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The seasonality, regionality, and nature of the association between tropical convection and the 5-day wavenumber-1 Rossby–Haurwitz wave are examined. Spectral coherences between daily outgoing longwave radiation (OLR), a proxy for convection, and 850-hPa zonal wind over the period January 1979–February 2013 are compared for different seasons and for phases of El Niño–Southern Oscillation (ENSO) and the quasi-biennial oscillation (QBO). Increased coherence, indicating a stronger association, occurs in boreal spring and autumn, with slightly reduced coherence in boreal summer and significantly reduced coherence in boreal winter. The regionality of the association is examined using lagged-regression techniques. Significant local signals in tropical convection are found over West Africa, the tropical Andes, the eastern Pacific Ocean, and the Marshall Islands. The relative phasing between the 5-day wave wind and OLR signals is in quadrature in Africa and the Marshall Islands, in phase with easterlies over the Andes, and out of phase with easterlies over the eastern Pacific. Frequency spectra of precipitation averaged over the identified local regions reveal spectral peaks in the 4–6-day range. The phasing between the large-scale wind and local convection signals suggests that the 5-day wave is actively modulating the convection around the Americas.

A sharp reduction in precipitation was observed on the island of Dominica in the Caribbean during a 2011 field campaign when the trade winds weakened and convection transitioned from mechanically to thermally driven. The authors propose four hypotheses for this reduction, which relate to (i) the triggering mechanism, (ii) dry-air entrainment, (iii) giant sea-salt aerosol, and (iv) small-island-derived aerosol. The plausibility of the first three hypotheses is the focus of this study. Aircraft observations show the dynamics of the orographic cumulus clouds at flight level are surprisingly similar, irrespective of how they are triggered. However, the orographic cumulus clouds are consistently shallower when the trade winds are weak, which the authors attribute to a drier and shallower cloud layer compared to days with stronger trade winds. The strong negative influence of dry-air entrainment in a drier environment on cumulus depth and liquid water content is qualitatively demonstrated using an entraining plume model and the WRF Model. Although the models appear more sensitive than observations to entrainment and cloud size, the sensitivity tests have some resemblance to observations. The authors also find evidence of sea-salt aerosol entering the base of marine cumulus on strong wind days using an aircraft-mounted lidar and other instruments. Although each hypothesis is plausible, the complex interplay of these processes makes determining the controlling mechanisms difficult. Ultimately, the authors’ analysis rejects the hypothesis (i) triggering, while supporting (ii) entrainment and (iii) sea-salt aerosol.

Even though the vital role of thermocline fluctuation in El Nino–Southern Oscillation (ENSO) cycle has been established previously, the direct relationship between the thermocline depth and sea surface temperature (SST) anomalies in the equatorial Pacific is yet to be fully understood, especially its seasonality. Thermocline depth anomalies have been found to lead SST anomalies in time with a longitude-dependent delay, but our study also suggests that the relationship shows considerable seasonal dependency and is strongest (weakest) during the boreal spring (summer). Over the eastern equatorial Pacific where there is least delay (compared to that in the western and central Pacific), the connection between thermocline and SST is the weakest during the boreal spring. This feature may be one of causes for ENSO spring persistence barrier. Furthermore, the thermocline-SST connections exhibit significant decadal variations, which are remarkably consistent with the decadal changes in the persistence barrier of SST anomalies over the eastern Pacific. It is also found that the decadal shift in the timing of the thermocline-SST connection barrier is caused by the changes in the seasonal cycle of tropical trade winds and thermocline depths.

Guided by ground-based radar and lidar profiling at the Barbados Cloud Observatory (BCO), this study evaluates trade-wind cloudiness in ECMWF's Integrated Forecast System (IFS) and nine CMIP5 models using their single-timestep output at selected grid points. The observed profile of cloudiness is relatively evenly distributed between two important height levels: the lifting condensation level (LCL) and the tops of the deepest cumuli near the trade-wind inversion (2–3 km). Cloudiness at the LCL dominates the total cloud cover, but is relatively invariant. Variance in cloudiness instead peaks at the inversion. The IFS reproduces the depth of the cloud field and its variability, but underestimates cloudiness at the LCL and the inversion. A few CMIP5 models produce a single stratocumulus-like layer near the LCL, but more than half of the CMIP5 models reproduce the observed cloud layer depth in long-term mean profiles. At single-time steps, however, half of the models do not produce cloudiness near cloud tops along with the (almost ever-present) cloudiness near the LCL. In seven models, cloudiness is zero at both levels 10 to 65% of the time, compared to 3% in the observations. Models therefore tend to overestimate variance in cloudiness near the LCL. This variance is associated with longer time scales than in observations, which suggests that modeled cloudiness is too sensitive to large-scale processes. To conclude, many models do not appear to capture the processes that underlie changes in cloudiness, which is relevant for cloud feedbacks and climate prediction.

Observations and cloud-resolving simulations of elongated cloud plumes (or “cloud trails”) past the Lesser Antilles islands in the Caribbean Sea are presented. Analysis of one year of visible satellite images reveals that each island forms cloud trails on 30%–40% of days, typically in the afternoon in response to diurnal island heating. On around 10% of days the cloud bands are very well organized, with lengths of and durations of min. Radiosonde analysis suggests that the well-organized events are favored by moderate-to-strong trade winds (6–10 m s−1) and stronger trade inversions. The simulated cloud trails, which are consistent with observations in their morphology and diurnal cycle, are organized by quasi-linear bands of thermally forced convergence within the heated island wake. They are sensitive to overland surface fluxes, inversion strength and height, terrain height, and trade-wind speed. While surface fluxes control the strength of the wake thermal circulations, the inversion controls precipitation and the disruption of cloud trails by subcloud cold pools. The impacts of terrain height and wind speed are multifaceted, including control over (i) the mechanical flow regime, (ii) the intensity of wake turbulence, (iii) the cloud-trail length, (iv) the wake thermal anomaly, and (v) elevated-heating effects (which strengthen the thermal convergence). Dimensional analysis is used to develop empirical scalings for the wake thermal circulation, which describe the suite of numerical sensitivity tests reasonably well.

Because of the need for information related to the variability and predictability of sea level on season-to-longer time scales, the Pacific ENSO Applications Climate (PEAC) Center runs the El Niño-Southern Oscillation (ENSO)-based canonical correlation analysis (CCA) statistical model to generate sea level forecasts for the U.S.-affiliated Pacific Islands (USAPI) region with lead times of 3–6 months in advance. However, in order to meet the increasing demand for longer lead-time (e.g., 6–12 months) forecasts, the PEAC Center, as part of the advances in operational sea level forecasts, recently incorporated both SST and zonal wind components of trade winds (U) for modulating sea level variability on longer time scales. The combined SST and U-based forecasts are found to be more skillful on longer time scales. This improvement has enabled the capability of our clients in the USAPI region to develop a more efficient long-term response plan for hazard management. In a recent “Regional Integrated Water Level Service” meeting, it was revealed that the development and distribution of “seasonal water level outlooks” in the Pacific basin region is an area of mutual interest. We therefore synthesize the current operational forecasting, warning, and response activities of the PEAC Center and discuss the manner in which our experience in the USAPI region can contribute to the development of adaptation strategies for longer time-scale climate variability and change for the non-USAPI region in the south Pacific.

