Cyclone Frequency Research Articles

Local and remote atmospheric responses to soil moisture anomalies in Australia

AbstractThree sets of model experiments are performed with the Community Earth System Model to study the role of soil moisture anomalies as a boundary forcing for the formation of upper-level Rossby wave patterns during Southern Hemisphere summer. In the experiments, soil moisture over Australia is set to ±1STD of an ERA-Interim reanalysis derived soil moisture reconstruction for the years 2009 to 2016 and 50 ensemble members are run. The local response is a positive heating anomaly in the dry simulations that results in a thermal low-like circulation anomaly with an anomalous surface low and upper-level anticyclone. Significant differences in convective rainfall over Australia are related to differences in convective instability and associated with changes in near surface moisture and moisture advection patterns. A circum-hemispheric flow response is identified both in the upper-level flow and in the surface storm tracks that overall resembles a positive Southern Annular Mode-like flow anomaly in the dry simulations. The structure of this atmospheric response strongly depends on the background flow. The results point to a modulation of the hemispheric flow response to the forcing over Australia by the El Niño Southern Oscillation. Significant changes of precipitation over the Maritime continent and South Africa are found and significant differences in the frequency of surface cyclones are present all along the storm tracks.

Tropical cyclones shape mangrove productivity gradients in the Indian subcontinent

Recent literature on the impact of cyclones on mangrove forest productivity indicates that nutrient fertilizations aided by tropical cyclones enhance the productivity of mangrove forests. We probe the implications of these predictions in the context of Indian mangroves to propose potential future directions for mangrove research in the subcontinent. First, we look at the time series trend (2000–2020) in satellite-derived gross primary productivity (GPP) datasets for seven mangrove forests across the country’s coastline. Second, we compare seasonal changes in soil nutrient levels for a specific site to further the arguments proposed in the literature and investigate the role of potential drivers of mangrove productivity. We find overall increasing trends for GPP over the past two decades for all seven mangrove sites with seasonal fluctuations closely connected to the tropical storm activities for three sites (Bhitarkanika, Pichavaram, and Charao). Additionally, organic carbon and nitrogen levels showed no significant trend, but phosphorus levels were higher during the post-monsoon-winter period for Bhitarkanika. Our findings expand the predictions of previous studies that emphasized the role of storm-induced nutrient fluxes and freshwater supply as primary drivers of productivity gradients in mangroves. Our study provides insights on how mangrove productivity may change with fluctuating frequency and magnitude of cyclones under a changing climate, implying the need for more mechanistic studies in understanding the long-term impact on mangrove productivity in the region.

Trends and Variability of North American Cool-Season Extratropical Cyclones: 1979–2019

AbstractExtratropical cyclones are the primary driver of sensible weather conditions across the mid-latitudes of North America, often generating various types of precipitation, gusty non-convective winds, and severe convective storms throughout portions of the annual cycle. Given ongoing modifications of the zonal atmospheric thermal gradient due to anthropogenic forcing, analyzing the historical characteristics of these systems presents an important research question. Using the North American Regional Reanalysis, boreal cool-season (October–April) extratropical cyclones for the period 1979–2019 were identified, tracked, and classified based on their genesis location. Additionally, bomb cyclones—extratropical cyclones that recorded a latitude normalized pressure fall of 24 hPa in 24-hr—were identified and stratified for additional analysis. Cyclone lifespan across the domain exhibits a log-linear relationship, with 99% of all cyclones tracked lasting less than 8 days. On average, ≈ 270 cyclones were tracked across the analysis domain per year, with an average of ≈ 18 year−1 being classified as bomb cyclones. The average number of cyclones in the analysis domain has decreased in the last 20 years from 290 year−1 during the period 1979–1999 to 250 year−1 during the period 2000–2019. Spatially, decreasing trends in the frequency of cyclone track counts were noted across a majority of the analysis domain, with the most significant decreases found in Canada’s Northwest Territories, Colorado, and east of the Graah mountain range. No significant interannual or spatial trends were noted with bomb cyclone frequency.

