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Mesoscale datasets are used to study coastal gradients in the marine climate and oceanography in False Bay, south of Cape Town. Building on past work, satellite and ocean–atmosphere reanalyses are used to gain new insights into the mean structure, circulation and meteorological features. HYCOM v3 hindcasts represent a coastward reduction of mixing that enhances stratification and productivity inshore. The mean summer currents are westward 0.4 m s−1 along the shelf edge and weakly clockwise within False Bay. The marine climate is dominated by southeasterly winds that accelerate over the mountains south of Cape Town and fan out producing dry weather. Virtual buoy time series in December 2012–February 2013 exhibit weather-pulsed upwelling in early summer interspersed with quiescent spells in late summer. Intercomparisons between model, satellite and station data build confidence that coupled reanalyses yield opportunities to study air–sea interactions in coastal zones with complex topography. The 0.083∘ HYCOM reanalysis has 16 data points in False Bay, just adequate to resolve the coastal gradient and its impacts on ocean productivity.

Near-surface winds around the mountainous Caribbean islands contribute to orographic lifting and thermal diurnal rainfall that requires mesoscale analysis. Here, a new perspective is presented via high-resolution satellite and reanalysis products. Singular value decomposition is applied to 5 km cold-cloud duration satellite data to understand the leading mode of seasonal hydro-climate variability and its regional controls. The spatial loadings reflect wet islands in a dry marine climate, while temporal amplitude is modulated by the large-scale zonal circulation. When summer-time trade winds weaken, daytime confluence around Caribbean islands enlarges, gathering and lifting more moisture. In addition to the static geographic forcing, transient easterly waves impart the majority of marine rainfall between June and September. Higher resolution products capture the thermal orographic effect and reveal upward trends in island rainfall and soil moisture over the satellite era, while lower resolution products miss this effect. The climate of mountainous Caribbean islands is trending toward increased runoff and soil moisture.

The rate of change in the marine environment over the eastern Agulhas Bank along the south coast of South Africa (32–37∘ S, 20–30∘ E) is studied using reanalysis observations for 1900–2015 and coupled ensemble model projections for 1980–2100. Outcomes are influenced by resolution and time span: ∼ 1∘ datasets covering the whole period capture large-scale changes, while ∼ 0.5∘ datasets in the satellite era better distinguish the cross-shelf gradients. Although sea surface temperatures offshore are warming rapidly (0.05 ∘C yr−1 since 1980), a trend toward easterly winds and a locally stronger Agulhas Current have intensified nearshore upwelling (−0.03 ∘C yr−1). The subtropical ridge is gradually moving poleward, leading to a drier climate.

South Indian Ocean Rossby waves (SIO-RW) are identified in the Global Ocean Data Assimilation System (GODAS) 1.5–7 yr filtered sea surface height (SSH) time series. There is a persistent three-year...

Sea level (SL) is rising in Puerto Rico due to regional influences from weaker trade winds, in addition to global influences of thermal expansion and polar ice melt. The linear increase of SL has steepened in recent decades from +0.175 to +0.725 cm/yr. The faster rate of SL rise is partly attributed to diminishing ice volume (r = −0.80), notwithstanding a recent decline in the Atlantic Multi-decadal Oscillation. A sophisticated point-to-field regression analysis (N = 5980) demonstrates that daily fluctuations of SL in Puerto Rico are significantly enhanced by locally warmer sea temperatures via reduced evaporation, and correspond with lower air pressure accompanying late summer storms. These features point to regional air-sea interactions that affect SL rise over and above the background global signal. Extrapolating these trends, a rise of more than 0.3 m is expected by 2050.

Jury, M.R., 2018. Characteristics and meteorology of Atlantic swells reaching the Caribbean. The characteristics of Atlantic swells reaching the Caribbean (19° N, 66° W) are described using wave hindcast and buoy datasets. The methods include calculation of histograms, scatterplots, temporal trends, ranking of extremes, meteorological case analysis, comparison of alternative datasets, and an assessment of similarity between cases. Northerly swells occur 29% of the time, with a mean height and period of 2 m and 8 seconds. A slight upward trend in wave period during 1998–2013 was related to an expanding anticyclonic Hadley circulation in the northwest Atlantic. An extreme case analysis illustrates how a storm near Bermuda on 16–20 March 2008 intensified as high pressure near Greenland blocked its progression. The cold air outbreak from the storm and 20 m/s northerly wind gusts induced heat fluxes up to 1000 W/m2 over the Gulf Stream outflow. Swells >6 m traveled southward, attenuating to 4–5 m and ...

The modulation of near-surface currents off Durban (29.9S, 31E) is studied using monthly and daily ocean and atmosphere reanalysis products. Poleward flow on the shelf-edge exhibits long-lived 2–3 yr and 50–150 day fluctuations, whereas cyclonic circulations inshore exhibit short-lived ∼ 6 day pulsing by coastal winds. Monthly meridional currents near Durban 1979–2015 relate to lower air pressure over the SW Indian Ocean ( ∼ 37S, 40E) that slows the offshore anticyclonic gyre and shelf-edge Agulhas Current. Daily meridional currents near Durban 2009–2015 relate to a pattern of offshore positive / inshore negative sea surface temperatures that propagate poleward at ∼ 7 km/day. The upper ocean structure and circulation off KwaZulu-Natal is analyzed using daily 8 km resolution fields over the area 28–31.5S, 30–33E. The shelf oceanography of a cyclonic shear event on 25–26 October 2010 corresponds with a transient low pressure cell, 12 m/s southwest winds and 5 m swells. A coastal wind jet near Durban deepens the mixed layer >50 m during a cold air outbreak with latent heat flux >250 W/m2. While the regional atmosphere modulates longshore winds and inshore currents at high frequency, the offshore anticyclonic gyre pulses the shelf-edge Agulhas Current at low frequency in association with poleward moving eddies. As these advance down the coast, water draws off the shelf contributing to upwelling and productivity.

