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International audience; The Atlantic meridional overturning circulation (AMOC) represents the zonally integrated stream function of meridional volume transport in the Atlantic Basin. The AMOC plays an important role in transporting heat meridionally in the climate system. Observations suggest a heat transport by the AMOC of 1.3 PW at 26°N-a latitude which is close to where the Atlantic northward heat transport is thought to reach its maximum. This shapes the climate of the North Atlantic region as we know it today. In recent years there has been significant progress both in our ability to observe the AMOC in nature and to simulate it in numerical models. Most previous modeling investigations of the AMOC and its impact on climate have relied on models with horizontal resolution that does not resolve ocean mesoscale eddies and the dynamics of the Gulf Stream/North Atlantic Current system. As a result of recent increases in computing power, models are now being run that are able to represent mesoscale ocean dynamics and the circulation features that rely on them. The aim of this review is to describe new insights into the AMOC provided by high-resolution models. Furthermore, we will describe how high-resolution model simulations can help resolve outstanding challenges in our understanding of the AMOC.

Extreme weather events such as hurricanes are a significant hazard to shipping. We show that traditional methods to model weather related risks using naval architecture or historical incidents fail to accurately predict the potential risk of an accident by failing to account for risk mitigation actions taken by the bridge team. We therefore propose the use of unsupervised machine learning to identify clusters in risk response by ships to perceived high risk scenarios. This risk classification method is based on the analysis of large heterogenous datasets including vessel traffic, metocean and hurricane path data from the US Atlantic Hurricane Season. Clusters in vessel behaviour to these storms are identified and the risk perception by storm severity compared. The results of this analysis can be used to better understand the impact of extreme weather events on navigation safety and develop an early warning system for coast guard search and rescue response.

There is compelling evidence of a strong relation between the Atlantic Meridional Overturning Circulation (AMOC) and millennial scale climate variability during the last glacial period. Part of the advances in understanding the underlying mechanisms rely on the analysis of the sedimentary Pa/Th ratio, which can be used to qualitatively infer past flow rates in the Atlantic. The compilation of existing North Atlantic records indicates repeated, consistent and significant Pa/Th increases across millennial-scale events, indicating significant reductions of deep-water formation in the Northwest Atlantic. However, the use of sedimentary Pa/Th as a pure kinematic circulation proxy is challenging because Pa and Th are also highly sensitive to changes in particulate flux intensity and composition that have probably occurred across these millennial scale events. A primary control of particles on the available Pa/Th records has been ruled out ensuring the absence of correlation between the reconstructed particle fluxes (e.g. Th-normalized opal fluxes) and the sedimentary Pa/Th. However, quantitative estimates of the impact of particles on the available paleo Pa/Th are still missing.In this study, we use the Pa/Th enabled iLOVECLIM Earth System Model of Intermediate Complexity to decipher the impact of particles on the sedimentary Pa/Th. We evaluate the impact of imposed changes in biogenic particle flux intensity and composition on the Atlantic Pa/Th in a 3-D geographical perspective. We find that up to 30% of the observed Pa/Th increase across Heinrich Stadial 1 could be explained by changes in particle fluxes and composition. Besides, changes in the Particulate Organic Carbon (POC) most efficiently affects the sedimentary Pa/Th, followed by biogenic opal. Last but not least, the global Atlantic sedimentary Pa/Th response is very sensitive to shifts in the geographical distribution of particles and high scavenging areas. In our simulations, a decrease of the opal production in the Northwest Atlantic can induce a far field Pa/Th increase in a large part of the North Atlantic basin, suggesting that a local monitoring of the particle fluxes might not be enough to rule out any influence of the particles on paleo sedimentary Pa/Th records.

The North Atlantic tropical cyclones (TCs) are iconic weather extremes of the SEUS. Although TCs are weather events, their periodic seasonal occurrence in the North Atlantic Basin and their landfalls along the SEUS coastline has derived significant interest on their low frequency variability. A rich body of theoretical, observational, and empirical work to understand the morphology and intensity features of TC has also been discussed in this chapter including metrics to measure their intensity and seasonal activity.

The aims of this study were to identify floristic assemblages for alluvial forests in the Atlantic Forest and Pampa regions in Brazil, assess the level of floristic similarity between assemblages, and determine environmental gradients and indicator species for these assemblages. Surveys carried out in alluvial forests in the Atlantic Forest and Pampa regions were selected, based on which a presence/absence matrix was built for tree species. A cluster analysis was performed to verify the existence of species assemblages. Floristic similarity was determined by means of the Sorensen Distance measure, from which a dendrogram was developed. The floristic matrix was ordinated by means of NMDS. A PCA was performed with climatic data from areas to determine environmental gradients. An assessment of indicator species was carried out afterwards. Two groups of areas not related to the separation of the regions became visible from the dendrogram and were corroborated by NMDS. Temperature, rainfall and altitude gradients were synthesized by the PCA. Gymnanthes klotzschiana and Andira fraxinifolia were the most relevant species, respectively, in the Paraná-Uruguay and Atlantic assemblages. Alluvial forests were gradually separated in two floristic assemblages associated with river basins and migration routes, while especially influenced by tropicality and altitude gradients.

The new CNRM-CM6 release of the CNRM/CERFACS atmospheric general circulation model has been used in a rotated/stretched configuration that allows a local horizontal resolution of less than 15 km over the tropical North Atlantic basin. Sea surface temperatures (SST) arise from a previous lower resolution simulation of the Coupled Model Intercomparison Project-5 exercise and corrected through a quantile–quantile method. Moreover, five-member ensemble simulations have been performed for both present and RCP8.5 scenario climates. For validation purposes, another five-member ensemble simulation has been performed with prescribed observed SST. Tracking of tropical cyclones (TCs) in these simulations reveals that the intensity of the simulated TCs are quite realistic and may reach the strongest hurricane ever observed, allowing to distinguish between TC categories in the analysis. Although the model tends to underestimate the occurrence of TCs over low latitudes, the realism of simulated TCs has nevertheless improved compared to previous versions of the model, due to both increased resolution and changes in the parameterizations used in the model. Changes observed in the simulations between present and future climates confirm previous results stating that there is no clear change in the overall number of TCs but an increase in the intensity of major hurricanes as well as an increase of rainfall in all TC categories. A new result suggests that TC activity response to climate warming may be significantly different from 1 month of the hurricane season to another. In our simulations we observe a robust decrease of TCs in the tropics in July while August and September experience a large increase of TCs over the mid-latitudes. Finally, we find a relation between a large increase in TC activity near the African coast and changes in the African atmospheric dynamics and rainfall in September.

