| 1. |
- Wendisch, M., et al.
(författare)
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Atmospheric and Surface Processes, and Feedback Mechanisms Determining Arctic Amplification: A Review of First Results and Prospects of the (AC)(3) Project
- 2023
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Ingår i: Bulletin of the American Meteorological Society. - : American Meteorological Society. - 0003-0007 .- 1520-0477. ; 104:1
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Tidskriftsartikel (refereegranskat)abstract
- Mechanisms behind the phenomenon of Arctic amplification are widely discussed. To contribute to this debate, the (AC)(3) project was established in 2016 (www.ac3-tr.de/). It comprises modeling and data analysis efforts as well as observational elements. The project has assembled a wealth of ground-based, airborne, shipborne, and satellite data of physical, chemical, and meteorological properties of the Arctic atmosphere, cryosphere, and upper ocean that are available for the Arctic climate research community. Short-term changes and indications of long-term trends in Arctic climate parameters have been detected using existing and new data. For example, a distinct atmospheric moistening, an increase of regional storm activities, an amplified winter warming in the Svalbard and North Pole regions, and a decrease of sea ice thickness in the Fram Strait and of snow depth on sea ice have been identified. A positive trend of tropospheric bromine monoxide (BrO) column densities during polar spring was verified. Local marine/biogenic sources for cloud condensation nuclei and ice nucleating particles were found. Atmospheric-ocean and radiative transfer models were advanced by applying new parameterizations of surface albedo, cloud droplet activation, convective plumes and related processes over leads, and turbulent transfer coefficients for stable surface layers. Four modes of the surface radiative energy budget were explored and reproduced by simulations. To advance the future synthesis of the results, cross-cutting activities are being developed aiming to answer key questions in four focus areas: lapse rate feedback, surface processes, Arctic mixed-phase clouds, and airmass transport and transformation.
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| 2. |
- Ritter, C., et al.
(författare)
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Microphysical properties and radiative impact of an intense biomass burning aerosol event measured over Ny-angstrom lesund, Spitsbergen in July 2015
- 2018
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Ingår i: Tellus. Series B, Chemical and physical meteorology. - : Stockholm University Press. - 0280-6509 .- 1600-0889. ; 70
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Tidskriftsartikel (refereegranskat)abstract
- In this work, an evaluation of an intense biomass burning event observed over Ny-angstrom lesund (Spitsbergen, European Arctic) in July 2015 is presented. Data from the multi-wavelengths Raman-lidar KARL, a sun photometer and radiosonde measurements are used to derive some microphysical properties of the biomass burning aerosol as size distribution, refractive index and single scattering albedo at different relative humidities. Predominantly particles in the accumulation mode have been found with a bi-modal distribution and dominance of the smaller mode. Above 80% relative humidity, hygroscopic growth in terms of an increase of particle diameter and a slight decrease of the index of refraction (real and imaginary part) has been found. Values of the single scattering albedo around 0.9 both at 355nm and 532nm indicate some absorption by the aerosol. Values of the lidar ratio are around 26sr for 355nm and around 50sr for 532nm, almost independent of the relative humidity. Further, data from the photometer and surface radiation values from the local baseline surface radiation network (BSRN) have been applied to derive the radiative impact of the biomass burning event purely from observational data by comparison with a clear background day. We found a strong cooling for the visible radiation and a slight warming in the infra-red. The net aerosol forcing, derived by comparison with a clear background day purely from observational data, obtained a value of -95 W/m(2) per unit AOD500.
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| 3. |
- Dicke, B., et al.
(författare)
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Transferring the entatic-state principle to copper photochemistry
- 2018
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Ingår i: Nature Chemistry. - : NATURE PUBLISHING GROUP. - 1755-4330 .- 1755-4349. ; 10:3, s. 355-362
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Tidskriftsartikel (refereegranskat)abstract
- The entatic state denotes a distorted coordination geometry of a complex from its typical arrangement that generates an improvement to its function. The entatic-state principle has been observed to apply to copper electron-transfer proteins and it results in a lowering of the reorganization energy of the electron-transfer process. It is thus crucial for a multitude of biochemical processes, but its importance to photoactive complexes is unexplored. Here we study a copper complex-with a specifically designed constraining ligand geometry-that exhibits metal-to-ligand charge-transfer state lifetimes that are very short. The guanidine-quinoline ligand used here acts on the bis(chelated) copper(I) centre, allowing only small structural changes after photoexcitation that result in very fast structural dynamics. The data were collected using a multimethod approach that featured time-resolved ultraviolet-visible, infrared and X-ray absorption and optical emission spectroscopy. Through supporting density functional calculations, we deliver a detailed picture of the structural dynamics in the picosecond-to-nanosecond time range.
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| 4. |
- Dicke, B., et al.
