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The Sun's chromosphere is a critical region to understand when considering energy and mass deposition into the transition region and corona, but many of the smaller, faster events which transport a portion of this mass and energy are still difficult to observe, identify and model. Solar Spicules are small, spike-like events in the solar chromosphere that have the potential to transfer energy and mass to the transition region, but whose energetic origins are still being researched. Chromospheric spicule activity on-disk can be identified by observing temporary excursions in the red and blue wings of chromospheric emission lines. Researchers have demonstrated this in Hydrogen~Alpha (H{\alpha}, 6563 {\AA}), Ca II (8542 {\AA}, k 3934 {\AA}), Mg II (h 2803 {\AA}, k 2796 {\AA}), and Si IV (1394 {\AA}, 1405 {\AA}) spectral observations, with the vast majority of identification efforts focused on lower chromospheric observations of H$\alpha$ and Ca II. Because any spicules which deposit mass and energy into the transition region must necessarily pass through the upper chromosphere, observations from this region such as Mg II or Hydrogen Lyman Alpha (Ly$\alpha$ 1216 {\AA}) in enough quantity to perform proper statistics will be critical to fully characterizing spicules' impact on mass and energy transfer in the Sun. This research proposes a definition with numerical limits for how spicules appear in Mg II wavelengths, tunes an algorithm for automatically detecting spicules in Mg II spectral observations, and uses K Means Clustering to identify and display the full range of spicule spectrum shapes. This work will help allow statistical studies on spicules in the upper chromosphere to be as thorough as those of the lower chromosphere, allowing researchers to better understand the physical nature of spicules and their role in energy transfer and deposition in the solar atmosphere., Comment: Submitted an early draft, was not ready for full submission

The Solar eruptioN Integral Field Spectrograph (SNIFS) is a solar-gazing spectrograph scheduled to fly in the summer of 2025 on a NASA sounding rocket. Its goal is to view the solar chromosphere and transition region at a high cadence (1s) both spatially (0.5") and spectrally (33 m{\AA}) viewing wavelengths around Lyman Alpha (1216 {\AA}), Si iii (1206 {\AA}) and O v (1218 {\AA}) to observe spicules, nanoflares, and possibly a solar flare. This time cadence will provide yet-unobserved detail about fast-changing features of the Sun. The instrument is comprised of a Gregorian-style reflecting telescope combined with a spectrograph via a specialized mirrorlet array that focuses the light from each spatial location in the image so that it may be spectrally dispersed without overlap from neighboring locations. This paper discusses the driving science, detailed instrument and subsystem design, and pre-integration testing of the SNIFS instrument., Comment: 22 pages (not including references), 7 figures, submitting to Solar Physics

Three generations of the Miniature X-ray Solar Spectrometer (MinXSS) have flown on small satellites with the goal "to explore the energy distribution of soft X-ray (SXR) emissions from the quiescent Sun, active regions, and during solar flares, and to model the impact on Earth's ionosphere and thermosphere". The primary science instrument is the Amptek X123 X-ray spectrometer that has improved with each generation of the MinXSS experiment. This third generation MinXSS-3 has higher energy resolution and larger effective area than its predecessors and is also known as the Dual-zone Aperture X-ray Solar Spectrometer (DAXSS). It was launched on the INSPIRESat-1 satellite on 2022 February 14, and INSPIRESat-1 has successfully completed its 6-month prime mission. The INSPIRESat-1 is in a dawn-dusk, Sun-Synchronous Orbit (SSO) and therefore has 24-hour coverage of the Sun during most of its mission so far. The rise of Solar Cycle 25 (SC-25) has been observed by DAXSS. This paper introduces the INSPIRESat-1 DAXSS solar SXR observations, and we focus the science results here on a solar occultation experiment and multiple flares on 2022 April 24. One key flare result is that the reduction of elemental abundances is greatest during the flare impulsive phase and thus highlighting the important role of chromospheric evaporation during flares to inject warmer plasma into the coronal loops. Furthermore, these results are suggestive that the amount of chromospheric evaporation is related to flare temperature and intensity., Comment: 44 pages including 19-page Appendix A, 8 figures, 7 tables

