Towards construction of a solar wind “reanalysis” dataset: application to the first perihelion pass of parker solar probe

Accurate reconstruction of global solar-wind structure is essential for connecting remote and in situ observations of solar plasma, and hence understanding formation and release of solar wind. Information can routinely be obtained from photospheric magnetograms, via coronal and solar-wind modelling, and directly from in situ observations, typically at large heliocentric distances (most commonly near 1 AU). Magnetogram-constrained modelling has the benefit of reconstructing global solar-wind structure, but with relatively large spatial and/or temporal errors. In situ observations, on the other hand, make accurate temporal measurements of solar-wind structure, but are highly localised. We here use a data assimilative (DA) approach to combine these two sources of information as a first step towards producing a solar-wind “reanalysis” dataset that optimally combines model and observation. The physics of solar wind stream interaction is used to extrapolate in heliocentric distance, while the assumption of steady-state solar-wind structure enables extrapolation in longitude. The major challenge is extrapolating in latitude. Using solar-wind speed during the interval of the first perihelion pass of Parker Solar Probe (PSP) in November 2018 as a test bed, we investigate two approaches. The first is to assume the solar wind is two-dimensional and thus has no latitudinal structure within the ±7∘ bounded by the heliographic equatorial and ecliptic planes. The second assumes in situ solar-wind observations are representative of some (small) latitudinal range. We show how observations of the inner heliosphere, such as will be provided by PSP, can be exploited to constrain the latitudinal representivity of solar-wind observations to improve future solar-wind reconstruction and space-weather forecasting

Modelling of an inexpensive 9M satellite dish from 3D point clouds captured by terrestrial laser scanners

This paper presents the use of Terrestrial laser scanners (TLS) to model the surface of satellite dish. In this case, the dish was an inexpensive 9m parabolic satellite dish with a mesh surface, and was to be utilised in radio astronomy. The aim of the modelling process was to determine the deviation of the surface away from its true parabolic shape, in order to estimate the surface efficiency with respect to its principal receiving frequency. The main mathematical problems were the optimal and unbiased estimation the orientation of the dish and the fitting of a parabola to the local orientation or coordinate system, which were done by both orthogonal and algebraic minimization using the least-squares method. Due to the mesh structure of the dish, a classification method was also applied to filter out erroneous points being influenced by the supporting structure behind the dish. Finally, a comparison is performed between the ideal parabolic shape, and the data collected from three different temporal intervals

Asteropyginae (Trilobita)

127 p. : ill., map ; 26 cm.Includes bibliographical references (p. 123-127)."This paper presents a phylogenetic analysis of the Asteropyginae Delo, 1935. Sixty-six characters and 39 taxa were employed in a cladistic analysis that produced a single most parsimonious tree that is presented as a hypothesis of asteropyginid relationships. In addition to the phylogeny generated, 11 new genera are diagnosed: Philipsmithiana, Coltraneia, Stummiana, Bellacartwrightia, Deloops, Tolkienia, Braunops, Armorigreenops, Kennacryphaeus, Modellops, and Hallandclarkeops, and 12 new species are described: Philipsmithiana hyfinkeli, P. burtandmimiae, Armorigreenops leoi, Pelitlina smeenki, Bellacartwrightia jennyae, B. whiteleyi, B. phyllocaudata, B. calderonae, Greenops widderensis, G. barberi, G. grabaui, and Kennacryphaeus harrisae. Traditionally, asteropyginine taxa in the Appalachian and Michigan Basins of Eastern North America had been assigned to Greenops Delo, 1935, or Greenops (Neometacanthus) Richter and Richter, 1948. A core of five Eastern North American species--Greenops boothi (Green, 1837), G. widderensis, new species, G. chilmanae Stumm, 1965, G. grabaui, new species, and G. barberi, new species--can still be assigned to Greenops. All other asteropyginine taxa in Eastern North America must be assigned to different genera. Species referable to Neometacanthus Richter and Richter, 1948, may be known from the Illinois Basin of Eastern North America, and a species referable to Tolkienia, new genus, may be known from the Michigan Basin of Eastern North America. The single most parsimonious cladogram was also used to investigate biogeographic patterns. In particular, the number of times that independent lineages of asteropyginines invaded from what are now Europe and North Africa (called Armorica herein) into Eastern North America during the Devonian was ascertained. Phylogenetic analysis suggested that there must have been at least four such invasions, with clades that had primitive European or North African affinities giving rise to Eastern North American taxa, although no species are shared between Armorica and Eastern North America. One of the lineages that invaded Eastern North America subsequently reinvaded Armorica. The timing of these invasions and their relation to overall patterns of faunal evolution in the Middle Devonian of Eastern North America are also discussed. These patterns suggest that the different taxa that make up a fauna often arrive during different time intervals, not all at once"--P. 3

