Late Decay Phase Research Articles

Spatial Evolution of 20 MeV Solar Energetic Proton Events

The longitudinal extents of solar energetic (E > 10 MeV) particle (SEP) events in the heliosphere are a characteristic important for understanding SEP acceleration and transport as well as their space weather effects. SEP detectors on the STEREO A and B spacecraft launched in 2008, combined with those on Earth-orbiting spacecraft, have enabled recent studies of this characteristic for many events. Each SEP event distribution has been characterized by a single central longitude, width, and amplitude derived from Gaussian fits to peak intensities or fluences at each spacecraft. To capture dynamic changes of those parameters through SEP events, we apply Gaussian fits in solar-based Carrington longitude coordinates with 1 hr resolution to four selected large 20 MeV proton events. The limitations of single-Gaussian fits for very extended events is discussed. In all four examples the widths are increasing throughout the event, as expected, while the projected Gaussian centers at SEP onset start from 30° to 100° east of the associated flare, move westward, then remain stationary well east of the flare for several days before moving west as the event amplitudes decrease. Late decay phases can be characterized by eastward movements away from the flare longitudes. We introduce schematic Buffett plots to show successive snapshots of event longitudes and amplitudes.

A Hot Cusp-shaped Confined Solar Flare

Abstract We analyze a confined flare that developed a hot cusp-like structure high in the corona (H ∼ 66 Mm). A growing cusp-shaped flare arcade is a typical feature in the standard model of eruptive flares, caused by magnetic reconnection at progressively larger coronal heights. In contrast, we observe a static hot cusp during a confined flare. Despite an initial vertical temperature distribution similar to that in eruptive flares, we observe a distinctly different evolution during the late (decay) phase, in the form of prolonged hot emission. The distinct cusp shape, rooted at locations of nonthermal precursor activity, was likely caused by a magnetic field arcade that kinked near the top. Our observations indicate that the prolonged heating was a result of slow local reconnection and an increased thermal pressure near the kinked apexes due to continuous plasma upflows.

Coronal Elemental Abundances in Solar Emerging Flux Regions

Abstract The chemical composition of solar and stellar atmospheres differs from the composition of their photospheres. Abundances of elements with low first ionization potential (FIP) are enhanced in the corona relative to high-FIP elements with respect to the photosphere. This is known as the FIP effect and it is important for understanding the flow of mass and energy through solar and stellar atmospheres. We used spectroscopic observations from the Extreme-ultraviolet Imaging Spectrometer on board the Hinode observatory to investigate the spatial distribution and temporal evolution of coronal plasma composition within solar emerging flux regions inside a coronal hole. Plasma evolved to values exceeding those of the quiet-Sun corona during the emergence/early-decay phase at a similar rate for two orders of magnitude in magnetic flux, a rate comparable to that observed in large active regions (ARs) containing an order of magnitude more flux. During the late-decay phase, the rate of change was significantly faster than what is observed in large, decaying ARs. Our results suggest that the rate of increase during the emergence/early-decay phase is linked to the fractionation mechanism that leads to the FIP effect, whereas the rate of decrease during the later decay phase depends on the rate of reconnection with the surrounding magnetic field and its plasma composition.

Changes in fatty acids profile, monosaccharide profile and protein content during batch growth ofIsochrysis galbana(T.iso)

To investigate the nutritional value of the marine micro-alga Isochrysis galbana Tahitian Isochrysis strain (T.iso) as an alternative feed for aquaculture during culture age, its biochemical composition was studied under autotrophic and controlled culture conditions at different growth stages: exponential phase, early and late stationary phases and decay phase. Analysis showed that C14:0, C16:0, C16:1, C18:4 (n-3) and C22:6 (n-3) were the most abundant fatty acids in this alga at different growth stages. The highest values of monounsaturated fatty acids were recorded at the late stationary and the decay phases. However, the highest levels of polyunsaturated fatty acids were observed at the early stationary phase. At all growth stages, I. galbana (T.iso) contained arabinose, xylose, mannose, galactose and glucose. Glucose represented the main sugar, and its content per dry alga biomass weight increased with increasing age of the culture and reached about fourfold in the decay phase. The maximum protein content was also observed during this last phase.