The chromospheric Lyman-alpha line of neutral hydrogen (Ly$\alpha$; 1216 \r{A}) is the most intense emission line in the solar spectrum, yet until recently observations of flare-related Ly$\alpha$ emission have been scarce. Here, we examine the relationship between nonthermal electrons accelerated during the impulsive phase of three M3 flares that were co-observed by RHESSI, GOES, and SDO, and the corresponding response of the chromosphere in Ly$\alpha$. Despite having identical X-ray magnitudes, these flares show significantly different Ly$\alpha$ responses. The peak Ly$\alpha$ enhancements above quiescent background for these flares were 1.5%, 3.3%, and 6.4%. However, the predicted Ly$\alpha$ enhancements from FISM2 were consistently <2.5%. By comparing the properties of the nonthermal electrons derived from spectral analysis of hard X-ray observations, flares with a harder spectral index were found to produce a greater Ly$\alpha$ enhancement. The percentage of nonthermal energy radiated by the Ly$\alpha$ line during the impulsive phase was found to range from 2.0-7.9%. Comparatively, the radiative losses in He II (304 \r{A}) were found to range from 0.6-1.4% of the nonthermal energy while displaying enhancements above the background of 7.3-10.8%. FISM2 was also found to underestimate the level of He II emission in two out of the three flares. These results may have implications for space weather studies and modelling the response of the terrestrial atmosphere to changes in the solar irradiance, and will guide the interpretation of flare-related Ly$\alpha$ observations that will become available during Solar Cycle 25.

In the next decade, there is an opportunity for very high return on investment of relatively small budgets by elevating the priority of smallsat funding in heliophysics. We've learned in the past decade that these missions perform exceptionally well by traditional metrics, e.g., papers/year/\$M (Spence et al. 2022 -- arXiv:2206.02968). It is also well established that there is a "leaky pipeline" resulting in too little diversity in leadership positions (see the National Academies Report at https://www.nationalacademies.org/our-work/increasing-diversity-in-the-leadership-of-competed-space-missions). Prioritizing smallsat funding would significantly increase the number of opportunities for new leaders to learn -- a crucial patch for the pipeline and an essential phase of career development. At present, however, there are far more proposers than the available funding can support, leading to selection ratios that can be as low as 6% -- in the bottom 0.5th percentile of selection ratios across the history of ROSES. Prioritizing SmallSat funding and substantially increasing that selection ratio are the fundamental recommendations being made by this white paper., Comment: White paper submitted to the Decadal Survey for Solar and Space Physics (Heliophysics) 2024-2033; 6 pages, 1 figure

We have developed an algorithm to identify solar spicules in the first ever systematic survey of on-disk spicules exclusively using Mg II spectral observations. Using this algorithm we identify 2021 events in three Interface Region Imaging Spectrograph (IRIS) data sets with unique solar feature targets spanning a total of 300 minutes: (1) active region, (2) decayed active region/active network, and (3) coronal hole. We present event statistics and relate occurrence rates to the underlying photospheric magnetic field strength. This method identifies spicule event densities and occurrence rates similar to previous studies performed using H{\alpha} and Ca II observations of active regions. Additionally, this study identifies spicule-like events at very low rates at magnetic field intensities below 20 G, and increasing significantly between 100 and 200 G in active regions and above 20 G in coronal holes, which can be used to inform future observation campaigns. This information can be be used to help characterize spicules over their full lifetimes, and compliments existing H{\alpha} spectral capabilities and upcoming Ly{\alpha} spectral observations with the Solar eruptioN Integral Field Spectrograph (SNIFS) sounding rocket. In total, this study presents a method for detecting solar spicules exclusively using Mg II spectra, and provides statistics for spicule occurrences in the Mg II h line with respect to the magnetic field strength for the purpose of predicting spicule occurrences., Comment: 15 pages, 9 figures, presented at the AGU Fall 2022 conference, Submitted to APJ, published Apr 1 2023

We report the discovery and characterization of high-speed (>100 km/s) horizontal flows in solar active regions, making use of the Sun-as-a-star spectroscopy in the range 5-105 nm provided by the EVE (Extreme Ultraviolet Variability Experiment) spectrometers on the Solar Dynamics Observatory. These apparent flows are persistent on time scales of days, and are well observed in lines of Mg X, Si XII and Fe XVI for example. They are prograde, as evidenced directly by blueshifts/redshifts peaking at the east/west limb passages of isolated active regions. The high-speed flow behavior does not depend upon active-region latitude or solar cycle, with similar behavior in Cycles 24 and 25.

