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International audience; From23Januaryto13February2020,20ATR-42scientificflightswereconductedintheframework of the EUREC4A field campaign over the tropical Atlantic, off the coast of Barbados (13◦30′ N, −58◦30′ W). By means of a sideway-pointing lidar, these flights allowed us to retrieve the optical properties of the aerosols found in the sub-cloud layer and below the trade wind inversion. Two distinct periods with significant aerosol contents were identified in relationship with the so-called trade wind and tropical regimes, respectively. For these two regimes, mixings of two air mass types encompassing dust and carbonaceous aerosols have been highlighted. Both were mainly from West Africa with similar optical contributions and linked to dust uptake above Sahara and biomass burning between Guinea-Bissau and Côte d’Ivoire. In the tropical transport regime, the wind within the planetary boundary layer is stronger and favours a contribution of marine aerosols (sulfate and sea salt aerosol components) in shallower aerosol layers than for the trade wind transport regime. The latter is responsible for advecting dust–biomass-burning-aerosol mixtures in the deeper, well-mixed layer, in part due to the complex interactions of the easterly flow from West Africa with mid-latitude dynamics. The aerosol vertical structures appear to be well reproduced using atmospheric composition reanalyses from CAMS when comparing with lidar-derived vertical profiles. The competition between the two types of transport regimes leads to strong heterogeneity in the optical properties of the horizontal aerosol field. Our study highlights the transport regime under which a significant mixture of dust and biomass burning aerosols from West Africa can be observed over the Caribbean and Barbados in particular, namely the trade wind regime.

Mass flux is a key quantity in parameterizations of shallow convection. To estimate the shallow convective mass flux as accurately as possible, and to test these parameterizations, observations of this parameter are necessary. In this study, we show how much the mass flux varies and how this can be used to test factors that may be responsible for its variation. Therefore, we analyze long-term Doppler radar and Doppler lidar measurements at the Barbados Cloud Observatory over a time period of 30 months, which results in a mean mass flux profile with a peak value of 0.03 kg m−2 s−1 at an altitude of ~730 m, similar to observations from Ghate et al. at the Azores Islands. By combining Doppler radar and Doppler lidar measurements, we find that the cloud-base mass flux depends mainly on the cloud fraction and refutes an idea based on large-eddy simulations that the velocity scale is in major control of the shallow cumulus mass flux. This indicates that the large-scale conditions might play a more important role than what one would deduce from simulations using prescribed large-scale forcings.

The Guinea Coast is the southern part of the West African continent. Its summer rainfall variability mostly occurs on interannual timescales and is highly influenced by the sea surface temperature (SST) variability in the eastern equatorial Atlantic, which is known as the Atlantic Niño (ATL3). Using historical simulations from 31 General Circulation Models (GCMs) participating in the sixth phase of the Coupled Model Intercomparison Project (CMIP6), we first show that these models are able to simulate reasonably well the rainfall annual cycle in the Guinea Coast, with, however, a wet bias during boreal summer. This bias is associated with too high mean summer SSTs in the eastern equatorial and south Atlantic regions. Next, we analyze the near-term, mid-term and long-term changes of the Atlantic Niño mode relative to the present-day situation, in a climate with a high anthropogenic emission of greenhouse gases. We find a gradual decrease of the equatorial Atlantic SST anomalies associated with the Atlantic Niño in the three periods of the future. This result reflects a possible reduction of the Atlantic Niño variability in the future due to a weakening of the Bjerkness feedback over the equatorial Atlantic. In a warmer climate, an oceanic extension of the Saharan Heat Low over the North Atlantic and an anomalous higher sea level pressure in the western equatorial Atlantic relative to the eastern equatorial Atlantic weaken the climatological trade winds over the equatorial Atlantic. As a result, the eastern equatorial Atlantic thermocline is deeper and responds less to Atlantic Niño events. Among the models that simulate a realistic rainfall pattern associated with ATL3 in the present-day climate, there are 15 GCMs which project a decrease of the Guinean Coast rainfall response related to ATL3, and 9 GCMs which show no substantial change in the patterns associated with ATL3. In these 15 models, the zonal wind response to the ATL3 over the equatorial Atlantic is strongly attenuated in the future climate. Similar results are found when the analysis is focused on the rainfall response to ATL3 over the equatorial Atlantic. There is a higher confidence in the reduction of the rainfall associated with ATL3 over the Atlantic Ocean than over the Guinea Coast. We also found a decrease of the convection associated with ATL3 in the majority of the models.

The westerlies and trade winds over the South Atlantic and Indian Ocean are important drivers of the regional oceanography around southern Africa, including features such as the Agulhas Current, the Agulhas leakage, and the Benguela upwelling. Agulhas leakage constitutes a fraction of warm and saline water transport from the Indian Ocean into the South Atlantic. The leakage is stronger during intensified westerlies. Here, we analyze the wind stress of different observational and modeled atmospheric data sets (covering the last 2 millennia, the recent decades, and the 21st century) with regard to the intensity and position of the southeasterly trades and the westerlies. The analysis reveals that variations of both wind systems go hand in hand and that a poleward shift of the westerlies and trades and an intensification of westerlies took place during the recent decades. Furthermore, upwelling in South Benguela is slightly intensified when trades are shifted poleward. Projections for strength and position of the westerlies in the 21st century depend on assumed CO2 emissions and on their effect relative to the ozone forcing. In the strongest emission scenario (RCP8.5) the simulations show a further southward displacement, whereas in the weakest emission scenario (RCP2.6) a northward shift is modeled, possibly due to the effect of ozone recovery dominating the effect of anthropogenic greenhouse forcing. We conclude that the Agulhas leakage has intensified during the last decades and is projected to increase if greenhouse gas emissions are not reduced. This will have a small impact on Benguela upwelling strength and may also have consequences for water mass characteristics in the upwelling region. An increased contribution of Agulhas water to the upwelling water masses will import more preformed nutrients and oxygen into the upwelling region.

