Evidence for or against a common origin of hard X-rays and microwaves from solar flares

The problem of whether hard X-rays and microwaves are emitted from the same electrons in common or closely separated sources is reviewed on direct and indirect observational evidence. Detailed analyses of time structure and peak flux suggest that hard X-rays and microwaves are emitted from nearly co-spatial sources due to electrons streaming down to the chromosphere. However this model has not been confirmed yet by direct imaging observations.

     

A statistical study of moving type IV bursts based on Culgoora radioheliograph observations

Thirty-one moving type IV (IV(M)) bursts recorded with the Culgoora radioheliograph are examined to deduce their characteristic features, such as spatial distribution, projected velocity, etc., and their relation to other phenomena. The distribution of the projected velocity suggests that less than 15% of the total IV(M) bursts have fast velocities (>1000 km s^–1), almost equal to MHD shock velocity, and that the remaining IV(M) bursts have slower velocities (400 km s^–1) and are probably not associated with MHD shock waves. Most of the slow IV(M) bursts (and 70% of the total IV(M) bursts) are of an isolated plasmoid type. Even if they are associated with minor H flares, IV(M) bursts of the isolated-plasmoid type have 10³¹ ergs in the form of magnetic energy. They are in many cases closely associated with extended flare-continuum sources; this seems plausible if the flare continuum is interpreted as an interaction of a plasmoid with a large-scale magnetic arch.The association of IV(M) bursts with energetic proton events seems to be poor - contrary to expectation.     

Flow cytometric detection and enumeration of DNA and RNA viruses infecting marine eukaryotic microalgae

Sample preparation protocols for flow cytometry (FCM) analysis with five algal viruses were optimized: Heterocapsa circularisquama virus (HcV), Heterosigma akashiwo virus (HaV), Chaetoceros salsugineum nuclear inclusion virus (CsNIV), Rhizosolenia setigera RNA virus (RsRNAV) and H. circularisquama RNA virus (HcRNAV). The optimum staining protocols differed significantly among the viruses tested. FCM counts for the large DNA algal viruses HaV and HcV (∼0.2 μm in diameter) were similar to numbers determined by epifluorescence microscopy (EFM). In contrast, FCM counts of viruses smaller than 40 nm that harbor DNA (CsNIV) or RNA genomes (RsRNAV, HcRNAV) were comparable to or lower than most probable number (MPN) values, which indicate only infectious virus number, suggesting that the FCM counts were underestimates. This is presumably because their single particle fluorescence signals were below the detection limit for the flow cytometer. These results indicate that a large portion of the smaller viruses in the aquatic plankton virus community may be overlooked by FCM.     

Effects of irradiance on excystment of tintinnids from marine sediments

The effects of irradiance on the excystment of tintinids from marine sediments were examined by incubating sediment samples in filtered seawater under various light levels. The total incidence of tintinnid excystment over five days was significantly less at low irradiance at and less than 2.5 E m^–2sec^–1 comparing to that at higher irradiance, at and more than 6.9 E m^–2sec^–1 (p<0.01), indicating that excystment of tintinnids is inhibited under low irradiance conditions. These results imply that water depth, disturbance of surface sediments and vertical mixing of water influence the excystment of tintinnids in coastal areas because these factors determine the light levels to which the tintinnid cysts are exposed.     

Emergence of polar-jet polygons from jet instabilities in a Saturn model

Voyager flybys of Saturn in 1980-1981 revealed a circumpolar wave at ≈78° north planetographic latitude. The feature had a dominant wavenumber 6 mode, and has been termed the Hexagon from its geometric appearance in polar-projected mosaics. It was also noted for being stationary with respect to Saturn’s Kilometric Radiation (SKR) rotation rate. The Hexagon has persisted for over 30 years since the Voyager observations until now. It has been observed from ground based telescopes, Hubble Space Telescope and multiple instruments onboard Cassini in orbit around Saturn. Measurements of cloud motions in the region reveal the presence of a jet stream whose path closely follows the Hexagon’s outline. Why the jet stream takes the characteristic six-sided shape and how it is stably maintained across multiple saturnian seasons are yet to be explained. We present numerical simulations of the 78.3°N jet using the Explicit Planetary Isentropic-Coordinate (EPIC) model and demonstrate that a stable hexagonal structure can emerge without forcing when dynamic instabilities in the zonal jet nonlinearly equilibrate. For a given amplitude of the jet, the dominant zonal wavenumber is most strongly dependent on the peak curvature of the jet, i.e., the second north-south spatial derivative of the zonal wind profile at the center of the jet. The stable polygonal shape of the jet in our simulations is formed by a vortex street with cyclonic and anticyclonic vortices lining up towards the polar and equatorial side of the jet, respectively. Our result is analogous to laboratory experiments of fluid motions in rotating tanks that develop polygonal flows out of vortex streets. However, our results also show that a vortex street model of the Hexagon cannot reproduce the observed propagation speed unless the zonal jet’s speed is modified beyond the uncertainties in the observed zonal wind speed, which suggests that a vortex street model of the Hexagon and the observed zonal wind profile may not be mutually compatible.     

