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11.
The dual-beam mini-DOAS technique—measurements of volcanic gas emission,plume height and plume speed with a single instrument 总被引:2,自引:0,他引:2
Mattias Johansson Bo Galle Yan Zhang Claudia Rivera Deliang Chen Klaus Wyser 《Bulletin of Volcanology》2009,71(7):747-751
The largest error in determining volcanic gas fluxes using ground based optical remote sensing instruments is typically the
determination of the plume speed, and in the case of fixed scanning instruments also the plume height. We here present a newly
developed technique capable of measuring plume height, plume speed and gas flux using one single instrument by simultaneously
collecting scattered sunlight in two directions. The angle between the two measurement directions is fixed, removing the need
for time consuming in-field calibrations. The plume height and gas flux is measured by traversing the plume and the plume
speed is measured by performing a stationary measurement underneath the plume. The instrument was tested in a field campaign
in May 2005 at Mt. Etna, Italy, where the measured results are compared to wind fields derived from a meso-scale meteorological
model (MM5). The test and comparison show that the instrument is functioning and capable of estimating wind speed at the plume
height. 相似文献
12.
This paper presents a method to reconstruct the gas distribution inside a vertical cross section of a gas plume by combining
data from two or more scanning DOAS instruments using a tomographic algorithm. The method can be applied to gas plumes from
any single, elevated point source, such as a volcano or industrial chimney. Such two-dimensional concentration distributions
may prove to be useful for example in plume chemistry, dispersion and environmental impact studies. Here we show the case
with one scanning DOAS instrument located on each side of the plume, which is the easiest and most economic setup as well
as the most useful in routine monitoring of e.g. volcanic gas emissions. The paper investigates the conditions under which
tomographic reconstructions can be performed and discusses limitations of this setup. The proposed method has been studied
theoretically by numerical simulations and has been experimentally tested during two field campaigns, with measurements of
SO2 emissions from a volcano and a power plant. The simulations show that, under good measurement conditions, the algorithm presented
performs well, which is further confirmed by the experimental results. 相似文献
13.
Focal-ratio degradation (FRD) of light launched into high-numerical aperture (NA) single-annulus all-silica undoped air-clad fibres at an NA of 0.54 is reported. The measured annular light distribution remained Gaussian after 30 m of propagation, but the angular FWHM of the output annulus doubled from 4° after 1 m propagation to 8.5° after 30 m, which is significantly larger than that reported of standard doped-silica fibres (NA < 0.22). No significant diffractive effects were observed. The design of air-clad fibres for broad-band, high-NA astrophotonics applications is discussed. 相似文献
14.
This study reports results from an analysis of the relationship between atmospheric forcing and model‐simulated water and energy fluxes for the North American Land Data Assimilation System Project Phase 2 (NLDAS‐2). The relationships between mean monthly precipitation and total runoff are stronger in the Sacramento (SAC) and variable infiltration capacity (VIC) models, which grew out of the hydrological community, than in the Noah and Mosaic models, which grew out of the soil‐vegetation‐atmosphere transfer (SVAT) community. The reverse is true for the relationship between mean monthly precipitation and evapotranspiration. In addition, surface energy fluxes in VIC are less sensitive to model forcing (except for air temperature) than those in the Noah and Mosaic model. Notwithstanding these general conclusions, the relationships between forcings and model‐simulated water and energy fluxes for all models vary for different seasons, variables, and regions. These findings will ultimately inspire a combination of SVAT‐type model energy components with hydrological model water components to develop a SVAT‐hydrology model to improve both evapotranspiration and total runoff simulations. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
15.
16.
Empirical laws and statistics of earthquakes are valuable as a basis for a better understanding of the earthquake cycle. In this paper we focus on the postseismic phase and the physics of aftershock sequences. Using interevent time distributions for a catalogue of Icelandic seismicity, we infer that the parameter C2 in the Omori law, often considered to represent incomplete detection of aftershocks, is at least in part related to the physics of the earthquake process. We investigate the role of postseismic pore pressure diffusion after two Icelandic earthquakes on the rate of aftershocks and what we can infer about the physical meaning of C2 from the diffusion process. Using the Mohr–Coulomb failure criterion we obtain a rate of triggered points in our diffusion model that agrees with the modified Omori law, with a value of C2 that is consistent with data. Our pore pressure diffusion model suggests that C2 is related to the process of reducing high pore pressure gradients existing across a fault zone at short times after a main shock. 相似文献
17.
