Response Of Tropical Cyclone Research Articles

A Machine Learning-Based Parameterized Tropical Cyclone Precipitation Model

AbstractCurrent simulation models considerably underestimate local-scale, short-duration extreme precipitation induced by tropical cyclones (TCs). This problem needs to be addressed to establish active response policies for TC-induced disasters. Taking Shanghai, a coastal megacity, as a study area and based on the observations from 192 meteorological stations in the city during 2005–2018, this study optimized the parameterized Tropical Cyclone Precipitation Model (TCPM) initially designed for TCs at the national scale (China) to the local or regional scales by using machine learning (ML) methods, including the random forest (RF), extreme gradient boosting (XGBoost), and ensemble learning (EL) algorithms. The TCPM-ML was applied for multiple temporal scale hazard assessment. The results show that: (1) The TCPM-ML not only improved TCPM performance for simulating hourly extreme precipitations, but also preserved the physical meaning of the results, contrary to ML methods; (2) Machine learning algorithms enhanced the TCPM ability to reproduce observations, although the hourly extreme precipitations remained slightly underestimated; (3) Best performance was obtained with the XGBoost or EL algorithms. Combining the strengths of both XGBoost and RF, the EL algorithm yielded the best overall performance. This study provides essential model support for TC disaster risk assessment and response at the local and regional scales in China.

Simulating the Response of Tropical Cyclones to Potential Nuclear War

AbstractNuclear war would cause massive amounts of smoke from its associated explosions and fires that would subsequently inject copious amounts of aerosols into the stratosphere. There would also be considerable changes to the global climate system, threatening human health and sustainability. Our work reveals a reduction of global‐scale tropical cyclones (TCs) from a simulation of a nuclear war scenario that could produce ∼150 million tons of smoke. In response to nuclear war, there would be spatially uneven cooling that would result in an anomalous sea surface temperature (SST) gradient pattern. Associated with this would be an anomalous zonal vertical circulation, tending to suppress upward motion and increase vertical wind shear over all TC main development regions, largely explaining the observed TC reduction at regional and global scales. This study improves our understanding of the impact of nuclear war on the TC environment.

Sensitivity of Philippine historically damaging tropical cyclone events to surface and atmospheric temperature forcings

As the climate warms, sea surface temperature (SST) is projected to increase, along with atmospheric variables which may have an impact on tropical cyclone (TC) properties. Climate models have well-known errors in simulating current climate SSTs that will likely affect future TC projections. Therefore, a better understanding of the impact of SST changes will help us identify the largest uncertainty in projecting TC changes. This study employs three different and independent methodologies to investigate the impact of sea surface and atmospheric temperature changes and tropical cyclone (TC) characteristics, focusing on three historically damaging TCs in the Philippines: Typhoons Haiyan, Bopha, and Mangkhut. These methodologies include initially simulations with uniform SST anomalies between −4 to +4°C, then experiments using delta from CMIP6 CESM2 for SST and atmospheric temperature in the far future, and, finally, simulations imposing Radiative-Convective Equilibrium (RCE) conditions. The experiments reveal significant insights into TC dynamics under varying environmental conditions. Changes in SSTs resulted in changes in TC track, intensity, and rainfall. In the positive SST simulations, TCs tended to move northwards and resulted in substantial increases in maximum wind speeds reaching a difference of up to 10, 13, 23 ms−1 for Typhoons Haiyan, Bopha, and Mangkhut, respectively. Analysis of the accumulated rainfall also showed that increased SST results in increased rainfall. Inclusion of atmospheric warming offsets the intensification due to SST change. Moreover, warmer SSTs resulted in slower-moving TCs and increased TC size. Further analyses incorporating atmospheric temperature adjustments derived from CESM2 and RCE simulations offer better insights on TC response. Under near-RCE conditions, TCs exhibit reduced sensitivity to SST changes, with smaller intensity and size modifications simulated when stable relative humidity is imposed. The smaller changes in TC intensity and size observed in these experiments suggest that maintaining atmospheric stability through pre-storm atmospheric adjustments dampens the response of TCs to SST warming.

