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Title: A model-based analysis of meteorological processes important for North African dust emission
Author: Fiedler, Stephanie
ISNI:       0000 0004 5356 1135
Awarding Body: University of Leeds
Current Institution: University of Leeds
Date of Award: 2014
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Dust aerosol is abundant and important in the Earth system due to its influence on the radiation balance, the hydrological cycle, human health and ecosystems. Reducing the currently large uncertainties in dust effects requires realistic simulations of the lifecycle of dust aerosol which depends on the time, location and amount of dust emission. Emission estimates from models show a large variety, the reduction of which requires a systematic evaluation of dust-emitting winds. Different processes are known, but their relative importance was previously poorly quantified. This work investigates dust-emitting winds in North Africa based on single meteorological processes which helps guiding future model development. Based on 32 years of ERA-Interim data and a dust model, the emission amounts associated with nocturnal low-level jets (NLLJs), atmospheric depressions and mobile, long-lived cyclones are estimated climatologically for the first time. The results highlight NLLJs as an important driver for dust emission, particularly in the Bodélé Depression during winter. Associated maxima in mid-morning emission underline the importance of temporally high-resolved winds for dust modelling. ERA-Interim systematically underestimates NLLJ core wind speeds, likely due to artificially increased mixing in stable boundary layers. Derived emission frequencies over the Bodélé Depression agree well with observations, but differ elsewhere. Atmospheric depressions, often in the form of heat lows and lee depressions, occur frequently and coincide with the majority of dust emission. Few depressions develop into mobile and long-lived cyclones which coincide with particularly intense events. The largest emission fractions associated with cyclones are found in northeast Africa during spring, primarily at day with a small emission reduction by soil moisture. Smaller West African areas show similar fractions, likely associated with nearsurface signatures of African Easterly Waves. Comparing results derived from ERA-Interim against the Earth system model of the UK Met Office shows considerable disagreement in NLLJ core wind speeds and dust emissions. In depth analysis underlines the urgency for model development that improves the synoptic-scale conditions and the stable boundary layer. Such model improvements hold the potential to advance the scientific understanding of dust aerosol in the Earth system.
Supervisor: Knippertz, Peter ; Ross, Andrew Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available