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371.
Roland B. Stull 《Boundary-Layer Meteorology》1993,62(1-4):21-96
Some of the larger eddies in a turbulent region can be coherent structures that turbulently advect air parcels across large vertical distances before smaller eddies mix the parcels with the environment. Such a process is nonlocal rather than diffusive. Transilient turbulence theory, named after a Latin word maaning jump over, provides a framework for considering the ensemble-averaged effect of many eddies of different sizes on the net nonlocal mixing in the vertical. Nonlocal turbulence statistics can then be examinated, and nonlocal first-order closure can be formulated. 相似文献
372.
Oscillator strengths have been obtained for the first time for 12 transitions of Tb ii. Solar implications based on these f-values and on recent hyperfine structure data are discussed. More especially, a detailed investigation of a weak absorption feature located around 3658 is presented. 相似文献
373.
This study evaluates the potential of using chironomid assemblages to estimate past temperature changes by comparing chironomid-inferred temperatures to meteorological data for the last 87 years. This comparison is made using high-resolution (i.e., sub-decadally resolved) short cores of four lakes along a gradient of altitude (Lake Njulla, 999 m a.s.l., Lake 850, 850 m a.s.l., Lake Alanen Laanijavri, 365 m a.s.l. and Lake Vuoskkujavri, 348 m a.s.l.), vegetation (pine forest to alpine tundra vegetation) and temperature (mean July temperature of 12.4 to 8.1°C). Patterns of chironomid-inferred changes in mean July air temperature were highly comparable to changes in the meteorological data. Moreover, instrumental data were almost always within the specific errors of the quantitative estimates using chironomids. These results indicate that chironomids can be used as a powerful tool to reconstruct temperatures and that chironomids are sensitive enough to record temperature changes of low magnitude such as those recorded during the Holocene. Although this relationship between temperature and chironomid community is strong for the last 87 years, we cannot assume that other environmental factors such as organic matter, changes of lake water depth or oxygen availability were not more significant over longer temporal scales of the Holocene, or longer. 相似文献
374.
Michael Gerding Christoph Ritter Marion Müller Roland Neuber 《Atmospheric Research》2004,71(4):289-302
Ground-based lidars can provide continuous observations of tropospheric humidity profiles using the Raman scattering of light by water vapour and nitrogen molecules. We will present specific humidity profiles obtained at the high Arctic location Ny-Ålesund (Spitsbergen, 79°N). Under nighttime conditions the observations cover a range from about 500 m altitude up to the upper troposphere. Daylight limits the observations to the lower troposphere, depending on atmospheric transmission and the water vapour content. In a case study on 29 January, simultaneous observations of humidity and aerosol extinction show distinct differences in the various altitudes during the advection of aerosol-rich air masses. In the boundary layer, the aerosol is less affected by the humidity. In the free troposphere, the lidar ratio was observed to be up to 60 sr with some evidence for the uptake of water vapour by the aerosol particles. In another case study from 28 February 2002, the influence of the mean wind direction and the orography on the water vapour concentration near the ground and in the free troposphere will be discussed. During wintertime, a humidity inversion up to about 1.5 km altitude with dry air near the ground has frequently been found with wind from the southeast. Such local effects and small-scale structures observed by stationary lidar mostly cannot be resolved by other sounding methods like passive satellite soundings. 相似文献
375.
Roland B. Stull 《Boundary-Layer Meteorology》1991,55(1-2):67-90
The parameterization for transilient turbulence coefficients suggested by Stull and Driedonks (SD. 1987) is tested against the large-eddy simulations (LES) of Ebert et al. (ESS, 1989) for the special case of an idealized convective boundary layer. The SD parameterization is based on a nonlocal approximation to the turbulence kinetic energy (TKE) equation, and requires turbulent exchange (i.e., the matrix of transilient mixing coefficients is assumed to be symmetric) and dominance of the smaller eddies (i.e., elements closer to the main diagonal of the matrix are greater). Measurements from the LES model, however, show that the transilient matrix is asymmetric in convective situations, with larger eddies dominating.Mean-state conditions such as the deep convective mixing and mixed-layer growth are satisfactorily described by the parameterization, but the surface layer is too deep and the entrainment zone thickness is poorly defined. Turbulence properties such as skewed vertical velocity distributions are not possible within the constraint of a symmetric matrix, and partial convective overturning is also not possible because of the restriction that small eddies dominate. Future improved parametcrizations might continue to be based on the TKE equation, but should allow transilient matrix asymmetry.Research was performed while the author worked at the Institute of Atmospheric Physics, German Aerospace Research Establishment (DLR), D-8031 Weling. Germany. 相似文献
376.
