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221.
Based on the prognostic equations of mixed-layer theory assuming a zeroth order jump at the entrainment zone, analytical solutions for the boundary-layer height evolution are derived with different degrees of accuracy. First, an exact implicit expression for the boundary-layer height for a situation without moisture is analytically derived without assuming any additional relationships or specific initial conditions. It is shown that to expand the solution to include moisture, only minor approximations have to be made. Second, for relatively large boundary-layer heights, the implicit representation is simplified to an explicit function. Third, a hybrid expression is proposed as a reasonable representation for the boundary-layer height evolution during the entire day. Subsequently, the analysis is extended to present the evolution of any boundary-layer averaged scalar, either inert or under idealized chemistry, as an analytical function of time and boundary-layer height. Finally, the analytical solutions are evaluated. This evaluation includes a sensitivity analysis of the boundary-layer height for the entrainment ratio, the free tropospheric lapse rate of the potential temperature, the time-integrated surface flux and the initial boundary-layer height and potential temperature jump. 相似文献
222.
223.
Stable isotope and trace element contents of Cyprideis torosa valves from the Lower Pleistocene marginal lacustrine sequence of Barranco León, Baza Basin (Southern Spain), allow us to
reconstruct the geochemical record of environmental change in this marginal area of the basin and to compare these data with
the environmental changes inferred from the faunal associations. Hydrochemical features of the Baza Lake system have been
influenced by changes in water source, solute composition, and water level during the past. Three water types may have been
involved in a complex mixing in the marginal area during the studied intervals (1) waters of the Baza lacustrine system that
underwent large P/E changes, (2) dilute, meteoric water inputs (surface and shallow groundwaters), (3) saline groundwater
inputs of meteoric origin that acquired their salinity by halite and gypsum dissolution. Four stages in the Pleistocene paleoenvironmental
evolution of the Barranco León area have been differentiated: stage I records a high lake level (highstand) of the saline
closed-lake system. Stage II corresponds to very shallow, palustrine conditions. Stage III records the varying influence of
the three water types under changing water level in a closed-lake. Stage IV corresponds to a through-flowing, open lacustrine
environment mainly fed by meteoric saline groundwaters with minor inputs of stream waters. This small through-flowing lake
was connected to a larger, inner saline closed-lake system. The BL 5 mammal site with lithic tools of an early human occupation
phase in Western Europe corresponds to a particular episode within this stage of the environmental evolution in the marginal
zone of the Baza Lake.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
224.
In Ouwersloot and Vilà-Guerau de Arellano (Boundary-Layer Meteorol. doi:10.1007/s10546-013-9816-z, 2013, this issue), the analytical solutions for the boundary-layer height and scalar evolutions are derived for the convective boundary layer, based on the prognostic equations of mixed-layer slab models without taking subsidence into account. Here, we include and quantify the added effect of subsidence if the subsidence velocity scales linearly with height throughout the atmosphere. This enables analytical analyses for a wider range of observational cases. As a demonstration, the sensitivity of the boundary-layer height and the potential temperature jump to subsidence and the free tropospheric stability is graphically presented. The new relations show the importance of the temporal distribution of the surface buoyancy flux in determining the evolution if there is subsidence. 相似文献
225.
Núria Marbà Carlos M. Duarte Elena Díaz-Almela Jorge Terrados Elvira Álvarez Regino Martínez Rocío Santiago Esperança Gacia Antoni M. Grau 《Estuaries and Coasts》2005,28(1):53-62
Direct census of shoots tagged in permanent plots was used to assess the present (2000–2002)Posidonia oceanica population dynamics in 25 meadows along the Spanish Mediterranean Coast. Shoot density ranged from 154±8 to 1,551±454 shoots
m−2, absolute shoot mortality from 5±0 to 249±53 shoots m−2 yr−1, and absolute shoot recruitment from <5 ±1 to 62±42 shoots m−2yr−1. Specific shoot mortality and recruitment rates, which are mathematically and statistically (p>0.05) independent of shoot
density, varied from 0.015±0.006 to 0.282±0.138 yr−1 and 0.018±0.005 to 0.302±0.093 yr−1, respectively. Absolute shoot mortality rate was scaled to shoot density (Pearson correlation, r=0.78, p<0.0001), and variability
in specific shoot recruitment rate was partially due to differences in the percentage of growing apexes, which produce most
of the recruits within the population (Pearson correlation, r=0.50, p<0.001), demonstrating the existence of structural constraints
on shoot demography. Shoot half-life was estimated to range from 2.5 to 60.4 yr and meadow turnover times between 6.7 yr and
more than a century, provided current estimates of shoot mortality, recruitment rates, and density remain uniform. There were
differences in shoot mortality and recruitment at the regional scale, with the meadows developing along the coast of the Spanish
mainland experiencing the highest shoot mortality (Tukey test, p<0.05) and tending to exhibit the highest shoot recruitment.
