别为800 km和600 km)
Figure 11. The 700 hPa storm-centered mean geopotential height (shaded,unit: dgpm) and winds (vector) of the strong (a—d) and weak (e—h) members at (a,e) 6,(b,f) 18,(c,g) 30,(d,h) 42 h and the difference between the geopotential height composites (strong—weak) is also plotted at these time (i—l) (the circle in Fig. a indicates the main circulation area centered at a radius of 300 km from the cyclone center,and the length and width of the rectangles to the east and west of the center are 800 km and 600 km respectively)
图 12 (a) 图11a台风西 (蓝色) 、东 (红色) 侧斜线区域强、弱成员位势高度平均值差值和 (b) 强弱成员台风西、东侧平均位势高度差随时间变化 (黑色虚线为强成员、实线为强成员平均,灰色虚线为弱成员、实线为弱成员平均)
Figure 12. (a) The difference between the mean height of the strong members and the mean height of the weak members in the blue (red) diagonal area to the west (east) of the typhoon,(b) the difference between the mean geopotential height of western side and the eastern side of the typhoon (the black (gray) dashed lines are the strong (weak) members,and the black (gray) solid line is their mean)
图 14 (a) 强、(b) 弱成员中台风中心以西和以东各300 km范围内平均相对湿度随距台风中心的距离和时间的变化 (灰色虚线代表台风中心位置,黑色实线为60%相对湿度线)
Figure 14. The variation of average relative humidity with the distance from the cyclone center and time within 300 km west and east of cyclone center in (a) strong members and (b) weak members (the gray dashed line represents the location of the cyclone center and the solid black line represents the 60% relative humidity)
图 15 模式积分15 h后200 (a—c) 和850 (d—f) hPa强 (a、d) 、弱 (b、e) 成员合成风场及差值 (c、f) (矢量代表风场,黑色矢量为6 m/s,a、b、d、e中红色矢量为1 m/s,c和f中红色矢量为0.5 m/s;色阶代表风速;内圆环为200 km半径,外圆环为800 km半径)
Figure 15. Composites wind (vector) and wind speeds (shaded) and differences (c,f) between strong (a,d) and weak (b,e) members at 200 (a—c) and 850 (d—f) hPa at 15 h of model integration (the red arrows characterize the average environmental wind within the circle,in Fig. a,b,d and e the red reference vector values are 1 m/s,while in Fig. c and f the red reference vector values are 0.5 m/s,the black reference vector values in all plots are 6 m/s;the gray inner circle is 200 km radius and the outer circle is 800 km radius)
图 17 强 (a—d) 、弱 (e—h) 成员在15 (a,e)、26 (b,f)、34 (c,g) 和40 (d,h) h合成最大雷达反射率 (色阶)、水平风垂直切变 (矢量) (矢量为1 m/s,红色实线为成员500 hPa涡度质心偏离850 hPa涡度质心的距离)
Figure 17. The storm-centered maximum simulated radar reflectivity (shaded) and deep-layer shear vectors composites of the strong (a—d) and weak (e—h) groups at (a,e) 15,(b,f) 26,(c,g) 34,and (d,h) 40 hours (vector values are 1 m/s,the direction and magnitude of how the centers tilt with height (between 850 and 500 hPa) is plotted in red line)
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