The global value of coastal wetlands for storm protection

Coastal wetlands provide a range of valuable ecosystem services, including protecting coastal communities from storms. We estimated for the first time the global value of these storm protection services for all coastal wetlands for both damages avoided and lives saved. We used the historical tracks of 1,014 tropical cyclones since 1902 that recorded property damage and/or human casualties in 71 countries/regions. We used Bayesian and OLS statistical techniques to relate storm damages and lives lost to: wind speed, storm forward speed, the year of the storm, the volume of ocean water proximal to landfall, and GDP, population, and coastal wetlands in the swath of the storm. Based on current storm probabilities, we estimate the median annual global value of coastal wetlands for storm protection at $447 billion/yr (2015$US) ($213 - $837 billion/yr, 90% CI) and 4,620 lives saved per year (3,320 – 6,550, 90% CI). The 40 million hectares of coastal wetlands in storm prone areas provided an average of $11,000/ha/yr in avoided storm damages. The frequency and intensity of tropical cyclones has been increasing in recent decades and is projected to further increase with climate change. Consequently, the already significant benefits from protecting and restoring coastal wetlands will become increasingly important and valuable in the future. These results justify much larger investments in conservation and restoration of coastal wetlands.

How do trees survive a cyclone? The relative role of individual and site characteristics over mortality

AbstractCyclones are an increasing disturbance in the subtropical region of South America, but their impacts over the forests are still poorly documented. Here, we evaluate the effects of an extratropical cyclone over tree mortality in Araucaria Forest remnants in southern Brazil. We surveyed 116 sites (10 × 20 m each) and collected data on all tree individuals presenting DBH ≥ 4.8 cm before (2009) and after (2014) the occurrence of an extratropical cyclone. Using GLM models, we checked how the cyclone occurrence, different plant traits (DBH, trunk branching, wood density, successional group and evolutionary distinctiveness) and site characteristics (basal area, exposure, landscape protection, nearest border distance, cyclone border distance and the presence of native bamboo species) could impact tree mortality. The GLM model selection shows that the lowest AIC model considers all predictors separately and their interaction with the cyclone. The results showed that the cyclone occurrence and some site characteristics (bamboo presence, site exposure, landscape protection, nearest border distance and cyclone border distance) and plant traits (successional group and evolutionary distinctiveness) are related to tree mortality. The intense deforestation and fragmentation of the Araucaria Forest coupled with the increase in cyclone frequency expected for the region due to climate change may increase mortality rates of these forests, affecting their resilience and phylogenetic structure. Further biodiversity conservation efforts in the Araucaria Forest need to consider the characteristics of sites for enabling the protection of forest remnants in areas under different exposures to cyclone impacts.

Meteorological conditions during the MOSAiC expedition

This article sets the near-surface meteorological conditions during the Multidisciplinary drifting Observatory for the Study of Arctic Climate expedition in the context of the interannual variability and extremes within the past 4 decades. Hourly ERA5 reanalysis data for the Polarstern trajectory for 1979–2020 are analyzed. The conditions were relatively normal given that they were mostly within the interquartile range of the preceding 4 decades. Nevertheless, some anomalous and even record-breaking conditions did occur, particularly during synoptic events. Extreme cases of warm, moist air transported from the northern North Atlantic or northwestern Siberia into the Arctic were identified from late fall until early spring. Daily temperature and total column water vapor were classified as being among the top-ranking warmest/wettest days or even record-breaking based on the full record. Associated with this, the longwave radiative fluxes at the surface were extremely anomalous for these winter cases. The winter and spring period was characterized by more frequent storm events and median cyclone intensity ranking in the top 25th percentile of the full record. During summer, near melting point conditions were more than a month longer than usual, and the July and August 2020 mean conditions were the all-time warmest and wettest. These record conditions near the Polarstern were embedded in large positive temperature and moisture anomalies over the whole central Arctic. In contrast, unusually cold conditions occurred during the beginning of November 2019 and in early March 2020, related to the Arctic Oscillation. In March, this was linked with anomalously strong and persistent northerly winds associated with frequent cyclone occurrence to the southeast of the Polarstern.