The low shoot recruitment did not balance shoot mortality in most (60%) of the meadows, showing a prevalence of declining
populations among the 25 meadows studied (Wilcoxon ranked sign test, p<0.0005). This study demonstrates the power of direct
census of seagrass shoots in permanent plots to evaluate the present status of seagrass meadows, to detect on-going population
decline, and to provide some insight onto the possible factors involved. The incorporation of direct census of seagrass meadows
to monitoring programs will help provide the early-warning signals necessary to support management decisions to conserve seagrass
meadows. 相似文献
226.
We present a new technique to extract the cosmological information from high-redshift supernova data in the presence of calibration errors and extinction due to dust. While in the traditional technique the distance modulus of each supernova is determined separately, in our approach we determine all distance moduli at once, in a process that achieves a significant degree of self-calibration. The result is a much reduced sensitivity of the cosmological parameters to the calibration uncertainties. As an example, for a strawman mission similar to that outlined in the SNAP satellite proposal, the increased precision obtained with the new approach is roughly equivalent to a factor of five decrease in the calibration uncertainty. 相似文献
227.
Dan Hammarlund Ramon Aravena Lena Barnekow Bjørn Buchardt Göran Possnert 《Journal of Paleolimnology》1997,18(3):219-233
A 9000-year carbonate-rich sediment sequence from a small hard-water lake in northernmost Sweden was studied by means of multi-component stable carbon isotope analysis. Radiocarbon dating of different sediment fractions provides chronologic control and reveals a rather constant hard-water effect through time, suggesting that the lake has remained hydrologically open throughout the Holocene. Successive depletion of 13C in fine-grained calcite and carbonate shells during the early Holocene correlate with a change in catchment vegetation from pioneer herb communities to boreal forest. The vegetational change and associated soil development likely gave rise to an increased supply of 13C-depleted carbon dioxide in groundwater recharging the lake. This process is therefore believed to be the main cause of decreasing values of 13C in dissolved inorganic carbon of the lake and thereby in limnic carbonates. Strongly 13C-depleted sedimentary organic matter may be related to enhanced kinetic fractionation during photosynthetic assimilation by means of proton pumping in Characean algae. This interpretation is supported by a substantial offset between 13C of DIC as recorded by mollusc shells and 13C of fine-grained calcite. 相似文献
228.
229.
Joan Bech Nicolau Pineda Tomeu Rigo Montserrat Aran Jéssica Amaro Miquel Gayà Joan Arús Joan Montanyà Oscar van der Velde 《Atmospheric Research》2011,100(4):621-637
This study presents an analysis of a severe weather case that took place during the early morning of the 2nd of November 2008, when intense convective activity associated with a rapidly evolving low pressure system affected the southern coast of Catalonia (NE Spain). The synoptic framework was dominated by an upper level trough and an associated cold front extending from Gibraltar along the Mediterranean coast of the Iberian Peninsula to SE France, which moved north-eastward. South easterly winds in the north of the Balearic Islands and the coast of Catalonia favoured high values of 0–3 km storm relative helicity which combined with moderate MLCAPE values and high shear favoured the conditions for organized convection. A number of multicell storms and others exhibiting supercell features, as indicated by Doppler radar observations, clustered later in a mesoscale convective system, and moved north-eastwards across Catalonia. They produced ground-level strong damaging wind gusts, an F2 tornado, hail and heavy rainfall. Total lightning activity (intra-cloud and cloud to ground flashes) was also relevant, exhibiting several classical features such as a sudden increased rate before ground level severe damage, as discussed in a companion study. Remarkable surface observations of this event include 24 h precipitation accumulations exceeding 100 mm in four different observatories and 30 minute rainfall amounts up to 40 mm which caused local flash floods. As the convective system evolved northward later that day it also affected SE France causing large hail, ground level damaging wind gusts and heavy rainfall. 相似文献
230.
Zsolt Sàndor Róbert Balla Ferenc Téger Bálint Érdi 《Celestial Mechanics and Dynamical Astronomy》2001,79(1):29-40
We applied the method of the short time Lyapunov indicators to the planar circular and to the planar elliptic restricted three-body problem in order to study the structure of the phase space in some selected regions. In the circular case we computed the short-time averages of the stretching numbers to distinguish between regular and chaotic domains of the phase space. The results obtained in this way are in good agreement with the corresponding Poincaré's surface of sections. Using the short time Lyapunov indicators we determined the detailed structure of the phase space in the semi-major axis-eccentricity plane of the test particle both in the circular and in the elliptic restricted problem (in the latter case for some values of the eccentricities of the primaries) and we studied the main features of the phase space.This revised version was published online in October 2005 with corrections to the Cover Date. 相似文献