Relation of Convective Bursts to Changes in the Intensity of Typhoon Lionrock (2016) during the Decay Phase Simulated by an Atmosphere-Wave-Ocean Coupled Model
Relation of Convective Bursts to Changes in the Intensity of Typhoon Lionrock (2016) during the Decay Phase Simulated by an Atmosphere-Wave-Ocean Coupled Model
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DOI：
10.2151/jmsj.2018-052
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发表时间：
2018-08
影响因子：
3.1
通讯作者：
A. Wada;R. Oyama
中科院分区：
文献类型：
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作者：
A. Wada;R. Oyama
台风狮子山（2016 年）在日本北部太平洋一侧登陆。其中一件有趣的事件是在 8 月 31 日登陆之前连续发生的深层对流（对流爆发，CB）。尽管狮子山沿轨道明显引起了海面冷却（SSC），但狮子山暂停了风暴强度的衰减。为了研究CB对衰减阶段风暴强度变化的影响，利用3公里网格耦合大气-波浪-海洋模型进行了数值模拟。耦合模型成功模拟了近地表辐合区以北CB的出现，该辐合区是由风暴切向风与来自周围有义波高高区域的近地表摩擦螺旋流入汇合形成的。同时，保持了相对较快的平移和不对称的热带气旋（TC）结构。尽管SSC导致风暴内核内的海气潜热通量减少，但汇聚区域周围的低对流层水平湿气通量有所增强。与CB相关的局部向上湿气通量增加了上游侧对流层中上层的凝结加热。这导致上游侧对流层低层压力梯度局部增大。即使在衰减阶段，这也有利于暂停模拟风暴强度的衰减。关于耦合模型执行时间的敏感性实验表明，当不使用耦合模型时，风暴发生前表面摩擦辐合区域周围的垂直湿度通量和CB 数量可能会增加。这表明，在有利的海洋条件下，中纬度地区的风暴可能会局部增加最大表面风速。 CB 的数量和分布确实对海洋条件很敏感，并且被认为会影响风暴路径模拟和最大表面风速。
Typhoon Lionrock (2016) made landfall in the Pacific side of northern Japan. One of the intriguing events was consecutive deep convections (convective bursts, CBs) occurred before making landfall on 31 August. Lionrock paused the decay of the intensity of the storm, although sea surface cooling (SSC) was induced distinctly by Lionrock along the track. To examine the influence of CBs on changes in storm intensity during the decay phase, numerical simulations were conducted with a 3 km mesh coupled atmosphere-wave-ocean model. The coupled model successfully simulated the occurrence of CBs north of the near-surface-convergence area, which was formed by the confluent of the storm’s tangential winds with near-surface frictional spiral inflow from the surrounding region where the significant wave height was high. Simultaneously, the relatively fast translation and asymmetric tropical cyclone (TC) structure were maintained. Lower tropospheric horizontal moisture fluxes have enhanced around the convergence area, although SSC resulted in reduction of the air-sea latent heat fluxes within the storm’s inner core. Local occurrences of upward moisture fluxes associated with CBs increased the mid-toupper tropospheric condensational heating on the upstream side. This caused local increase in lower-tropospheric pressure gradient on the upstream side. This was favorable for pausing the decay of the simulated storm intensity even during the decay phase. Sensitivity experiments regarding the execution time of the coupled model showed that the vertical moisture fluxes and number of CBs could increase around the surface frictional convergence area ahead of the storm when the coupled model was not used. This suggests that the storm in mid-latitude could locally increase the maximum surface wind speed under favorable oceanic conditions. The number and distribution of CBs are indeed sensitive to oceanic conditions and are considered to affect the storm-track simulation and maximum surface wind speeds.