Three centuries of Slovakian drought dynamics

Tree-ring data from Slovakia are used to reconstruct decadal-scale fluctuations of the self-calibrated Palmer Drought Severity Index (scPDSI) over 1744–2006. The ring width chronology correlates at 0.58 (annual) and 0.88 (decadal) with regional-scale (48–50°N and 18–20°E) summer (June–August) scPDSI variations (1901–2002). Driest and wettest years common to the tree-ring and target data are 1947, 1948, 1964, and 1916, 1927, 1938, 1941, respectively. The model indicates decadal-scale drought ~1780–1810, 1850–1870, 1940–1960, and during the late twentieth century. The wettest period occurred ~1745–1775. Instrumental measurements and documentary evidence allow the reconstructed drought extremes to be verified and also provide additional insights on associated synoptic drivers and socioeconomic impacts. Comparison of anomalous dry conditions with European-scale fields of 500 hPa geopotential height retains positive pressure anomalies centered over Central Europe leading to atmospheric stability, subsidence and dry conditions. Negative mid-tropospheric geopotential height anomalies over Western Europe are connected with anomalous wet conditions over Slovakia. Nine existing, annually resolved hydro-climatic reconstructions from Central Europe, which were herein considered for comparison with the Slovakian findings, reveal significant high- to low-frequency coherency among the majority of records. Differences between the Slovakian and the other reconstructions are most evident at the end of the nineteenth century.     

GHOST – A Novel Airborne Gas Chromatograph for In Situ Measurements of Long-Lived Tracers in the Lower Stratosphere: Method and Applications

A novel fully-automated airborne gas chromatograph for in situmeasurements of long-lived stratospheric tracers hasbeen developed, combining the high selectivity of a megabore PLOTcapillary column with recently developed sampling and separationtechniques. The Gas cHromatograph for theObservation of Stratospheric Tracers (GHOST)has been successfully operated during three STREAM campaigns(Stratosphere TRoposphere Experiment byAirborne Measurement) onboard a Cessna Citation IIaircraft in two different modes: Either N₂O andCF₂Cl₂(CFC-12) or CFC-12 and CFCl₃ (CFC-11) have been measuredsimultaneously, with a time resolution of 2 min for both modes.Under flight conditions the instrument precision (1) forthese species is better than 0.9%, and the accuracy(1) is better than 2.0% of the tropospheric values ofall measured compounds. The detection limits (3) arebelow 28 ppb for N₂O, 14 ppt for CFC-12, and 8 ppt forCFC-11, respectively, i.e., well below 10 % of the troposphericvalues of all measured compounds. Post-mission optimization of thechromatographic separation showed a possible enhancement of thetime resolution by up to a factor of 2, associated with acomparable increase in precision and detection limit. As test ofactual performance of GHOST results from an in-flight N₂Ointercomparison with a tunable diode laser absorptionspectrometer (TDLAS) are presented. They yield an excellentagreement between both instruments. Furthermore, on the basis ofthe hitherto most extensive set of upper tropospheric and lowerstratospheric data, the relative stratospheric N₂2O lifetime isre-assessed. When referenced to the WMO reference CFC-11 lifetimeof 45 ± 7 years an N₂O lifetime of 91 ± 15 yearsis derived, a value substantially smaller than the WMO referencelifetime of 120 years. Moreover, this value implies astratospheric N₂O sink strength of 16.3 ± 2.7 Tg (N)yr^–1 which is 30% larger than previous estimates.     

Changes in the cloud properties in response to El Niño: a bivariate approach

We analyse the dependence of the cloud radiative effect (CRE) and cloud amount on mid-tropospheric pressure velocity (ω ₅₀₀) and sea surface temperature (SST) and point out the shortcomings of using these two proxies separately as means to separate cloud regimes. A bivariate approach is proposed to overcome these shortcomings and it is used to systematically investigate marine cloud properties at different spatial and time scales in the present-day (1985–2001) tropical climate. During the 1997–1998 El Niño, the greatest regional change in CRE and cloud cover coincides with the greatest local change in circulation and SST. In addition, we find that the cooling effect of the stratiform low clouds reduces at the rate of approximately 1 W/m² per percent of cloudiness reduction in the subsident cold pools of the Pacific ocean. During El Niño, the transition between different cloud regimes gives rise to opposing cloud feedbacks. The sign of the total feedback is controlled by the cloud optical thickness. More generally, we find that the largest part of the cloud response to El Niño, when averaged over the tropical Pacific, is not directly associated with ω ₅₀₀ and SST changes, so other factors must play a role as well.     