About 44% of the cold-season heavy rainfall/flood (HRF) events around the South China Sea require six days or longer to develop from the formation time of their parent cold surge vortices (CSVs). Formations for both the parent CSV and HRF event are involved with interactions of the concerned vortices with two different cold surge flows. The occurrence frequency of the East Asian cold surge flow varies from 4.5 to 6 days. The longevous CSVs enable their developments to interact with the second cold surge flows between formations of these CSVs and HRF events. Two requirements for the formation of HRF events are 1) synchronized occurrence of the HRF event and the northwestern Pacific explosive cyclone and 2) simultaneous occurrence of the maximum speeds among westerlies of the northwestern Pacific explosive cyclone and easterlies of the tropical trade winds and the HRF event. These requirements cannot be met by the CSV at its second maximum peak intensity, but the CSV at this stage plays an indispensible role for the formation of the HRF event to make its intensity and rainfall amount larger than those HRF events without this relay intensification. The development of an HRF event through multiple interactions of CSVs with sequential cold surge flows may pose difficulties to numerically simulate/predict the occurrence of these HRF events over the cold-season rainfall centers around the South China Sea.

This paper presents a new style of bedload parting from western Torres Strait, northern Australia. Outputs from a hydrodynamic model identified an axis of bedload parting centred on the western Torres Strait islands (~142°15′E). This bedload parting is similar to others documented from mixed tidal regimes as it is driven dominantly by the O1, K1 and M2 tidal constituents. However, parting is aided by overtides on the eastern, mixed semidiurnal side of the strait. Bedload parting is also strongly impacted by wind-driven currents. Wind-driven currents during the trade wind season lead to the average estimates of bedload transport to be directed west, through the strait, over the 8 year model duration. As a result, east and west directed bedload parting is only active during the monsoon season when the influence of wind-driven circulation is negligible. A simulation of bedload transport using a range of sediment grain sizes indicated that sediments with a grainsize greater than ~2 mm were transported in a direction consistent with tidally driven bedload parting, as opposed to residual wind-driven flow.

International audience; In order to better constrain the construction and the erosion rates affecting the volcanic island of Basse-Terre Island (Guadeloupe, F.W.I), an enlarged K-Ar ages dataset has been combined with reconstruction of the paleo-topography. Two different methods of interpolation of the present topography have been cross-checked to better support the erosion rates obtained and their associated uncertainties. The present study focusses on the Monts-Caraïbes volcanoes and on the main geomorphic feature of the Piton de Bouillante volcano, the Beaugendre Valley. The Monts-Caraïbes volcanoes were constructed in 83 kyr at a rate of 0.12 ± 0.04 km3/kyr. During the last 450 kyr, they have experienced an erosion rate of 610 ± 550 t/km2/yr. In the Piton de Bouillante volcano eleven new K-Ar ages have been obtained, constraining the duration of its volcanic activity between 880 ± 14 and 712 ± 12 ka, and involving a construction rate of 0.70 ± 0.20 km3/kyr. For this volcano, an erosion rate of 1,220 ± 700 t/km2/yr has been obtained for the last 700 kyr. Our study also shows, based on the contemporaneity of the ages in the entire Beaugendre Valley added to the mean erosion rate of 1,350 ± 550 t/km2/yr, that the flank collapse hypothesis cannot explain the formation of this valley. Finally, the similarity of the erosion rates computed for different locations of the Basse-Terre Island shows that the time-integrated erosion appears independent to the trade wind effect and suggests that the barrier effect due to the relief is not present here.

International audience; The tourism of the Cape Verde Islands is rapidly expanding, in particular thanks to the attendance of the island of Sal, at thenorth of the archipelago. This island presents an important tourism potential, thanks to its natural heritage : volcanism, white sandbeaches, picturesque landscapes. This development leads to a more and more intense use of the natural resources of the Island,in particular energy and water resources. The salt works of Pedra Lume is one of the most important site of the island. Through itshistoric and current development, it illustrates the various phases of the economic development which knew the island of Sal sincealmost six centuries.; Le tourisme du Cap-Vert est en plein essor, notamment grâce à la fréquentation de l’Île de Sal, au nord de l’archipel. Cetteîle présente un potentiel touristique important, grâce à son patrimoine naturel : volcanisme, plages de sable blanc, paysagespittoresques. Ce développement entraîne un usage de plus en plus intense des ressources naturelles de l’île, notammenténergétique et hydrique. La saline de Pedra Lume est un des points d’orgue de ce développement touristique. Au travers de samise en valeur historique et actuelle, elle illustre les différentes phases de développement économique qu’a connu l’Île de Saldepuis près de six siècles.; O turismo de Cabo Verde está crescendo, especialmente graças à freqüentação da Ilha do Sal, na parte norte do arquipélago.Esta ilha tem um importante potencial turístico graças ao seu património natural: vulcanismo, praia de areia branca, paisagenspitorescas. Este desenvolvimento leva a um uso cada vez mais intenso dos recursos naturais da Ilha, em particular energia e água.Sal de Pedra Lume é um dos destaques deste desenvolvimento turístico. Através do seu desenvolvimento histórico e atual, ilustraas diferentes fases do desenvolvimento econômico que tem sido a ilha de Sal por quase seis séculos.

This paper investigates the influence of El Nino Southern Oscillation (ENSO) activity through precipitable water vapor (PWV) variability to understand ENSO dynamics. PWV data over the western Pacific Ocean taken from Global Positioning System (GPS) and Radiosonde has been analyzed. An ENSO event represented by a sea surface temperature anomaly (SSTa) in the Nino 3.4 and 4 regions for the period of 2009–2011 was chosen. During this period, the PWV time series during increasing El Nino intensity were dominated by the seasonal cycle and a strong correlation found with SSTa for PIMO (R2 = 0.81) and a modest correlation for TOW2 (R2 = 0.66). An anticorrelation between SSTa and PWV was found at PIMO and TOW2 stations due to the fact that they are in opposite hemispheres, and a positive correlation was shown for the station near the equatorial line. This suggests that the strengthening and weakening of the trade winds moving from the central to the western Pacific Ocean during a La Nina event will bring to the surface warm water from the central to the western Pacific and cause PWV increases, and vice versa for an El Nino event.