Awareness level of climate change among paddy farmers

This study examined the awareness level of paddy farmers on climate change. Among the 29 districts of Tamil Nadu, Nagapattinam district was selected to conduct the present study. This is situated in coastal area and very often subjected to natural calamities which were mainly reflected on the rice cultivation to the worst status. Data for the study were collected from 200 respondents selected through simple random sampling technique. The study revealed that majority (71.50 %) of the respondent had medium level of awareness of climate change followed by high (17.00 %) and low (11.50 %) category. More than eighty per cent of the respondents were aware about the issues viz., receipt of low rain fall (90.50 %), uneven distribution of rain fall (89.00 %), frequent cyclone (87.00 %) and reduction in number of rainy days (86.50 %). The awareness level was found to be minimum in the issues like acid rain (34.50 %), variation in wind speed and direction (44.50 %), increasing heat and cold waves (48.00 %). The study concluded that the majority of farmers were aware of climate change but some of them were lacked in detail information about climate change. Therefore, it is suggested that extension education should be strengthened to boost farmers’ awareness level on climate change in detailed and prepare them for adaptation measures and that appropriate technologies be promoted for adaptation by farmers.

Very Low Stocks and Inputs of Necromass in Wind-affected Tropical Forests

The relationships between climate and forest dynamics can help us to interpret patterns of ecosystem carbon and to predict how forests react to climatic changes. We report mass dynamics of deadwood (necromass) from tropical forest ecosystems subject to some of the highest frequency of tropical cyclones in the world and to regular, persistent seasonal monsoon winds. Plots that are influenced by typhoons but exposed to different degrees of monsoon winds were monitored. We expected that stocks and inputs of necromass would reflect the seasonal intensity of wind events and be higher in the high wind exposure forest than in the low wind exposure forest, especially for fallen woody debris. The results showed that necromass input was indeed influenced by the magnitude of typhoons and aggravated by monsoon winds. However, while there was no significant difference in stock of necromass between plots, inputs of standing necromass were significantly higher in the high wind exposure plot; these were mostly derived from dead resprouts. Both our forests had very low values of total necromass stocks (3.47–4.32 Mg C ha−1) and inputs (2.1–2.5 Mg C ha−1 y−1) compared with tropical forests worldwide. Our results show that both monsoon and typhoon winds shape these tropical forests, favouring low stature individuals and trees with ability to resprout and that these strategies provide these forests with remarkable resistance and resilience to wind disturbances. Our findings from some of the most wind-affected forests in the world indicate how woody carbon dynamics and forest structure in other regions may respond to future changes in the frequency and intensity of winds.

Characterizing the highest tropical cyclone frequency in the Western North Pacific since 1984

The 2018 boreal summer in the Western North Pacific (WNP) is highlighted by 17 tropical cyclones (TC)—the highest record during the reported reliable years of TC observations. We contribute to the existing knowledge pool on this extreme TC frequency record by showing that the simultaneous highest recorded intensity of the WNP summer monsoon prompted the eastward extension of the monsoon trough and enhancement of tropical convective activities, which are both favorable for TC development. Such changes in the WNP summer monsoon environment led to the extreme TC frequency record during the 2018 boreal summer. Meanwhile, the highest record in TC frequency and the intensity of the WNP summer monsoon are both attributed with the combined increase in the anomalous westerlies originating from the cold tropical Indian Ocean sea surface temperature (SST) anomalies drawn towards the convective heat source that is associated with the warm central Pacific SST anomalies. Our results provide additional insights in characterizing above normal tropical cyclone and summer monsoon activities in the WNP in understanding seasonal predictable horizons in the WNP, and in support of disaster risk and impact reduction.

