A Strong Mesoscale Convective Process in Landfalling Typhoon

Xu Wenhui; Ni Yunqi

Vol.20, NO.3, 2009

Article Contents

Article Navigation > Journal of Applied Meteorological Science > 2009 > 20(3): 267-275

Xu Wenhui, Ni Yunqi. A strong mesoscale convective process in landfalling typhoon. J Appl Meteor Sci, 2009, 20(3): 267-275.

Citation:

Xu Wenhui, Ni Yunqi. A strong mesoscale convective process in landfalling typhoon. J Appl Meteor Sci, 2009, 20(3): 267-275.

Xu Wenhui, Ni Yunqi. A strong mesoscale convective process in landfalling typhoon. J Appl Meteor Sci, 2009, 20(3): 267-275.

Citation:

Xu Wenhui, Ni Yunqi. A strong mesoscale convective process in landfalling typhoon. J Appl Meteor Sci, 2009, 20(3): 267-275.

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A Strong Mesoscale Convective Process in Landfalling Typhoon

Xu Wenhui¹,
Ni Yunqi²

1.
Department of Atmospheric Sciences, Nanjing University, Nanjing 210093
2.
State Key Laboratory of Severe Weather, Chinese Academy of Meteorological Sciences, Beijing 100081

Received Date: 2008-03-05
Rev Recd Date: 2009-02-02
Publish Date: 2009-06-30

Abstract

Abstract

The fifth typhoon named Haitang landfalls in Fujian in 2005, and then moved northwestward. During this moving, there is a mesoscale convective cloud increasing markedly, within the periphery cloud cinctures of typhoon connecting with tropic convergence cinctures. Moreover, the mesoscale convective cloud passes the east and the north of Wenzhou, and causes heavy rainfalls in these places. This case indicates clearly that a strong mesoscale convective system can be developed under appropriate circumstance, even if the landing typhoon is abating. Severe weather can be resulted from the strong mesoscale convective system, even more dangerous than typhoon. Therefore, principles of strong mesoscale convective system in landing typhoon should be discussed on the structure and evolution of MCS to forecast rainstorm caused by the landfalling typhoon better in the future.The evolution of MCS in landfalling typhoon can be seen through the nephogram and radar reflecting data. Research on the structure of MCS by the NCEP data shows that the MCS along landing typhoon is gradient in maturation period.The synoptic situation, occurring two hours before MCS formed, could be analyzed by NCEP data. Then the formation of MCS is found attributing to two factors. One factor is the convective instability. The profound southeast current of typhoon transports the warm and wet air into the cold area in the north of Wenzhou. In this situation, the cold air is meeting the warm and wet air. So the convective instability is caused and increasing gradually. Meanwhile, the convergence of air is coming out in the influence of the special landform of the north of Wenzhou. However, the air will be moving upward vertically, which is caused by this convergence. So the vertical upward of air is the other factor.Using the theory of slantwise vorticity development and moist potential vorticity, the evaluative theory of this strong mesoscale convective system is obtained. The evolution of MCS could be shown by looking into the situation of MCS in maturation. MCS begins to develop from the area where the cold air pile meets the warm air. In this region, there is slantwise moist isentropic surface. The northwest cold pile forces warm air to climb up along the slantwise moist isentropic surface, so the cyclonic vorticity develops. Because of the interaction between the condition instability at low level and the condition-symmetric instability at middle layer, the convective-symmetric instability develops. In this circumstance, the stream slantwise and ascend at middle layer is widely formed by the vorticity caused by the slantwise isentropic surface. On the other hand, the increasing in vertical shear of horizontal wind or enhancing in moist baroclinity, because of the slantwise of moist isentropic surface, results in intensifying the development of vertical vorticity and stretching towards northwest of MCS.
- landfalling typhoon;
- strong mesoscale convective system;
- convective-symmetric instability;
- moist potential vorticity;
- slantwise vorticity development

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References(16)

Figures and Tables

图 1 2005年7月19日21:00—20日06:00每3 h实况降水量分布图 (单位: mm)

Fig. 1 Observed rainfall at 3-hour intervals from 21:00 19 Jul to 06:00 20 Jul 2005 (unit: mm)

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图 2 2005年7月20日02:00的850 hPa 上各物理量分布

(虚椭圆表示暴雨区) (a) 等风速场(等值线，单位: m/s) 和垂直速度w场 (阴影为w≤-0.2 Pa/s的区域)，(b) 温度场(等值线，单位: ℃) 和水汽通量散度场 (阴影，单位: 10^-7g·s^-1· hPa^-1·cm^-2)