18.
G. Svensson A. A. M. Holtslag V. Kumar T. Mauritsen G. J. Steeneveld W. M. Angevine E. Bazile A. Beljaars E. I. F. de Bruijn A. Cheng L. Conangla J. Cuxart M. Ek M. J. Falk F. Freedman H. Kitagawa V. E. Larson A. Lock J. Mailhot V. Masson S. Park J. Pleim S. S?derberg W. Weng M. Zampieri 《Boundary-Layer Meteorology》2011,140(2):177-206
We present the main results from the second model intercomparison within the GEWEX (Global Energy and Water cycle EXperiment) Atmospheric Boundary Layer Study (GABLS). The target is to examine the diurnal cycle over land in today??s numerical weather prediction and climate models for operational and research purposes. The set-up of the case is based on observations taken during the Cooperative Atmosphere-Surface Exchange Study-1999 (CASES-99), which was held in Kansas, USA in the early autumn with a strong diurnal cycle with no clouds present. The models are forced with a constant geostrophic wind, prescribed surface temperature and large-scale divergence. Results from 30 different model simulations and one large-eddy simulation (LES) are analyzed and compared with observations. Even though the surface temperature is prescribed, the models give variable near-surface air temperatures. This, in turn, gives rise to differences in low-level stability affecting the turbulence and the turbulent heat fluxes. The increase in modelled upward sensible heat flux during the morning transition is typically too weak and the growth of the convective boundary layer before noon is too slow. This is related to weak modelled near-surface winds during the morning hours. The agreement between the models, the LES and observations is the best during the late afternoon. From this intercomparison study, we find that modelling the diurnal cycle is still a big challenge. For the convective part of the diurnal cycle, some of the first-order schemes perform somewhat better while the turbulent kinetic energy (TKE) schemes tend to be slightly better during nighttime conditions. Finer vertical resolution tends to improve results to some extent, but is certainly not the solution to all the deficiencies identified. 相似文献
19.
ABSTRACT A cave in granitic rocks was studied in Mezesse, South Cameroon. Coralloid speleothems, draperies and dissolution traces on the cave walls attest to its truly karstic nature. The speleothems consist of microlayers of opal and taranakite (K,NH4 )Al3 (PO4 )3 (OH).9H2 O. They indicate a significant mobilization of silica, Al and K from granite during the formation of the cave. Identification of silicified bacteria in the speleothems layers suggests a possible role of these micro-organisms in silica deposition. The presence of taranakite and of silicified organic remains within the speleothems lead to a better understanding of the genesis of the cave. 相似文献
20.
Arsenic in shallow groundwater of Bangladesh: investigations from three different physiographic settings 总被引:1,自引:0,他引:1
M. Aziz Hasan K. Matin Ahmed Ondra Sracek Prosun Bhattacharya Mattias von Brömssen Sandra Broms Johan Fogelström M. Lutful Mazumder Gunnar Jacks 《Hydrogeology Journal》2007,15(8):1507-1522
Occurrences of arsenic (As) in the Bengal Basin of Bangladesh show close relationships with depositional environments and sediment textures. Hydrochemical data from three sites with varying physiography and sedimentation history show marked variations in redox status and dissolved As concentrations. Arsenic concentration in groundwater of the Ganges Flood Plain (GFP) is characteristically low, where high Mn concentrations indicate redox buffering by reduction of Mn(IV)-oxyhydroxides. Low DOC, \( {\text{HCO}}^{ - }_{3} \), \( {\text{NH}}^{ + }_{4} \) and high \( {\text{NO}}^{ - }_{3} \) and \( {\text{SO}}^{{2 - }}_{4} \) concentrations reflect an elevated redox status in GFP aquifers. In contrast, As concentration in the Ganges Delta Plain (GDP) is very high along with high Fe and low Mn. In the Meghna Flood Plain (MFP), moderate to high As and Fe concentrations and low Mn are detected. Degradation of organic matter probably drives redox reactions in the aquifers, particularly in MFP and GDP, thereby mobilising dissolved As. Speciation calculations indicate supersaturation with respect to siderite and vivianite in the groundwater samples at MFP and GDP, but groundwater in the GFP wells is generally supersaturated with respect to rhodochrosite. Values of log PCO2 at MFP and GDP sites are generally higher than at the GFP site. This is consistent with Mn(IV)-redox buffering suggested at the GFP site compared to Fe(III)-redox buffering at MFP and GDP sites. 相似文献