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This dataset includes the time-averaged outputson the pressure level(i.e., output_plev_XXXX.nc) and the original daily outputs on the model sigma level (i.e., swmodelout_XXXX.nc) from the SWM for the paper entitled "A global increase in nearshore tropical cyclone intensification" submitted to Nature Climate Changein 2023. The purpose of these experiments was to elucidate the factors leading to the projected decrease in vertical wind shear across the majority of coastal regions in the Northern Hemisphere. output_plev_CTRL.nc; swmodelout_CTRL.nc - simulates the large-scale winds and vertical wind shearin near future(2015-2034) output_plev_Future.nc; swmodelout_Future.nc - simulates the large-scale winds and vertical wind shear at the end of the 21st century(2081-2100) output_plev_CTRL_plus_delta_BS.nc; swmodelout_CTRL_plus_delta_BS.nc - investigates the effect of future changes in zonal-mean basic state (e.g., pressure, wind, temperature) onthe large-scale winds and vertical wind shear output_plev_CTRL_plus_enhanced_upper_warming; swmodelout_CTRL_plus_enhanced_upper_warming -a experiment thatonly retains the enhanced future upper-level warming (i.e., projected increase in static stability). This experiment was conducted to clarify the influenceofamplified warming in the upper troposphere on the reduced vertical wind shearover Northeast Asia and the North Indian Ocean output_plev_CTRL_plus_delta_DH.nc; swmodelout_CTRL_plus_delta_DH.nc - investigates the effect of future changes in diabatic heating (i.e., precipitation)on the large-scale winds and vertical wind shear output_plev_CTRL_plus_delta_TranF.nc; swmodelout_CTRL_plus_delta_TranF.nc - investigates the effect of future changes in synoptic transient eddies onthe large-scale winds and vertical wind shear Detail information of different experiments isdescribed in the text of the paper, as well as text S1in the supporting information.

During the boreal summer of 2021, the central and eastern equatorial Atlantic experienced persistent sea surface temperature (SST) anomalies of more than +1°C for several months. These episodic extreme events are referred to as Atlantic Niños, with 2021 marking the strongest event since 1984. Atlantic Niños are known to have far-reaching impacts on, for instance, rainfall over the surrounding continents, and on ocean dynamics through changes in thermohaline gradients and circulation. A pronounced event like the 2021 Atlantic Niño in combination with the steadily expanding coverage by satellite and in-situ observations provides the rare opportunity to study an Atlantic Niño event in unprecedented detail. Here we focus on the influence of the 2021 Atlantic Niño on tropical instability wave (TIW) activity and surface chlorophyll concentration.The 2021 Atlantic Niño was initiated by a strong downwelling Kelvin wave excited by westerly wind bursts in the western and central equatorial Atlantic. The eastward propagating Kelvin wave induced strong eastward flow anomalies on the equator causing a reduction of the meridional shear of the near-surface zonal flow in the central equatorial Atlantic. At the same time, the Kelvin wave-induced deepening of the thermocline weakened the seasonal development of the equatorial Atlantic cold tongue. The reduction of both the meridional SST gradient and the meridional shear of zonal velocity largely suppressed barotropic and baroclinic instability, which is required for the generation of TIWs. Consistent with these changes, we find that 2021 was one of the least active years in terms of TIW-related temperature, salinity, sea level, and current variability. The overall reduction in TIW activity is characterized by weak TIW activity before and enhanced TIW activity after the climatological TIW peak resulting in a delay of the TIW season. This delayed onset of TIW activity is expected to have considerable consequences for the local heat and freshwater budgets. Low TIW activity and positive SST anomalies also impacted the concentration and distribution of surface chlorophyll as observed by daily gap-free satellite observations. After the initial Kelvin wave, surface chlorophyll concentration dropped to extraordinarily low values and was anti-correlated with the evolution of SST anomalies. The absence of TIWs is also apparent in weaker than normal surface chlorophyll concentration variability on intraseasonal time scales, highlighting the interplay of TIWs and chlorophyll. Our results demonstrate how the 2021 Atlantic Niño impacted oceanic variability, but further analysis is needed to better understand the consequences of such events for regional heat and freshwater budgets as well as for nutrients, productivity, and marine ecosystems.