Regional factors modulating eastern Venezuela coastal upwelling emerge from this observational study. Trade winds of 3–9 m/s are a persistent feature of the shelf zone, and drive offshore Ekman transport and pumping, cooling SST by 1–3 °C especially in spring. Wavelet spectral analysis of SST anomalies (11oN, 65oW) show significant intra-seasonal (9, ∼ 45, ∼ 100 days) and inter-annual oscillations ( ∼ 3, 9 years). A case study upwelling event of 3–5 May 2014 is distinguished by a low level wind jet on the shelf edge. An ocean eddy propagated westward along the shelf, initially suppressing then enhancing offshore transport. Venezuela SST variability reflects atmospheric control by the North Atlantic anticyclone and associated trade wind-driven shelf water transport and regional evaporation. Eastern Venezuela coastal upwelling involves an atmospheric meridional overturning circulation that affects the frequency of Caribbean hurricanes.

Climatic trends in the southeastern Antilles island chain are analysed via reanalysis datasets in the period 1980–2014. Although a homogeneous marine climate surrounds these small islands embedded in northeast trade winds, the analysis presented here reveals spatial gradients in climatic trends during the satellite era. In the axis of the fresh North Brazil Current, sea surface temperature (SST) trends are steep (+0.04 °C year−1) and correspond with weaker winds and rising ozone concentrations (+0.15 DU year−1). Subsidence and meridional wind trends are related to an acceleration in the Hadley overturning atmospheric circulation which heats the trade wind inversion. Expanded wind shadows induce warmer SST, greater latent heat flux and deeper convection west of the Antilles islands. While rainfall has decreased in Trinidad and eastern Venezuela, the mountainous islands of Guadeloupe, Dominica and Martinique have increasing rainfall (+0.02 mm day−1 year−1) in the satellite era. Weakening ocean currents near Grenada may reflect a diminishing of the global thermohaline meridional overturning circulation.

Jury, M.R., 2017. Multiple drivers of intense coastal upwelling at Cape Town. Cape Town, South Africa is well known for its intense coastal upwelling during austral summer. This study provides new insights using daily 4–9 km resolution satellite and ocean reanalysis datasets in the period 2009–2015. A key purpose of this work is to highlight the value of these finely detailed products in coastal research. The most intense case of 23–24 January 2011 revealed a cold plume

Over the past three decades, marine resource management has shifted conceptually from top-down sectoral approaches towards the more systems-oriented multi-stakeholder frameworks of integrated coastal management and ecosystem-based conservation. However, the successful implementation of such frameworks is commonly hindered by a lack of cross-disciplinary knowledge transfer, especially between natural and social sciences. This review represents a holistic synthesis of three decades of change in the oceanography, biology and human dimension of False Bay, South Africa. The productivity of marine life in this bay and its close vicinity to the steadily growing metropolis of Cape Town have led to its socio-economic significance throughout history. Considerable research has highlighted shifts driven by climate change, human population growth, serial overfishing, and coastal development. Upwelling-inducing winds have increased in the region, leading to cooling and likely to nutrient enrichment of the bay. Subsequently the distributions of key components of the marine ecosystem have shifted eastward, including kelp, rock lobsters, seabirds, pelagic fish, and several alien invasive species. Increasing sea level and exposure to storm surges contribute to coastal erosion of the sandy shorelines in the bay, causing losses in coastal infrastructure and posing risk to coastal developments. Since the 1980s, the human population of Cape Town has doubled, and with it pollution has amplified. Overfishing has led to drastic declines in the catches of numerous commercially and recreationally targeted fish, and illegal fishing is widespread. The tourism value of the bay contributes substantially to the country’s economy, and whale watching, shark-cage diving and water sports have become important sources of revenue. Compliance with fisheries and environmental regulations would benefit from a systems-oriented approach whereby coastal systems are managed holistically, embracing both social and ecological goals. In this context, we synthesize knowledge and provide recommendations for multidisciplinary research and monitoring to achieve a better balance between developmental and environmental agendas.

Cape Frio at the Angola-Namibia border, is the northern-most coastal upwelling cell of the Benguela Current (~17S, 11E) and is sensitive to climate variability. This study provides new insights using daily high resolution satellite and ocean-atmosphere reanalysis datasets in the period 1985–2015. The annual cycle of SST follows two months behind the net heat balance and wind stress curl, reaching a minimum in July–September. Ranking the daily SST record, two intense multi-day upwelling events stand out. The more recent case of 26–29 August 2005 is studied, given the greater density and sophistication of satellite data. A coastal wind jet >10 m s−1 develops next to Cape Frio, with sharp edges imposed by a thermal inversion and the mountainous cape. The cold plume

The bi-modal climate of SE Ethiopia shares attributes with East Africa, notably that El Nino enhances rainfall, particularly in Sep–Nov season. In this study SE Ethiopia’s continuous and seasonal rainfall relationships to global climate are studied to extend our knowledge of its determinants and predictability. A statistical forecast algorithm for the Sep–Nov short rains accounts for 54% of variance in 1980–2010. The Apr–Jun predictors include South Atlantic sea surface temperature, east Indian Ocean sea level air pressure and China upper zonal wind. Cooling in the South Atlantic coincides with a strengthened sub-tropical anticyclone, and later to changes in low level winds that bring orographic convection to SE Ethiopia. The slower El Nino–Southern Oscillation (ENSO) interacts with the faster Indian Ocean Dipole (IOD), but both signals mature too late for direct use in statistical prediction of Sep–Nov rainfall. Composite differences of the upper divergent circulation exhibit a global wave-2 pattern consistent with satellite-observed convection. One key feature is a zonal gradient in upper velocity potential over the Indian Ocean corresponding with a zonal atmospheric circulation. One outcome of this research is useful forecasts of SE Ethiopia Sep–Nov rainfall that will assist in agricultural planning.