Preface

The fisheries sector in India plays a key role in the Indian economy, providing livelihood to more than 20 million fishers and fish farmers. The Gross Value Added (GVA) of the fisheries sector during 2018–2019 was INR 2,12,915 crores and constituted 1.24% of the total National GVA and 7.28% share of Agricultural GVA. The annual growth rate of 10.88% was achieved during the years 2014–15 to 2018–19. The fish production reached at an all-time high of 13.758 million metric tons during 2018–19. The major fishery resource originates from rivers (29 000 km) followed by reservoirs, ponds, floodplain wetlands, and tanks.Climatic variability and events have intensified in India during the last few decades. This has resulted in frequent cyclones, storms, hurricanes, floods, heatwaves, and untimely monsoons, resulting in climatic disasters. The addition of these unusual climatic events to the increasing anthropogenic stressors would further complicate the dynamics and sustainability of inland fisheries resource especially inland open water resources. These fisheries resources are important for nutrition, employment, income generation, livelihood of fishers contributing >6% of the world's annual animal protein supplies.Tropical inland open water fisheries in India are also vulnerable to overfishing, pollution, biodiversity loss, invasive species and habitat destruction in addition to climate change. Major impacts on inland open waters include change in base flow, altered hydrology, thermal stress to aquatic flora and fauna, extended range and increased occurrence of extreme events, habitat degradation, alteration in breeding and spawning behavior, and life history traits, leading to adverse consequence on aquatic biodiversity and fisheries. This may consequently have more of an impact on the subsistence fishers—their income and livelihood.A detailed publication dealing with the impact of these uncertainties on inland fisheries is not available covering the whole of India. Recent approaches emphasizing ecosystem based management in a regional context specific to inland fisheries for combating climatic changes is either preliminary or lacking so far. In this connection, ICAR-Central Inland Fisheries Research Institute (CIFRI), India has undertaken research under a multi-institutional research project, National Innovations for Climate Resilient Agriculture. Considering the lack of compiled comprehensive information on various aspects of climate change and inland fisheries, the institute has taken the lead in exploring and perusing research during the last decade and fortunately significant progress has been made in this direction.This special issue on climate change and the inland fisheries of India (Fig. 1) is being published due to the active collaboration of CIFRI and Aquatic Ecosystem Health and Management Society (AEHMS) and originated from the Pantnagar conference on Inland waters (February 2020). The present issue includes 9 research papers on climate change, which have been categorized in to two groups covering a variety of topics representing the current status of advances and development of climate smart inland fisheries in India:Research advances in climate and environmental change impacts on inland fisheries of India: Status, vulnerability, and mitigation strategiesInvasion meltdown and burgeoning threats of invasive fish species in inland waters of India in the era of climate changeImpacts of climate change and adaptations in shrimp aquaculture: A study in coastal Andhra Pradesh, IndiaAnalysis of constraints faced by fish seed producers of Lower Brahmaputra Valley Zone, Assam, India because of extreme climatic events and adaptive strategiesFloodplain wetlands of eastern India in a changing climate: Trophic characterization, ecological status, and implications for fisheriesEcosystem vulnerability of floodplain wetlands of the Lower Brahmaputra Valley, India, to climatic and anthropogenic factorsDynamics of river flows towards sustaining floodplain wetland fisheries under climate change: A case studyEnhancing adaptive capacity of wetland fishers through pen culture in the face of a changing climate: A case study from a tropical wetland, IndiaImpact of climate change-induced challenges on fisheries in the North Eastern Region of India, and the way aheadWe hope that this special issue, being first if its kind about India, will enhance our understanding about ecosystem changes due to climate change and its implications on inland fisheries of India (Fig. 2) and the vicinity as well as potential adaptation and mitigation strategies which will be a great help to researchers, managers, students, fishers, planners and policy makers. We take this opportunity to thank the organizers of the Inland water conference in Pantnagar, Utterkhand, namely G.B. Pant University of Agriculture, & Technology, ICAR-CIFRI, and AEHMS (Canada) for convening the conference and providing the opportunity which resulted in the publication of this issue. Thanks are due to Dr. A.P. Sharma for including the climate change session in the program. We are grateful to Dr. Ken Minns, Scientist Emeritus, Fisheries & Oceans Canada for contributing a thoughtful foreword for the special issue. We greatly appreciate the extensive assistance of the technical committee namely, J. Lorimer, M. Holmes and S. Blunt for processing and technical editing of the papers.

Assessing the Role of Social and Solidarity Initiatives in exploring Blue Economy: Evidences from Indian Sundarbans

Blue economy approach can mitigate the impacts of climate change on marine and coastal ecosystems. Sundarbans landscape is posed by the climate change of the region as reflected in the continued global warming, rising sea level, erosion of island area and increased frequency of cyclones. Thematic mapping of the Sundarbans region reveals a high ecological security in this region, whereas it is characterised by insecure economic efficiency and social equity. Through participatory observation methods, qualitative information of the operation of selected Social and Solidarity Economic (SSE) initiatives is screened in this study in the light of three sustainability pillars of the blue economy: ecological conservation measures, economic sustainability and social development services. Empirical evidence reveals a variation in the performance of the SSE actors, which is conditioned upon their scale of operation, level of financial assistance and range of activities.

