Oceanic response to the consecutive Hurricanes Dorian and Humberto (2019) in the Sargasso Sea

Understanding the oceanic response to tropical cyclones (TCs) is of importance for studies on climate change. Although the oceanic effects induced by individual TCs have been extensively investigated, studies on the oceanic response to the passage of consecutive TCs are rare. In this work, we assess the upper-oceanic response to the passage of Hurricanes Dorian and Humberto over the western Sargasso Sea in 2019 using satellite remote sensing and modelled data. We found that the combined effects of these slow-moving TCs led to an increased oceanic response during the third and fourth post-storm weeks of Dorian (accounting for both Dorian and Humberto effects) because of the induced mixing and upwelling at this time. Overall, anomalies of sea surface temperature, ocean heat content, and mean temperature from the sea surface to a depth of 100 m were 50 %, 63 %, and 57 % smaller (more negative) in the third-fourth post-storm weeks than in the first-second post-storm weeks of Dorian (accounting only for Dorian effects), respectively. For the biological response, we found that surface chlorophyll a (chl a) concentration anomalies, the mean chl a concentration in the euphotic zone, and the chl a concentration in the deep chlorophyll maximum were 16 %, 4 %, and 16 % higher in the third-fourth post-storm weeks than in the first-second post-storm weeks, respectively. The sea surface cooling and increased biological response induced by these TCs were significantly higher (Mann-Whitney test, p < 0.05) compared to climatological records. Our climatological analysis reveals that the strongest TC-induced oceanographic variability in the western Sargasso Sea can be associated with the occurrence of consecutive TCs and long-lasting TC forcing

Response of the Coastal Ocean to Tropical Cyclones

The Northwest Pacific and the South China Sea region are the birthplaces of most monsoon disturbances and tropical cyclones and are an important channel for the generation and transmission of water vapor. The Northwest Pacific plays a major role in regulating interdecadal and long-term changes in climate. China experiences the largest number of typhoon landfalls and the most destructive power affected by typhoons in the world. The hidden dangers of typhoon disasters are accelerating with the acceleration of urbanization, the rapid development of economic construction and global warming. The coastal cities are the most dynamic and affluent areas of China’s economic development. They are the strong magnetic field that attracts international capital in China, and are also the most densely populated areas and important port groups in China. Although these regions are highly developed, they are vulnerable to disasters. When typhoons hit, the economic losses and casualties caused by gale, heavy rain and storm surges were particularly serious. This chapter reviews the response of coastal ocean to tropical cyclones, included sea surface temperature, sea surface salinity, storm surge simulation and extreme rainfall under the influence of tropical cyclones

Contribution of hurricane-induced sediment resuspension to coastal oxygen dynamics

© The Author(s), 2018. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Scientific Reports 8 (2018): 15740, doi:10.1038/s41598-018-33640-3.Hurricanes passing over the ocean can mix the water column down to great depths and resuspend massive volumes of sediments on the continental shelves. Consequently, organic carbon and reduced inorganic compounds associated with these sediments can be resuspended from anaerobic portions of the seabed and re-exposed to dissolved oxygen (DO) in the water column. This process can drive DO consumption as sediments become oxidized. Previous studies have investigated the effect of hurricanes on DO in different coastal regions of the world, highlighting the alleviation of hypoxic conditions by extreme winds, which drive vertical mixing and re-aeration of the water column. However, the effect of hurricane-induced resuspended sediments on DO has been neglected. Here, using a diverse suite of datasets for the northern Gulf of Mexico, we find that in the few days after a hurricane passage, decomposition of resuspended shelf sediments consumes up to a fifth of the DO added to the bottom of the water column during vertical mixing. Despite uncertainty in this value, we highlight the potential significance of this mechanism for DO dynamics. Overall, sediment resuspension likely occurs over all continental shelves affected by tropical cyclones, potentially impacting global cycles of marine DO and carbon.Support for J. Moriarty was provided by the USGS Mendenhall Program

The Climate-G testbed: towards large scale distributed data management for climate change

Climate-G is a large scale distributed testbed devoted to climate change research. It is an unfunded effort started in 2008 and involving a wide community both in Europe and US. The testbed is an interdisciplinary effort involving partners from several institutions and joining expertise in the field of climate change and computational science. Its main goal is to allow scientists carrying out geographical and cross-institutional data discovery, access, analysis, visualization and sharing of climate data. It represents an attempt to address, in a real environment, challenging data and metadata management issues. This paper presents a complete overview about the Climate-G testbed highlighting the most important results that have been achieved since the beginning of this project