Large changes in tropical circulation from the mid-to-late 1990s to the present, in particular changes related to the summer monsoon and cooling of the sea surface in the equatorial eastern Pacific, are noted. The cause of such recent decadal variations in the tropics was studied using a meteorological reanalysis dataset. Cooling of the equatorial southeastern Pacific Ocean occurred in association with enhanced cross-equatorial southerlies that were associated with a strengthening of the deep ascending branch of the boreal summer Hadley circulation over the continental sector connected to stratospheric circulation. From boreal summer to winter, the anomalous convective activity center moves southward following the seasonal march to the equatorial Indian Ocean–Maritime Continent region, which strengthens the surface easterlies over the equatorial central Pacific. Accordingly, ocean surface cooling extends over the equatorial central Pacific. We suggest that the fundamental cause of the recent decadal change in the tropical troposphere and the ocean is a poleward shift of convective activity that resulted from a strengthening of extreme deep convection penetrating into the tropical tropopause layer, particularly over the African and Asian continents and adjacent oceans. We conjecture that the increase in extreme deep convection is produced by a combination of land surface warming due to increased CO2 and a reduction of static stability in the tropical tropopause layer due to tropical stratospheric cooling.

We present a climatology of trade cumulus cold pools and their associated changes in surface weather, vertical velocity and cloudiness based on more than 10 years of in situ and remote sensing data from the Barbados Cloud Observatory. Cold pools are identified by abrupt drops in surface temperature, and the mesoscale organization pattern is classified by a neural network algorithm based on Geostationary Operational Environmental Satellite 16 (GOES-16) Advanced Baseline Imager (ABI) infrared images. We find cold pools to be ubiquitous in the winter trades – they are present about 7.8 % of the time and occur on 73 % of days. Cold pools with stronger temperature drops (ΔT) are associated with deeper clouds, stronger precipitation, downdrafts and humidity drops, stronger wind gusts and updrafts at the onset of their front, and larger cloud cover compared to weaker cold pools, which agrees well with the conceptual picture of cold pools. The rain duration in the front is the best predictor of ΔT and explains 36 % of its variability. The mesoscale organization pattern has a strong influence on the occurrence frequency of cold pools. Fish has the largest cold-pool fraction (12.8 % of the time), followed by Flowers and Gravel (9.9 % and 7.2 %) and lastly Sugar (1.6 %). Fish cold pools are also significantly stronger and longer-lasting compared to the other patterns, while Gravel cold pools are associated with significantly stronger updrafts and deeper cloud-top height maxima. The diel cycle of the occurrence frequency of Gravel, Flowers, and Fish can explain a large fraction of the diel cycle in the cold-pool occurrence as well as the pronounced extension of the diel cycle of shallow convection into the early afternoon by cold pools. Overall, we find cold-pool periods to be ∼ 90 % cloudier relative to the average winter trades. Also, the wake of cold pools is characterized by above-average cloudiness, suggesting that mesoscale arcs enclosing broad clear-sky areas are an exception. A better understanding of how cold pools interact with and shape their environment could therefore be valuable to understand cloud cover variability in the trades.

Trade wind cumulus clouds have a significant impact on the earth's radiative balance, due to their extensive coverage in subtropical regions but due to their characteristic size are still parameterized.The feedback of low clouds on the climate system as well as biases still existing in their representation of Global Climate Models (GCMs) results in a climatic response with relatively large uncertainty and induce a significant divergence in GCMs. Many studies and campaigns have focused on a better understanding of the thermodynamic and macroscopic properties of cumulus clouds with ground-based and satellite-based remote sensingand also in-situ observations from aircraft flights, but few provide information on the three-dimensional properties of individual cumulus clouds. Our understanding of cumulus clouds is also based on high-resolution numerical simulations (LES: 25m, 5m of resolution) that reproduce theaverage characteristics of cumulus clouds fairly reliably, yet these simulations still depend on parametrizations (turbulence and microphysics).The development of a fleet the sampling of RPAs (Remotely Piloted Aircraft) contributes to the increase in the resolution of the sampling of the evolution of cloud microphysical properties. Recent studies have permitted to have an autonomous adaptive sampling and a mapping using GaussianProcess Regression to interpolate missed values during exploration.An experimental strategy has been developed and tested in a cumulus cloud field simulated in a LES simulation with the Meso-NH model by implementing a simulator of RPA flights. During the EUREC4A field campaign in Barbados in January-February, more than forty RPAs flights have been conducted and thermodynamic properties of cumulus clouds were studied in three dimensions using miniaturized instruments installed on-board (PTU probe, cloud sensor). We validate first the results of cloud sensor with an other microphysics instrument. Several clouds were followed for about ten minutes and their thermodynamic evolution have been compared to cumulus clouds simulated in the LES.