A phenomenon referred to here as Java–Sumatra Niño/Niña (JSN or JS Niño/Niña) is characterized by the appearance of warm/cold sea surface temperature anomalies (SSTAs) in the coastal upwelling region off Java–Sumatra in the southeastern equatorial Indian Ocean. JSN develops in July–September and sometimes as a precursor to the Indian Ocean dipole, but often without corresponding SSTAs in the western equatorial Indian Ocean. Although its spatiotemporal evolution varies considerably between individual events, JSN is essentially an intrinsic mode of variability driven by local atmosphere–ocean positive feedback, and thus does not rely on remote forcing from the Pacific for its emergence. JSN is an important driver of climate variability over the tropical Indian Ocean and the surrounding continents. Notably, JS Niña events developing in July–September project onto the South and Southeast Asian summer monsoons, increasing the probability of heavy rainfall and flooding across the most heavily populated regions of the world.

The northwestern Tropical Atlantic Ocean is a turbulent region, filled with mesoscale eddies and regional currents. In this intense dynamical context, several water masses with thermohaline characteristics of different origins are advected, mixed, and stirred at the surface and at depth. The EUREC4A-OA/ATOMIC experiment that took place in January and February 2020 was dedicated to assessing the processes at play in this region, especially the interaction between the ocean and the atmosphere. For that reason, four oceanographic vessels and different autonomous platforms measured properties near the air–sea interface and acquired thousands of upper-ocean (up to 400–2000 m depth) profiles. However, each device had its own observing capability, varying from deep measurements acquired during vessel stations to shipboard underway near-surface observations and measurements from autonomous and uncrewed systems (such as Saildrones). These observations were undertaken with a specific sampling strategy guided by near-real-time satellite maps and adapted every half day, based on the process that was investigated. These processes were characterized by different spatiotemporal scales, from mesoscale eddies, with diameters exceeding 100 km, to submesoscale filaments of 1 km width. This article describes the datasets gathered from the different devices and how the data were calibrated and validated. In order to ensure an overall consistency, the platforms' datasets are cross-validated using a hierarchy of instruments defined by their own specificity and calibration procedures. This has enabled the quantification of the uncertainty in the measured parameters when different datasets are used together, e.g., https://doi.org/10.17882/92071 (L'Hégaret et al., 2020a).

The northwestern Tropical Atlantic Ocean is a turbulent region, filled with mesoscale eddies and large-scale currents. In this intense dynamical context, several water masses with thermohaline characteristics of different origins are advected, mixed, and stirred, at the surface and at depth. The EUREC4A-OA/ATOMIC experiment that took place in January and February 2020 was dedicated to assess the processes at play in this region, especially the interaction between the ocean and the atmosphere. For that, four oceanographic vessels and different autonomous platforms measured properties near the air-sea interface and acquired thousands of upper-ocean (400–2000 m) profiles. However, each device had its own observing capability, varying from deep measurements acquired during vessel stations to shipboard underway near-surface observations and measurements from autonomous and uncrewed systems (such as Saildrones). These observations were undertaken with a specific sampling strategy guided by near-real time satellite images and adapted every half day based on the process that was investigated. These processes were characterized by different spatio-temporal scales: from mesoscale eddies, with diameters exceeding 100 km, to submesoscale filaments of 1 km width. This article describes the data sets gathered from the different devices and how the data were calibrated and validated, in order to ensure an overall consistency, the platforms' datasets are cross-validated using a hierarchy of instruments defined by their own specificity and calibration procedures. This has enabled the quantification of the uncertainty of the measured parameters when the different datasets are used together (https://doi.org/10.17882/92071).