Late Holocene tropical cyclones linked to climatic and solar variability

Response of tropical cyclone (TC) frequency to future climate change has important implications for society but remains poorly understood due to a lack of long-term reliable observational records. Here, we use high-resolution organic geochemical proxies (OGPs) with robust chronological control from two coastal lakes, >150 km apart, to reconstruct past TC activities in the northeastern Gulf of Mexico (GOM). Results show multi-decadal-to-centennial-scale fluctuations in TC frequency over the last 5500 years. We found that TC frequency either exceeded or was comparable to modern observations during a prolonged interval (∼1500-720 cal yr BP) that encompasses the Medieval Warm Period. We also found a nearly 90% reduction in TC activity, relative to modern, during an exceptionally quiescent period (650-280 cal yr BP) that overlaps the Little Ice Age. Warmer temperatures in the North Atlantic did not always support increased TC frequency in this region. We show, for the first time, that increased TC activities in the northeastern GOM track increased solar irradiance. High TC frequency is also coupled to periods of increased sea surface temperatures in the northern GOM, enhanced El Niño-Southern Oscillation, and positive phases of the Atlantic Multi-Decadal Oscillation. Our results highlight the importance of natural variability in climate and solar activity in modulating TC frequency.

Hemispheric asymmetric response of tropical cyclones to CO2 emission reduction

Tropical cyclones (TCs) are among the most devastating natural hazards for coastal regions, and their response to human activities has broad socio-economic relevance. So far, how TC responds to climate change mitigation remains unknown, complicating the design of adaptation policies. Using net-zero and negative carbon emission experiments, we reveal a robust hemisphere-asymmetric hysteretic TC response to CO2 reduction. During the decarbonization phase, the Northern Hemisphere TC frequency continues to decrease for several more decades, while the Southern Hemisphere oceans abruptly shifts to a stormier state, with the timescales depending on mitigation details. Such systematic changes are largely attributed to the planetary-scale reorganization of vertical wind shear and midlevel upward motion associated with the hysteretic southward migration of the Intertropical Convergence Zone, underpinned by the Atlantic Meridional Overturning Circulation and El Niño-like mean state changes. The hemispheric contrast in TC response suggests promising benefits for most of the world’s population from human action to mitigate greenhouse gas warming, but it may also exacerbate regional socioeconomic disparities, for example by putting more pressure on small open-ocean island states in the Southern Hemisphere to adapt to TC risks.

Implementation and evaluation of a spectral cumulus parametrization for simulating tropical cyclones in JMA‐GSM

AbstractA spectral cumulus parametrization (spectral scheme) developed using a cloud‐resolving model simulation was implemented in Global Spectral Model of the Japan Meteorological Agency (JMA‐GSM, GSM hereafter). The performance of the spectral scheme in terms of mean state, variability, and tropical cyclone (TC) properties was evaluated using atmosphere‐only model experiments by comparing results of the original convection scheme (based on Arakawa–Schubert scheme, AS scheme) and the spectral scheme. Parameter tunings were first conducted for the spectral scheme, through which the climatological errors of the cloud cover in the Southern Ocean and temperature were greatly improved. The spectral scheme showed comparable climatological errors to the AS scheme in the increased resolutions. The spectral scheme greatly improved tropical variability, that is, response to El Niño/Southern Oscillation and Madden–Julian Oscillation. Analyses on TC statistical data revealed that the spectral scheme improved TC properties in terms of genesis frequency, intensity, and the response of TC to tropical variability. Specifically, significant improvements were seen in the Northern Hemisphere. Further analyses on the TC structure revealed that higher TC intensity was sustained for longer times by the spectral scheme than by the AS scheme. The reason for this is that the spectral scheme better simulates convective heating by considering coexistence of different cloud types with parametrized vertically varying entrainment rates, especially from low to mid‐altitudes. The convective heating leads to a sharper vertical‐radial circulation in the TC structure, causing stronger incoming moisture flux toward the TC centre, and resulting in a stronger TC intensity. Consequently, the spectral scheme can simulate a comparable mean state, better variability, and better TC properties compared with the original scheme by simulating a more detailed convective structure. Therefore, it has a potential to increase the TC forecast skill for operational GSM.