The magnetic field environment of active region 12673 that produced the energetic particle events of September 2017

Forecasting solar energetic particles (SEPs), and identifying flare/CMEs from active regions (ARs) that will produce SEP events in advance is extremely challenging. We investigate the magnetic field environment of AR 12673, including the AR's magnetic configuration, the surrounding field configuration in the vicinity of the AR, the decay index profile, and the footpoints of Earth-connected magnetic field, around the time of four eruptive events. Two of the eruptive events are SEP-productive (2017 September 4 at 20:00~UT and September 6 at 11:56~UT), while two are not (September 4 at 18:05~UT and September 7 at 14:33~UT). We analysed a range of EUV and white-light coronagraph observations along with potential field extrapolations and find that the CMEs associated with the SEP-productive events either trigger null point reconnection that redirects flare-accelerated particles from the flare site to the Earth-connected field and/or have a significant expansion (and shock formation) into the open Earth-connected field. The rate of change of the decay index with height indicates that the region could produce a fast CME ($v >$ 1500~km~s$^{-1}$), which it did during events two and three. The AR's magnetic field environment, including sites of open magnetic field and null points along with the magnetic field connectivity and propagation direction of the CMEs play an important role in the escape and arrival of SEPs at Earth. Other SEP-productive ARs should be investigated to determine whether their magnetic field environment and CME propagation direction are significant in the escape and arrival of SEPs at Earth.Comment: Accepted in ApJ, 18 pages, 8 Figures, 2 Table

Modelling nearshore waves, runup and overtopping

Coastal flooding from wave overtopping causes considerable damage. Presently, to model wave overtopping one can either make use of physical model tests or empirical tools such as those described in the EurOtop manual. Both these methods have limitations; therefore, a quick and reliable numerical model for wave overtopping would be a very useful tool for a coastal engineer.This research aims to test and develop a numerical model (in one horizontal dimension) for nearshore waves, runup and overtopping. The Shallow Water And Boussinesq (SWAB) model solves the Boussinesq-type equations of Madsen and Sorensen (1992) for non breaking waves and the nonlinear shallow water equations for breaking waves. Through testing against a range of physical model data using regular and random waves, the SWAB model's transfer from non-breaking to breaking waves was optimised. It was found that a wave height to water depth ratio worked consistently well as a breaking criterion.A set of physical model tests were carried out, based on previous field testing of wave overtopping that had previously taken place at Anchorsholme, Blackpool. The SWAB model was used to simulate some of these physical model tests, giving good results for mean overtopping rates. SWAB models the force imposed by steep walls and recurve walls on the incident flow; this force was found to have a significant effect on overtopping rates. A comparison was made between mean overtopping rates from the SWAB model, the physical model tests, empirically-based software (PC-Overtopping) and the field data. The physical model and SWAB results compared well with the field data, though the empirical software gave large overestimates.The SWAB model was applied to the analysis of overtopping at Walcott, Norfolk. It was found that beach levels affected overtopping rates, but not as much as different randomly phased wave trains. A simulation of a recent storm event was performed, with overtopping rates being slightly lower than those reported by local residents. A joint probability analysis showed that the predicted frequency of such an event was in line with these reports.An alternative modelling technique was also tested, where a spectral energy model was coupled with a nonlinear shallow water solver. Results for wave runup parameters were very accurate, when the coupling location is at the seaward edge of the surf zone. Extension of this modelling technique into two horizontal dimensions would be more straightforward than with the SWAB model.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Detection of Crab Giant Pulses Using the Mileura Widefield Array Low Frequency Demonstrator Field Prototype System

