Energetics and morphology of powerful impulsive solar flares

We have studied the energetics of two impulsive solar flares of X-ray class X1.7 by assuming the electrons accelerated in several episodes of energy release to be the main source of plasma heating and reached conclusions about their morphology. The time profiles of the flare plasma temperature, emission measure, and their derivatives, and the intensity of nonthermal X-ray emission are compared; images of the X-ray sources and magnetograms of the flare region at key instants of time have been constructed. Based on a spectral analysis of the hard X-ray emission from RHESSI data and GOES observations of the soft X-ray emission, we have estimated the spatially integrated kinetic power of nonthermal electrons and the change in flare-plasma internal energy by taking into account the heat losses through thermal conduction and radiation and determined the parameters needed for thermal balance. We have established that the electrons accelerated at the beginning of the events with a relatively soft spectrum directly heat up the coronal part of the flare loops, with the increase in emission measure and hard X-ray emission from the chromosphere being negligible. The succeeding episodes of electron acceleration with a harder spectrum have virtually no effect on the temperature rise, but they lead to an increase in emission measure and hard X-ray emission from the footpoints of the flare loops.     

Erratum to: Width of Sunspot Generating Zone and Reconstruction of Butterfly Diagram

Based on the extended Greenwich – NOAA/USAF catalogue of sunspot groups, it is demonstrated that the parameters describing the latitudinal width of the sunspot generating zone (SGZ) are closely related to the current level of solar activity, and the growth of the activity leads to the expansion of the SGZ. The ratio of the sunspot number to the width of the SGZ shows saturation at a certain level of the sunspot number, and above this level the increase of the activity takes place mostly due to the expansion of the SGZ. It is shown that the mean latitudes of sunspots can be reconstructed from the amplitudes of solar activity. Using the obtained relations and the group sunspot numbers by Hoyt and Schatten (Solar Phys. 179, 189, 1998), the latitude distribution of sunspot groups (“the Maunder butterfly diagram”) for the eighteenth and the first half of the nineteenth centuries is reconstructed and compared with historical sunspot observations.     

Mid-infrared lightcurve of Vesta

We present a thermal mid-infrared lightcurve of Asteroid 4 Vesta and use this to infer variations in thermophysical properties over the surface. Vesta was observed over three nights during the May 2007 opposition with the Infrared Telescope Facility on Mauna Kea. Mid-infrared observations are compared to a model based on the Standard Thermal Model which is draped over a Vesta shape model derived from Hubble Space Telescope observations.A visible lightcurve with similar aspect was used to estimate the albedo as Vesta rotates. Shape and albedo can explain some of the features observed in the mid-infrared lightcurve. However, variations in the thermophysical properties, such as the “beaming parameter,” over Vesta’s surface are required to completely explain the observations.In order to match the mid-infrared magnitudes observed of Vesta, a beaming parameter of ∼0.862 is required which is higher than other Main Belt Asteroids such as Ceres and Pallas (0.756), indicating a smoother and/or rockier surface on Vesta. Variations in the beaming parameter with longitude are invoked to reproduce the observed thermal variations. Surface materials with relatively high beaming values, indicating a smoother and/or rockier surface, in the eastern hemisphere of Vesta coincide with locations where impact excavations may have produced surfaces that are younger and brighter relative to the western hemisphere.     

High kinetic energy density jets in the Earth’s magnetosheath: A case study

We study several high kinetic energy density jets observed during a traversal of the dayside magnetosheath by the Cluster spacecraft on March 17, 2001, at various distances from the magnetopause, generally characterised by anomalously high values of the local magnetosonic Mach number. We concentrate on two jets observed just outside the magnetopause, the first almost parallel to the GSM x axis and the second directed northward-tailward along the nominal magnetopause surface. We present evidence that none of them can be ascribed to magnetic reconnection at the magnetopause and show that the magnetopause is severely deformed by the jets, so that its local normal forms an angle of 97° with the quiet time magnetopause normal. On these grounds, we suggest that the indentation of the magnetopause is caused by an anti-sunward jet ramming into the magnetopause slightly equatorward of the northern cusp and that the northward-tailward jet is the result of its reflection at the deformed magnetopause. Finally, we briefly discuss our results by comparing them with past studies of events which in some way recall the one analysed herein.     

UV-controlled physical and chemical structure of protoplanetary disks

We study details of the UV radiation transfer in a protoplanetary disk, paying attention to the influence of dust growth and sedimentation on the disk density and temperature. Also, we show how the dust evolution affects photoreaction rates of key molecules, like CN and CS.     

The distribution of carbon monoxide in the lower atmosphere of Venus

We have obtained spatially resolved near-infrared spectroscopy of the Venus nightside on 15 nights over three observing seasons. We use the depth of the CO absorption band at 2.3 μm to map the two-dimensional distribution of CO across both hemispheres. Radiative transfer models are used to relate the measured CO band depth to the volume mixing ratio of CO. The results confirm previous investigations in showing a general trend of increased CO abundances at around 60° latitude north and south as compared with the equatorial regions. Observations taken over a few nights generally show very similar CO distributions, but significant changes are apparent over longer periods. In past studies it has been assumed that the CO latitudinal variation occurs near 35 km altitude, at which K-band sensitivity to CO is greatest. By modeling the detailed spectrum of the excess CO at high latitudes we show that it occurs at altitudes around 45 km, much higher than has previously been assumed, and that there cannot be significant contribution from levels of 36 km or lower. We suggest that this is most likely due to downwelling of CO-rich gas from the upper atmosphere at these latitudes, with the CO being removed by around 40 km through chemical processes such as the reaction with SO₃.     

