Multi-Wavelength Signatures of Magnetic Reconnection of a Flare-Associated Coronal Mass Ejection

The evolution of an X2.7 solar flare, that occurred in a complex β γ δ magnetic configuration region on 3 November 2003 is discussed by utilizing a multi-wavelength data set. The very first signature of pre-flare coronal activity is observed in radio wavelengths as a type III burst that occurred several minutes prior to the flare signature in Hα. This type III burst is followed by the appearance of a loop-top source in hard X-ray (HXR) images obtained from RHESSI. During the main phase of the event, Hα images observed from ARIES solar tower telescope, Nainital, reveal well-defined footpoint (FP) and loop-top (LT) sources. As the flare evolves, the LT source moves upward and the separation between the two FP sources increases. The co-alignment of Hα with HXR images shows spatial correlation between Hα and HXR footpoints, whereas the rising LT source in HXR is always located above the LT source seen in Hα. The evolution of LT and FP sources is consistent with the reconnection models of solar flares. The EUV images at 195 Å taken by SOHO/EIT reveal intense emission on the disk at the flaring region during the impulsive phase. Further, slow-drifting type IV bursts, observed at low coronal heights at two time intervals along the flare period, indicate rising plasmoids or loop systems. The intense type II radio burst at a time in between these type IV bursts, but at a relatively greater height, indicates the onset of CME and its associated coronal shock wave. The study supports the standard CSHKP model of flares, which is consistent with nearly all eruptive flare models. More importantly, the results also contain evidence for breakout reconnection before the flare phase.     

The first MEMIN shock recovery experiments at low shock pressure (5–12.5 GPa) with dry,porous sandstone

Abstract– As part of the MEMIN research program this project is focused on shock deformation experimentally generated in dry, porous Seeberger sandstone in the low shock pressure range from 5 to 12.5 GPa. Special attention is paid to the influence of porosity on progressive shock metamorphism. Shock recovery experiments were carried out with a high‐explosive set‐up that generates a planar shock wave, and using the shock impedance method. Cylinders of sandstone of average grain size of 0.17 mm and porosity of about 19 vol%, and containing some 96 wt% SiO₂, were shock deformed. Shock effects induced with increasing shock pressure include: (1) Already at 5 GPa the entire pore space is closed; quartz grains show undulatory extinction. On average, 134 fractures per mm are observed. Dark vesicular melt (glass) of the composition of the montmorillonitic phyllosilicate component of this sandstone occurs at an average amount of 1.6 vol%. (2) At 7.5 GPa, quartz grains show weak but prominent mosaicism and the number of fractures increases to 171 per millimeter. Two additional kinds of melt, both based on phyllosilicate precursor, could be observed: a light colored, vesicular melt and a melt containing large iron particles. The total amount of melt (all types) increased in this experiment to 2.4 vol%. Raman spectroscopy confirmed the presence of shock‐deformed quartz grains near the surface. (3) At 10 and 12.5 GPa, quartz grains also show weak but prominent mosaicism, the number of fractures per mm has reached a plateau value of approximately 200, and the total amount of the different melt types has increased to 4.8 vol%. Diaplectic quartz glass could be observed locally near the impacted surface. In addition, local shock effects, most likely caused by multiple shock wave reflections at sandstone‐container interfaces, occur throughout the sample cylinders and include locally enhanced formation of PDF, as well as shear zones associated with cataclastic microbreccia, diaplectic quartz glass, and SiO₂ melt. Overall findings from these first experiments have demonstrated that characteristic shock effects diagnostic for the confirmation of impact structures and suitable for shock pressure calibration are rare. So far, they are restricted to the limited formation of PDF and diaplectic quartz glass at shock pressures of 10 GPa and above.     

Predicting contaminant fate and transport in sediment caps: Mathematical modelling approaches

Sediment capping is a remedial option for managing contaminated sediments that involves the artificial placement of a layer of material over a contaminated area. Sorbent materials such as activated C and coke can be used to amend sand caps to improve cap performance. In this study, analytical and numerical modelling approaches were compared for predicting contaminant fate and transport in sediment caps using several diffusion-controlled and advection-dominated contaminant transport scenarios. An analytical tool was used to predict cap performance at steady-state. These results were compared with the results from the numerical CoReTranS model in which the effective diffusivity and degradation rates were modelled as discontinuous functions at a prescribed bioturbation depth. The numerical approach was also applied to modelling a sorptive cap. It was shown that, while the analytical approach can be used to predict steady-state contaminant transport, the numerical approach is needed to evaluate multiple sediment layers with different transport and sorption characteristics and to examine the transient performance between the time that the single layer transient is applicable (i.e., before penetration of the cap containment layer) and until steady-state in the upper layer. For the 30 cm thick sand cap that was considered in this study, the predicted time to reach steady-state conditions for a diffusion-controlled scenario is 1 ka. For an advection-dominated transport, the time to reach steady-state conditions is reduced to 100 a. The activated C-amended sand cap was more effective in isolating the contaminant within the sorbent layer for a sustained period of time (∼100 a). Results from both modelling approaches showed that capping can effectively reduce contaminant flux to the overlying water with critical variables being cap thickness, groundwater velocity, and sediment sorptivity.     

