We have evaluated the energetics of 38 solar eruptive events observed by a variety of spacecraft instruments between 2002 February and 2006 December, as accurately as the observations allow. The ...measured energetic components include: (1) the radiated energy in the Geostationary Operational Environmental Satellite 1-8 A band, (2) the total energy radiated from the soft X-ray (SXR) emitting plasma, (3) the peak energy in the SXR-emitting plasma, (4) the bolometric radiated energy over the full duration of the event, (5) the energy in flare-accelerated electrons above 20 keV and in flare-accelerated ions above 1 MeV, (6) the kinetic and potential energies of the coronal mass ejection (CME), (7) the energy in solar energetic particles (SEPs) observed in interplanetary space, and (8) the amount of free (non-potential) magnetic energy estimated to be available in the pertinent active region. Major conclusions include: (1) the energy radiated by the SXR-emitting plasma exceeds, by about half an order of magnitude, the peak energy content of the thermal plasma that produces this radiation; (2) the energy content in flare-accelerated electrons and ions is sufficient to supply the bolometric energy radiated across all wavelengths throughout the event; (3) the energy contents of flare-accelerated electrons and ions are comparable; (4) the energy in SEPs is typically a few percent of the CME kinetic energy (measured in the rest frame of the solar wind); and (5) the available magnetic energy is sufficient to power the CME, the flare-accelerated particles, and the hot thermal plasma.
The Solar Dynamics Observatory (SDO) Pesnell, W. Dean; Thompson, B. J.; Chamberlin, P. C.
Solar physics,
2012/1, Letnik:
275, Številka:
1-2
Journal Article
Recenzirano
Odprti dostop
The
Solar Dynamics Observatory
(SDO) was launched on 11 February 2010 at 15:23 UT from Kennedy Space Center aboard an Atlas V 401 (AV-021) launch vehicle. A series of apogee-motor firings lifted SDO ...from an initial geosynchronous transfer orbit into a circular geosynchronous orbit inclined by 28° about the longitude of the SDO-dedicated ground station in New Mexico. SDO began returning science data on 1 May 2010. SDO is the first space-weather mission in NASA’s
Living With a Star
(LWS) Program. SDO’s main goal is to understand, driving toward a predictive capability, those solar variations that influence life on Earth and humanity’s technological systems. The SDO science investigations will determine how the Sun’s magnetic field is generated and structured, how this stored magnetic energy is released into the heliosphere and geospace as the solar wind, energetic particles, and variations in the solar irradiance. Insights gained from SDO investigations will also lead to an increased understanding of the role that solar variability plays in changes in Earth’s atmospheric chemistry and climate. The SDO mission includes three scientific investigations (the
Atmospheric Imaging Assembly
(AIA),
Extreme Ultraviolet Variability Experiment
(EVE), and
Helioseismic and Magnetic Imager
(HMI)), a spacecraft bus, and a dedicated ground station to handle the telemetry. The Goddard Space Flight Center built and will operate the spacecraft during its planned five-year mission life; this includes: commanding the spacecraft, receiving the science data, and forwarding that data to the science teams. The science investigations teams at Stanford University, Lockheed Martin Solar Astrophysics Laboratory (LMSAL), and University of Colorado Laboratory for Atmospheric and Space Physics (LASP) will process, analyze, distribute, and archive the science data. We will describe the building of SDO and the science that it will provide to NASA.
The Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft has been continuously observing the variability of solar soft X‐rays and EUV irradiance, monitoring the upstream solar wind and ...interplanetary magnetic field conditions and measuring the fluxes of solar energetic ions and electrons since its arrival to Mars. In this paper, we provide a comprehensive overview of the space weather events observed during the first ∼1.9 years of the science mission, which includes the description of the solar and heliospheric sources of the space weather activity. To illustrate the variety of upstream conditions observed, we characterize a subset of the event periods by describing the Sun‐to‐Mars details using observations from the MAVEN solar Extreme Ultraviolet Monitor, solar energetic particle (SEP) instrument, Solar Wind Ion Analyzer, and Magnetometer together with solar observations using near‐Earth assets and numerical solar wind simulation results from the Wang‐Sheeley‐Arge‐Enlil model for some global context of the event periods. The subset of events includes an extensive period of intense SEP electron particle fluxes triggered by a series of solar flares and coronal mass ejection (CME) activity in December 2014, the impact by a succession of interplanetary CMEs and their associated SEPs in March 2015, and the passage of a strong corotating interaction region (CIR) and arrival of the CIR shock‐accelerated energetic particles in June 2015. However, in the context of the weaker heliospheric conditions observed throughout solar cycle 24, these events were moderate in comparison to the stronger storms observed previously at Mars.