Inactivation and Gene Expression of a Virulent Wastewater Escherichia coli Strain and the Nonvirulent Commensal Escherichia coli DSM1103 Strain upon Solar Irradiation.

This study examined the decay kinetics and molecular responses of two Escherichia coli strains upon solar irradiation. The first is E. coli PI-7, a virulent and antibiotic-resistant strain that was isolated from wastewater and carries the emerging NDM-1 antibiotic resistance gene. The other strain, E. coli DSM1103, displayed lower virulence and antibiotic resistance than E. coli PI-7. In a buffer solution, E. coli PI-7 displayed a longer lag phase prior to decay and a longer half-life compared with E. coli DSM1103 (6.64 ± 0.63 h and 2.85 ± 0.46 min vs 1.33 ± 0.52 h and 2.04 ± 0.36 min). In wastewater, both E. coli strains decayed slower than they did in buffer. Although solar irradiation remained effective in reducing the numbers of both strains by more than 5-log10 in <24 h, comparative genomics and transcriptomics revealed differences in the genomes and overall regulation of genes between the two E. coli strains. A wider arsenal of genes related to oxidative stress, cellular repair and protective mechanisms were upregulated in E. coli PI-7. Subpopulations of E. coli PI-7 expressed genes related to dormancy and persister cell formation during the late decay phase, which may have accounted for its prolonged persistence. Upon prolonged solar irradiation, both E. coli strains displayed upregulation of genes related to horizontal gene transfer and antibiotic resistance. Virulence functions unique to E. coli PI-7 were also upregulated. Our findings collectively indicated that, whereas solar irradiation is able to reduce total cell numbers, viable E. coli remained and expressed genes that enable survival despite solar treatment. There remains a need for heightened levels of concern regarding risks arising from the dissemination of E. coli that may remain viable in wastewater after solar irradiation.

Evolution of the magnetic field distribution of active regions

Aims. Although the temporal evolution of active regions (ARs) is relatively well understood, the processes involved continue to be the subject of investigation. We study how the magnetic field of a series of ARs evolves with time to better characterise how ARs emerge and disperse. Methods. We examine the temporal variation in the magnetic field distribution of 37 emerging ARs. A kernel density estimation plot of the field distribution was created on a log-log scale for each AR at each time step. We found that the central portion of the distribution is typically linear and its slope was used to characterise the evolution of the magnetic field. Results. The slopes were seen to evolve with time, becoming less steep as the fragmented emerging flux coalesces. The slopes reached a maximum value of ~ -1.5 just before the time of maximum flux before becoming steeper during the decay phase towards the quiet Sun value of ~ -3. This behaviour differs significantly from a classical diffusion model, which produces a slope of -1. These results suggest that simple classical diffusion is not responsible for the observed changes in field distribution, but that other processes play a significant role in flux dispersion. Conclusions. We propose that the steep negative slope seen during the late decay phase is due to magnetic flux reprocessing by (super)granular convective cells.

Should reference conditions be drawn from a single 10 ha plot? Assessing representativeness in a 10,000 ha old‐growth European beech forest

