D. R. McMullin

Bio: D. R. McMullin is an academic researcher from Praxis. The author has contributed to research in topics: Coronal loop & Irradiance. The author has an hindex of 5, co-authored 8 publications receiving 1741 citations.

Sun Earth Connection Coronal and Heliospheric Investigation (SECCHI)

Abstract: The Sun Earth Connection Coronal and Heliospheric Investigation (SECCHI) is a five telescope package, which has been developed for the Solar Terrestrial Relation Observatory (STEREO) mission by the Naval Research Laboratory (USA), the Lockheed Solar and Astrophysics Laboratory (USA), the Goddard Space Flight Center (USA), the University of Birmingham (UK), the Rutherford Appleton Laboratory (UK), the Max Planck Institute for Solar System Research (Germany), the Centre Spatiale de Leige (Belgium), the Institut d’Optique (France) and the Institut d’Astrophysique Spatiale (France). SECCHI comprises five telescopes, which together image the solar corona from the solar disk to beyond 1 AU. These telescopes are: an extreme ultraviolet imager (EUVI: 1–1.7 R⊙), two traditional Lyot coronagraphs (COR1: 1.5–4 R⊙ and COR2: 2.5–15 R⊙) and two new designs of heliospheric imagers (HI-1: 15–84 R⊙ and HI-2: 66–318 R⊙). All the instruments use 2048×2048 pixel CCD arrays in a backside-in mode. The EUVI backside surface has been specially processed for EUV sensitivity, while the others have an anti-reflection coating applied. A multi-tasking operating system, running on a PowerPC CPU, receives commands from the spacecraft, controls the instrument operations, acquires the images and compresses them for downlink through the main science channel (at compression factors typically up to 20×) and also through a low bandwidth channel to be used for space weather forecasting (at compression factors up to 200×). An image compression factor of about 10× enable the collection of images at the rate of about one every 2–3 minutes. Identical instruments, except for different sizes of occulters, are included on the STEREO-A and STEREO-B spacecraft.

The Heliospheric HeII 30.4 nm Solar Flux During Cycle 23

Abstract: Because of the orbit characteristics of the vast majority of spacecraft, the solar flux has predominantly been measured at Earth or at least in the plane of the ecliptic. Therefore, the existing data do not directly demonstrate the fact that the latitudinal distribution of the extreme-ultraviolet (EUV) solar flux is largely anisotropic. Indeed, in the EUV the nonuniform distribution of very contrasted bright features (i.e., active regions) and dark features (i.e., coronal holes) at the surface of the Sun produces both the obvious rotational (or longitudinal) modulation of the flux and also a strong latitudinal anisotropy. Although largely ignored up to now, the latitudinal anisotropy affects the physical conditions in the corona and heliosphere and should therefore be taken into account in several solar and heliospheric physics applications. We describe in this paper a technique for computing the He II 30.4 nm flux at an arbitrary position in the heliosphere from Solar and Heliospheric Observatory (SOHO) EUV Imaging Telescope (EIT) images. This procedure was used to produce daily all-sky maps of the 30.4 nm flux from 1996 January to 2003 August, covering the first 8 yr of solar cycle 23. As could be expected from the examination of the EIT images, the 30.4 nm flux was found to be strongly anisotropic. The anisotropy Ipol/Ieq between the fluxes computed for viewpoints located above the solar poles and within the solar equatorial plane ranges from 0.9 at solar minimum to 0.6 at solar maximum. A 20% difference was also discovered between the north and south polar fluxes. The generalization of this technique to other lines of the EUV and far-ultraviolet (FUV) spectrum is discussed.

The Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory (SDO)

Abstract: The Atmospheric Imaging Assembly (AIA) provides multiple simultaneous high-resolution full-disk images of the corona and transition region up to 0.5 R ⊙ above the solar limb with 1.5-arcsec spatial resolution and 12-second temporal resolution. The AIA consists of four telescopes that employ normal-incidence, multilayer-coated optics to provide narrow-band imaging of seven extreme ultraviolet (EUV) band passes centered on specific lines: Fe xviii (94 A), Fe viii, xxi (131 A), Fe ix (171 A), Fe xii, xxiv (193 A), Fe xiv (211 A), He ii (304 A), and Fe xvi (335 A). One telescope observes C iv (near 1600 A) and the nearby continuum (1700 A) and has a filter that observes in the visible to enable coalignment with images from other telescopes. The temperature diagnostics of the EUV emissions cover the range from 6×104 K to 2×107 K. The AIA was launched as a part of NASA’s Solar Dynamics Observatory (SDO) mission on 11 February 2010. AIA will advance our understanding of the mechanisms of solar variability and of how the Sun’s energy is stored and released into the heliosphere and geospace.

