Field Measurements of Atmospheric Photolysis Frequencies for O3, NO2, HCHO, CH3CHO, H2O2, and HONO by UV Spectroradiometry

A calibrated spectroradiometer was used for the measurement of spectra of the absolute actinic flux F during the POPCORN field campaign in Pennewitt (53.8° N, 11.7° E, sea level) in August 1994. The obtained set of actinic flux spectra was used to determine the photolysis frequencies J(O1D), J(NO2), J(HCHO), J(H2O2), J(HONO), and J(CH3CHO), using molecular photodissociation data from literature. The accuracy of the actinic flux measurement was about ±5%. The accuracy of the photolysis frequency determination is limited by the uncertainties of the molecular absorption cross section and quantum yield data. A good agreement within the experimental uncertainties was found in comparison with measurements of J(O1D) and J(NO2) by filterradiometer which were calibrated absolutely against chemical actinometer. A comparison of this work's photolysis frequency measurements at 40° solar zenith angle with respective measured and modeled data from the literature also shows good agreement for most of the processes considered in this work. However, in the case of J(NO2) data reported in the literature as a function of solar zenith angle differences up to a factor of 1.6 with respect to this work's J(NO2) data are observed. Since this is far beyond the estimated experimental uncertainties, other atmospheric variables, such as aerosols, seem to affect J(NO2) to an extent that is underestimated by now and make indirect comparisons of J(NO2) measurements difficult.     

Hydrothermal convection in carbonaceous chondrite parent bodies

Numerical simulations of the thermal evolution of carbonaceous chondrite parent bodies indicate a period of several million years during which convective motion of water could occur. The present study considers variations of permeability, radiogenic heating, and body radius. The model accounts for the radial variation of gravity within the body, melting of ice, freezing of liquid water, and variable water properties and incorporates a realistic equation of state for water. Some regions of a parent body experience no pore water flow while other regions experience hundreds of pore volumes of liquid water flow. The spatial heterogeneity in pore water flow reflects the convective pattern in the body. Hydrothermal alteration of minerals inside the parent body will accordingly vary greatly with location in the body, and one parent body could be the source of chemically diverse meteorites.     

Neue Spezialforschungen im Allgäu (Molasse und Flysch)

Ohne Zusammenfassung     

Trans-Atlantic Geopotentials During the July 2000 Solar Event and Geomagnetic Storm

The large solar activity in mid-July 2000 produced a severe geomagnetic storm at Earth during the last half of 15 July universal time. The enhancements and changes in the ionosphere electrical current systems caused large geopotentials to be induced over oceanic distances. Across the northern Atlantic, from New Jersey to near the French coast, a geopotential as large as 0.05 V km⁻¹ (a peak-to-peak voltage of about 300 V) was measured during the geomagnetic storm. While large, this was not among the four largest such geopotentials that have been recorded in the last 60 years across AT&T telecommunications cable routes, ocean and continental. The geomagnetic and geopotential data that were measured during the storm event are presented and discussed.     

Evolutionary relationship between the γ-ray flares and millimeter wave outbursts in PKS 0528+134

During the period of 1991–1993 two strong high energy γ-ray flares were observed by the Compton Gamma Ray Observatory in the flat spectrum radio source PKS 0528+134. They were associated with strong mm-radio outbursts with a few months time-delays. In this paper the spectral energy distributions (SED) of the radiations in the γ-hand X-ray and the IR-optical bands are analysed. It is shown that the high energy γ-ray radiation may be due to the inverse Compton scattering of the ambient UV and soft X-ray photons by the relativistic electrons in the jet. Basing on the comparison between the properties of the synchrotron radiation of the γ-ray source and the spectral evolution of the mm-radio outbursts, the evolutional relationship between the γ-ray emitting blobs and the mm-radio emitting blobs is discussed.     

