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Malte Jäger

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Malte Jäger
Institution: Institute for Environmental Physics (IUP), University of Bremen
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PhD project:

Deposition of Desert Dust observed from Space

Desert dust plays a prominent role in climate as it influences the radiation budget in the atmosphere and, if being transported to the ocean, affects the ecosystem, e.g. by acting as fertilizer. Each year large masses of desert dust originating from the Saharan area are transported by westerly trade winds over the Atlantic Ocean towards the American continent. Deposits of this mineral dust are regularly measured in the Caribbean and have even been found in the Amazon region.

Measurements of dust deposition are usually performed using collectors on land and on buoys as well as sediment traps deployed across the Atlantic Ocean. However, regional to continental coverage can be only achieved with satellites. The main part of my PhD project is to develop a new methodology for the assessment of desert dust deposition from top-of-atmosphere reflected solar irradiance measured by satellite. This methodology is based on the observation of changes in columnar aerosol optical thickness (AOT) along the transport path of dust outflows from the Sahara. The guiding idea is that, if transport orientation is correctly estimated, a decrease in AOT across the Atlantic can be linked to the deposition of aerosols onto the ocean surface.
Consequently the implementation of the wind fields for trajectory prediction and the choice of comparison sites are of critical importance for deposition estimation. Therefore several approaches will be tested: AOT data from polar orbiting satellite instruments like SeaWiFS, MERIS and MISR will be used as well as data from geostationary instruments like MSG SEVIRI, which offers special insights to the transport of the dust due to the high temporal resolution. The transport paths will also be calculated in several ways: In a first step using a simple approach based on seasonal predominant wind directions. Increased precision shall be achieved by the application of wind fields from meteorological reanalysis data. Additionally long range trajectories from meteorological models will be used to follow air parcels loaded with dust along their way as precisely as possible.

Finally the deposition results from the new satellite based retrieval will be compared with in-situ records from on-land dust collectors, buoys, sediment traps and ship cruises. Further, the fertilizing effect of deposited desert dust shall be researched using the new deposition maps together with satellite based marine productivity products.

Thesis committee:

Prof. Dr. John Burrows University of Bremen
Prof. Dr. Astrid Bracher University of Bremen
Dr. Luca Lelli University of Bremen
Dr. Jan-Berend Stuut University of Bremen and Royal Netherlands Institute for Sea Research (NIOZ)