Aerosol transport

Research on Desert Dust Transport

Desert dust is an important component of the climate system. It can directly reflect incoming sunlight, influence the development of precipitation in clouds, or fertilise the ocean with iron and other nutrients. Modelling the long-range transport of mineral aerosol is however complicated by the different scale of the involved processes. This includes the mobilisaiton of dust in the desert, uplift into the free atmosphere, long-range transport, and finally wet or dry deposition back to the surface. The aim of this work is to understand the full transport history of the desert dust.

Sahara dust transport events to the Alps

On several occasions a year dust from the Sahara desert crosses the Mediterranean, and is deposited over central Europe. In a study we examined the occurence of desert dust in an ice core from Piz Zupo in the Swiss Alps. Curiously, the desert dust was associated with high concentrations of MSA, a substance that is known to originate from phytoplankton, i.e. organisms living in ocean surface waters.
A detailed modelling study of the dust transport based on backward trajectories revealed that dust can be transported over quite long distances and several days to the Alps. It appears most likely that the MSA was incorporated into the dust plume during the transport over the Mediterranean, possibly due to convective mixing with moist marine boundary layer air.

See also the animations of two dust transport events, which is an electronic supplement to the corresponding paper (Sodemann et al., 2006).

Figure 1: Chlorophyll-a and selected dust transport trajectories. (a) March 2000, (b) October 2000.

Seasonality of Sahara dust export

In a further study, it was explored which synoptic features typically are associated with dust export from the Sahara during one particular year. A one-year climatology of dust export based on the same back-trajectory method as for stuying the transport events revealed a compilcated pattern of dust export. Large dust eruptions of several days into the eastern Atlantic dominate along the African west coast. Dust transport into the Mediterranean is very variable. Short episodes are mostly associated with mid-latitude or Mediterranean cyclones, that are associated with dust transport to the north.

Figure 2: Seasonality of dust export during 2000 along boundaries of the Sahara desert.

Relevant publications

  • Sodemann, H., Palmer, A. S., Schwierz, C., Schwikowski, M. and Wernli, H., 2006: The transport history of two Saharan dust events archived in an Alpine ice core, Atmos. Chem. Phys.,6, 667-688. [Abstract, Paper, PDF, 2MB, Electronic supplement, Online discussion]
  • Sodemann, H., 2006: Tropospheric transport of water vapour: Lagrangian and Eulerian perspectives, Diss. No. 16623, ETH Zurich. Logos Verlag, Berlin, 250 pp. [order a print copy] [request a PDF]
  • Bürzle, S., October 2004: Untersuchung des Saharastaubtransportes an die nordafrikanische Küste im Jahre 2000, Diploma Thesis, IACETH, ETH Zürich, 71 pp.
  • Sodemann, H., Schwierz, C., Wernli, H., Palmer, A. S. and Schwikowski, M., 2005: Transport history of Saharan dust archived in an Alpine ice core, Annual Report 2004, Paul-Scherrer Institute, pg. 29.