Implications of Non-cylindrical Flux Ropes for Magnetic Cloud Reconstruction Techniques and the Interpretation of Double Flux Rope Events

Magnetic clouds (MCs) are a subset of interplanetary coronal mass ejections (ICMEs) which exhibit signatures consistent with a magnetic flux rope structure. Techniques for reconstructing flux rope orientation from single-point in situ observations typically assume the flux rope is locally cylindrical, e.g., minimum variance analysis (MVA) and force-free flux rope (FFFR) fitting. In this study, we outline a non-cylindrical magnetic flux rope model, in which the flux rope radius and axial curvature can both vary along the length of the axis. This model is not necessarily intended to represent the global structure of MCs, but it can be used to quantify the error in MC reconstruction resulting from the cylindrical approximation. When the local flux rope axis is approximately perpendicular to the heliocentric radial direction, which is also the effective spacecraft trajectory through a magnetic cloud, the error in using cylindrical reconstruction methods is relatively small (≈ 10^∘). However, as the local axis orientation becomes increasingly aligned with the radial direction, the spacecraft trajectory may pass close to the axis at two separate locations. This results in a magnetic field time series which deviates significantly from encounters with a force-free flux rope, and consequently the error in the axis orientation derived from cylindrical reconstructions can be as much as 90^∘. Such two-axis encounters can result in an apparent ‘double flux rope’ signature in the magnetic field time series, sometimes observed in spacecraft data. Analysing each axis encounter independently produces reasonably accurate axis orientations with MVA, but larger errors with FFFR fitting.     

The Kansas University meteorit

Abstract— A new 2.8 kg meteorite find from the United States, Kansas University, is classified as an L6 (S3) chondrite based on optical microscopy and electron microprobe analysis of mafic minerals. Natural thermo-luminescence (TL) and ¹⁴C measurements suggest that the Kansas University meteorite has a short terrestrial age compared to other meteorite finds from this area and is not paired with the other local meteorite finds, Densmore (1879), Lawrence, Kansas and Long Island, Kansas.     

Source characterisation by mixing long-running tsunami wave numerical simulations and historical observations within a metamodel-aided ABC setting

Uncertainty related to the source parameters of earthquake can largely impact the tsunami-induced wave characteristics, especially in the case of near-field tsunami source. The combination of numerical simulations and historical eyewitness accounts can be used to better constrain those uncertainties. In the present study, we propose a Bayesian procedure to infer (i.e. learn) the probability distribution of the source parameters of the earthquake. The strategy is based on the combination of: (1) kriging-based metamodelling techniques to overcome the high computation time cost of the numerical simulator; and (2) Approximate Bayesian Computation (ABC) procedure to perform the Bayesian inference. The procedure is applied to the Ligurian (North West of Italy) 1887 tsunami case, for which tsunami-induced sea surface elevations at the coast have been reported at four locations, namely Marseille, Imperia, Diano-Marina and Genoa. The kriging metamodels are trained using only 300 long-running numerical simulations that were performed using the FUNWAVE-TVD code. Contrary to recent inversion exercises that can benefit from current modern observation networks (like tide gauges, sea bottom pressure gauges, GPS-mounted buoys), the case of historical tsunami like Liguria is complicated by the imprecision and scarcity of the observations: this is accounted for by conducting the combined ABC-kriging procedure a large number of times (i.e. 1000); each time a new set of observations being randomly generated to account for this observational error. The combined analysis of the inference results and of the observation uncertainty reveals that: (1) the coseismic slip is the most important source parameter with a very peaky density distribution around low values ranging from 0.3 to 0.6 m; (2) The fault width has a peaky density distribution around low values ranging from 10 to 12 km; (3) The rake and azimuth distribution only slightly deviate from the uniform prior, hence indicating a low influence of those parameters; (4) The bi-modal distribution of the dip is also evidenced.     