Tropical Instability Waves (TIWs) are the dominant source of intraseasonal variability in the central equatorial Atlantic and play an important role in the redistribution of heat in the upper ocean. Here we use multidecadal records of sea surface temperature, sea level anomaly, sea surface salinity, and near-surface currents constructed from in situ and satellite observations to reveal a long-term intensification of the intraseasonal variability of these variables due to an increase of TIW activity. Enhanced barotropic energy conversion from increased covariance of horizontal current fluctuations, rather than low-frequency changes of the mean zonal currents, drives the TIW intensification. As a consequence, boreal summer cooling of tropical North Atlantic surface waters through horizontal eddy temperature advection increased by 0.03°C month−1 decade−1 during 1993–2021, a change of 74% ± 53% relative to the long-term mean. The presented multidecadal TIW trends are strongly modulated by interannual variations like the 2021 Atlantic Niño. Key Points: - In situ and satellite observations show a long-term intensification of Tropical Instability Waves (TIWs) in the tropical North Atlantic - Enhanced TIW activity is mainly due to increased barotropic instability associated with increased covariance of velocity fluctuations - As a result, TIW-driven sea surface cooling north of the equator due to eddy temperature advection has increased by 74% from 1993 to 2021

The Atlantic Tradewind Ocean-Atmosphere Mesoscale Interaction Campaign (ATOMIC) took place from 7 January to 11 July 2020 in the tropical North Atlantic between the eastern edge of Barbados and 51∘ W, the longitude of the Northwest Tropical Atlantic Station (NTAS) mooring. Measurements were made to gather information on shallow atmospheric convection, the effects of aerosols and clouds on the ocean surface energy budget, and mesoscale oceanic processes. Multiple platforms were deployed during ATOMIC including the NOAA RV Ronald H. Brown (RHB) (7 January to 13 February) and WP-3D Orion (P-3) aircraft (17 January to 10 February), the University of Colorado's Robust Autonomous Aerial Vehicle-Endurant Nimble (RAAVEN) uncrewed aerial system (UAS) (24 January to 15 February), NOAA- and NASA-sponsored Saildrones (12 January to 11 July), and Surface Velocity Program Salinity (SVPS) surface ocean drifters (23 January to 29 April). The RV Ronald H. Brown conducted in situ and remote sensing measurements of oceanic and atmospheric properties with an emphasis on mesoscale oceanic–atmospheric coupling and aerosol–cloud interactions. In addition, the ship served as a launching pad for Wave Gliders, Surface Wave Instrument Floats with Tracking (SWIFTs), and radiosondes. Details of measurements made from the RV Ronald H. Brown, ship-deployed assets, and other platforms closely coordinated with the ship during ATOMIC are provided here. These platforms include Saildrone 1064 and the RAAVEN UAS as well as the Barbados Cloud Observatory (BCO) and Barbados Atmospheric Chemistry Observatory (BACO). Inter-platform comparisons are presented to assess consistency in the data sets. Data sets from the RV Ronald H. Brown and deployed assets have been quality controlled and are publicly available at NOAA's National Centers for Environmental Information (NCEI) data archive (https://www.ncei.noaa.gov/archive/accession/ATOMIC-2020, last access: 2 April 2021). Point-of-contact information and links to individual data sets with digital object identifiers (DOIs) are provided herein.

This study finds that the winter (December–February) barrier layer (BL) in the Bay of Bengal (BoB) acts as a dynamical thermostat, modulating the subsequent summer BoB SST variability and potentially affecting the Indian summer monsoon (ISM) onset and associated rainfall variability. In the years when the prior winter BL is anomalously thick, anomalous sea surface cooling caused by intensified latent heat flux loss appears in the BoB starting in October and persists into the following year by positive cloud–SST feedback. During January–March, the vertical entrainment of warmer subsurface water induced by the anomalously thick BL acts to damp excessive cooling of the sea surface caused by atmospheric forcing and favors development of deep atmospheric convection over the BoB. During March–May, the thinner mixed layer linked to the anomalously thick BL allows more shortwave radiation to penetrate below the mixed layer. This tends to maintain existing cold SST anomalies, advancing the onset of ISM and enhancing June ISM precipitation through an increase in the land–sea tropospheric thermal contrast. We also find that most CMIP5 models fail to reproduce the observed relationship between June ISM rainfall and the prior winter BL thickness. This may be attributable to their difficulties in realistically simulating the winter BL in the BoB and ISM precipitation. The present results indicate that it is important to realistically capture the winter BL of the BoB in air–sea coupled models for improving the simulation and prediction of ISM.

