19 research outputs found
A time dependent relation between EUV solar flare light-curves from lines with differing formation temperatures
Extreme ultraviolet (EUV) solar flare emissions evolve in time as the
emitting plasma heats and then cools. Although accurately modeling this
evolution has been historically difficult, especially for empirical
relationships, it is important for understanding processes at the Sun, as well
as for their influence on planetary atmospheres. With a goal to improve
empirical flare models, a new simple empirical expression is derived to predict
how cool emissions will evolve based on the evolution of a hotter emission.
This technique is initially developed by studying 12 flares in detail observed
by the EUV Variability Experiment (EVE) onboard the Solar Dynamics Observatory
(SDO). Then, over 1100 flares observed by EVE are analyzed to validate these
relationships. The Cargill and Enthalpy Based Thermal Evolution of Loops
(EBTEL) flare cooling models are used to show that this empirical relationship
implies the energy radiated by a population of hotter formed ions is
approximately proportional to the energy exciting a population of cooler formed
ions emitting when the peak formation temperatures of the two lines are up to
72% of each other and above 2 MK. These results have practical implications for
improving flare irradiance empirical modeling and for identifying key emission
lines for future monitoring of flares for space weather operations; and also
provide insight into the cooling processes of flare plasma.Comment: Final version accepted for publication by the Journal of Space
Weather and Space Climate on 23 November 201
Low Electron Temperatures Observed at Mars by MAVEN on Dayside Crustal Magnetic Field Lines
An edited version of this paper was published by AGU. Copyright 2019 American Geophysical Union.The ionospheric electron temperature is important for determining the neutral/photochemical escape rate from the Martian atmosphere via the dissociative recombination of O2+. The Langmuir Probe and Waves instrument onboard MAVEN (Mars Atmosphere and Volatile EvolutioN) measures electron temperatures in the ionosphere. The current paper studies electron temperatures in the dayside for two regions where (1) crustal magnetic fields are dominant and (2) draped magnetic fields are dominant. Overall, the electron temperature is lower in the crustalâfield regions, namely, the strong magnetic field region, which is due to a transport of cold electrons along magnetic field lines from the lower to upper atmosphere. The electron temperature is also greater for high solar extreme ultraviolet conditions, which is associated with the local extreme ultraviolet energy deposition. The current models underestimate the electron temperature above 250âkm altitude in the crustalâfield region. Electron heat conduction associated with a photoelectron transport in the crustalâfield regions is altered due to kinetic effects, such the magnetic mirror and/or ambipolar electric field because the electron mean free path exceeds the relevant length scale for electron temperature. The mirror force can affect the electron and heat transport between low altitudes, where the neutral density and related electron cooling rates are the greatest, and high altitudes, while the ambipolar electric field decelerates the electron's upward motion. These effects have not been included in current models of the electron energetics, and consideration of such effects on the electron temperature in the crustalâfield region should be considered for future numerical simulations
Model insights into energetic photoelectrons measured at Mars by MAVEN
Photoelectrons are important for heating, ionization, and airglow production in planetary atmospheres. Measured electron fluxes provide insight into the sources and sinks of energy in the Martian upper atmosphere. The Solar Wind Electron Analyzer instrument on board the MAVEN (Mars Atmosphere and Volatile EvolutioN) spacecraft measured photoelectrons including Auger electrons with 500âeV energies. A two-stream electron transport code was used to interpret the observations, including Auger electrons associated with K shell ionization of carbon, oxygen, and nitrogen. It explains the processes that control the photoelectron spectrum, such as the solar irradiance at different wavelengths, external electron fluxes from the Martian magnetosheath or tail, and the structure of the upper atmosphere (e.g., the thermal electron density). Our understanding of the complex processes related to the conversion of solar irradiances to thermal energy in the Martian ionosphere will be advanced by model comparisons with measurements of suprathermal electrons by MAVEN
Small Platforms, High Return: The Need to Enhance Investment in Small Satellites for Focused Science, Career Development, and Improved Equity
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 figur
A time dependent relation between EUV solar flare light-curves from lines with differing formation temperatures
Extreme ultraviolet (EUV) solar flare emissions evolve in time as the emitting plasma heats and then cools. Although accurately modeling this evolution has been historically difficult, especially for empirical relationships, it is important for understanding processes at the Sun, as well as for their influence on planetary atmospheres. With a goal to improve empirical flare models, a new simple empirical expression is derived to predict how cool emissions evolve based on the evolution of a hotter emission. This technique is initially developed by studying 12 flares in detail observed by the EUV variability experiment (EVE) onboard the Solar Dynamics Observatory (SDO). Then, over 1100 flares observed by EVE are analyzed to validate these relationships. The Cargill and Enthalpy Based Thermal Evolution of Loops (EBTEL) flare cooling models are used to show that this empirical relationship implies the energy radiated by a population of hotter formed ions is approximately proportional to the energy exciting a population of cooler formed ions emitting when the peak formation temperatures of the two lines are up to 72% of each other and above 2âMK. These results have practical implications for improving flare irradiance empirical modeling and for identifying key emission lines for future monitoring of flares for space weather operations; and also provide insight into the cooling processes of flare plasma
The MAVEN EUVM model of solar spectral irradiance variability at Mars: Algorithms and results
Solar extreme ultraviolet (EUV) radiation is a primary energy input to the Mars atmosphere, causing ionization and driving photochemical processes above approximately 100Â km. Because solar EUV radiation varies with wavelength and time, measurements must be spectrally resolved to accurately quantify its impact on the Mars atmosphere. The Mars Atmosphere and Volatile EvolutioN (MAVEN) EUV Monitor (EUVM) measures solar EUV irradiance incident on the Mars atmosphere in three bands. These three bands drive a spectral irradiance variability model called the Flare Irradiance Spectral Model (FISM)âMars (FISMâM) which is an iteration of the FISM model by Chamberlin et al. (2007, 2008) for spectral irradiance at Earth. In this paper, we report the algorithms used to derive FISMâM and its associated uncertainties, focusing on differences from the original FISM. FISMâM spectrally resolves the solar EUV irradiance at Mars from 0.5 to 189.5Â nm at 1min cadence, and 0.1Â nm resolution in the 6â106Â nm range or 1Â nm resolution otherwise. FISMâM is suitable for both daily average and flaring spectral irradiance estimates and is based on the linear association of the broadband EUVM measurements with spectral irradiance measurements, including recent high time cadence 0.1Â nm resolution measurements from the EUV Variability Experiment (EVE) on the Space Dynamics Observatory (SDO) between 6 and 106Â nm. In addition, we present examples of model outputs for EUV irradiance variability due to solar flares, solar rotations, Mars orbit eccentricity, and the solar cycle, between October 2015 and November 2016.Key PointsA new algorithm specifies variations of solar EUV irradiance at Mars with typical relative uncertainties near 5%Daily average and flare irradiances are derived from SDO EVE measurements from 6 to 106Â nmExamples of EUV variability for the MAVEN primary mission are presentedPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/136701/1/jgra53381.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/136701/2/jgra53381_am.pd