Within an imaging instrument's field of view, there may be many observational targets of interest. Similarly, within a spectrograph's bandpass, there may be many emission lines of interest. The brightness of these targets and lines can be orders of magnitude different, which poses a challenge to instrument and mission design. A single exposure can saturate the bright emission and/or have a low signal to noise ratio (SNR) for faint emission. Traditional high dynamic range (HDR) techniques solve this problem by either combining multiple sequential exposures of varied duration or splitting the light to different sensors. These methods, however, can result in the loss of science capability, reduced observational efficiency, or increased complexity and cost. The simultaneous HDR method described in this paper avoids these issues by utilizing a special type of detector whose rows can be read independently to define zones that are then composited, resulting in areas with short or long exposure measured simultaneously. We demonstrate this technique for the sun, which is bright on disk and faint off disk. We emulated these conditions in the lab to validate the method. We built an instrument simulator to demonstrate the method for a realistic solar imager and input. We then calculated SNRs, finding a value of 45 for a faint coronal mass ejection (CME) and 200 for a bright CME, both at 3.5 $R_{\odot}$ -- meeting or far exceeding the international standard for digital photography that defines a SNR of 10 as acceptable and 40 as excellent. Future missions should consider this type of hardware and technique in their trade studies for instrument design., Comment: 9 pages, 5 figures, accepted to ApJ

The Sun Coronal Ejection Tracker (SunCET) is an extreme ultraviolet imager and spectrograph instrument concept for tracking coronal mass ejections through the region where they experience the majority of their acceleration: the difficult-to-observe middle corona. It contains a wide field of view (0-4~\Rs) imager and a 1~\AA\ spectral-resolution-irradiance spectrograph spanning 170-340~\AA. It leverages new detector technology to read out different areas of the detector with different integration times, resulting in what we call "simultaneous high dynamic range", as opposed to the traditional high dynamic range camera technique of subsequent full-frame images that are then combined in post-processing. This allows us to image the bright solar disk with short integration time, the middle corona with a long integration time, and the spectra with their own, independent integration time. Thus, SunCET does not require the use of an opaque or filtered occulter. SunCET is also compact -- $\sim$15 $\times$ 15 $\times$ 10~cm in volume -- making it an ideal instrument for a CubeSat or a small, complementary addition to a larger mission. Indeed, SunCET is presently in a NASA-funded, competitive Phase A as a CubeSat and has also been proposed to NASA as an instrument onboard a 184 kg Mission of Opportunity., Comment: 22 pages, 12 figures, 5 tables, in press at Journal of Space Weather and Space Climate special issue called "Space Weather Instrumentation"

By 2050, we expect that CME models will accurately describe, and ideally predict, observed solar eruptions and the propagation of the CMEs through the corona. We describe some of the present known unknowns in observations and models that would need to be addressed in order to reach this goal. We also describe how we might prepare for some of the unknown unknowns that will surely become challenges., Comment: 3 pages, 2 figures, White Paper submitted to the Heliophysics 2050 Workshop

The Geostationary Operational Environmental Satellite R (GOES-R) series of four satellites are the next generation NOAA GOES satellites. Once on orbit and commissioned, they are renamed GOES 16-19, making critical terrestrial and space weather measurements through 2035. GOES 16 and 17 are currently on orbit, having been launched in 2016 and 2018, respectively. The GOES-R satellites include the EUV and X-ray Irradiance Sensors (EXIS) instrument suite, which measures calibrated solar irradiance in 8 lines or bands between 25 and 285 nm with the Extreme Ultraviolet Sensors (EUVS) instrument. EXIS also includes the X-Ray Sensor (XRS) instrument, which measures solar soft X-ray irradiance at the legacy GOES bands. The EUVS measurements are used as inputs to the EUVS Model, a solar spectral irradiance model for space weather operations that predicts irradiance in twenty-two 5 nm wide intervals from 5 nm to 115 nm, and one 10 nm wide interval from 117 to 127 nm at 30 second cadence. Once fully operational, NOAA will distribute the EUVS Model irradiance with 1 minute latency as a primary space weather data product, ushering in a new era of rapid dissemination and measurement continuity of EUV irradiance spectra. This paper describes the EUVS Model algorithms, data sources, calibration methods and associated uncertainties. Typical model (relative) uncertainties are less than $\sim$5\% for variability at time-scales longer than 6 hours, and are $\sim$25\% for solar flare induced variability. The absolute uncertainties, originating from the instruments used to calibrate the EUVS Model, are $\sim$10\%. Examples of model results are presented at both sub-daily and multi-year timescales to demonstrate the model's capabilities and limitations. Example solar flare irradiances are also modeled., Comment: Accepted by Journal of Space Weather and Space Climate on 20 November 2019

