Modeling of wave-induced irradiance variability in the upper ocean mixed layer

A Monte Carlo based radiative transfer model has been developed for calculating the availability of solar radiation within the top 100 m of the ocean. The model is optimized for simulations of spatial high resolution downwelling irradiance Ed fluctuations that arise from the lensing effect of waves at the water surface. In a first step the accuracy of simulation results have been verified by measurements of the oceanic underwater light field and through intercomparison with an established radiative transfer model. Secondly the potential depth-impact of nonlinear shaped single waves, from capillary to swell waves, is assessed by considering the most favorable conditions for light focusing, i.e. monochromatic light at 490 nm, very clear oceanic water with a low chlorophyll a content of 0.1 mg m−3 and high sun elevation. Finally light fields below irregular wave profiles accounting for realistic sea states were simulated. Our simulations suggest that under open ocean conditions light flashes with 50 % irradiance enhancements can appear down to 35 m depth, and light variability in the range of ±10 % compared to the mean Ed is still possible in 100 m depth

High-density correlation energy expansion of the one-dimensional uniform electron gas

We show that the expression of the high-density (i.e small-$r_s$) correlation energy per electron for the one-dimensional uniform electron gas can be obtained by conventional perturbation theory and is of the form \Ec(r_s) = -\pi^2/360 + 0.00845 r_s + ..., where $r_s$ is the average radius of an electron. Combining these new results with the low-density correlation energy expansion, we propose a local-density approximation correlation functional, which deviates by a maximum of 0.1 millihartree compared to the benchmark DMC calculations.Comment: 7 pages, 2 figures, 3 tables, accepted for publication in J. Chem. Phy

Measurement of solid precipitation with an optical disdrometer

A study about measurements of solid precipitation using an optical disdrometer is presented. The optical disdrometer is an improved version of the ODM 470 disdrometer. It allows to measure hydrometeors within a size range of 0.4 to 22 mm in diameter. <br><br> The main advantage of this instrument is its ability to estimate accurately precipitation even under strong wind conditions (Großklaus, 1996). To measure solid precipitation a geometrical model was developed to determine the mean cross-sectional area of snow crystals for different predefined shapes and sizes. It serves to develop an algorithm, which relates the mean cross sectional area of snow crystals to their maximum dimension, liquid water content, and terminal velocity. The algorithm was applied to disdrometer measurements during winter 1999/2000 in Uppsala/Sweden. Resulting precipitation was compared to independent measurements of a Geonor gauge and to manual measurements. In terms of daily precipitation the disdrometer shows a reliable performance

The impact of ice crystal shapes, size distributions and spatial structures of cirrus clouds on solar radiative fluxes

The solar radiative properties of cirrus clouds depend on ice particle shape, size, and orientation, as well as on the spatial cloud structure. Radiation schemes in atmospheric circulation models rely on estimates of cloud optical thickness only. In the present work, a Monte Carlo radiative transfer code is applied to various cirrus cloud scenarios to obtain the radiative response of uncertainties in the above-mentioned microphysical and spatial cloud properties (except orientation). First, plane-parallel homogeneous (0D) clouds with different crystal shapes (hexagonal columns, irregular polycrystals) and 114 different size distributions have been considered. The resulting variabilities in the solar radiative fluxes are in the order of a few percent for the reflected and about 1% for the diffusely transmitted fluxes. Largest variabilities in the order of 10% to 30% are found for the solar broadband absorptance. However, these variabilities are smaller than the flux differences caused by the choice of ice particle geometries. The influence of cloud inhomogeneities on the radiative fluxes has been examined with the help of time series of Raman lidar extinction coefficient profiles as input for the radiative transfer calculations. Significant differences between results for inhomogeneous and plane-parallel clouds were found. These differences are in the same order of magnitude as those arising from using extremely different crystal shapes for the radiative transfer calculations. From this sensitivity study, the ranking of cirrus cloud properties according to their importance in solar broadband radiative transfer is optical thickness, ice crystal shape, ice particle size, and spatial structure

Evaluation of the shortwave cloud radiative effect over the ocean by use of ship and satellite observations