한국 여름철 집중호우의 종관 및 역학적 특징

학위논문(박사) -- 서울대학교대학원 : 자연과학대학 지구환경과학부, 2023. 2. 손석우.Heavy rainfall events (HREs) are the most frequent natural disaster from which people in South Korea recurrently suffer every summer. However, our understanding of their mechanisms has been still limited because many previous studies were confined to case studies or qualitative analyses. In this dissertation, the synoptic–dynamic characteristics of HREs in the summer monsoon period in South Korea are elaborated both quantitatively and qualitatively based on all historical events that occurred in the recent four decades. First, by separately considering the HREs resulting from tropical cyclones (TCs; 18.9%) and those not directly related to TCs (81.1%), their climatological features are drawn through composite and statistical analyses. This result is then extended to their further synoptic–dynamic details as below. By numerically solving the quasigeostrophic omega equation, it is found that the vertical motion of non-TC-induced HREs (hereafter, simply HREs) is initially driven dynamically, but diabatic uplift becomes dominant in the mature stage of HREs. This implies the importance of dynamic processes in triggering HREs and nonlinear dynamic–diabatic feedback in the subsequent growth of HREs. By decomposing Q vectors into shearwise and transverse components to delineate the dynamical processes, it is further revealed that the dynamic omega is closely associated with a baroclinically-deepening trough in the upper troposphere. The role of thermally-direct secondary circulation on the entrance region of the upper-level jet, which has been emphasized in the literature as a key driver of HREs, turns out to be relatively minor. The quasigeostrophic diagnosis of vertical motion of HREs can be robustly applied to most summertime HREs, but the clustering analysis shows that HREs could occur under various surface weather patterns depending on the strengths and/or locations of surface synoptic-scale cyclones and the North Pacific high. Each cluster exhibits a distinct temporal evolution of surface weather patterns with different favorable seasons and regions. This result provides important forecasting factors to be differently considered depending on the synoptic categorization of HREs. While most previous studies on TC rainfall in South Korea have focused on the characteristics of TC itself and local factors (e.g., topography), it is found that TC-induced HREs (hereafter, TC-HREs) are also largely sensitive to midlatitude condition. The TC-HREs under strongly baroclinic condition are characterized by amplifying tropopause circulation (by negative potential vorticity advection by TC-induced divergent outflow) and structural changes of TC (reminiscent of extratropical transition). The synergistic TC–midlatitude flow interaction allows for widely enhanced quasigeostrophic forcing for ascent, causing heavy rainfall even before TC gets close to South Korea. The TC-HREs under weakly baroclinic condition, in contrast, do not accompany the meandering tropopause flow. In the absence of strong interaction with midlatitude flow, TC rapidly dissipates after entering midlatitude, and the upward motion is confined to the inherent diabatic TC convection. As a result, heavy rainfall occurs only when TC locates in the right vicinity of the country. Lastly, the record-breaking monsoon rainfall in the summer of 2020 is investigated. The abrupt change of HRE nature in late July is particularly of interest. While the HREs from 29 June to 27 July (P1) were determined by the passage of extratropical cyclones, those from 28 July to 15 August (P2) mainly occurred by the quasi-stationary monsoon rainband and mesoscale