The management targets of modern forestry are often dictated by a desire to restore natural conditions, largely considered to be those found in contemporary reference sites. Beech reference sites are usually subjectively placed plots located in old‐growth reserves. Given the inherent variability in old‐growth, the validity of using a single such plot to guide restoration efforts is questionable. We therefore applied 3 methods to assess the representativeness of a 10 ha research plot in an old‐growth European beech (Fagus sylvatica L.) forest in Ukraine compared to an inventory of the entire 10,282 ha forest reserve. We compared the research plot to the 500‐m2 inventory plots using (1) permutation tests of structure metrics, (2) synthetic multivariate structural condition, and (3) functional condition via the proportion of area assigned to 8 forest development phases. Despite up to 82% distributional overlap for some metrics, both the averages and distributions of individual structural metrics (e.g. basal area, tree diameters) differed significantly between the RP and the inventory, as did the synthetic structural condition and the proportion of late optimal and decay phases. Extrapolations from this subjectively placed plot to the surrounding old‐growth matrix would overestimate several stereotypical “old‐growth” structures. These results support the need to draw on multiple reference sites and metrics and to select restoration target conditions that account for the variability associated with naturally dynamic ecosystems. A lack of absolute representativeness does not, however, necessarily preclude the generalizability of process‐based dynamics from old‐growth remnants.

Longitudinal distribution of solar cosmic rays observed in the events of 2012

The longitudinal distribution of the intensity of the solar cosmic ray (SCR) flux in the heliosphere during different stages of powerful proton events in 2012 is considered, based on the data from the SOHO and STEREO-A and -B spacecraft separated by ∼120° at 1 AU. The SCR distribution during an event’s initial stage corresponds to the belief that the role of the magnetic connection between a source and an observer (the arrival of protons from west, central, and east parent flares) is important. The convection of SCRs changes the relationship between the intensities observed by different spacecraft, when the structures containing SCRs reach any spacecraft as a result of a radial or co-rotational solar wind motion. The SCR intensities during the late prolonged decay phase are approximately equal (the reservoir effect) at points separated by 120° (STEREO A/B and/or SOHO). The reservoir effect is observed not only behind a shock front but also over a much wider region, indicating that the role of perpendicular diffusion in the SCR propagation is crucial.

Investigation of the X-Ray Emission of the Large Arcade Flare of 2 March 1993

A large arcade flare of 2 March 1993 has been investigated using X-ray observations recorded by the {\sl Yohkoh} and GOES satellites and the {\sl Compton Gamma Ray Observatory}. We analyzed quasi-periodicity of the hard-X-ray (HXR) pulses in the flare impulsive phase and found close similarity between the quasi-periodic sequence of the pulses with that observed in another large arcade flare of 2 November 1991. This similarity helped to explain the strong HXR pulses which were recorded at the end of the impulsive phase, as due to an inflow of dense plasma (coming from the chromospheric evaporation) into the acceleration volume inside the cusp. In HXR images a high flaring loop was seen with a triangular cusp structure at the top, where the electrons were efficiently accelerated. The sequence of HXR images allowed us to investigate complicated changes in the precipitation of the accelerated electrons toward the flare footpoints. We have shown that all these impulsive-phase observations can be easily explained in terms of the model of electron acceleration in oscillating magnetic traps located within the cusp structure. Some soft-X-ray (SXR) images were available for the late decay phase. They show a long arcade of SXR loops. Important information about the evolution of the flare during the slow decay phase is contained in the time variation of the temperature, $T(t)$, and emission measure, EM$(t)$. This information is the following: i) weak heating occurs during the slow decay phase and it slowly decreases; ii) the decrease in the heating determines slow and smooth decrease in EM; iii) the coupling between the heating and the amount of the hot plasma makes the flare evolve along a sequence of quasi-steady states during the slow decay phase (QSS evolution).