The temporal variability of the Atlantic Meridional Overturning Circulation (AMOC) is driven both by direct wind stresses and by the buoyancy-driven formation of North Atlantic Deep Water over the Labrador Sea and Nordic Seas. In many models, low-frequency density variability down the western boundary of the Atlantic basin is linked to changes in the buoyancy forcing over the Atlantic subpolar gyre (SPG) region, and this is found to explain part of the geostrophic AMOC variability at 26∘ N. In this study, using different experiments with an ocean general circulation model (OGCM), we develop statistical methods to identify characteristic vertical density profiles at 26∘ N at the western and eastern boundaries, which relate to the buoyancy-forced AMOC. We show that density anomalies due to anomalous buoyancy forcing over the SPG propagate equatorward along the western Atlantic boundary (through 26∘ N), eastward along the Equator, and then poleward up the eastern Atlantic boundary. The timing of the density anomalies appearing at the western and eastern boundaries at 26∘ N reveals ∼ 2–3-year lags between boundaries along deeper levels (2600–3000 m). Record lengths of more than 26 years are required at the western boundary (WB) to allow the buoyancy-forced signals to appear as the dominant empirical orthogonal function (EOF) mode. Results suggest that the depth structure of the signals and the lagged covariances between the boundaries at 26∘ N may both provide useful information for detecting propagating signals of high-latitude origin in more complex models and potentially in the observational RAPID (Rapid Climate Change programme) array. However, time filtering may be needed, together with the continuation of the RAPID programme, in order to extend the time period.

This study quantifies the amount of rainfall supplied by tropical cyclones (TCs) to Cuba. It uses the long&ndash, term global gridded Multi&ndash, Source Weighted&ndash, Ensemble Precipitation (MSWEP) v2 data set, with a resolution of 0.1&deg, in latitude and longitude, and a temporal resolution of 3 h during the hurricane seasons from 1980&ndash, 2016. During this study period, 146 TCs were identified within a 500&ndash, km radius of Cuba. The contribution of TCs to the total precipitation over Cuba during the cyclonic season was ~11%. The maximum contribution occurs in October and November, representing 18% and 28% of the total precipitation, respectively. The interannual precipitation contribution shows a positive correlation (~0.74) with the number of TCs, but without a significant trend for the period. A climatological spatial analysis of the rainfall associated with TCs revealed great heterogeneity, although the major contribution was observed along the southern coast of the eastern and central provinces of Cuba, and in the western province of Pinar del R&iacute, o. No significant difference was observed between the number of TCs that affected Cuba and their rainfall contribution under the positive and negative phases of the El Ni&ntilde, o Southern Oscillation. However, the negative phase of the NAO led to an increase in the genesis of TCs that later affected Cuba, which led to a greater contribution to precipitation compared to that obtained from TCs during the positive phase of this oscillation. Our results also confirm that anomalous warmth of the tropical Atlantic Ocean, revealed through the Atlantic Meridional Mode, and enlargement of the Atlantic Warm Pool, enhances the genesis in the North Atlantic Basin of the TCs that affect Cuba, which was associated with an increase of the rainfall contribution to the total precipitation compared to that calculated for TCs formed during the opposite phases.

Classified as a Category 5 hurricane at its peak, Hurricane Maria is regarded as the worst natural disaster on record to affect the islands located in the northeastern Caribbean, most notably Dominica and Puerto Rico. It is also considered to be one of the deadliest Atlantic hurricanes on record. While Maria is only one of a number of hurricanes since Katrina to have resulted in widespread damage and loss of life along with climigration, it offers some insight into the impacts of climate change on historical patterns of migration around the world, on the one hand, and the linkage between climigration and income disparities and economic vulnerability on the other. In many respects, climigration after Hurricane Maria bears closer resemblance to the climigration experience from New Orleans and the Gulf Coast after Hurricane Katrina. However, unlike Katrina, the climigration experience subsequent to Hurricane Maria also revealed the importance of cultural differences between many of the climigrants and their host communities.

In northern Europe, beach erosion, coastal flooding and associated damages to engineering structures are linked to mid-latitude storms that form through cyclogenesis and post-tropical cyclones, when a tropical cyclone moves north from its tropical origin. The present work analyses the hydrodynamic forcing and morphological changes observed at three beaches in the north coast of Northern Ireland (Magilligan, Portrush West&rsquo, s southern and northern sectors, and Whiterocks), prior to, during, and immediately after post-tropical cyclone Katia. Katia was the second major hurricane of the active 2011 Atlantic hurricane season and impacted the British Isles on the 12&ndash, 13 September 2011. During the Katia event, offshore wave buoys recorded values in excess of 5 m at the peak of the storm on the 13 September, but nearshore significant wave height ranged from 1 to 3 m, reflecting relevant wave energy dissipation across an extensive and shallow continental shelf. This was especially so at Magilligan, where widespread refraction and attenuation led to reduced shore-normal energy fluxes and very minor morphological changes. Morphological changes were restricted to upper beach erosion and flattening of the foreshore. Longshore transport was evident at Portrush West, with the northern sector experiencing erosion while the southern sector accreted, inducing a short-term rotational response in this embayment. In Whiterocks, berm erosion contributed to a general beach flattening and this resulted in an overall accretion due to sediment influx from the updrift western areas. Taking into account that the post-tropical cyclone Katia produced &pound, 100 m ($157 million, 2011 USD) in damage in the United Kingdom alone, the results of the present study represent a contribution to the general database of post-tropical storm response on Northern European coastlines, informing coastal response prediction and damage mitigation.

Little is known about how Atlantic hurricane activity changes on long timescales. This thesis uses proxy development and proxy-model integration to constrain the spatiotemporal variability in hurricane activity in the Bahama Archipelago over the past millennium. I present annually-resolved archives of storm activity derived from sediment cores from blue holes on three islands in the Bahama Archipelago: South Andros, Long Island, and Middle Caicos. Dramatic differences between these records suggest localized controls on the hurricane patterns observed by each island. Thus, compiling these records together more accurately captures regional variations in hurricane strikes. Integrating our new Bahama Archipelago compilation with compiled paleohurricane records from the U.S. coastline indicates shifting patterns of hurricane activity over the past millennium between the Gulf Coast and the Bahama Archipelago/New England. Finally, I address whether variability in hurricane strikes observed in Bahamian paleohurricane records is related to climate or random variability using hurricane model output. The signal observed in any individual record of paleohurricane activity from the Bahama Archipelago is driven more by random variability in hurricane tracks than by climate. This thesis lays the groundwork for creating high-resolution paleohurricane records from blue holes and using hurricane models to inform our interpretations of these records.

From Atlantic hurricanes to the Indian monsoons, storms are getting worse and becoming more erratic. From Atlantic hurricanes to the Indian monsoons, storms are getting worse and becoming more erratic.

Superstorm Sandy struck the New York metropolitan region on October 29, 2012. The storm, which became a tropical cyclone, or hurricane, on October 24 near the island of Jamaica, had lost its hurricane-strength winds by the time it made landfall in southern New Jersey, hence the “superstorm” moniker. This chapter examines the post-Sandy recovery process in New York City specifically, focusing on housing recovery, business recovery and workforce development, and community recovery. Sandy was a large and powerful storm that also caused damage in Jamaica, Cuba, the Bahamas, and 24 US states; it killed at least 117 people in the US alone. When the storm struck the New York metropolitan region on October 29, 2012, it was the largest Atlantic hurricane ever recorded. There were approximately 69,000 housing units in New York City directly damaged by Sandy, and many thousands more affected by utility outages or damage to surrounding neighbourhood.

