The Winchcombe fireball—That lucky survivor

On February 28, 2021, a fireball dropped ∼0.6 kg of recovered CM2 carbonaceous chondrite meteorites in South-West England near the town of Winchcombe. We reconstruct the fireball's atmospheric trajectory, light curve, fragmentation behavior, and pre-atmospheric orbit from optical records contributed by five networks. The progenitor meteoroid was three orders of magnitude less massive (∼13 kg) than any previously observed carbonaceous fall. The Winchcombe meteorite survived entry because it was exposed to a very low peak atmospheric dynamic pressure (∼0.6 MPa) due to a fortuitous combination of entry parameters, notably low velocity (13.9 km s⁻¹). A near-catastrophic fragmentation at ∼0.07 MPa points to the body's fragility. Low entry speeds which cause low peak dynamic pressures are likely necessary conditions for a small carbonaceous meteoroid to survive atmospheric entry, strongly constraining the radiant direction to the general antapex direction. Orbital integrations show that the meteoroid was injected into the near-Earth region ∼0.08 Myr ago and it never had a perihelion distance smaller than ∼0.7 AU, while other CM2 meteorites with known orbits approached the Sun closer (∼0.5 AU) and were heated to at least 100 K higher temperatures.     

Temporal Interpolation of Spatially Dynamic Polygons

In this study we compare two methods of interpolating simple metrics from polygons that change over time. Conventional methodology involves computing values of the metrics at points in time where the polygon is observed, and interpolating between these observed values to estimate values at other points in time. An alternative method applies interpolation techniques to the locations of vertices composing polygons are interpolated between observations and metrics are computed from the interpolated polygon shapes. We conducted a Monte Carlo simulation of both techniques using simulated polygons composed of varying numbers of vertices, which were allowed to move randomly over varying numbers of discrete time periods. We observed differences in the success of the two methods when applied to three metrics: Area, Perimeter, and Area/Perimeter Ratio. We found the two techniques to perform differently depending upon the metric being interpolated. Full results are presented and possible reasons why the techniques succeeded or failed under various conditions are discussed.     

Atom Probe Tomography: Development and Application to the Geosciences

Atom probe tomography (APT) is an analytical technique that provides quantitative three‐dimensional elemental and isotopic analyses at sub‐nanometre resolution across the whole periodic table. Although developed and mostly used in the materials science and semiconductor fields, recent years have seen increasing development and application in the geoscience and planetary science disciplines. Atom probe studies demonstrate compositional complexity at the nanoscale and provide fundamental new insights into the atom‐scale mechanisms taking place in minerals over geological time. Here, we provide an overview of APT, including the historical development and technical aspects of the instrumentation, and the fundamentals of data acquisition, data processing and data reconstruction. We also review previous studies and highlight the potential future applications of nanoscale geochemical studies of natural materials.     

Science of Nowcasting Olympic Weather for Vancouver 2010 (SNOW-V10): a World Weather Research Programme Project

A World Weather Research Programme (WWRP) project entitled the Science of Nowcasting Olympic Weather for Vancouver 2010 (SNOW-V10) was developed to be associated with the Vancouver 2010 Olympic and Paralympic Winter Games conducted between 12 February and 21 March 2010. The SNOW-V10 international team augmented the instrumentation associated with the Winter Games and several new numerical weather forecasting and nowcasting models were added. Both the additional observational and model data were available to the forecasters in real time. This was an excellent opportunity to demonstrate existing capability in nowcasting and to develop better techniques for short term (0–6 h) nowcasts of winter weather in complex terrain. Better techniques to forecast visibility, low cloud, wind gusts, precipitation rate and type were evaluated. The weather during the games was exceptionally variable with many periods of low visibility, low ceilings and precipitation in the form of both snow and rain. The data collected should improve our understanding of many physical phenomena such as the diabatic effects due to melting snow, wind flow around and over terrain, diurnal flow reversal in valleys associated with daytime heating, and precipitation reductions and increases due to local terrain. Many studies related to these phenomena are described in the Special Issue on SNOW-V10 for which this paper was written. Numerical weather prediction and nowcast models have been evaluated against the unique observational data set now available. It is anticipated that the data set and the knowledge learned as a result of SNOW-V10 will become a resource for other World Meteorological Organization member states who are interested in improving forecasts of winter weather.     

