The mysterious long-range transport of giant mineral dust particles Van der Does, M., Knippertz, P., Zschenderlein, P., Harrison, R.G., Stuut, J-B.W. This could well be possible, especially in summer when there are many such fronts of convective cells. Using the ambient meteorological conditions during the time period when the above dust particles were collected, wind trajectories were calculated and it turned out that only four such repeated uplift cycles already suffice to bridge the distance between African coast and buoy Michelle at 12 oN/38 oW (>2,000km). Before hitting the ocean surface, they could well be lifted up in a new (or moving along) convective cell and be lifted up into the atmosphere again. At the anvil at the top of these clouds, particles can be ejected and settle towards the ocean. In these cells, air rises at a speed of up to 20 m/s and as a result, particles are lifted to several kilometers altitude within minutes. Below you see a photo of a cumulonimbus cloud near Barbados (photo credits: Stuart Axe, published on flickr), which results from convective cells, and which typically occur along latitudinal bands in the (sub)tropics. One of these is repeated uplift by convective cells. In the paper Michèlle and her colleagues propose and discuss a number of potential mechanisms. Somehow these large particles are kept aloft. Below you see photos of individual particles collected on these buoys. There were three PhD students in the project: Carmen Friese, Laura Korte and Michèlle van der Does and each of them had "their own" buoy. In the projects TRAFFIC (funded by NWO) and DUSTTRAFFIC (funded by ERC) we constructed dust-collecting buoys and deployed them in the middle of the equatorial north Atlantic Ocean, right below the core of the Saharan dust plume and up to 3,500km from the African coast. In their new paper, Van der Does and colleagues push these boundaries even more with particles up to 400µm collected from the atmosphere over the remote Atlantic Ocean. In addition, already in the 1980's so-called "giant particles" (>75µm) were found at remote places that could only have travelled through the air. In climate models that are based on physical laws and meteorological principles, dust particles were always assumed to be smaller than 10µm although in numerous studies it was shown that particles collected from the atmosphere at sea as well as found in marine sediment cores were much larger: up to several hundreds of micrometers.
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