An integrated framework of coastal flood modelling under the failures of sea dikes: a case study in Shanghai

Climate change leads to sea level rise worldwide, as well as increases in the intensity and frequency of tropical cyclones (TCs). Storm surge induced by TC’s, together with spring tides, threatens to cause failure of flood defenses, resulting in massive flooding in low-lying coastal areas. However, limited research has been done on the combined effects of the increasing intensity of TCs and sea level rise on the characteristics of coastal flooding due to the failure of sea dikes. This paper investigates the spatial variation of coastal flooding due to the failure of sea dikes subject to past and future TC climatology and sea level rise, via a case study of a low-lying deltaic city- Shanghai, China. Using a hydrodynamic model and a spectral wave model, storm tide and wave parameters were calculated as input for an empirical model of overtopping discharge rate. The results show that the change of storm climatology together with relative sea level rise (RSLR) largely exacerbates the coastal hazard for Shanghai in the future, in which RSLR is likely to have a larger effect than the TC climatology change on future coastal flooding in Shanghai. In addition, the coastal flood hazard will increase to a large extent in terms of the flood water volume for each corresponding given return period. The approach developed in this paper can also be utilized to investigate future flood risk for other low-lying coastal regions.

Decadal Modulation of Trans-basin Variability on Extended Boreal Summer Tropical Cyclone Activity in the Tropical North Pacific and Atlantic Basins

AbstractThis study analyzes decadal modulation of trans-basin variability (TBV) on extended boreal summer (May-October) tropical cyclone frequency (TCF) over the western North Pacific (WNP), central-eastern North Pacific (CENP) and North Atlantic (NATL) basins. There are distinct decadal regimes (P1:1979-1997, P2:1998-2008, and P3:2009-2019) with changes in the interannual relationship between TBV and TCF over these three basins. During P1 and P3, there is a significant inter-annual TBV-TCF relationship over the CENP and NATL, but these relationships become insignificant during P2. Changes in the interannual TBV-TCF relationship over the WNP are opposite to those over the CENP and NATL basins, with significant relationship during P2 but insignificant relationship during P1 and P3. Changes in all three basins coincide with decadal changes in large-scale parameters associated with TBV. Consistent basin-wide changes in lower-tropospheric vorticity (vertical wind shear) associated with TBV appear to be largely responsible for changes in total TCF over the NATL (CENP) during P1 and P3. In contrast, a dipole pattern in lower-tropospheric vorticity and vertical wind shear anomalies associated with TBV over the NATL and CENP basins occurs during P2, leading to an insignificant interannual TBV-TCF relationship over the NATL and CENP basins. Over the WNP, a basin-wide consistent distribution of lower-tropospheric vorticity associated with TBV is consistent with changes in total TCF during P2, while a dipole correlation pattern between TBV-associated factors and TCF during P1 and P3 leads to a weak correlation between TBV and WNP TCF. These three distinct observed decadal regimes may be associated with interactions between ENSO and the Pacific Decadal Oscillation on decadal timescales.

Chemical and morphological characterization and pulping of Casuarina equisetifolia

Abstract Bangladesh is very much successful in coastal afforestation programmes, which protects from frequent cyclones. Casuarina equisetifolia has showed a climate resilient and promising species. No study has been done on industrial application of C. equisetifolia in Bangladesh. In this study, C. equisetifolia was characterized in terms of chemical, morphological and anatomical properties. It is characterized with higher α-cellulose, similar hemicelluloses and lignin as compared to other hardwood species grown in Bangladesh. The C. equisetifolia lignin contained mainly of syringyl unit followed by guaiacyl unit. The fiber of C. equisetifolia was shorter in length with very thick cell wall and narrow lumen, consequently the wood density and runkel ratio were very high (2.89). The C. equisetifolia was also fractionated by formic acid (FA) at atmospheric pressure to pulp, dissolved lignin and hemicelluloses. Pulp yield was 50 % with kappa number of 40 at the conditions of 3 h treatment with 90 % FA followed by 2 h peroxyformic acid treatment. But in the kraft process, C. equisetifolia produced pulp yield of 44 % with kappa number 17. Both pulps showed good bleachability. The papermaking properties were in acceptable range. Finally, it can be said that C. equisetifolia is promising species for pulping.