instability thereon. This sudden synoptic transition is explained by atmospheric teleconnections. During P1, the subtropical high anomalously extended westward but its northward expansion was hindered by the suppressed convection over the South China Sea. In contrast, the enhanced South China Sea convection in P2 prompted an abrupt northward jump of the subtropical high. The resulting monsoon circulations established favorable environments for extratropical cyclones and monsoon rainband, respectively, in the two subperiods. The atmosphere–ocean coupled mode over the Indo-western Pacific was particularly related to the suppressed convection over the South China Sea in P1. The summer North Atlantic oscillation also secondarily contributed to the anomalous monsoon flows in P1 and P2 with opposite phases, although the reasons for its synchronized phase transition with the South China Sea convection is still unclear. The summer of 2020 implies that multiscale analyses would be beneficial in future work for a better understanding of HREs.여름철 집중호우는 해마다 발생하는 가장 빈번한 자연재해이나 그간의 국내 연구들은 주로 사례 연구나 정성정 분석에 집중되어 있어 관련 메커니즘에 대한 완전한 이해는 담보되지 않은 상태이다. 본 논문에서는 최근 40년 동안 발생한 모든 여름철 집중호우 사례들을 활용하여 집중호우의 종관기상학적 특성을 정성적, 정량적으로 상세분석하였다. 기상청 호우주의보 기준인 12시간 누적강수량 110 mm로 정의된 집중호우 사례들을 태풍에 의해 발생한 사례(TC-HREs; 전체의 약 18.9%)와 태풍과 직접적으로 연관되지 않은 사례(HREs; 전체이 약 81.1%)로 구분하고, 합성장 및 통계적 분석을 통해 각각의 기후학적 특성을 먼저 도출하였다. 이를 기반으로 HREs와 TC-HREs의 종관 및 역학적 특징을 아래와 같이 더욱 상세화하였다. HREs의 경우, 집중호우 발생 전부터 상층 요란이 유의미하게 풍상측에 나타났으며 이는 시간에 따라 조직화된 상층골로 발달하는 것으로 확인되었다. 준지균 오메가 방정식의 수치적 해를 통해 집중호우의 발달기에는 역학적 강제력과 비단열적 강제력이 상승운동에 비슷한 정도의 역할을 하지만 집중호우 최성기가 되면 연직운동은 비단열 강제력에 지배되는 것으로 나타났다. 이는 집중호우가 역학적 강제력에 의해 촉발되고 이어 역학적-비단열적 되먹임 통해 빠르게 발달함을 암시한다. Q 벡터의 자연좌표계에서의 물리적 분해를 통해 역학적 강제력은 특히 하층 저기압과 경압불안정을 통해 발달하는 상층 골에 의해 지배되는 것으로 확인되었는데, 이는 선행연구에서 강조되어온 상층제트 입구에서 발생하는 이차순환의 역할이 다소 과장되었음을 의미한다. 집중호우 연직운동의 준지균적 진단은 대부분의 사례에 적용될 수 있으나, 집중호우는 조직화된 저기압의 위치/유무, 북태평양 고기압의 위치/강도 등의 차이 등에 따라 다양한 지상 일기 패턴하에서 발생할 수 있다. 이러한 집중호우의 다양성은 인공신경망 알고리즘을 이용한 군집분석을 통해 발견되었는데, 각 군집들은 저마다 다른 일기 패턴의 발달양상을 보여주며 주요 발생시기 및 발생지역 또한 뚜렷한 차이를 보이는 것으로 나타났다. 따라서 지상 일기 패턴 기반 집중호우 유형 분류는 여름철 집중호우의 종합적인 이해 뿐만 아니라 예보에 있서도 도움이 될 것으로 기대된다. TC-HREs에 관한 기존의 연구들은 주로 태풍 자체의 특성이나 지형 등과 같은 국지적인 요소들에 집중해왔으나, 태풍에 의한 집중호우는 중위도 조건에 의해서도 매우 민감하게 반응하는 것으로 확인되었다. 중위도 순환이 경압적으로 불안정한 조건에 놓여있는 경우, 태풍이 유도한 상층 발산류가 음의 잠재와도 이류를 일으켜 중위도 대류권계면의 파동활동이 두드러지고(예: 상층 기압골의 정체 및 상층 기압능, 제트의 강화), 북상하는 태풍의 온대저기압화 또한 빠르게 이루어진다. 이는 태풍과 중위도 순환 사이에 강한 상호작용이 이루어지기 때문인데, 이는 태풍 전면의 넓은 지역에 강한 준지균 상승운동을 유발하고 그 결과 태풍이 한반도에 미처 상륙하기 전부터 집중호우가 발생할 위험을 초래한다. 반면, 중위도 경압 조건이 약한 경우 이러한 태풍-중위도 순환 상호작용이 거의 나타나지 않으며 태풍 또한 중위도로 진입 후 빠르게 약화되는 특성을 보인다. 집중호우와 연관된 연직운동은 주로 태풍의 잔여 비단열적 대류에 지배되는 양상을 보이며 그 결과 태풍이 한반도에 상륙하거나 가까이 접근했을 때 비로소 집중호우가 발생한다. 마지막으로, 이례적으로 많은 호우 피해가 발생한 2020년 여름에 대한 사례분석을 수행하였다. 특히, 집중호우의 양상이 7월 말 갑자기 바뀐 것에 주목하였는데, 6월 29일부터 7월 27일까지의 기간(P1) 동안 집중호우는 온대저기압의 통과에 의해 발생한 반면, 7월 28일부터 8월 15일까지의 기간(P2) 동안 집중호우는 정체한 몬순강우대 상의 중규모 불안정에 의해 발생하였다. 이러한 종관적 특성의 급변을 이해하기 위해 대규모 순환을 분석한 결과, P1에는 북태평양 고기압이 서쪽으로 강하게 확장했으나 남중국해 대류 약화에 따른 파동 반응에 의해 북상하지 못한 채 남쪽에 머물렀고 그 결과 한반도로 온대저기압이 통과하기 좋은 조건이 만들어진 것으로 나타났다. 반면, P2에는 다시 대류가 강화되어 북태평양 고기압의 가장자리의 강한 기압경도가 한반도 위에 놓이게 되어 몬순 정체전선이 발달하기 좋은 환경이 형성된 것으로 확인되었다. 