Recent studies have demonstrated that the difference in sea surface temperature anomalies (SSTAs) between the tropical Atlantic main development region (MDR) and the tropical Pacific (Nino 3...

Process studies are designed to improve our understanding of poorly described physical processes that are central to the behavior of the climate system. They typically include coordinated efforts of intensive field campaigns in the atmosphere and/or ocean to collect a carefully planned set of in situ observations. Ideally the observational portion of a process study is paired with numerical modeling efforts that lead to better representation of a poorly simulated or previously neglected physical process in operational and research models. This article provides a framework of best practices to help guide scientists in carrying out more productive, collaborative, and successful process studies. Topics include the planning and implementation of a process study and the associated web of logistical challenges; the development of focused science goals and testable hypotheses; and the importance of assembling an integrated and compatible team with a diversity of social identity, gender, career stage, and scientific background. Guidelines are also provided for scientific data management, dissemination, and stewardship. Above all, developing trust and continual communication within the science team during the field campaign and analysis phase are key for process studies. We consider a successful process study as one that ultimately will improve our quantitative understanding of the mechanisms responsible for climate variability and enhance our ability to represent them in climate models.

A phenomenon referred to here as Java-Sumatra Niño/Niña (JSN or JS Niño/Niña) is characterized by the appearance of warm/cold sea surface temperature anomalies (SSTAs) in the coastal upwelling region off Java-Sumatra in the southeastern equatorial Indian Ocean. JSN develops in July-September and sometimes as a precursor to the Indian Ocean Dipole, but often without corresponding SSTAs in the western equatorial Indian Ocean. Although its spatiotemporal evolution varies considerably between individual events, JSN is essentially an intrinsic mode of variability driven by local atmosphere-ocean positive feedback, and thus does not rely on remote forcing from the Pacific for its emergence. JSN is an important driver of climate variability over the tropical Indian Ocean and the surrounding continents. Notably, JS Niña events developing in July-September project onto the South and Southeast Asian summer monsoons, increasing the probability of heavy rainfall and flooding across the most heavily populated regions of the world.

It is found that the average genesis location of tropical cyclones (TCs) in the postmonsoon (October–December) Bay of Bengal (BoB) shows a notable meridional oscillation during 1980–2015. During years when the average genesis location shifts northward (north-years), the average maximum sustained wind speed, the average landfall wind speed and the number of category 4–5 TCs are all larger than those during years when the average genesis location displaces southward (south-years). Genesis potential index analysis shows that changes in relative humidity and vertical wind shear are mainly responsible for the meridional oscillation of the average genesis location of TCs. The changes in relative humidity and wind shear are closely related to changes in atmospheric circulation. Composite analysis reveals that sea surface temperature (SST) anomalies over the equatorial Pacific Ocean show a La Nina-like pattern (El Nino-like pattern) during north-years (south-years) of TC genesis locations. The SST anomalies over the equatorial Pacific Ocean induce a strengthened (weakened) Walker circulation during north-years (south-years) of TC genesis locations, influencing the atmospheric circulation over the tropical Indian Ocean. In addition, a stationary Rossby wave train from the North Pacific to the Iranian Plateau (east of Iranian Plateau) during north-years (south-years) induces changes in atmospheric circulation over the extratropical North Indian Ocean. Together, the tropical and extratropical influences contribute to the north–south patterns of relative humidity and vertical wind shear anomalies in the postmonsoon BoB, which drive the meridional oscillation of TC genesis locations. This study has significant implications for the prediction of TCs and disaster prevention and mitigation over the BoB.