Polychlorinated biphenyls (PCB) and organochlorine pesticides in sediments of the baltic and coastal waters of Mecklenburg-Vorpommern

Summary The distribution of polychlorinated biphenyls (PCB) and organochlorine pesticides, e.g. the isomers of hexachlorocyclohexane (HCH), hexachlorobenzene (HCB), p,p’-dichiorodiphenyitrichloroethane (DDT) and its primary metabolites DDE and DDD was investigated in surface sediments (0–2 cm) and sediment cores (0–45 cm) from the western Baltic Sea and the coastal waters of Mecklenburg-Vorpommern. Sediment sampling was carried out in the Belt Sea, the Arkona Basin, the Pomeranian Bight and in almost all Bodden and Haff areas of Mecklenburg-Vorpommern in autumn 1993 and 1994. The highest concentrations of PCB and DDT compounds, measured in the innercoastal waters, reached 214 ng g^-1 dry weight (d. w.). The values of HCH isomers ranged between 0.01 and 2.9 ng g^-1 d.w., the highest levels being those of Β-HCH. Levels of chlorinated hydrocarbons, which varied depending on the sediment properties, indicated increased riverine inputs (Oder, Peene, and Uecker). Elevated levels in the Oderhaff and Peenestrom characterize that area as a sink and, due to remobilization of the upper sediment layer (fluffy layer) into the pelagic, also as a source of organic contaminants. Input from agriculture and industrial point sources (shipyards, shipbuilding) was observed in the coastal waters. The homogeneous PCB and DDT distribution (TOC standardization) observed in the surface sediments of some areas in the western Baltic indicates high sediment dynamics. This is supported by the results of sediment core analyses which showed a constant PCB and DDT distribution down to a depth of 15 to 20 cm.

---

Polychlorierte Biphenyle (PCB) und Organochlorpestizide im Sediment der Ostsee und der Küsten-gew?sser Mecklenburg-Vorpommerns

Zusammenfassung Die Verteilungen von polychlorierten Biphenylen (PCB) und Organochlorpestiziden (DDT, HCH und HCB) wurden in Oberfl?chensedimenten (0–2 cm) und in Sedimentkernen (0–45 cm) der westlichen Ostsee und der Küstengew?sser Mecklenburg-Vorpommerns untersucht. Die Sedimentprobenahme erfolgte in der Beltsee, der Arkonasee, der Pommerschen Bucht und in nahezu allen Bodden-und Haffgew?ssern Mecklenburg-Vorpommerns im Herbst 1994 und 1995. Die h?chsten Konzentrationen wurden für die PCB-und DDT-Verbindungen bis 214 ng g^-1 Trockenmasse (TM) in den Küstengew?ssern gemessen. Für die HCH-Isomeren lagen die Werte zwischen 0,01 und 2,9 ng g^-1 TM, mit h?chsten Konzentrationen für das Β-HCH. Die Werte der chlorierten Kohlenwasserstoffe (CKW) variieren nach der Sedimentbeschaffenheit und weisen auf erh?hte Eintr?ge über die Flu\systeme (Oder und Peene) hin. Die h?heren Konzentrationen in den Bodden-und Haffgew?ssern charakterisieren diese Gebiete als Senke und durch erneute Mobilisierung der oberen Sedimentschicht in das Pelagial auch als Quelle für die organischen Schadstoffe. Insbesondere konnten die Eintr?ge aus der Landwirtschaft und aus industriellen Punktquellen (Werftstandorte, Schiffbau) in den Küstengew?ssern festgestellt werden. Die nahezu homogene PCB-und DDT-Verteilung im Oberfl?chensediment der westlichen Ostsee ist ein Hinweis auf die hohe Sedimentdynamik in diesem Gebiet. Dieses wird durch die Ergebnisse der Untersuchungen an Sedimentkernen unterstützt, die eine konstante PCB-und DDT-Verteilung bis zu einer Tiefe von 15 bis 20 cm zeigten.