In this study the shortwave cloud radiative effect (SWCRE) over ocean calculated by the ECHAM 5 climate model is evaluated for the cloud property input derived from ship based measurements and satellite based estimates and compared to ship based radiation measurements. The ship observations yield cloud fraction, liquid water path from a microwave radiometer, cloud bottom height as well as temperature and humidity profiles from radiosonde ascents. Level-2 products of the Satellite Application Facility on Climate Monitoring (CM~SAF) from the Spinning Enhanced Visible and InfraRed Imager (SEVIRI) have been used to characterize clouds. Within a closure study six different experiments have been defined to find the optimal set of measurements to calculate downward shortwave radiation (DSR) and the SWCRE from the model, and their results have been evaluated under seven different synoptic situations. Four of these experiments are defined to investigate the advantage of including the satellite-based cloud droplet effective radius as additional cloud property. The modeled SWCRE based on satellite retrieved cloud properties has a comparable accuracy to the modeled SWCRE based on ship data. For several cases, an improvement through introducing the satellite-based estimate of effective radius as additional information to the ship based data was found. Due to their different measuring characteristics, however, each dataset shows best results for different atmospheric conditions

Episode of unusual high solar ultraviolet radiation over central Europe due to dynamical reduced total ozone in May 2005

In late May 2005 unusual high levels of solar ultraviolet radiation were observed over central Europe. In Northern Germany the measured irradiance of erythemally effective radiation exceeded the climatological mean by more than about 20%. An extreme low ozone event for the season coincided with high solar elevation angles and high pressure induced clear sky conditions leading to the highest value of erythemal UV-radiation ever observed over this location in May since 1994. This hereafter called "ozone mini-hole" was caused by an elevation of tropopause height accompanied with a poleward advection of ozone-poor air from the tropics. The resultant increase in UV-radiation is of particular significance for human health. Dynamically induced low ozone episodes that happen in late spring can considerably enhance the solar UV-radiation in mid latitudes and therefore contribute to the UV-burden of people living in these regions

Bands, resonances, edge singularities and excitons in core level spectroscopy investigated within the dynamical mean field theory

Using a recently developed impurity solver we exemplify how dynamical mean field theory captures band excitations, resonances, edge singularities and excitons in core level x-ray absorption (XAS) and core level photo electron spectroscopy (cPES) on metals, correlated metals and Mott insulators. Comparing XAS at different values of the core-valence interaction shows how the quasiparticle peak in the absence of core-valence interactions evolves into a resonance of similar shape, but different origin. Whereas XAS is rather insensitive to the metal insulator transition, cPES can be used, due to nonlocal screening, to measure the amount of local charge fluctuation

