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21.
Jun?InoueEmail author Branko?Kosovi? Judith?A.?Curry 《Boundary-Layer Meteorology》2005,117(2):213-230
To investigate the processes of development and maintenance of low-level clouds during major synoptic events, the cloudy boundary
layer under stormy conditions during the summertime Arctic has been studied using observations from the Surface Heat Budget
of the Arctic Ocean (SHEBA) experiment and large-eddy simulations (LES). On 29 July 1998, a stable Arctic cloudy boundary-layer
event was observed after the passage of a synoptic low pressure system. The local dynamic and thermodynamic structure of the
boundary layer was determined from aircraft measurements including the analysis of turbulence, cloud microphysics and radiative
properties. After the upper cloud layer advected over the existing cloud layer, the turbulent kinetic energy (TKE) budget
indicated that the cloud layer below 200 m was maintained predominantly by shear production. Observations of longwave radiation
showed that cloud-top cooling at the lower cloud top has been suppressed by radiative effects of the upper cloud layer. Our
LES results demonstrate the importance of the combination of shear mixing near the surface and radiative cooling at the cloud
top in the storm-driven cloudy boundary layer. Once the low-level cloud reaches a certain height, depending on the amount
of cloud-top cooling, the two sources of TKE production begin to separate in space under continuous stormy conditions, suggesting
one possible mechanism for the cloud layering. The sensitivity tests suggest that the storm-driven cloudy boundary layer is
possibly switched to the shear-driven system due to the advection of upper clouds or to the buoyantly driven system due to
the lack of wind shear. A comparison is made of this storm-driven boundary layer with the buoyantly driven boundary layer
previously described in the literature. 相似文献
22.
The influence of the main large-scale wind directions on thermally driven mesoscale circulations at the Baltic southwest coast, southeast of Sweden, is examined. The aim of the study is to highlight small-scale alterations in the coastal atmospheric boundary layer. A numerical three-dimensional mesoscale model is used in this study, which is focused on an overall behaviour of the coastal jets, drainage flows, sea breezes, and a low-level eddy-type flow in particular. It is shown that synoptic conditions, together with the moderate terrain of the southeast of Sweden (max. height h0 206 m), governs the coastal mesoscale dynamics triggered by the land-sea temperature difference T. The subtle nature of coastal low-level jets and sea breezes is revealed; their patterns are dictated by the interplay between synoptic airflow, coastline orientation, and T.The simulations show that coastal jets typically occur during nighttime and vary in height, intensity and position with respect to the coast; they interact with downslope flows and the background wind. For the assigned land surface temperature (varying ±8 K from the sea temperature) and the opposing constant geostrophic wind 8 m s-1, the drainage flow is more robust to the opposing ambient flow than the sea breeze later on. Depending on the part of the coast under consideration, and the prevailing ambient wind, the sea breeze can be suppressed or enhanced, stationary at the coast or rapidly penetrating inland, locked up in phase with another dynamic system or almost independently self-evolving. A low-level eddy structure is analyzed. It is governed by tilting, divergence and horizontal advection terms. The horizontal extent of the coastal effects agrees roughly with the Rossby radius of deformation. 相似文献
23.
Jelena Pantić Vladimir Urbanovich Vesna Poharc-Logar Bojan Jokić Marija Stojmenović Aleksandar Kremenović Branko Matović 《Physics and Chemistry of Minerals》2014,41(10):775-782
Sphene (CaTiSiO5), a calcium titanosilicate ceramic has been prepared from a powder mixture of CaCO3, TiO2 and SiO2 using vibro-milling for homogenization and activation of precursors. During the high-pressure and high-temperature synthesis (HPS) process at 4 GPa and 1,200 °C, sphene undergoes into phase transition, from room-temperature phase P21 /a to high-temperature phase A2/a. Evidence of that structural phase transition is given in this paper using infrared, Raman spectroscopy and X-ray powder diffraction. Rietveld refinement was employed to get the structural information of the synthesized powder. The most important structural change due to phase transition, the disappearance of the characteristic out-of-center distortion of the Ti atom and moving to the center of octahedra, was confirmed. HPS is an effective method for producing full-dense ceramics without any additives. Reduction of particle size occurred during high-pressure compaction. Microstructure and particle size of both phases were analyzed by scanning electron microscopy. 相似文献
24.
This study investigates the size, age and growth of Corallium rubrum which is a key species of the only large reef-like structure in the Mediterranean Sea, the coralligéne. Two populations were studied in the Ligurian Sea at a depth between 36 and 42 m. Basal diameter, colony height and numbers of branches of 230 colonies were measured, and age and growth rates were assessed from 25 colonies. Mean growth rate was 0.2 mm yr−1 of basal diameter growth, corresponding to a mean annual total branch length increase of 5 mm. These results point to a coral growth much slower than assumed in many earlier studies. Additionally, age and size at first reproduction were analysed. Male colonies were shown to become sexually mature at a minimum age of six years (1.2 mm of basal diameter), while female colonies reached maturity when at least 10 years old (2 mm of basal diameter). We further discuss the implications of slow growth and early sexual maturity for red coral management and conservation. 相似文献
25.
