Hard X-rays,ejecta, and their associated decimetric radio emission in solar flares

We investigate temporal and spatial correlations in solar flares of hard X-rays (HXR) and decimetric continuum emissions, ejecta, and CMEs. The focus is on three M-class flares, supported by observations from other flares. The main conclusions of our observations are that (1) major hard X-ray flares are often associated with ejecta seen in soft X-rays or EUV. (2) Those ejecta seem to start before HXR or related decimetric radio continua (DCIM emission). (3) DCIM occurring nearly simultaneously with the first HXR peak are located very close to the HXR source. Later in the flare, DCIM generally becomes stronger, drifts to lower frequency and occurs far from the HXR source. Thus the positions at high frequency are generally closer to the HXR source. DCIM emission consists of pulses that drift in frequency. The very high and sometimes positive drift rate suggests spatially extended sources or type III like beams in an inhomogeneous source. Movies of selected flares used in this study can be found on the CD-ROM accompanying this volume. Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1026194227110     

Effect of snowpack removal on energy balance,melt and runoff in a small supraglacial catchment

Modelling melt and runoff from snow‐ and ice‐covered catchments is important for water resource and hazard management and for the scientific study of glacier hydrology, dynamics and hydrochemistry. In this paper, a distributed, physically based model is used to determine the effects of the up‐glacier retreat of the snowline on spatial and temporal patterns of melt and water routing across a small (0·11 km²) supraglacial catchment on Haut Glacier d'Arolla, Switzerland. The melt model uses energy‐balance theory and accounts for the effects of slope angle, slope aspect and shading on the net radiation fluxes, and the effects of atmospheric stability on the turbulent fluxes. The water routing model uses simplified snow and open‐channel hydrology theory and accounts for the delaying effects of vertical and horizontal water flow through snow and across ice. The performance of the melt model is tested against hourly measurements of ablation in the catchment. Calculated and measured ablation rates show a high correlation (r² = 0·74) but some minor systematic discrepancies in the short term (hours). These probably result from the freezing of surface water at night, the melting of the frozen layer in the morning, and subsurface melting during the afternoon. The performance of the coupled melt/routing model is tested against hourly discharge variations measured in the supraglacial stream at the catchment outlet. Calculated and measured runoff variations show a high correlation (r² = 0·62). Five periods of anomalously high measured discharge that were not predicted by the model were associated with moulin overflow events. The radiation and turbulent fluxes contribute c. 86% and c. 14% of the total melt energy respectively. These proportions do not change significantly as the surface turns from snow to ice, because increases in the outgoing shortwave radiation flux (owing to lower albedo) happen to be accompanied by decreases in the incoming shortwave radiation flux (owing to lower solar incidence angles) and increases in the turbulent fluxes (owing to higher air temperatures and vapour pressures). Model sensitivity experiments reveal that the net effect of snow pack removal is to increase daily mean discharges by c. 50%, increase daily maximum discharges by >300%, decrease daily minimum discharges by c. 100%, increase daily discharge amplitudes by >1000%, and decrease the lag between peak melt rates and peak discharges from c. 3 h to c. 50 min. These changes have important implications for the development of subglacial drainage systems. Copyright © 2002 John Wiley & Sons, Ltd.     

Stabilization of Kepler's problem

A regularization of Kepler's problem due to Moser is used to ‘stabilize’ the equations of motion, that is, imbed a particular solution of Kepler's problem in a Lyapounov stable system.     

A REFRACTORY GLASS CHONDRULE IN THE VIGARANO CHONDRITE

Vigarano, a type 3 carbonaceous chondrite, contains a chondrule composed of highly refractory Ca and Al rich glass with minor spinel. The chondrule formed from material similar to the Ca, Al, Ti-rich aggregates that are common in Vigarano and other type 3 chondrites and formation of these refractory aggregates must predate formation of some Vigarano chondrules. Experiments with synthetic analogues and a comparison with studies in the system CaO-MgO-Al₂O₃-SiO₂ indicate a temperature for formation of the chondrule at or above 1700 °C followed by very rapid cooling.     

Influence of glacier hydrology on the dynamics of a large Quaternary ice sheet

The influence of glacier hydrology on the time-dependent morphology and flow behaviour of the late Weichselian Scandinavian ice sheet is explored using a simple one-dimensional ice sheet model. The model is driven by orbitally induced radiation variations, ice-albedo feedback and eustatic sea-level change. The influence of hydrology is most marked during deglaciation and on the southern side of the ice sheet, where a marginal zone of rapid sliding, thin ice and low surface slopes develops. Such a zone is absent when hydrology is omitted from the model, and its formation results in earlier and more rapid deglaciation than occurs in the no-hydrology model. The final advance to the glacial maximum position results from an increase in the rate of basal sliding as climate warms after 23000 yr BP. Channelised subglacial drainage develops only episodically, and is associated with relatively low meltwater discharges and high hydraulic gradients. The predominance of iceberg calving as an ablation mechanism on the northern side of the ice sheet restricts the occurrence of surface melting. Lack of meltwater penetration to the glacier bed in this area means that ice flow is predominantly by internal deformation and the ice sheet adopts a classical parabolic surface profile.     

