Extreme Ultraviolet Late-Phase Flares: Before and During the Solar Dynamics Observatory Mission

The solar extreme-ultraviolet (EUV) observations from the Solar Dynamics Observatory (SDO) have revealed interesting characteristics of warm coronal emissions, such as Fe xvi 335 Å emission, which peak soon after the hot coronal X-ray emissions peak during a flare and then sometimes peak for a second time hours after the X-ray flare peak. This flare type, with two warm coronal emission peaks but only one X-ray peak, has been named the EUV late phase (Woods et al., Astrophys. J. 739, 59, 2011). These flares have the distinct properties of i) having a complex magnetic-field structure with two initial sets of coronal loops, with one upper set overlaying a lower set, ii) having an eruptive flare initiated in the lower set and disturbing both loop sets, iii) having the hot coronal emissions emitted only from the lower set in conjunction with the X-ray peak, and iv) having the first peak of the warm coronal emissions associated with the lower set and its second peak emitted from the upper set many minutes to hours after the first peak and without a second X-ray enhancement. The disturbance of the coronal loops by the eruption is at about the same time, but the relaxation and cooling down of the heated coronal loops during the post-flare reconnections have different time scales with the longer, upper loops being significantly delayed from the lower loops. The difference in these cooling time scales is related to the difference between the two peak times of the warm coronal emission and is also apparent in the decay profile of the X-ray emissions having two distinct decays, with the first decay slope being steeper (faster) and the delayed decay slope being smaller (slower) during the time of the warm-coronal-emission second peak. The frequency and relationship of the EUV late-phase decay times between the Fe xvi 335 Å two flare peaks and X-ray decay slopes are examined using three years of SDO/EUV Variability Experiment (EVE) data, and the X-ray dual-decay character is then exploited to estimate the frequency of EUV late-phase flares during the past four solar cycles. This study indicates that the frequency of EUV late-phase flares peaks before and after each solar-cycle minimum.     

Natural diet of the seahorse Hippocampus abdominalis

This investigation examined the diet of adult wild seahorses, Hippocampus abdominalis Leeson 1827, from Wellington Harbour, New Zealand. Diet of seahorses (n = 59) collected from shallow subtidal macroalgal stands consisted largely of crustaceans, in particular amphipods (e.g., caprellid and ischyrocerid amphipods), caridean shrimp (i.e., Hippolyte bifidirostris), and peracarids (i.e., the mysid Tenagomysis similis). There were no differences in diet between male and female seahorses. Smaller seahorses consumed a greater amount of crustaceans than larger seahorses, as a result of the greater proportion of amphipods in their gut contents. There were some seasonal differences in diet, with amphipod consumption peaking in spring and summer, and decapod consumption lowest in autumn.     

Erratum to “The Albian-Cenomanian boundary at Eggardon Hill, Dorset (England): An anomaly resolved?” [Proc. Geol. Assoc. 120 (2009) 108-120]

Re-examination of the classic exposures of the Eggardon Grit (topmost Upper Greensand Formation) at Eggardon Hill, Dorset shows that the upper part of this unit has a more complex stratigraphy than has been previously recognised. The Eggardon Grit Member, as described herein, is capped by a hardground and associated conglomerate, and is entirely of Late Albian age. The hardground is probably the lateral equivalent of the Small Cove Hardground, which marks the top of the Upper Greensand succession in southeast Devon. The conglomerate is overlain by a thin sandy limestone containing Early Cenomanian ammonites. This limestone is almost certainly the horizon of the Early Cenomanian ammonite fauna that has previously been attributed to the top of the Eggardon Grit. The limestone is regarded as a thin lateral equivalent of the Beer Head Limestone Formation (formerly Cenomanian Limestone) exposed on the southeast Devon coast. The fauna of the limestone at Eggardon suggests that it is probably the age equivalent to the two lowest subdivisions of the Beer Head Limestone in southeast Devon, with a remanié fauna of the Pounds Pool Sandy Limestone Member combined with indigenous macrofossils of the Hooken Nodular Limestone Member. The next highest subdivision of the Beer Head Limestone in southeast Devon (Little Beach Bioclastic Limestone Member), equates with the ammonite-rich phosphatic conglomerate of the ‘Chalk Basement Bed’, which caps the Beer Head Limestone at Eggardon, and which was previously regarded as the base of the Chalk Group on Eggardon Hill.Petrographic analysis of the Eggardon Grit shows that lithologically it should more correctly be described as a sandy limestone rather than sandstone. The original stratigraphical definition of the unit should probably be modified to exclude the softer, nodular calcareous sandstones that have traditionally been included in the lower part of the member.Without the apparently clear evidence of unbroken sedimentation across the Albian-Cenomanian boundary, suggested by the previous interpretation of the Eggardon succession, it is harder to argue for this being a prevalent feature of Upper Greensand stratigraphy in southwest England. Correlation of the Eggardon succession with successions in Dorset and southeast Devon reveals a widespread regional break in sedimentation at the Albian-Cenomanian boundary. The sand-rich facies above this unconformity represent the true base of the Chalk Group, rather than the ‘Chalk Basement Bed’ of previous interpretations.Selected elements of regionally important Upper Greensand ammonite faunas previously reported from Shapwick Quarry, near Lyme Regis, and Babcombe Copse, near Newton Abbot, are newly figured herein.     