Changes in tropical cyclone response to the Boreal Summer Intraseasonal Oscillation in the western North Pacific under global warming in EC-Earth3P-HR

EC-Earth3P-HR reproduces well the observed Boreal Summer Intraseasonal Oscillation (BSISO) and its impacts on tropical cyclone genesis (TCG) in the western North Pacific (WNP). Hence, the historical simulation (1950–1979) and future projection under the SSP5-8.5 scenario (2020–2049) in EC-Earth3P-HR are adopted to explore possible changes in the BSISO's modification of WNP TCG under global warming to enhance the understanding of TC activities in the WNP. Results show that the BSISO circulation in the WNP shifts northeastward under global warming. This leads to enhanced convection in a northwest–southeast-oriented band crossing the WNP. Along the band, the BSISO-related TCG anomalies are enhanced. Analyses of genesis potential index show that changes in the BSISO-related mid-tropospheric relative humidity play the dominant role in modifying the BSISO's impacts on WNP TCG under global warming. The enhanced BSISO convection in the band moistens the middle troposphere, which helps reduce the entrainment of generally dry mid-tropospheric air in the updrafts and the modification of the boundary layer by the downdraft of generally dry mid-tropospheric air, leading to enhanced TCG.摘要北半球夏季季内振荡 (BSISO) 对西北太平洋 (WNP) 热带气旋形成 (TCG) 有显著的影响, 并且为TC的次季节预报提供重要依据, 因此研究其在全球变暖下的变化有重要意义. EC-Earth3P-HR模式较好地再现了观测到的BSISO及其对TCG的影响. 因此, 采用EC-Earth3P-HR的历史模拟 (1950–1979) 和SSP5-8.5情景 (2020–2049) 下的未来预估, 探讨全球变暖下BSISO对WNP上TCG调制的可能变化. 结果表明, 在全球变暖影响下, WNP上的BSISO环流向东北方向移动, 表现为西北-东南方向分布的增强对流带. 在对流带上, BSISO相关的TCG异常增强. 成因潜力指数分析表明, 全球变暖背景下, 与BSISO相关的对流层中部相对湿度的变化对BSISO对TCG的调制起主导作用. 带内增强的BSISO对流使对流层中部空气变湿润, 这有利于减少上升气流对通常干燥的对流层空气的夹带以及下沉气流对边界层的修正, 从而导致TCG的增强.

Air-sea coupling influence on projected changes in major Atlantic hurricane events

Tropical cyclone (TC) projections with atmosphere-only models are associated with uncertainties due to their inability to represent TC-ocean interactions. However, global coupled models, which represent TC-ocean interactions, can produce basin-scale sea surface temperature biases in seasonal to centennial simulations that lead to challenges in representing TC activity. Therefore, focusing on recent individual major hurricane events, we investigated the influence of TC-ocean coupling on the response of TCs to anthropogenic change using atmosphere-only and coupled atmosphere-ocean regional model simulations. Under an extremely warm scenario, coupling does not influence the signs of projected TC rainfall and intensity responses. Coupling, however, does influence the magnitude of projected intensity and especially rainfall. Within a 500 km radius region of the TCs, the projected rainfall increases in coupled simulations are 3–59 % less than in the atmosphere-only simulations, driven by enhanced TC-induced sea surface temperature cooling in the former. However, the influence of coupling on the magnitude of projected rainfall could vary considerably over the regions of highest rainfall generated by TCs.

Modeled variations of tropical cyclone genesis potential during Marine Isotope Stage 3

To advance our understanding of the responses of tropical cyclones (TCs) to abrupt climate transitions, we investigate the variation of genesis potential and the underlying mechanisms during Marine Isotope Stage 3 (MIS 3) that is characterized by frequent millennial-scale oscillations, using a set of coupled model simulations. We illustrate that genesis potential mainly increases over the eastern North Pacific and South Pacific in the storm season during MIS 3 interstadial relative to preindustrial, whereas it decreases over the western North Pacific, North Atlantic, South Indian Ocean, and Australian coast. The relative importance of each genesis factor to genesis potential change varies across oceans. During the transition from warm interstadial to cold stadial induced by freshwater injection, TC genesis potential generally decreases in the Northern Hemisphere, while increases in the Southern Hemisphere. These changes are associated with asymmetric variations of genesis factors between Northern and Southern Hemisphere, which are further tied to the adjustment of large-scale environmental factors in response to the weakened Atlantic meridional overturning circulation. Additionally, TC genesis potential exhibits a regional “overshoot” phenomenon when the freshwater injection is terminated, manifested by an increase over the eastern North Pacific and North Atlantic and a decrease over the South Pacific, compared with the initial interstadial state. Our results may help improve our knowledge on past TC behaviors and shed lights on TC response to potential abrupt climate transitions in a warmer future.