Unusual Migration of Prominence Activities in the Southern Hemisphere during Cycles 23-24

Abstract The solar activity in Cycles 23-24 shows differences from the previous cycles that were observed with modern instruments, e.g., long cycle duration and a small number of sunspots. To appreciate the anomalies further, we investigated the prominence eruptions and disappearances observed with the Nobeyama Radioheliograph for over 20 years. Consequently, we found that the occurrence of prominence activities in the northern hemisphere is normal because the period of the number variation is 11 years, and the migration of the producing region of the prominence activities traces the migration of 11 years ago. On the other hand, the migration in the southern hemisphere significantly differs from that in the northern hemisphere and the previous cycles. The prominence activities occurred over -50° latitude in spite of the late decay phase of Cycle 23, and the number of prominence activities in the higher latitude region (over -65°) is very small, even near the solar maximum of Cycle 24. The results suggest that the anomalies of the global magnetic field distribution started at the solar maximum of Cycle 23. A comparison of the butterfly diagram of the prominence activities with the magnetic butterfly diagram indicates that the timing of “the rush to the pole” and the polar magnetic field closely relates to unusual migration. Considering that the rush to the pole is made of the sunspots, the hemispheric asymmetry of the sunspots and the strength of the polar magnetic fields are essential for understanding the anomalies of the prominence activities.

THE DISCOVERY OF AN X-RAY/UV STELLAR FLARE FROM THE LATE-K/EARLY-M DWARF LMC 335

We report the discovery of an X-ray/UV stellar flare from the source LMC 335, captured by XMM-Newton in the field of the Large Magellanic Cloud. The flare event was recorded continuously in X-ray for its first 10 hours from the precursor to the late decay phases. The observed fluxes increased by more than two orders of magnitude at its peak in X-ray and at least one in the UV as compared to quiescence. The peak 0.1-7.0 keV X-ray flux is derived from the two-temperature APEC model to be ~(8.4 +/- 0.6) x 10^-12 erg cm-2 s-1. Combining astrometric information from multiple X-ray observations in the quiescent and flare states, we identify the NIR counterpart of LMC 335 as the 2MASS source J05414534-6921512. The NIR color relations and spectroscopic parallax characterize the source as a Galactic K7-M4 dwarf at a foreground distance of (100 - 264) pc, implying a total energy output of the entire event of ~(0.4 - 2.9) x 10^35 erg. This report comprises detailed analyses of this late-K / early-M dwarf flare event that has the longest time coverage yet reported in the literature. The flare decay can be modeled with two exponential components with timescales of ~28 min and ~4 hours, with a single component decay firmly ruled out. The X-ray spectra during flare can be described by two components, a dominant high temperature component of ~40-60MK and a low temperature component of ~10MK, with a flare loop length of about 1.1-1.3 stellar radius.

State-space methods for calculating concentration dynamics in multizone buildings

This work explores analytic solutions to contaminant transport in multizone systems as a means of solving concentration dynamics more rapidly and providing insight into system behaviour. A general formulation is developed that is consistent with state-space theory. This is used to provide general and specific solutions for the concentration time series. In particular, an analytical expression is presented for the case of constant system parameters and constant input conditions using the eigenvalues and eigenvectors for the case of a diagonalisable state matrix for the multizone system. A method for using this expression to solve concentrations over a series of varying building and input states is developed, with potential for use as a rapid means of calculating concentrations at any time. In principle, this method could be used as a complementary method for solving concentration dynamics within multizone software. Analytical expressions for cumulative exposure for the same case are also presented. The characteristic behaviour of the solutions and their dependence on the eigenvalues and eigenvectors of the state matrix are explored for the steady state case and the decay solution. In particular, the behaviour in the late decay phase is shown to be characterised by a single decay rate, given by the smallest magnitude eigenvalue, and a fixed concentration ratio, given by the associated eigenvector. The independence of the concentration ratio in this phase to the initial conditions is also demonstrated. Two example cases are used to illustrate these and additional features.