The Lower Albian (Lower Cretaceous) Monk's Bay Sandstone Formation (formerly the Carstone) of the Isle of Wight: Its distribution, litho- and biostratigraphy

The Monk's Bay Sandstone Formation (MBSF) is the new name for the Lower Albian ferruginous sandstone that was formerly known as the Carstone of the Isle of Wight. The new term was proposed to remove any confusion with the Carstone, of similar age and lithology, described from the separate Lower Cretaceous sedimentary basin of Eastern England. This paper formalises the nomenclatural change outlined in the Lower Cretaceous Framework Report, ratified by the Geological Society Stratigraphy Commission.The MBSF, representing a major mid-Albian transgressive event, is described from a series of boreholes drilled by the British Geological Survey across the Isle of Wight, and from additional coastal exposures, together with reinterpretations of sections described in earlier works.The age range of the MBSF is determined in relation to recent biostratigraphical schemes supported with new data from the previously unknown presence of foraminifera. Deposits, belonging to the Leymeriella regularis Subzone, were previously considered to be absent from the succession and represent the stratigraphical gap separating the formation from the underlying Sandrock Formation. However a first occurrence of tubular foraminifera resembling Hyperammina/‘Rhizammina cf dichotomata’ suggest that the oldest part of the formation in the northeast of the island may be of regularis Subzone age. This unconformity is correlated with the sequence boundary LG4 of Hesselbo and the presence of the Sonneratia kitchini Subzone at the base of the MBSF on the Isle of Wight suggests that this boundary should be placed at the lower of two candidate horizons within the successions of the Weald.The formation is restricted to the Isle of Wight but is coeval with similar coarse-grained sediments, e.g. the Carstone and ‘JunctionBeds’ to the north. The palaeogeography of the formation and the relationship with these similar deposits and the implications for the timing of mid-Albian structural events is briefly discussed. The identification of older Lower Greensand Group sediments beneath the MBSF in boreholes north of the Isle of Wight structure, together with new survey data indicating north-south orientated faulting affecting the early Cretaceous implies a tectonic element to the distribution the Lower Greensand Group sediments. Taken together these imply a complex interaction of tectonics and transgressive events throughout the Aptian and Albian over this structural high.     

Consistency between hydrological models and field observations: linking processes at the hillslope scale to hydrological responses at the watershed scale

The purpose of this paper is to identify simple connections between observations of hydrological processes at the hillslope scale and observations of the response of watersheds following rainfall, with a view to building a parsimonious model of catchment processes. The focus is on the well‐studied Panola Mountain Research Watershed (PMRW), Georgia, USA. Recession analysis of discharge Q shows that while the relationship between dQ/dt and Q is approximately consistent with a linear reservoir for the hillslope, there is a deviation from linearity that becomes progressively larger with increasing spatial scale. To account for these scale differences conceptual models of streamflow recession are defined at both the hillslope scale and the watershed scale, and an assessment made as to whether models at the hillslope scale can be aggregated to be consistent with models at the watershed scale. Results from this study show that a model with parallel linear reservoirs provides the most plausible explanation (of those tested) for both the linear hillslope response to rainfall and non‐linear recession behaviour observed at the watershed outlet. In this model each linear reservoir is associated with a landscape type. The parallel reservoir model is consistent with both geochemical analyses of hydrological flow paths and water balance estimates of bedrock recharge. Overall, this study demonstrates that standard approaches of using recession analysis to identify the functional form of storage–discharge relationships identify model structures that are inconsistent with field evidence, and that recession analysis at multiple spatial scales can provide useful insights into catchment behaviour. Copyright © 2008 John Wiley & Sons, Ltd.     