Moisture control of tropical cyclones in high-resolution simulations of paleoclimate and future climate

The intensity of tropical cyclones (TCs) is expected to increase in response to greenhouse warming. However, how future climate change will affect TC frequencies and tracks is still under debate. Here, to further elucidate the underlying sensitivities and mechanisms, we study TCs response to different past and future climate forcings. Using a high-resolution TC-resolving global Earth system model with 1/4° atmosphere and 1/10° ocean resolution, we conducted a series of paleo-time-slice and future greenhouse warming simulations targeting the last interglacial (Marine Isotope Stage (MIS) 5e, 125 ka), glacial sub-stage MIS5d (115 ka), present-day (PD), and CO2 doubling (2×CO2) conditions. Our analysis reveals that precessional forcing created an interhemispheric difference in simulated TC densities, whereas future CO2 forcing impacts both hemispheres in the same direction. In both cases, we find that TC genesis frequency, density, and intensity are primarily controlled by changes in tropospheric thermal and moisture structure, exhibiting a clear reduction in TC genesis density in warmer hemispheres.

The Influence of Large-Scale Radiation Anomalies on Tropical Cyclone Frequency

Abstract The response of tropical cyclone (TC) frequency to sea surface warming is uncertain in climate models. We hypothesize that one source of uncertainty is the anomalies of large-scale atmospheric radiation in response to climate change, and whose influence on TC frequency is investigated. Given two atmospheric models with opposite TC frequency responses to uniform sea surface warming, we interchange their atmospheric radiation anomalies in experiments with prescribed radiative heating rates. The largest model discrepancy occurs in the western North Pacific, where the TC frequency tends to increase with anomalous large-scale ascent caused by prescribed positive radiation anomalies, while the TC frequency tends to decrease with anomalous large-scale descent caused by prescribed negative radiation anomalies. The model spread in TC frequency response is approximated by the model spread in the frequency response of pre-TC vortices (seeds), which is explained by changes in the large-scale circulation using a downscaling formula known as the seed propensity index. We further generalize the index to predict the influence of large-scale radiation anomalies on TC seed frequency. The results show that model spread in TC and seed frequency response can be reduced when constraining the large-scale radiation anomalies. Significance Statement It is difficult to predict whether tropical cyclones will occur more or less frequently in the future and by how much. We show that tropical cyclone frequency is strongly influenced by the global pattern of heating and cooling due to radiation, a process that has been neglected in existing theories. Our theory improves understanding of how tropical cyclones respond to climate change, explaining why one model may predict a frequency increase while a different but equally realistic model may predict a frequency decrease. One reason for the difficulty in predicting tropical cyclone frequency is found to be the difficulty in predicting how global cloud distribution will change in the future.

Understanding the Variation and Mechanisms of Tropical Cyclone Genesis Potential over the Western North Pacific during the Past 20 000 Years

Abstract To deepen our understanding of the behavior of tropical cyclones (TCs) over the western North Pacific (WNP) and its response to various external forcings, we investigate the variation of TC genesis potential over the WNP during the past 20 ka that experienced several large forcings. Using a set of transient simulations and a genesis potential index, our results indicate that TC genesis potential in the storm season shows an overall increase averaged over the WNP during the Heinrich Stadial 1 (HS1; ∼17–16 ka) relative to the Last Glacial Maximum. Subsequently, there is a sharp decrease in genesis potential during the Bølling–Allerød (BA; ∼13.5 ka) relative to the HS1, which is followed by an increase during the Younger Dryas (YD; ∼12.9–11.7 ka). During the Holocene, TC genesis potential shows a slight decrease during the early–middle Holocene (∼11.7–6 ka) and a significant increasing trend afterward. Further analysis shows that the contribution of each genesis factor to the genesis potential change varies greatly with time, which is in turn tied to changes in external forcings. The increased meltwater fluxes dominate the increased genesis potential during the HS1 and YD, whereas all external forcings (i.e., changes in meltwater, ice sheets, CO2, and insolation) contribute to genesis potential change during the BA. The long-term increasing trend from the mid-Holocene to the present is controlled by orbital insolation. These results may help improve our understanding on past TC activity and shed lights on TC response to various external forcings in a long-term future.