In February 2020, a 120km‐wide freshwater plume was documented by satellite and in situ observations near the Demerara Rise (7°N/54‐56°W). It was initially stratified in the upper 10 m with a freshwater content of 2 to 3 meters of Amazon water distributed down to 40 m. On February 2nd, ship transects indicate an inhomogeneous shelf structure with a propagating front in its midst, whereas minimum salinity close to 30 pss was observed close to the shelf break on February 5th. The salinity minimum eroded in time but was still observed 13 to 16 days later with 33.3 pss minimum value up to 400 km from the shelf break. At this time, the mixed layer depth was close to 20 m. The off‐shelf flow lasted 10 days, contributing to a plume area extending over 100000 km2 and associated with a 0.15 106 m3 s‐1 freshwater transport. The off‐shelf plume was steered northward by a North Brazil Current ring up to 12°N and then extended westward toward the Caribbean Sea. Its occurrence followed 3 days of favourable wind direction closer to the Amazon estuary, which contributed to north‐westward freshwater transport on the shelf. Other such events of freshwater transport in January‐March are documented since 2010 in salinity satellite products in 7 out of 10 years, and in 6 of those years, they were preceded by a change in wind direction between the Amazon estuary and the Guianas favouring the north‐westward freshwater transport toward the shelf break. Plain Language Summary This paper documents how freshwater from the Amazon reaches the deep ocean up to 12°N in the northwest tropical Atlantic in January‐March. The classical view is that the water is channelled along the shelf to the Caribbean Sea. Here, we document a freshwater plume from in situ and satellite observations during the EUREC4A‐OA/ATOMIC program in 2020. This plume separated from the shelf near 55°W north of French Guiana on February 2‐5. This fresher water was stirred by a North Brazil Current ring up to 12°N before mostly spreading westward. The near‐surface water was initially very stratified at least until 10‐m from the surface. More than 14 days later and 400 km farther north, salinity as low as 33.3 pss with mixing depths on the order of only 20‐m was still encountered. The total area of the freshwater plume reached 100000 km2 with a flow of freshwater on the order of 0.15 Sv (106 m3 s‐1) during 10 days. This phenomenon seems to be triggered by changes in the wind direction on the shelf closer to the equator, and has also been observed in satellite products in 7 out of 10 years since 2010.

The direct response of the tropical mixed layer to near-inertial waves (NIWs) has only rarely been observed. Here, we present upper-ocean turbulence data that provide evidence for a strongly elevated vertical diffusive heat flux across the base of the mixed layer in the presence of a NIW, thereby cooling the mixed layer at a rate of 244 W m−2 over the 20 h of continuous measurements. We investigate the seasonal cycle of strong NIW events and find that despite their local intermittent nature, they occur preferentially during boreal summer, presumably associated with the passage of atmospheric African Easterly Waves. We illustrate the impact of these rare but intense NIW induced mixing events on the mixed layer heat balance, highlight their contribution to the seasonal evolution of sea surface temperature, and discuss their potential impact on biological productivity in the tropical North Atlantic. How the tropical mixed layer of the ocean reacts to near-inertial waves has rarely been observed directly. Here, the authors present new data that shows strongly elevated vertical diffusive heat flux in the presence of near-inertial waves, causing a cooling of the mixed layer that is particularly strong in summer.

In January-February 2020, the EUREC4A-OA/ATOMIC experiment took place in the Northwest Tropical Atlantic Ocean with the overall objective of understanding the role of fine scale processes in the internal ocean dynamics and air-sea interaction. Four oceanographic vessels, the French Atalante, German Maria S Merian and Meteor, and the American Ron Brown, closely coordinated with air-borne observations and autonomous ocean platforms (gliders, saildrones, and drifters) to simultaneously measure the ocean and atmosphere east of the island of Barbados and the coast of Guyana in the western Tropical Atlantic. A whole battery of instruments measuring the thermohaline and dynamic characteristics of the region was launched. The fixed CTD stations, reaching great depths while measuring salinity, temperature, and oxygen concentrations, serve as a reference to calibrate and validate other devices, in particular, shallower uCTD, TSG, and MVP, acquired during ship transits, and autonomous gliders and saidrones. Combined, these datasets increase the horizontal resolution and thus the description of structures ranging from mesoscale to fine scale.The Northwest Tropical Atlantic Ocean is a dynamical region filled with mesoscale eddies of different origins and transporting various water masses across the region. These eddies have rich and diverse characteristics ranging from shallow cyclonic and anticyclonic eddies to the deep reaching North Brazil Current (NBC) Rings. On the surface, down to 200 m depth, the signatures of shallow cyclones and anticyclones (NBC rings) were measured. The shallow mesoscale eddies, with core centered around a density of 25.5 kg m-3, advect highly saline and warm waters, with low oxygen concentrations compared to the surrounding water masses. Below, evolving at density around 26.7 kg m-3, thick anticyclones were observed, characterized by low temperature and salinity but with high values of oxygen, indicative of a South Atlantic origin. One was observed drifting slowly northward and another one at the NBC retroflection. Similarly, mesoscale cyclonic eddies were also observed both at the surface and at depth. Surface and subsurface eddies are not aligned vertically and they seem to evolve independently. The large number and diversity (ship-mounted or autonomous) of observing platforms implemented in the project made made it possible to innovatively sample the upper-ocean frontal scales and stratification. It has been found that the interaction between the particularly fresh waters from the Amazon River, flowing northward along the shelf-break, and NBC rings create a rich variety of submesoscale fronts and a strong barrier layer, leading to interleaving. With the high vertical and horizontal resolutions, we quantify the layering and mixing processes at play.