This article provides a reckoning of the 2017 Atlantic Hurricane Season’s place in\ud history to ascertain how unique it was from other hurricane seasons. A research\ud strategy involving qualitative, descriptive and analytical research approaches,\ud including content analysis, sequential description of events and comparative\ud analysis, were used to assess how and why the 2017 AHS season is distinct from\ud others. Findings reveal that the 2017 AHS was extraordinary by all meteorological\ud standards— in many ways, being hyperactive, and producing a frenetic stretch of\ud huge, long-lived and dramatic, tropical storms including 10 hurricanes. The season\ud was, arguably, the most expensive in history and will be remembered for the\ud unprecedented devastation caused by the season’s major hurricanes (Harvey, Irma\ud and Maria). While the extremely active season can be attributed to anomalously\ud high, climate change induced, hurricane friendly environmental conditions in the\ud Atlantic basin, early forecasts did not also predict the hyperactivity of the season.\ud This article, therefore, advances for a more strategic anticipatory and proactive\ud approach in dealing with these severe storms, underpinned by effective mitigation\ud of their effects. Furthermore, the article adds value to the literature examining\ud extreme natural forces, particularly in understanding variations in the ferocity of\ud the meteorological events associated with hurricane seasons.

There have been no high-frequency aircraft observations of tropical cyclone (TC) eyewall boundary layer turbulence since two flights into Atlantic hurricanes in the 1980s. We present an analysis of the first TC boundary layer flight observations in the South China Sea by the Hong Kong Observatory comprising four eyewall penetrations. We derive the vertical flux of momentum and vertical momentum diffusivity from observed turbulence parameters. We observe negative (upward) vertical fluxes of tangential momentum near the eyewall consistent with a jet below the flight level near the radius of maximum wind. Our observations of vertical momentum diffusivity support a superlinear relationship between diffusivity and wind speed at the high wind speeds in the inner-core of TCs (power-law exponent of 1.73 ± 0.20) while the few existing boundary layer hurricane observations in the North Atlantic suggest a more linear relationship.

This study investigates moisture origin, characteristics and intra-event scale variability of the isotopic signature of rainfall in a Mediterranean mountain area, based on data from the Vallcebre Research Catchments, NE Spain. Weekly data and samples were used to analyse the general dynamics of the isotopic composition of precipitation and its relationship with meteorological variables at the sampling site. Then, based on the data and samples available at the intra-event scale, the variability of the isotopic signature during rainfall events was characterised and an explanation of what caused the observed variability was attempted. Results at the weekly time scale show that the maximum relative deviation of the heavy isotopic content with respect to Standard Mean Ocean Water (δ18O) of the precipitation signature occurred during summer months and, in contrast, the minimum during winter months. The intra-annual trend of rainfall δ18O roughly followed the mean monthly air temperature. Using intra-event information, three main types of δ18O isotopic trends were found during rainfall events: most of the events had a V-shaped isotopic trend, followed by L-shaped and constant trend events. Changes in moisture sources ’diagnosed using a Lagrangian approach and a previously existing contribution algorithm’ were one of the causes of the isotopic variability and changes at the intra-event scale, but these may also have been influenced by sub-cloud processes that modified the isotopic signature. Moisture sources for analysed events showed the main influence of the Mediterranean area, but also an important influence of the Atlantic Basin. © 2019 Elsevier B.V., This study derived from a first author internship in the Surface Hydrology and Erosion group at IDAEA-CSIC. Generous support from members of the group is acknowledged. The authors are grateful to the NOAA Air Resources Laboratory (ARL) for the provision of the HYSPLIT transport and dispersion model and READY website ( http://www.ready.noaa.gov) used in this publication. This study was supported by the TransHyMed (CGL2016-75957-R AEI/FEDER, UE), MASCC-DYNAMITE (PCIN-2017-061/AEI), CGL2015-65627-C3-2-R (MINECO/FEDER) and CGL2016-81828-REDT (MINECO) and was performed in the framework of the HYdrological cycle in the Mediterranean EXperiment (HyMeX). The authors would also like to acknowledge the helpful and constructive suggestions and comments from three anonymous reviewers that have improved this study.

The frequency of Atlantic hurricanes has been predicted to increase significantly by the end of this century. Watershed disturbance initiated by hurricanes can alter dissolved organic matter (DOM) quantity and quality in source water dramatically. DOM is an important disinfection by-product (DBP) precursor, and thus hurricanes can have a significant impact on water treatability and drinking water safety. The interactions between land use and land cover (LULC) of a watershed and DBP formation potential (FP) in source water under hurricane events have rarely been evaluated. Here, we quantified the FPs of two carbonaceous (trihalomethanes [THMs] and haloacetic acids [HAA]) and two nitrogenous (haloacetonitrile [HAN] and N-nitrosodimethylamine [NDMA]) DBPs at eighteen sub-watersheds with varying LULC along the Yadkin-Pee Dee River basin across North and South Carolina during and after the flooding condition caused by the 2016 Hurricane Matthew. Using chlorine as a disinfectant, THM FP was 238% (±117%) higher (p .001) under the flooding condition than baseflow condition, while HAA FP did not change significantly as a result of the flooding. DOM composition under the flooding condition changed in favor of the formation of THMs rather than HAAs by a decrease of fulvic acid-like compounds and an increase in DOM aromaticity (SUVA). The FPs of studied DBPs under the flooding condition compared with the baseflow, followed the order of HAN (356.5%) NDMA (246.4%) THM (115.2%) using chloramine as a disinfectant. Higher HAN FP and NDMA FP compared to THM FP suggested that more nitrogenous than carbonaceous DBPs precursors were released during this hurricane event. LULC analysis revealed that forested wetlands were the major contributor of THM, HAA, and HAN precursors, whereas NDMA precursor was derived from developed areas. This unique study highlights the dynamic interplay between LULC and exports of carbonaceous and nitrogenous DBPs precursors during and after hurricanes.

In 2017, Cuba was pummeled by Hurricane Irma, one of the strongest and most devastating Atlantic basin hurricanes in history. Twelve of Cuba’s 15 provinces and 90 percent of the population were affected, and there was island-wide loss of electrical power. Despite the significant damage, ongoing economic hardships, and the political realities that required Cuba to handle the situation without response support from other nations, Cuba’s recovery was swift and effective. Cuba’s disaster self-sufficiency and timely response to Hurricane Irma was grounded on 5 decades of disaster planning coupled with ongoing evolution of disaster risk reduction and management strategies. While the central command center, with local dispatch response teams, and mandated citizen engagement are features unique to Cuba’s political structure, in this study, we highlight 5 defining attributes of Cuba’s hurricane response that can constructively inform the actions of other island and coastal nations vulnerable to Atlantic tropical cyclones. These attributes are: (1) actively learning and incorporating lessons from past disaster events, (2) integrating healthcare and public health professionals on the frontlines of disaster response, (3) proactively engaging the public in disaster preparedness, (4) incorporating technology into disaster risk reduction, and (5) infusing science into risk planning. In terms of hurricane response, as a geopolitically isolated nation, Cuba has experienced particular urgency when it comes to protecting the population and creating resilient infrastructure that can be rapidly reactivated after the onslaught of storms of ever-increasing intensity. This includes planning for worsening future disaster scenarios based on a clear-eyed appreciation of the realities of climate change.

