Llansadwrn (Anglesey) Weather
from the observer's notebook
Deposits of coloured dust on snow covered European mountaintops has been seen on many occasions. The origin of these dusts has been thought to be from the Sahara Desert on the other side of the Mediterranean Sea. But modern methods of numerical trajectory analysis has help to prove, for the first time, that dust from China's TaklaMakan Desert is an alternative source. In a recent retrospective study¹ the dust was shown to have travelled more than 20,000 kilometres over a period of 2 weeks.
Research done in 1994 identified more than 20 red dustfall events on the French Alps and Pyrenees in the previous 20 years. Deposits had been collected and stored in the hope that one day the origin could be identified. Chemical analysis of the minerals in the dust can by comparison indicate likely sources, but trajectory analysis is needed for confirmation. This latest work, using meteorological data from 1990, was able to demonstrate that dust over China on 25 February travelled counterclockwise via the North Pacific, North America and North Atlantic passing just to the south of the UK before being deposited on the Alps on 7 March.
The Global Ozone Chemistry Aerosol Radiation Transport computer model² uses the winds, soil moisture, and surface characteristics to simulate dust generation and transport. The National Oceanic and Atmospheric Administration's (NOAA) Air Resources Laboratory (ARL)³models showed paths of air masses, as they moved around the world, from the time the dust was swept into the atmosphere to when it settled on the Alps.
¹ The findings are highlighted in a paper authored by Francis E. Grousset of the Lamont-Doherty Earth Observatory of Columbia University (LDEOCU), Palisades, N.Y., and Universite Bordeaux, France; Aloys Bory and Pierre E. Biscaye, also of LDEOCU; and Paul Ginoux, University of Maryland, Baltimore County (UMBC) and NASA's Goddard Space Flight Center (GSFC), Greenbelt, Md. The study appeared in a recent issue of the American Geophysical Union's Geophysical Research Letters.
² Global Ozone Chemistry Aerosol Radiation Transport Model
³ ARL (Air Resources Laboratory)
There is further information at GSFC/ NASADustfalls on Anglesey originating from the Great Western and Great Eastern Deserts of Algeria on 25/26 February 2003.
These pages are designed and written by Donald Perkins © 1998 - 2003
Document dated 18 May 2003http://www.llansadwrn-wx.co.uk