This study analyzes a convective outbreak over the Red Sea on 25 August 2009 that generated easterly waves over the Sahel, floods in Ouagadougou, and a hurricane in the east Atlantic. The convective outbreak occurred on the equatorward flank of the African easterly jet 18°–22°N and associated meridional heating gradients over the Arabian Peninsula. The Rift Valley mountains induced a vertical orographic undulation and cyclonic perturbation. Two thunderstorm clusters over the southern Red Sea received moist inflow from the Ethiopian highlands and northern Red Sea. This group of three easterly waves intensified downstream over the Sahel. One of the convective triggers was enhancement of the Arabian Ridge by the northern subtropical jet. Statistical analyses indicate that African easterly waves and subsequent tropical storms are more influenced by upstream kinematic shear than thermodynamic energy. The work offers new insights on the formation of easterly waves over the northern Rift Valley.

Sand transport around the northeastern Caribbean Virgin Islands (VI) is studied using global data-assimilation products and satellite measurements; with a focus on seasonal and event characteristics in the period 2002–2019. A review of applied research and a local statistical analysis indicate that currents accompanied by waves and wind mixing are capable of scouring near-shore sand bars. VI area (18.4–18.6N, 65.5–64.5W) time series analysis offer insights on the processes underlying suspended sediment concentrations estimated by 5 km resolution MODIS and VIIRS satellite red-band radiance. The winter season peak in turbidity derives from trade wind-driven waves and currents that reach critical thresholds to mobilize and transport the coarse sands. Instead of wave height, wave steepness and mixed layer depth are applied as coefficients to HYCOM3 near-surface currents, to create a multi-variate sand transport index. Statistical regression shows that a strengthened North Atlantic anticyclone and associated winter trade winds in the VI archipelago results in surface cooling and a deep mixed layer, making steep waves and westward currents more effective in sand transport. The leading case of satellite red-band radiance followed many months after the passage of tropical cyclones in September 2017. A sustained spell of intense trade winds in February 2018 induced 3 m waves of 3% steepness and near-surface currents up to 0.5 m/s. Rapid sea level oscillations >0.05 m suggest that long-period waves joined local wind-waves to mobilize coarse sands within a mixed layer >50 m deep. The plume of sand exhibited composite VIIRS red-band radiance of 0.1 W m−2 μm−1 sr −1; supplying coarse light-colored sands to downstream Caribbean islands. This study has universal application to near-shore sand transport by demonstrating the use of a high-resolution multi-variate index from freely available global data-assimilation products. Given rising sea levels, beach erosion and limited field data, such an index is an essential tool in coastal management.

Inter-relationships between physical ocean-atmosphere processes over the eastern Agulhas Bank are explored using data assimilation by the Hybrid Coordinate Ocean Model (HYCOM), which provides daily fields and time series off the south coast of South Africa (33.75–34.5S, 24.0–26.5E) in the period 2009–2017. Our objectives are: i) to describe and understand the sharp gradients over the shelf, ii) to quantify the temporal controls and lagged uptake of weather events and, iii) to analyze the spatial effects of capes on mesoscale oceanographic structure. Sea surface temperature (SST) and zonal winds (U-wind) were cross-correlated with salinity, currents, waves and atmospheric variables such as heat budget components, air pressure (SLP), air temperature. Correlations were made over daily and annual time scales to identify the leading ocean-atmosphere interactions and the strength of processes. At daily time scales weak correlations were found between SST and a variety of ocean-atmosphere parameters, suggesting that multiple processes affect the thermodynamic condition. SST showed most correlation with radiation and heat budget components (r = −0.35, 0.39), SLP (r = −0.30) and meridional currents (r = −0.26). In contrast, the simultaneous correlation of SST with U-wind was weak (r = −0.08). We attribute this to: i) delayed response, ii) opposing effects of coastal upwelling and summer heating, and iii) competing shelf-edge processes. Over the mean annual cycle, correlations between SST, U-winds, salinity, radiative fluxes and V-currents were strong, indicating how kinematic and thermodynamic controls conspire to induce seasonality. SST was well correlated (r Case studies of transient cold and warm events south of South Africa are described to reveal the large-scale atmospheric forcing of local SST. In addition, comparisons between the HYCOM reanalysis time series and independent insitu data are provided as a measure of confidence in global data assimilation systems, which open new opportunities for mesoscale oceanographic research in coastal zones.

Trends in near-surface currents passing through the southeastern Caribbean are described using ocean reanalysis and a coupled model projection. The decline of Caribbean through-flow is linked with tropical and polar forcing. In the upstream zone, the North Brazil Current shows increasing retroflection as the southern Hadley Cell expands across the equatorial Atlantic. This inhibits northwestward transport next to the Amazon River plume. In the downstream zone, the Labrador Current feeds low saline Arctic waters into the Gulf Stream, inducing an equatorward shift and reduced flow. Evidence is growing for spin-down of the North Atlantic gyre and its feeder currents, that inhibit poleward heat exchange and contribute to climatic shifts. Eastward trends of winds and currents in the equatorial Atlantic is projected to bring a drier climate to the lower Amazon basin and southeastern Caribbean, hence greater salinity with knock-on effects for regional sea temperatures.