Sensitivity of Northern Hemisphere Cyclone Detection and Tracking Results to Fine Spatial and Temporal Resolution using ERA5

AbstractLagrangian detection and tracking algorithms are frequently used to study the development, distribution, and trends of extratropical cyclones. Past research shows that results from these algorithms are sensitive to both spatial and temporal resolution of the gridded input fields, with coarser resolutions typically underestimating cyclone frequency by failing to capture weak, small, and short-lived systems. The fifth-generation atmospheric reanalysis from the European Centre for Medium-Range Weather Forecasts (ERA5) offers finer resolution, and therefore more precise information regarding storm locations and development than previous global reanalyses. However, our sensitivity tests show that using ERA5 sea-level pressure fields at their finest possible resolution does not necessarily lead to better cyclone detection and tracking. If a common number of nearest neighbors is used when detecting minima in sea-level pressure (like past studies), finer spatial resolution leads to noisier fields that unrealistically break up multi-center cyclones. Using a common search distance instead (with more neighbors at finer resolution) resolves the issue without smoothing inputs. Doing this also makes cyclone frequency, lifespan, and average depth insensitive to refining spatial resolution beyond 100 km. Results using 6-h and 3-h temporal resolutions have only minor differences, but using 1-h temporal resolution with a maximum allowed propagation speed of 150 km h-1 leads to unrealistic track splitting. This can be counteracted by increasing the maximum propagation speed, but modest sensitivity to temporal resolution persists for several cyclone characteristics. Therefore, we recommend caution if applying existing algorithms to temporal resolutions finer than 3-h and careful evaluation of algorithm settings.

Responses of Arctic cyclones to biogeophysical feedbacks under future warming scenarios in a regional Earth system model

Arctic cyclones, as a prevalent feature in the coupled dynamics of the Arctic climate system, have large impacts on the atmospheric transport of heat and moisture and deformation and drifting of sea ice. Previous studies based on historical and future simulations with climate models suggest that Arctic cyclogenesis is affected by the Arctic amplification of global warming, for instance, a growing land-sea thermal contrast. We thus hypothesize that biogeophysical feedbacks (BF) over the land, here mainly referring to the albedo-induced warming in spring and evaporative cooling in summer, may have the potential to significantly change cyclone activity in the Arctic. Based on a regional Earth system model (RCA-GUESS) which couples a dynamic vegetation model and a regional atmospheric model and an algorithm of cyclone detection and tracking, this study assesses for the first time the impacts of BF on the characteristics of Arctic cyclones under three IPCC Representative Concentration Pathways scenarios (i.e. RCP2.6, RCP4.5 and RCP8.5). Our analysis focuses on the spring- and summer time periods, since previous studies showed BF are the most pronounced in these seasons. We find that BF induced by changes in surface heat fluxes lead to changes in land-sea thermal contrast and atmospheric stability. This, in turn, noticeably changes the atmospheric baroclinicity and, thus, leads to a change of cyclone activity in the Arctic, in particular to the increase of cyclone frequency over the Arctic Ocean in spring. This study highlights the importance of accounting for BF in the prediction of Arctic cyclones and the role of circulation in the Arctic regional Earth system.

Fewer deep cyclones projected for the midlatitudes in a warming climate, but with more intense rainfall

Cyclones are a major cause of extreme weather in the extratropics. Projections of future climate change have focussed on extratropical cyclones identified close to the surface, but cyclones identified at multiple levels of the atmosphere (‘deep’ cyclones) make the largest contributions to total and extreme rainfall. Here we use ten CMIP5 models to assess projected changes in cyclone frequency and associated heavy rainfall between 1979–2005 and 2070–2099 under a high emissions scenario (RCP8.5), with a focus on changes in vertically organised (‘deep’) systems with cyclones present at both the surface and 500 hPa. We find a robust decrease in the number of deep cyclones by the end of the 21st century, together with an increase in the number of extreme rainfall events caused by deep cyclones. In contrast to deep cyclones, shallow cyclones identified only at the surface are found to produce less rain and are projected to increase in frequency in the future, particularly over land areas. Our findings demonstrate the benefits of considering vertically deep cyclones, as their connection to extreme rainfall has implications for risk assessment and climate adaptation strategies.

