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

Reconstruction of the solar EUV irradiance from 1996 to 2010 based on SOHO/EIT images

The solar Extreme UltraViolet (EUV) spectrum has important effects on the Earth’s upper atmosphere. For a detailed investigation of these effects it is important to have a consistent data series of the EUV spectral irradiance available. We present a reconstruction of the solar EUV irradiance based on SOHO/EIT images, along with synthetic spectra calculated using different coronal features which represent the brightness variation of the solar atmosphere. The EIT images are segmented with the SPoCA2 tool which separates the features based on a fixed brightness classification scheme. With the SOLMOD code we then calculate intensity spectra for the 10–100 nm wavelength range and each of the coronal features. Weighting the intensity spectra with the area covered by each of the features yields the temporal variation of the EUV spectrum. The reconstructed spectrum is then validated against the spectral irradiance as observed with SOHO/SEM. Our approach leads to good agreement between the reconstructed and the observed spectral irradiance. This study is an important step toward understanding variations in the solar EUV spectrum and ultimately its effect on the Earth’s upper atmosphere

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