This is a study of the environmental conditions and primary phytoplankton production in a Sahelian shallow lake of Senegal, West Africa. Environmental descriptors (nutrient, water transparency, temperature and hydrochemistry) and their effects on primary production were studied. Samples were collected monthly from March 2002 to February 2003 in 3 stations of the central part of water body. Climatic variables show a marked annual pattern following two dominant wind directions: NNE (North-North-East) and NNW (North- North-West). This cyclic evolution affects hydrobiological variables. In this central part of the lake, water body was not stratified with same measures between surface and bottom. Lake water was turbid with lower values during the maritime trade winds period characterized by high water temperatures and conductivity. Water pH was relatively higher than seven (07) associated with high contents of oxygen (approximately 90%) in all stations. The station Typha is marked by a low pH and high fluctuations in the rates of oxygen (20 to 120%). Nutrient concentrations were low, with high variability (from 0 to 30 μg.l -1 for DIN and from 0 to 18 μg.l -1 for PO 4 ). The primary production in Guiers Lake was high; it showed a vertical gradient with production of 2400 mgC.m -3 .days -1 in surface and a low of 200 mgC.m -3 days -1 at the bottom. In this shallow system, environmental conditions regulate the primary production. Keywords : Environmental descriptors, primary production, shallow lake, Senegal.

Strong gusts negatively affect wind turbines in many ways. They (1) harm their structural safety; (2) reduce their wind energy output; and (3) lead to a shorter wind turbine rotor blade fatigue life. Therefore, the goal of this study was to provide a global assessment of the gust climate, considering its influence on wind turbines. The gust characteristics analyzed were: (1) the gust speed return values for 30, 50 and 100 years; (2) the share of gust speed exceedances of cut-out speed; and (3) the gust factor. In order to consider the seasonal variation of gust speed, gust characteristics were evaluated on a monthly basis. The global monthly wind power density was simulated and geographical restrictions were applied to highlight gust characteristics in areas that are generally suitable for wind turbine installation. Gust characteristics were computed based on ERA-interim data on a 1° × 1° spatial resolution grid. After comprehensive goodness-of-fit evaluation of 12 theoretical distributions, Wakeby distribution was used to compute gust speed return values. Finally, the gust characteristics were integrated into the newly developed wind turbine gust index. It was found that the Northeastern United States and Southeast Canada, Newfoundland, the southern tip of South America, and Northwestern Europe are most negatively affected by the impacts of gusts. In regions where trade winds dominate, such as eastern Brazil, the Sahara, southern parts of Somalia, and southeastern parts of the Arabian Peninsula, the gust climate is well suitable for wind turbine installation.

As part of an NERC-funded project investigating the southern methane anomaly, a team drawn from the Universities of Bristol, Birmingham and Royal Holloway flew small unmanned multirotors from Ascension Island for the purposes of atmospheric sampling. The objective of these flights was to collect air samples from below, within and above a persistent atmospheric feature, the Trade Wind Inversion, in order to characterise methane concentrations and their isotopic composition. These parameters allow the methane in the different air masses to be tied to different source locations, which can be further analysed using back trajectory atmospheric computer modelling. This paper describes the campaigns as a whole including the design of the bespoke eight rotor aircraft and the operational requirements that were needed in order to collect targeted multiple air samples up to 2.5 km above the ground level in under 20 min of flight time. Key features of the system described include real-time feedback of temperature and humidity, as well as system health data. This enabled detailed targeting of the air sampling design to be realised and planned during the flight mission on the downward leg, a capability that is invaluable in the presence of uncertainty in the pre-flight meteorological data. Environmental considerations are also outlined together with the flight plans that were created in order to rapidly fly vertical transects of the atmosphere whilst encountering changing wind conditions. Two sampling campaigns were carried out in September 2014 and July 2015 with over one hundred high altitude sampling missions. Lessons learned are given throughout, including those associated with operating in the testing environment encountered on Ascension Island.

The 1981–2014 climatology and variability of the March–May eastern Horn of Africa boreal spring wet season are examined using precipitation, upper- and lower-level winds, low-level specific humidity, and convective available potential energy (CAPE), with the aim of better understanding the establishment of the wet season and the cause of the recent observed decline. At 850 mb, the development of the wet season is characterized by increasing specific humidity and winds that veer from northeasterly in February to southerly in June and advect moisture into the region, in agreement with an earlier study. Equally important, however, is a substantial weakening of the 200-mb climatological easterly winds in March. Likewise, the shutdown of the wet season coincides with the return of strong easterly winds in June. Similar changes are seen in the daily evolution of specific humidity and 200-mb wind when composited relative to the interannual wet season onset and end, with the easterlies decreasing (increasing) several days prior to the start (end) of the wet season. The 1981–2014 decrease in March–May precipitation has also coincided with an increase in 200-mb easterly winds, with no attendant change in specific humidity, leading to the conclusion that, while high values of specific humidity are an important ingredient of the wet season, the recent observed precipitation decline has resulted mostly from a strengthening of the 200-mb easterlies. This change in the easterly winds appears to be related to an increase in convection over the Indonesian region and in the associated outflow from that enhanced heat source.

A dinâmica climatica do semiarido de Petrolina traduz uma complexidade de grandes proporcoes. A disponibilidade de dados climaticos nessa area permitiu a adocao do Principio da Analogia, usado em Geografia, onde desse foram deduzidos diversos aspectos da dinâmica atmosferica do Semiarido e mais especificamente do municipio de Petrolina-PE. Os dados foram trabalhados em programas como o CLIMAP e Excel para gerar os graficos que deram suporte a discussao apresentada. Ao final chegou-se as seguintes conclusoes: 1. O semiarido nordestino e muito mais uma consequencia da circulacao atmosferica do que o resultado das influencias topograficas e do efeito de continentalidade; 2. A altitude mais baixa camada de inversao dos alisios e o fator determinante da semiaridez do vale medio do Sao Francisco. 3. E possivel correlacionar a altitude da camada de inversao dos alisios de SE verificada sobre a corrente fria de Benguela e o Sudoeste africano desertico com a semiaridez instalada sobre o saliente nordestino brasileiro. 4. Os dados termicos do municipio de Petrolina-PE demonstram uma tendencia para acrescimos de temperatura no periodo de 1961 e 2012 5. Os dados de pluviosidade do municipio de Petrolina-PE permitem concluir que ha uma tendencia para diminuicao das precipitacoes anuais no periodo de 1961 ate 2012. Normal 0 false false false EN-US X-NONE X-NONE /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Tabela normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:"Calibri",sans-serif;} A B S T R A C T Climate dynamics of the semiarid region of Petrolina reflects a high complexity. The availability of weather data allows this and was used the Analogy Principle, used in geography, where this were deducted various aspects of dynamic atmospheric Semi-Arid and more specifically Petrolina municipality. The data were worked in programs like CLIMAP and Excel to generate graphics that supported the discussion. At the end the following conclusions were reached: 1. The semi-arid northeast is much more a consequence of atmospheric circulation than the result of topographical influences and continentality effect; 2. The lowest elevation of the trade inversion layer is the determining factor of the middle valley semiaridez of San Francisco. 3. It is possible to correlate the altitude of the inversion layer of the SE trade winds checked on the cold Benguela current and the African desert Southwest with semiaridez installed on prominent Brazilian Northeastern. 4. The thermal data of Petrolina municipality demonstrate a tendency for temperature increases in 1961 and 2012 period 5. The rainfall data from Petrolina municipality indicate that there is a tendency to decrease in annual rainfall in the period 1961 to 2012. Keywords: brazilian northeastern semiarid region, Benguela Current, Trade Winds Inversion Layer, droughts, CLIMAP, Kalahari desert, Petrolina’ climate

