Variability of Solar Five-Minute Oscillations in the Corona as Observed by the Extreme Ultraviolet Spectrophotometer (ESP) on the Solar Dynamics Observatory Extreme Ultraviolet Variability Experiment (SDO/EVE)

Solar five-minute oscillations have been detected in the power spectra of two six-day time intervals from soft X-ray measurements of the Sun observed as a star using the Extreme Ultraviolet Spectrophotometer (ESP) onboard the Solar Dynamics Observatory (SDO) Extreme Ultraviolet Variability Experiment (EVE). The frequencies of the largest amplitude peaks were found matching within 3.7 microHz the known low-degree (l = 0--3) modes of global acoustic oscillations, and can be explained by a leakage of the global modes into the corona. Due to strong variability of the solar atmosphere between the photosphere and the corona the frequencies and amplitudes of the coronal oscillations are likely to vary with time. We investigate the variations in the power spectra for individual days and their association with changes of solar activity, e.g. with the mean level of the EUV irradiance, and its short-term variations due to evolving active regions. Our analysis of samples of one-day oscillation power spectra for a 49-day period of low and intermediate solar activity showed little correlation with the mean EUV irradiance and the short-term variability of the irradiance. We suggest that some other changes in the solar atmosphere, e.g. magnetic fields and/or inter-network configuration may affect the mode leakage to the corona.Comment: 17 pages, 7 figure

Analytical Representations for Characterizing the Global Aviation Radiation Environment Based on Model and Measurement Databases

The Nowcast of Atmospheric Ionizing Radiation for Aviation Safety climatological model and the Automated Radiation Measurements for Aerospace Safety (ARMAS) statistical database are presented as polynomial fit equations. Using equations based on altitude, L shell, and geomagnetic conditions an effective dose rate for any location from a galactic cosmic ray (GCR) environment can be calculated. A subset of the ARMAS database is represented by a second polynomial fit equation for the GCR plus probable relativistic energetic particle (REP; Van Allen belt REP) effective dose rates within a narrow band of L shells with altitudinal and geomagnetic dependency. Solar energetic particle events are not considered in this study since our databases do not contain these events. This work supports a suggestion that there may be a REP contribution having an effect at aviation altitudes. The ARMAS database is rich in Western Hemisphere observations for L shells between 1.5 and 5; there have been many cases of enhanced radiation events possibly related to effects from radiation belt particles. Our work identifies that the combined effects of an enhanced radiation environment in this L shell range are typically 15% higher than the GCR background. We also identify applications for the equations representing the Nowcast of Atmospheric Ionizing Radiation for Aviation Safety and ARMAS databases. They include (i) effective dose rate climatology in comparison with measured weather variability and (ii) climatological and statistical weather nowcasting and forecasting. These databases may especially help predict the radiation environment for regional air traffic management, for airport overflight operations, and for air carrier route operations of individual aircraft

Investigating the origins of two extreme solar particle events: proton source profile and associated electromagnetic emissions

We analyze the high-energy particle emission from the Sun in two extreme solar particle events, in which protons are accelerated to relativistic energies and can cause a significant signal even in the ground-based particle detectors. Analysis of a relativistic proton event is based on modeling of the particle transport and interaction, from a near-Sun source through the solar wind and the Earth’s magnetosphere and atmosphere to a detector on the ground. This allows us to deduce the time profile of the proton source at the Sun and compare it with observed electromagnetic emissions. The 2 May 1998 event is associated with flare and coronal mass ejection (CME) well observed by the Nan¸cay Radioheliograph, so that the images of radio sources are available. For the 2 November 2003 event, there are available the low-corona images of the CME liftoff obtained at the Mauna Loa Solar Observatory. Those complementary data sets are analyzed jointly with the broadband dynamic radio spectra, EUV images and other data available for both events. We find a common scenario for both eruptions, including the flare’s dual impulsive phase, the CME-launch-associated decimetric-continuum burst, and the late, low-frequency type III radio bursts at the time of the relativistic proton injection into the interplanetary medium. The analysis supports the idea that the two considered events start with emission of relativistic protons previously accelerated during the flare and CME launch, then trapped in large-scale magnetic loops and later released by the expanding CME