The tropical Atlantic upper-ocean circulation experiences multiannual to decadal changes associated with different climate modes and is simultaneously adjusting to climate warming. The most energetic current in the tropical Atlantic is the Equatorial Undercurrent (EUC), which flows eastwards along the Equator. On the basis of long-term moored observations, we show that the EUC strengthened by more than 20% from 2008 to 2018. The intensification of the EUC is associated with increasing subsurface oxygen concentrations and a thickening of the upper-ocean oxygenated layer in the equatorial Atlantic. These changes counteract climate-warming-induced deoxygenation in the region. The EUC strengthening is found to be mainly forced by trade wind changes in the western tropical North Atlantic. A 60-yr dataset reveals that the recent oxygen increase in the upper equatorial Atlantic is associated with multidecadal variability. This variability is characterized by low oxygen concentrations in the 1990s and early 2000s, and high oxygen concentrations in the 1960s and 1970s. The observed oxygen variability seems to be linked to a compression and expansion of the habitat of tropical pelagic fish, and must be accounted for when evaluating the possible consequences of deoxygenation for marine ecosystems and fisheries. Recent strengthening of the Equatorial Undercurrent counteracts warming-induced deoxygenation in the equatorial Atlantic, according to an analysis of long-term moored observations.

The diversity of El Niño is a critical field of the climate research. The eastern Pacific (EP) and central Pacific (CP) types of El Niño have been identified in the previous studies. However, the extreme El Niño event that occurred in 2015–2016 is quite different from both the EP and CP El Niño events. The sea surface temperatures anomalies (SSTA) for this event widely spread in both the central and eastern Pacific and have a small zonal gradient in the central-eastern Pacific. Many researchers regarded this event as a mixed type of El Niño. Using the regression-EOF method, the Mix El Niño pattern is extracted from the tropical Pacific SSTA field during the period from 1900 to 2019. Here, we reveal that the Mix El Niño is a very usual rather than a new type of El Niño, it is just that the EP and CP El Niño events are more frequent since the 1980s, while the Mix El Niño events frequently appear before the 1980s. The time-spatial features of the Mix El Niño are further investigated. The results demonstrate a unique westward propagation of the maximum SSTA for the Mix El Niño from the far eastern Pacific to the central Pacific. In contrast, the SSTA center is locked in the far eastern Pacific region for the EP El Niño and the central Pacific region for the CP El Niño. The evolutions of subsurface ocean temperature anomalies and sea surface height anomalies are also examined to support this. The ocean–atmosphere interaction plays an important role in the evolution of the Mix El Niño. The anomalous atmospheric Walker circulation for the Mix El Niño is mainly in the western and central Pacific as well as very weak in the eastern Pacific. In contrast, there are significant westerlies/easterlies in the eastern Pacific for the EP/CP El Niño. The small gradient of SSTA in the central-eastern Pacific for the Mix El Niño leads to weak zonal wind anomalies, which further weaken the zonal gradient of SSTA. All this suggests that the Mix El Niño is not unusual and fundamentally different from the EP and CP El Niño with important implications for global climate effects.

Understanding the coupling between convective clouds and the general circulation, as well as addressing the gray zone problem in convective parameterization, requires insight into the genesis and maintenance of spatial patterns in cumulus cloud populations. In this study, a simple toy model for recreating populations of interacting convective objects as distributed over a two‐dimensional Eulerian grid is formulated to this purpose. Key elements at the foundation of the model include i) a fully discrete formulation for capturing discrete behavior in convective properties at small population sample sizes, ii) object age‐dependence for representing life‐cycle effects, and iii) a prognostic number budget allowing for object interactions and co‐existence of multiple species. A primary goal is to optimize the computational efficiency of this system. To this purpose the object birth rate is represented stochastically through a spatially aware Bernoulli process. The same binomial stochastic operator is applied to horizontal advection of objects, conserving discreteness in object number. The applicability to atmospheric convection as well as behavior implied by the formulation is assessed. Various simple applications of the BiOMi model (Binomial Objects on Microgrids) are explored, suggesting that important convective behavior can be captured at low computational cost. This includes i) subsampling effects and associated powerlaw scaling in the convective gray zone, ii) stochastic predator‐prey behavior, iii) the downscale turbulent energy cascade, and iv) simple forms of spatial organization and convective memory. Consequences and opportunities for convective parameterization in next‐generation weather and climate models are discussed., Plain Language Summary: Convective clouds play a crucial role in Earth's climate. The way they interact with the atmospheric circulation is not well understood, and is associated with long‐standing problems in weather forecasting and climate prediction. Recent research has suggested that the spatial structure of these cloud fields is a key factor in this problem, and that improving our understanding of such convective cloud patterns is crucial for making progress. This study explores a new model framework for generating such cloud patterns, consisting of populations of convective objects on small grids. The objects are born in a random way, complete a life cycle, and can freely move around on the grid. They can also interact and form larger clusters, obeying certain rules of interaction. The way the objects behave and move around features some key innovations compared to previous ecosystem models of this kind. These are introduced to optimize the performance and reduce run time on a computer. Various experiments are conducted to explore the new model, illustrating that well‐known behavior of convective populations is reproduced. These tests also highlight opportunities created for improving convection in weather and climate models., Key Points: A scale‐aware stochastic number generator based on a Bernoulli process is applied to model object births and advection on Eulerian grids. Discreteness in object number is conserved, while an age dimension is included to represent object life cycle effects. Population subsampling effects in the convective gray zone are reproduced, while simple applications capture well‐known convective behavior., U.S. Department of Energy (DOE) http://dx.doi.org/10.13039/100000015