During the summer, sustained winds in the ‘Alenuihāhā Channel, Hawaii, may exceed 20 m s−1 with higher gusts. The Advanced Research Weather Research and Forecasting model is used to diagnose airflow in the Hawaiian coastal waters. High-resolution (2 km) runs are performed for July 2005 covering the ‘Alenuihāhā Channel and nested in a 6-km state domain. Under normal trade wind conditions (7–8 m s−1), winds at the channel entrance are 1–2 m s−1 faster than upstream due to the convergence of the deflected airflows by the islands of Maui and Hawaii, and accelerate through the channel due to along-gap pressure gradients and lower pressure in the wakes of both islands. The acceleration is accompanied by descending airflow (>9 cm s−1) in the exit region with lowering of the trade wind inversion. Deceleration occurs downstream of the channel exit with a rapid change from sinking motion to rising motion (>3 cm s−1). Under normal or strong trade wind conditions, the flow is subcritical [Froude number (Fr) < 1] upstream of the channel, supercritical (Fr > 1) in the exit region, and subcritical again (Fr < 1) downstream with a weak hydraulic jump. The localized sinking motion on the lee side of bordering ridgelines (>1 m s−1) is most significant in the afternoon hours and results in warming and lowering of surface pressure on the lee side, into the channel, and farther downstream. As a result, the channel winds and the wind speed maximum along the southeastern coast of Maui exhibit an afternoon maximum.

Most state-of-the-art climate models show significant systematic biases in the tropical southeastern Pacific (SEP) and tropical North Atlantic (TNA). These biases manifest themselves as the sea surface temperature (SST) in the SEP being too warm and the SST in the TNA being too cold. That is, as the cold SST biases appear in the TNA, the warm SST biases also occur in the SEP. This indicates that if climate models cannot succeed in simulating the TNA variability, they will also fail at least partially in the SEP. Our coupled model experiments show that the cold SST bias in the TNA results in a weakening of the Hadley-type circulation from the TNA to the SEP. This meridional circulation reduces the South Pacific subtropical anticyclone and the associated subsidence, which in turn leads to a reduction of low clouds, a weakening of the easterly trade wind, and thus an increase of the warm SST bias in the SEP.

This study examined the short-term variability of concentrations measured at the Gosan site (, ) in Jeju, Korea for the last 9 years from 2002 to 2010. The weekly distribution shows higher concentrations during weekends than weekdays which implies the impact of local emissions because Jeju Island is one of the top tourist attraction in Korea. In diurnal variation, concentration reached the maximum at 6 am and the minimum at 1 pm. The high concentrations were mostly associated with lower wind speed (below 4 m/s) and easterlies, which was typical of summer night. In other seasons, however, the high concentrations were encountered under strong westerlies (8~16 m/s), which implies the influence of Chinese outflows. concentrations were found to be highly correlated with meteorological parameters including wind speed, temperature, humidity, and solar radiation except for winter.

This study provides a pertinent ground for acquiring deeper insight about the low-frequency variability of precipitation and its extremes over India and its homogeneous monsoon regions under the combined interplay of both the Atlantic multidecadal oscillation (AMO) and the interdecadal Pacific oscillation (IPO). The percent of variance in the total/heavy rainfall on decadal-to-multidecadal timescales that can be attributed to these oceanic indices is 88.3/76.7 % for west central and 84.4/72.6 % for northeast regions, which implies that the recent changes in rainfall and it extremes over respective regions is mainly caused by internal natural variability. The opposite phases of AMO and IPO together modulates the total/moderate rainfall over west central and northeast regions in an asymmetric manner; whereas their warm phase stimulates the heavy rainfall over west central region, while their opposite phases together influences the precipitation extremes over northeast region. Based on the projected conditions of these oceanic indices the outlook for west central/northeast regions is fairly good/bad and these regions will experience above-/below-normal precipitation in the upcoming decade or two. The rainfall over northwest region is mainly influenced by the IPO and this region will also likely to receive above-normal precipitation in the upcoming decade or so due to the present cold phase of IPO. Wind circulation pattern divulges that during the warm phase of AMO the southwesterlies over Indian region are strengthened by the equatorial Atlantic winds coming through the equatorial Africa, while in the cold phase of IPO it gets strengthen by the easterlies from the equatorial Pacific.

Accumulating evidence suggests that Atlantic populations of Leach's Storm-Petrels (Oceanodroma leucorhoa) are experiencing significant declines. To better understand possible causes of these declines, we used geolocators to document movements of these small (50-g) pelagic seabirds during migration and the non-breeding period. During 2012 and 2013, movement tracks were obtained from two birds that traveled in a clock-wise direction from two breeding colonies in eastern Canada (Bon Portage Island, Nova Scotia, and Gull Island, Newfoundland) to winter in tropical waters. The bird from Bon Portage Island started its migration towards Cape Verde in October, arrived at its wintering area off the coast of eastern Brazil in January, and started migration back to Nova Scotia in April. The bird from Gull Island staged off Newfoundland in November and then again off Cape Verde in January before its geolocator stopped working. Movements of Leach's Storm-Petrels in our study and those of several other procellariiforms during the non-breeding period are likely facilitated by the prevailing easterly trade winds and the Antilles and Gulf Stream currents. Although staging and wintering areas used by Leach's Storm-Petrels in our study were characterized by low productivity, the West Africa and northeastern Brazilian waters are actively used by fisheries and discards can attract Leach's Storm-Petrels. Our results provide an initial step towards understanding movements of Leach's Storm-Petrels during the non-breeding period, but further tracking is required to confirm generality of their migratory routes, staging areas, and wintering ranges. RESUMEN. Movimientos migratorios yinvernales de Oceanodroma leucorhoa seguidos utilizando geolocaliza-dores La evidencia acumulada sugiere que las poblaciones del atlde Oceanodroma leucorhoa estexperimentando una disminuci´ on significativa. En un esfuerzo para entender mejor las posibles causas de esta disminuci´ on, usamos geolocaliza-dores para documentar los movimientos de esta peque˜ na (50-g) ave marina peldurante la migraci´ on y el periodo no reproductivo. Durante el 2012 y 2013, trayectorias de los movimiento fueron obtenidas basada en dos aves que viajaron en la direcci´