The chromospheric Lyman-alpha line of neutral hydrogen (\lya; 1216\AA) is the strongest emission line in the solar spectrum. Fluctuations in \lya\ are known to drive changes in planetary atmospheres, although few instruments have had the ability to capture rapid \lya\ enhancements during solar flares. In this paper we describe flare-associated emissions via a statistical study of 477 M- and X-class flares as observed by the EUV Sensor on board the 15th Geostationary Operational Environmental Satellite, which has been monitoring the full-disk solar \lya\ irradiance on 10~s timescales over the course of Solar Cycle 24. The vast majority (95\%) of these flares produced \lya\ enhancements of 10\% or less above background levels, with a maximum increase of $\sim$30\%. The irradiance in \lya\ was found to exceed that of the 1-8 \AA\ X-ray irradiance by as much as two orders of magnitude in some cases, although flares that occurred closer to the solar limb were found to exhibit less of a \lya\ enhancement. This center-to-limb variation was verified through a joint, stereoscopic observation of an X-class flare that appeared near the limb as viewed from Earth, but close to disk center as viewed by the MAVEN spacecraft in orbit around Mars. The frequency distribution of peak \lya\ was found to have a power-law slope of $2.8\pm0.27$. We also show that increased \lya\ flux is closely correlated with induced currents in the ionospheric E-layer through the detection of the solar flare effect as observed by the Kakioka magnetometer., Comment: Accepted for publication in Space Weather journal. 24 pages, 11 figures, 1 table

The second Miniature X-ray Solar Spectrometer (MinXSS-2) CubeSat, which begins its flight in late 2018, builds on the success of MinXSS-1, which flew from 2016-05-16 to 2017-05-06. The science instrument is more advanced -- now capable of greater dynamic range with higher energy resolution. More data will be captured on the ground than was possible with MinXSS-1 thanks to a sun-synchronous, polar orbit and technical improvements to both the spacecraft and the ground network. Additionally, a new open-source beacon decoder for amateur radio operators is available that can automatically forward any captured MinXSS data to the operations and science team. While MinXSS-1 was only able to downlink about 1 MB of data per day corresponding to a data capture rate of about 1%, MinXSS-2 will increase that by at least a factor of 6. This increase of data capture rate in combination with the mission's longer orbital lifetime will be used to address new science questions focused on how coronal soft X-rays vary over solar cycle timescales and what impact those variations have on the earth's upper atmosphere., Comment: 7 pages, 5 figures, 1 table; accepted for publication in Advances in Space Research

The Miniature X-ray Solar Spectrometer (MinXSS) CubeSat is the first solar science oriented CubeSat mission flown for the NASA Science Mission Directorate, with the main objective of measuring the solar soft X-ray (SXR) flux and a science goal of determining its influence on Earth's ionosphere and thermosphere. These observations can also be used to investigate solar quiescent, active region, and flare properties. The MinXSS X-ray instruments consist of a spectrometer, called X123, with a nominal 0.15 keV full-width-half-maximum (FWHM) resolution at 5.9 keV and a broadband X-ray photometer, called XP. Both instruments are designed to obtain measurements from 0.5 - 30 keV at a nominal time cadence of 10 seconds. A description of the MinXSS instruments, performance capabilities, and relation to the Geostationary Operational Environmental Satellite (GOES) 0.1 - 0.8 nm flux are discussed in this article. Early MinXSS results demonstrate the capability to measure variations of the solar spectral SXR flux between 0.8 - 12 keV from at least GOES A5 - M5 (5 $\times$ 10$^{-8}$ - 5 $\times$ 10$^{-5}$ W m$^{-2}$) levels and infer physical properties (temperature and emission measure) from the MinXSS data alone. Moreover, coronal elemental abundances can be inferred, specifically Fe, Ca, Si, Mg, S, Ar, and Ni, when there is sufficiently high count rate at each elemental spectral feature. Additionally, temperature response curves and emission measure loci demonstrate the MinXSS sensitivity to plasma emission at different temperatures. MinXSS observations coupled with those from other solar observatories can help address some of the most compelling questions in solar coronal physics. Finally, simultaneous observations by MinXSS and Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) can provide the most spectrally complete soft X-ray solar flare photon flux measurements to date., Comment: 45 pages, 16 figures, accepted for publication in Solar Physics