Background. Acute respiratory infection (ARI) is one of the leading causes of morbidity among children under five in the developing world, including Nigeria. Objective. The study’s purpose is to analyse the geographical patterns, drivers and hotspots of ARI so as to provide a guide towards ARI interventions in Nigeria. Methods. Data for the study were obtained from the 2013 edition of the Nigerian Demographic and Health Survey (NDHS) report and the Annual Abstract of Statistics in Nigeria (2012). Spatial and statistical analyses were based on the local Getis Ord statistics and stepwise regression techniques. Results. There was substantial spatial variation in ARI prevalence, and significant hotspots were detected in Yobe, Jigawa, Kano, Bauchi, Gombe and Taraba states. The disease hotspots were attributed to one or more of the following: Boko Haram terrorism, prevailing dustladen north-east trade winds, and frequent sandstorms in the region. Overcrowding was found to be the only significant underlying factor responsible for the observed spatial pattern (B=0.479; R2 =0.229; p

Motivated by an observed relationship between marine low cloud cover and surface wind speed, this study investigates how vertical wind shear affects trade‐wind cumulus convection, including shallow cumulus and congestus with tops below the freezing level. We ran large‐eddy simulations for an idealized case of trade‐wind convection using different vertical shears in the zonal wind. Backward shear, whereby surface easterlies become upper westerlies, is effective at limiting vertical cloud development, which leads to a moister, shallower, and cloudier trade‐wind layer. Without shear or with forward shear, shallow convection tends to deepen more, but clouds tops are still limited under forward shear. A number of mechanisms explain the observed behavior: First, shear leads to different surface wind speeds and, in turn, surface heat and moisture fluxes due to momentum transport, whereby the weakest surface wind speeds develop under backward shear. Second, a forward shear profile in the subcloud layer enhances moisture aggregation and leads to larger cloud clusters, but only on large domains that generally support cloud organization. Third, any absolute amount of shear across the cloud layer limits updraft speeds by enhancing the downward oriented pressure perturbation force. Backward shear—the most typical shear found in the winter trades—can thus be argued a key ingredient at setting the typical structure of the trade‐wind layer., Key Points Shear in the zonal wind influences cloud‐top heights via the effect of momentum transport on the surface wind and surface fluxesBackward shear (surface easterlies turn westerlies) lowers cloud tops and shallows and moistens the trade‐wind layerAny absolute amount of wind shear limits in‐cloud updraft speeds and enhances low‐level cloud fraction

1. Large-scale environmental forces can influence biodiversity at different levels of biological organization. Climate, in particular, is often associated with species distributions and diversity gradients. However, its mechanistic link to population dynamics is still poorly understood. 2. Here, we unravelled the full mechanistic path by which a climatic driver, the Atlantic trade winds, determines the viability of a bird population. 3. We monitored the breeding population of Eleonora's falcons in the Canary Islands for over a decade (2007–2017) and integrated different methods and data to reconstruct how the availability of their prey (migratory birds) is regulated by trade winds. We tracked foraging movements of breeding adults using GPS, monitored departure of migratory birds using weather radar and simulated their migration trajectories using an individual-based, spatially explicit model. 4. We demonstrate that regional easterly winds regulate the flux of migratory birds that is available to hunting falcons, determining food availability for their chicks and consequent breeding success. By reconstructing how migratory birds are pushed towards the Canary Islands by trade winds, we explain most of the variation (up to 86%) in annual productivity for over a decade. 5. This study unequivocally illustrates how a climatic driver can influence local-scale demographic processes while providing novel evidence of wind as a major determinant of population fitness in a top predator

This study investigates the potential impacts of multi-timescale atmospheric modes on tropical cyclone (TC) abrupt track turnings over the western North Pacific during the period of 2000–2019. The composite large-scale environmental flow patterns of the sudden right-turning (SRT) and left-turning (SLT) TCs show that the SRT process is generally accompanied by the continuous deepening westerly trough, the weakening and eastward retreat of subtropical high favoring the strengthening of the asymmetric southwesterly around TC center, while the SLT cases are mainly steered by the stronger easterlies to the north which are attributed to the increased pressure meridional gradient. Furthermore, the TCs with sudden track changes are divided into 5 categories according to the quantitative contribution of wave modes. The composite analyses indicate that: (1) The synoptic-scale wave poses influence on most of the SRT cases through a southeast-northwest-oriented wave train to the northeast of the TC, inducing the prominent southerly flows in the vicinity of TC center. (2) The intra-seasonal oscillation (ISO) pattern for the SRT cases is characterized by a southeast-northwest-oriented circulation dipole, and the TCs embedded between the two dipole components are impacted by the strengthened southwesterly anomalies. In contrast, the SLT events are located in the northwest of a zonally-elongated cyclonic ISO circulation, which enhances the northeasterly flows for the sharply left turning. (3) The SRT cases dominated by the basic background flow are situated in the western flank of a broad anticyclonic circulation and subject to the northward steering flow anomalies, while for the SLT cases, the left track turning is mainly induced by the uniform easterly trade winds at the lower latitudes.