The science guiding the EUREC4A campaign and its measurements is presented. EUREC4A comprised roughly 5 weeks of measurements in the downstream winter trades of the North Atlantic – eastward and southeastward of Barbados. Through its ability to characterize processes operating across a wide range of scales, EUREC4A marked a turning point in our ability to observationally study factors influencing clouds in the trades, how they will respond to warming, and their link to other components of the earth system, such as upper-ocean processes or the life cycle of particulate matter. This characterization was made possible by thousands (2500) of sondes distributed to measure circulations on meso- (200 km) and larger (500 km) scales, roughly 400 h of flight time by four heavily instrumented research aircraft; four global-class research vessels; an advanced ground-based cloud observatory; scores of autonomous observing platforms operating in the upper ocean (nearly 10 000 profiles), lower atmosphere (continuous profiling), and along the air–sea interface; a network of water stable isotopologue measurements; targeted tasking of satellite remote sensing; and modeling with a new generation of weather and climate models. In addition to providing an outline of the novel measurements and their composition into a unified and coordinated campaign, the six distinct scientific facets that EUREC4A explored – from North Brazil Current rings to turbulence-induced clustering of cloud droplets and its influence on warm-rain formation – are presented along with an overview of EUREC4A's outreach activities, environmental impact, and guidelines for scientific practice. Track data for all platforms are standardized and accessible at https://doi.org/10.25326/165 (Stevens, 2021), and a film documenting the campaign is provided as a video supplement.

International audience; Decade-long satellite sea surface slinity (SSS) observations show that rain dilution prevails in wakes of tropical depressions (∼-0.1 pss) and tropical storms (∼-0.05 pss) on the left (right) side of Northern (Southern) Hemisphere storms. For stronger storms, the rain-induced dilution is dominated by the saltier water entrainment, leading to surface median salinification of 0.3 pss for the most intense storms, peaking on the right-hand side at around twice the maximum wind radius. The magnitude of the salty wake increases for stronger slowly moving storms. The vertical salinity gradient in the upper ocean is a key factor explaining the geographic distribution of the SSS response. A striking example is the systematic mixing of fresh near-surface river plume waters with saltier subsurface waters. It is also found that barrier layers lead to saltier and warmer storm wakes compared to wakes produced over barrier layer free areas.

This study finds that the winter barrier layer (BL) in the Bay of Bengal (BoB) can modulate the subsequent Indian summer monsoon (ISM) onset and associated rainfall variability. In the years when the prior winter BL is anomalously thick, there is anomalous sea surface cooling caused by intensified latent heat flux loss, and this anomalous cooling persists into the following year due to positive cloud–SST feedback. During December–February, it is shown that the vertical entrainment of warmer subsurface water due to anomalously thick BL acts to limit excessive cooling of the sea surface and maintain deep atmospheric convection over the BoB. Then, during March–May, the thinner mixed layer linked to anomalously thick BL allows more shortwave radiation to penetrate below the mixed layer. This tends to reinforce the cold SST anomalies, and advance the onset of ISM and enhance June ISM precipitation through an increase in the tropospheric temperature gradient between land and sea. We also find that most CMIP5 models fail to reproduce the observed relationship between June ISM rainfall and the prior winter BL. This may be attributable to their difficulties in realistically simulating the winter BL in the BoB and ISM precipitation. The present results indicate that it is important to realistically capture the winter BL of the BoB in air–sea coupled models for improving the simulation and prediction of ISM.