특히 P1 시기의 남중국해 대류활동은 인도-북태평양에서 이루어진 대규모 대기-해양 상호작용과 연관되어 있었으며, 북대서양 여름 진동 또한 7월 말 갑작스런 위상 변화를 통해 P1과 P2의 동아시아 몬순 순환에 서로 다른 영향을 준 것으로 판단된다. 2020년 사례는 향후 집중호우 연구에서 중규모-종관규모-대규모 순환을 아우르는 다중규모 분석이 필요함을 시사한다.Chapter 1. Introduction 5 1.1. Background 5 1.1.1. Precipitation climatology in South Korea 5 1.1.2. East Asian summer monsoon (EASM) 6 1.1.3. Large-scale modulation of EASM 7 1.1.4. Changma 8 1.1.5. Synoptic features of HREs 9 1.1.6. Mesoscale features of HREs 10 1.1.7. Thermodynamic characteristics of HREs 11 1.1.8. Tropical cyclones (TCs) 11 1.2. Aims of dissertation 13 Chapter 2. Climatological features of HREs and TC-HREs 14 2.1. Motivation 14 2.2. Data and methods 15 2.2.1. Data 15 2.2.2. Definition of HRE and TC-HRE 15 2.3. Composited synoptic conditions 18 2.3.1. HREs 18 2.3.2. TC-HREs 22 2.4. Spatiotemporal occurrence distributions 26 Chapter 3. Quasi-geostrophic diagnosis of HREs 28 3.1. Motivation 28 3.2. Data and methods 31 3.2.1. Dataset 31 3.2.2. QG diagnosis of vertical motion 31 3.2.3. Transverse and shearwise components of Q vector 32 3.3. QG forcing: Dynamic versus diabatic forcings 33 3.4. QG dynamic forcing: Transverse versus shearwise Q-vector forcings 39 3.5. Discussion 47 Chapter 4. Diverse synoptic weather patterns of HREs 49 4.1. Motivation 49 4.2. Data and methods 50 4.2.1. Dataset 50 4.2.2. Classification of HREs 50 4.3. Overview of the SOM clustering results 51 4.4. Synoptic patterns of the six HRE clusters 55 4.4.1. Quasi-stationary frontal boundary between low and high (C1 and C3) 55 4.4.2. ETC from eastern China (C2 and C5) 58 4.4.3. Local disturbance at the edge of the NPH (C4) 61 4.4.4. Moisture pathway between continental and oceanic highs (C6) 63 4.5. Discussion 68 Chapter 5. Role of midlatitude condition in TC-HREs 69 5.1. Motivation 69 5.2. Literature review of ET 70 5.2.1. Structure changes of TC 70 5.2.2. Impacts on midlatitude flow 71 5.3. Data and methods 73 5.3.1. Data 73 5.3.2. Definition of TC-HREs 74 5.3.3. Classification of TC-HREs 75 5.3.4. PV tendency equation 78 5.3.5. QG omega equation 78 5.4. Overview of the SOM clustering results 79 5.5. Synoptic evolutions under different tropopause patterns 83 5.5.1. Upper- and low-level evolutions 83 5.5.2. Vertical cross sections 90 5.6. Quantitative assessments 94 5.6.1. TC influence on the tropopause circulation 94 5.6.2. QG diagnosis of vertical motion 99 5.7. Discussion 106 Chapter 6. Record-breaking rainfall in the summer of 2020 108 6.1. Motivation 108 6.2. Data and methods 109 6.3. Overview of the 2020 summer rainfall 111 6.3.1. Record-breaking rainfall amount 111 6.3.2. Weather patterns of the HREs 113 6.4. Subseasonal variation of HREs and background flow 117 6.4.1. Synoptic characteristics of HREs in P1 and P2 117 6.4.2. Background monsoon flows in P1 and P2 121 6.5. Possible mechanisms of the monsoon circulation change 126 6.5.1. Meridional wave train by the SCS convection 126 6.5.2. Zonal wave train by the SNAO 129 6.5.3. Combined effect of the SCS convection and SNAO 130 6.6. Discussion 134 6.6.1. IPOC effect 134 6.6.2. BSISO 137 6.6.3. Other possible factors 138 Chapter 7. Conclusions and final remarks 139 7.1. Overall 139 7.2. Summary of dissertation 141 7.2.1. Chapter 2 Climatological features of HREs and TC-HREs 141 7.2.2. Chapter 3 Quasi-geostrophic diagnosis of HREs 142 7.2.3. Chapter 4 Diverse synoptic weather patterns of HREs 142 7.2.4. Chapter 5 Role of midlatitude condition in TC-HREs 144 7.2.5. Chapter 6 Record-breaking rainfall in the summer of 2020 145 7.3. Future directions 147 Appendix A 148 A1. Integrated water vapor transport 148 A2. 2D frontogenesis 148 A3. Curvature and shear components of geostrophic relative vorticity 148 A4. Wave activity flux by stationary Rossby wave 149 Appendix B 151 B1. Q-vector-form QG omega equation 151 B2. Numerical details of the QG omega equation inversion 154 B3. Transverse and shearwise Q vectors 156 B3.1. Mathematical expression and key physical meanings 156 B3.2. Further physical meanings 157 B3.3. Cartesian expression 159 Appendix C 160 C1. SOM algorithm 160 C1.1. Overview 160 C1.2. Topology and arrangement of nodes 160 C1.3. Iterative training procedure 162 Appendix D 164 D1. PV tendency equation 164 REFERENCES 165 국문초록 181박

