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Impact of Assimilation of Radiosonde and UAV Observations from the Southern Ocean in the Polar WRF Model

Weather forecasting in the Southern Ocean and Antarctica is a challenge above all due to the rarity of observations to be assimilated in numerical weather prediction(NWP) models. As observations are expensive and logistically challenging,it is important to evaluate the benefit that additional observations could bring to NWP. Atmospheric soundings applying unmanned aerial vehicles(UAVs) have a large potential to supplement conventional radiosonde sounding observations.Here, we applied UAV and rad...     

Quality Assurance of Hydrocarbon Measurements for the German Tropospheric Research Focus (TFS)

In the German Focus on Tropospheric Research (TFS) independent quality assurance procedures were implemented in order to obtain information on data quality and comparability of the different measurements made in the different field campaigns. This paper describes the results for measurements of hydrocarbons using in-situ gas chromatographictechniques and off line analysis of samples collected in canisters (analysed by two central laboratories CL-1 and CL-2) and samples collected on adsorption tubes. The QA-procedures included comparisons with synthetic standards (prepared by EN 45001 certified laboratories), absolute calibration with a diffusion source, and an instrument/methodology comparison in ambient air. Harmonisation of the ambient measurements was achieved with a complex mixture (NCAR/BERLIOZ) containing 70 commonly observed hydrocarbons at mixing ratios of 0.2 to 10 ppb (mole fraction) in nitrogen, which was calibrated by referencing to hydrocarbon standards of the National Institute for Standards and Technology (NIST).For the certified synthetic standards, the experienced groups agreed to within ± 20% for most compounds. Much larger discrepancies were observed for the new Airmotec HC2010 instruments due to problems with identification, co-elution and blanks/memory effects. The results in ambient air were similar: Reasonable agreement was found for the results from the experienced groups with well characterised in situ instruments andfor the charcoal tubes, whereas larger discrepancies were observed for the results from new groups and instruments. For the latter, only selected compounds met the data quality objectives (DQO). The canister samples analysed by CL-2 were in good agreement with the reference instrument, whereas large deviations were found for a number of compounds in the analysis of the same canisters by CL-1. The results of the comparison provided the final basis for flagging and harmonising the data from all participants prior to their submission to the TFS central data bank.     

Diffuse volcanic degassing and thermal energy release from Hengill volcanic system, Iceland

We report the first detailed study of spatial variations on the diffuse emission of carbon dioxide (CO₂) and hydrogen sulfide (H₂S) from Hengill volcanic system, Iceland. Soil CO₂ and H₂S efflux measurements were performed at 752 sampling sites and ranged from nondetectable to 17,666 and 722?g?m^?2?day^?1, respectively. The soil temperature was measured at each sampling site and used to evaluate the heat flow. The chemical composition of soil gases sampled at selected sampling sites during this study shows they result from a mixing process between deep volcanic/hydrothermal component and air. Most of the diffuse CO₂ degassing is observed close to areas where active thermal manifestations occur, northeast flank of the Hengill central volcano close to the Nesjavellir power plant, suggesting a diffuse degassing structure with a SSW?CNNE trend, overlapping main fissure zone and indicating a structural control of the degassing process. On the other hand, H₂S efflux values are in general very low or negligible along the study area, except those observed at the northeast flank of the Hengill central volcano, where anomalously high CO₂ efflux and soil temperatures were also measured. The total diffuse CO₂ emission estimated for this volcanic system was about 1,526?±?160?t?day^?1 of which 453?t?day^?1 (29.7?%) are of volcanic/hydrothermal origin. To calculate the steam discharge associated with the volcanic/hydrothermal CO₂ output, we used the average H₂O/CO₂ mass ratio from 12 fumarole samples equal to 88.6 (range, 9.4?C240.2) as a representative value of the H₂O/CO₂ mass ratios for Hengill fumarole steam. The resulting estimate of the steam flow associated with the gas flux is equal to 40,154?t?day^?1. The condensation of this steam results in thermal energy release for Helgill volcanic system of 1.07?×?10¹⁴?J?day^?1 or to a total heat flow of 1,237?MW_t.     

Quasi-Saturated Layer: Implications for Estimating Recharge and Groundwater Modeling

This study presents an extension of the concept of “quasi-saturation” to a quasi-saturated layer, defined as the uppermost dynamic portion of the saturated zone subject to water table fluctuations. Entrapped air here may cause substantial reductions in the hydraulic conductivity (K) and fillable pore water. Air entrapment is caused by a rising water table, usually as a result of groundwater recharge. The most significant effects of entrapped air are recharge overestimation based on methods that use specific yield (S_y), such as the water table fluctuation method (WTF), and reductions in K values. These effects impact estimation of fluid flow velocities and contaminant migration rates in groundwater. In order to quantify actual groundwater recharge rates and the effects of entrapped air, numerical simulations with the FEFLOW (Version 7.0) groundwater flow model were carried out using a quasi-saturated layer for a pilot area in Rio Claro, Brazil. The calculated recharge rate represented 16% of the average precipitation over an 8-year period, approximately half of estimates using the WTF method. Air entrapment amounted to a fillable porosity of 0.07, significant lower that the value of 0.17 obtained experimentally for S_y. Numerical results showed that the entrapped air volume in the quasi-saturated layer can be very significant (0.58 of the air fraction) and hence can significantly affect estimates of groundwater recharge and groundwater flow rates near the water table.     

