Climatology of coastal wind regimes in Benin

Guédjé, François Kossi; Houeto, A.; Houngninou, E.; Fink, Andreas H.; Knippertz, Peter

doi:10.1127/metz/2019/0930

Cited by 10 publications

(24 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This agrees with Guedje et al . (), who investigated measurements from a buoy off the Beninese coast. Surprisingly, there is a difference in temperatures over sea of more than 0.6 C between the models, with UKMO being the warmest and IFS and ICON OPS the coldest.…”

Section: Resultsmentioning

confidence: 99%

“…() showed that the choice of the radiation scheme influences the north–south gradient in surface temperature and thus the strength of the monsoon flow. An important feature along the Guinea Coast is the land–sea breeze (Guedje et al ., ), which in summer interacts with the monsoon flow to form the Maritime Inflow of the Gulf of Guinea, a stationary front about 30 km from the coast that begins to propagate inland in the late afternoon (Adler et al ., ). The stationarity is caused by the strong daytime turbulence over land (Deetz et al ., ).…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

An evaluation of operational and research weather forecasts for southern West Africa using observations from the DACCIWA field campaign in June–July 2016

Kniffka

Knippertz

Fink

et al. 2020

Quart J Royal Meteoro Soc

Self Cite

View full text Add to dashboard Cite

Reliable and accurate weather forecasts, particularly those of rainfall and its extremes, have the potential to improve living conditions in densely populated southern West Africa (SWA). The limited availability of observations has long impeded a rigorous evaluation of current state-of-the-art forecast models.The field campaign of the Dynamics-Aerosol-Chemistry-Cloud Interactions in West Africa (DACCIWA) project in June-July 2016 has created an unprecedentedly dense set of measurements from surface stations and radiosondes.Here we present results from a comprehensive evaluation of both numerical model forecasts and satellite products using these data on a regional and local level. Results reveal a substantial observational uncertainty showing considerable underestimations in satellite estimates of rainfall and low-cloud cover with little correlation at the local scale. Models have a dry bias of 0.1-1.9 mm ⋅ day −1 in rainfall and too low column relative humidity. They tend to underestimate low clouds, leading to excess surface solar radiation of 43 W ⋅ m −2 . Remarkably, most models show some skill in representing regional modulations of rainfall related to synoptic-scale disturbances, while local variations in rainfall and cloudiness are hardly captured. Slightly better results are found with respect to temperature and for the post-onset rather than for the pre-onset period. Delicate local features such as the Maritime Inflow phenomenon are also rather poorly represented, leading to too cool, dry and cloudy conditions at the coast. Differences between forecast days 1 and 2 are relatively small and hardly systematic, suggesting a relatively quick error saturation. Using explicit convection leads to more realistic spatial variability in rainfall, but otherwise no marked improvement. Future work should aim at improving the subtle balance between the diurnal This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

show abstract

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

An evaluation of operational and research weather forecasts for southern West Africa using observations from the DACCIWA field campaign in June–July 2016

Kniffka

Knippertz

Fink

et al. 2020

Quart J Royal Meteoro Soc

Self Cite

View full text Add to dashboard Cite

show abstract

“…The Global Fire Assimilation System (GFAS) data are used for biomass burning emissions with a scale factor of 3.4 applied to the organic carbon emissions as recommended by Kaiser et al (2012). The model uses MEGAN v2.1 (Guenther et al, 2012) for biogenic emissions of volatile organic compounds, biogenic soil NO x emissions from Hudman et al (2012) and interactive lightning NO x (Murray et al, 2012). More details of the processing of organic aerosol in the model can be found in Park et al (2003).…”

Section: Regional Modellingmentioning

confidence: 99%

Remote biomass burning dominates southern West African air pollution during the monsoon

