Climatology of nocturnal low‐level jets over North Africa and implications for modeling mineral dust emission

Fiedler, Stephanie; Schepanski, Kerstin; Heinold, Bernd; Knippertz, Peter; Tegen, Ina

doi:10.1002/jgrd.50394

Cited by 139 publications

(267 citation statements)

References 85 publications

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“…Other external driving data sets, e.g. potential dust sources, are chosen as in previous studies (summarized above, Fiedler et al 2013Fiedler et al , 2014Heinold et al 2013) and are the same for all offline calculations. This approach allows to assign differences in the offline dust emission calculations to the wind speed.…”

Section: Dust Emissionmentioning

confidence: 99%

“…The diurnal cycle of dust emission from H2ES-I, T-H2ES-O and T-EI-O as well as box-and-whisker plots of the near-surface wind speed from HadGEM2-ES and ERAInterim forecasts seasonally averaged for 1980-2009 are analyzed for the sub-domains S1 over parts of West Africa and S3 enclosing the Bodélé Depression. The geographical location of these sub-domains follows the definition in Fiedler et al (2013) and are shown in Fig. 4.…”

Section: Diurnal Cyclementioning

confidence: 99%

“…The focus is set on the NLLJ as an important driver for dust emission in North Africa (e.g. Washington and Todd 2005;Schepanski et al 2009;Fiedler et al 2013;Heinold et al 2013). NLLJs in North Africa can be formed by different mechanisms, namely inertial oscillations (e.g.…”

Section: Introductionmentioning

confidence: 99%

“…Washington and Todd 2005;Todd et al 2008). Hourly output from HadGEM2-ES in combination with the automated detection tool for NLLJs by Fiedler et al (2013) offers the unique opportunity to statistically analyze this dust-emitting process on sub-daily scales over a climatological time period of 30 years for new insights into the model performance. Since a long-term observational data set of dust emission does not exist, the dust emission climatology from the model by Tegen et al (2002) calculated with wind speeds from ERA-Interim as in Fiedler et al (2013Fiedler et al ( , 2014 is used here as a benchmark.…”

Section: Introductionmentioning

confidence: 99%

“…Hourly output from HadGEM2-ES in combination with the automated detection tool for NLLJs by Fiedler et al (2013) offers the unique opportunity to statistically analyze this dust-emitting process on sub-daily scales over a climatological time period of 30 years for new insights into the model performance. Since a long-term observational data set of dust emission does not exist, the dust emission climatology from the model by Tegen et al (2002) calculated with wind speeds from ERA-Interim as in Fiedler et al (2013Fiedler et al ( , 2014 is used here as a benchmark. Quantifying the relative importance of NLLJs as a dust-emitting process from the models helps identifying systematic model behavior affecting dust emission, providing the basis for further advances in Earth system model development.…”

Section: Introductionmentioning

confidence: 99%

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A process-based evaluation of dust-emitting winds in the CMIP5 simulation of HadGEM2-ES

et al. 2015

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Medium-Range Weather Forecasts. Compared to ERAInterim, a stronger pressure ridge over northern Africa in winter and the southward displaced heat low in summer result in differences in location and strength of NLLJs. Particularly the larger geostrophic winds associated with the stronger ridge have a strengthening effect on NLLJs over parts of West Africa in winter. Stronger NLLJs in summer may rather result from an artificially increased mixing coefficient under stable stratification that is weaker in HadGEM2-ES. NLLJs in the Bodélé Depression are affected by stronger synoptic-scale pressure gradients in HadGEM2-ES. Wintertime geostrophic winds can even be so strong that the associated vertical wind shear prevents the formation of NLLJs. These results call for further model improvements in the synoptic-scale dynamics and the physical parametrization of the nocturnal stable boundary layer to better represent dust-emitting processes in the atmospheric model. The new approach could be used for identifying systematic behavior in other models with respect to meteorological processes for dust emission. This would help to improve dust emission simulations and contribute to decreasing the currently large uncertainty in climate change projections with respect to dust aerosol.