The ocean plays a vital role in the global climate system and biosphere, providing crucial resources for humanity including water, food, energy and raw materials. There is a compelling need to develop an integrated basin-scale ocean observing system to support of ocean management. We articulate a vision for basin-scale ocean observing - A comprehensive All-Atlantic Ocean Observing Systems that benefits all of us living, working and relying on the ocean. Until now, basin-scale ocean observation has been conducted through loosely-aligned arrangements of national and international efforts. The All-Atlantic Ocean Observing System (AtlantOS) is an ntegrated concept for a forward-looking framework and basin-scale partnership to establish a comprehensive ocean observing system for the Atlantic Ocean as a whole. The system will be sustainable, multi-disciplinary, multi-thematic, efficient, and fit-for-purpose. Platforms, networks, and systems do already exist that operate at various maturity levels. AtlantOS will go beyond the status quo by bringing together the observing communities and countries of the Atlantic basin, providing the opportunity to join and support the system. AtlantOS will build upon the coordinated work of the Global Ocean Observing System (GOOS) and the Group on Earth Observations (GEO), two international bodies that support and coordinate global ocean observing. AtlantOS will complement those efforts and offers a new approach to organizing ocean observing at the basin-scale. The new SystemAtlantOS will focus not only on the physics but also the biology, ecology and biogeochemistry of the ocean and seafloor and will enhance new partnerships among between governments, science, civil society and the private sector.

Rain and temperature retrievals from a common algorithm based on microwave sensors onboard five polar orbiting satellites are included to study tropical cyclone (TC) rain rate characteristics and warm core structure. The retrieval algorithm used here is NOAA’s operational Microwave Integrated Retrieval System (MiRS). The five satellites/sensors are S-NPP/ATMS, NOAA-20/ATMS, Metop-B/AMSUA-MHS, Metop-C/AMSUA-MHS, and GPM/GMI. Hurricane Florence occurred, which occured in the Atlantic basin in 2018, is chosen as the study case. Hurricane Matthew in 2016 (before NOAA-20 and Metop-C were launched) is also included to illustrate warm core structure retrieved by MiRS.

Based on 12 years (2004-2015) of GOES-East satellite infrared (IR) imagery over the North Atlantic basin, the diurnal cycle of the tropical cyclone (TC) Deviation Angle Variation (DAV) value is analysed, and a backward 24-hr time average DAV is selected to filter the noise in the DAV-TC intensity estimation. The effect of satellite observation angle on the DAV-TC intensity estimation is analysed in theory, in a case study, and in the longer-term statistics. Based on these results, an improvement to the DAV-TC intensity estimation is presented and evaluated in this study. The results show that, after taking the observation angle into account, the new DAV-TC intensity estimation is shown to produce smaller errors and higher correlations than the previous versions, especially for major hurricanes.

Conveying uncertainty in information artifacts is difficult; the challenge only grows as the demand for mass communication through multiple channels expands. In particular, as natural hazards increase with changing global conditions, including hurricanes which threaten coastal areas, we need better means of communicating uncertainty around risks that empower people to make good decisions. We examine how people share and respond to a range of visual representations of risk from authoritative sources during hurricane events. Because these images are now shared widely on social media platforms, Twitter provides the means to study them on a large scale as close to in vivo as possible. Using mixed methods, this study analyzes diffusion of and reactions to forecast and other risk imagery during the highly damaging 2017 Atlantic hurricane season to describe the collective response to visual representations of risk.

The flight operations of the Cyclone Global Navigation Satellite System (CYGNSS), a constellation of eight microsatellites built and operated by Southwest Research Institute (SwRI), designed to improve the intensity forecasts of Tropical Cyclones, has seen a litany of changes to its concept of operations, software, processes, and personnel. In this paper, we detail how the operations team responded to several challenges such as the reduction in personnel after the Launch and Early Orbit Operations phase, the addition of a downlink antenna in Japan, high-fidelity collection requests during the unusually active 2017 Atlantic hurricane season, and the increased demands of team members from other projects. These pressures forced the CYGNSS operations team to innovate their way to efficient operations. These innovations were enabled by embracing modern open-source tools such as Django, Bokeh, Git, the various libraries available in the Python programming language, and the capabilities that come with all of our operations engineers being competent in software development. The CYGNSS team took the approach of automating the most time-intensive tasks first, which freed up time to carefully design and test more elaborate automation solutions. We utilized the spirit of the Agile Methodology to make incremental improvements to our software suite which further enabled more sophisticated automation. Finally, we chart a path forward to fully closing the automation loop between our mission planning, and real-time Command and Control.

The intensity, frequency, and duration of North Atlantic hurricanes have increased since the early 1980s. Every year these storms impact the Mid-Atlantic Bight (MAB), a region that includes the coastline with the highest US coastal population density, important commercial and naval ports, and commercial and recreational fisheries. The interaction between the storms and the surface currents, including tides and coastal trapped waves (CTWs), have a large economic and destructive impact as well as great implications on marine debris transport before, during, and after storms. The effect of storms on CTWs is the least understood of these interactions. Observations of CTWs from high-frequency radar (HFR) SeaSonde data indicate typical surface velocity amplitudes of 10–20 cm s−1, while maximum velocities can reach as high as 100 cm s−1 during strong storms. This suggests that storm-induced CTWs are capable of transporting marine debris farther than typical, non-storm conditions. Focusing on 2012 Hurricane Sandy, which had a major impact in the MAB, the study area is seeded with 100 artificial Lagrangian particles just before Hurricane Sandy made landfall in New Jersey and we calculate their trajectories over five days using observed HFR velocities. The distance traveled and particle paths for full velocity are compared to a CTW-only velocity case during Hurricane Sandy, as well as for a five day non-storm period. In all cases, particles are transported farther under Hurricane Sandy storm conditions than non-storm conditions, with percentage increases between 150–250 %. CTWs have a larger contribution to the total distance traveled using full velocity under storm conditions (47 %) than non-storm conditions (33 %) although CTW increases in distance traveled is directly proportional to increases in wind strength. Furthermore, particle trajectories suggest estuaries disrupt theoretical CTW propagation patterns.

The 2020 Atlantic hurricane season was notable for a record-setting 30 named storms while, contemporaneously, the COVID-19 pandemic was circumnavigating the globe. The active spread of COVID-19 complicated disaster preparedness and response actions to safeguard coastal and island populations from hurricane hazards. Major hurricanes Eta and Iota, the most powerful storms of the 2020 Atlantic season, made November landfalls just two weeks apart, both coming ashore along the Miskito Coast in Nicaragua's North Caribbean Coast Autonomous Region. Eta and Iota bore the hallmarks of climate-driven storms, including rapid intensification, high peak wind speeds, and decelerating forward motion prior to landfall. Hurricane warning systems, combined with timely evacuation and sheltering procedures, minimized loss of life during hurricane impact. Yet these protective actions potentially elevated risks for COVID-19 transmission for citizens sharing congregate shelters during the storms and for survivors who were displaced post-impact due to severe damage to their homes and communities. International border closures and travel restrictions that were in force to slow the spread of COVID-19 diminished the scope, timeliness, and effectiveness of the humanitarian response for survivors of Eta and Iota. Taken together, the extreme impacts from hurricanes Eta and Iota, compounded by the ubiquitous threat of COVID-19 transmission, and the impediments to international humanitarian response associated with movement restrictions during the pandemic, acted to exacerbate harms to population health for the citizens of Nicaragua.