Hydro-meteorology conditions in the Southwest Cape of South Africa are analyzed for historical trends in satellite and station measurements. Results show an increase of coastal upwelling, low-level subsidence and shorter winters. The shearing by offshore easterly winds causes a circulation over the SW Cape which entrains dry air from the south coast upwelling zone. Potential evaporation exceeds precipitation and streamflow discharge has declined particularly northwest of the Hottentots Holland mountains. Many of Cape Town's water reservoirs are drying up, and show steep in-creases in surface temperature (+.2 C/yr) and browning of perimeter vegetation. The unfavorable wind shear is compounded by negative sensible heat flux and a capping inversion, so alongshore winds and mountain-top clouds divert seaward, desiccating the upper Berg River catchment.

This study reconsiders the role of the Agulhas Current in South African climate variability. Here, the Agulhas Current is delimited by its anticyclonic looping flow and cluster analysis of detrended SST anomalies that lead to an area 28°–37°S, 18°–35°E, poleward of South Africa. Regression of detrended Agulhas SST with rainfall anomaly fields in the years 1950–2012 yields a surprising negative influence over the interior. In summer, the negative regression exhibits a northwest axis consistent with reduced cloud band activity. Positive influence is confined to the eastern escarpment in the September–November season when cutoff lows are prevalent. The overall negative influence of the Agulhas SST is confirmed by regression with the vegetation fraction and latent heat flux in the satellite era. Mechanisms of South African rainfall suppression were investigated. The Agulhas SST index is positively related to the multivariate ENSO index at the 1–3-month lead time. Hence, warm years in the Agulhas Current follow Pacific El Niño. Composite ocean analysis shows enhanced westerly winds offshore and a westward extension of warm salty water from the anticyclonic south Indian Ocean gyre. Composite atmospheric analysis exhibits moist uplifted air over the Agulhas Current folding into an equatorward circulation that sinks over the interior plateau. Because Agulhas SST partially follows ENSO, its suppression of interior rainfall is concluded to be passive.

Climate variability in the eastern Antilles island chain is analyzed via principal component analysis of high-resolution monthly rainfall in the period 1981–2013. The second mode reflecting higher rainfall in July–October season between Martinique and Grenada is the focus of this study. Higher rainfall corresponds with a weakened trade wind and boundary current along the southern edge of the Caribbean. This quells the coastal upwelling off Venezuela and builds the freshwater plume east of Trinidad. There is corresponding upper easterly wind flow that intensifies passing tropical waves. During a storm event over the Antilles on 4–5 October 2010, there was inflow from east of Guyana where low salinity and high sea temperatures enable surplus latent heat fluxes. A N–S convective rain band forms ∼500 km east of the cyclonic vortex. Many features at the weather timescale reflect the seasonal correlation and composite difference maps and El Nino Southern Oscillation (ENSO) modulation of oceanic inter-basin transfers.

This study considers tropical cyclones Irene in Puerto Rico from 2011 and Isaac in the Dominican Republic from 2012. Impacts trailed more than a day after the storm in both cases. Irene passed Puerto Rico on 22 August 2011, yet bands of heavy rainfall caused floods and disruption on 23 August. In the second case, Isaac passed Hispaniola on 24 August 2012, but stormy weather continued on 25 August. Onshore winds, 4-m waves, and associated tides and river outflow closed the harbor of Santo Domingo. Emergency managers and maritime operators should be aware of the delayed impacts of tropical cyclones in the Caribbean Sea region.

Interannual variability of tropical cyclones (TCs) in the eastern Caribbean is studied using MIT-Hurdat fields during the July–October season from 1979 to 2008. TC intensity shows local climate sensitivity particularly for upper ocean currents, salinity and mixed-layer depth, and 200–850 mb wind shear. Remote influences from the Southern Oscillation, Saharan dust, and the South American monsoon are also identified as important. Ocean currents diminish along the coast of South America, so interbasin transfer between the North Brazil and Caribbean Currents declines in seasons of frequent and intense TCs. This is related to a dipole pattern in the sea surface height formed mainly by reduced trade wind upwelling northeast of Venezuela. A low-salinity plume from the Orinoco River spreads across the eastern Caribbean. It is the weaker currents and shallower mixed layer that conspire with surplus heat to build thermodynamic energy available for TC intensification.

Annual field surveys conducted at Ponta do Ouro in Southern Mozambique have determined that coastal variability is driven by high wave energy and consequent northward longshore drift. There is a log-spiral headland-bay system marked by 80 m tall forested dunes in the south that give way to a broad flat sandy beach. Marine climate processes that affect coastal erosion and accretion are studied using local and remote data sets. Since surveys began, the climate has undergone a prolonged dry spell (2002-2007) followed by increased run-off and easterly winds (2010-2013) that have re-built the beaches. Sand grain sizes vary from 240 - 410 i­m (coarser south – finer north) and are mobilized by frequent longshore wind events > 10 m/s. Ocean drifters reveal a northward current in the outer surf zone of 0.6 m/s and an onshore gyre of 0.1 m/s in the recessed bay. Wave-driven sand transport is estimated at 5 106 kg/yr/m. While the upper beach has flattened due to pedestrian traffic and urban development, the lower beach has recovered from erosion due to a greater frequency of easterly waves and rainy weather. Key words: Beach, coastal erosion, marine climate.