The Atlantic Tradewind Ocean-Atmosphere Mesoscale Interaction Campaign (ATOMIC) took place from January 7 to July 11, 2020 in the tropical North Atlantic between the eastern edge of Barbados and 51° W, the longitude of the Northwest Tropical Atlantic Station (NTAS) mooring. Measurements were made to gather information on shallow atmospheric convection, the effects of aerosols and clouds on the ocean surface energy budget, and mesoscale oceanic processes. Multiple platforms were deployed during ATOMIC including the NOAA RV Ronald H. Brown (RHB) (Jan. 7 to Feb. 13) and WP-3D Orion (P-3) aircraft (Jan. 17 to Feb. 10), the University of Colorado's RAAVEN Uncrewed Aerial System (UAS) (Jan. 24 to Feb. 15), NOAA- and NASA-sponsored Saildrones (Jan. 12 to Jul. 11), and Surface Velocity Program Salinity (SVPS) surface ocean drifters (Jan. 23 to Apr. 29). The RV Ronald H. Brown conducted in situ and remote sensing measurements of oceanic and atmospheric properties with an emphasis on mesoscale oceanic-atmospheric coupling and aerosol-cloud interactions. In addition, the ship served as a launching pad for Wave Gliders, Surface Wave Instrument Floats with Tracking (SWIFTs), and radiosondes. Details of measurements made from the RV Ronald H. Brown, ship-deployed assets, and other platforms closely coordinated with the ship during ATOMIC are provided here. These platforms include Saildrone 1064 and the RAAVEN UAS as well as the Barbados Cloud Observatory (BCO) and Barbados Atmospheric Chemistry Observatory (BACO). Inter-platform comparisons are presented to assess consistency in the data sets. Data sets from the RV Ronald H. Brown and deployed assets have been quality controlled and are publicly available at the NOAA Physical Sciences Laboratory (PSL) ATOMIC ftp server (ftp://ftp2.psl.noaa.gov/Projects/ATOMIC/data/ (Quinn et al., 2020). In addition, the data have been submitted to NOAA's National Centers for Environmental Information (NCEI) data archive (https://www.ncei.noaa.gov/) for Digital Object Identifiers (DOIs). Point of contact information and links to individual data sets are provided herein.

We show the importance of salinity for rapidly intensifying Atlantic tropical cyclones and demonstrate the potential for improved prediction of rapid intensification through the inclusion of salinity. Tropical Cyclone (TC) rapid intensification (RI) is difficult to predict and poses a formidable threat to coastal populations. A warm upper ocean is well-known to favor RI, but the role of ocean salinity is less clear. This study shows a strong inverse relationship between salinity and TC RI in the eastern Caribbean and western tropical Atlantic due to near-surface freshening from the Amazon-Orinoco River system. In this region, rapidly intensifying TCs induce a much stronger surface enthalpy flux compared to more weakly intensifying storms, in part due to a reduction in SST cooling caused by salinity stratification. This reduction has a noticeable positive impact on TCs undergoing RI, but the impact of salinity on more weakly intensifying storms is insignificant. These statistical results are confirmed through experiments with an ocean mixed layer model, which show that the salinity-induced reduction in SST cold wakes increases significantly as the storm’s intensification rate increases. Currently, operational statistical-dynamical RI models do not use salinity as a predictor. Through experiments with a statistical RI prediction scheme, it is found that the inclusion of surface salinity significantly improves the RI detection skill, offering promise for improved operational RI prediction. Satellite surface salinity may be valuable for this purpose, given its global coverage and availability in near real-time.