Background An increasing incidence of MS in the city of Catania was reported during 1975–2004, with a higher incidence along the south-eastern flank of the Mt.Etna. We evaluated the incidence of MS in the entire province of Catania during 2005–2015 and the spatial distribution of MS-cases using a cluster analysis. Methods Patients were considered as incident MS-cases if they fulfilled the revised McDonald criteria for MS during 2005–2015 and were residents in the province of Catania at the time of disease onset. Cluster analysis was performed using both LISA and Kulldorff's spatial scan statistic. Residence address at disease onset was considered for each case. Communalities were assessed considering the centroid of their inhabited area. Results A total of 973 MS-cases were identified. Mean annual incidence risk was 8.2/100,000 person-years (95%CI 7.7–8.7), significantly higher among women (10.5/100,000 versus 5.7/100,000). LISA identified a spatial aggregation of MS-cases in the eastern side of the province of Catania and Kulldorff's statistics confirmed the existence of a statistically significant spatial cluster in this area (SIR 1.23,95%CI 1.08–1.23, p-value 0.04). Conclusions Our study confirms a high incidence of MS in the province of Catania and the presence of a spatial cluster along the eastern side of the province. This area is considered the most exposed to volcanogenic ashes due to the prevailing westerly to north-westerly trade winds. Even if such distribution could be related with a greater exposure to volcanogenic metals, further studies are needed to explore possible alternative hypotheses.

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.

This article establishes a linkage between the mineral dust cycle and loess deposits during the Last Glacial Maximum (LGM) in Europe. To this aim, we simulate the LGM dust cycle at high resolution using a regional climate-dust model. The model-simulated dust deposition rates are found to be comparable with the mass accumulation rates of the loess deposits determined from more than 70 sites. In contrast to the present-day prevailing westerlies, winds from northeast, east and southeast (36 %) and cyclonic regimes (22 %) were found to prevail over central Europe during the LGM. This supports the hypothesis that the recurring east sector winds associated with a high-pressure system over the Eurasian ice sheet (EIS) dominated the dust transport from the EIS margins in eastern and central Europe. The highest dust emission rates in Europe occurred in summer and autumn. Almost all dust was emitted from the zone between the Alps, the Black Sea and the southern EIS margin. Within this zone, the highest emission rates were located near the southernmost EIS margins corresponding to the present-day German-Polish border region. Coherent with the persistent easterlies, westwards running dust plumes resulted in high deposition rates in western Poland, northern Czechia, the Netherlands, the southern North Sea region and on the North German Plain including adjacent regions in central Germany. The agreement between the climate model simulations and the mass accumulation rates of the loess deposits corroborates the proposed LGM dust cycle hypothesis for Europe.

Interannual and long-term variability of the low level jetstream (LLJ) of the Asian summer monsoon during June to September was studied using reanalysis wind data. In order to study the variability, the domain of the LLJ covering the Indian and west Pacific Oceans was divided into six regions (boxes) based on their physical characteristics. The long term variability of LLJ and its relation with Indian monsoon rainfall and El Nino index were analysed. The low level circulation over Indian Ocean becomes weak during the positive phase of El Nino Southern Oscillation leads to warmer sea surface temperature over Indian Ocean. The strength of the low level jet over India depends on the convective heating of the atmosphere and not on the strength of the south Indian Ocean trade wind (ITz) which remains a passive component of the LLJ. The LLJ flow through peninsular India is weaker and the flow south of peninsular India is stronger during the recent decades in association with increasing number of break monsoon days. The cross equatorial flow over west Pacific Ocean has statistically significant increasing trend related to the increasing convection in the west Pacific Ocean.

Waves are the dominant influence on coastal morphology and ecosystem structure of tropical islands. The geographical positioning of Mauritius near to the Tropic of Capricorn ensures that the eastern regions benefit from the persistent southeast trade winds which influence the incoming surface waves. In this study, we present the high dependence of the wave regimes of windward offshore site on the trade winds. The higher occurrence of incoming waves in the winter season directed in the southeast direction indicates that the trade winds are more prevalent in the winter season. Storms within the extratropical South Atlantic, Indian and Pacific oceans generally propagate towards the east such that extratropical South Atlantic swell energy spreads through the entire Indian Ocean. Since waves are very directional and tend to get shadowed by land masses, Mauritius situated in the line of sight from those sources end up in the shadow region due to the geographical location of Reunion island. In this study, we support the explanation on how the western region of the island gets influenced by episodic swell events. A detailed wave energy resource assessment is provided for different targeted coastal environments around the island. It is revealed that the mean wave power observed in the summer season at one of the sites can attain 28.8 kW/m and is found to be lower as compared to the winter season (31.7 kW/m).