Evidence for Decreased Precipitation Variability in the Yucatán Peninsula During the Mid‐Holocene

AbstractThe Yucatán Peninsula (YP) has a complex hydroclimate with many proposed drivers of interannual and longer‐term variability, ranging from coupled ocean–atmosphere processes to frequency of tropical cyclones. The mid‐Holocene, a time of higher Northern Hemisphere summer insolation, provides an opportunity to test the relationship between YP precipitation and ocean temperature. Here, we present a new, ∼annually resolved speleothem record of stable isotope (δ18O and δ13C) and trace element (Mg/Ca and Sr/Ca) ratios for a section of the mid‐Holocene (5.2–5.7 kyr BP), before extensive agriculture began in the region. A meter‐long stalagmite from Río Secreto, a cave system in Playa del Carmen, Mexico, was dated using U–Th geochronology and layer counting, yielding multidecadal age uncertainty (median 2SD of ±70 years). New proxy data were compared to an existing late Holocene stalagmite record from the same cave system, allowing us to examine changes in hydrology over time and to paleoclimate records from the southern YP. The δ18O, δ13C, and Mg/Ca data consistently indicate higher mean precipitation and lower precipitation variability during the mid‐Holocene compared to the late Holocene. Despite this reduced variability, multidecadal precipitation variations were persistent in regional hydroclimate during the mid‐Holocene. We therefore conclude that higher summer insolation led to increased mean precipitation and decreased precipitation variability in the northern YP but that the region is susceptible to dry periods across climate mean states. Given projected decreases in wet season precipitation in the YP’s near future, we suggest that climate mitigation strategies emphasize drought preparation.

The Influence of Large-Scale Environment on the Extremely Active Tropical Cyclone Activity in November 2019 over the Western North Pacific

In November 2019, tropical cyclone (TC) frequency over the western North Pacific reached its record high. In this study, the possible causes and formation mechanisms of that record high TC frequency are investigated by analyzing the effect of large-scale environmental factors. A comparison between the extremely active TC years and extremely inactive TC years is performed to show the importance of the large-scale environment. The contributions of several dynamic and thermodynamic environmental factors are examined on the basis of two genesis potential indexes and the box difference index that can measure the relative contributions of large-scale environmental factors to the change in TC genesis frequency. Results indicate that dynamical factors played a more important role in TC genesis in November 2019 than thermodynamic factors. The main contributions were from enhanced low-level vorticity and strong upward motion accompanied by positive anomalies in local sea surface temperature, while the minor contribution was from changes in vertical wind shear. Changes in these large-scale environmental factors are possibly related to sea surface temperature anomalies over the Pacific (e.g., strong Pacific meridional mode).

Potential Predictability of the Tropical Cyclone Frequency Over the Western North Pacific With 50‐km AGCM Ensemble Experiments

AbstractThe potential predictability determined by sea surface temperature (SST) of the frequency distribution of tropical cyclones (TCs) is studied using ensemble simulations with a 50‐km resolution atmospheric general circulation model (AGCM). In this experiment, the interannual variability of the TC frequency over the western North Pacific (WNP) is primarily determined by SST, as the simulated ensemble mean signal is dominant over the ensemble spread and effectively follows the observed TC frequency in June‐July‐August (JJA). In contrast, the correlation between the observed and simulated TC frequency variability is less significant in September‐October‐November (SON). To explore the TC frequency‐SST linkage, the relationship between the TC frequency variability over the WNP and climate modes determined by SST indices is investigated. Through a correlation analysis, we found that El Niño Modoki is the major driver of the TC frequency variability over the WNP in JJA. Partial correlation analysis further reveals that internal atmospheric dynamics are important for the TC frequency variability over the WNP in SON. These results suggest that the tropical climate mode is responsible for the seasonal predictability of the TC frequency variability over the WNP and that the prediction skill is seasonally dependent with a high (low) skill in JJA (SON).