C. B. Farmer B. Carli A. Bonetti M. Carlotti B. M. Dinelli H. Fast W. F. J. Evans N. Louisnard C. Alamichel W. Mankin M. Coffey I. G. Nolt D. G. Murcray A. Goldman G. M. Stokes D. W. Johnson W. A. Traub K. V. Chance R. Zander G. Roland L. Delbouille 《Journal of Atmospheric Chemistry》1990,10(2):237-272
All of the techniques used to measure stratospheric HCl during the two BIC campaigns involved high resolution infrared spectroscopy. The balloon-borne instruments included five different spectrometers, three operating in the solar absorption mode and two in emission (at distinctly different wavelengths). Ground-based and aircraft correlative measurements were made close to the balloon locations, again by near-infrared spectroscopy.Within this set of results, comparisons between different techniques (absorption vs emission) viewing the same airmass (i.e., on the same gondola) were possible, as were comparisons between the same technique used on different gondolas spaced closely in time and location. The final results yield a mean profile of concentration of HC1 between 18 and 40 km altitude; an envelope of ±15% centered on this profile encompasses all of the results within one standard deviation of their individual mean values. The absolute accuracy of the final profile is estimated to be no worse than 10%. It is concluded also that the measurement techniques for HCl have reached a level of performance where a precision of 10% to 15% can be confidently expected. 相似文献
377.
Differential geodetic stereo SAR with TerraSAR-X by exploiting small multi-directional radar reflectors 总被引:1,自引:0,他引:1
Christoph Gisinger Martin Willberg Ulrich Balss Thomas Klügel Swetlana Mähler Roland Pail Michael Eineder 《Journal of Geodesy》2017,91(1):53-67
In this paper, we report on the direct positioning of small multi-directional radar reflectors, so-called octahedrons, with the synthetic aperture radar (SAR) satellite TerraSAR-X. Its highest resolution imaging mode termed staring spotlight enables the use of such octahedron reflectors with a dimension of only half a meter, but still providing backscatter equivalent to 1–2 cm observation error. Four octahedrons were deployed at Wettzell geodetic observatory, and observed by TerraSAR-X with 12 acquisitions in three different geometries. By applying our least squares stereo SAR algorithm already tested with common trihedral corner reflectors (CRs), and introducing a novel differential extension using one octahedron as reference point, the coordinates of the remaining octahedrons were directly retrieved in the International Terrestrial Reference Frame (ITRF). Contrary to our standard processing, the differential approach does not require external corrections for the atmospheric path delays and the geodynamic displacements, rendering it particularly useful for joint geodetic networks employing SAR and GNSS. In this paper, we present and discuss both methods based on results when applying them to the aforementioned Wettzell data set of the octahedrons. The comparison with the independently determined reference coordinates confirms the positioning accuracy with 2–5 cm for the standard approach, and 2–3 cm for the differential processing. Moreover, we present statistical uncertainty estimates of the observations and the positioning solutions, which are additionally provided by our parameter estimation algorithms. The results also include our 1.5 m CR available at Wettzell, and the outcomes clearly demonstrate the advantage of the multi-directional octahedrons over conventional CRs for global positioning applications with SAR. 相似文献
378.
379.