The South Asian summer monsoon (SASM) during the mid-Piacenzian is analyzed through climate modelling with CAM4. The model results reveal a non-uniform spatial difference in the SASM during the mid-Piacenzian compared to the pre-industrial era, with the SASM being more intense north of ~20°N but weaker south of ~20°N. In particular, summer precipitation is higher in South Asia north of ~20°N, accompanied by anomalous low-level southwesterlies from the Arabian Sea, whereas the precipitation is lower in South Asia south of ~20°N, with anomalous low-level easterlies. These differences in the SASM are related to changes in sea level pressure (SLP) due to the different boundary conditions between the two periods. Further analysis isolates the climate effects of the different boundary conditions and indicates the combined difference in atmospheric carbon dioxide concentration and SST to be the most important factor in this difference in the SASM through the changes in SLP. By comparison, the differences in vegetation and topography have limited effects. The availability of geological evidence is relative greater in northern India than in southern India, and comparison with this geological evidence shows the simulated monsoon climate to be qualitatively consistent with it, particularly for the wetter climate in northern India.

Long‐distance migratory flights are predicted to be associated with higher mortality rates when individuals encounter adverse weather conditions. However, directly connecting environmental conditions experienced in‐flight with the survival of migrants has proven difficult. We studied how the in‐flight mortality of 53 satellite‐tagged Black‐tailed Godwits (Limosa limosa limosa) during 132 crossings of the Sahara Desert, a major geographical barrier along their migration route between The Netherlands and sub‐Saharan Africa, is correlated with the experienced wind conditions and departure date during both southward and northward migration. We show that godwits experienced higher wind assistance during southward crossings, which seems to reflect local prevailing trade winds. Critically, we found that fatal northward crossings (15 deaths during 61 crossings) were associated with adverse wind conditions. Wind conditions during migration can thus directly influence vital rates. Changing wind conditions associated with global change may thus profoundly influence the costs of long‐distance migration in the future., Black‐tailed Godwits (Limosa limosa limosa) cross the Sahara Desert twice a year while migrating from their breeding grounds to the sub‐Saharan African wintering grounds. During southward Sahara crossings, godwits experience a higher wind assistance than during northward crossings. Critically, fatal northward crossings were associated with a low wind assistance. In‐flight experienced wind conditions can thus influence the probability to successfully cross a major geographic barrier. Photo: Jan van de Kam.

Sea salt aerosol in the boundary layer below shallow cumulus clouds is remotely observed with a Ka-band cloud radar at the Barbados Cloud Observatory and is detected in 76% of the measurements over 1 year. Carried by convection, sea salt particles with a diameter larger than 500 nm show an upward motion of 0.2 m s−1 below shallow cumulus clouds for a 2-day case study. Caused by an increasing relative humidity with increasing altitude, the sea salt particles become larger as they move closer to the cloud base. By using combined measurements of a Ka-band cloud radar and a Raman lidar, the retrieved equivolumetric diameter of the hygroscopically grown sea salt particles is found to be between 6 and 11 μm with a total number concentration of 20 cm−3 near cloud base. Assuming a fixed shape parameter, a size distribution of sea salt particles under high-relative-humidity conditions below cloud base is estimated and agrees with measurements taken by a dry-deposition sampler and online aerosol observations. The methods outlined in this paper can be used in future studies to get a better understanding of the vertical and temporal sea salt distribution in the boundary layer and sea salt aerosol–cloud interaction processes.

The westerlies and trade winds over the South Atlantic and Indian Ocean are important drivers of the regional oceanography around Southern Africa, including features such as the Agulhas current, the Agulhas leakage and the Benguela upwelling. The Agulhas leakage is the transport of warm and saline water from the Indian Ocean into the South Atlantic. The leakage is stronger during intensified westerlies and probably also when the wind systems are shifted poleward. Here we analyzed the wind stress of different observational and modelled atmospheric data sets (covering the last two millennia, the recent decades and the 21st century) with regard to the intensity and position of the south-easterly trades and the westerlies. The analysis reveals that variations of both wind systems go hand in hand. A poleward shift and intensification of westerlies and trades took place during the recent decades. Furthermore, the upwelling in South Benguela slightly intensified and the characteristics of the water masses fed into the upwelling region changed with a poleward shift of the trades. Projections for strength and position of the westerlies in the 21st century depend on assumed CO2 emissions. In the strongest emission scenario a further southward displacement will occur, whereas a northward shift is modelled in the weakest emission scenario, possibly due to the dominating driving effect of ozone recovery. Thus, the Agulhas leakage has intensified during the last decades and is projected to increase if greenhouse gas emission are not reduced. This will have a small impact on Benguela upwelling strength, but will have consequences for water mass characteristics in the upwelling region. An increased contribution of Agulhas water to the upwelling feed water masses will import more preformed nutrients and oxygen into the upwelling region.