Thermal response to sequential tropical cyclone passages: Statistic analysis and idealized experiments

The cold wake caused by a tropical cyclone (TC) extends for hundreds of kilometers and persists for several weeks, thus influencing the surface response for any subsequent TCs that might pass over it. It is commonly accepted that sea-surface temperature (SST) cooling, as produced by a single TC, occurs primarily through vertical mixing. However, when there are sequential TCs, the earlier TC can dramatically change the thermal structure of the upper ocean, which may influence the subsequent development of a latter-occurring TC (LTC). Therefore, the contribution of horizontal advection and vertical mixing to SST-cooling during the passage of LTCs is of great interest. Using a 19-year-long observational dataset and the heat budget analysis of an idealized numerical simulation, the SST change during the passage of sequential TCs is investigated. The results demonstrate that, on average, the SST cooling caused by the LTC shows an overall decreasing trend with enhanced lingering wakes. Budget analysis of the model simulations suggests that an earlier TC can suppress the vertical mixing induced by an LTC mainly through an alteration of dynamics within the deepened mixed layer and that the contribution of vertical mixing to the SST cooling is weaker due to the intensification of the earlier TC. The weakened vertical mixing dominates the decreased SST cooling induced by an LTC. In contrast, the cold wake generated by an earlier TC can produce more cold water on the right side of the TC’s track, which contributes to stronger horizontal advection upon the arrival of the LTC. In general, the effects of the earlier TC can suppress the sea-surface thermal response to an LTC. If the contribution of the horizontal advection to SST cooling is neglected, the SST cooling induced by an LTC could be reduced by about 40%. As for the response of the sub-surface water to the passage of an LTC, the weakened warm anomaly induced by vertical mixing and the enhanced cooling anomaly caused by the vertical advection explain the reduced tendency for the mixed layer to deepen. As a result, the tendency for the mixed layer depth (MLD) to increase is suppressed during the passage of an LTC. These results highlight the importance of optimally depicting cold wakes in numerical simulations to improve the prediction of the upper ocean’s response to sequential TCs

The Extratropical Transition of Tropical Cyclones: Forecast Challenges, Current Understanding, and Future Directions

A significant number of tropical cyclones move into the midlatitudes and transform into extratropical cyclones. This process is generally referred to as extratropical transition (ET). During ET a cyclone frequently produces intense rainfall and strong winds and has increased forward motion, so that such systems pose a serious threat to land and maritime activities. Changes in the structure of a system as it evolves from a tropical to an extratropical cyclone during ET necessitate changes in forecast strategies. In this paper a brief climatology of ET is given and the challenges associated with forecasting extratropical transition are described in terms of the forecast variables (track, intensity, surface winds, precipitation) and their impacts (flooding, bush fires, ocean response). The problems associated with the numerical prediction of ET are discussed. A comprehensive review of the current understanding of the processes involved in ET is presented. Classifications of extratropical transition are described and potential vorticity thinking is presented as an aid to understanding ET. Further sections discuss the interaction between a tropical cyclone and the midlatitude environment, the role of latent heat release, convection and the underlying surface in ET, the structural changes due to frontogenesis, the mechanisms responsible for precipitation, and the energy budget during ET. Finally, a summary of the future directions for research into ET is given

