The EVE Doppler Sensitivity and Flare Observations (original) (raw)
Related papers
New Solar Extreme-Ultraviolet Irradiance Observations During Flares
The Astrophysical Journal, 2011
New solar extreme-ultraviolet (EUV) irradiance observations from the NASA Solar Dynamics Observatory (SDO) EUV Variability Experiment provide full coverage in the EUV range from 0.1 to 106 nm and continuously at a cadence of 10 s for spectra at 0.1 nm resolution and even faster, 0.25 s, for six EUV bands. These observations can be decomposed into four distinct characteristics during flares. First, the emissions that dominate during the flare's impulsive phase are the transition region emissions, such as the He ii 30.4 nm. Second, the hot coronal emissions above 5 MK dominate during the gradual phase and are highly correlated with the GOES X-ray. A third flare characteristic in the EUV is coronal dimming, seen best in the cool corona, such as the Fe ix 17.1 nm. As the post-flare loops reconnect and cool, many of the EUV coronal emissions peak a few minutes after the GOES X-ray peak. One interesting variation of the post-eruptive loop reconnection is that warm coronal emissions (e.g., Fe xvi 33.5 nm) sometimes exhibit a second large peak separated from the primary flare event by many minutes to hours, with EUV emission originating not from the original flare site and its immediate vicinity, but rather from a volume of higher loops. We refer to this second peak as the EUV late phase. The characterization of many flares during the SDO mission is provided, including quantification of the spectral irradiance from the EUV late phase that cannot be inferred from GOES X-ray diagnostics.
on the Solar Dynamics Observatory Extreme Ultraviolet Variability Experiment (SDO/EVE)
2016
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 µHz 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 49day 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.
Solar Physics, 2012
The highly variable solar extreme ultraviolet (EUV) radiation is the major energy input to the Earth's upper atmosphere, strongly impacting the geospace environment, affecting satellite operations, communications, and navigation. The Extreme ultraviolet Variability Experiment (EVE) onboard the NASA Solar Dynamics Observatory (SDO) will measure the solar EUV irradiance from 0.1 to 105 nm with unprecedented spectral resolution (0.1 nm), temporal cadence (ten seconds), and accuracy (20%). EVE includes several irradiance instruments: The Multiple EUV Grating Spectrographs (MEGS)-A is a grazingincidence spectrograph that measures the solar EUV irradiance in the 5 to 37 nm range with 0.1-nm resolution, and the MEGS-B is a normal-incidence, dual-pass spectrograph that measures the solar EUV irradiance in the 35 to 105 nm range with 0.1-nm resolution. To provide MEGS in-flight calibration, the EUV SpectroPhotometer (ESP) measures the solar EUV irradiance in broadbands between 0.1 and 39 nm, and a MEGS-Photometer measures the Sun's bright hydrogen emission at 121.6 nm. The EVE data products include a near real-time space-weather product (Level 0C), which provides the solar EUV irradiance in specific bands and also spectra in 0.1-nm intervals with a cadence of one minute and with a time delay of less than 15 minutes. The EVE higher-level products are Level 2 with the solar EUV irradiance at higher time cadence (0.25 seconds for photometers and ten seconds for spectrographs) and Level 3 with averages of the solar irradiance over a day and over each one-hour period. The EVE team also plans to advance existing models of solar EUV irradiance and to operationally use the EVE measurements in models of Earth's ionosphere and thermosphere. Improved understanding of the evolution of solar flares and extending the various models to incorporate solar flare events are high priorities for the EVE team.
SUMER observations of Doppler shift in the quiet Sun and in an active region
Astronomy and Astrophysics, 1999
The UV spectral lines formed at transition region temperatures in the solar atmosphere, show a prevailing redshifted emission. Using the Solar Ultraviolet Measurements of Emitted Radiation spectrometer flown on the Solar and Heliospheric Observatory spacecraft, we measure the amount of line shift as a function of the temperature for several spectral lines formed in the range between 10 4 and 10 6 K. We analyze spectrograms relative to the quiet Sun and to the active region NOAA 7946. The velocities derived are increasing from a redshift of ∼ 0 km s −1 at ∼ 20000 K to 10 km s −1 at 1.9 10 5 K for the quiet Sun, and to ∼ 15 km s −1 at 10 5 K for the active region. At higher temperature an opposite behaviour is observed. In the quiet Sun a blueshift of ∼ −2 km s −1 is observed at the Ne viii formation temperature (6.3 10 5 K), while in the active region, a blue-shifted value around −8 km s −1 is observed for the same spectral line. The finding of blueshift in Ne viii is due to the adoption of a new rest wavelength of 770.428Å. By 10 6 K the blueshift is ∼ −10 km s −1 in the active region as measured by Fe xii 1242.