Mineral dust is an important component of Earth’s climate system and biogeochemical cycles on a global scale. In order to understand the relationship between climate processes in the source areas and the properties of aerosols at distant receptor sites, we must be able to identify the source provenance of dust. Here we present a multiproxy study that characterizes the temporal variability in the geochemical composition of long-range African dust (LRAD) collected between 2003 and 2011 in the trade winds on the Caribbean island of Barbados. We find systematic differences between Sr-Nd-Hf isotopic composition and rare earth element anomalies of individual dust events and evidence of seasonal shifts in dust source activity and transport. These results indicate that coherent geochemical source signatures of LRAD can be preserved even after transport across thousands of kilometers. We investigated the possibility of identifying the potential source areas through comparisons with literature data. However, these data are almost entirely based on measurements of soil and sediment samples; this could lead to biases because of soil-aerosol particle size and composition differences. Nonetheless, our data suggest that many samples are linked to sources in Mali and sub-Saharan regions. Radiogenic Nd-Hf composition of aerosols can potentially be a useful proxy to study the proximity of mineral dust sources to depositional sites. In order to establish firmer links between LRAD and dust source areas, however, we require much more data on the geochemical composition of aerosols from potential source areas in North Africa.

Observations of precipitating trade wind cumuli show convective invigoration on the downwind side of their cold pools. The authors study convection and cold pools using a nested–Weather Research and Forecasting Model simulation of 19 January 2005—a day from the Rain in Cumulus over the Ocean experiment. The temperature and water vapor mixing ratio drops in simulated cold pools fall within the envelope of observed cases, and the wind enhancement matches observations more closely. Subcloud updrafts downwind and near the cold pool boundary are statistically compared to updrafts further from cold pools. Updrafts near cold pool outflows are moister than the other updrafts and are more likely to originate from overall moister regions. Cold pool–influenced updrafts tend to exceed the other updrafts in vertical velocity and are associated with more cloud liquid water. The strength of circulation within the cold pool boundary is unable to match that because of the low-level environmental wind shear, and the lifted updrafts advect faster than the environmental wind, thereby accessing the ambient environmental moisture converged by cold pool expansion. Cases with higher rain rates correspond to larger cloud cover through the shearing off of the upper-level cloud, consistent with observations. This study suggests that it is the ability of cold pools to lift thermodynamically favorable air that is critical for secondary convection of trade wind cumuli.

High-resolution measurements of the turbulent, thermodynamic, and microphysical structure of the edges of trade wind cumuli have been performed with the Airborne Cloud Turbulence Observation System. Lateral entrainment of subsaturated air into the cloud region leads to an evaporative cooling effect. The negatively buoyant air partly enhances the compensating downdraft, forming a subsiding shell at cloud edge. Based on the presented observations, the subsiding shell is divided into a turbulent and humid inner shell adjacent to the cloud interior and a nonbuoyant, nonturbulent outer shell. In the trade wind region, continuous development of shallow cumuli over the day allows for an analysis of the properties of both shells as a function of different cloud evolution stages. The shallow cumuli are divided into actively growing, decelerated, and dissolving based on cloud properties. As the cumuli evolve from actively growing to dissolving, the subsaturated environmental air is mixed deeper and deeper into the cloud region and the subsiding shell grows at the expense of the cloud. This measured evolution of the subsiding shell compares favorably with the predictions of a direct numerical simulation of an idealized subsiding shell. The thickness of the measured outer shell decreases with the evolution of the cumuli while the intensity of the downdraft is nearly constant.

Resuming earlier work and based on recently available data sources, this study explores interannual rainfall variability in Central America and underlying circulation mechanisms during 1958–2012. With the changes of circulation in the annual cycle, precipitation increases into May–June, become scarcer in July–August (JA), yet most abundant in September–October; the edge of the Atlantic subtropical high extending westward most markedly and the Pacific Intertropical Convergence Zone (ITCZ) retreating southward in JA. Interannual variations of rainfall are accompanied with circulation changes involving vertical motion over Central America. Overall, with weaker Atlantic trade winds southerly wind component over Pacific tends to be stronger and Central America rains more abundant. Regarding long-term variations from protracted dry regime 1971–1978 to protracted wet regime 2005–2012, on the Atlantic side ocean surface warmed, pressure dropped, trade winds weakened, whereas over the Pacific northward pressure gradient and winds increased. The study builds on work half a century ago and extends analysis into the most recent decades, using recent and updated circulation and raingauge data sets.

This paper focuses on the impacts of convective momentum transport (CMT) on simulations of the tropical intraseasonal oscillation (TIO) in SAMIL. Two sets of experiments are performed, which give different reality of the Madden-Julian Oscillation (MJO). The Tiedtke cumulus parameterization scheme is used for all experiments. It is found that simulations of the TIO can be influenced by CMT, and the impacts on the simulated TIO depend on the model capability in simulating the MJO. CMT tends to have large influences to the model that can simulate the eastward propagation of the MJO. CMT can further influence the long-term mean of zonal wind and its vertical shear. Zonal wind suffers from easterlies biases at low level and westerlies biases at upper level when CMT is introduced. Such easterlies biases at low level reduce the reality of the simulated tropical intraseasonal oscillation. When CMT is introduced in the model, MJO signals disappear but the model’s mean state improves. Therefore, a more appropriate way is needed to introduce CMT to the model to balance the simulated mean state and TIO signals.

The persistent strengthening of the trade winds over the Pacific Ocean over the past 20 years has recently been proposed as a driver for the increase of ocean heat uptake linked to the hiatus in surface global warming. Crucial aspects in this argument are the reliability of the wind signal, usually derived from atmospheric reanalyses, and the ability of models to represent it. This study addresses these two aspects by comparing various observations with reanalyses and model integrations from the European Centre for Medium-Range Weather Forecasts system. We show that the strengthening of trades over the Pacific is a robust feature in several observational data sets as well as in the reanalyses based on full and limited sets of observations. The wind trend is also reproduced in an atmospheric model integration forced by sea surface temperature analysis, a result that opens the doors to further investigation on the nature of the changes.

The rate of coastal sea level change in the northeast Pacific (NEP) has decreased in recent decades. The relative contributions to the decreased rate from remote equatorial wind stress, local longshore wind stress, and local windstress curl are examined. Regressions of sea level onto wind stress time series and comparisons between NEP and Fremantle sea levels suggest that the decreased rate in the NEP is primarily due to oceanic adjustment to strengthened trade winds along the equatorial and coastal waveguides. When taking care to account for correlations between the various wind stress time series, the roles of longshore wind stress and local windstress curl are found to be of minor importance in comparison to equatorial forcing. The predictability of decadal sea level change rates along the NEP coastline is therefore largely determined by tropical variability. In addition, the importance of accounting for regional, wind-driven sea level variations when attempting to calculate accelerations in the long-term rate of sea level rise is demonstrated.