On the Importance of the Flare's Late Phase for the Solar Extreme Ultraviolet Irradiance

The new solar extreme ultraviolet (EUV) irradiance observations from NASA Solar Dynamics Observatory (SDO) have revealed a new class of solar flares that are referred to as late phase flares. These flares are characterized by the hot 2-5 MK coronal emissions (e.g., Fe XVI 33.5 nm) showing large secondary peaks that appear many minutes to hours after an eruptive flare event. In contrast, the cool 0.7-1.5 MK coronal emissions (e.g., Fe IX 17.1 nm) usually dim immediately after the flare onset and do not recover until after the delayed second peak of the hot coronal emissions. We refer to this period of 1-5 hours after the fl amrea sin phase as the late phase, and this late phase is uniquely different than long duration flares associated with 2-ribbon flares or large filament eruptions. Our analysis of the late phase flare events indicates that the late phase involves hot coronal loops near the flaring region, not directly related to the original flaring loop system but rather with the higher post-eruption fields. Another finding is that space weather applications concerning Earth s ionosphere and thermosphere need to consider these late phase flares because they can enhance the total EUV irradiance flare variation by a factor of 2 when the late phase contribution is included

Investigating the Origins of Two Extreme Solar Particle Events: Proton Source Profile and Associated Electromagnetic Emissions

We analyze the high-energy particle emission from the Sun in two extreme solar particle events. in which protons are accelerated to relativistic energies and can cause a significant signal even in the ground-based particle detectors. Analysis of a relativistic proton event is based on modeling of the particle transport and interaction, from a near-Sun source through the solar wind and the Earth's magnetosphere and atmosphere to a detector on the ground. This allows us to deduce the time profile of the proton source at the Sun and compare it with observed electromagnetic emissions. The 1998 May 2 event is associated with a. flare and a coronal mass ejection (CME), which were well observed by the Nancay Radioheliograph, thus. the images of the. radio sources are available. For the 2003 November 2 event, the low corona images of the CME liftoff obtained at the Mauna Loa Solar Observatory. are available. Those complementary data sets are analyzed jointly with the broadband dynamic radio spectra, EUV images, and other data available for both events. We find a common scenario for both eruptions, including the flare's dual impulsive phase, the CME-launch-associated decimetric-continuum burst, and the late, low-frequency type III radio bursts at the time of the relativistic proton injection into the interplanetary medium. The analysis supports the idea that the two considered events start with emission of relativistic protons previously accelerated during the flare and CME launch, then trapped in large-scale magnetic loops and later released by the expanding CME

PROGRESS TOWARDS AVIATION RADIATION MONITORING

The aerospace environment has several sources of ionizing radiation. Exposure to this radiation is one of the natural hazards faced by aircrew, high-altitude pilots, frequent flyers, and commercial space travelers. Galactic cosmic rays (GCRs) and solar energetic particles (SEPs) almost always are the most important sources of ionizing radiation, particularly when traveling at or above commercial aviation altitudes (8 km or 26,000 ft). GCRs originate from outside the solar system and consist mostly of energetic protons with some alpha particles and a few heavier ions such as iron. SEPs originate on the Sun and are similar in composition to GCRs, being predominantly protons but with relatively fewer heavier ions. Recent measurements also suggest that secondary bremsstrahlung gamma-rays from precipitating Van Allen Belt relativistic electrons may also contribute dose at aviation altitudes. Regardless of their sources, charged particles transit Earth’s magnetosphere and interact with its atmosphere depending upon cutoff rigidity where the Earth’s magnetic field acts like a high-pass filter. During normal geomagnetic conditions, cutoff rigidity varies approximately inversely with geographic latitude; only particles with relatively high rigidity can make it to the atmosphere at latitudes near the equator, while even the lowest rigidity particles can enter the atmosphere at the geomagnetic poles. As a result, the largest primary radiation fluxes enter at high latitudes, with maxima surrounding the geomagnetic poles. We describe the ISWAT workshop results reviewing the state-of-art for aviation radiation monitoring and report the first results of the ARMAS Dual Monitor project demonstrating 24/7 monitoring as well as improved understanding of the particles and processes that create the aviation radiation environment