Relationships between Atmospheric Circulation and Wind Erosion in Southern Sweden and Australia

Detta är en avhandling från Marie Ekström, Dept. of Phys. Geog. and Ecos. Anal., V-huset John Ericssons väg 1, 2nd floor

Sammanfattning: Wind erosion is a serious threat to soil resources as it causes depletion of the fine fractions that may result in a less fertile soil. Wind erosion encompasses several processes of which many are related to climate variables. To date, there is little work performed on how wind erosion relates to climate and climate change. In this thesis, atmospheric circulation and wind erosion were analysed to improve the understanding of these relationship in Scania (southern Sweden) and Australia. Low-frequency variability of the atmospheric circulation in Scania was examined using surface wind from the 20th century. Analysis of the relationship between wind erosion and atmospheric circulation was based on de-seasonalized mean-sea-level pressure patterns (PPs), describing the main modes of atmospheric circulation. For Scania, the PPs were related to wind erosion inferred from area damage in the sugar beet district Jordberga (1973-1991). For Australia, the PPs were related to dust storm data from meteorological stations (1960-1999). Relationships between dust storms and the atmospheric circulation were further analysed using atmospheric flow indices (1960-1999). In Scania, the analysis of the PPs showed that the majority (74 %) of crop damage due to wind erosion was associated with an easterly and then a westerly flow pattern (5 %). The former was associated with relatively dry conditions and moderate wind speeds whilst the westerly flow PP characterised short episodes of high wind speeds. Analysis of the wind series showed large shifts in wind conditions during the 20th century, particularly during the spring. The westerly winds dominated throughout the century, although the period 1930-1960 showed increased frequencies of easterly winds. In Australia, at least two regions existed where dust storms were limited by different factors. In much of the coastal region dust storms were most common in summer when the region was at its driest. In the continental region dust storms were most common during late spring to early summer when the non-precipitation cold front was most frequent. Increased dust storm activity was found during the 1960s and early 1990s for the continental interior region and during the 1990s for the coastal region. It was suggested that increased dust storm activity during the 1960s was due to higher frequencies of a circulation that allowed for a further northward pathway of the fronts over the continent in combination with larger numbers of mid-latitude cyclones. The increase during the 1990s was most likely linked to the pronounced El Niño conditions, associated with less than average rainfall in much of Australia, during these years.

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