This study considers eastern Antilles (11°–18°N, 64°–57°W) weather and climate interactions in the context of the 2013 Christmas storm. This unseasonal event caused flash flooding in Grenada, St. Vincent, St. Lucia, Martinique, and Dominica from 24 to 25 December 2013, despite having winds

The Southern Benguela cape upwelling plumes have inshore wind shadows prone to red tides in late summer. Their intensity and coverage are estimated by satellite fluorescence measurements in the period 1997–2012 and qualified by in situ reports. High satellite fluorescence cases are identified at daily to seasonal time scales, and characteristics of the upper ocean and lower atmosphere are studied using third generation reanalyses. A dominant feature is easterly winds over the Cape Peninsula (34°S, 18°E) induced by a ridging anticyclone-coastal low weather pattern. Over Cape Columbine (33°S), there is a wind shadow with cyclonic wind and current shear. Composite atmospheric profiles reveal a 4°C temperature inversion near 500 m that traps a coastal wind jet >6 m/s below 200 m. The composite shelf oceanography shows a relic upwelling plume below 10 m overtopped by warmer water near the coast, providing the thermal stratification needed for biotic aggregation. Data from the IPSL5 coupled climate model over the period 1980–2080 indicates that environmental conditions favoring red tides may become more frequent.

This observational study examines zonal gradients in the lower atmosphere and upper ocean across the windward Antilles during midsummer 2012. While earlier work reported on meridional confluence, here the focus is on the zonal enrichment of trade winds by upstream shallow seas and islands. Intercomparisons along 18.2°N are made between modern reanalysis and satellite estimates, and coastal station, moored buoy, aircraft, and radiosonde observations for one case and as a June–July 2012 average. Mean gradients per 100 km east of Puerto Rico were 0.2 g kg−1 for 925-hPa specific humidity, 0.16°C for SST, 0.01 m for sea level, and 2.0 × 10−3 g kg−1 for cloud water. Zonal changes in the lower atmosphere occur in three stages: 1) Atlantic, where westward ocean currents, strong trade winds, and subsidence prevail; 2) Antilles, where ocean currents diminish and sea temperatures increase; and 3) island, where trade winds abate [−1 m s−1 (100 km)−1] and diurnal evapotranspiration greater than 10 mm day−1 offsets large-scale subsidence producing a localized convection.

A plume of fresh water, originating from the Amazon and Orinoco Rivers, infiltrates the southeastern Caribbean. Here, some of factors underlying changes of near-surface salinity are investigated using ocean and atmosphere reanalyses that include winds, currents, sea temperature, salinity, rainfall, and river basin run-off during pre-season (April–June) and in-season (July–September) periods 1980–2016. Composite results demonstrate that increased northeasterly trade winds and an accelerated North Brazil Current feed Amazon and Orinoco River water northwestward into the Caribbean, underpinning a 0.5C warming of sea temperature and an increase in the frequency and intensity of passing hurricanes. This chain of events is partially related to the Atlantic meridional mode.

The Turks and Caicos Islands (TCI) climate is described using mesoscale ocean and atmosphere datasets with a focus on thermodynamic versus kinematic controls, the influence of the nearby island of Hispaniola, and factors affecting early colonization and fluctuations of marine resources. The key findings include the following: trade winds accelerate to 7 m s−1 north of Hispaniola and enhance anticyclonic subsidence; there is a dry-south/wet-north pattern of rainfall that opposes surface temperature and salinity fields; ocean currents near TCI are northwestward but there is a counterclockwise gyre near Haiti that guided colonization; conch catch increases when trade winds strengthen and SST declines; TCI's dry climate limits groundwater resources, food production, and population density; and Caicos Island sheds a wind wake that boosts SST and local convection, as evident in Quick Scatterometer (QuikSCAT) observations and operational model products. Further studies of small island climates will benefit from an ever-increasing stream of mesoscale datasets.

This study contrasts the pattern of low-frequency (LF) and high-frequency (HF) climate variability in the eastern Caribbean. A low-pass Butterworth filter is used to study oscillations in rainfall and regional SST on time scales of greater and less than 8 yr in the period 1901–2002. The results show that the southern and northern Antilles are dominated by HF variability, whereas rainfall fluctuations in the eastern Antilles oscillate at quasi-decadal periods over the 102-yr record. In the southern Antilles, the HF rainfall signal derives from a late-summer response to the ENSO phase: warm and dry versus cool and wet. In the northern Antilles, the HF signal relates to a combination of an ENSO and North Atlantic Oscillation (NAO) phase: a warm ENSO and a negative NAO bring wetter conditions, while a cool ENSO and a positive NAO bring drier conditions. The early rainfall LF signal in SST is characterized by a dipole between the North Atlantic and South Atlantic and is associated with cross-equatorial winds that promote convection in the Caribbean. The study analyzes the upper-ocean structure—in particular, a low (high) salinity signal in the tropical North Atlantic (North Pacific) that relates to LF (HF) climate variability.

Ocean and atmosphere reanalysis fields are used to study environmental conditions and their relation to commercial fish catch in the central Benguela upwelling zone, using both targeted and objective techniques. Composite maps and sections indicate a 10%–20% weakening of southeasterly winds, a 0.5°C warming of sea temperatures over the shelf, and changes in currents and subsurface upwelling associated with higher fish catch. During periods of high fish catch, recirculating gyres form that may aid the retention of eggs and larvae. Offshore winds contribute to poleward Ekman transport in a 50-m-deep layer within 100 km of the coast. In addition to composite analysis, the natural variability is studied by principal component analysis of wind stress, sea level, temperature, salinity, currents, and vertical motion in the period 1970–2007. Comparison of interannual time scores and fisheries data indicate that anomalous poleward winds and warmer temperatures in the Lüderitz plume, driven by an atmospheric trough in the South Atlantic, are associated with higher catch rates.