Satellite observations of brightness temperature from the Advanced Technology Microwave Sounder (ATMS) and Microwave Humidity Sounder (MHS) humidity sounding channels can provide relatively high horizontal resolution information about cloud and atmospheric moisture in the troposphere, thus revealing the structures of tropical cyclones (TCs). There is usually a high brightness temperature in a TC eye region and low brightness temperature reflecting spiral rain bands. An azimuthal spectral analysis method is used as a center-fixing algorithm to determine the TC center objectively using the brightness temperature observations of the ATMS humidity-sounding channel 18 (183.31 ± 7.0 GHz) and MHS humidity-sounding channel 5 (190.31 GHz). The position in the brightness temperature field encompassing a TC that achieves the largest symmetric component is regarded as the TC center. Two Atlantic hurricanes in 2012, Hurricanes Sandy and Isaac, are first used to analyze the performance of the TC center-fixing technique. Compared with the National Hurricane Center best track, the root-mean-square differences of the center fixing results for Hurricanes Sandy and Isaac are less than 47.3 and 34.3 km, respectively. It is found that the uncertainty of the TC center-fixing algorithm and thus the difference from the best track increases when the brightness temperature distribution within a TC is significantly asymmetric. Then, the TC center-fixing technique is validated for all tropical storms and hurricanes over Northern Atlantic and Western Pacific in 2019. Compared with the best track data, the root-mean-square differences for tropical storms and hurricanes are 33.81 and 26.20 km, respectively. The demonstrated successful performance of the proposed TC center-fixing algorithm to use the single channel of microwave humidity sounders for TC positioning is important for vortex initialization in operational hurricane forecasts.

The combined effect of the sea surface temperature (SST) and the North Atlantic subtropical high-pressure system (NASH) in the interannual variability of the genesis of tropical cyclones (TCs) and landfalling in the period 1980–2019 is explored in this study. The SST was extracted from the Centennial Time Scale dataset from the National Oceanic and Atmospheric Administration (NOAA), and TC records were obtained from the Atlantic Hurricane Database of the NOAA/National Hurricane Center. The genesis and landfalling regions were objectively clustered for this analysis. Seven regions of TC genesis and five for landfalling were identified. Intercluster differences were observed in the monthly frequency distribution and annual variability, both for genesis and landfalling. From the generalized least square multiple regression model, SST and NASH (intensity and position) covariates can explain 22.7% of the variance of the frequency of TC genesis, but it is only statistically significant (p &lt, 0.1) for the NASH center latitude. The SST mostly modulates the frequency of TCs formed near the West African coast, and the NASH latitudinal variation affects those originated in the Lesser Antilles arc. For landfalling, both covariates explain 38.7% of the variance, however, significant differences are observed in the comparison between each region. With a statistical significance higher than 90%, SST and NASH explain 33.4% of the landfalling variability in the archipelago of the Bahamas and central–eastern region of Cuba. Besides, landfalls in the Gulf of Mexico and Central America seem to be modulated by SST. It was also found there was no statistically significant relationship between the frequency of genesis and landfalling with the NASH intensity. However, the NASH structure modulates the probability density of the TCs trajectory that make landfall once or several times in their lifetime. Thus, the NASH variability throughout a hurricane season affects the TCs trajectory in the North Atlantic basin. Moreover, we found that the landfalling frequency of TCs formed near the West Africa coast and the central North Atlantic is relatively low. Furthermore, the SST and NASH longitude center explains 31.6% (p &lt, 0.05) of the variance of the landfalling intensity in the archipelago of the Bahamas, while the SST explains 26.4% (p &lt, 0.05) in Central America. Furthermore, the 5-year moving average filter revealed decadal and multidecadal variability in both genesis and landfalling by region. Our findings confirm the complexity of the atmospheric processes involved in the TC genesis and landfalling.

The eastern United States is extremely vulnerable to Atlantic basin tropical cyclones (TCs) and their associated precipitation. While many studies have focused on the magnitude or contribution of tropical cyclone precipitation (TCP) to overall rainfall, there is a need for a detailed climatology of spatial characteristics of inland TCP extent for this region. In this study, we develop a Geographic Information System method to delineate rainfall swaths for 257 US landfalling TCs during 1948 to 2014 using a daily gridded dataset. We then describe spatial patterns of TCP using three methods. First, we measure the rainfall swath areas and average widths over land, and find that TCs that spend longer periods over land have wider average widths so that rainfall swaths cover larger areas. Second, trends in the change of left extent of TCP swaths are analysed and TC attributes related to these trends are explored. Seventy of 85 TCs have rain swaths that expand on the left side at some points as they move inland. The TCs exhibiting expansion were hurricanes at landfall, re-intensifying over land, undergoing extratropical transition, and/or moving near the coastline. Last, we construct a series of maps with return intervals and frequency distributions for inland TCP and tropical storm-force winds. The results show that 94% of 2435 counties over the eastern United States are more frequently exposed to rainfall than wind from TCs. While cumulative rainfall shows a gradual decrease from southeastern coast inland, many inland regions have received five to six TCP events in a single season, which confirms that TCP should be a concern for people living inland as well as near the coast. This study's analysis of the spatial characteristics of TCP inland extent from a climatological perspective should benefit forecasting, hazard mitigation, and risk analysis of TC hazards.

The paper traces the development of capitalism in England, the Americas, and West Africa over a long time period, 1450–1900. The developments in these major regions of the Atlantic Basin during the period were strongly interconnected and ultimately gave rise to the nineteenth-century Atlantic economy which integrated the major economies of the Atlantic world. The development of capitalism in the three specified geographical areas is analyzed in the context of the interconnected developments. Central to the historical analysis is a discussion of the contending conceptions of capitalism as a socioeconomic system. The paper shows that the original conception by Karl Marx, which identified free wage earners separated from their means of production and entrepreneurs who own those means of production as the defining elements, was generally accepted by supporters and critics for several decades; attempts to redefine began in the 1960s. The paper contends that, unlike the original Marxian conception, the ...