Combined mass spectrometric composition measurements of positive and negative ions in the lower ionosphere—I. Positive ions

Recent improvements in rocket-borne mass spectrometer technology have made it possible to measure lower ionospheric ions with greater sensitivity and to extend the measurements to lower heights. The improvements made to the instrument and positive ion results from a flight of this instrument will be reported here. In addition to the previously known ions, such as NO⁺(H₂O)_n and H⁺(H₂O)_n, new ion species were found. The total fractional count rate of these ions was found to be constant with height indicating an upper altitude source. Possible identifications of these ions are proposed along with possible production mechanisms.     

Stratospheric aerosol sulfuric acid: First direct in situ measurements using a novel balloon-based mass spectrometer apparatus

The first direct in situ measurements of the sulfuric acid contained in stratospheric aerosol particles were made using a novel balloon-based Ion Molecule Reaction Mass Spectrometer instrument (IMRMS) equipped with an aerosol vaporizer. The IMRMS method employed offers direct aerosol sulfuric acid measurements with high spatial resolution. The balloon flight took place on 23 October 1995 in middle latitudes (44°N) and reached a maximum altitude of 24 km. Measured molecular number densities of aerosol sulfuric acid decreased with increasing altitude from about 2.9 × 109 cm-3 at 15km altitude to about 2.4 × 108 cm-3 at 21 km. Corresponding mass mixing ratios are 2.5 and 0.6 ppbm, respectively. Calculated sulfuric acid mixing ratios from aerosol volumes inferred from aerosol size distribution measurements on the same balloon agree well with the IMRMS data using standard assumption aerosol composition.     

Toward more realistic formulations for the analysis of laccoliths

The published laccolith analyses are based on the linear plate bending theory and the a priori assumption that the width of the laccolith is fixed. This is not the case in an actual situation. The dimension of the laccolith in the horizontal plane has to result from an additional matching condition at the separation lines. The published analyses are generalized by dropping the a priori assumption that the width of the laccolith is prescribed, by assuming that the magmatic pressure is not constant, and by taking into consideration the vertical compressibility of the overburden “plate” and base in the contact region. In order to determine the magnitude of the magmatic pressure, a condition is postulated that equates the measured volume of the intruded magma in a laccolith with the corresponding analytical expression for the volume. The obtained closed-form solution appears to satisfy many of the intuitive expectations. It was evaluated numerically and the results are presented as graphs. It may be concluded that even very small laccoliths may exist, provided the magmatic pressure is sufficiently larger than the overburden weight. We also show the dependence of the laccolith size on its stratigraphic position; the thicker the overburden h the larger the size of the laccolith, for an overburden plate of given thickness, the larger the volume V of the intruded magma, the larger the laccolith width 2a and its height. The paper concludes by discussing a published analysis for laccolith with flexible underburden and overburden. It is shown that this analysis is based on a formulation that is of questionable validity.     

Heating Events in the Quiet Solar Corona

Sensitive observations of the quiet Sun observed by EIT on the SOHO satellite in high-temperature iron-line emission originating in the corona are presented. The thermal radiation of the quiet corona is found to fluctutate significantly, even on the shortest time scale of 2 min and in the faintest pixels. The power spectrum of the emission measure time variations is approximately a power law with an exponent of 1.79±0.08 for the brightest pixels and 1.69±0.08 for the average and the faintest pixels. The more prominent enhancements are identified with previously reported X-ray network flares (Krucker et al., 1997) above the magnetic network of the quiet chromosphere. In coronal EUV iron lines they are amenable to detailed analysis suggesting that the brightenings are caused by additional plasma injected from below and heated to slightly higher temperature than the preexisting corona. Statistical investigations are consistent with the hypothesis that the weaker emission measure enhancements originate from the same parent population. The power input derived from the impulsive brightenings is linearly proportional to the radiative loss in the observed part of the corona. The absolute amount of impulsive input is model-dependent. It cannot be excluded that it can satisfy the total requirement for heating. These observations give strong evidence that a significant fraction of the heating in quiet coronal regions is impulsive.     

On the choice of timescale in glacial rebound modelling: mantle viscosity estimates and the radiocarbon timescale

Most glacial rebound studies have been carried out with respect to the radiocarbon timescale, whose departures from the calendar timescale are becoming increasingly well established. In consequence, it has sometimes been argued that the choice of the radiocarbon timescale may invalidate some of the conclusions drawn from rebound and sea-level analyses. The purpose of this note is to compare rebound model results based on both timescales, using the British Isles data for the test. The results indicate that the choice of timescale is unimportant provided that the time dimension of viscosity is appropriately defined. The results confirm that the radiocarbon viscosities are about 15 per cent less than the corresponding calendar-time viscosities. Also, provided that consistency of timescales is maintained in the analysis, and that the time-accuracy estimates of the radiocarbon data reflect the departures from a linear timescale, the use of the radiocarbon timescale does not impinge on inferences drawn about the timing of melting of ice sheets or eustatic sea-level change.