This is one of the first studies on lightning incidents that take place in the neighbourhood of Lake Victoria, the largest tropical lake in the world that borders Uganda, Tanzania and Kenya. Lightning accident statistics in the region have been documented segment wise. The number of lightning occurrences in the north-western shore and that in the north-eastern shore were compared. The region has a distinctly recognizable season with high lightning accident density which runs from May to November and low lightning accident period from December to April. August peaks in lightning incidents. Lightning-related incidents are very much prevalent during the period between May and August due to the dominant south easterlies. The study reveals that the north-western part has slightly higher lightning accidents than the north-eastern part. North-eastern part records relatively high number of lightning accidents in the morning hours whereas the north-western sector experiences the same in the afternoon hours. Many features of lightning accidents and their locations have features that are in agreement with the same observed in other parts of East Africa. Following the statistics collected and incidents observed, suitable safety measures have been recommended for the communities that reside in the shores and nearby areas of Lake Victoria.

Air advected equatorward by the trade winds off the coast of California is associated with decreasing cloud cover and is subjected to increasingly warmer sea surface temperatures. These gradients imply large gradients in the surface energy fluxes. Based on the surface energy balance and on the assumption of a small net surface energy flux, which is supported by reanalysis data, a cloud cover model of the climatological stratocumulus to cumulus transition in the northeastern subtropical Pacific Ocean is developed. Using climatological meteorological surface variables, the model, despite its simplicity, is able to describe the transition from stratocumulus to cumulus reasonably well in terms of cloud cover.

South African rainfall in the period 1960–2010 exhibits ∼12-year oscillations of similar amplitude to those at 2–5 years. Corresponding global climate signals, as deduced from principal component analysis, include ocean heat content (HC2) and upper zonal winds (2U1) primarily in the Pacific sector. Composites of wet and dry summers are analyzed as depth and height sections to understand the ocean–atmosphere coupling that generates low frequency oscillations. Point-to-field correlations with respect to decadal-filtered South African rainfall (SA1) reveal how the Pacific signals connect with Africa through upper zonal winds, vorticity cells, sea temperature, and aerosol concentration. A regression algorithm of HC2 and 2U1 explains 58 % of the decadal SA1 variance and peak years 1976 and 2000. Although the HC2 pattern is asymmetric and independent, 2U1 principal component time scores follow the Multivariate El Nino Southern Oscillation Index and Pacific Decadal Oscillation. The conveyor of tropical easterlies that dips over the SW Indian Ocean subsequently rises over southern Africa bringing rain with a decadal frequency.

Reanalysis data are very useful for studying the stratosphere. They can be used for analysis of long-term trends (temperature, wind speed, humidity, etc.) or analysis of global atmospheric dynamics, etc. There are various reanalysis projects that provide outputs which are not identical. In this paper, we mutually compare three of them, ERA-40, ERA-Interim and NCEP/NCAR, and compare them with balloon radiosonde observations from Prague, Port Hardy and Valentia stations. This comparison is done for wind speed and direction at pressure levels 100 and 10 hPa and for various periods between 1957 and 2009. The results show that the differences between reanalysis vary. Wind speed data from all three analyses reasonably agree except for the 10 hPa historical data before 1966 and particularly ERA-40 data at the end of the data series (1998–2001). The quality of the ERA-40 10 hPa stratospheric wind data has been proven to be substantially worse over the last four ERA-40 years of 1998–2001 (2002) compared to previous years, both in wind speed and wind direction. The reanalysis data results are compared with radiosonde observations from Prague, Port Hardy and Valentia stations at 10 hPa for the months of February between 1989 and 2009. The results show that there are sometimes surprisingly large differences, more for ERA-Interim versus Prague measurements. Differences in wind direction greater than 45° (outliers) between the reanalysis data and Prague observations in wind direction occur in Februaries predominantly when winds in Prague are in "minor" sectors, such as north, northeast and east (easterlies), whereas "major" sectors, particularly the dominant W (westerlies) wind sector, exhibit almost no outliers.

Several recent studies utilizing global climate models predict that the Pacific Equatorial Undercurrent (EUC) will strengthen over the twenty-first century. Here, historical changes in the tropical Pacific are investigated using the Simple Ocean Data Assimilation (SODA) reanalysis toward understanding the dynamics and mechanisms that may dictate such a change. Although SODA does not assimilate velocity observations, the seasonal-to-interannual variability of the EUC estimated by SODA corresponds well with moored observations over a ~20-yr common period. Long-term trends in SODA indicate that the EUC core velocity has increased by 16% century−1 and as much as 47% century−1 at fixed locations since the mid-1800s. Diagnosis of the zonal momentum budget in the equatorial Pacific reveals two distinct seasonal mechanisms that explain the EUC strengthening. The first is characterized by strengthening of the western Pacific trade winds and hence oceanic zonal pressure gradient during boreal spring. The second entails weakening of eastern Pacific trade winds during boreal summer, which weakens the surface current and reduces EUC deceleration through vertical friction. EUC strengthening has important ecological implications as upwelling affects the thermal and biogeochemical environment. Furthermore, given the potential large-scale influence of EUC strength and depth on the heat budget in the eastern Pacific, the seasonal strengthening of the EUC may help reconcile paradoxical observations of Walker circulation slowdown and zonal SST gradient strengthening. Such a process would represent a new dynamical “thermostat” on CO2-forced warming of the tropical Pacific Ocean, emphasizing the importance of ocean dynamics and seasonality in understanding climate change projections.

South easterly trade winds have long been thought to transport aeolian dust across northwest Australia, but very little is known about the chemical and particle size characteristics of this material. From July 2008 to May 2009, 36 aeolian dust samples were collected monthly at four sites across Australia’s northwest. The results of ion beam analysis indicate that the samples consisted of four major elemental groups, one of which appeared to be transported across the sites during months in winter and summer. This group (characterised by higher ratios of Fe, Ti and Mn/Si than the Earth’s Crustal Average) also showed a decrease in particle sizes towards the west. This suggests that the dust may have had a central Australian source, while other groups richer in Si appear to have been locally derived. These results support previous models of seasonal dust transport, and may have relevance in regional climate modelling, the transport of nutrients into the Indian Ocean, mineral exploration and studies of respiratory health.

We report a documented record of a Great Frigatebird Fregata minor at Fernando de Noronha, 360 km off the coast of northeast Brazil in the equatorial Atlantic. We presume that the bird at Fernando de Noronha originated from Trindade Island, c.1,800 km to the south, since it is the species' nearest breeding site, and we hypothesise that it moved with the south-east trade winds towards the north-east Brazilian coast.