The paper uses observational data from 1950 to 2014 to investigate rapid intensification (RI) variability of tropical cyclones (TCs) in the North Atlantic and its relationships with large-scale climate variations. RI is defined as a TC intensity increase of at least 15.4 m/s (30 knots) in 24 h. The seasonal RI distribution follows the seasonal TC distribution, with the highest number in September. Although an RI event can occur anywhere over the tropical North Atlantic (TNA), there are three regions of maximum RI occurrence: (1) the western TNA of 12°N–18°N and 60°W–45°W, (2) the Gulf of Mexico and the western Caribbean Sea, and (3) the open ocean southeast and east of Florida. RI events also show a minimum value in the eastern Caribbean Sea north of South America—a place called a hurricane graveyard due to atmospheric divergence and subsidence. On longer time scales, RI displays both interannual and multidecadal variability, but RI does not show a long-term trend due to global warming. The top three climate indices showing high correlations with RI are the June-November ENSO and Atlantic warm pool indices, and the January-March North Atlantic oscillation index. It is found that variabilities of vertical wind shear and TC heat potential are important for TC RI in the hurricane main development region, whereas relative humidity at 500 hPa is the main factor responsible for TC RI in the eastern TNA. However, the large-scale oceanic and atmospheric variables analyzed in this study do not show an important role in TC RI in the Gulf of Mexico and the open ocean southeast and east of Florida. This suggests that other factors such as small-scale changes of oceanic and atmospheric variables or TC internal processes may be responsible for TC RI in these two regions. Additionally, the analyses indicate that large-scale atmospheric and oceanic variables are not critical to TC genesis and formation; however, once a tropical depression forms, large-scale climate variations play a role in TC intensification.

The opportunity to examine the structure and evolution of the various upper-tropospheric precursors to the formation of North Atlantic (NATL) subtropical cyclones (STCs) that undergo tropical transition (TT) motivates this study. Intraseasonal variability associated with the location and frequency of NATL STCs forming in the presence of similar upper-tropospheric features, as well as similarities and differences in the various upper-tropospheric precursors to the formation of NATL STCs that undergo TT, are examined. NATL STCs that undergo TT are categorized according to the upper-tropospheric features associated with their formation during 1979–2010 using the 0.5° NCEP Climate Forecast System Reanalysis dataset. This categorization allows for the documentation of the location and frequency of STCs forming in the presence of similar upper-tropospheric features and for the construction of cyclone-relative composites during the five days prior to STC formation. NATL STCs that undergo TT are separated into one of three categories based on the upper-tropospheric features associated with their formation: 1) cutoff lows, 2) meridional troughs, and 3) zonal troughs. STCs included in the cutoff low and meridional trough categories typically develop poleward of ~25°N over the western, central, and eastern NATL during September–November and August–November, respectively. In contrast, STCs included in the zonal trough category typically develop equatorward of ~30°N over the western NATL during June–September. Cyclone-relative composites reveal that ~61% of the categorized NATL STCs that undergo TT form in association with an upper-tropospheric feature whose structure and evolution are linked to anticyclonic wave breaking.

Paleotempestology, the study of past tropical cyclones (TCs) using geological proxy techniques, is a growing discipline that utilizes data from a broad range of sources. Most paleotempestological studies have been conducted using “established proxies,” such as grain-size analysis, loss-on-ignition, and micropaleontological indicators. More recently, however, researchers have been applying more advanced geochemical analyses, such as X-ray fluorescence core scanning and stable isotopic geochemistry, to generate new paleotempestological records. In this paper we begin by providing a list of paleotempestological studies for the western North Atlantic Basin and illustrate the spatial coverage of these studies. We then review the premises behind both established and new proxies and discuss their strengths and limitations at resolving past hurricane activity. Lastly, we suggest future directions for paleotempestological research based on our review of the literature that we argue will ultimately lead to a better understanding of TC dynamics under future climate change scenarios.

The economic impact of natural disasters on developing economies can be severe with the recovery diverting scarce funds that might otherwise be targeted at development projects and stimulating the need for international aid. In view of the likely sensitivity of low-lying Pacific Islands to anticipated changes in climate, a 122-year record of major flooding depths at the Rarawai Sugar Mill on the Ba River in the northwest of the Fijian Island of Viti Levu is analysed. Reconstructed largely from archived correspondence of the Colonial Sugar Refining Company, the time series comprises simple measurements of height above the Mill floor. It exhibits no statistically significant trends in either frequency or flood heights, once the latter have been adjusted for average relative sea-level rise. This is despite persistent warming of air temperatures as characterized in other studies. There is a strong dependence of frequency (but not magnitude) upon El Nino-Southern Oscillation (ENSO) phase, with many more floods in La Nina phases. The analysis of this long-term data series illustrates the difficulty of detecting a global climate change signal from hazard data, even given a consistent measurement methodology (cf HURDAT2 record of North Atlantic hurricanes) and warns of the strong dependence of any statistical significance upon choices of start and end dates of the analysis.

Despite the dangers associated with tropical cyclones and their rainfall, the origin of the moisture in these storms, which include destructive hurricanes and typhoons, remains surprisingly uncertain. Existing studies have focused on the region 40–400 km from a cyclone's center. It is known that the rainfall within this area cannot be explained by local processes alone but requires imported moisture. Nonetheless, the dynamics of this imported moisture appears unknown. Here, considering a region up to three thousand kilometers from cyclone center, we analyze precipitation, atmospheric moisture and movement velocities for severe tropical cyclones – North Atlantic hurricanes. Our findings indicate that even over such large areas a hurricane's rainfall cannot be accounted for by concurrent evaporation. We propose instead that a hurricane consumes pre-existing atmospheric water vapor as it moves. The propagation velocity of the cyclone, i.e. the difference between its movement velocity and the mean velocity of the surrounding air (steering flow), determines the water vapor budget. Water vapor available to the hurricane through its movement makes the hurricane self-sufficient at about 700 km from the hurricane center obviating the need to concentrate moisture from greater distances. Such hurricanes leave a dry wake, whereby rainfall is suppressed by up to 40% compared to the local long-term mean. The inner radius of this dry footprint approximately coincides with the hurricane's radius of water self-sufficiency. We discuss how Carnot efficiency considerations do not constrain the power of such open systems. Our findings emphasize the incompletely understood role and importance of atmospheric moisture stocks and dynamics in the behavior of severe tropical cyclones.

This paper evaluates the relative effectiveness of FEMA expenditures on hurricane induced property losses. We find that spending on FEMA ex-ante mitigation and planning projects leads to greater reductions in property losses than spending on ex-post adaptation programs – specifically, a one percent increase in annual spending on ex-ante risk reduction and warning projects reduces damages by 0.21 percent while a one percent increase in ex-post recovery and clean-up spending reduces damages by 0.12. Although both types of program spending are effective, we find the marginal return from spending on programs that target long-term mitigation and risk management to be almost twice that of spending on ex-post recovery programs. With the predicted increases in the frequency and severity of North Atlantic hurricanes in the future, our findings suggest there are important potential gains that could be realized from the further diversification of FEMA spending across project categories.

A new parametric model is developed to describe the wind field asymmetry commonly observed in tropical cyclones or hurricanes in a reference frame fixed at its center. Observations from 21 hurricanes from the North Atlantic basin and TC Roger (1993) in the Coral Sea are analyzed to determine the azimuthal and radial asymmetry typical in these mesoscale systems after removing the forward speed. On the basis of the observations, a new asymmetric directional wind model is proposed which adjusts the widely used Holland (1980) axisymmetric wind model to account for the action of blocking high-pressure systems, boundary layer friction, and forward speed. The model is tested against the observations and demonstrated to capture the physical features of asymmetric cyclones and provides a better fit to observed winds than the Holland model. Optimum values and distributions of the model parameters are derived for use in statistical modeling. Finally, the model is used to investigate the asymmetric character of TC systems, including the azimuth of the maximum wind speed, the degree of asymmetry, and the relationship between asymmetry and forward speed.

