UC San Diego
The Role the Saharan Heat Low Plays in the Variability of Dust Emission and Transport in North Africa from Synoptic to Decadal Scales
- Author(s): Wang, Weijie
- Advisor(s): Evan, Amato T
- et al.
Dust over the Atlantic undergoes decadal variability. Over the past three decades, satellite and in-situ measurements show a downward trend in dust concentration over the Atlantic, indicating there is less dust emission in the Sahara. Meanwhile, observations show an upward trend in the Sahel precipitation. However, it is unknown what affects dust emission in the Sahara and precipitation in the Sahel simultaneously. Dust emission in North Africa also undergoes synoptic variability and high concentration of dust is often observed in the western Sahara, but it is unclear whether dust over the western Sahara is due to local emission or dust transport from the east.
The aim of this thesis is twofold, first, to examine the role the Saharan heat low (SHL) plays in dust emission and precipitation from synoptic to decadal timescales. and second, to identify bias of dust in the model. To do so I use reanalysis and satellite products to construct the time series of dust, precipitation and the SHL and perform regression analysis to examine the effect of the SHL on precipitation and winds, which are associated with dust emission. Then I study the lead and lag relationship between the SHL and dust concentration in North African on the synoptic scale to identify source regions. Lastly, I identify the biases in a dust source function using dust output from a climate model.
The results from this thesis suggest that the warming of the SHL results in the increase of precipitation in the Sahel and the reduction in dust emission by changing low-level winds on the decadal timescale. On the synoptic scale, cool phases of the SHL is associated with more dust emission and 10% of the dust over western Africa is from source regions to the east. Lastly, the dust source function may overestimate dust emission in the Sahel and western Africa.