The slowdown in surface warming in the early twenty-first century has been traced to strengthening of the Pacific trade winds. The search for the causes identifies a planetary-scale see-saw of atmosphere and ocean between the Atlantic and Pacific basins.

The present study aims to determine the factors influencing the transition from shallow to deep convection in the trade winds region using an observational approach, with emphasis in the Yucatan Peninsula in eastern Mexico. The methodology is based on a discrimination of two regimes of convection: a shallow cumulus regime, usually with little or no precipitation associated, and an afternoon deep convection regime, with large amounts of precipitation, preceded by a short period of shallow convection. Then, composites of meteorological fields at surface and several vertical levels, for each of the two convection regimes, are compared to infer which meteorological factors are involved in the development of deep convection in this region. Also, the relationship between meteorological variables and selected regime-transition parameters is evaluated only for deep convection regime days. Results indicate the importance of dynamic factors, such as the meridional wind component, in the transition from shallow to deep convection. As expected, thermodynamic variables, such as the low-level specific humidity in the shallow cumulus layer, also contribute to the regime transition. The presence of a southerly component of wind at low- to mid-levels during the early morning in deep convection days provides the shallow cumulus with a more favorable environment so that transition can occur, since abundant moisture from the Caribbean is supplied through this prevailing southern wind. The results can be relevant for reducing uncertainties regarding some important parameters in global and regional models, which could lead to improved simulations of the transition from shallow to deep convection and precipitation.

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.

One of the weather-related shipping hazards in the Caribbean Islands is an intense anticyclone during winter. Surges of trade winds cause steeply sloped short-period ( 2 m) waves to penetrate the shipping lanes near Puerto Rico. In addition to the large-scale air pressure gradient (5 hPa/300 km), the Antilles Islands funnel the winds (>10 m/s) and accentuate the surface heat fluxes (>200 W/m2) and air-sea momentum transfer. Here, the weather scenario surrounding a case of damage to a supply ship 30–31 December 2015 is presented, when the wave height-to-length ratio exceeded 3%. This case is placed in context by statistical analysis of climate and weather features contributing to intensified trade winds. A negative Pacific-North America pattern during La Nina enhances an anticyclonic ridge north of Puerto Rico, contributing to steep waves. The research highlights the hazard to shipping of short-period waves produced by surges of trade winds.

[1] Deep cycle mixing in the cold tongue of the equatorial Pacific Ocean is associated with a mean flow regime in which the gradient Richardson number Ri (a ratio of stratification to shear that affects the evolution of turbulence) fluctuates about a critical value near 14. This is the state of marginal instability (MI), a stable equilibrium between forcing by the trade winds (which works to reduce Ri) and turbulence (which works to increase Ri). Besides providing insight into the physics of deep cycle turbulence, MI is easily recognized in moored records of currents and density, and may therefore provide a valuable indicator of turbulence in historical data where direct turbulence measurements were not made. In this initial study, the seasonal cycle of MI is described. MI is present for 9 months of the year but disappears in March, April, and May, consistent with the recently discovered springtime minimum of equatorial turbulence.

This paper describes climate simulations of the Community Atmosphere Model, version 5 (CAM5), coupled with a higher-order turbulence closure known as Cloud Layers Unified by Binormals (CLUBB). CLUBB is a unified parameterization of the planetary boundary layer (PBL) and shallow convection that is centered around a trivariate probability density function (PDF) and replaces the conventional PBL, shallow convection, and cloud macrophysics schemes in CAM5. CAM–CLUBB improves many aspects of the base state climate compared to CAM5. Chief among them is the transition of stratocumulus to trade wind cumulus regions in the subtropical oceans. In these regions, CAM–CLUBB provides a much more gradual transition that is in better agreement with observational analysis compared to CAM5, which is too abrupt. The improvement seen in CAM–CLUBB can be largely attributed to the gradual evolution of the simulated turbulence, which is in part a result of the unified nature of the parameterization, and to the general improved representation of shallow cumulus clouds compared to CAM5. In addition, there are large differences in the representation and structure of marine boundary layer clouds between CAM–CLUBB and CAM5. CAM–CLUBB is also shown to be more robust, in terms of boundary layer clouds, to changes in vertical resolution for global simulations in a preliminary test.

A three-dimensional photochemistry model is applied to analyze three unusual high O 3 episodes that occurred continuously in Taiwan from May 1 to 11, 2007. During this period, the first high ozone episode was observed in northern and central western Taiwan on May 4. Following this episode, the second episode was observed throughout Taiwan on May 7, and continued for several days until May 10, when the third episode was observed in central western and southwestern Taiwan. This was the worst O 3 period in Taiwan over the past two decades. During this period, 70% of the local air quality station reported an O 3 concentration of over 120 ppb, and a maximum O 3 concentration of 175 ppb was observed in background Taiwan. Based on model analyses, the sources of the three high O 3 episodes differ. The high O 3 concentration observed during the first episode is mainly attributed to the northeastward transport of O 3 precursors and concentrations from northern and central western Taiwan under southwesterlies prior to frontal passage, chemically producing O 3 over 30 ppb h −1 in northern Taiwan. During the second episode, horizontal advection of Asian outflow during the passage of an anticyclone and front contributes a maximum of 25 ppb h −1 in both northern and southern tip of Taiwan, respectively, increasing to more than 75 ppb h −1 in southwestern Taiwan because of the combination with the local source. During the third episode when the prevailing easterlies associated with a departing anticyclone to the east of Taiwan is blocked by the high central mountain, local O 3 chemical production and horizontal transport contribute a maximum of 25 ppb h −1 and 35 ppb h −1 in central and southwestern Taiwan, respectively, under a calm and high background O 3 condition. Source from Taiwan contributes more than half of the high O 3 concentration over northwestern Taiwan prior to frontal passage during the first episode, but decreases to mostly below 40% over western Taiwan during the second episode when Asian outflow occurs, and increases to more than 60% over central and southwestern Taiwan due to pollution accumulation under an anticyclonic departure.