Tropical cyclone (TC) climatological characteristics with passage from the Western North Pacific (WNP) into the South China Sea (SCS) during the June - November season are analyzed in this study. These TCs tend to form in the WNP west of 150°E, and on average westward by 7 - 12° in longitude than TCs that do not track into the SCS. Their formation locations migrate with the monsoon trough, moving northward from June to August, and southward from September to November. The probability of a WNP TC moving into the SCS varies seasonally, with only 12 - 18% of the WNP TCs doing so during August-September due to more northern TC formation. However, this probability rises to 25 - 26% in June - July and 25 - 32% in October - November with more southern TC formation. The passage-type TCs generally form in the eastern part of an elongated lower-level cyclonic anomaly of the 10-day low-pass filtered environmental circulation in the 10 - 20°N zone, which is paired with an anticyclonic anomaly to the north. Between this circulation pair, anomalous easterly flows steer these TCs westward, giving them a westward track into the SCS. The formation of these passage-type TCs is associated with a southward displacement of the monsoon trough and a westward intensification of the Pacific subtropical high in August and September. During June - July (October - November), the associated features appear as a southeastward (meridional) expansion of the monsoon trough and a northward displacement of the Pacific subtropical high.

In general, if there are fewer Atlantic hurricanes, those near the US coast are more likely to intensify, whereas if there are many hurricanes, then those near the coast are more likely to weaken because of high local wind shear and low sea surface temperatures. Hurricanes approaching land sometimes intensify and sometimes weaken, but why? James Kossin shows that when numerous Atlantic hurricanes are formed, their intensification near the US coast tends to be blocked by high wind shear and low sea surface temperatures. In general, when many hurricanes are formed, weaker intensification occurs near land, but when few hurricanes are formed, there is stronger intensification near land. At present, it remains unclear how these patterns might persist in a warming climate. The North Atlantic ocean/atmosphere environment exhibits pronounced interdecadal variability that is known to strongly modulate Atlantic hurricane activity1,2,3,4,5,6. Variability in sea surface temperature (SST) is correlated with hurricane variability through its relationship with the genesis and thermodynamic potential intensity of hurricanes7. Another key factor that governs the genesis and intensity of hurricanes is ambient environmental vertical wind shear8,9,10 (VWS). Warmer SSTs generally correlate with more frequent genesis and greater potential intensity, while VWS inhibits genesis and prevents any hurricanes that do form from reaching their potential intensity. When averaged over the main hurricane-development region in the Atlantic, SST and VWS co-vary inversely11,12, so that the two factors act in concert to either enhance or inhibit basin-wide hurricane activity. Here I show, however, that conditions conducive to greater basin-wide Atlantic hurricane activity occur together with conditions for more probable weakening of hurricanes near the United States coast. Thus, the VWS and SST form a protective barrier along the United States coast during periods of heightened basin-wide hurricane activity. Conversely, during the most-recent period of basin-wide quiescence, hurricanes (and particularly major hurricanes) near the United States coast, although substantially less frequent, exhibited much greater variability in their rate of intensification, and were much more likely to intensify rapidly. Such heightened variability poses greater challenges to operational forecasting and, consequently, greater coastal risk during hurricane events.

Environmental determinists predict that people move away from places experiencing frequent weather hazards, yet some of these areas have rapidly growing populations. This analysis examines the relationship between weather events and population change in all U.S. counties that experienced hurricanes and tropical storms between 1980 and 2012. Our database allows for more generalizable conclusions by accounting for heterogeneity in current and past hurricane events and losses and past population trends. We find that hurricanes and tropical storms affect future population growth only in counties with growing, high-density populations, which are only 2 percent of all counties. In those counties, current year hurricane events and related losses suppress future population growth, although cumulative hurricane-related losses actually elevate population growth. Low-density counties and counties with stable or declining populations experience no effect of these weather events. Our analysis provides a methodologically informed explanation for contradictory findings in prior studies.

Hurricane Sandy, one of the largest Atlantic hurricanes on record, made landfall as an extratropical cyclone on the coast of New Jersey (29 October 2012) along a track almost perpendicular to the coast. Ten days later a northeaster caused heavy precipitation and elevated water levels along the coast. Two years of pre-storm monitoring and research in marshes of Barnegat Bay and the Delaware Estuary provided an opportunity to evaluate the impacts of Hurricane Sandy and the succeeding northeaster across the region. Peak water levels during Sandy ranged from 111 to 184 cm above the marsh surface in Barnegat Bay and 75–135 cm above the marsh surface in the Delaware Estuary. Despite widespread flooding and damage to coastal communities, the storm had modest and localized impacts on coastal marshes of New Jersey. Measurements made on the marsh platform illustrated localized responses to the storms including standing biomass removal, and changes in peak biomass the following summer. Marsh surface and elevation changes were variable within marshes and across the region. Localized elevation changes over the storm period were temporary and associated with subsurface processes. Over the long-term, there was no apparent impact of the 2012 storms, as elevations and regression slopes pre- and several months post-storm were not significant. Vegetation changes in the summer following the fall 2012 storms were also variable and localized within and among marshes. These results suggest that Hurricane Sandy and the succeeding northeaster did not have a widespread long-term impact on saline marshes in this region. Possible explanations are the dissipation of surge and wave energy from the barrier island in Barnegat Bay and the extreme water levels buffering the low-lying marsh surface from waves, winds, and currents, and carrying suspended loads past the short-statured marsh grasses to areas of taller vegetation and/or structure. These findings demonstrate that major storms that have substantial impacts on infrastructure and communities can have short-term localized effects on coastal marshes in the vicinity of the storm track.

We use a high resolution numerical simulation of Atlantic Hurricane Earl (2010) to increase our understanding of Earl's intensification in relatively strong vertical shear in the context of a recent paradigm for tropical cyclone intensification. The integrity of the simulation is judged by comparing analyses thereof with those of the unprecedented observational data gathered in Earl. Consistent with the classical view of spin up, the amplification of the tangential wind field above the boundary layer is found to occur as the absolute angular momentumsurfaces are drawn inwards by the aggregate heating of the rotating convective clouds in the interior of the vortex. In addition to this classical pathway, spin up occurs within the inner-core boundary layer, where the maximum tangential winds occur. The latter is another element of the new paradigm. Despite the detrimental influence of the shear on the vortex alignment and on depressing the pseudo-equivalent potential temperature outside the developing eyewall, the combined eddy processes associated with the vortical plume structures in and around the developing eyewall region are shown to contribute to an enhanced overturning circulation and an intensifying storm. These eddy processes are distinctly agradient effects that are not features of the classical spin up mechanism. It remains to be understood how the rotating convective updraughts combine to produce the diagnosed structures of the eddy terms, themselves, and how vortex Rossby waves and other eddies contribute to the alignment of the vortex during intensification.