Fig. 2 Synoptic situation at 850 hPa at 02:00 20 Jul 2005

(dashed ellipse represents the area of rain) (a) horizontal wind speed (isoline, unit: m/s) and vertical speed w (shaded area is for vertical wind speed smaller than-0.2 Pa/s), (b) temperature (isoline, unit: ℃) and moisture flux divergence (shaded area, unit: 10^-7g·s^-1·cm^-2)

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图 3 2005年7月20日02:00各层以风矢量为背景各物理量分布

(a) 850 hPa 散度场 (单位: 10^-5s^-1), (b) 600 hPa 散度场 (单位: 10^-5s^-1), (c) 300 hPa (单位: 10^-5s^-1), (d) 300 hPa 位势高度场 (等值线，单位: gpm) 和等风速场（阴影，单位: m/s; 方框表示图 3c中的强辐散区）

Fig. 3 Synoptic situation at different leveks at 02:00 20 Jul 2005

(a) divergence at 850 hPa (unit: 10^-5s^-1), (b) divergence at 600 hPa (unit: 10^-5s^-1), (c) divergence at 300 hPa (unit:10^-5s^-1), (d) geopotential height (isoline, unit:gpm) and horizontal wind speed at 300 hPa (shaded, unit: m/s; pane represents the strong divergence area in Fig.3c)

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图 4 2005年7月20日02:00沿图 2b中AB剖面的各物理量分布（表示暴雨区，下同）

(a) 流场 (实线) 和温度距平场 (虚线表示温度距平≤0℃), (b) 涡度场分布 (实线表示正涡度，虚线表示负涡度，单位：10^-5s^-1), (c) 散度场分布 (实线表示辐散区，细虚线表示辐合区，粗虚线为强辐合中心轴线，单位：10^-5s^-1)

Fig. 4 Vertical cross sections along line AB in Fig.2b for synoptic situation at 02:00 20 Jul 2005 ( represents the area of heavy rainfall)

(a) streamlines (solid line) and temperature dispatch (dashed line is for the area that temperature dispatch amsller than 0 ℃), (b) vorticity (solid line represents positive, dash line represents negative, unit: 10^-5s^-1), (c) divergence (solid line represents divergence, thin dashed line represents comvergence, thick dashed line represents the axes of center of convergence, unit: 10^-5s^-1 )

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图 5 2005年7月19日20:00各物理量分布 ( 表示对流系统形成位置)

(a) 850 hPa风矢量场、温度 (等值线，单位：℃) 和水汽通量散度（阴影，单位：10^-7g·s^-1·hPa^-1·cm^-2), (b) 沿图 5a 中CD剖面的流场、相当位温 (长虚线，单位：K) 和温度距平场 (阴影表示≤０ ℃的区域), (c) 沿图 5a中CD剖面的散度场 (虚线，单位：10^-5s^-1) 和垂直速度 (实线，单位：Pa/s ), (d) 沿图 5a中CD剖面的涡度场 (实线表示正涡度，虚线表示负涡度，单位：10^-5s^-1)

Fig. 5 Synopic situation at 20:00 19 Jul 2005

(a) wind vector, temperature (isoline, unit: ℃) and moisture flux divergence (shaded area, unit: 10^-7g·s^-1·hPa^-1·cm^-2) at 850 hPa, (b) vertical cross sections along CD in Fig. 5a for streamlines (solid line), equivalent potential temperature (long-dash line, unit: K) and temperature dispatch (shaded area represents temperature dispatch smaller than 0℃), (c) vertical cross sections along line CD in Fig. 5a for divergence (dash line, unit: 10^-5s^-1) and vertical speed w (solid line, unit: Pa/s), (d) vertical cross sections along line CD in Fig. 5a for vorticity (solid line represents positive, dashed line represents negative, unit: 10^-5s^-1)

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图 6 2005年7月20日02:00沿图 3b中AB剖面的θ_e，绝对动量和MPV分布

(a) θ_e (实线，单位: K) 和绝对动量 (虚线，单位: m/s) 分布, (b) MPV (单位: PVU)

Fig. 6 Vertical cross sections along line AB in Fig.3b for θ_e, M and MPV at 02:00 20 Jul 2005

(a) distribution of θ_e (solid line, unit: K) and M (dashed line, unit: m/s), (b) MPV (unit: PVU)

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图 7 2005年7月20日02:00沿图AB剖面的MPV1 (a) , MPV2 (b) 的分布

(单位：PVU；虚线为负值，实线为非负值)

Fig. 7 Vertical cross sections along line AB in Fig. 2b for MPV1 (a) and MPV2 (b) at 02:00 20 Jul 2005

(unit: PVU; dash line represents negative, solid line represents postive)

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