This study describes an improved seasonal sea level forecasting scheme by the Pacific ENSO Applications Climate Center (PEAC). Since 2005, an operational sea level forecasting scheme (3–5 months in advance) for the US-affiliated Pacific Islands (USAPI) has been instrumental (http://www.prh.noaa.gov/peac/sea-level.php). The El Nino-Southern Oscillation (ENSO) climate cycle and the sea-surface temperatures (SSTs) in the tropical Pacific Ocean are taken as the primary factors in modulating these forecasts on seasonal time scales. The current SST-based canonical correlations analysis (CCA) hindcast forecasts have been found to be skillful. However, the skill gradually decreases as the lead-time increases. This has motivated us to revisit the forecasting scheme at PEAC. In contrast to previous endeavours which relied only on SSTs, we now incorporate both trade winds and SSTs for modulating sea level variability on seasonal time scales. The average forecasts for zero to three seasons' lead-times are found to be 0.647, 0.598, and 0.625 for combined SST and the zonal component of the trade wind (U), SST, and wind (U), respectively. It is therefore revealed that the combined SST-wind-based forecasts are more skillful than the SST or wind-based forecasts alone. It is particularly more efficient on longer time scales for most of the stations (e.g. 10–25% improvement on two to three seasons' lead-times). The improvements of these forecasts have enabled the capability of our clients in the USAPI region to develop a more efficient long-term response plan for hazard management.

Most global climate models (GCMs) suffer from biases of a reversed zonal gradient in sea surface temperature (SST) and weak surface easterlies (the westerly bias) in the equatorial Atlantic during boreal spring. These biases exist in atmospheric GCMs (AGCMs) and are amplified by air–sea interactions in atmospheric–oceanic GCMs. This problem has persisted despite considerable model improvements in other aspects. This study proposes a hypothesis that there are two possible root causes for the westerly bias. The first is insufficient lower-tropospheric diabatic heating over Amazonia. The second is erroneously weak zonal momentum flux (entrainment) across the top of the boundary layer. This hypothesis is based on a scale analysis of a simple model for a well-mixed equatorial boundary layer and diagnoses of simulations from eight AGCMs. Severe westerly biases in AGCMs tend to occur when the diabatic heating at low levels (850–700 hPa) over Amazonia is too weak. Deficient low-level diabatic heating weakens the zonal gradient in sea level pressure along the Atlantic equator, introducing westerly biases. In addition, westerly biases may also occur when easterly momentum flux due to entrainment is underestimated.

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The relationship between El Nino Modoki and the East Asian-western North Pacific summer monsoon (EA-WNPSM) has been revealed to be under the influence of Indian Ocean Dipole (IOD). When a pure El Nino Modoki occurs without a positive IOD, a strong EA-WNPSM is observed with a significant anomalous low-level cyclone over the western North Pacific (WNP), excessive rainfall there and deficient Meiyu–Baiu rainfall. In contrast, when an El Nino Modoki happens simultaneously with a positive IOD, the anomalous EA-WNPSM tends to be much weaker. This difference is attributed to a positive IOD effect. The results demonstrate that a positive IOD usually leads to a strong South Asian summer monsoon heating, which further causes easterly anomalies in the western Pacific. These anomalous easterlies tend to strengthen the WNP anticyclonic vorticity leading to a weak EA-WNPSM. Therefore, a positive IOD weakens the relationship between the El Nino Modoki and the EA-WNPSM. In addition, numerical experiments verified that the strong low-level WNP cyclonic anomaly is built through the off-equatorial heating associated with the local cyclonic circulation. The anomalous WNP anticyclonic vorticity induced by a positive IOD weakens this off-equatorial heating, thus leading to a weak EA-WNPSM.

Air–sea coupling in the IntraAmerican seas (IAS; Caribbean Sea and Gulf of Mexico) is studied through analyses of observational data from satellite, reanalysis products, and in situ measurements. A strong coupling is found between the easterly trade wind −U and meridional SST gradient ∂T/∂y across a localized region of the southern-central Caribbean Sea from seasonal and interannual to decadal time scales. The ∂T/∂y anomaly is caused by a variation in the strength of coastal upwelling off the Venezuelan coast by the wind, which in turn strengthens (weakens) for stronger (weaker) ∂T/∂y. Wind speeds and seasonal fluctuations in IAS have increased in the past two decades with a transition near 1994 coinciding approximately with when the Atlantic multidecadal oscillation (AMO) turned from cold to warm phases. In particular, the seasonal swing from summer's strong to fall's weak trade wind has become larger. The ocean's upper-layer depth has also deepened, by as much as 50% on average in the eastern Gulf of Mexico. These conditions favor the shedding of eddies from the Loop Current, making it more likely to shed at a biannual frequency, as has been observed from altimetry data.

Response of climate conditions in the Atlantic hurricane main development region (MDR) to doubling of atmospheric CO2 has been explored using the new high-resolution coupled climate model, version 2.5 (CM2.5), developed at the Geophysical Fluid Dynamics Laboratory (GFDL). In the annual mean, the SST in the MDR warms by about 2°C in the CO2 doubling run relative to the control run; the trade winds become weaker in the northern tropical Atlantic and the rainfall increases over the ITCZ and its northern region. The amplitude of the annual cycle of the SST over the MDR is not significantly changed by CO2 doubling. However, the authors find that the interannual variations show significant responses to CO2 doubling; the seasonal maximum peak of the interannual variations of the SST over the MDR is about 25% stronger than in the control run. The enhancement of the interannual variations of the SST in the MDR is caused by changes in effectiveness of the wind–evaporation–SST (WES) positive feedback; WES remains a positive feedback until boreal early summer in the CO2 doubling run. The enhancement of the interannual variability of the SST over the MDR in boreal early summer due to CO2 doubling could lead to serious damages associated with the Atlantic hurricane count and drought (or flood) in the Sahel and South America in a future climate.

Wilson and Sidorenkov find that there are four extended pressure features in the summer (DJF) mean sea-level pressure (MSLP) anomaly maps that are centred between 30 and 50° S and separated from each other by approximately 90° in longitude. In addition, they show that, over the period from 1947 to 1994, these patterns drift westward in longitude at rates that produce circumnavigation times that match the 18.6 year lunar Draconic cycle. These type of pressure anomaly pattern naturally produce large extended regions of abnormal atmospheric pressure that pass over the semi-permanent South Pacific sub-tropical high roughly once every ∼ 4.5 years. These moving regions of higher/lower than normal atmospheric pressure increase/decrease the MSLP of the semi-permanent high pressure system, temporarily increasing/reducing the strength of the East-Pacific trade winds. This leads to conditions that preferentially favor the onset of La Niña /El Niño events that last for approximately 30 years. Wilson and Sidorenkov find that the pressure of the moving anomaly pattern changes in such a way as to favor La Niña over El Niño events between 1947 and 1970 and favor El Niño over La Niña events between 1971 and 1994. This is in agreement with the observed evolution of the El Niño/ La Niña events during the latter part of the 20th century. They speculate that the transition of the pattern from a positive to a negative pressure anomaly follows a 31/62/93/186 year lunar tidal cycle that results from the long-term interaction between the Perigee-Syzygy and Draconic lunar tidal cycles. Hence, the IPCC needs to take into consideration the possibility that long term Lunar atmospheric tides could be acting as a trigger to favor either El Niño or La Niña conditions and that these changes in the relative frequency of these two type of events could be responsible for much of the observed changes in the world mean temperature during the 20th century.