NAN;Intercomparison between Supertyphoons Mangkhut and Yutu (2018): Rapid Intensification and Track Evolution as Explored by the Ocean-Coupled HWRF

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Title:	NAN;Intercomparison between Supertyphoons Mangkhut and Yutu (2018): Rapid Intensification and Track Evolution as Explored by the Ocean-Coupled HWRF
Authors:	阮氏青;Chinh, Nguyen Thi
Contributors:	大氣科學學系
Keywords:	NAN;Ocean-Coupled HWRF;Supertyphoon;Rapid intensification;Track evolution
Date:	2021-01-26
Issue Date:	2021-03-18 16:41:06 (UTC+8)
Publisher:	國立中央大學
Abstract:	2018年超級颱風玉兔(Yutu)及山竹(Mangkhut) 生成於西北太平洋且經歷快速增強，並接連登陸於菲律賓北部。本研究使用HWRF模式進行海洋耦合(CTL)及非耦合(UN)之兩實驗，探討海洋對颱風之影響，進一步了解兩個颱風個別的快速增強過程及路徑變化。模式結果顯示，UN會明顯高估颱風強度，於CTL改善過強的強度，尤其於颱風玉兔模擬中更加明顯。當颱風玉兔增強時，受到眼牆區域之強垂直平均角動量平流及垂直渦流角動量平流影響，增強颱風底層入流及高層外流，將強角動量向內傳遞，導致颱風玉兔快速增強過程強於颱風山竹，此強不對稱徑向入流是透過眼牆與附近較高溫的海水交互作用而產生，且特別常發生於典型的強颱風。研究亦進行海溫敏感度測試，當颱風所經過區域海溫降低1oC，颱風山竹將不會快速增強，而颱風玉兔受其影響較小，颱風強度仍會快速增強。颱風玉兔環境場中較弱的深層垂直風切導致移動速度較慢，相較於移動速度較快的颱風山竹，此現象有利於颱風玉兔更快發展快速增強。模式模擬中，相較於初始海洋溫度的調整，快速增強後的發展主要受到物理參數化方法影響。路徑方面，在模擬時間的前面兩天(山竹)或前面三天（玉兔），海洋耦合、非耦合、移除地形及調整海洋溫度的實驗皆獲得相當好的路徑模擬，但經過這段時間後，兩個颱風皆往北偏。相較於CTL，UN在實驗中顯現出較好的路徑模擬，特別是在颱風山竹。雖然菲律賓及呂宋島對山竹的路徑向北偏折?有產生明顯的影響，但會?弱玉兔的向北偏折。實驗中也有將初始海溫降低1oC，會使兩個颱風向北偏折的情形減弱，若將海溫升高1oC，則會使向北偏折增強。這兩個颱風在靠近北菲律賓時的路徑偏折主要受到物理參數化方法和初始時間影響，而物理參數化方法對於颱風玉兔的路徑模擬有較大的影響，對於颱風山竹的強度影響較小。於位渦趨勢收支中顯示山竹在北菲律賓的向北偏折主要受到水平位渦平流導致的向西北移動趨勢及絕熱加熱導致的向西但微向北移動趨勢所影響，而颱風玉兔在靠近登陸時的向北偏折主要受到水平位渦平流導致的向西北方移動趨勢影響。 ;Consecutive Supertyphoons Mangkhut and Yutu in 2018 underwent rapid intensifications (RI) over the western North Pacific (WNP) and made landfall at the northern Philippines. Hurricane Weather Research and Forecasting System (HWRF) was used to investigate the different processes in RI over the WNP and track evolution near the northern Philippines between both typhoons. Both ocean-coupled (CTL) and uncoupled (UN) experiments were conducted for comparison. The model results show that CTL improves the over-predicted typhoon intensity of UN as a result of typhoon-ocean interactions, particularly for Yutu. Stronger angular momentum (AM) is transported inward by the intensifying radial inflow flow at lower levels and outflow at upper levels for Yutu, which then leads to a stronger RI than Mangkhut, mainly contributed by the larger positive vertical mean AM advection in the troposphere and vertical eddy AM advection at low levels near the eyewall. The simulated RI will not occur if the initial ocean temperature along the Mangkhut track is decreased by 1oC, while Yutu’s RI is much less affected by the same temperature decrease or increase. Environmental weaker deep-layer vertical wind shear associated with the slower-moving Yutu is favorable for the faster development of RI as compared to the faster-moving Mangkhut. The later development after RI onset for both typhoons is more dominated by physics schemes applied in the simulations than the initial ocean temperature change; however, their induced RI onsets and rates are only slightly changed. For the typhoon approaching the northern Philippines, all coupled and uncoupled, no-terrain, and ocean temperature change experiments obtain good simulated tracks in the first two days (for Mangkhut) or first three days (for Yutu) and then followed by a northward deflection for both typhoons. UN gives a better-simulated track than CTL, particularly for Mangkhut. The Philippines and Luzon terrains do not affect significantly the northward deflection for Mangkhut, but they ease the northward track deflection for Yutu. The northward track deflection for both typhoons decreases when their initial ocean temperature is reduced by 1oC, while it increases when their initial ocean temperature is increased by 1oC. The track deflection near the northern Philippines of both typhoons is much more sensitive to physics schemes and initial time. However, the physics schemes have a more effective control on the track of Yutu, but with a less influence in determining Mangkhut intensity. Diagnostics of potential vorticity (PV) tendency budget shows that the northward deflection for Mangkhut near the northern Philippines can be explained by the northwestward tendency induced by horizontal PV advection and the westward but with slightly northward tendency induced by diabatic heating, while the northward deflection for Yutu near landfall is mainly dominated by the northwestward tendency induced by horizontal PV advection.
Appears in Collections:	[Department of Atmospheric Sciences and Graduate Institute of Atmospheric Physics ] Department of Earth Sciences

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