Patterns in the evolution of physiological specialization in salt-marsh animals

Patterns of tolerance to stressful abiotic variables among animals that have colonized salt marshes provide models for the study of the evolution of physiological specialization. We provide an overview of some closely related pairs or groups of species that show hierarchical gradations in tolerance, and thereby physiological mechanisms of compensation, along a line perpendicular to the shore. However, a full understanding of the evolution of physiological specialization requires that we evaluate the role of abiotic factors in light of the biotic interactions in which salt-marsh species are embedded. The common occurrence of salt-marsh endemics in a species-poor environment must be related to the unusual character of this habitat, in which the reduced importance of some biotic forces is paired with highly stressful abiotic factors. The salt marsh is probably not a refuge for competitively inferior forms so much as it is a highly selective environment that admits only those specialized species that can muster the necessary physiological adaptations. Thus the apparently lower competitive ability of salt-marsh species under conditions that are not abiotically stressful is likely to be a secondary consequence of the costs of mechanisms conferring tolerance, and of life in a species-poor habitat. Salt marshes provide an arena in which it is possible to experimentally evaluate the evolutionary and ecological importance of abiotic stress, especially in relation to parapatric or allotopic distributions. Yet very few studies have provided such a rigorous approach, despite a long-standing recognition that abiotic factors interact strongly with biotic forces in the salt marsh.     

Steady-state characteristics of inversions capping a well-mixed planetary boundary layer

The type of inversion discussed in this paper is essentially defined by subsidence, mixing due to thermally generated turbulent energy and a radiative flux difference at the inversion. A concept similar to that of Lilly (1968) is applied, assuming a well-mixed layer below the inversion and including advective and radiative processes.The characteristics of the inversion and of the whole PBL (e.g., height of inversion, height of cloud base, strength of inversion, flux-profiles) are investigated for their dependence on external parameters such as horizontal wind field divergence, advection, surface temperature excess, wind speed and surface temperature. This is done for steady-state conditions and gives considerable insight into the processes maintaining the type of inversion under consideration.A second goal is to present typical inversion structures, which can be found in certain climatic regions. The profiles of the state parameters and the energy-fluxes for the Trade-Wind region, the cold water area off the west-coast of California, the Norwegian Sea and the Arctic Ocean differ considerably.     

Meteorological Aspects, Ozone, and Solar Radiation Measurements During POPCORN 1994

Meteorological data, ozone mixing ratios, and photolysis frequencies for the period August 2 to August 24, 1994, are presented and discussed in support of the field campaign POPCORN (Photochemistry of Plant Emitted Compounds and OH Radicals in Northeastern Germany). Measurements of temperature, ozone, and wind speed at different heights are used to evaluate micro-meteorological parameters. The observations provide information about local influences on the air mass composition. The analysis of radio sonde data of nearby stations provides the height of the planetary boundary layer.     

Characterisation of Apatites as Potential Uranium Reference Materials for Fission‐track Dating by LA‐ICP‐MS

We report homogeneity tests on large natural apatite crystals to evaluate their potential as U reference materials for apatite fission‐track (AFT) thermochronology by laser ablation‐inductively coupled plasma‐mass spectrometry (LA‐ICP‐MS). The homogeneity tests include the measurements of major element concentrations by electron probe microanalysis (EPMA), whereas for U concentration, isotope dilution (ID) ICP‐MS and laser ablation (LA) ICP‐MS were employed. Two apatite crystals are potential reference materials for LA‐ICP‐MS analysis: a 1 cm³ fraction of a Durango crystal (7.5 μg g^?1 U) and a 1 cm³ Mud Tank crystal (6.9 μg g^?1 U). The relative standard deviation (1 RSD) of the U concentration determined by ID‐ICP‐MS of both apatite crystals was ≤ 1.5%, whereas 1 RSD for the LA‐ICP‐MS results was better than 4%, providing sufficient homogeneity for fission‐track dating. The results on the U homogeneity for two different apatite samples are an important step towards establishing in situ dating routines for AFT analysis by LA‐ICP‐MS.     

Low-cost long-term monitoring of global climate forcings and feedbacks

We describe the rationale for long-term monitoring of global climate forcings and radiative feedbacks as a contribution to interpretation of long-term global temperature change. Our discussion is based on a more detailed study and workshop report (Hansenet al., 1993b). We focus on the potential contribution of a proposed series of inexpensive small satellites, but we discuss also the need for complementary climate process studies and ground-based measurements. Some of these measurements could be made inexpensively by students, providing both valuable climate data and science educational experience.