Peak Frequency Dynamics in Solar Microwave Bursts

We analyze the dynamics of the broadband frequency spectrum of 338 microwave bursts observed in the years 2001 – 2002 with the Owens Valley Solar Array. A subset of 38 strong microwave bursts that show a single spectral maximum are studied in detail. Our main goal is to study changes in spectral peak frequency νpk with time. We show that, for a majority of these simple bursts, the peak frequency shows a high positive correlation with flux density – it increases on the rise phase in ≈83% of 24 bursts where it could be cleanly measured, and decreases immediately after the peak time in ≈62% of 34 bursts. This behavior is in qualitative agreement with theoretical expectations based on gyrosynchrotron self-absorption. However, for a significant number of events (≈30 – 36%) the peak frequency variation is much smaller than expected from self-absorption, or may be entirely absent. The observed temporal behavior of νpk is compared with a simple model of gyrosynchrotron radio emission. We show that the anomalous behavior is well accounted for by the effects of Razin suppression, and further show how an analysis of the temporal evolution of νpk can be used to uniquely determine the relative importance of self-absorption and Razin suppression in a given burst. The analysis technique provides a new, quantitative diagnostic for the gyrosynchrotron component of solar microwave bursts. Applying this analysis technique to our sample of bursts, we find that in most of the bursts (60%) the spectral dynamics of νpk around the time of peak flux density is caused by self-absorption. On the other hand, for a significant number of events (≈70%), the Razin effect may play the dominant role in defining the spectral peak and dynamics of νpk, especially on the early rise phase and late decay phase of the bursts.

Evolution of the Loop‐Top Source of Solar Flares: Heating and Cooling Processes

We present a study of the spatial and spectral evolution of the loop-top (LT) sources in a sample of 6 flares near the solar limb observed by {\it RHESSI}. A distinct coronal source, which we identify as the LT source, was seen in each of these flares from the early ``pre-heating'' phase through the late decay phase. Spectral analyses reveal an evident steep power-law component in the pre-heating and impulsive phases, suggesting that the particle acceleration starts upon the onset of the flares. In the late decay phase the LT source has a thermal spectrum and appears to be confined within a small region near the top of the flare loop, and does not spread throughout the loop, as is observed at lower energies. The total energy of this source decreases usually faster than expected from the radiative cooling but much slower than that due to the classical Spitzer conductive cooling along the flare loop. These results indicate the presence of a distinct LT region, where the thermal conductivity is suppressed significantly and/or there is a continuous energy input. We suggest that plasma wave turbulence could play important roles in both heating the plasma and suppressing the conduction during the decay phase of solar flares. With a simple quasi-steady loop model we show that the energy input in the gradual phase can be comparable to that in the impulsive phase and demonstrate how the observed cooling and confinement of the LT source can be used to constrain the wave-particle interaction.

Critical interval of somal calcium transient after neurite transection determines B104 cell survival

Nerve cells may survive or die after axonal or dendritic transection. After neurite transection near (<50 mum) the cell body of Fura-2-loaded B 104 neuroblastoma (rat brain-derived) cells, the somal calcium concentration (SCC) undergoes a three-phase transient change: a rapid (0-0.15-min post-transection [PT]) rise phase, followed by an early (0.15--1.5-min PT) rapid decay phase, and succeeded by a late (1.5-60-min PT) slower decay phase that restores SCC to preinjury levels. The SCC in a critical interval (1.5-12.5 min PT) of the third transient phase correlates with cell fate, i.e., most transected cells that exclude dye (restore a barrier) and die have a significantly higher (P<0.005) SCC in this critical interval than do transected cells that exclude dye and survive at 24-hr PT. Loading BAPTA (chelation of somal Ca(2+)) before, but not after, the critical interval increases the percentage of cells that survive compared to that of cells transected without BAPTA loading. Furthermore, most transected cells that die despite successful barrier restoration exhibit characteristics consistent with apoptosis initiated during the critical interval of the SCC, including caspase activation and plasmalemmal phosphatidylserine translocation. These data suggest that decreased cell survival for injuries near the soma is due to Ca(2+)-initiated apoptosis during the critical interval of the third phase of the SCC transient. (c) 2005 Wiley-Liss, Inc.