Key Points
We present a comprehensive overview of the first 1.9 years of MAVEN space weather conditions measured upstream at Mars
We characterize a subset of Mars‐impacting events due to an extensive period of SEP electrons, a succession of ICMEs, and a strong CIR
We discuss the space weather implications of the weaker solar cycle 24 heliospheric conditions on the events observed by MAVEN
The Extreme Ultraviolet (EUV) monitor is an instrument on the NASA Mars Atmosphere and Volatile EvolutioN (MAVEN) mission, designed to measure the variability of the solar soft x-rays and EUV ...irradiance at Mars. The solar output in this wavelength range is a primary energy input to the Mars atmosphere and a driver for the processes leading to atmospheric escape. The MAVEN EUV monitor consists of three broadband radiometers. The radiometers consist of silicon photodiodes with different bandpass-limiting filters for each channel. The filters for the radiometers are: Channel A: thin foil C/Al/Nb/C for 0.1–3 nm and 17–22 nm, Channel B: thin foil C/Al/Ti/C for 0.1–7 nm, and Channel C: interference filter for 121–122 nm. A fourth, covered photodiode is used to monitor variations in dark signal due to temperature and radiation background changes. The three science channels will monitor emissions from the highly variable corona and transition region of the solar atmosphere. The EUV monitor is mounted on the top deck of the MAVEN spacecraft and is pointed at the Sun for most of its orbit around Mars. The measurement cadence is 1-second. The broadband irradiances can be used to monitor the most rapid changes in solar irradiance due to flares. In combination with time-interpolated observations at Earth of slower varying solar spectral emissions, the broadband MAVEN EUV monitor measurements will also be used in a spectral irradiance model to generate the full EUV spectrum at Mars from 0 to 190 nm in 1-nm bins on a time cadence of 1-minute and daily averages.
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 grazing-incidence 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.
Habitability at the surface of a planet depends on having an atmosphere long enough for life to develop. The loss of atmosphere to space is an important component in assessing planetary surface ...habitability. Current models of atmospheric escape from exoplanets are not well constrained by observations. Atmospheric escape observations from the terrestrial planets are available in public data archives. We recast oxygen escape rates from Earth derived from an instrument on Dynamics Explorer‐1 as function of solar wind and compare them to similar data from Mars. Analysis demonstrates that oxygen escape rates from Mars are not as sensitive to variations in solar power components as those from Earth. Available data from Venus can confirm or refute the assertion that oxygen escape from magnetized planets is more sensitive than that from unmagnetized planets.
Plain Language Summary
Habitability of a planet depends on having an atmosphere long enough for life to develop. NASA and ESA data archives contain information about atmospheric escape from the terrestrial planets. For these planets oxygen ions dominate atmospheric escape. The data archives are just beginning to be analyzed and presented in a form that allows comparison with, and validation of, models of the interaction of stellar winds with exoplanets. We derive oxygen escape rates from Earth as a function of solar power components from a recasting of Dynamics Explorer‐1 data and compare them to similar data from Mars. Our analysis demonstrates that oxygen escape rates from Mars are not as sensitive to variations in the solar power components as those from Earth. These data and similar data from Venus will prove to be important constrains on models of stelar wind/atmosphere interactions and atmospheric escape from exoplanets.
Key Points
We recast oxygen escape rates from Earth derived from an instrument on Dynamics Explorer‐1 as a function of solar energy inputs
We compare escape rates for a magnetized planet (Earth) and an unmagnetized planet (Mars) as a function of solar energy inputs
Oxygen escape rates from Mars are not as sensitive to variations in the solar power components as those from Earth
The EUV Variability Experiment (EVE) onboard the Solar Dynamics Observatory has provided unprecedented measurements of the solar EUV irradiance at high temporal cadence with good spectral resolution ...and range since May 2010. The main purpose of EVE was to connect the Sun to the Earth by providing measurements of the EUV irradianceas a driver for space weather and Living With a Star studies, but after launch the instrument has demonstrated the significance of its measurements in contributing to studies looking at the sources of solar variability for pure solar physics purposes. This paper expands upon previous findings that EVE can in fact measure wavelength shifts during solar eruptive events and therefore provide Doppler velocities for plasma at all temperatures throughout the solar atmosphere from the chromosphere to hot flaring temperatures. This process is not straightforward as EVE was not designed or optimized for these types of measurements. In this paper we describe the many detailed instrumental characterizations needed to eliminate the optical effects in order to provide an absolute baseline for the Doppler shift studies. An example is given of a solar eruption on 7 September 2011 (SOL2011-09-07), associated with an X1.2 flare, where EVE Doppler analysis shows plasma ejected from the Sun in the He II 30.38 nm emission at a velocity of almost 120 km s(exp -1) along the line-of-sight.
