In-situ Measurements of Tropospheric Hydroxyl Radicals by Folded Long-Path Laser Absorption During the Field Campaign POPCORN

Absolutely calibrated in-situ measurements of tropospheric hydroxyl radicals, formaldehyde, sulfur dioxide, and naphthalene (C10H8) were performed by long-path laser absorption spectroscopy during the field campaign POPCORN. The absorption light path was folded into an open optical multiple reflection cell with a mirror separation of 38.5 m. Using a light path length of 1848 m and an integration time of 200 s, the average 1-detection limits of OH, HCHO, SO2 and C10H8 during POPCORN were 8.7 · 105 cm–3, 8.3 · 109 cm–3, 2.4 · 109 cm–3, 1.5 · 108 cm–3, respectively. In total, 392 identifications of OH in air spectra were made in a rural environment between August 5 and August 23, 1994. We present and discuss OH absorption spectra and diurnal OH concentration profiles of three days which are representative for measurements under different pollution conditions during POPCORN. The observed maximum and median OH radical concentrations are 1.3 · 107 OH/cm3 and 4.0 · 106 OH/cm3, respectively. The measured diurnal variation of the OH concentration shows a good correlation with the primary formation reaction of OH radicals which is the photolysis of ambient ozone. Deviations from this correlation in the morning and evening hours, when the OH concentration is higher than expected from the ozone photolysis, demonstrate the importance of other photochemical HOx production pathways during POPCORN.     

Scenarios of extreme temperature events

Based on the principles of the probability theory a statistical model has been developed assessing the likelihood of occurrence of extreme temperature events from the knowledge of the statistical characteristics of the daily temperature extremes. It is demonstrated that the probability of such events is more sensitive to changes in the variability of climate than to changes in its average. Further, this sensitivity increases at a nonlinear rate the more extreme the event. The applicability of the model has been verified by comparing the simulated frequencies of a large spectrum of temperature events with the observed numbers derived from a long time series of daily temperature extremes at Potsdam. Accordingly, the relative simulation errors increase significantly as the events become more extreme. A correction is possible, because most of these errors are systematic rather than random. Moreover, in accordance with the climate observations the simulations reveal statistically significant linear trends in the number of extreme events since the end of the last century. Local scenarios of extreme temperature events have been derived for the city of Berlin by considering both hypothetical new climate states and climate changes simulated by a General Circulation Model (GCM). As a consequence of an increase in the atmospheric concentration of greenhouse gases up to the end of the next century according to the IPCC Scenario A the repetition rate of extreme events in summer (e.g., hot days) is expected to rise considerably relative to the current climate. Moreover, in the winter season cold days will become extremely rare.     

Photogrammetry as a tool for detecting recent crustal movements

Progress in model building and in advanced exposure and evaluation methods is leading photogrammetry up into the field of precise point determination, up to now solved by classical geodetic triangulation and/or trilateration. In combination with the statistical test theory, photogrammetry can be used as a tool to detect recent crustal movements or deformations of man-made constructions, such as in coal mining or oil and gas exploitation.

For these reasons, this paper deals with model building for modern aerial triangulation with respect to hypothesis tests to detect point displacements greater than the measurement noise. An example from brown-coal mining demonstrates accuracies and the application of some statistical tests shows the efficiency of advanced aerial photogrammetry.     

An optimized chemiluminescence detector for tropospheric NO measurements

A detector for the chemiluminescent measurement of NO in background air is described. A large reduction of interferences is achieved by using a stabilized ozone generator which allows operation of the instrument at lower O₃ concentrations. Purification and humidification of the O₃ stream further reduces interferences and shortens the instrumental clean-up time, which is important for aircraft missions. From a series of laboratory tests and from measurements performed aboard an aircraft it is demonstrated that the remaining interferences are acceptable for measurements in the undisturbed troposphere. In particular, no remnant NO signal is observed in clean air at night. During flight, a detection limit (2) of 20 ppt is achieved for a 1 min integration time.     