Indigenous peoples across the world observe the motions and positions of stars to develop seasonal calendars. Additionally, changing properties of stars, such as their brightness and colour, are also used for predicting weather. Combining archival studies with ethnographic fieldwork in Australia's Torres Strait, we explore the various ways Indigenous peoples utilise stellar scintillation (twinkling) as an indicator for predicting weather and seasonal change, discussing the scientific underpinnings of this knowledge. By observing subtle changes in the ways the stars twinkle, Meriam people gauge changing trade winds, approaching wet weather, and temperature changes. We then explore how the Northern Dene of Arctic North America utilise stellar scintillation to forecast weather., Proceedings of the Royal Society of Victoria

Recent paleoclimatic studies suggest that changes in the tropical rainbelt across the Atlantic Ocean during the past two millennia are linked to a latitudinal shift of the Intertropical Convergence Zone (ITCZ) driven by the Northern Hemisphere (NH) climate. However, little is known regarding other potential drivers that can affect tropical Atlantic rainfall, mainly due to the scarcity of adequate and high-resolution records. In this study, we fill this gap by reconstructing precipitation changes in Northeastern Brazil during the last 2,300 years from a high-resolution lake record of hydrogen isotope compositions of plant waxes. We find that regional precipitation along the coastal area of South America was not solely governed by north-south displacements of the ITCZ due to changes in NH climate, but also by the contraction and expansion of the tropical rainbelt due to variations in sea surface temperature and southeast trade winds in the tropical South Atlantic Basin., We thank Fanny Kaczmar (LOCEAN-UPMC) and Ralph Kreutz (MARUM) for their support during the analyses, Igor M. Venancio (INPE) for comments about this paper. The lipid extractions were supported by LOCEAN/IRD. The isotope analyses were supported by the DFG-Research Center/Cluster of Excellence, “The Ocean in the Earth System” at MARUM - Center for Marine Environmental Sciences. This work was supported by the Fundação de Amparo a Pesquisa do Estado de São Paulo (FAPESP), Brazil through NSF Dimensions-Biota FAPESP grant 2013/50297 and PIRE NSF-FAPESP Grants 2017/50085-3 to F.W.C as well as the post-doc fellowship to V.F.N (2016/15807-5) and the US National Science Foundation NSF grants AGS-1303828 and OISE-1743738 to MV and 1103403 to R.L.E and H.C. We thank Coordenação de Aperfeiçoamento de Pessoal de Nível Superior, Brazil (CAPES) fellowship to G.U. Grant 99999.012754/2013-07 as well as the post-doc fellowship through the Postgraduate Program on Geochemistry and Geotectonics, Geoscience Institute of the University of São Paulo.

One year of deep-water wave hourly records collected by a buoy deployed off Ceará state, northeastern Brazilian coast, were used to estimate some regional wave climate characteristic sand annual cycles. Waves generated by four wind sources were identified. Southeastern direction showed to be the most effective, especially in the period from June to November due to southeast trade winds system intensification. Several dispersive arrivals of north Atlantic swell were recorded, and their generation zones were identified, which allows determining the region of main sources of these northern waves. Analysis of sea storms showed that although most of them had southeast direction, they could also come from the north. These northern storms sometimes are highly energetic, leading to damage in coastal structures. Only 37 records in the analyzed dataset around 0.4% of the total contained rogue waves. Although the number of occurrences of rogue waves was small, all of them were higher than 2.5 m. One year of deep-water wave hourly records collected by a buoy deployed off Ceará state, northeastern Brazilian coast, were used to estimate some regional wave climate characteristic sand annual cycles. Waves generated by four wind sources were identified. Southeastern direction showed to be the most effective, especially in the period from June to November due to southeast trade winds system intensification. Several dispersive arrivals of north Atlantic swell were recorded, and their generation zones were identified, which allows determining the region of main sources of these northern waves. Analysis of sea storms showed that although most of them had southeast direction, they could also come from the north. These northern storms sometimes are highly energetic, leading to damage in coastal structures. Only 37 records in the analyzed dataset around 0.4% of the total contained rogue waves. Although the number of occurrences of rogue waves was small, all of them were higher than 2.5 m. 2020-11-01

Resumo Neste trabalho é apresentada uma revisão sobre métodos para cálculo do desvio padrão da direção do vento horizontal (σθ). Três diferentes métodos clássicos encontrados na literatura [Verral e Williams, 1982 (VW), Ackermann, 1983 (ACK), e Yamartino, 1984 (YM)] são avaliados a partir de intercomparação entre eles utilizando-se dados de vento obtidos por radiossondagens. Estas medidas foram realizadas a cada seis horas durante um período de 11 dias do mês de setembro de 2008 (estação seca da região Norte do NE do Brasil, com ventos alísios intensos). Os cálculos mostraram que o método de YM apresentou-se o mais confiável, sendo que os resultados de VW foram muito próximos de YM. Comparando os métodos dois a dois, as máximas diferenças foram de 29 graus entre ACK e YM e 26,3 graus entre ACK e VW, enquanto que entre YM e VW a máxima diferença foi de apenas 2,6 graus. Segundo a literatura revisada, YM é o método mais estável ao longo da variação de σθ, com erro de, no máximo, 2%. Abstract In this paper, a review about three classical methods for calculating the standard deviation of the horizontal wind direction (σθ) is presented. These methods described by Verral and Williams, 1982 (VW), Ackermann, 1983 (ACK), and Yamartino, 1984 (YM) are evaluated by intercomparison between them using wind data obtained from radiosonde measurements. These measurements were taken every six hours over a period of 11 days of September 2008 (dry season of the north of NE region of Brazil, with strong trade winds). Calculations indicated that YM method showed to be the most reliable, whereas the results of VW were very close to YM. Comparing the methods two by two, the maximum differences were 29 degrees between ACK and YM and 26.3 degrees between ACK and VW, while between YM and VW the maximum difference was only 2.6 degrees. According to the reviewed literature, YM is the most stable method over the range of σθ, with maximum error of 2%.

