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The North African coastal low-level jet (NACLLJ) lies over the cold Canary current and is synoptically linked to the Azores Anticyclone and to the continental thermal low over the Sahara Desert. Although being one of the most persistent and horizontally extended coastal wind jets, this is the first high resolution modelling effort to investigate the NACLLJ climate. The current study uses a ROM atmospheric hindcast simulation with ~ 25 km resolution, for the period 1980–2014. Additionally, the underlying surface wind features are also scrutinized using the CORDEX-Africa runs. These runs allow the building of a multi-model ensemble for the coastal surface flow. The ROM and the CORDEX-Africa simulations are extensively evaluated showing a good ability to represent the surface winds. The NACLLJ shows a strong seasonal cycle, but, unlike most coastal wind jets, e.g. the California one, it is significantly present all year round, with frequencies of occurrence above 20%. In spring and autumn, the maxima frequencies are around 50%, and reach values above 60% in summer. The location of maximum frequency of occurrence migrates meridionally from season to season, being in winter and spring upwind of Cap-Vert, and in summer and autumn offshore the Western Sahara. Analogously, the lowest jet wind speeds occur in winter, when the median is below 15 m/s. In summer, the jet wind speed median values are ~ 20 m/s and the maxima are above 30 m/s. The jet occurs at heights ~ 360 m. A momentum balance is pursued disclosing that the regional flow is almost geostrophic, dominated by the pressure gradient and Coriolis force. Over the jet areas the ageostrophy is responsible for the jet acceleration. [ABSTRACT FROM AUTHOR]

The North African Coastal Low-Level Jet (NACLLJ) is a semi-permanent feature offshore the north western African coast, linked to the cold nearshore upwelling of the Canary Eastern Boundary Current system. Its main synoptic drivers are the Azores Anticyclone over the ocean and the inland Sahara thermal low. The coastal jet events occur in one of the world's most productive fisheries region, thus the evaluation of the effects of global warming in its properties is imperative. This study proposes an analysis of the annual and intra-annual attributes of the NACLLJ for two time periods 1976–2005 (historical) and 2070–2199 (future), resorting to coupled and uncoupled atmosphere–ocean simulations with the ROM model, as well as near surface offshore wind speed from the CORDEX-Africa ensemble. The future simulations follow the RCP8.5 greenhouse gas emissions scenario. Overall, the ROM coupled simulation presents the best performance in reproducing the present-climate near surface wind speed, offshore northwest Africa, compared to the remaining RCM simulations. The higher SST resolution in the coupled simulations favours much localised colder upwelling strips near the coast and consequently stronger jets. In future climate, a small increase in the surface wind speed is projected, mainly linked to the regions of coastal jet presence. The NACLLJ is projected to be more frequent and intense, encompassing larger areas. An increase of the jet seasonal frequencies of occurrence is projected for all seasons, which is larger from spring to autumn (up to 15, 16 and 22% more frequent, respectively). However, in some offshore areas the winter NACLLJ persistency is likely to double, relatively to present-climate. Higher inter-annual variability is also projected for the future NACLLJ seasonal frequencies. The strengthening of the coastal jet speeds is also significant, between 5 and 12% in all seasons. Additionally, the jet's diurnal cycle shows an increase in jet occurrence across the day, particularly in the mid and late afternoon. [ABSTRACT FROM AUTHOR]

The soil moisture-temperature coupling represents a determinant role in the evolution of weather and climate, as these interactions are of utmost importance for extreme phenomena. For this study, daily data taken from all CORDEX-Africa simulations are considered. Two periods were selected, a historical (1971-2000) and a future (2071-2100) period which features two Intergovernmental Panel for Climate Change Representative Concentration Pathways (IPCC-RCP) scenarios: the RCP 8.5 and the RCP 4.5. A throughout assessment of the ability of the models to express the coupling signal in current climate is performed. A multi-model ensemble mean is built. The ensemble mean outperforms individual models in almost all situations, representing the best estimate for both current and future climates. The soil moisture-temperature coupling strength is assessed with the evaporative fraction, correlations with 10 days of non-overlapping means between soil moisture and evaporative fraction and between latent and sensible heat fluxes. In general, individual models are consistent in representing the weak, no-coupling and strong coupling regions, corresponding to the humid, arid and semi-arid or Mediterranean environments, as identified by the evaporative fraction. However, some inter-model variability is found regarding the intensity of each regime. In desert areas such as Sahara and Namib deserts, where precipitation is overestimated, and over large areas of central Africa, characterized by an overall dry bias, both induce an overestimation of the coupling strength. For future conditions, the increase of the surface energy budget and changes in precipitation regimes, hints towards an expansion of the arid climates. On the other hand, the intensification of the coupling strength over humid and semi-humid areas, suggest a shift of the strong coupling regions. The increase of the available surface energy and changes in coupling regimes, projected for the end of the 21st century, reveal an overall increase of sensible heating and a consequently widespread warming of up to 7 oC, for the worst-case scenario.AcknowledgementsThe authors wish to acknowledge project SOLAR (PTDC/GEOMET/7078/2014) and FCT - project UID/GEO/50019/ 2019 - Instituto Dom Luiz [ABSTRACT FROM AUTHOR]