Nowcasting sunshine number using logistic modeling

In this paper, we present a formalized approach to statistical modeling of the sunshine number, binary indicator of whether the Sun is covered by clouds introduced previously by Badescu (Theor Appl Climatol 72:127–136, 2002). Our statistical approach is based on Markov chain and logistic regression and yields fully specified probability models that are relatively easily identified (and their unknown parameters estimated) from a set of empirical data (observed sunshine number and sunshine stability number series). We discuss general structure of the model and its advantages, demonstrate its performance on real data and compare its results to classical ARIMA approach as to a competitor. Since the model parameters have clear interpretation, we also illustrate how, e.g., their inter-seasonal stability can be tested. We conclude with an outlook to future developments oriented to construction of models allowing for practically desirable smooth transition between data observed with different frequencies and with a short discussion of technical problems that such a goal brings.     

Sensitivity of last glacial maximum climate to sea ice conditions in the Nordic Seas

Published reconstructions of last glacial maximum (LGM) sea surface temperatures and sea ice extent differ significantly. We here test the sensitivity of simulated North Atlantic climates to two different reconstructions by using these reconstructions as boundary conditions for model experiments. An atmospheric general circulation model has been used to perform two simulations of the (LGM) and a modern-day control simulation. Standard (CLIMAP) reconstructions of sea ice and sea surface temperatures have been used for the first simulation, and a set of new reconstructions in the Nordic Seas/Northern Atlantic have been used for the second experiment. The new reconstruction is based on 158 core samples, and represents ice-free conditions during summer in the Nordic Seas, with accordingly warmer sea surface temperatures and less extensive sea ice during winter as well. The simulated glacial climate is globally 5.7 K colder than modern day, with the largest changes at mid and high latitudes. Due to more intense Hadley circulation, the precipitation at lower latitudes has increased in the simulations of the LGM. Relative to the simulation with the standard CLIMAP reconstructions, reduction of the sea ice in the North Atlantic gives positive local responses in temperature, precipitation and reduction of the sea level pressure. Only very weak signatures of the wintertime Icelandic Low occur when the standard CLIMAP sea surface temperature reconstruction is used as the lower boundary condition in LGM. With reduced sea ice conditions in the Nordic Seas, the Icelandic Low becomes more intense and closer to its present structure. This indicates that thermal forcing is an important factor in determining the strength and position of the Icelandic Low. The Arctic Oscillation is the most dominant large scale variability feature on the Northern Hemisphere in modern day winter climate. In the simulation of the LGM with extensive sea ice this pattern is significantly changed and represents no systematic large scale variability over the North Atlantic. Reduction of the North Atlantic sea ice extent leads to stronger variability in monthly mean sea level pressure in winter. The synoptic variability appears at a lower level in the simulation when standard reconstructions of the sea surface in the LGM are used. A closer inspection of storm tracks in this model experiment shows that that the synoptic lows follow a narrow band along the ice edge during winter. The trajectories of synoptic lows are not constrained to the sea ice edge to the same degree when the sea ice extent is reduced. Seasonally open waters in the Nordic Seas in the new reconstruction apparently act as a moisture source, consistent with the current understanding of the rapid growth of the Fennoscandian and Barents Ice Sheets, during the LGM. The signal from the intensified thermal forcing in the North Atlantic in Boreal winter is carried zonally by upper tropospheric waves, and thus generates non-local responses to the changed sea ice cover.     

Influence of a cyclic and dynamic loading history on dynamic properties of dry sand, part II: cyclic axial preloading

Initial fabric of a soil induced by its cyclic strain history is an important parameter among others like void ratio, state of stress and amplitude concerning the further accumulation of deformations under cyclic loading. It is of high importance to determine methods in order to estimate the initial fabric of the grain skeleton or the cyclic loading history of the soil. An attempt is made in this paper to correlate small strain stiffness of non-cohesive soil with its cyclic loading history. For this purpose several cyclic triaxial tests with specimens subjected to cyclic axial loading were performed and changes of small strain soil properties due to this cyclic loading were studied. All these tests showed only moderate changes of small strain stiffnesses independently of the different boundary conditions. Thus, a correlation between fabric or strain history and small strain stiffnesses seems not to be possible.