Measurement of Ambient,Interstitial, and Residual Aerosol Particles on a Mountaintop Site in Central Sweden using an Aerosol Mass Spectrometer and a CVI

The Aerodyne aerosol mass spectrometer (Q-AMS) was coupled with a counterflow virtual impactor (CVI) for the first time to measure cloud droplet residuals of warm tropospheric clouds on Mt. Åreskutan in central Sweden in July 2003. Operating the CVI in different operational modes generated mass concentration and species-resolved mass distribution data for non-refractory species of the ambient, interstitial, and residual aerosol. The ambient aerosol measurements revealed that the aerosol at the site was mainly influenced by long-range transport and regional photochemical generation of nitrate and organic aerosol components. Four different major air masses were identified for the time interval of the experiment. While two air masses that approached the site from northeastern Europe via Finland showed very similar aerosol composition, the other two air masses from polar regions and the British Islands had a significantly different composition. During cloud events the larger aerosol particles were found to be activated into cloud droplets. On a mass basis the activation cut-off diameter was approximately 150 nm for nitrate and organics dominated particles and 200 nm for sulfate dominated particles. Generally nitrate and organics were found to be activated into cloud droplets with higher efficiency than sulfate. While a significant fraction of the nitrate in ambient particles was organic nitrates or nitrogen-containing organic species, the nitrate found in the cloud droplet residuals was mainly ammonium nitrate. After passage of clouds the ambient aerosol size distribution had shifted to smaller particle sizes due to the predominantly activation of larger aerosol particles without a significant change in the relative composition of the ambient aerosol.     

The axial angular momentum balance of a global ocean general circulation model

In this study we examine the axial angular momentum balance of a non-eddy-resolving global ocean general circulation model, from the perspective of the geographical and seasonal variability of angular momentum and from the perspective of the torques acting on the ocean through its surfaces. Our purpose is to provide an estimate of the magnitude of the seasonal storage of angular momentum in the ocean and hence the oceanic excitation of variability in length of day, and to elucidate the role of the ocean in transferring angular momentum between the atmosphere and the Earth's crust. We provide an assessment of the reliability of the model results by examining the sensitivity of the angular momentum and torque distributions to several model parameters.Although the Southern Ocean region containing the Antarctic Circumpolar Current (ACC) makes the largest contribution to both the annual mean oceanic angular momentum and its seasonal variability, inclusion of the rest of the world ocean reduces both of these quantities to about two-thirds of the value of the Southern Ocean alone. The annual, global mean angular momentum is found to be insensitive to most model choices except for the isopycnal diffusivity. The seasonal variability, on the other hand, is insensitive to the isopycnal diffusivity, but sensitive to the smoothness of the representation of topography and moderately sensitive to horizontal and vertical friction parameterizations. The torque balance at all latitudes, including within the Antarctic circumpolar belt, is between wind stress and bottom pressure torques. Horizontal friction torques are small but non-negligible. Bottom friction and storage of angular momentum are negligible in angular momentum budgets on seasonal time scales. Two commonly used wind stress climatologies, one based on historical marine meteorological observations and the other based on operational weather analyses, differ in the sign of the globally integrated wind stress torque.     

Advancing Science with VGI: Reproducibility and Replicability of Recent Studies using VGI

In scientific research, reproducibility and replicability are requirements to ensure the advancement of our body of knowledge. This holds true also for VGI‐related research and studies. However, the characteristics of VGI suggest particular difficulties in ensuring reproducibility and replicability. In this article, we aim to examine the current situation in VGI‐related research, and identify strategies to ensure realization of its full potential. To do so, we first investigate the different aspects of reproducibility and replicability and their impact on VGI‐related research. These impacts are different depending on the objectives of the study. Therefore, we examine the study focus of VGI‐related research to assess the current body of research and structure our assessment. This work is based on a rigorous review of the elements of reproducibility and a systematic mapping and analysis of 58 papers on the use of VGI in the crisis management field. Results of our investigation show that reproducibility issues related to data are a serious concern, while reproducibility issues related to analysis methods and processes face fewer challenges. However, since most studies still focus on analyzing the source data, reproducibility and replicability are still an unsolved problem in VGI‐related research. Therefore, we show initiatives tackling the problem, and finally formulate strategies to improve the situation.     