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Section: Dust Emissionmentioning

confidence: 99%

Section: Diurnal Cyclementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

A process-based evaluation of dust-emitting winds in the CMIP5 simulation of HadGEM2-ES

et al. 2015

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Intraseasonal variability and atmospheric controls on daily dust occurrence frequency over the central and western Sahara during the boreal summer

Ashpole

Washington

2013

JGR Atmospheres

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[1] We classify satellite-derived maps of daily dust occurrence frequency over the central and western Sahara (CWS) during the boreal summer in order to identify typical patterns using the neural network based system of self-organized maps. Resulting dust states vary in terms of the frequency of dust occurrence and its location. The most commonly occurring dust states are those of relatively low dust detection frequency. On days with relatively high dust occurrence, dust tends to favor either a location close to the Algeria-Mali-Niger border triple point (TP) or further to the northwest across the western half of the Mali-Algeria border (MAB). States in which dust is detected at both locations simultaneously are rare. There is a distinct intraseasonal progression in preferred dust location from the TP in the early season to the MAB later in the season. The evolution of dust states reveals a one-way transition from dust at the TP to dust at the MAB and then to reduced daily dust occurrence frequency. There is a distinct degree of interannual variability in the occurrence frequency of the different states, dominated by the extremes of high and low dust detection frequency. Analysis of climatological composites demonstrates that monsoon surges into the Saharan heat low are associated with days of high dust detection frequency, while a strong Harmattan into the CWS is linked to days with less frequent dust presence. The CWS atmospheric dust budget for June-August is thus strongly linked to the dynamics of the West African monsoon.Citation: Ashpole, I., and R. Washington (2013), Intraseasonal variability and atmospheric controls on daily dust occurrence frequency over the central and western Sahara during the boreal summer,

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Evidence of a weakly absorbing intermediate mode of aerosols in AERONET data from Saharan and Sahelian sites

et al. 2013

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Accurate retrievals of aerosol size distribution are necessary to estimate aerosols' impact on climate and human health. The inversions of the Aerosol Robotic Network (AERONET) usually retrieve bimodal distributions. However, when the inversion is applied to Saharan and Sahelian dust, an additional mode of intermediate size between the coarse and fine modes is sometimes seen. This mode explains peculiarities in the behavior of the Ångström exponent, along with the fine mode fraction retrieved using the spectral deconvolution algorithm, observed in a March 2006 dust storm. For this study, 15 AERONET sites in northern Africa and on the Atlantic are examined to determine the frequency and properties of the intermediate mode. The mode is observed most frequently at Ilorin in Nigeria. It is also observed at Capo Verde and multiple sites located within the Sahel but much less frequently at sites in the northern Sahara and the Canary Islands. The presence of the intermediate mode coincides with increases in Ångström exponent, fine mode fraction, single‐scattering albedo, and to a lesser extent percent sphericity. The Ångström exponent decreases with increasing optical depth at most sites when the intermediate mode is present, but the fine mode fraction does not. Single‐scattering albedo does not steadily decrease with fine mode fraction when the intermediate mode is present, as it does in typical mixtures of dust and biomass‐burning aerosols. Continued investigation is needed to further define the intermediate mode's properties, determine why it differs from most Saharan dust, and identify its climate and health effects.

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Climatology of nocturnal low‐level jets over North Africa and implications for modeling mineral dust emission

Cited by 139 publications

References 85 publications

A process-based evaluation of dust-emitting winds in the CMIP5 simulation of HadGEM2-ES

A process-based evaluation of dust-emitting winds in the CMIP5 simulation of HadGEM2-ES

Intraseasonal variability and atmospheric controls on daily dust occurrence frequency over the central and western Sahara during the boreal summer

Evidence of a weakly absorbing intermediate mode of aerosols in AERONET data from Saharan and Sahelian sites

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