The Nature of Premaximum Halts of Classical Nova Outbursts: V723 Cassiopeiae and V463 Scuti

We present a new interpretation of long premaximum halts of nova outbursts. For V723 Cas (Nova Cas 1995) and V463 Sct (Nova Sct 2000), we have reproduced light curves, excluding the brightness maxima, starting from the long premaximum halt through the late decay phase of the outbursts using a steady-state optically thick wind model. When the hydrogen-rich envelope of the white dwarf (WD) is massive enough, the star expands to \sim 100 R_\sun or over and its surface temperature decreases to below 7000 K. At this supergiant mimicry stage, the changes in both the photospheric radius and the temperature are small against the large increase in the envelope mass. These changes cause a saturation in visual magnitude that lasts a long time before it begins to decline. This saturation is known as the premaximum halt of a classical nova outburst. The visual magnitude during the saturation is close to the bolometric magnitude, which is an upper limit for a given WD mass. Since the WD masses are estimated to be 0.59 M_\sun for V723 Cas and 1.1 M_\sun for V463 Sct by fitting the decline rate of nova light curves, we can determine the absolute magnitude of premaximum halts. It is a refined Eddington luminosity. Thus, the premaximum halt of a nova works as a standard candle.

Seemingly intersecting flaring loops in microwaves: Possible radio evidence for reconnection

We present possible radio evidence of magnetic reconnection in a solar flare—an LDE event of GOES class M3.2 that was observed on 1999 February 16 on the disk. Our evidence is based upon the facts that we observed a bright microwave source-blob at 17 and 34 GHz near the intersection of two seemingly intersecting flaring loops or as a loop-top source above one flaring loop. The bright microwave source is clearly non-thermal and its time profile is similar to those of the flaring footpoint microwave sources; and in the late decay phase of the event the microwave source structure is similar to that of the corresponding SXR source.

Occurrence and transformation of dissolved dimethyl sulfur species in stratified seawater (western Mediterranean Sea)

Dimethyl sulfide (DMS), dissolved dimethylsulfoniopropionate (DMSPd) and dimethylsulfoxide (DMSO) were measured in Mediterranean seawater. In the open surface waters of late spring to early summer, DMSO (18 nM) was the main methylated sulfur compound and dominated over DMS (1.7 nM) by 1 order of magnitude. Conversely, DMSPd occurred at lower concentrations (0.55 nM) than DMS. The higher abundance of DMS over DMSPd, the poor correlation between surface DMS and chlorophyll a, and microscopic examination of the algal populations suggest that DMS essentially originated from decompos~tion of the DMSP, generated in a late decay phase of the spring phytoplankton development. On the other hand, the vertical profile of the dissolved dimethyl sulfur species and the depth distribution of both biological DMS production and consumption rates point to the concurrence of the biogenic cycles of DMS and carbon. Thus, highest DMS production occurs near the subsurface chlorophyll maximum in coincidence with the water column layers of highest microbial heterotrophic activity. Finally, the high DMSO concentrations suggest that this species may act as a major nonvolatile dimethyl sulfur pool in these waters.

Time of flight measurement of ion temperatures in spheromaks

The energy distribution of neutral particles is detected from spheromak plasmas by a time of flight neutral atom spectrometer. These particles originate in charge exchange interactions within the bulk plasma and carry the temperature of the majority ion component. This is the first direct measurement of temperatures of the main ion species in spheromaks. The data are found to be in the range of 500 eV during the sustainment and late decay phases and are in agreement with impurity Doppler temperatures for species expected to be localized to the plasma centre.

Lower thermospheric density structure derived from late decay phases of satellite orbits

In order to obtain new insight into the detailed structure of the lower thermosphere the long-established method of drag analysis again proves to be a powerful tool. For near-circular satellite orbits, in addition to the semi-major axis, the eccentricity and the argument of perigee are strongly influenced by atmospheric drag. With the help of a new computational scheme, which is based on fundamental equations of satellite drag analysis, the amplitudes and phases of global density variations are derived.