[Extract] The preservation of coral reefs under a changing climate requires a coordinated approach that integrates observational, experimental, and modeling efforts with practical management and sound government policy. Coral reefs are among the most species-rich habitats in the world, but also among the most vulnerable to our current high-emission path. Observations of the climate system have shown an increase in global average surface temperature during the twentieth century, with an increased rate of warming since 1950.

The long-term behavior of the tropical Atlantic ocean/atmospheric system prior to the 20th century is not well characterized due to a lack of high-resolution proxy records to extend the short instrumental record. Here we present the first reconstruction of rainfall variability for the western tropical Atlantic that spans the past 8 centuries and is derived from the δ18O of speleothem calcite. The δ18O of speleothem calcite at this Puerto Rican location varies primarily in response to changes in the amount of summer-time precipitation. The speleothem documents multi-decadal to centennial length oscillations in δ18O that point to large variations in rainfall that have not been manifest in the short instrumental period. Since AD 1850, variations in δ18O have tracked shifts in the Atlantic Multidecadal Oscillation (AMO). We tentatively suggest that the speleothem δ18O-based rainfall record from Puerto Rico extends the history of the AMO to the 12th century.

The meteorological conditions of hurricanes passing near Puerto Rico (18N, 68W) are analyzed using composite daily reanalysis and satellite data. When an intense hurricane is present, the regional circulation is dominated by upper easterly flow over the Caribbean and central Atlantic and a surge of low-level westerly anomalies across the tropics. Warm SST anomalies extend along the coast of Venezuela, doubling the convective energy available to Caribbean hurricanes. Intensifying hurricanes tend to propagate westward with an atmospheric ridge over the Gulf Stream, in an environment with aerosol optical depth

A Caribbean fishery index is used to identify contrasting environmental conditions in atmosphere and ocean reanalysis fields associated with high- and low-catch years over the period 1971–2004. A number of composite features are noted: cooler surface temperatures and warmer, drier weather across the southern half of the Caribbean favors higher catch rates. There is a ridge of elevated sea level on 16°N. South of the ridge the Caribbean Current is strengthened while north of the ridge anomalous eastward currents flow past the Antilles Islands. The atmospheric Hadley circulation weakens in years of high catch and tropical cyclones are rare. This paper uncovers basin-scale forcing of aggregate fish catch, reflecting a north-south gradient in land-atmosphere hydrology, and composite oceanographic differences based on reanalysis data. In addition, seasonal and interannual cycles of ocean productivity are investigated using satellite ocean color. Summertime upwelling along the coast of Venezuela joins fresher waters from the North Brazil Current to infuse the Caribbean ecosystem with higher nutrients.

Climatic conditions that affect the interannual variability of Caribbean hurricanes are studied. Composite meteorological and oceanographic reanalysis fields are constructed for active and inactive seasons since 1979, and differences are calculated for spring and summer periods to provide guidance in statistical analysis. Predictors are extracted for areas exhibiting high contrast between active and inactive seasons, and intercomparisons are made. Zonal winds north of Venezuela exhibit westerly anomalies prior to active years, so coastal upwelling and the north Brazil current are diminished. Rainfall increases in the Orinoco River basin, creating a fresh warm plume north of Trinidad. The predictor time series are regressed onto an index of Caribbean hurricanes, and multivariate algorithms are formulated. It is found that atmospheric kinematic and convective predictors explain only ∼20% of hurricane variance at 3–5-month lead time. Subsurface ocean predictors offer higher levels of explained hurricane variance (42%) at 3–5-month lead time, using 1–200-m-depth-averaged temperatures in the east Pacific and southern Caribbean. We place the statistical results in a conceptual framework to better understand climatic processes anticipating Caribbean hurricanes.

Upper ocean conditions in the Caribbean Sea are studied for long-term variability and trends using filtered surface observations and ocean model reanalysis fields. A principal component analysis is made, and trends in the leading mode are extracted. Sea surface temperature shows an accelerating upward trend while air pressure exhibits quasidecadal fluctuations. Sea surface height and subsurface temperature rise linearly while subsurface salinity exhibits fresher upper and saltier lower layers. The amplitude of warming is highest in the southern Caribbean east of 75°W near 150 m and lowest near the surface, indicating little role for a top-down process such as air-sea exchange. The freshening surface layer does not appear connected to river discharge or regional rainfall, so changes in ocean advection and sources are the likely drivers. Westward currents exhibit a reduction of throughflow and an influx from the Windward Passage. The Caribbean Current has slowed ~0.06 m/s in the reanalysis era. Crop yields show little sensitivity to ocean conditions but tend to follow rainfall. Marine catch per capita in the Caribbean follows subsurface currents and vertical motion but is less affected by temperature and salinity.

The meteorological scenario of Ethiopian highlands floods is studied. Daily rainfall in the period 1997–2007 reveals two peaks: 23–28 July 2006 and 26–31 July 2007. National Center for Environmental Prediction (NCEP) composites suggest that anomalous southerly monsoon flow over the West Indian Ocean is re-directed by an anomalous Arabian ridge westward across the Red Sea and Ethiopia. A tongue of moisture stretches from the Congo towards the highlands, but westerly equatorial wind anomalies are absent. Anomalous sinking motions and dry conditions are evident over the West Indian Ocean. Diurnal analysis reveals northwesterly flow over eastern Sudan during afternoon hours, whilst back-trajectory analysis highlights a Red Sea source and lifting over the eastern escarpment of Ethiopia. The upper level tropical easterly jet connects Indian and Ethiopian rainfall at intra-seasonal (~40 days) time scale; whilst low-level meridional flow convergence is evident during flood events. Hovmoller analysis on 10°N reveals cyclonic signals propagating westward from the Arabian Sea at 500 km day−1 that produces a 10-day cycle in Ethiopian rainfall. The floods in 2006–2007 occurred at the peak of the annual cycle, with diurnal controls inducing ¾ of rain in the late evening. Whilst cold surges from southern Africa played a role in the 2006 flood, bursts in the northern Hadley cell are a more general determinant. The convection associated with the 2007 flood went on to become a destructive Atlantic hurricane.