The effect of organic compounds in the oxidation kinetics of Cr(III) by H2O2

The oxidation of Cr(III) has been studied in NaCl solutions in the presence of two siderophore models, acetohydroxamic acid (Aha) and benzohydroxamic acid (Bha), the natural siderophore Desferal (DFOB) and the synthetic aminocarboxilate (ethylenedinitrilo)-tetra-acetic acid (EDTA) as a function of pH (8-9), ionic strength (0.01-2 M) and temperature (10-50 °C), at different Cr(III)-organic compound ratios. The addition of Aha and Bha caused the rates to increase at low ligand/Cr(III) ratios and decrease at high ratios. The variation of the pseudo first order rate constant (k₁) as a function of the ligand concentration has been attributed to the formation of three Cr(III)-organo species (1:1, 1:2, 1:3), which can form in the presence of monohydroxamic acids. A kinetic model has been developed that gives a value of 600 (min⁻¹) for the pseudo first order rate constant k_1CrAha²⁺ and values approaching zero for and k_1CrAha3. These kinetic results demonstrate that these monohydroxamic acids are able to bind with Cr(III) under experimental conditions that may occur in natural waters and can increase the oxidation rates of Cr(III) with H₂O₂ by a factor of 3.5 at an Aha/Cr(III) ratio of about 50-100.The monohydroxamic acids also affect the rates on aged products of Cr(III), suggesting that these ligands are able to affect the oxidation rates by releasing reactive Cr(III). DFOB and EDTA do not have a great effect on the oxidation of Cr(III) with H₂O₂. This is thought to be due to the much longer times they need to form complexes with Cr(III) compared to Aha and Bha. The rates for the formation of DFOB and EDTA complexes with Cr(III) are not competitive with the rates of the formation of aged Cr(III). After allowing Cr(III) and DFOB to react for 5 days to form the complex, reaction rates of Cr(III) with H₂O₂ appear to be lowered probably because of steric hindrance of the chelated Cr(III).     

Comparing the Upper Triassic Deep-sea Flysch of theShannan Terrane with the Coeval Shallow Shelf Sediments ofthe Tethys Himalaya,Southern Tibet

The provenance and paleogeography of the Upper Triassic deep-sea flysch Langjiexue Group(LG) of the Shannan Terrane in the northeastern Himalaya orogen, south of Yarlung Zangbo, have been disputed in recent years since its affinity to the Tethys Himalaya was suspected during the early 2000 s. Based on the earlier discoveries of the Upper Permian–Triassic basalts and mafic dykes from the LG and of coeval detrital zircons from the Qulonggongba Formation(QF) in shallow shelf sediments of the Tethys Himalaya, the previous viewpoints on the basin and tectonics of the LG have been recently rejected. We compared the two units of the Upper Triassic, and our results reveal a number of differences,discrepancies, and inconsistencies in the debate, raising crucial questions on the postulation and provenance model of the remote Gondwanide Orogen for the LG. It is suggested that more observations and evidence are needed to further improve the paleogeographic understanding and relationship of the two units.     

Contrôle morphostructural de l’histoire d’un réseau hydrographique : le site de capture de la Moselle

Résumé

La comparaison entre la structure tectonique des calcaires du Bajocien, la répartition des alluvions anciennes et la morphologie permet de retracer l’évolution du relief de côtes et l’évolution des axes de drainage depuis la fin du Tertiaire. Les alluvions conservées en inversion de relief sur le plateau d’érosion au sommet de la côte de Moselle, témoignent en faveur des cours divaguants de la « Paléo-Meurthe » et de la Haute-Moselle et du manque de vigueur du relief à la fin du Tertiaire. Le dégagement des surfaces structurales ne commence qu’au début du Pléistocène (stade 350 m) en relation avec un changement climatique. L’encaissement du réseau hydrographique et le déblaiement des dépressions argileuses ne font, depuis lors, que donner de l’amplitude au relief de côte malgré un recul qui a pu être chiffré entre 6 et 21 km, en fonction du contexte structural.

Les cours d’eau principaux sont presque totalement surimposés à la structure. Les affluents de rive gauche de la « Paléo- Meurthe », d’abord adaptés au cadre morphostructural, coulent dans la plaine argileuse du Callovien dans laquelle ils migrent et s’allongent en fonction du recul des côtes, avant de se surimposer dans les calcaires du Bajocien. Seuls apparaissent adaptés à la structure quelques petits ruisseaux orthoclinaux qui s’assèchent rapidement après incrustation dans les calcaires. N’étant pas alimentés par l’amont, ils s’enfoncent moins vite que les cours d’eau de rive gauche, qui drainent d’abord les argiles du Callovien avant de recouper la nappe des calcaires bajociens. La capture de la Moselle s’explique par l’adaptation au cadre morphostuctural du « Paléo-Terrouin », affluent de rive gauche de la « Paléo-Meurthe », s’écoulant à contre-pendage. Le recul important de la côte de Meuse dans le « synclinal » de Toul, passant d’un relief inverse à un relief conforme dans la cuvette de Dieulouard, a permis l’élargissement progressif de la plaine argileuse du Callovien et l’accroissement du bassin-versant du « Paléo-Terrouin ». Celui-ci a fini par capturer la « Rivière de la Haie Plaisante », puis par son intermédiaire, la Haute-Moselle elle-même. Dans l’avenir, il est probable qu’il capture également la Haute-Meuse. © Elsevier, Paris