Neue Einsichten in Lehren, Lernen und Kompetenz

Ziel des Beitrags ist es, die Arbeiten der Autoren im Bereich Lehr-Lern-Forschung zusammenzufassen und ein handlungstheoretisch begründetes Konzept für eine lern-lehr-theoretische Didaktik vorzustellen. Ausgehend von einem allgemeinen begrifflichen Rahmen für eine Lern-Lehr-Theorie untersuchen wir die Ansätze der ›lerntheoretischen‹ Didaktik (Heimann, Otto & Schulz 1965) und der kritisch-konstruktiven Didaktik (Klafki 1980), die bis heute in der bundesdeutschen Lehrkräfteausbildung eine wichtige Rolle spielen. Festzuhalten ist, dass beide Ansätze lern-lehr-theoretisch nicht begründet sind, den Lern-Lehr-Zusammenhang vielmehr nur aus der Perspektive der Lehrenden thematisieren. Unter Rückgriff auf lern-lehr-theoretische Vorarbeiten der Gruppe um Eigler (1976) formulieren wir drei Kernfragen und ein Konzept einer Lern-Lehr-Theorie, das von einem mehrdimensionalen Handlungsbegriff ausgeht, Information vom Verstehen her bestimmt und herausarbeitet, dass aufgrund des unauflöslichen Zusammenspiels von Handeln und Information Verstehen der Verständigung bedarf, also Interaktion und Kommunikation zentrale Voraussetzungen für Lernen und Lehren sind. Ein solcher handlungstheoretischer Zugang zeigt auch die Schwachstellen und Inkonsistenzen der Taxonomie von Anderson & Krathwohl (2001) sowie der deutschen Übersetzung von ›knowledge‹ im Allgemeinen und ›declarative‹ sowie ›procedural knowledge‹ im Besonderen und ihre Irrelevanz für berufliche Kompetenzforschung. Das entwickelte Konzept nutzen wir, die derzeit breit rezipierten Ansätze des ›Cognitive Apprenticeship‹ (Collins, Brown & Newman 1989) und der ›Gestaltung integrierter Lernumgebungen‹ (Reinmann & Mandl 2006) zu analysieren und zu zeigen, dass beide die lerntheoretische Begründung und Stringenz des ›meaningful verbal learning‹ (Ausubel 1968) und des guided discovery learning‹ (Bruner 1966) nicht erreichen. Dieses Ergebnis führt uns zu der These, dass die derzeit betriebene Bachelorisierung der Lehrkräfteausbildung Gefahr läuft, trotz inzwischen umfangreicher lern-lehr-theoretischen Erkenntnisse vom Ziel ›mastering the teaching model‹ auf ein ›modelling the master teacher‹ (Stolurow 1965) zurückzufallen. (DIPF/Orig.)New Insights in Teaching, Learning and Competence The aim of this article is to summarize the authors\u27 work in the field of teaching and learning research and to present a concept of learning and teaching theoretical didactics based on the theory of action. We set out from a general conceptual framework of learning and teaching theory and discuss the approaches of ›learning theoretical‹ didactics (Heimann, Otto & Schulz 1965) and critical-constructivist didactics (Klafki 1980), which still play an important part in German teacher education. It has to be concluded that these two approaches have no foundation in learning and teaching theory and instead address the relationship of learning and teaching only from the teachers\u27 perspectives. Recurring to prior work in the field of learning and teaching theory by the group around Eigler (1976) we formulate three fundamental questions and a concept of learning and teaching theory which presupposes a multidimensional concept of action, defines information by reference to understanding, and points out that due to the inextricable interaction of action and information any understanding needs communication, which means that interaction and communication are essential prerequisites for learning and teaching. This action theoretical approach also reveals the weak points and inconsistencies of the taxonomy by Anderson and Krathwohl (2001) and of the German translations of ›knowledge‹ in general and ›declarative‹ and ›procedural knowledge‹ in particular as well as their irrelevance for research on vocational competence development. We employ the concept developed here to analyse the models of ›Cognitive Apprenticeship‹ (Collins, Brown & Newman 1989) and ›design of integrated learningenvironments‹ (Reinmann & Mandl 2006), which currently receive broad attention, and to show that these two concepts do not attain the learning theoretical soundness and consistency of ›meaningful verbal learning‹ (Ausubel 1968) and ›guided discovery learning‹ (Bruner 1966). This result leads to the conclusion that the current shift to Bachelor programmes in teacher education entails the risk that despite the extensive knowledge in learning and teaching theory available today the objective of ›mastering the teaching model‹ is once again replaced with ›modelling the master teacher‹ (Stolurow 1965). (DIPF/orig.

Electronic depth profiles with atomic layer resolution from resonant soft x-ray reflectivity

The analysis of x-ray reflectivity data from artificial heterostructures usually relies on the homogeneity of optical properties of the constituent materials. However, when the x-ray energy is tuned to an absorption edge, this homogeneity no longer exists. Within the same material, spatial regions containing elements at resonance will have optical properties very different from regions without resonating sites. In this situation, models assuming homogeneous optical properties throughout the material can fail to describe the reflectivity adequately. As we show here, resonant soft x-ray reflectivity is sensitive to these variations, even though the wavelength is typically large as compared to the atomic distances over which the optical properties vary. We have therefore developed a scheme for analyzing resonant soft x-ray reflectivity data, which takes the atomic structure of a material into account by "slicing" it into atomic planes with characteristic optical properties. Using LaSrMnO4 as an example, we discuss both the theoretical and experimental implications of this approach. Our analysis not only allows to determine important structural information such as interface terminations and stacking of atomic layers, but also enables to extract depth-resolved spectroscopic information with atomic resolution, thus enhancing the capability of the technique to study emergent phenomena at surfaces and interfaces.Comment: Completely overhauled with respect to the previous version due to peer revie

Optical precursors in transparent media

We theoretically study the linear propagation of a stepwise pulse through a dilute dispersive medium when the frequency of the optical carrier coincides with the center of a natural or electromagnetically induced transparency window of the medium (slow-light systems). We obtain fully analytical expressions of the entirety of the step response and show that, for parameters representative of real experiments, Sommerfeld-Brillouin precursors, main field and second precursors "postcursors" can be distinctly observed, all with amplitudes comparable to that of the incident step. This behavior strongly contrasts with that of the systems generally considered up to now