10 pages, 4 figures, supporting information https://doi.org/10.1029/2020GL087108.-- The HadISST1 data were provided by UK Met Office at https://www.metoffice.gov.uk/hadobs/hadisst. The NCEP‐NCAR reanalysis, the NOAA gauge observation‐based global land precipitation reconstruction data, the COBE data and the ERSST5 data were provided by NOAA/ESRL/PSD at http://www.esrl.noaa.gov/psd. The ORAS4 data were provided by the Copernicus Marine Environment Monitoring Service (CMEMS) at ftp://ftp‐icdc.cen.uni‐hamburg.de/EASYInit/ORA‐S4/monthly_1x1, The spatiotemporal evolutions of equatorial Atlantic sea surface temperature anomalies (SSTAs) during Atlantic Niño events and the associated climate impacts on the surrounding continents are extremely diverse. In this study, we construct longitude‐time maps of equatorial Atlantic SSTAs for each observed Atlantic Niño event during 1948–2019 and perform a spatiotemporal empirical orthogonal function analysis to identify the four most frequently recurring Atlantic Niño varieties. The first two contrast the timing of dissipation (early terminating vs. persistent) and the other two the timing of onset (early onset vs. late onset). Largely consistent with the differences in the timings of onset and dissipation, these four varieties display remarkable differences in rainfall response over West Africa and South America. Most of the varieties are subject to onset mechanisms that involve preconditioning in boreal spring by either the Atlantic meridional mode or Pacific El Niño, while for the late onset variability there is no clear source of external forcing, This work was supported by the Spanish Government funding through projects VA‐DE‐RETRO (CTM2014‐56987‐P) and SAGA (RTU2018‐100844‐B‐C33) and by NOAA's Climate Program Office, Climate Variability and Predictability Program (award GC16‐207) and NOAA/AOML. I. V. C. was funded through FPI contract (BES‐2015‐071314), With the funding support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S), of the Spanish Research Agency (AEI)

Rapid Intensification (RI) of hurricanes is difficult to predict and poses a formidable threat to coastal populations. While a warm upper-ocean is well-known to favor RI, the role of salinity is less clear. In this study, using a suite of observations, we demonstrate that the subsurface oceans' influence on Atlantic hurricane RI exhibits two regimes. In the western region, which includes the Gulf of Mexico and the western Caribbean Sea, temperature stratification plays an important role in hurricane RI with little impact from salinity. On the other hand, in the eastern region dominated by the Amazon-Orinoco plume, salinity stratification prominently impacts RI. While a weak temperature stratification aids cold wake reduction for hurricanes in the western region, a strong salinity stratification causes less hurricane-induced mixing and surface cooling in the eastern region. Finally, in both regions, the relevance of the cold wake, and consequently the ocean sub-surface, is enhanced during RI compared to weaker intensification.

The causes of the seasonal cycle of vertical turbulent cooling at the base of the mixed layer are assessed using observations from moored buoys in the tropical Atlantic Intertropical Convergence Zone (ITCZ) (4°N, 23°W) and trade wind (15°N, 38°W) regions together with mixing parameterizations and a one-dimensional model. At 4°N the parameterized turbulent cooling rates during 2017–2018 and 2019 agree with indirect estimates from the climatological mooring heat budget residual: both show mean cooling of 25–30 W m (Formula presented.) during November–July, when winds are weakest and the mixed layer is thinnest, and 0–10 W m (Formula presented.) during August–October. Mixing during November–July is driven by variability on multiple time scales, including subdiurnal, near-inertial, and intraseasonal. Shear associated with tropical instability waves (TIWs) is found to generate mixing and monthly mean cooling of 15–30 W m (Formula presented.) during May–July in 2017 and 2019. At 15°N the seasonal cycle of turbulent cooling is out of phase compared to 4°N, with largest cooling of up to 60 W m (Formula presented.) during boreal fall. However, the relationships between wind speed, mixed layer depth, and turbulent mixing are similar: weaker mean winds and a thinner mixed layer in the fall are associated with stronger mixing and turbulent cooling of SST. These results emphasize the importance of seasonal modulations of mixed layer depth at both locations and shear from TIWs at 4°N.