The Flare Irradiance Spectral Model (FISM) is an important tool for estimating solar variability for a myriad of space weather research studies and applications, and FISM Version 2 (FISM2) recently ...was released. FISM2 is an empirical model of the solar ultraviolet irradiance created to fill spectral and temporal gaps in the satellite observations. FISM2 estimates solar ultraviolet irradiance variations due to the solar cycle, solar rotations, and solar flares. The major improvement provided by FISM2 is that it is based on multiple new, more accurate instruments that have now captured almost a full solar cycle and thousands of flares, drastically improving the accuracy of the modeled FISM2 solar irradiance spectra. Specifically, these new instruments are the Solar Dynamics Observatory (SDO)/Extreme Ultraviolet Variability Experiment (EVE), Solar Radiation and Climate Experiment (SORCE)/X‐ray Photometer System (XPS), and SORCE/Solar Stellar Irradiance Comparison Experiment (SOLSTICE). FISM2 is also improved to 0.1‐nm spectral bins across the same 0‐ to 190‐nm spectral range and is already being used in research to estimate space weather changes due to solar irradiance variability in planetary thermospheres and ionospheres.
Key Points
FISM2 accurately models spectral irradiance variations due to the solar cycle, solar rotation, and solar flares
FISM2 fills temporal, from 1947 to present, and spectral, from 0–190 nm, gaps in the measurements of SORCE/XPS, SDO/EVE, and SORCE/SOLSTICE
FISM2 is a much improved solar ultraviolet irradiance model over the first version released more than 15 years ago
On 10 September 2017, irradiance from a magnitude X8.2 solar flare impacted Mars while the Mars Atmosphere and Volatile EvolutioN (MAVEN) orbiter was characterizing the Mars upper atmosphere. This ...solar flare was the largest to occur during the MAVEN mission to date, nearly tripling the ionizing irradiance impacting Mars in tens of minutes, and provides an opportunity to study the planet's response to extreme irradiance changes. This letter reports in situ observations of the Mars topside ionosphere's response to this flare above 155 km made 1.67 hr after the flare soft X‐ray peak. The observed plasma density increase is higher than expected based solely on increased ionization, and the electron temperature decreases below 225 km; both effects can be explained by an expanded neutral atmosphere, which efficiently dissipates any flare‐induced heating of the thermal electrons at altitudes where CO2 is the dominant species. Further, the ion density and composition change significantly at both fixed altitude and pressure level, which can be explained by a change in the O:CO2 density ratio, highlighting the importance this ratio has in determining ionospheric structure.
Plain Language Summary
On 10 September 2017, a large solar flare erupted from the Sun sending intense radiation into the upper atmosphere of Mars. This radiation ionized the gases in Mars's upper atmosphere, resulting in significant changes in its structure and composition. Because solar flares are short‐lived events, studying how the Mars atmosphere responds to them can unmask phenomena that may otherwise be hidden when the Sun varies more gradually. This letter reports the first in situ observations of the how the ions and electrons in the Mars upper atmosphere, above 155 km, change during solar flares. This region of the atmosphere interfaces with the space environment, where it can be stripped away and lost. The rate of loss is believed to be strongly dependent on the same radiation released by flares. Therefore, understanding how Mars responds to flares can provide insight into how its atmosphere evolved early in its history, when the Sun is believed to have produced larger flares more frequently, and Mars is believed to have had an atmosphere capable of supporting large amounts of liquid water. In addition to Mars researchers, these results will be of particular interest to those studying space weather, planetary atmospheres, and the habitability of exoplanets.
Key Points
Ionizing EUV flux increased by 170% at the flare peak, causing changes in the observed (>150 km) plasma density, temperature, and composition
Ionospheric changes are a result of an expanded neutral atmosphere, and the increased relative abundance of O at fixed pressure level
Photochemical escape of O increased moderately for observations made 80 min after the flare peak
Electron densities in planetary ionospheres increase substantially during solar flares in response to the increased solar irradiance at soft X‐ray and extreme ultraviolet wavelengths. Here we modify ...an existing model of the ionosphere of Mars to incorporate time‐dependent solar irradiances and use it to simulate ionospheric conditions during the X14.4 and M7.8 solar flares of 15 and 26 April 2001, respectively. Simulations were validated by comparison to Mars Global Surveyor radio occultation measurements of vertical profiles of ionospheric electron density. Adjustments to the model's representation of the neutral atmosphere were required to adequately reproduce the observations before and during these solar flares. An accurate representation of electron‐impact ionization, an important process in the lower ionosphere of Mars, is required in order to adequately simulate the doubling of electron densities that can occur in the lower ionosphere of Mars during a solar flare. We used the W‐value representation of electron‐impact ionization, in which the number of ion‐electron pairs created per photon absorbed equals the ratio of the difference between photon energy and the ionization potential of carbon dioxide to the W‐value. A range of possible W‐values for Mars have been suggested in the literature, and a value of 28 eV led to the best reproduction of flare‐affected observations. Simulated enhancements in the electron density are largest and persist the longest in the M1 region. We predict that the peak electron density in the M1 region can exceed that of the M2 region for short periods during intense solar flares.
Key Points
Simulation of the ionosphere of Mars during a solar flare
Validation against observations
Electron density in M1 region may exceed M2 densities