Mechanisms of tropical cyclone response under climate change in the community earth system model

Climate change induces a myriad of effects which influences the global tropical cyclone (TC) genesis frequency. Here we explore how North Atlantic and Western Pacific TCs are affected under climate change using a present-day and a future (1% pCO2 scenario) ensemble of high resolution simulations. We find that the number of TCs decreases (-45%) in the North Atlantic but increases (+15%) in the Western Pacific. Part of these opposing variations are linked to differences in the ocean’s meridional overturning circulation, which gives rise to a different sea surface temperature response and air-sea fluxes between the two basins. The results show the important role of oceanic climate change on TC response.

Patterns and frequency of projected future tropical cyclone genesis are governed by dynamic effects

Potential future changes in the genesis frequency and distribution of tropical cyclones are important for society, yet uncertain. Confidence in the model projections largely relies on whether we can physically explain why the models projected such changes. Here we analyze multi-model climate simulations, and find that future changes in the patterns and frequency of tropical cyclone genesis are largely governed by dynamic effects—that is, by human-induced changes in the atmospheric circulation. These large-scale circulation changes include decreases in the mid-level upward motion and lower-to-mid level cyclonic vorticity, and increases in vertical wind shear. Conversely, the thermodynamic effect—a result of increased maximum potential intensity in a warmer climate—would yield tropical cyclone genesis patterns that are opposite to the model projections. We conclude that dynamic changes in response to anthropogenic greenhouse gas emissions are an important factor in determining the response of tropical cyclones to global warming.

Hemisphere-asymmetric tropical cyclones response to anthropogenic aerosol forcing

How anthropogenic forcing could change tropical cyclones (TCs) is a keen societal concern owing to its significant socio-economic impacts. However, a global picture of the anthropogenic aerosol effect on TCs has not yet emerged. Here we show that anthropogenic aerosol emission can reduce northern hemisphere (NH) TCs but increase southern hemisphere (SH) TCs primarily through altering vertical wind shear and mid-tropospheric upward motion in the TC formation zones. These circulation changes are driven by anthropogenic aerosol-induced NH-cooler-than-SH and NH-increased versus SH-decreased meridional (equator to mid-latitudes) temperature gradients. The cooler NH produces a low-level southward cross-equatorial transport of moist static energy, weakening the NH ascent in the TC formation zones; meanwhile, the increased meridional temperature gradients strengthen vertical wind shear, reducing NH TC genesis. The opposite is true for the SH. The results may help to constrain the models’ uncertainty in the future TC projection. Reduction of anthropogenic aerosol emission may increase the NH TCs threat.

Hurricane annual cycle controlled by both seeds and genesis probability

Understanding tropical cyclone (TC) climatology is a problem of profound societal significance and deep scientific interest. The annual cycle is the biggest radiatively forced signal in TC variability, presenting a key test of our understanding and modeling of TC activity. TCs over the North Atlantic (NA) basin, which are usually called hurricanes, have a sharp peak in the annual cycle, with more than half concentrated in only 3 mo (August to October), yet existing theories of TC genesis often predict a much smoother cycle. Here we apply a framework originally developed to study TC response to climate change in which TC genesis is determined by both the number of pre-TC synoptic disturbances (TC "seeds") and the probability of TC genesis from the seeds. The combination of seeds and probability predicts a more consistent hurricane annual cycle, reproducing the compact season, as well as the abrupt increase from July to August in the NA across observations and climate models. The seeds-probability TC genesis framework also successfully captures TC annual cycles in different basins. The concise representation of the climate sensitivity of TCs from the annual cycle to climate change indicates that the framework captures the essential elements of the TC climate connection.

The Intensity- and Size-Dependent Response of Tropical Cyclones to Increasing Vertical Wind Shear

AbstractThis study describes a set of idealized simulations in which westerly vertical wind shear increases from 3 to 15 m s−1 at different stages in the lifecycle of an intensifying tropical cyclone (TC). The TC response to increasing shear depends on the intensity and size of the TC’s tangential wind field when shear starts to increase. For a weak tropical storm, increasing shear decouples the vortex and prevents intensification. For Category 1 and stronger storms, increasing shear causes a period of weakening during which vortex tilt increases by 10–30 km before the TCs reach a near-steady Category 1–3 intensity at the end of the simulations. TCs exposed to increasing shear during or just after rapid intensification tend to weaken the most. Backward trajectories reveal a lateral ventilation pathway between 8–11 km altitude that is capable of reducing equivalent potential temperature in the inner core of these TCs by nearly 2°C. In addition, these TCs exhibit large reductions in diabatic heating inside the radius of maximum winds (RMW) and lower-entropy air parcels entering downshear updrafts from the boundary layer, which further contributes to their substantial weakening. The TCs exposed to increasing shear after rapid intensification and an expansion of the outer wind field reach the strongest near-steady intensity long after the shear increases because of strong vertical coupling that prevents the development of large vortex tilt, resistance to lateral ventilation through a deep layer of the middle troposphere, and robust diabatic heating within the RMW.