et al. 2019

Self Cite

View full text Add to dashboard Cite

Abstract. Vast stretches of agricultural land in southern and central Africa are burnt between June and September each year, which releases large quantities of aerosol into the atmosphere. The resulting smoke plumes are carried west over the Atlantic Ocean at altitudes between 2 and 4 km. As only limited observational data in West Africa have existed until now, whether this pollution has an impact at lower altitudes has remained unclear. The Dynamics-aerosol-chemistry-cloud interactions in West Africa (DACCIWA) aircraft campaign took place in southern West Africa during June and July 2016, with the aim of observing gas and aerosol properties in the region in order to assess anthropogenic and other influences on the atmosphere. Results presented here show that a significant mass of aged accumulation mode aerosol was present in the southern West African monsoon layer, over both the ocean and the continent. A median dry aerosol concentration of 6.2 µg m−3 (standard temperature and pressure, STP) was observed over the Atlantic Ocean upwind of the major cities, with an interquartile range from 5.3 to 8.0 µg m−3. This concentration increased to a median of 11.1 µg m−3 (8.6 to 15.7 µg m−3) in the immediate outflow from cities. In the continental air mass away from the cities, the median aerosol loading was 7.5 µg m−3 (5.9 to 10.5 µg m−3). The accumulation mode aerosol population over land displayed similar chemical properties to the upstream population, which implies that upstream aerosol is a significant source of aerosol pollution over the continent. The upstream aerosol is found to have most likely originated from central and southern African biomass burning. This demonstrates that biomass burning plumes are being advected northwards, after being entrained into the monsoon layer over the eastern tropical Atlantic Ocean. It is shown observationally for the first time that they contribute up to 80 % to the regional aerosol loading in the monsoon layer over southern West Africa. Results from the COSMO-ART (Consortium for Small-scale Modeling – Aerosol and Reactive Trace gases) and GEOS-Chem models support this conclusion, showing that observed aerosol concentrations over the northern Atlantic Ocean can only be reproduced when the contribution of transported biomass burning aerosol is taken into account. As a result, the large and growing emissions from the coastal cities are overlaid on an already substantial aerosol background. Simulations using COSMO-ART show that cloud droplet number concentrations can increase by up to 27 % as a result of transported biomass burning aerosol. On a regional scale this renders cloud properties and precipitation less sensitive to future increases in anthropogenic emissions. In addition, such high background loadings will lead to greater pollution exposure for the large and growing population in southern West Africa. These results emphasise the importance of including aerosol from across country borders in the development of air pollution policies and interventions in regions such as West Africa.

show abstract

“…Consistently for both experiments, regional maxima of wet biases occur a bit inland from the coasts that could be related to the occurrence of convection related to the sea‐breeze circulation (e.g. Guedje et al ., ).…”

Section: Influence On Ecmwf Forecastsmentioning

confidence: 99%

The influence of DACCIWA radiosonde data on the quality of ECMWF analyses and forecasts over southern West Africa

Linden

Knippertz

Fink

et al. 2020

Quart J Royal Meteoro Soc

Self Cite

View full text Add to dashboard Cite

During the DACCIWA (Dynamics–Aerosol–Chemistry–Cloud Interactions in West Africa) field campaign ∼900 radiosondes were launched from 12 stations in southern West Africa from 15 June to 31 July 2016. Subsequently, data‐denial experiments were conducted using the Integrated Forecasting System of the European Centre for Medium‐range Weather Forecasts (ECMWF) to assess the radiosondes' impact on the quality of analyses and forecasts. As observational reference, satellite‐based estimates of rainfall and outgoing long‐wave radiation (OLR) as well as the radiosonde measurements themselves are used. With regard to the analyses, the additional observations show positive impacts on winds throughout the troposphere and lower stratosphere, while large lower‐tropospheric cold and dry biases are hardly reduced. Nonetheless, downstream, that is farther inland from the radiosonde stations, we find a significant increase (decrease) in low‐level night‐time temperatures (monsoon winds) when incorporating the DACCIWA observations, suggesting a possible linkage via weaker cold air advection from the Gulf of Guinea. The associated lower relative humidity leads to reduced cloud cover in the DACCIWA analysis. Closer to the coast and over Benin and Togo, DACCIWA observations increase low‐level specific humidity and precipitable water, possibly due to changes in advection and vertical mixing. During daytime, differences between the two analyses are generally smaller at low levels. With regard to the forecasts, the impact of the additional observations is lost after a day or less. Moderate improvements occur in low‐level wind and temperature but also in rainfall over the downstream Sahel, while impacts on OLR are ambiguous. The changes in precipitation appear to also affect high‐level cloud cover and the tropical easterly jet. The overall rather small observation impact suggests that model and data assimilation deficits are the main limiting factors for better forecasts in West Africa. The new observations and physical understanding from DACCIWA can hopefully contribute to reducing these issues.

show abstract

Climatology of coastal wind regimes in Benin

Cited by 10 publications

References 0 publications

An evaluation of operational and research weather forecasts for southern West Africa using observations from the DACCIWA field campaign in June–July 2016

An evaluation of operational and research weather forecasts for southern West Africa using observations from the DACCIWA field campaign in June–July 2016

Remote biomass burning dominates southern West African air pollution during the monsoon

The influence of DACCIWA radiosonde data on the quality of ECMWF analyses and forecasts over southern West Africa

Contact Info

Product

Resources

About