The interaction of ash flows with ridges

 Using both laboratory experiments and theoretical models, we examine the different flow regimes that may develop when an ash flow encounters a ridge. For very small ridges, all the flow may pass over the ridge. For intermediate-size ridges, the flow may be partially blocked, with a fraction of the flow reflected upstream as a travelling bore. In this case, the remainder of the flow, which does pass over the ridge, is hydraulically controlled at the ridge crest. Finally, if the ridge is sufficiently high, then the flow will be totally blocked. New laboratory experiments show that the sedimentation patterns associated with these flow regimes may be very different. Most importantly, flows that involve partial blocking and the formation of upstream propagating bores display enhanced sedimentation upstream of the ridge, analogous to valley-ponded and caldera-fill deposits. In contrast, under some circumstances, if the flow is able to scale a ridge, the deposit may be relatively unaffected by the presence of the ridge. The minimum ridge height that leads to total blocking of the flow increases with mass eruption rate and has a complex variation with distance from the source. In a one-dimensional channel, the minimum ridge height that causes blocking increases with distance downstream. This is because the flow becomes less dense through sedimentation of particles and entrainment of air and so requires less energy to scale a ridge of a particular height. In axisymmetric flow, the minimum ridge height initially decreases with distance downstream as the flow spreads radially, but subsequently increases as the flow becomes less dense through sedimentation and entrainment. A new quantitative model of dilute ash flows propagating over ridges indicates that flows with mass fluxes in excess of 10⁸–10⁹ kg/s can partially scale barriers as high as 1000 m at distances of tens of kilometres from the source, whereas smaller flows are likely to be totally blocked by such an obstacle. Our results shed new insight on the possible long-range transport mechanism of several large flows including the Ata, Fisher and Aniakchak pyroclastic flows. Received: 20 December 1996 / Accepted: 15 March 1998     

Oceanic mantle beneath the southern Rio Grande rift

Major element and modal trends in spinel lherzolites from Salt Lake Crater, Hawaii, and Kilbourne Hole, New Mexico, are essentially identical. These trends have developed through 5–30% partial melting of the same pyrolite-like parent composition. The melting events probably took place at mid-ocean ridges.Using Cr/(Cr + Al + Fe³⁺) in spinel as an index of the degree of depletion in fusible components in each of a large number of lherzolite inclusions, we have subdivided both suites into relatively parental, intermediate, and refractory groups, and computed an average bulk composition for each group. Compositions of hypothetical melts generated from these rocks are characterized by high MgO (about 18%), low Ti and K, and CaO/Al₂O₃ around 1.0.The strongly similarity between the two xenolith suites suggests that south central New Mexico is underlain by oceanic mantle. We propose that the Kilbourne Hole lherzolites represent oceanic lithosphere which was buried beneath offshore sediments during a Precambrian ocean basin formation, later to be preserved when subduction further offshore created new additions to the continent above that near-shore oceanic lithosphere. In addition, we propose that the Mg-rich, Ti- and K-poor calculated melts reported here are the primitive precursors to mid-ocean ridge basalts. Early dunite and wehrlite cumulates from some ophiolite sequences may record the fractionation histories these liquids follow prior to eruption at the surface.     

Book review of Land Use Transitions and Rural Restructuring in China by Hualou Long

Journal of Geographical Sciences -     

Hydrological data assimilation with the ensemble Kalman filter: Use of streamflow observations to update states in a distributed hydrological model

This paper describes an application of the ensemble Kalman filter (EnKF) in which streamflow observations are used to update states in a distributed hydrological model. We demonstrate that the standard implementation of the EnKF is inappropriate because of non-linear relationships between model states and observations. Transforming streamflow into log space before computing error covariances improves filter performance. We also demonstrate that model simulations improve when we use a variant of the EnKF that does not require perturbed observations. Our attempt to propagate information to neighbouring basins was unsuccessful, largely due to inadequacies in modelling the spatial variability of hydrological processes. New methods are needed to produce ensemble simulations that both reflect total model error and adequately simulate the spatial variability of hydrological states and fluxes.     

Observations and Modelling of the Pre-flare Period of the 29 March 2014 X1 Flare

On 29 March 2014, NOAA Active Region (AR) 12017 produced an X1 flare that was simultaneously observed by an unprecedented number of observatories. We have investigated the pre-flare period of this flare from 14:00 UT until 19:00 UT using joint observations made by the Interface Region Imaging Spectrometer (IRIS) and the Hinode Extreme Ultraviolet Imaging Spectrometer (EIS). Spectral lines providing coverage of the solar atmosphere from the chromosphere to the corona were analysed to investigate pre-flare activity within the AR. The results of the investigation have revealed evidence of strongly blue-shifted plasma flows, with velocities up to \(200~\mbox{km}\,\mbox{s}^{-1}\), being observed 40 minutes prior to flaring. These flows are located along the filament present in the active region and are both spatially discrete and transient. In order to constrain the possible explanations for this activity, we undertake non-potential magnetic field modelling of the active region. This modelling indicates the existence of a weakly twisted flux rope along the polarity inversion line in the region where a filament and the strong pre-flare flows are observed. We then discuss how these observations relate to the current models of flare triggering. We conclude that the most likely drivers of the observed activity are internal reconnection in the flux rope, early onset of the flare reconnection, or tether-cutting reconnection along the filament.