Dynamical and collisional evolution of Halley-type comets

The number of observed Halley-type comets is hundreds of times less than predicted by models (Levison, H.F., Dones, L., Duncan, M.J. [2001]. Astron. J. 121, 2253–2267). In this paper we investigate the impact of collisions with planetesimals on the evolution of Halley-type comets. First we compute the dynamical evolution of a sub-set of 21 comets using the Mercury integrator package over 100 Myr. The dynamical lifetime is determined to be of the order of 10⁵–10⁶ years in agreement with previous work. The collisional probability of Halley-type comets colliding with known asteroids, a simulated population of Kuiper-belt objects, and planets, is calculated using a modified, Öpik-based collision code. Our results show that the catastrophic disruption of the cometary nucleus has a very low probability of occurring, and disruption through cumulative minor impacts is concluded to be negligible. The dust mantle formed from ejected material falling back to the comet’s surface is calculated to be less than a few centimeters thick, which is insignificant compared to the mantle formed by volatile depletion, while planetary encounters were found to be a negligible disruption mechanism.     

Observational Tracking of the 2D Structure of Coronal Mass Ejections Between the Sun and 1 AU

The Solar TErrestrial RElations Observatory (STEREO) provides high cadence and high resolution images of the structure and morphology of coronal mass ejections (CMEs) in the inner heliosphere. CME directions and propagation speeds have often been estimated through the use of time-elongation maps obtained from the STEREO Heliospheric Imager (HI) data. Many of these CMEs have been identified by citizen scientists working within the SolarStormWatch project ( www.solarstormwatch.com ) as they work towards providing robust real-time identification of Earth-directed CMEs. The wide field of view of HI allows scientists to directly observe the two-dimensional (2D) structures, while the relative simplicity of time-elongation analysis means that it can be easily applied to many such events, thereby enabling a much deeper understanding of how CMEs evolve between the Sun and the Earth. For events with certain orientations, both the rear and front edges of the CME can be monitored at varying heliocentric distances (R) between the Sun and 1?AU. Here we take four example events with measurable position angle widths and identified by the citizen scientists. These events were chosen for the clarity of their structure within the HI cameras and their long track lengths in the time-elongation maps. We show a linear dependency with R for the growth of the radial width (W) and the 2D aspect ratio (??) of these CMEs, which are measured out to ???0.7?AU. We estimated the radial width from a linear best fit for the average of the four CMEs. We obtained the relationships W=0.14R+0.04 for the width and ??=2.5R+0.86 for the aspect ratio (W and R in units of?AU).     

Galactic Cosmic Ray Modulation and the Last Solar Minimum

In this work the galactic cosmic ray modulation in relation to solar activity indices and heliospheric parameters during the years 1996??C?2010 covering solar cycle 23 and the solar minimum between cycles 23 and 24 is studied. A new perspective of this contribution is that cosmic ray data with a rigidity of 10 GV at the top of the atmosphere obtained from many ground-based neutron monitors were used. The proposed empirical relation gave much better results than those in previous works concerning the hysteresis effect. The proposed models obtained from a combination of solar activity indices and heliospheric parameters give a standard deviation <?10?% for all the cases. The correlation coefficient between the cosmic ray variations of 10?GV and the sunspot number reached a value of r=?0.89 with a time lag of 13.6±0.4 months. The best reproduction of the cosmic ray intensity is obtained by taking into account solar and interplanetary indices such as sunspot number, interplanetary magnetic field, CME index, and heliospheric current sheet tilt. The standard deviation between the observed and calculated values is about 7.15?% for all of solar cycle 23; it also works very well during the different phases of the cycle. Moreover, the use of the cosmic ray intensity of 10?GV during the long minimum period between cycles 23 and 24 is of special interest and is discussed in terms of cosmic ray intensity modulation.     

First 4D Reconstruction of an Eruptive Prominence Using Three Simultaneous View Directions

Data from the STEREO (Solar Terrestrial Relations Observatory) mission are intensively used for 3D reconstruction of solar coronal structures. After the launch of the SDO (Solar Dynamic Observatory) satellite, its additional observations give the possibility to have a third eye for more accurate 3D reconstruction in the very low corona (<?1.5?R _??). With our reconstruction code MBSR (Multi-view B-spline Stereoscopic Reconstruction), we use three view directions (STEREO A, B, and SDO) to perform the 3D reconstruction and evolution of a prominence which triggered a CME on 1 August 2010. In the paper we present the reconstruction of this prominence from the moment it starts to erupt until it leaves the field of view of the coronagraph. We also determine the evolution of the leading edge of the CME. Based on the temporal evolution, we analyze some of its properties, such as velocity, acceleration, opening and rotation angles and evolution of the cavity.