Microflares and the Statistics of X-ray Flares

This review surveys the statistics of solar X-ray flares, emphasising the new views that RHESSI has given us of the weaker events (the microflares). The new data reveal that these microflares strongly resemble more energetic events in most respects; they occur solely within active regions and exhibit high-temperature/nonthermal emissions in approximately the same proportion as major events. We discuss the distributions of flare parameters (e.g., peak flux) and how these parameters correlate, for instance via the Neupert effect. We also highlight the systematic biases involved in intercomparing data representing many decades of event magnitude. The intermittency of the flare/microflare occurrence, both in space and in time, argues that these discrete events do not explain general coronal heating, either in active regions or in the quiet Sun.     

Damping Mechanisms for Oscillations in Solar Prominences

Small amplitude oscillations are a commonly observed feature in prominences/filaments. These oscillations appear to be of local nature, are associated to the fine structure of prominence plasmas, and simultaneous flows and counterflows are also present. The existing observational evidence reveals that small amplitude oscillations, after excited, are damped in short spatial and temporal scales by some as yet not well determined physical mechanism(s). Commonly, these oscillations have been interpreted in terms of linear magnetohydrodynamic (MHD) waves, and this paper reviews the theoretical damping mechanisms that have been recently put forward in order to explain the observed attenuation scales. These mechanisms include thermal effects, through non-adiabatic processes, mass flows, resonant damping in non-uniform media, and partial ionization effects. The relevance of each mechanism is assessed by comparing the spatial and time scales produced by each of them with those obtained from observations. Also, the application of the latest theoretical results to perform prominence seismology is discussed, aiming to determine physical parameters in prominence plasmas that are difficult to measure by direct means.     

Recent Results from Titan��s Ionosphere

Titan has the most significant atmosphere of any moon in the solar system, with a pressure at the surface larger than the Earth??s. It also has a significant ionosphere, which is usually immersed in Saturn??s magnetosphere. Occasionally it exits into Saturn??s magnetosheath. In this paper we review several recent advances in our understanding of Titan??s ionosphere, and present some comparisons with the other unmagnetized objects Mars and Venus. We present aspects of the ionospheric structure, chemistry, electrodynamic coupling and transport processes. We also review observations of ionospheric photoelectrons at Titan, Mars and Venus. Where appropriate, we mention the effects on ionospheric escape.     

Sprite-Producing Lightning-Ionosphere Coupling and Associated Low-Frequency Phenomena

Theoretical and experimental evidence is collected for additional ionization regions in the mesosphere above lightning discharges and their connection with transient luminous events (TLE). New insights are reported into the different appearances in the Very Low Frequency (VLF) link traces as affected by the mesospheric ionization regions. Based on these findings, physical processes going on in the ionization regions and their coupling to the primary lightning discharge process are conceptualized. Thereafter, some diagnostic potential is outlined. Finally, the ionization regions are considered as a transmitter of secondary low-frequency waves. The distinction is made between the primary electromagnetic waves emitted by the lightning and the secondary waves. As a consequence the Extremely Low Frequency (ELF) and Ultra Low Frequency (ULF) transient signatures observed on the ground are understood as a composite of both wave types. In addition a novel method is introduced to extract the charge moment change of a sprite producing lightning discharge.     

Efficacy of an ototoxic aminoglycoside (gentamicin) on the differentiation of the inner ear of cichlid fish.

Previous investigations revealed that the growth of fish inner ear otoliths depends on the amplitude and the direction of gravity, thus suggesting the existence of a (negative) feedback mechanism. In the course of these experiments, it was shown that altered gravity both affected otolith size (and thus the provision of the proteinacious matrix) as well as the incorporation of calcium. It is hitherto unknown, as of whether sensory hair cells are involved either in the regulation of otolith growth or in the provision of otolithic material (such as protein or inorganic components) or even both. The ototoxic aminoglycoside gentamicin (GM) damages hair cells in many vertebrates (and is therefore used for the treatment of Meniere's disease in humans). The present study was thus designed to determine as of whether vestibular sensory cells are needed for otolith growth by applying GM in order to induce a (functionally relevant) loss of these cells. Developing cichlid fish Oreochromis mossambicus were therefore immersed in 120 mg/l GM for 10 or 21 days. At the beginning and at the end of the experimental periods, the fish were incubated in the calcium-tracer alizarin complexone (AC). After the experiment, otoliths were dissected and the area grown during GM-exposure (i.e., the area enclosed by the two AC labellings) was determined planimetrically. The results showed that incubating the animals in a GM-solution had no effect on otolith growth, but the development of otolith asymmetry was affected. Ultrastructural examinations of the sensory hair cells revealed that they had obviously not been affected by GM-treatment (no degenerative morphological features observed). Overall, the present results suggest that hair cells are not affected by GM concerning their possible role in (general) otolith growth, but that these cells indeed might have transitionally been impaired by GM resulting in a decreased capacity of regulating otolith symmetry.     