Wind speed data obtained from the National Centers for Environmental Prediction (NCEP) Reanalysis project are used to construct winter (November–March) wind indices for the western Iberian Peninsula. The data used represent a 2.5&deg square area, centred at 41.0&deg N, 9.4&deg W, over the period 1948-2003. The NCEP data are well correlated with a time-series (1980–2001) of wind measurements from the Cape Carvoeiro lighthouse on the western Portuguese coast (39.4&deg N, 9.4&deg W). The new indices, of which there are four corresponding to northerlies, easterlies, southerlies and westerlies, constitute measures of numbers of significant wind event days, where a significant wind event is defined to be 4 or more consecutive days of wind speeds exceeding 4 m s-1. Results show both intra- and inter-annual variations in the numbers of significant wind event days, as well as clear decadal trends. A comparison between a hybrid index, composed of the numbers of significant northerly and easterly wind event days - both promote offshore transport, which is thought to have a negative impact on pelagic fish recruitment - and western Iberian sardine catch data, reveal an extensive period of significant negative correlation. The relationship over the most recent period, ~1999–2000, is unclear.

The southern Caribbean Sea experiences strong coastal upwelling between December and April due to the seasonal strengthening of the trade winds. A second upwelling was recently detected in the southeastern Caribbean during June–August, when local coastal wind intensities weaken. Using synoptic satellite measurements and in situ data, this mid-year upwelling was characterized in terms of surface and subsurface temperature structures, and its mechanisms were explored. The mid-year upwelling lasts 6–9 weeks with satellite sea surface temperature (SST) ~1–2° C warmer than the primary upwelling. Three possible upwelling mechanisms were analyzed: cross-shore Ekman transport (csET) due to alongshore winds, wind curl (Ekman pumping/suction) due to wind spatial gradients, and dynamic uplift caused by variations in the strength/position of the Caribbean Current. These parameters were derived from satellite wind and altimeter observations. The principal and the mid-year upwelling were driven primarily by csET (78–86%). However, SST had similar or better correlations with the Ekman pumping/suction integrated up to 100 km offshore (WE100) than with csET, possibly due to its influence on the isopycnal depth of the source waters for the coastal upwelling. The mid-year upwelling was not caused by dynamic uplift but it might have been enhanced by the seasonal intensification of the Caribbean Current during that period.

The period of Harmattan season in Nigeria occurs between the month November and March, this is characterized by dry and dusty north easterly trade wind which blows from the Sahara Desert over Nigeria. Samples of the dust were collected at Iwo (7o 63'N, 4o 19'E) and Oyo (8o 12'N, 3o 42'E). The samples were analysed using AAS (Atomic Absorption Spectroscopy) machine located at Bowen University Iwo. It was observed that the sample of dust particle collected by the means of distilled water in Iwo town contains Ca (22.278ppm), Mg (8.904ppm), and Fe (2.133ppm), and the sample of dust particle collected by the means of the first rain water of the year under consideration contains Ca (5.494ppm), Mg (6.417ppm), and Fe (0.741ppm). For Oyo location, it was observed that the sample of dust particle which was collected by the means of distilled water contains Ca (17.701ppm), Mg (11.751ppm), and Fe (3.729ppm). More so, the sample of dust particle collected by the means of rain water for Oyo contains Ca (4.138ppm), Mg (4.074ppm), and Fe (0.412ppm). The results showed that there was less effect of harmattan dust on human health due to zero or no lead (Pb) content present in the same collected during the period. Keywords: Harmattan, Distilled Water, Sahara Desert, Iwo and Oyo

Cruise data sets, satellite remote sensing observations, and model data analyses are combined to highlight the existence of a coastal surface poleward flow in the southwest of Madagascar: the Southwest MAdagascar Coastal Current (SMACC). The SMACC is a relatively shallow (

Predicting North Atlantic hurricane activity months in advance is of great potential societal significance. The ocean temperature, both in terms of North Atlantic/tropical averages and upper ocean heat content, is demonstrated to be a significant predictor. To investigate the relationship between the thermal state of the Atlantic Ocean and the tropical cyclone (TC) activity in terms of accumulated cyclone energy (ACE), we use observed 1980-2015 TC records and a 1/4 degrees resolution global ocean reanalysis. This paper highlights the nonlocal effect associated with eastern Atlantic Ocean temperature, via a reduction of wind shear, and provides additional predictive skill of TC activity, when considering subsurface temperature instead of sea surface temperature (SST) only. The most active TC seasons occur for lower than normal wind shear conditions over the main development region, which is also driven by reduced trade wind strength. A significant step toward operationally reliable TC activity predictions is gained after including upper ocean mean temperatures over the eastern Atlantic domain. Remote effects are found to provide potential skill of ACE up to 3 months in advance. These results indicate that consideration of the upper 40-m ocean average temperature improves upon a prediction of September Atlantic hurricane activity using only SST.