As many coupled atmosphere-ocean general circulation models, the coupled Earth System Model developed at the Max Planck Institute for Meteorology suffers from severe sea-surface temperature (SST) biases in the tropical Atlantic. We performed a set of SST sensitivity experiments with its atmospheric model component ECHAM6 to understand the impact of tropical Atlantic SST biases on atmospheric circulation and precipitation. The model was forced by a climatology of observed global SSTs to focus on simulated seasonal and annual mean state climate. Through the superposition of varying tropical Atlantic bias patterns extracted from the MPI-ESM on top of the control field, this study investigates the relevance of the seasonal variation and spatial structure of tropical Atlantic biases for the simulated response. Results show that the position and structure of the Intertropical Convergence Zone (ITCZ) across the Atlantic is significantly affected, exhibiting a dynamically forced shift of annual mean precipitation maximum to the east of the Atlantic basin as well as a southward shift of the oceanic rain belt. The SST-induced changes in the ITCZ in turn affect seasonal rainfall over adjacent continents. However not only the ITCZ position but also other effects arising from biases in tropical Atlantic SSTs, e.g. variations in the wind field, change the simulation of precipitation over land. The seasonal variation and spatial pattern of tropical Atlantic SST biases turns out to be crucial for the simulated atmospheric response and is essential for analyzing the contribution of SST biases to coupled model mean state biases. Our experiments show that MPI-ESM mean-state biases in the Atlantic sector are mainly driven by SST biases in the tropical Atlantic while teleconnections from other basins seem to play a minor role.

Hurricane Irene produced catastrophic rainfall and flooding in portions of the eastern United States from 27 to 29 August 2011. Like a number of tropical cyclones that have produced extreme flooding in the northeastern United States, Hurricane Irene was undergoing extratropical transition during the period of most intense rainfall. In this study the rainfall distribution of landfalling tropical cyclones is examined, principally through analyses of radar rainfall fields and high-resolution simulations using the Weather Research and Forecasting (WRF) Model. In addition to extratropical transition, the changing storm environment at landfall and orographic precipitation mechanisms can be important players in controlling the distribution of extreme rainfall. Rainfall distribution from landfalling tropical cyclones is examined from a Lagrangian perspective, focusing on times of landfall and extratropical transition, as well as interactions of the storm circulation with mountainous terrain. WRF simulations capture important features of rainfall distribution, including the pronounced change in rainfall distribution during extratropical transition. Synoptic-scale analyses show that a deep baroclinic zone developed and strengthened in the left-front quadrant of Irene, controlling rainfall distribution over the regions experiencing most severe flooding. Numerical experiments were performed with WRF to examine the role of mountainous terrain in altering rainfall distribution. Analyses of Hurricane Irene are placed in a larger context through analyses of Hurricane Hannah (2008) and Hurricane Sandy (2012).

The Atlantic Meridional Mode (AMM) is the dominant mode of tropical SST/wind coupled variability. Modeling studies have implicated wind-evaporation-SST (WES) feedback as the primary driver of the AMM’s evolution across the Atlantic basin; however, a robust coupling of the SST and winds has not been shown in observations. This study examines observed AMM growth, propagation, and decay as a result of WES interactions. Investigation of an extended maximum covariance analysis shows that boreal wintertime atmospheric forcing generates positive SST anomalies (SSTA) through a reduction of surface evaporative cooling. When the AMM peaks in magnitude during spring and summer, upward latent heat flux anomalies occur over the warmest SSTs and act to dampen the initial forcing. In contrast, on the southwestern edge of the SSTA, SST-forced cross-equatorial flow reduces the strength of the climatological trade winds and provides an anomalous latent heat flux into the ocean, which causes southwestward propagation of the initial atmosphere-forced SSTA through WES dynamics. Additionally, the lead-lag relationship of the ocean and atmosphere indicates a transition from an atmosphere-forcing-ocean regime in the northern subtropics to a highly coupled regime in the northern tropics that is not observed in the southern hemisphere. CMIP5 models poorly simulate the latitudinal transition from a one-way interaction to a two-way feedback, which may explain why they also struggle to reproduce spatially coherent interactions between tropical Atlantic SST and winds. This analysis provides valuable insight on how meridional modes act as links between extratropical and tropical variability and focuses future research aimed at improving climate model simulations.

The evolution of three successive hurricanes (Katia, Maria, and Ophelia) is investigated over the river plume area formed by the Amazon and Orinoco river outflows during September of 2011. The study focuses on hurricane impacts on the ocean structure and the ocean feedback influencing hurricane intensification. High-resolution (1/25° × 1/25° horizontal grid) numerical simulations of the circulation in the extended Atlantic Hurricane Region (Caribbean Sea, Gulf of Mexico, and Northwest Atlantic Ocean) were used to investigate the upper ocean response during the three hurricane-plume interaction cases. The three hurricanes revealed different evolution and intensification characteristics over an area covered by brackish surface waters. The upper ocean response to the hurricane passages over the plume affected region showed high variability due to the interaction of oceanic and atmospheric processes. The existence of a barrier layer (BL), formed by the offshore spreading of brackish waters, probably facilitated intensification of the first storm (Hurricane Katia) because the river-induced BL enhanced the resistance of the upper ocean to cooling. This effect was missing in the subsequent two hurricanes (Maria and Ophelia) as the eroded BL (due to Katia passage) allowed the upper ocean cooling to be increased. As a consequence, the amount of ocean thermal energy provided to these storms was greatly reduced, which acted to limit intensification. Numerical experiments and analyses, in tandem with observational support, lead to the conclusion that the presence of a river plume-induced BL is a strong factor in the ocean conditions influencing hurricane intensification.

Column water vapour (CWV) in the Tropics is well known to affect tropical deep convection. It has been established that the tropical deep convection required for tropical cyclone formation markedly increases after reaching a critical CWV threshold. Therefore, CWV values below this threshold represent an atmosphere that is too dry for tropical cyclone formation. The interannual variability of the occurrence of this dry air and its impacts on tropical cyclone activity over the Atlantic are examined. CWV empirical orthogonal function (EOF) analysis reveals a dominant mode of interannual variability of dry air events over the tropical North Atlantic, with strong variations over the central and eastern Atlantic between 15°N and 30°N. In the positive (negative) phase of the EOF modes, tropical cyclone activity is reduced (increased) over the Atlantic basin, particularly over the main development region. On the origin of dry air, the Saharan Air Layer does not explain the CWV EOF pattern, but the pattern is shown to be related to large-scale subsidence in association with enhanced anticyclonic vorticity. The leading mode shows significant correlations to several large-scale climate oscillations, including the Atlantic Multi-decadal Oscillation, Pacific Decadal Oscillation, Atlantic Meridional Mode, Pacific North American Pattern, and others. The EOF mode also indicates a relationship to the large-scale circulation via the Hadley cell. An evaluation of the steering flow for tropical cyclones from the modulation of the subtropical high and the values of deep layer vertical wind shear is consistent with the distribution of tropical cyclone activity in only certain limited areas, suggesting that the impacts of the dry air patterns are required to provide a more complete explanation of the activity.