Astrophysics and Space Science Library, 2013
The idea of measurement of X-ray lines Doppler shifts in spectra of the Sun, applied in DIOGENESS spectrometer, was previously developed and verified in rocket experiment with RDR X-ray Dopplerometer (Vertical-11 Rocket, 1981) [3]. Upon the obtained results two X-ray DIOGENESS spectrometers have been manufactured; the first one was operated aboard the CORONAS-I satellite (launch in 1994) [6], while the second was operated aboard the CORONAS-F. The general view of the instrument is shown in Fig. 1. The spectrometer with flat oscillating crystals is used for Doppler shifts measurement in DIOGENESS. According to Bragg law, the X-radiation, inciding crystal surface at  angle, is reflected from the crystal at the same angle at a single wavelength. The crystal, due to the interference, quench all radiation except the radiation with wavelength, defined by Bragg condition
The quiet Sun average Doppler shift of coronal lines up to 2 MK
Astronomy & Astrophysics, 2011
Context. The average Doppler shift shown by spectral lines formed from the chromosphere to the corona reveals important information on the mass and energy balance of the solar atmosphere, providing an important observational constraint to any models of the solar corona. Previous spectroscopic observations of vacuum ultra-violet (VUV) lines have revealed a persistent average wavelength shift of lines formed at temperatures up to 1 MK. At higher temperatures, the behaviour is still essentially unknown. Aims. Here we analyse combined SUMER (Solar Ultraviolet Measurements of Emitted Radiation)/SoHO (Solar and Heliospheric Observatory) and EIS (EUV Imaging Spectrometer)/Hinode observations of the quiet Sun around disk centre to determine, for the first time, the average Doppler shift of several spectral lines formed between 1 and 2 MK, where the largest part of the quiet coronal emission is formed. Methods. The measurements are based on a novel technique applied to EIS spectra to measure the difference in Doppler shift between lines formed at different temperatures. Simultaneous wavelength-calibrated SUMER spectra allow establishing the absolute value at the reference temperature of T ≈ 1 MK. Results. The average line shifts at 1 MK < T < 1.8 MK are modestly, but clearly bluer than those observed at 1 MK. By accepting an average blue shift of about (−1.8 ± 0.6) km s −1 at 1 MK (as provided by SUMER measurements), this translates into a maximum Doppler shift of (−4.4 ± 2.2) km s −1 around 1.8 MK. The measured value appears to decrease to about (−1.3 ± 2.6) km s −1 at the Fe xv formation temperature of 2.1 MK. Conclusions. The measured average Doppler shift between 0.01 and 2.1 MK, for which we provide a parametrisation, appears to be qualitatively and roughly quantitatively consistent with what foreseen by 3-D coronal models where heating is produced by dissipation of currents induced by photospheric motions and by reconnection with emerging magnetic flux.
Monthly Notices of the Royal Astronomical Society: Letters, 2008
The active region NOAA (National Oceanic and Atmospheric Administration) AR 10486 which appeared on the solar disc in 2003 October produced a lot of space weather related activity. Here, we report on the co-spatial evolution of the photospheric Doppler enhancements and the chromospheric Hα flare ribbons observed during the 4B/X17.2 class solar flare of 2003 October 28 in this active region. These velocity enhancements exactly match the Hα brightness enhancements in space, and are delayed by approximately 1 min in time. Hα brightness attains a maximum nearly at the same time as the peak seen in light curves in high-energy emission observed by KORONAS (Kuznetsov et al. 2006).
The Astrophysical Journal, 2005
Improving the accuracy and resolution of helioseismic inversions calls for more accurate modeling of the observational p-mode power spectra from which the solar oscillation frequencies are traditionally measured. We present a new technique of calculating the response function ( leakage matrix) for Doppler velocity measurements that is based largely on an analytical description of the relevant instrumental and physical effects. The computational efficiency of the new approach allows us to implement the response function in an adaptive manner: i.e., the compensation for instrumental or optical distortions of unknown magnitude can be performed as a part of the spectral fitting procedure.
Solar Physics, 2000
A distribution map of the large-scale chromospheric Doppler velocities on the solar disk for 5 June 2002 is presented. The map was obtained using a 2D-spectroscopy technique within the He I 10830 Å line. The spatial resolution of the map is about 30 arc sec. The map demonstrates a downflow in the chromosphere over active regions, especially significant around the spots and inside the plages. Positive Doppler velocities correspond to strong magnetic field areas, regardless of the field sign. Three major chromospheric outflow zones are observed: an equatorial and two polar ones. Each area of substantial negative Doppler velocities matches a zone of weak intensity of inner corona observed within the Fe IX-X 171 Å line by the SOHO spacecraft. A Doppler velocity histogram and the dependence of the Doppler velocities on the cosine of the heliocentric angle for the solar disk are calculated. The total mass outflow from the upper chromosphere is estimated as 2 × 10 13 g s −1. Four percent of this amount is sufficient to produce the fast solar wind.