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11.
Particulate emissions from Mt. Etna in the fine-size range below 100 nm were studied in June and September 1989. The aerosol particles were characterized by size, concentration and photoelectric activity. These quantities are sensitive to the physical and chemical properties of the magma. Concentrations varied from 104 to 107 cm-3. The size distributions peak below 20 nm (radius) and are very narrow. The particles are generated mainly by nucleation and condensation of magmatic volatiles in a strong temperature gradient. The photoelectric activity of these particles can indicate high magma levels and increased exsolution of volatiles. It is therefore related to the observed activity of the respective crater and may be helpful as a prediction tool when used in conjunction with other volcano-monitoring techniques. 相似文献
12.
Markus J. Aschwanden Jong Kwan Lee G. Allen Gary Michael Smith Bernd Inhester 《Solar physics》2008,248(2):359-377
The three-dimensional (3D) modeling of coronal loops and filaments requires algorithms that automatically trace curvilinear
features in solar EUV or soft X-ray images. We compare five existing algorithms that have been developed and customized to
trace curvilinear features in solar images: i) the oriented-connectivity method (OCM), which is an extension of the Strous pixel-labeling algorithm (developed by Lee,
Newman, and Gary); ii) the dynamic aperture-based loop-segmentation method (developed by Lee, Newman, and Gary); iii) unbiased detection of curvilinear structures (developed by Steger, Raghupathy, and Smith); iv) the oriented-direction method (developed by Aschwanden); and v) ridge detection by automated scaling (developed by Inhester). We test the five existing numerical codes with a TRACE image
that shows a bipolar active region and contains over 100 discernable loops. We evaluate the performance of the five codes
by comparing the cumulative distribution of loop lengths, the median and maximum loop length, the completeness or detection
efficiency, the accuracy, and flux sensitivity. These algorithms are useful for the reconstruction of the 3D geometry of coronal
loops from stereoscopic observations with the STEREO spacecraft, or for quantitative comparisons of observed EUV loop geometries
with (nonlinear force-free) magnetic field extrapolation models. 相似文献
13.
L’Her Alexandre Reinert Markus Prants Sergey Carton Xavier Morvan Mathieu 《Ocean Dynamics》2021,71(5):601-612
Ocean Dynamics - The Eastern Kamchatka Current (EKC) is the western boundary current of the North Pacific subpolar gyre. Southeast of the Kamchatka Peninsula lies a large anticyclonic eddy, the... 相似文献
14.
The European Water Framework Directive demands to assess and report the chemical and ecological status of water bodies (WB). Linking their status to drivers and pressures and deriving suitable mitigation measures require knowledge of the shape and area of WB catchments. We derived a network of 26 570 WB catchments in Germany using the hydrologically-defined drainage basins of the German federal states. We established a network of 338 149 drainage basins. This network underwent plausibility checks and a validation with the catchment areas of 348 monitoring stations across Germany. To this network, we assigned the longest intersecting or the next downstream WB code. To account for geometric inaccuracies we revised spurious intersections resulting in splittings and cycles in the WB network. As WB may be ecologically but not hydrologically well defined, we split them at confluences and intersections. The network of drainage basins matched the monitoring stations with a Nash-Sutcliffe efficiency of 1.00. The final WB network contained 11 005 out of the 11 586 original WBs longer than 1 m. The corresponding local catchment areas range from <<0.0001 to 446 km2, with a median of 10 km2. The dataset combines the requirements of hydrological and ecological modelling applications at basin or national scales with the needs of the EU reporting which can foster their acceptance by state authorities and river-basin management. 相似文献
15.
Stefan Jansen Eva Walpersdorf Ursula Werner Markus Billerbeck Michael E Böttcher Dirk de Beer 《Ocean Dynamics》2009,59(2):317-332
In this article, we describe the dynamics of pH, O2 and H2S in the top 5–10 cm of an intertidal flat consisting of permeable sand. These dynamics were measured at the low water line
and higher up the flat and during several seasons. Together with pore water nutrient data, the dynamics confirm that two types
of transport act as driving forces for the cycling of elements (Billerbeck et al. 2006b): Fast surface dynamics of pore water chemistry occur only during inundation. Thus, they must be driven by hydraulics (tidal
and wave action) and are highly dependent on weather conditions. This was demonstrated clearly by quick variation in oxygen
penetration depth: Seeps are active at low tide only, indicating that the pore water flow in them is driven by a pressure
head developing at low tide. The seeps are fed by slow transport of pore water over long distances in the deeper sediment.
In the seeps, high concentrations of degradation products such as nutrients and sulphide were found, showing them to be the
outlets of deep-seated degradation processes. The degradation products appear toxic for bioturbating/bioirrigating organisms,
as a consequence of which, these were absent in the wider seep areas. These two mechanisms driving advection determine oxygen
dynamics in these flats, whereas bioirrigation plays a minor role. The deep circulation causes a characteristic distribution
of strongly reduced pore water near the low water line and rather more oxidised sediments in the centre of the flats. The
two combined transport phenomena determine the fluxes of solutes and gases from the sediment to the surface water and in this
way create specific niches for various types of microorganisms. 相似文献
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Atmospheric boundary-layer structure observed during a haze event due to forest-fire smoke 总被引:1,自引:0,他引:1
Markus?PahlowEmail author Jan?Kleissl Marc?B.?Parlange 《Boundary-Layer Meteorology》2005,114(1):53-70
During a haze event in Baltimore, U.S.A. from July 6 to 8, 2002, smoke from forest fires in the Québec region (Canada), degraded air quality and impacted upon local climate, decreasing solar radiation and air temperature. The smoke particles in and above the atmospheric boundary layer (ABL) served as a tracer and provided a unique opportunity to investigate the ABL structure, especially entrainment. Elastic backscatter lidar measurements taken during the haze event distinctly reveal the downward sweeps (or wisps) of smoke-laden air from the free atmosphere into the ABL. Visualisations of mechanisms such as dry convection, the entrainment process, detrainment, coherent entrainment structures, and mixing inside the ABL, are presented. Thermals overshooting at the ABL top are shown to create disturbances in the form of gravity waves in the free atmosphere aloft, as evidenced by a corresponding ripple structure at the bottom of the smoke layer. Lidar data, aerosol ground-based measurements and supporting meteorological data are used to link free atmosphere, mixed-layer and ground-level aerosols. During the peak period of the haze event (July 7, 2002), the correlation between time series of elastic backscatter lidar data within the mixed layer and the scattering coefficient from a nephelometer at ground level was found to be high (R=0.96 for z =324 m, and R=0.89 for z=504 m). Ground-level aerosol concentration was at a maximum about 2 h after the smoke layer intersected with the growing ABL, confirming that the wisps do not initially reach the ground. 相似文献