The Miniature X-ray Solar Spectrometer (MinXSS) is a 3 Unit (3U) CubeSat designed for a 3-month mission to study solar soft X-ray spectral irradiance. The first of the two flight models was deployed from the International Space Station in 2016 May and operated for one year before its natural deorbiting. This was the first flight of the Blue Canyon Technologies XACT 3-axis attitude determination and control system -- a commercially available, high-precision pointing system. We characterized the performance of the pointing system on orbit including performance at low altitudes where drag torque builds up. We found that the pointing accuracy was 0.0042\degree\ - 0.0117\degree\ (15$''$ - 42$''$, 3$\sigma$, axis dependent) consistently from 190 km - 410 km, slightly better than the specification sheet states. Peak-to-peak jitter was estimated to be 0.0073\degree\ (10 s$^{-1}$) - 0.0183\degree\ (10 s$^{-1}$) (26$''$ (10 s$^{-1}$) - 66$''$ (10 s$^{-1}$), 3$\sigma$). The system was capable of dumping momentum until an altitude of 185 km. We found small amounts of sensor degradation in the star tracker and coarse sun sensor. Our mission profile did not require high-agility maneuvers so we are unable to characterize this metric. Without a GPS receiver, it was necessary to periodically upload ephemeris information to update the orbit propagation model and maintain pointing. At 400 km, these uploads were required once every other week. At $\sim$270 km, they were required every day. We also characterized the power performance of our electric power system, which includes a novel pseudo-peak power tracker -- a resistor that limited the current draw from the battery on the solar panels. With 19 30\% efficient solar cells and an 8 W system load, the power balance had 65\% of margin on orbit. We present several recommendations to other CubeSat programs throughout., Comment: 10 pages, 16 figures, accepted at Journal of Small Satellites

The goal of the Miniature X-ray Solar Spectrometer (MinXSS) CubeSat is to explore the energy distribution of soft X-ray (SXR) emissions from the quiescent Sun, active regions, and during solar flares, and to model the impact on Earth's ionosphere and thermosphere. The energy emitted in the SXR range (0.1 --10 keV) can vary by more than a factor of 100, yet we have limited spectral measurements in the SXRs to accurately quantify the spectral dependence of this variability. The MinXSS primary science instrument is an Amptek, Inc. X123 X-ray spectrometer that has an energy range of 0.5--30 keV with a nominal 0.15 keV energy resolution. Two flight models have been built. The first, MinXSS-1, has been making science observations since 2016 June 9, and has observed numerous flares, including more than 40 C-class and 7 M-class flares. These SXR spectral measurements have advantages over broadband SXR observations, such as providing the capability to derive multiple-temperature components and elemental abundances of coronal plasma, improved irradiance accuracy, and higher resolution spectral irradiance as input to planetary ionosphere simulations. MinXSS spectra obtained during the M5.0 flare on 2016 July 23 highlight these advantages, and indicate how the elemental abundance appears to change from primarily coronal to more photospheric during the flare. MinXSS-1 observations are compared to the Geostationary Operational Environmental Satellite (GOES) X-Ray Sensor (XRS) measurements of SXR irradiance and estimated corona temperature. Additionally, a suggested improvement to the calibration of the GOES XRS data is presented., Comment: Submitted to The Astrophysical Journal, Part 1 (30 November 2016); 3rd revision; 8 text pages, 4 figures

The Miniature X-ray Solar Spectrometer (MinXSS) is a 3-Unit (3U) CubeSat developed at the Laboratory for Atmospheric and Space Physics (LASP) at the University of Colorado, Boulder (CU). Over 40 students contributed to the project with professional mentorship and technical contributions from professors in the Aerospace Engineering Sciences Department at CU and from LASP scientists and engineers. The scientific objective of MinXSS is to study processes in the dynamic Sun, from quiet-Sun to solar flares, and to further understand how these changes in the Sun influence the Earth's atmosphere by providing unique spectral measurements of solar soft x-rays (SXRs). The enabling technology providing the advanced solar SXR spectral measurements is the Amptek X123, a commercial-off-the-shelf (COTS) silicon drift detector (SDD). The Amptek X123 has a low mass (~324 g after modification), modest power consumption (~2.50 W), and small volume (6.86 cm x 9.91 cm x 2.54 cm), making it ideal for a CubeSat. This paper provides an overview of the MinXSS mission: the science objectives, project history, subsystems, and lessons learned that can be useful for the small-satellite community., Comment: 32 pages, 13 figures, 1 table; submitted to Journal of Spacecraft and Rockets