<Emphasis Type="Italic">Landslides</Emphasis>: a review of achievements in the first 5 years (2004–2009)

The international journal Landslides was initiated in April 2004. It is the core project (IPL-C100) of the International Programme on Landslides, a joint initiative of the International Consortium on Landslides and the United Nations and other global organizations. The aims of Landslides are to promote landslide sciences, technology, and capacity building and strengthen global cooperation for landslide risk reduction within the United Nations International Strategy for Disaster Reduction. This paper presents an analysis of the first 5 years of Landslides, the study methods employed, the types and major causes of landslides, the number of different contributors per country, and the “times cited” per issue and most frequently cited papers and briefly discusses some of these. Strategies for future development of the journal involve obtaining input and suggestion from researchers and readers worldwide.     

Observation of the absolute intensity and the centre-to-limb variation of the sun in the vacuum ultraviolet region

The absolute intensities and the centre-to-limb variations of the Sun at three wavelengths of 1629 Å, 1684 Å, and 1739 Å were measured by a rocket-borne spectrometer flown from the Kagoshima Space Centre on 1 September 1971. The spectrometer was a double-dispersive trichrometer, whose spectral and spatial resolutions were 8.3 Å and 1.3 respectively. The results concerning the absolute intensities were similar to those measured by the Harvard College Observatory group. The results for the centre-to-limb variation at 1629 Å and 1684 Å seem to support the HSRA model but not those at 1739 Å.     

Evidence for or against a common origin of hard X-rays and microwaves from solar flares

The problem of whether hard X-rays and microwaves are emitted from the same electrons in common or closely separated sources is reviewed on direct and indirect observational evidence. Detailed analyses of time structure and peak flux suggest that hard X-rays and microwaves are emitted from nearly co-spatial sources due to electrons streaming down to the chromosphere. However this model has not been confirmed yet by direct imaging observations.     

Microwave sources of solar flares: Loop top or foot points?

The microwave images of solar flares obtained with the VLA are reviewed from a standpoint that the microwave source is near the top or foot point(s) of a flaring loop. The review is focused on whether extended structure is missed due to the lack of short baseline components leading to an incorrect interpretation of the processed images. We conclude that at short cm (< 2 cm) there is no conclusive evidence for the source near the loop top whereas at longer cm (6, 20 cm) the source tends to occupy a significant portion of a loop. The observed bipolar structure could be unambiguously interpreted as evidence for the source at the loop top, only when it is confirmed that a more extended structure has not been missed.Proceedings of the Second CESRA Workshop on Particle Acceleration and Trapping in Solar Flares, held at Aubigny-sur-Nère (France), 23–26 June, 1986.     

Species and concentrations of selenium and nutrients in Tanabe Bay during red tide due toGymnodinium nagasakiense

A red tide due toGymnodinium nagasakiense was observed in August 1988 in Tanabe Bay, Wakayama Prefecture, Japan. The maximum cell concentration ofG. nagasakiense reached 1×10⁵ cells ml^–1 at the surface water. From May to September 1988, the following were monitored: water temperature, salinity, chlorophylla, D.O., dissolved nutrients (NO₂–N, NO₃–N, NH₄–N, PO₄–P DON, DOP), particulate nutrients (PON, POP) and three dissolved selenium species [Se(IV), Se(VI), Organic Se]. Dissolved inorganic nitrogen (NO₃–N, NH₄–N) decreased but PON, POP, DON, DOP and inorganic phosphate increased at the peak of the bloom. The concentration of organic selenium increased up to the bloom initiation period which started on 5 July, and then the concentration of Se(IV) increased as the concentration of organic selenium decreased at the peak of the bloom (3 August). The strong relationship was found between the concentration of Se(IV) and the cell concentration ofG. nagasakiense (r ²=0.98). The Se(IV) requirement ofG. nagasakiense was 2.89×10^–17 moles cell^–1, which was agreed well with 4.4×10^–17 moles cell^–1 found in a laboratory experiment onG. nagasakiense using selenium spiked artificial sea water medium. The average ratio of Se(IV) to dissolved inorganic nitrogen (DIN) during the red tide bloom was 11441, the ratio of Se(IV) to DIN at the surface with the maximum cell concentration ofG. nagasakiense of 1×10⁵ cells ml^–1 was 1137. These results suggested that selenium may play an important role in red tide outbreak ofG. nagasakiense.