Eyjafjallajökull, a volcano in southern Iceland, erupted explosively in April and May 2010 depositing ash over a region of more than 3000 km2 to the east and southeast of the volcano. This deposited ash has been frequently remobilized by the wind causing concern for the health of Icelanders living in the region. An investigation was carried out to determine whether it would be possible to produce forecasts of days when high airborne ash concentrations were likely to occur. Information about the spatially varying surface characteristics of the region of deposited ash is not available so in the modeling approach adopted here ash is released from the surface at a rate proportional to the cube of the excess friction velocity (local friction velocity minus a threshold) only when the friction velocity exceeds a threshold. Movement of the resuspended ash is then modeled in a Lagrangian dispersion model. Modeled ash concentrations are compared to observed concentrations from two periods; PM10 observations between 23 May and 2 July 2010 and airborne particle counts between 21 September 2010 and 16 February 2011. More than 66% of the resuspension episodes between May and July are captured by the model and the relative magnitudes of the modeled episodes in this period are in good agreement with the observations. 66% of episodes between October and February are also captured by the model although there is an increase in the false alarm rate which appears to be due to the influence of precipitation.
The relations between the turbulent structures that contribute to the Reynolds shear stress and the transport of saltating grains and between the wind speed and the saltation are studied. The saltation of sand particles and the turbulent flow field over a beach surface in the Western Baltic Sea are measured with a saltiphone, a sonic anemometer and cup anemometers. Continuous, synchronous measurements of horizontal sand transport at 0.1 m above ground and turbulent velocity fluctuations at 0.55 m were made with a sampling frequency of 1 Hz and 10 Hz, respectively. The stress is considered to be resulting from various turbulent structures including sweeps, ejections, inward interactions and outward interactions using the quadrant technique. The instantaneous horizontal drag force on grains, which initiates saltation, seems to be well represented by the instantaneous horizontal wind measured well above the surface. Results indicate an almost instantaneous response of transport to instantaneous horizontal wind velocity. A new method to establish the threshold friction velocity for intermittent aeolian sand transport is introduced. The observed threshold friction velocity varied between 0.28 ms −1 to 0.36 ms −1. Zusammenfassung Der Zusammenhang zwischen den turbulenten Strukturen, die zur Reynolds-Schubspannung beitragen und dem Transport von durch Saltation bewegten Sandkörnern und der Zusammenhang zwischen der Windgeschwindigkeit und der Saltation wurden untersucht. Die Saltation von Sandkörnern und das turbulente Strömungsfeldüber einer Strandfläche der Westlichen Ostsee wurden mit einem Saltifon, einem akustischen Anemometer und mit Schalensternanemometern untersucht. Es wurden kontinuierliche, synchrone Messungen des horizontalen Sandtransports 0.,1 müber Grund und turbulente Windgeschwindigkeitsfluktuationen 0,55 müber Grund mit einer Abtastrate von 1 Hz bzw. 10 Hz durchgeführt. Die Schubspannung wurde der Quadranten-Technik folgend in die Klassen verzögerte Aufwärtsbewegung (ejection), beschleunigte Aufwärtsbewegung (outward interaction), beschleunigte Abwärtsbewegung (sweep) und verzögerte Abwärtsbewegung (inward interaction) eingeteilt. Die unmittelbaren an den Sandkörnern wirkenden horizontalen Widerstandskräfte, die zur Saltation führen, werden offenbar gut durch die augenblickliche horizontale Windgeschwindigkeit etwas weiterüber den Sandkörnern beschrieben. Die Ergebnisse zeigen fast eine augenblickliche Reaktion des Sandtransports auf die augenblickliche Horizontalwindgeschwindigkeit. Eine neue Methode zur Bestimmung der Schwellenschubspannungsgeschwindigkeit wird vorgestellt. Die beobachteten Schwellenschubspannungsgeschwindigkeiten variierten zwischen 0,28 ms −1 und 0,36 ms −1 .
The 2014-2015 Bárðarbunga fissure eruption at Holuhraun in central Iceland was distinguished by the high emission of gases, in total 9.6 Mt SO 2 , with almost no tephra. This work collates all ground-based measurements of this extraordinary eruption cloud made under particularly challenging conditions: remote location, optically dense cloud with high SO 2 column amounts, low UV intensity, frequent clouds and precipitation, an extensive and hot lava field, developing ramparts, and high-latitude winter conditions. Semi-continuous measurements of SO 2 flux with
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