We report on the detection of giant pulses from the Crab Nebula pulsar at a frequency of 200 MHz using the field deployment system designed for the Mileura Widefield Array's Low Frequency Demonstrator (MWA-LFD). Our observations are among the first high-quality detections at such low frequencies. The measured pulse shapes are deconvolved for interstellar pulse broadening, yielding a pulse-broadening time of 670$\pm$100 $\mu$s, and the implied strength of scattering (scattering measure) is the lowest that is estimated towards the Crab nebula from observations made so far. The sensitivity of the system is largely dictated by the sky background, and our simple equipment is capable of detecting pulses that are brighter than $\sim$9 kJy in amplitude. The brightest giant pulse detected in our data has a peak amplitude of $\sim$50 kJy, and the implied brightness temperature is $10^{31.6}$ K. We discuss the giant pulse detection prospects with the full MWA-LFD system. With a sensitivity over two orders of magnitude larger than the prototype equipment, the full system will be capable of detecting such bright giant pulses out to a wide range of Galactic distances; from $\sim$8 to $\sim$30 kpc depending on the frequency. The MWA-LFD will thus be a highly promising instrument for the studies of giant pulses and other fast radio transients at low frequencies.Comment: 10 pages, 6 figures, Accepted for publication in the Astrophysical Journa

Understanding the Relationship between Solar Coronal Abundances and F10.7 cm Radio Emission

Sun-as-a-star coronal plasma composition, derived from full-Sun spectra, and the F10.7 radio flux (2.8 GHz) have been shown to be highly correlated (r = 0.88) during solar cycle 24. However, this correlation becomes nonlinear during increased solar magnetic activity. Here we use cotemporal, high spatial resolution, multiwavelength images of the Sun to investigate the underlying causes of the nonlinearity between coronal composition (FIP bias) and F10.7 solar index correlation. Using the Karl G. Jansky Very Large Array, Hinode/EIS (EUV Imaging Spectrometer), and the Solar Dynamics Observatory, we observed a small active region, AR 12759, throughout the solar atmosphere from the photosphere to the corona. The results of this study show that the magnetic field strength (flux density) in active regions plays an important role in the variability of coronal abundances, and it is likely the main contributing factor to this nonlinearity during increased solar activity. Coronal abundances above cool sunspots are lower than in dispersed magnetic plage regions. Strong magnetic concentrations are associated with stronger F10.7 cm gyroresonance emission. Considering that as the solar cycle moves from minimum to maximum, the sizes of sunspots and their field strength increase with the gyroresonance component, the distinctly different tendencies of radio emission and coronal abundances in the vicinity of sunspots is the likely cause of saturation of Sun-as-a-star coronal abundances during solar maximum, while the F10.7 index remains well correlated with the sunspot number and other magnetic field proxies

Understanding the Relationship between Solar Coronal Abundances and F10.7 cm Radio Emission

Sun-as-a-star coronal plasma composition, derived from full-Sun spectra, and the F10.7 radio flux (2.8 GHz) have been shown to be highly correlated (r = 0.88) during solar cycle 24. However, this correlation becomes nonlinear during increased solar magnetic activity. Here, we use co-temporal, high spatial resolution, multi-wavelength images of the Sun to investigate the underlying causes of the non-linearity between coronal composition (FIP bias) and F10.7 solar index correlation. Using the Karl G. Jansky Very Large Array (JVLA), Hinode/EIS (EUV Imaging Spectrometer), and the Solar Dynamic Observatory (SDO), we observed a small active region, AR 12759, throughout the solar atmosphere from the photosphere to the corona. Results of this study show that the magnetic field strength (flux density) in active regions plays an important role in the variability of coronal abundances, and it is likely the main contributing factor to this non-linearity during increased solar activity. Coronal abundances above cool sunspots are lower than in dispersed magnetic plage regions. Strong magnetic concentrations are associated with stronger F10.7 cm gyroresonance emission. Considering that as the solar cycle moves from minimum to maximum, the size of sunspots and their field strength increase with gyroresonance component, the distinctly different tendencies of radio emission and coronal abundances in the vicinity of sunspots is the likely cause of saturation of Sun-as-a-star coronal abundances during solar maximum, while the F10.7 index remains well correlated with the sunspot number and other magnetic field proxies.Comment: 15 pages, 5 figures, 2 tables, accepted for publication in The Astrophysical Journa