Comprehensive chemical analyses of natural cordierites: implications for exchange mechanisms

Cordierite samples from pegmatites and metamorphic rocks have been analysed for major [electron microprobe analysis (EMPA)] and trace elements [inductively coupled plasma mass spectrometry (ICP-MS), secondary ion mass spectrometry analyses (SIMS)] as well as for H₂O and CO₂ (coulometric titration), and the results evaluated in conjunction with published data in order to determine which exchange mechanisms are significant. Apart from the homovalent substitutions FeMg₋₁ and MnMg₋₁ on the octahedral site, some minor KNa₋₁ on the Ch0 channel site, and Fe³⁺Al₋₁ on the T₁1 tetrahedral site, the three most important substitution mechanisms are those for the incorporation of Li on the octahedral sites (NaLi□₋₁Mg₋₁), and of Be and other divalent cations on the tetrahedral T₁1 site (NaBe□₋₁Al₋₁ and Na(Mg,Fe²⁺)□₋₁Al₋₁). The dominant role of the last vector is clearly demonstrated. We propose a new generalized formula for cordierite: ^Ch(Na,K)_0–1 ^VI(Mg,Fe²⁺,Mn,Li)₂ ^IVSi₅ ^IVAl₃ ^IV(Al, Be, Mg, Fe²⁺, Fe³⁺)O₁₈ *x^Ch(H₂O, CO₂…). Our results show that the population of (Mg, Fe²⁺) on the T₁1-site is limited to about 0.08 a.p.f.u. Other exchange mechanisms that were encountered in experiments operate only under P–T conditions or in bulk compositions that are rarely realized in nature. Routine analyses by electron microprobe in which Li and Be are not determined can be plotted as (Mg+Fe+Mn) versus (Si+Al) to assess whether significant amounts of Li and Be could be present. These amounts can be calculated as Li (a.p.f.u.)=Al+Na–4 and Be (a.p.f.u.)=10–2Al–M²⁺–Na.     

Evidence for explosive volcanic density currents on certain Martian volcanoes

A number of Martian volcanoes, especially Ceraunius Tholus, Uranius Tholus, Uranius Patera, and Hecates Tholus, show morphological features strikingly different from those of shield volcanoes but analogous to those of terrestrial cones and composite volcanoes such as Barcena Volcano, Mexico. The most distinguishing overall features are steep slope angles, and Krakatoa-type caldera morphologies. Erosional features comprise numerous radial channels which extend from below the rim toward the base of the dome, and in some cases, patterns of anastamosing gullies which contribute to the main radial channels. Constructional features include blanketed flanks interpreted as dune or fan-like deposits of ash, and perhaps lava deltas. A possible explanation for the morphological features associated with these volcanoes is that they were formed by explosive volcanic density currents. Such eruptions would be expected on Mars where a rising magma came in contact with a thick layer of permafrost generating a base surge or after a Vulcanian explosion of a separate gas phase producing a nuée ardente. Crater age data from the surface of Martian domes and shields indicate that such explosive activity occurred more frequently early in Martian geologic history. This is more consistent with the view that the volcanic density flows were base surges rather than nuées ardentes, the melting of permafrost supplying the water required in base surge generation. If atmospheric conditions were more clement at the time, allowing the recycling of water back to the ground water, then the length of duration of phreatic activity would have been longer, not being limited by depletion time of the local permafrost reservoir.     

Evolution of the West Andean Escarpment at 18°S (N. Chile) during the last 25 Ma: uplift, erosion and collapse through time

The geological record of the Western Andean Escarpment (WARP) reveals episodes of uplift, erosion, volcanism and sedimentation. The lithological sequence at 18°S comprises a thick pile of Azapa Conglomerates (25–19 Ma), an overlying series of widespread rhyodacitic Oxaya Ignimbrites (up to 900 m thick, ca. 19 Ma), which are in turn covered by a series of mafic andesite shield volcanoes. Between 19 and 12 Ma, the surface of the Oxaya Ignimbrites evolved into a large monocline on the western slope of the Andes. A giant antithetically rotated block (Oxaya Block, 80 km×20 km) formed on this slope at about 10–12 Ma and resulted in an easterly dip and a reversed drainage on the block's surface. Morphology, topography and stratigraphic observations argue for a gravitational cause of this rotation. A “secondary” gravitational collapse (50 km³), extending 25 km to the west occurred on the steep western front of the Oxaya Block. Alluvial and fluvial sediments (11–2.7 Ma) accumulated in a half graben to the east of the tilted block and were later thrust over by the rocks of the escarpment wall, indicating further shortening between 8 and 6 Ma. Flatlying Upper Miocene sediments (<5.5 Ma) and the 2.7 Ma Lauca–Peréz Ignimbrite have not been significantly shortened since 6 Ma, suggesting that recent uplift is at least partly caused by regional tilting of the Western Andean slope.     