Properties of Ground Level Enhancement Events and the Associated Solar Eruptions During Solar Cycle 23

Solar cycle 23 witnessed the most complete set of observations of coronal mass ejections (CMEs) associated with the Ground Level Enhancement (GLE) events. We present an overview of the observed properties of the GLEs and those of the two associated phenomena, viz., flares and CMEs, both being potential sources of particle acceleration. Although we do not find a striking correlation between the GLE intensity and the parameters of flares and CMEs, the solar eruptions are very intense involving X-class flares and extreme CME speeds (average ～2000?km/s). An M7.1 flare and a 1200?km/s CME are the weakest events in the list of 16 GLE events. Most (80?%) of the CMEs are full halos with the three non-halos having widths in the range 167 to 212?degrees. The active regions in which the GLE events originate are generally large: 1290?msh (median 1010?msh) compared to 934?msh (median: 790?msh) for SEP-producing active regions. For accurate estimation of the CME height at the time of metric type?II onset and GLE particle release, we estimated the initial acceleration of the CMEs using flare and CME observations. The initial acceleration of GLE-associated CMEs is much larger (by a factor of 2) than that of ordinary CMEs (2.3?km/s² vs. 1?km/s²). We confirmed the initial acceleration for two events for which CME measurements are available in the inner corona. The GLE particle release is delayed with respect to the onset of all electromagnetic signatures of the eruptions: type?II bursts, low frequency type?III bursts, soft X-ray flares and CMEs. The presence of metric type?II radio bursts some 17?min (median: 16?min; range: 3 to 48?min) before the GLE onset indicates shock formation well before the particle release. The release of GLE particles occurs when the CMEs reach an average height of ～3.09?R _s (median: 3.18?R _s ; range: 1.71 to 4.01?R _s ) for well-connected events (source longitude in the range W20–W90). For poorly connected events, the average CME height at GLE particle release is ～66?% larger (mean: 5.18?R _s ; median: 4.61?R _s ; range: 2.75–8.49?R _s ). The longitudinal dependence is consistent with shock accelerations because the shocks from poorly connected events need to expand more to cross the field lines connecting to an Earth observer. On the other hand, the CME height at metric type?II burst onset has no longitudinal dependence because electromagnetic signals do not require magnetic connectivity to the observer. For several events, the GLE particle release is very close to the time of first appearance of the CME in the coronagraphic field of view, so we independently confirmed the CME height at particle release. The CME height at metric type?II burst onset is in the narrow range 1.29 to 1.8?R _s , with mean and median values of 1.53 and 1.47?R _s . The CME heights at metric type?II burst onset and GLE particle release correspond to the minimum and maximum in the Alfvén speed profile. The increase in CME speed between these two heights suggests an increase in Alfvénic Mach number from?2 to?3. The CME heights at GLE particle release are in good agreement with those obtained from the velocity dispersion analysis (Reames in Astrophys. J. 693:812, 2009a; Astrophys. J. 706:844, 2009b) including the source longitude dependence. We also discuss the implications of the delay of GLE particle release with respect to complex type?III bursts by ～18?min (median: 16?in; range: 2 to 44?min) for the flare acceleration mechanism. A?similar analysis is also performed on the delay of particle release relative to the hard X-ray emission.     

REMS: The Environmental Sensor Suite for the Mars Science Laboratory Rover

The Rover Environmental Monitoring Station (REMS) will investigate environmental factors directly tied to current habitability at the Martian surface during the Mars Science Laboratory (MSL) mission. Three major habitability factors are addressed by REMS: the thermal environment, ultraviolet irradiation, and water cycling. The thermal environment is determined by a mixture of processes, chief amongst these being the meteorological. Accordingly, the REMS sensors have been designed to record air and ground temperatures, pressure, relative humidity, wind speed in the horizontal and vertical directions, as well as ultraviolet radiation in different bands. These sensors are distributed over the rover in four places: two booms located on the MSL Remote Sensing Mast, the ultraviolet sensor on the rover deck, and the pressure sensor inside the rover body. Typical daily REMS observations will collect 180 minutes of data from all sensors simultaneously (arranged in 5 minute hourly samples plus 60 additional minutes taken at times to be decided during the course of the mission). REMS will add significantly to the environmental record collected by prior missions through the range of simultaneous observations including water vapor; the ability to take measurements routinely through the night; the intended minimum of one Martian year of observations; and the first measurement of surface UV irradiation. In this paper, we describe the scientific potential of REMS measurements and describe in detail the sensors that constitute REMS and the calibration procedures.     

Perception of gravity by plants.

Physical principles can be used to predict some features about the gravity perception system in plants. The nature of the system has made it rather elusive, so this approach represents an additional source of information to help find it. For a gravitational stimulus to be detected, two masses must move relative to each other in a manner which causes a significant amount of work to be done on a receptor. Relative to cellular dimensions, the masses must be large, be dense and move noticeable distances. The main sources of noise are thermal motion and flexing of the plant tissue. Some new models for the function of amyloplasts as statoliths are presented.     

Space Debris at the United Nations

Rules for activities in outer space are agreed upon in the Committee on the Peaceful Uses of Outer Space of the United Nations. Several international treaties have been adopted in the 1970s, that is, at a time before space debris became a concern for the international community. In the years 1979–1988 numerous documents were prepared by the UN Secretariat on space debris, but no official discussions of the problem were initiated by states members of the COPUOS. First proposals for introducing the matter to the UN appeared around 1988, after important studies on the subject were published by states and leading intergovernmental organizations. Also the International Telecommunication Union became concerned about the proliferation of space debris in the geostationary orbit and adopted in 1993 a recommendation to restrict the generation of debris and to re-orbit satellites approaching the end of their active lives into disposal orbits beyond the belt populated by active satellites. In 1994, the UN started discussing scientific and technical aspects of space debris. In the following years, with the assistance of experts from prominent space agencies, it elaborated a Technical Report on space debris. Legal aspects of the problem have not yet begun being discussed because the necessary consensus among states members of the COPUOS has not yet been achieved. Very recently, the UN received first information on a wider subject, space traffic management.