This study of hurricanes passing through the Caribbean in the 1950–2005 period reveals that seasons with more intense hurricanes occur with the onset of Pacific La Niña events and when Atlantic SSTs west of Africa are above normal. Composites of NCEP reanalysis fields with regard to Caribbean hurricanes reveal development of an anomalous equatorial Atlantic zonal overturning circulation (upper easterly/lower westerly) that shifts toward the Caribbean coincident with a westward spread of the cold tongue in the east Pacific. Ocean–atmosphere coupling is promoted through interaction of the southern Hadley cell and the Atlantic ITCZ. A heat budget analysis suggests that evaporation governs SSTs in the major development region (MDR) and near Venezuela, but the signal is weak prior to May. Using the knowledge gained, statistical algorithms are developed to predict Caribbean hurricanes at seasonal lead times. These make use of equatorial Pacific SST, subtropical Atlantic SST, and the zonal Walker cell over the Atlantic.

Ethiopian decadal climate variability is characterized by application of singular value decomposition to gridded rainfall data over the period 1901–2007. Two distinct modes are revealed with different annual cycles and opposing responses to regional and global forcing. The northern zone that impacts the Nile River and underlies the tropical easterly jet has a unimodal rainy season that is enhanced by Atlantic Multidecadal Oscillation warm phase. This rainfall mode is linked with the Atlantic zonal overturning circulation and exhibits 10–12-year cycles through much of the twentieth century. The southern zone has a bimodal rainy season that is enhanced by Pacific Decadal Oscillation cool phase and the southern meridional overturning circulation. Multiyear wet and dry spells are characterized by sympathetic responses in the near-equatorial trough extending from Central America across the African Sahel to Southeast Asia. The interaction of Walker and Hadley cells over Africa appears to be a key feature that modulates Ethiopian climate at decadal frequency through anomalous north–south displacement of the near-equatorial trough.

The central Antilles Islands experience short periods of heavy rainfall during the spring season (April and May) when trade winds weaken across the Caribbean Sea. Composite analysis of the top 10 flood events in the period 1979–2005 is carried out to understand the meteorological forcing. Cases are selected when mean rainfall over Puerto Rico exceeds 50 mm day−1 and emergency management reports indicate the day is a “declared weather disaster.” In the NCEP–NCAR composite analyses, pulses of moisture shift westward across the tropical Atlantic about 10 days before a flood event. Five days before the composite flood a westerly trough penetrates eastward from the Gulf of Mexico. Northward flow develops over the Caribbean Sea and a southwest-oriented cloud band extends from Colombia toward Puerto Rico. A key feature of the midtropospheric circulation field is the development of anomalous twin rotors east of Florida in the mid- to upper troposphere. The flood events coincide with a change in zonal wind shear from westerly to easterly that is brought about by slow tropical and fast subtropical wave systems.

Teleconnections between equatorial African climate and the surrounding circulation are examined using a convective index over the Congo River Basin in March to May (MAM) and July to September (JAS) seasons. Its influence on the wider region is determined through lag correlation and cross-wavelet analysis. During seasons of deeper convection, easterly winds weaken over the tropical Atlantic (anomalous flow toward Africa), whilst upper westerly winds weaken over southern Africa (in JAS). We view this as zonal overturning with ascent over the equatorial African lowlands and Congo River Basin that spreads moisture to the North African Sahel, with influence from the Pacific El Nino. Another facet of our study is the relationship between East African highlands rainfall and the Indian Ocean circulation. We find coupling between the Indian Ocean Rossby wave, a thermocline oscillation and Walker cell over the Indian Ocean that induces shifts in rainfall, particularly in the October to December season.

The frequency of major hurricanes over the Atlantic Ocean has increased significantly since 1995, but it is still not clear whether this is due to global warming or natural variability. One way to address this question is to consider changes in hurricane frequency in the past, but reliable observations of Atlantic hurricane activity only cover a few decades. Nyberg et al. use proxy records from corals and a marine sediment core that appear to reflect changes in the two main parameters that influence hurricane activity — vertical wind shear and sea surface temperature — to reconstruct the frequency of major hurricanes over the Atlantic since 1730. The results indicate that the frequency was anomalously low during the 1970s and 1980s compared with the past 270 years, and that the phase of increased hurricane frequency since 1995 represents a recovery to 'normal' hurricane activity. These trends appear to be related to wind shear, but what caused this parameter to change remains uncertain. Proxy records from corals and marine sediment core that reflect changes in vertical wind shear and sea surface temperature (the two main parameters that influence hurricane activity) are used to reconstruct the frequency of major hurricanes over the Atlantic since 1730. The results indicate that the frequency of major hurricanes was anomalously low during the 1970s and 1980s compared to the past 270 years. Hurricane activity in the North Atlantic Ocean has increased significantly since 1995 (refs 1, 2). This trend has been attributed to both anthropogenically induced climate change3 and natural variability1, but the primary cause remains uncertain. Changes in the frequency and intensity of hurricanes in the past can provide insights into the factors that influence hurricane activity, but reliable observations of hurricane activity in the North Atlantic only cover the past few decades2. Here we construct a record of the frequency of major Atlantic hurricanes over the past 270 years using proxy records of vertical wind shear and sea surface temperature (the main controls on the formation of major hurricanes in this region1,3,4,5) from corals and a marine sediment core. The record indicates that the average frequency of major hurricanes decreased gradually from the 1760s until the early 1990s, reaching anomalously low values during the 1970s and 1980s. Furthermore, the phase of enhanced hurricane activity since 1995 is not unusual compared to other periods of high hurricane activity in the record and thus appears to represent a recovery to normal hurricane activity, rather than a direct response to increasing sea surface temperature. Comparison of the record with a reconstruction of vertical wind shear indicates that variability in this parameter primarily controlled the frequency of major hurricanes in the Atlantic over the past 270 years, suggesting that changes in the magnitude of vertical wind shear will have a significant influence on future hurricane activity.