Towards an integration of process measurements, archive analysis and modelling in geomorphology — the Kärkevagge experimental site, Abisko area, northern Sweden

The analysis of Holocene geomorphic process activity demands long–term data sets, which are available for the Kärkevagge catchment due to 50 years of intensive geomorphologic field studies. This data set is used in combination with additional field measurements, remote sensing and digital elevation model (DEM) analysis to provide input data for modelling Holocene valley development. On the basis of this information, geomorphic process units (GPUs) are defined by means of GIS modelling. These units represent areas of homogeneous process composition that transfer sediments. Since the data base enables the quantification of single processes, the interaction of processes within the units can also be quantified. Applying this concept permits calculation of recent sediment transfer rates and hence leads to a better understanding of actual geomorphic landscape development activity. To extrapolate these data in time and space the process–related sediments in the valley are analysed for depth and total volume, primarily using geophysical methods. In this fashion the validity of measured process rates is evaluated for the Holocene time scale. Results from this analysis are exemplified in a cross–profile showing some of the principal sediment units in the valley. For example, the measured modern rates on a slush torrent debris fan seem to represent the Holocene mean rate. This approach should also be suitable for revealing Holocene geomorphic landscape development in terms of climate change.     

Large wood potential,piece characteristics,and flood effects in Swiss mountain streams

We present results of two studies on the (1) potential wood load in steep headwater streams and (2) properties of large wood (LW) transported in mountain rivers during the large August 2005 flood event in Switzerland. Ten headwater reaches of 1000 m length were surveyed in different regions of Switzerland. The potential wood load was estimated for in-channel deadwood, and possible driving factors were explored. Correlations were found with dead wood volume on hillslopes and mean channel width. We established size distributions of LW pieces and identified probable recruitment processes. Four reaches were resurveyed after an exceptionally severe flood in August 2005, showing limited LW transport in channels but considerable wood input by mass wasting processes. In addition, characteristics of deposits of LW along mountain rivers affected by the 2005 flood were investigated. Diameter and length distribution of transported and deposited pieces were comparable to those of LW from steep headwater streams, yet with considerably fewer long pieces in the deposits of mountain rivers. Most LW pieces were fresh wood, indicating that the portion of in-channel deadwood transported during the 2005 flood was limited. Findings of the study contribute to a better understanding of LW dynamics in Alpine mountain streams.     

Gravity studies of Aphrodite Terra on Venus

Aphrodite Terra is the largest highland area on Venus of the size of Africa. It is traversed by the Aphrodite-Beta belt of troughs with a length of 21 000 km. There are two other large belts of troughs on Venus: Themis-Atla, 14 000 km long, and Beta-Phoebe, 8000 km long. In this paper, four gravity profiles across Aphrodite Terra are studied and compared with the morphology.Western Aphrodite and Niobe Planitia to the north seem to be in isostatic equilibrium under the assumption of Airy compensation with a mean crustal thickness of T = 50 km. The graben area in the middle part of Aphrodite Terra shows negative isostatic gravity anomalies indicating deficit masses. The adjacent Atla Regio to the east is regionally Airy compensated with T = 50 km, and the mountains Nokomis, Maat and Ozza Montes are locally undercompensated, i.e. they are associated with surplus masses in the depth. Ulfrun Regio, a hilly terrain just east of Atla Regio is Airy compensated with T = 30 km. These results give a mean crustal thickness around 50 km for Aphrodite Terra. The isostatic disturbed zones in the middle of Aphrodite (grabens) and Atla Regio as well as the undercompensated Beta Regio have been associated with recent volcanism from the observation of the concentrations of electrical discharges in these areas. Atla and Beta Regiones are both located at intersections of the systems of troughs described above.Contribution No. 308, Institut für Geophysik der Universität Kiel, F.R.G.