(författare)
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Transferring the entatic-state principle to copper photochemistry
- 2018
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Ingår i: Nature Chemistry. - : Springer Science and Business Media LLC. - 1755-4349 .- 1755-4330. ; 10:3, s. 355-362
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Tidskriftsartikel (refereegranskat)abstract
- The entatic state denotes a distorted coordination geometry of a complex from its typical arrangement that generates an improvement to its function. The entatic-state principle has been observed to apply to copper electron-transfer proteins and it results in a lowering of the reorganization energy of the electron-transfer process. It is thus crucial for a multitude of biochemical processes, but its importance to photoactive complexes is unexplored. Here we study a copper complex-with a specifically designed constraining ligand geometry-that exhibits metal-to-ligand charge-transfer state lifetimes that are very short. The guanidine-quinoline ligand used here acts on the bis(chelated) copper(I) centre, allowing only small structural changes after photoexcitation that result in very fast structural dynamics. The data were collected using a multimethod approach that featured time-resolved ultraviolet-visible, infrared and X-ray absorption and optical emission spectroscopy. Through supporting density functional calculations, we deliver a detailed picture of the structural dynamics in the picosecond-to-nanosecond time range.
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| 5. |
- Neuber, G., et al.
(författare)
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Generalized magneto-optical ellipsometry in ferromagnetic metals
- 2004
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Ingår i: Thin Solid Films. - 0040-6090 .- 1879-2731. ; 455, s. 39-42
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Tidskriftsartikel (refereegranskat)abstract
- We present spectral generalized magneto-optical ellipsometry as an optical tool to investigate magnetic and electronic properties of ferromagnetic materials. The advantage of the simultaneous observation of the dielectric and the magnetic responses within one measurement procedure is crucial for materials with coupled degrees of freedom near a phase transition or during annealing procedures to improve the film quality by removing grain boundaries. Moreover, we show the implementation of this technique within an UHV-cryostat for a temperature range between 4.2 and 800 K and fields up to 40 mT. Examplary measurements on iron and Permalloy demonstrate the comfortable application of this technique. (C) 2003 Elsevier B.V. All rights reserved.
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| 6. |
- Neuber, G., et al.
(författare)
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Temperature-dependent spectral generalized magneto-optical ellipsometry
- 2003
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Ingår i: Applied Physics Letters. - 0003-6951 .- 1077-3118. ; 83, s. 4509-4511
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Tidskriftsartikel (refereegranskat)abstract
- We present a setup for temperature-dependent spectral generalized magneto-optical ellipsometry (SGME). This technique gives access to the electronic as well as the magnetic properties of ferromagnetic materials within one single magneto-optical measurement. It also allows the determination of the orientation of the magnetization. We show spectra of the real and the imaginary part of the refractive index N as well as the magneto-optical coupling parameter Q of permalloy and iron films for in-plane magnetization. Our findings demonstrate the relevance of SGME for the understanding of the interplay between electronic and magnetic properties of ferromagnetics. (C) 2003 American Institute of Physics.
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| 7. |
- Rauer, R., et al.
(författare)
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Magneto-optical investigation of spin polarisation of La0.71Ca0.3MnO3 and La0.7Sr0.3MnO3
- 2005
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Ingår i: Journal of Magnetism and Magnetic Materials. ; 290, s. 948-951
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the ferromagnetic phase of thin epitaxial films of the CMR manganites La0.7Ca0.3MnO3 and La0.7Sr0.3MnO3 by temperature-dependent spectral generalised magneto-optical ellipsometry (SGME). The phase transitions from a paramagnetic insulator to a ferromagnetic metal take place at T-C ≈ 265 K and T-C ≈ 335 K, respectively. The measurements covering a spectral range of 0.5-5eV are performed in the temperature range of 25-425 K. SGME allows a complete magneto-optical characterisation consisting of the determination of the diagonal components as well as the off-diagonal components ε(xx) of the dielectric tensor within a single measurement. Upon cooling through the Curie temperature, we observe the development of a Drude-like free-carrier response in ε(xx), indicating the release of previously bound charges. Meanwhile, ε(xx) exhibits a rising magneto-optical response. This reflects, via the increasing degree of spin polarisation of the bands involved in optical transitions, the emergence of ferromagnetism. We tentatively assign spectral features between 2.5 and 4.5 eV to transitions involving the Mn-d shell, especially the e(g) and t(2g) levels. © 2004 Elsevier B.V. All rights reserved.
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| 8. |
- Rauer, R., et al.
(författare)
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Temperature-dependent spectral generalized magneto-optical ellipsometry for ferromagnetic compounds
- 2005
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Ingår i: Review of Scientific Instruments. - 0034-6748 .- 1089-7623. ; 76
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Tidskriftsartikel (refereegranskat)abstract
- Spectral generalized magneto-optical ellipsometry is presented as an optical tool for the simultaneous measurement of the complex index of refraction n=n+ik, the complex magneto-optical coupling parameter Q=Q(r)+iQ(i) (i.e., the Voigt-parameter), and the orientation of the saturation magnetization M-s of isotropic ferromagnetic bulk materials. For wavelengths between 220 nm and 790 nm and at temperatures between 4.2 K and 800 K measurements on iron and permalloy demonstrate the comfortable application of this technique in order to resolve the spectral response of spin-polarized carriers and bands, which can provide valuable insight about the formation of the ferromagnetic state. (C) 2005 American Institute of Physics.
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