SDO/EVE provides rich information of the thermodynamic processes of solar activities, particularly of solar flares. Here, we develop a method to construct thermodynamic spectrum (TDS) charts based on the EVE spectral lines. This tool could be potentially useful to the EUV astronomy to learn the eruptive activities on the distant astronomical objects. Through several cases, we illustrate what we can learn from the TDS charts. Furthermore, we apply the TDS method to 74 flares equal to or greater than M5.0-class, and reach the following statistical results. First, EUV peaks are always behind the soft X-ray (SXR) peaks and stronger flares tend to have a faster cooling rate. There is a power law correlation between the peak delay times and the cooling rates, suggesting a coherent cooling process of flares from SXR to EUV emissions. Second, there are two distinct temperature drift patterns, called Type I and Type II. For Type I flares, the enhanced emission drifts from high to low temperature like a quadrilateral, whereas for Type II flares, the drift pattern looks like a triangle. Statistical analysis suggests that Type II flares are more impulsive than Type I flares. Third, for late-phase flares, the peak intensity ratio of the late phase to the main phase is roughly correlated with the flare class, and the flares with a strong late phase are all confined. We believe that the re-deposition of the energy carried by a flux rope, that unsuccessfully erupts out, into thermal emissions is responsible for the strong late phase found in a confined flare. Besides, with some cases we illustrate the signatures of the flare thermodynamic process in the chromosphere and transition region in TDS charts. These results provide new clues to advance our understanding of the thermodynamic processes of solar flares and associated solar eruptions, e.g., coronal mass ejections., Comment: Submitted to ApJS, 43 pages, 22 figures, 5 tables

Despite being the most prominent emission line in the solar spectrum, there has been a notable lack of studies devoted to variations in Ly$\alpha$ emission during solar flares in recent years. However, the few examples that do exist have shown Ly$\alpha$ emission to be a substantial radiator of the total energy budget of solar flares (on the order of 10%). It is also a known driver of fluctuations in earth's ionosphere. The EUV Variability Experiment (EVE) onboard the Solar Dynamics Observatory now provides broadband, photometric Ly$\alpha$ data at 10 s cadence with its Multiple EUV Grating Spectrograph-Photometer (MEGS-P) component, and has observed scores of solar flares in the 5 years since it was launched. However, the MEGS-P time profiles appear to display a rise time of tens of minutes around the time of the flare onset. This is in stark contrast to the rapid, impulsive increase observed in other intrinsically chromospheric features (H$\alpha$, Ly$\beta$, LyC, C III, etc.). Furthermore, the emission detected by MEGS-P peaks around the time of the peak of thermal soft X-ray emission, rather than during the impulsive phase when energy deposition in the chromosphere - often assumed to be in the form of nonthermal electrons - is greatest. Given that spectrally-resolved Ly$\alpha$ observations during flares from SORCE/SOLSTICE peak during the impulsive phase as expected, this suggests that the atypical behaviour of MEGS-P data is a manifestation of the broadband nature of the observations. This could imply that other lines and/or continuum emission that becomes enhanced during flares could be contributing to the passband. Users are hereby urged to exercise caution when interpreting broadband Ly$\alpha$ observations of solar flares. Comparisons have also been made with other broadband Ly$\alpha$ photometers such as PROBA2/LYRA and GOES/EUVS-E., Comment: Submitted to A&A Research Notes, 5 pages 4 figures

This paper presents measurements of the energy radiated by the lower solar atmosphere, at optical, UV, and EUV wavelengths, during an X-class solar flare (SOL2011-02-15T01:56) in response to an injection of energy assumed to be in the form of nonthermal electrons. Hard X-ray observations from RHESSI were used to track the evolution of the parameters of the nonthermal electron distribution to reveal the total power contained in flare accelerated electrons. By integrating over the duration of the impulsive phase, the total energy contained in the nonthermal electrons was found to be $>2\times10^{31}$ erg. The response of the lower solar atmosphere was measured in the free-bound EUV continua of H I (Lyman), He I, and He II, plus the emission lines of He II at 304\AA\ and H I (Ly$\alpha$) at 1216\AA\ by SDO/EVE, the UV continua at 1600\AA\ and 1700\AA\ by SDO/AIA, and the WL continuum at 4504\AA, 5550\AA, and 6684\AA, along with the Ca II H line at 3968\AA\ using Hinode/SOT. The summed energy detected by these instruments amounted to $\sim3\times10^{30}$ erg; about 15% of the total nonthermal energy. The Ly$\alpha$ line was found to dominate the measured radiative losses. Parameters of both the driving electron distribution and the resulting chromospheric response are presented in detail to encourage the numerical modelling of flare heating for this event, to determine the depth of the solar atmosphere at which these line and continuum processes originate, and the mechanism(s) responsible for their generation., Comment: 14 pages, 18 figures. Accepted for publication in Astrophysics Journal