Ahmad Redaa Juraj Farkaš Sarah Gilbert Alan S. Collins Stefan Löhr Davood Vasegh Marnie Forster Morgan Blades Thomas Zack Andrea Giuliani Roland Maas Andre Baldermann Martin Dietzel Dieter Garbe-Schönberg 《Geostandards and Geoanalytical Research》2023,47(1):23-48
Reference materials (RMs) with well-characterised composition are necessary for reliable quantification and quality control of isotopic analyses of geological samples. For in situ Rb-Sr analysis of silicate minerals via laser ablation inductively coupled plasma tandem mass spectrometry (LA-ICP-MS/MS) with a collision/reaction cell, there is a general lack of mineral-specific and matrix-matched RMs, which limits wider application of this new laser-based dating technique to certain minerals. In this work, pressed nano-powder pellets (NP) of four RMs, GL-O (glauconite), Mica-Mg (phlogopite), Mica-Fe (biotite) and FK-N (K-feldspar), were analysed and tested for in situ Rb-Sr dating, complemented by isotope dilution (ID) MC-ICP-MS Rb-Sr analyses of GL-O and Mica-Mg. In addition, we attempted to develop alternative flux-free and fused ‘mineral glasses’ from the above RMs for in situ Rb-Sr dating applications. Overall, the results of this study showed that among the above RMs only two NP (Mica-Mg-NP and GL-O-NP) were suitable and robust for in situ dating applications. These two nano-powder reference materials, Mica-Mg-NP and GL-O-NP, were thus used as primary RMs to normalise and determine Rb-Sr ages for three natural minerals: MDC phlogopite and GL-O glauconite grains, and also Mica-Fe-NP (biotite). Our in situ analyses of the above RMs yielded Rb-Sr ages that are in good agreement (within 8%) of published ages, which suggests that both Mica-Mg-NP and GL-O-NP are suitable RMs for in situ Rb-Sr dating of phlogopite, glauconite and biotite. However, using secondary RMs is recommended to monitor the quality of the obtained ages. 相似文献
380.
Roland Schmidt Monika Roth Richard Tessadri Kaarina Weckström 《Journal of Paleolimnology》2008,40(1):453-469
Major and trace elements, minerals and grain-size were analysed from a sediment core covering the last 4,000 years of an Austrian
Alpine lake (Oberer Landschitzsee, ObLAN, 2,076 m a.s.l.). These analyses were combined with autumn and spring temperature
anomalies and ice-cover estimated from a diatom and chrysophyte cyst, thermistor-based regional calibration dataset and selected
pollen markers published previously. Diatom-inferred pH (Di-pH) and DOC (Di-DOC) completed the multi-proxy approach, which,
together with ordination techniques (PCA and RDA), helped (1) to confirm proposed climatic patterns and hypotheses, and (2)
to disentangle the complex interactions between climatic and anthropogenic impacts. Shifts in chemical and physical weathering,
erosion, production, lake stratification, redox potentials and air pollution were the major processes that have affected Oberer
Landschitzsee in relation to climate, lake/catchment interactions, and human impact. Geochemistry supported the finding that
the four waves of high-altitude land use (Early to Middle Bronze, ca. 1,800–1,300 B.C.; Late Bronze to Hallstatt, ca. 1,000–500
B.C.; Celtic to Roman, ca. 300 B.C.–400 A.D.; and Medieval, ca. 1,000–1,600 A.D.) were coupled mainly with warm periods. Increased
production, onset of lake stratification, and the deterioration of hypolimnetic oxygen conditions were the major changes governing
in-lake processes during climate warming. They resulted in specific element assemblages associated with organic matter accumulation
(Br), oxygen depletion (As, Ga, Cu, S), and changes in redox (Fe/Mn). The Se/Di-DOC ratio was introduced to track shifts between
in-lake production and allochthonous sources. Nutrient loading from pastures, coupled with climate warming, could explain
that in-lake production was highest during Roman and Medieval land use. Lithogenic elements mainly originated from chemical
weathering of silicate bedrock and they increased when intense land-use was coupled with climate deterioration and/or increased
humidity. These perturbations were highest during a High Medieval climate fluctuation around 1,000 A.D. The association of
sand with LOI and C/N and the decoupling of sand from quartz and feldspar separates erosion from physical weathering. Di-DOC,
S, and C/N showed hybrid characters in relation to climate and human impact. The mineral proportions indicated gradients in
relation to weathering, snow-cover and running waters, as well as vegetation. Air pollution by metallurgic industries, starting
during the High Medieval and culminating during the Late Medieval, caused lead accumulation and could have contributed to
As and S enrichment. Corresponding features in the distribution of selected elements and pollen tracers, as well as changes
in mineral proportions, supported the hypotheses of shifts in seasonal climate and an overall trend towards more continental
climate conditions since Medieval times. 相似文献