The WKB method is used in conjunction with the variation of parameters technique to find an approximate analytical solution for Ekman layers with eddy viscosity and horizontal pressure gradient that are each variable with height from the surface. Behaviour of the solution is illustrated by comparing model output when several eddy viscosity and horizontal pressure gradient profiles are used. Cases where the pressure gradient decreases with height accentuate the super-geostrophic peak in the wind velocity profile, with decreasing eddy viscosity with height further enhancing this effect. Increasing pressure gradient with height reduces or eliminates the peak. The model output when using an eddy viscosity that has a low-level peak fits marine boundary-layer data taken during ASTEX better than the classic solution - the model giving greater low-level mixing which is seen in ASTEX data as well as in data from ERICA. 相似文献
26.
27.
Golem Petar Toman Ivan Večenaj Željko Kozmar Hrvoje Grisogono Branko 《Boundary-Layer Meteorology》2022,183(3):495-504
Boundary-Layer Meteorology - Unique data from a 100-m meteorological mast located on the windward side of the Dinaric Alps, Croatia, are compared to high-resolution Weather Research and Forecasting... 相似文献
28.
Gregor Muri Branko Čermelj Radojko Jaćimović Dragomir Skaberne Andrej Šmuc Martina Burnik Šturm Janja Turšič Polona Vreča 《Journal of Paleolimnology》2013,50(4):457-470
Several geological and geochemical parameters were determined in the sediments of the 5th (5 J) and 6th (6 J) Triglav Lakes, Julian Alps (NW Slovenia), in order to study the impact of natural catchment characteristics and anthropogenic activity. Fish were introduced into both lakes in 1991 and a mountain hut lies on the shore of 5 J. Sedimentary grain size (GS) was distinctly coarser in 5 J than 6 J, with arithmetic means ranging between 46 and 60 and 23–36 μm, respectively. In contrast, the mineralogical composition of the two sediments was similar. Calcite predominated strongly, comprising more than 77 % of total minerals, while dolomite and quartz were rare. Organic carbon (OC) and total nitrogen (TN) concentrations were highest in surficial sediments, with levels of 14.4 and 1.8 %, and 19.3 and 2.4 % observed in 5 J and 6 J, respectively. C/N ratios (atomic) were lowest in the same surface sediments, with the two lakes characterized by similar values (9.6 vs. 9.4, respectively), suggesting a predominance of autochthonous organic matter (OM) in both lakes. Contemporary δ13C values were lower in 5 J (?21.0 ‰) than 6 J (?18.5 ‰) sediments. Considerable changes in these four parameters were observed in recently deposited material, reflecting a shift in the trophic status of both lakes that was likely induced by the introduction of fish. In addition, the smaller and shallower 6 J seemed to respond to changes faster than the larger and deeper 5 J, indicating the higher sensitivity of the former. δ15N values in surface sediments of 5 J and 6 J were ?2.9 and ?4.4 ‰, respectively, with levels increasing gradually with depth to approximately +1.0 ‰ in deeper sediments. The observed changes could most likely be attributed to the atmospheric deposition of reactive nitrogen. The mountain hut has seemingly not had a significant enough impact on the lakes to be recorded in their sediments. 相似文献
29.
Katabatic flows over high-latitude long glaciers experience the Coriolis force. A sloped atmospheric boundary-layer (ABL)
flow is addressed which partly diffuses upwards, and hence, becomes progressively less local. We present the analytical and
numerical solutions for (U ,V, θ) depending on (z, t) in the katabatic flow, where U and V are the downslope and cross-slope wind components and θ is the potential temperature perturbation. A Prandtl model that accounts for the Coriolis effect, via f, does not approach a steady state, because V diffuses upwards in time; the rest, i.e., (U, θ), are similar to that in the classic Prandtl model. The V component behaves in a similar manner as the solution to the 1st Stokes (but inhomogeneous) problem. A WKB approach to the
problem of the sloped ABL winds is outlined in the light of a modified Ekman-Prandtl model with gradually varying eddy diffusivity
K(z). Ideas for parameterizing these high-latitude persistent flows in climate models are revealed.
After Wentzel, Kramers and Brillouin, who popularized the method in theoretical physics. 相似文献
30.
Branko Grisogono 《Boundary-Layer Meteorology》2003,107(1):157-175
An analytic improvement of the classic Prandtl model for pure katabatic flows is obtained. The one-dimensional unsteady problem employs gradually-varying eddy diffusivity K(z) fixed in time. A new solution is found for thefourth-order governing equation that couples the momentum and heat transfer in an approximate but still systematic way. The solution for wind and temperature perturbations is a generalization of the Prandtl solution allowing for: (1) Local andcumulative K(z) effects, (2) gradual evolution from the initial, discontinuous- towardthe steady-state profiles and (3) the given two-dimensional background potential temperature gradient, the surface slope and its potential temperature deficit atthe surface. The solution that is based on a relaxation equation compares adequatelywith its numerical counterpart soon after the estimated flow onset. It is a product ofthe steady-state solution with a spatio-temporal transfer function. The results can beuseful for data analyses, especially for the scale estimations of inclined stable boundarylayers and for surface flux calculations. 相似文献