Tropical ocean thermocline variability is studied using gridded data assimilated by an ocean model in the period 1950–2000. The dominant patterns and variability are identified using EOF analysis applied to E–W depth slices of sea temperatures averaged over the tropics. After removing the annual cycle, an east–west ‘see-saw’ with an interannual to decadal rhythm is the leading mode in each of the tropical basins. In the case of the leading mode in the Pacific, the thermocline oscillation forms a dipole structure, but in the (east) Atlantic and (southwest) Indian Ocean there is a single center of action. The interaction of the ocean thermocline and atmospheric Walker circulations is studied through cross-modulus analysis of wavelet-filtered EOF time scores. Our study demonstrates how tropical ocean thermocline variability contributes to zonal circulation anomalies in the atmosphere. The equatorial Pacific thermocline oscillation explains 62 and 53% of the variability of the Pacific and Atlantic zonal overturning circulations, the latter driving convective polarity between North Africa and South America. The Pacific sea-saw leads the Atlantic zonal circulation by a few months.

We analyze the time-longitude structure of composite cases from model-assimilated ocean data in the period 1958–1998, following on from earlier work by Huang and Kinter (J. Geophys. Res. 107(C11) (2002) 3199) that studied east–west thermocline variability in the Indian Ocean. Our analysis focuses on the Rossby wave signal along the thermocline ridge in the tropical SW Indian Ocean (101S, 60–801E), where wind stress curl is important. Anomalous winds in the equatorial east Indian Ocean force successive Rossby waves westward at speeds of 0.1 m s � 1 730%. With a wavelength of � 7000 km, the period of oscillation is in the range 1.9–5.2 years. The Indian Ocean Rossby wave is partially resonant with the global influence of the El Nino–Southern Oscillation, except during quasi-biennial rhythm. The presence of the Rossby wave offers potential predictability for east–west atmospheric circulation systems and climate that affect resources in countries surrounding the Indian Ocean. r 2004 Elsevier Ltd. All rights reserved.

The structure of the upper ocean and surface atmospheric conditions are described during a ship cruise across the central Indian Ocean from December 1995 to January 1996. In situ data on currents, temperature, salinity and surface heat fluxes are described and compared with expected climatological values. Thermocline uplift in the 6-7°S latitude band is linked to the cyclonic shear of near-surface currents. A comparison of quiescent and windy periods demonstrates that evaporative fluxes become amplified near cyclonic vortices fed by southerly meridional winds. The ocean density structure is influenced by salinity gradients, driven by the precipitation-evaporation balance. Near the inter-tropical convergence zone (ITCZ), freshwater fluxes create a stable surface layer and helps to maintain the eastward equatorial counter-current. An analysis of the atmospheric boundary layer from NCEP re-analysis data seeks to place the in situ results into the context of weather conditions at the time of the cruise. Further studies of this kind will improve our understanding of relationships between the Indian Ocean monsoon and surrounding climates.

The seasonal progression of summer wet spells over southern Africa is investigated. The November to March rainy season is modulated at the intraseasonal scale, with major wet spells every 20-30 days and internal evolution at higher frequencies. Corresponding circulation patterns for each wet spell illustrate the variable dynamics and physics as the season progresses. Early summer rainfall is associated with enhanced baroclinic westerly shear from the upper troposphere of the tropical Atlantic Ocean, whereas low-level moisture is advected from the central Indian )cean. Extratropical westerly wave action is an important influence during early summer. As the summer season progresses, heating causes a retreat of the subtropical westerly jet stream. A quasi-stationary line of confluence along 20°S develops in the low levels during late summer, and extends from the Mozambique Channel to Angola. This trough is supported by an influx of moisture from the Congo and southern Mozambique Channel. Composite differences between early and late summer wet spells are evaluated numerically for the first time in this presentation.

The vertical distribution of ozone recorded over northern Namibia during SAFARI-92 is examined as a function of prevailing atmospheric circulation. Two dominant synoptic weather types, namely, anticyclonic flow and flow associated with a westerly trough, are identified and composite ozone profiles produced for each weather type. In both cases an elevated, enriched ozone layer (9–12 km), where ozone concentrations exceed 80 ppbv on average, and 100–120 ppbv on individual days, is present. Under anticyclonic conditions, ozone increases steadily from surface values of around 40 ppbv to about 60–80 ppbv throughout the troposphere. In contrast, the westerly trough is characterized by a midtropospheric (4–8 km) ozone minimum, where values are 20 ppbv lower. This gives rise to a double ozone maximum in the troposphere. The elevated, enriched layer is thought to be a pervasive layer equatorward of 20°S and to result from biomass burning.