Performance of GOCE and GRACE-derived mean dynamic topographies in resolving Antarctic Circumpolar Current fronts

Presently, two satellite missions, Gravity Recovery and Climate Experiment (GRACE) and Gravity field and steady-state Ocean Circulation Explorer (GOCE), are making detailed measurements of the Earth’s gravity field, from which the geoid can be obtained. The mean dynamic topography (MDT) is the difference between the time-averaged sea surface height and the geoid. The GOCE mission is aimed at determining the geoid with superior accuracy and spatial resolution, so that a more accurate MDT can be estimated. In this study, we determine the mean positions of the Antarctic Circumpolar Current fronts using the purely geodetic estimates of the MDT constructed from an altimetric mean sea surface and GOCE and GRACE geoids. Overall, the frontal positions obtained from the GOCE and GRACE MDTs are close to each other. This means that these independent estimates are robust and can potentially be used to validate frontal positions obtained from sparse and irregular in situ measurements. The geodetic frontal positions are compared to earlier estimates as well as to those derived from MDTs based on satellite and in situ measurements and those obtained from an ocean data synthesis product. The position of the Sub-Antarctic Front identified in the GOCE MDT is found to be in better agreement with the previous estimates than that identified in the GRACE MDT. The geostrophic velocities derived from the GOCE MDT are also closer to observations than those derived from the GRACE MDT. Our results thus show that the GOCE mission represents an improvement upon GRACE in terms of the time-averaged geoid.     

Links between bacterial communities in marine sediments and trace metal geochemistry as measured by in situ DET/DGT approaches

Our current view about the relationship between metals and bacteria in marine sediments might be biased because most studies only use ex situ approaches to quantify metals. The aim of the present research was to compare ex situ and in situ methods of metal measurement (DET and DGT--diffusive equilibration or diffusive gradients in thin-films) and relate the results with two commonly used microbiological variables (bacterial biomass and bacterial diversity as revealed by DGGE). No previous studies have used such in situ approaches in microbial ecology. For biomass and most of the investigated trace metals (Ag, Cd, Sn, Cr, Ni, Cu, Pb, and Al) no significant correlations were found. The exceptions were Fe, Mn, Co, and As which behave like micronutrients. For bacterial diversity, no relevant relationships were found. We conclude that in situ methods are more adapted tools for microbial ecologists but that ex situ approaches are still necessary.     

Virtual dipole moment variations through the Proterozoic-Phanerozoic eons

The international bank of virtual dipole moment (VDM) data, combined with materials from recent publications (3384 values in total), served as a basis for the analysis of the VDM??s distribution through the Proterozoic and Phanerozoic eons (0?C2.6 Ga). The VDM distribution obtained by the method of a moving average exhibits a positive linear trend from 3.7 × 10²² Am² 2.6 Ga ago to 5.8 × 10²² Am² at present. Against the background of this linear growth, fluctuations with a periodicity of approximately 390 Ma are defined. The obtained data substantially specify the available data on the behavior of the magnetic field during the Proterozoic and Phanerozoic eons and should be taken into consideration for modeling the physical processes in the development of the Earth in the geological past and predicting its ecological and energetic evolution in the future.     

Metamorphosis of Magnetospirillum magneticum AMB-1 cells

Magnetospirillum magneticum strain AMB-1 belongs to the family of magnetotactic bacteria. It possesses a magnetosome chain aligning, with the assistance of cytoskeleton filaments MamK, along the long axis of the spiral cells. Most fresh M. magneticum AMB-1 cells exhibit spiral morphology. In addition, other cell shapes such as curved and spherical were also observed in this organism. Interestingly, the spherical cell shape increased steadily with prolonged incubation time. As the actin-like cytoskeleton protein MreB is involved in maintenance of cell shapes in rod-shaped bacteria such as Escherichia coli and Bacillus subtilis, the correlation between MreB protein levels and cell shape was investigated in this study. Immunoblotting analysis showed that the quantity of MreB decreased when the cell shape changed along with incubation time. As an internal control, the quantity of MamA was not obviously changed under the same conditions. Cell shape directs cell-wall synthesis during growth and division. MreB is required for maintaining the cell shape. Thus, MreB might play an essential role in maintaining the spiral shape of M. magneticum AMB-1 cells.     

Scapolite stoichiometry

Over the range Ca/(Ca + Na) from zero to 0.75, scapolites vary linearly between Na₄Al₃Si₉O₂₄Cl and NaCa₃Al₅Si₇O₂₄CO₃, by means of a coupled replacement of Na₃Si₂Cl by Ca₃Al₂CO₃. Ca includes minor Sr, Na includes K, and CO₃ may include substantial SO₄. From Ca/(Ca + Na) = 0.75 to 1.00, variation is between NaCa₃Al₅Si₇O₂₄CO₃ and Ca₄Al₆Si₆O₂₄CO₃, by means of a coupled replacement of NaSi by CaAl, as in plagioclase. Anion substitution is complete at the 0.75 point. Recalculation of scapolite analyses on the basis of Al + Si atoms = 12.0, as suggested by computed unit cell contents, offers a reasonable basis for normalization of atomic proportions. On this basis, Ca + Sr + Na + K + Fe atoms total very close to 4.0. New limits on the minor element content of scapolite are proposed. In view of the inflection at 0.75, subdivision of the scapolites at Ca/(Ca + Na) ratios of 0.25, 0.5, and 0.75 seems more logical than the 0.2, 0.5, and 0.8 limits used hitherto for marialite, dipyre, mizzonite, and meionite.