An Observational Overview of Solar Flares

Abstract: We present an overview of solar flares and associated phenomena, drawing upon a wide range of observational data primarily from the RHESSI era Following an introductory discussion and overview of the status of observational capabilities, the article is split into topical sections which deal with different areas of flare phenomena (footpoints and ribbons, coronal sources, relationship to coronal mass ejections) and their interconnections We also discuss flare soft X-ray spectroscopy and the energetics of the process The emphasis is to describe the observations from multiple points of view, while bearing in mind the models that link them to each other and to theory The present theoretical and observational understanding of solar flares is far from complete, so we conclude with a brief discussion of models, and a list of missing but important observations

Coronal Mass Ejections: Observations

Abstract: Solar eruptive phenomena embrace a variety of eruptions, including flares, solar energetic particles, and radio bursts. Since the vast majority of these are associated with the eruption, development, and evolution of coronal mass ejections (CMEs), we focus on CME observations in this review. CMEs are a key aspect of coronal and interplanetary dynamics. They inject large quantities of mass and magnetic flux into the heliosphere, causing major transient disturbances. CMEs can drive interplanetary shocks, a key source of solar energetic particles and are known to be the major contributor to severe space weather at the Earth. Studies over the past decade using the data sets from (among others) the SOHO, TRACE, Wind, ACE, STEREO, and SDO spacecraft, along with ground-based instruments, have improved our knowledge of the origins and development of CMEs at the Sun and how they contribute to space weather at Earth. SOHO, launched in 1995, has provided us with almost continuous coverage of the solar corona over more than a complete solar cycle, and the heliospheric imagers SMEI (2003–2011) and the HIs (operating since early 2007) have provided us with the capability to image and track CMEs continually across the inner heliosphere. We review some key coronal properties of CMEs, their source regions and their propagation through the solar wind. The LASCO coronagraphs routinely observe CMEs launched along the Sun-Earth line as halo-like brightenings. STEREO also permits observing Earth-directed CMEs from three different viewpoints of increasing azimuthal separation, thereby enabling the estimation of their three-dimensional properties. These are important not only for space weather prediction purposes, but also for understanding the development and internal structure of CMEs since we view their source regions on the solar disk and can measure their in-situ characteristics along their axes. Included in our discussion of the recent developments in CME-related phenomena are the latest developments from the STEREO and LASCO coronagraphs and the SMEI and HI heliospheric imagers.

Differences between CME‐driven storms and CIR‐driven storms

Abstract: Twenty one differences between CME-driven geomagnetic storms and CIR-driven geomagnetic storms are tabulated. (CME-driven includes driving by CME sheaths, by magnetic clouds, and by ejecta; CIR-driven includes driving by the associated recurring high-speed streams.) These differences involve the bow shock, the magnetosheath, the radiation belts, the ring current, the aurora, the Earth's plasma sheet, magnetospheric convection, ULF pulsations, spacecraft charging in the magnetosphere, and the saturation of the polar cap potential. CME-driven storms are brief, have denser plasma sheets, have strong ring currents and Dst, have solar energetic particle events, and can produce great auroras and dangerous geomagnetically induced currents; CIR-driven storms are of longer duration, have hotter plasmas and stronger spacecraft charging, and produce high fluxes of relativistic electrons. Further, the magnetosphere is more likely to be preconditioned with dense plasmas prior to CIR-driven storms than it is prior to CME-driven storms. CME-driven storms pose more of a problem for Earth-based electrical systems; CIR-driven storms pose more of a problem for space-based assets.

Forward Modeling of Coronal Mass Ejections Using STEREO/SECCHI Data

Abstract: We describe a forward modeling method developed to study the coronal mass ejections observed with STEREO/SECCHI. We present a survey of 26 CMEs modeled with this method. We selected most of the bright events observed since November 2007 to August 2008, after when the separation was greater than 40° degrees, thus showing noticeable differences between the two views. From these stereoscopic observations and using a geometric model of a flux rope, we are able to determine the three-dimensional direction of propagation, the three-dimensional velocity and acceleration of the CME front, and in most of the cases the flux rope orientation and length. We define a merit function that allows us to partially automate the fit, as well as perform a sensitivity analysis on the model parameters. We find a precision on the longitude and latitude to be of a maximum of ±17° and ±4°, respectively, for a 10% decrease of the merit function but a precision on the flux rope orientation and length to be almost one order of magnitude larger, showing that these parameters are more difficult to estimate using only coronagraph data. Finally, comparison with independent measurements shows a good agreement with the direction and speed we estimated.