A Comparison of Tropical Cyclone Projections in a High-resolution Global Climate Model and from Downscaling by Statistical and Statistical-deterministic Methods

AbstractIn this study, we investigate the response of tropical cyclones (TCs) to climate change by using the Princeton environment-dependent probabilistic tropical cyclone (PepC) model and a statistical-deterministic method to downscale TCs using environmental conditions obtained from the Geophysical Fluid Dynamics Laboratory (GFDL) High-resolution Forecast-oriented Low Ocean Resolution (HiFLOR) model, under the Representative Concentration Pathway 4.5 (RCP4.5) emissions scenario for the North Atlantic basin. The downscaled TCs for the historical climate (1986-2005) are compared with those in the mid- (2016-35) and late-twenty-first century (2081-2100). The downscaled TCs are also compared with TCs explicitly simulated in HiFLOR. We show that while significantly more storms are detected in HiFLOR towards the end of the twenty-first century, the statistical-deterministic model projects a moderate increase in TC frequency, and PepC projects almost no increase in TC frequency. The changes in storm frequency in all three datasets are not significant in the mid-twenty-first century. All three project that storms will become more intense and the fraction of major hurricanes and Category 5 storms will significantly increase in the future climates. However, HiFLOR projects the largest increase in intensity while PepC projects the least. The results indicate that HiFLOR’s TC projection is more sensitive to climate change effects and statistical models are less sensitive. Nevertheless, in all three datasets, storm intensification and frequency increase lead to relatively small changes in TC threat as measured by the return level of landfall intensity.

Influence of a spectral cumulus parametrization on simulating global tropical cyclone activity in an AGCM

AbstractThe influence of a new spectral cumulus parametrization (the spectral scheme) on simulating global tropical cyclone (TC) activity in an Atmospheric General Circulation Model (AGCM) is investigated. Experiments are performed using AFES (AGCM for the Earth Simulator) and two different convection schemes – the original convection scheme of the AGCM (the Emanuel scheme) and the spectral scheme. The result shows that the both schemes can capture qualitative features of global TC activity in terms of climatology, variability, and intensity. However, the spectral scheme simulates TC genesis and track density better than the original convection scheme by improving the cold bias in the upper troposphere. The spectral scheme also provides better results for TC response to interannual variability (i.e., El Niño Southern Oscillation, ENSO) by suppressing excessive convection response to ENSO. The spectral scheme is capable of simulating the variability of TC genesis related to the Madden–Julian Oscillation (MJO) much better than the original convection scheme. Consequently, the spectral scheme can outperform the original convection scheme in simulating global TC activity from various perspectives, and thus the scheme is expected to be useful for TC prediction and future projections.

Helices of disaster memory: How forgetting and remembering influence tropical cyclone response in Mauritius

Tropical cyclones have had a considerable impact on Mauritius. Large cyclones are relatively rare, and in popular imagination are thought to hit Mauritius every 15 years. Yet it has been over 25 years since the last cyclone widely considered as ‘significant’. Critically, there is little known about the role of memory in responses to cyclones and details regarding responses to past cyclones in Mauritian history are scant.This article examines past experiences and impacts of cyclones in Mauritius, as well as contemporary perceptions of cyclone vulnerability and memories of historical cyclones. The analysis draws on both community interviews and archival research conducted in Mauritius and takes a longue durée approach. This approach combines an examination of both event and process with historical discourses in an effort to uncover the long-standing and slowly changing relationships between people and extreme events.The results reveal a number of repetitive patterns of responses that act out over the long term and repeat for many of the largest cyclones, indicating that tropical cyclone impact and recovery in Mauritius is strongly conditioned by complex, cultural, and place based memory (and forgetting). While these patterns could be characterised as cycles, the research instead presents a concept of ‘helices’ as a new conceptualisation of long term disaster memory patterns. This research is part of a growing literature arguing for the need to account for the historical processes fundamental to understanding vulnerability. This has implications for disaster risk reduction (including climate change adaptation) in Mauritius, other small islands, and elsewhere.