Aspects of interannual climate variability

Interannual climate variability during the northern summer season has been investigated in this study. After Walker\u27s pioneering work (Walker and Bliss 1932, 1937), many previous studies have documented and discussed the structure and the dynamical/thermodynamical causes (e.g., Bjerkness 1969). However, relatively less attention have been devoted on the summer climate variability. Thus, two different aspects of the interannual climate variability during the northern summer season have been discussed. One is the interannual variation of the boreal-forest rainbelts, and the other is the interannual variation of the North American monsoon rainfall. Also, the summer climatological aspect of the boreal-forest rainbelts from a hydrological and dynamical perspectives was presented in prior to its interannual variability.;The boreal forests comprise one third of the global woodlands, while the warm-season runoff from the boreal-forest rainbelts provide a major amount of freshwater to the Arctic Ocean. It is shown the boreal-forest rainbelts are maintained by the convergence of water vapor by transients along these rainbelts and the interannual variation of these rainbelts is caused by the collective response of these rainbelts to the North Atlantic Oscillation and the East-Asian teleconnection monsoon pattern in Eurasia and the Nitta-like short-wave train and the North Atlantic Oscillation in the Alaska-Canadian subarctic region. It was hypothesized by our recent study that the North American Monsoon (including both the Mexican and the Southwest U.S. monsoon) is maintained by the east-west differential heating between the Western Tropical Atlantic heating and the Eastern Tropical Pacific cooling. Diagnostic analysis with NCEP/NCAR reanalysis data in this study substantiated this hypothesis. Our current study has primarily focused on diagnostic analysis of observations and reanalysis. Further analysis with the global climate model such as NCAR CAM or NASA NSIPP and the regional climate model is suggested to further substantiate our hypothesis proposed in this study

Consecutive dual-vortex interactions between quadruple Typhoons Noru, Kulap, Nesat and Haitang during the 2017 North Pacific Typhoon season

© 2019 by the authors. This study utilizes remote sensing imagery, a differential averaging technique and empirical formulas (the \u27Liou-Liu formulas\u27) to investigate three consecutive sets of dual-vortex interactions between four cyclonic events and their neighboring environmental air flows in the Northwest Pacific Ocean during the 2017 typhoon season. The investigation thereby deepens the current understanding of interactions involving multiple simultaneous/sequential cyclone systems. Triple interactions between Noru-Kulap-Nesat and Noru-Nesat-Haitung were analyzed using geosynchronous satellite infrared (IR1) and IR3 water vapor (WV) images. The differential averaging technique based on the normalized difference convection index (NDCI) operator and filter depicted differences and generated a new set of clarified NDCI images. During the first set of dual-vortex interactions, Typhoon Noru experienced an increase in intensity and a U-turn in its direction after being influenced by adjacent cooler air masses and air flows. Noru\u27s track change led to Fujiwhara-type rotation with Tropical Storm Kulap approaching from the opposite direction. Kulap weakened and merged with Noru, which tracked in a counter-clockwise loop. Thereafter, in spite of a distance of 2000-2500 km separating Typhoon Noru and newly-formed Typhoon Nesat, the influence of middle air flows and jet flows caused an \u27indirect interaction\u27 between these typhoons. Evidence of this second interaction includes the intensification of both typhoons and changing track directions. The third interaction occurred subsequently between Tropical Storm Haitang and Typhoon Nesat. Due to their relatively close proximity, a typical Fujiwhara effect was observed when the two systems began orbiting cyclonically. The generalized Liou-Liu formulas for calculating threshold distances between typhoons successfully validated and quantified the trilogy of interaction events. Through the unusual and combined effects of the consecutive dual-vortex interactions, Typhoon Noru survived 22 days from 19 July to 9 August 2017 and migrated approximately 6900 km. Typhoon Noru consequently became the third longest-lasting typhoon on record for the Northwest Pacific Ocean. A comparison is made with long-lived Typhoon Rita in 1972, which also experienced similar multiple Fujiwhara interactions with three other concurrent typhoons