In this paper, the cooling of 72 M- and X-class flares is examined using GOES/XRS and SDO/EVE. The observed cooling rates are quantified and the observed total cooling times are compared to the predictions of an analytical 0-D hydrodynamic model. It is found that the model does not fit the observations well, but does provide a well defined lower limit on a flare's total cooling time. The discrepancy between observations and the model is then assumed to be primarily due to heating during the decay phase. The decay phase heating necessary to account for the discrepancy is quantified and found be ~50% of the total thermally radiated energy as calculated with GOES. This decay phase heating is found to scale with the observed peak thermal energy. It is predicted that approximating the total thermal energy from the peak is minimally affected by the decay phase heating in small flares. However, in the most energetic flares the decay phase heating inferred from the model can be several times greater than the peak thermal energy., Comment: Published in the Astrophysical Journal, 2013

We present the lessons learned about the degradation observed in several space solar missions, based on contributions at the Workshop about On-Orbit Degradation of Solar and Space Weather Instruments that took place at the Solar Terrestrial Centre of Excellence (Royal Observatory of Belgium) in Brussels on 3 May 2012. The aim of this workshop was to open discussions related to the degradation observed in Sun-observing instruments exposed to the effects of the space environment. This article summarizes the various lessons learned and offers recommendations to reduce or correct expected degradation with the goal of increasing the useful lifespan of future and ongoing space missions.

We have evaluated the energetics of 38 solar eruptive events observed by a variety of spacecraft instruments between February 2002 and December 2006, as accurately as the observations allow. The measured energetic components include: (1) the radiated energy in the GOES 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 (nonpotential) 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.

Observations of extreme-ultraviolet (EUV) emission from an X-class solar flare that occurred on 2011 February 15 at 01:44 UT are presented, obtained using the EUV Variability Experiment (EVE) onboard the Solar Dynamics Observatory. The complete EVE spectral range covers the free-bound continua of H I (Lyman continuum), He I, and He II, with recombination edges at 91.2, 50.4, and 22.8 nm, respectively. By fitting the wavelength ranges blue-ward of each recombination edge with an exponential function, lightcurves of each of the integrated continua were generated over the course of the flare, as well as emission from the free-free continuum (6.5-37 nm). The He II 30.4 nm and Lyman-alpha 121.6 nm lines, and soft X-ray (0.1-0.8 nm) emission from GOES are also included for comparison. Each free-bound continuum was found to have a rapid rise phase at the flare onset similar to that seen in the 25-50 keV lightcurves from RHESSI, suggesting that they were formed by recombination with free electrons in the chromosphere. However, the free-free emission exhibited a slower rise phase seen also in the soft X-ray emission from GOES, implying a predominantly coronal origin. By integrating over the entire flare the total energy emitted via each process was determined. We find that the flare energy in the EVE spectral range amounts to at most a few per cent of the total flare energy, but EVE gives us a first comprehensive look at these diagnostically important continuum components., Comment: 6 pages, 3 figures, 1 table. Accepted to ApJ Letters

Solar extreme ultraviolet (EUV; 10-120 nm) and soft X-ray (XUV; 0-10 nm) radiation are major heat sources for the Mars thermosphere as well as the primary source of ionization that creates the ionosphere. In investigations of Mars thermospheric chemistry and dynamics, solar irradiance models are used to account for variations in this radiation. Because of limited proxies, irradiance models do a poor job of tracking the significant variations in irradiance intensity in the EUV and XUV ranges over solar rotation time scales when the Mars-Sun-Earth angle is large. Recent results from Earth observations show that variations in photoelectron energy spectra are useful monitors of EUV and XUV irradiance variability. Here we investigate photoelectron energy spectra observed by the Mars Global Surveyor (MGS) Electron Reflectometer (ER) and the FAST satellite during the interval in 2005 when Earth, Mars, and the Sun were aligned. The Earth photoelectron data in selected bands correlate well with calculations based on 1 nm resolution observations above 27 nm supplemented by broadband observations and a solar model in the 0-27 nm range. At Mars, we find that instrumental and orbital limitations to the identifications of photoelectron energy spectra in MGS/ER data preclude their use as a monitor of solar EUV and XUV variability. However, observations with higher temporal and energy resolution obtained at lower altitudes on Mars might allow the separation of the solar wind and ionospheric components of electron energy spectra so that they could be used as reliable monitors of variations in solar EUV and XUV irradiance than the time shifted, Earth-based, F(10.7) index currently used.