The stability of hydrous phases beyond antigorite breakdown for a magnetite-bearing natural serpentinite between 6.5 and 11 GPa

Phase relations for a natural serpentinite containing 5 wt% of magnetite have been investigated using a multi-anvil apparatus between 6.5 and 11 GPa and 400–850 °C. Post-antigorite hydrous phase assemblages comprise the dense hydrous magnesium silicates (DHMSs) phase A (11.3 wt% H₂O) and the aluminous phase E (Al-PhE, 11.9 wt% H₂O). In addition, a ferromagnesian hydrous silicate (11.1 wt% H₂O) identified as balangeroite (Mg,Fe)₄₂Si₁₆O₅₄(OH)₄₀, typically described in low pressure natural serpentinite, was found coexisting with Al-PhE between 650 and 700 °C at 8 GPa. In the natural antigorite system, phase E stability is extended to lower pressures (8 GPa) than previously reported in simple chemical systems. The reaction Al-phase E?=?garnet?+?olivine?+?H₂O is constrained between 750 and 800 °C between 8 and 11 GPa as the terminal boundary between hydrous mineral assemblages and nominally anhydrous assemblages, hence restricting water transfer into the deep mantle to the coldest slabs. The water storage capacity of the assemblage Al-PhE?+?enstatite (high-clinoenstatite)?+?olivine, relevant for realistic hydrated slab composition along a relatively cold temperature path is estimated to be ca. 2 wt% H₂O. Attempts to mass balance run products emphasizes the role of magnetite in phase equilibria, and suggests the importance of ferric iron in the stabilization of hydrous phases such as balangeroite and aluminous phase E.     

Determination of actual limit angles to the surface and their comparison with the empirical values in the Upper Silesian Basin (Czech Republic)

This study deals with the determination of the actual limit angles in the long-term formed subsidence basin in the Czech part of the Upper Silesian Basin (the remaining part lays in Poland). Here there was the most extensive underground exploitation of black coal in the north-east of the Czech Republic. A limit angle is absolutely decisive in the determination of deep mining influences in relation to the current and future utilisation of this territory. The two CSM and Paskov mine localities on the edge of the subsidence basin were selected for this study, since they could not have been affected by mining in neighbouring mines. On the grounds of the long-term levelling monitoring of points on the surface which started prior to mining, the horizontal distance between the mined out area and the undisturbed ground surface was identified. The impact of limit angle on the surface was calculated by means of the horizontal distance and the established mining depth. Such identified actual limit angles reached the values of 36° at the CSM Mine and 25° for the Paskov Mine. The calculated values are significantly lower when compared with the currently applied empirical values of 57° for the CSM Mine and 56° for the Paskov Mine. This means that the extent of the undermining effects is unambiguously wider by 611 m at the CSM Mine and by 883 m at the Paskov Mine. This study thus establishes the existence of a significantly vaster area influenced by coal deep mining than previously expected. The identified facts lead to the conclusion that regular revisions and follow-up updates of the empirically determined parameters are recommended.     

Modelling the biological half-life and seasonality of ¹⁴C in Fucus vesiculosus from the east coast of Ireland: implications for the estimation of future trends

Radiocarbon levels were recorded in Fucus vesiculosus samples collected on a monthly basis over a three-year period at a site on the east coast of Ireland. The resulting data was analysed using a numerical model which estimates the transit times from the Sellafield plant to the sampling location, and the mean availability time of ¹⁴C in seaweed. With the inclusion of a model parameter allowing for seasonal variability in uptake by the Fucus, good correlation was observed between the predicted and measured concentrations. Future temporal trends of ¹⁴C Fucus concentrations along the eastern Irish coastline were modelled with the application of three possible prospective discharge scenarios, predicting ¹⁴C Fucus concentrations to reduce to ambient background levels within 2.5-years of discharges being set to zero. Such projections may prove helpful in assessing the consequences of discharge management and policy making in the context of the OSPAR convention.     

Determination of the Geopotential Scale Factor from TOPEX/POSEIDON Satellite Altimetry

The geopotential scale factor R _o = GM/W _o (the GM geocentric gravitational constant adopted) and/or geoidal potential Wo have been determined on the basis of the first year's (Oct 92 – Dec 93) ERS-1/TOPEX/POSEIDON altimeter data and of the POCM 4B sea surface topography model: R _o °=(6 363 672.58°±0.05) m, W _o °=(62 636 855.8°±0.05)m ² s ^–2 . The 2°–°3 cm uncertainty in the altimeter calibration limits the actual accuracy of the solution. Monitoring dW _o /dt has been projected.