This paper describes the methods used to obtain the thermal evolution and radiative output during solar flares as observed by the Extreme u ltraviolet Variability Experiment (EVE) onboard the Solar Dynamics Ob servatory (SDO). Presented and discussed in detail are how EVE measur ements, due to its temporal cadence, spectral resolution and spectral range, can be used to determine how the thermal plasma radiates at v arious temperatures throughout the impulsive and gradual phase of fla res. EVE can very accurately determine the radiative output of flares due to pre- and in-flight calibrations. Events are presented that sh ow the total radiated output of flares depends more on the flare duration than the typical GOES X-ray peak magnitude classification. With S DO observing every flare throughout its entire duration and over a la rge temperature range, new insights into flare heating and cooling as well as the radiative energy release in EUV wavelengths support exis ting research into understanding the evolution of solar flares.

We have evaluated the energetics of the larger solar eruptive events recorded with a variety of spacecraft instruments between February 2002 and December 2006. All of the energetically important components of the flares and of the accompanying coronal mass ejections and solar energetic particles have been evaluated as accurately as the observations allow. These components include the following : (1) the total energy in the high temperature plasma determined from the RHESSI thermal X-ray observations; (2) the total energies in accelerated electrons above 20 keV and ions above 1 MeV from RHESSI hard X-ray and gamma-ray observations, respectively; (3) the potential and kinetic energies of the CME from SOHO/LASCO observations; (4) the solar energetic particle (SEP) energy estimates from in situ measurements on ACE, GOES, and SOHO; (5) the total radiated energy from the SORCEITSI measurements where available, and otherwise from the Flare Irradiance Spectral Model (FISM). The results are assimilated and discussed relative to the probable amount of non potential magnetic energy estimated to be available in the flaring active regions from MDI line-of-sight magnetograms.

We have evaluated the energetics of 38 solar eruptive events observed by a variety of spacecraft instruments between February 2002 and December 2006, as accurately as the observations allow. The measured energetic components include: (1) the radiated energy in the GOES 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 are-accelerated electrons above 20 keV and in ions above 1 MeV; (6) the kinetic and potential energies of the coronal mass ejection (CME); (7) the energy in solar energetic particles (SEPs); and (8) the amount of free (nonpotential) 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 are-accelerated electrons and ions is sufficient to supply the bolometric energy radiated across all wavelengths throughout the event; (3) the energy contents of are-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 are-accelerated particles, and the hot thermal plasma.

The solar photon output, which was once thought to be constant, varies over all time scales from seconds during solar flares to years due to the solar cycle. These solar variations cause significant deviations in the Earth and space environments on similar time scales, such as affecting the atmospheric densities and composition of particular atoms, molecules, and ions in the atmospheres of the Earth and other planets. Presented and discussed will be examples of unprecedented observations from NASA's new solar observatory, the Solar Dynamics Observatory (SDO). Using three specialized instruments, SDO measures the origins of solar activity from inside the Sun, though its atmosphere, then accurately measuring the Sun's radiative output in X-ray and EUV wavelengths (0.1-121 nm). Along with the visually appealing observations will be discussions of what these measurements can tell us about how the plasma motions in all layers of the Sun modifies and strengthens the weak solar dipole magnetic field to drive large energy releases in solar eruptions. Also presented will be examples of how the release of the Sun's energy, in the form of photons and high energy particles, physically influence other bodies in the solar system such as Earth, Mars, and the Moon, and how these changes drive changes in the technology that we are becoming dependent upon. The presentation will continuously emphasize how SDO, the first satellite in NASA's Living with a Star program, improving our understanding of the variable Sun and its Heliospheric influence.

The NASA Solar Dynamics Observatory (SDO), scheduled for launch in early 2010, incorporates a suite of instruments including the Extreme Ultraviolet Variability Experiment (EVE). EVE has multiple instruments including the Multiple Extreme ultraviolet Grating Spectrographs (MEGS) A, B, and P instruments, the Solar Aspect Monitor (SAM), and the Extreme ultraviolet SpectroPhotometer (ESP). The radiometric calibration of EVE, necessary to convert the instrument counts to physical units, was performed at the National Institute of Standards and Technology (NIST) Synchrotron Ultraviolet Radiation Facility (SURF III) located in Gaithersburg, Maryland. This paper presents the results and derived accuracy of this radiometric calibration for the MEGS A, B, P, and SAM instruments, while the calibration of the ESP instrument is addressed by Didkovsky et al. . In addition, solar measurements that were taken on 14 April 2008, during the NASA 36.240 sounding-rocket flight, are shown for the prototype EVE instruments.