Amir Caspi

Amir Caspi
Southwest Research Institute · Planetary Science Directorate

PhD

About

141
Publications
21,370
Reads
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1,743
Citations
Additional affiliations
October 2016 - October 2019
Southwest Research Institute
Position
  • Senior Research Scientist
November 2014 - October 2016
Southwest Research Institute
Position
  • Research Scientist
July 2011 - November 2014
University of Colorado Boulder
Position
  • Research Associate
Education
August 2001 - May 2010
August 2001 - May 2010
August 1996 - May 2001

Publications

Publications (141)
Article
Full-text available
We present a new analytical technique, combining Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) high-resolution imaging and spectroscopic observations, to visualize solar flare emission as a function of spectral component (e.g., isothermal temperature) rather than energy. This computationally inexpensive technique is applicable to al...
Article
Full-text available
The solar corona is orders of magnitude hotter than the underlying photosphere, but how the corona attains such high temperatures is still not understood. Soft X-ray (SXR) emission provides important diagnostics for thermal processes in the high-temperature corona, and is also an important driver of ionospheric dynamics at Earth. There is a crucial...
Article
Full-text available
Deriving a well-constrained differential emission measure (DEM) distribution for solar flares has historically been difficult, primarily because no single instrument is sensitive to the full range of coronal temperatures observed in flares, from 2 to 50 MK. We present a new technique, combining extreme ultraviolet (EUV) spectra from the EUV Variabi...
Article
Full-text available
We use Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) high-resolution imaging and spectroscopy observations from ~6 to 100 keV to determine the statistical relationships between measured parameters (temperature, emission measure, etc.) of hot, thermal plasma in 37 intense (GOES M- and X-class) solar flares. The RHESSI data, most sens...
Article
Full-text available
We use RHESSI high-resolution imaging and spectroscopy observations from ~5 to 100 keV to characterize the hot thermal plasma during the 2002 July 23 X4.8 flare. These measurements of the steeply falling thermal X-ray continuum are well fit throughout the flare by two distinct isothermal components: a super-hot (T > 30 MK) component that peaks at ~...
Preprint
Full-text available
The middle corona, the region roughly spanning heliocentric altitudes from $1.5$ to $6\,R_\odot$, encompasses almost all of the influential physical transitions and processes that govern the behavior of coronal outflow into the heliosphere. Eruptions that could disrupt the near-Earth environment propagate through it. Importantly, it modulates inflo...
Article
Full-text available
Electron ring velocity space distributions have previously been seen in numerical simulations of magnetic reconnection exhausts and have been suggested to be caused by the magnetization of the electron outflow jet by the compressed reconnected magnetic fields (Shuster et al., 2014, https://doi.org/10.1002/2014GL060608). We present a theory of the d...
Preprint
Electron ring velocity space distributions have previously been seen in numerical simulations of magnetic reconnection exhausts and have been suggested to be caused by the magnetization of the electron outflow jet by the compressed reconnected magnetic fields [Shuster et al., ${\it Geophys.~Res.~Lett.}, {\bf 41}$, 5389 (2014)]. We present a theory...
Article
Full-text available
When the first CubeSats were launched nearly two decades ago, few people believed that the miniature satellites would likely prove to be a useful scientific tool. Skeptics abounded. However, the last decade has seen the highly successful implementation of space missions that make creative and innovative use of fast-advancing CubeSat and small satel...
Article
Full-text available
We conduct a wide-band X-ray spectral analysis in the energy range of 1.5–100 keV to study the time evolution of the M7.6-class flare of 2016 July 23, with the Miniature X-ray Solar Spectrometer (MinXSS) CubeSat and the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) spacecraft. With the combination of MinXSS for soft X-rays and RHESS...
Preprint
Full-text available
We conduct a wide-band X-ray spectral analysis in the energy range of 1.5-100 keV to study the time evolution of the M7.6 class flare of 2016 July 23, with the Miniature X-ray Solar Spectrometer (MinXSS) CubeSat and the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) spacecraft. With the combination of MinXSS for soft X-rays and RHESS...
Article
Full-text available
Plain Language Summary Critical technology for satellites and scientific detectors has recently been miniaturized and become commercially available. This has made small satellites (collectively called SmallSats, which includes CubeSats) attractive as low‐cost solutions for research into space weather and, potentially, for future forecasting and eva...
Preprint
Full-text available
Recent advances in miniaturization and commercial availability of critical satellite subsystems and detector technology have made small satellites (SmallSats, including CubeSats) an attractive, low-cost potential solution for space weather research and operational needs. Motivated by the 1st International Workshop on SmallSats for Space Weather Res...
Article
Full-text available
The ‘middle corona’ is a critical transition between the highly disparate physical regimes of the lower and outer solar coronae. Nonetheless, it remains poorly understood due to the difficulty of observing this faint region (1.5–3 R☉). New observations from the Solar Ultraviolet Imager of a Geostationary Operational Environmental Satellite in Augus...
Preprint
Full-text available
The "middle corona" is a critical transition between the highly disparate physical regimes of the lower and outer solar corona. Nonetheless, it remains poorly understood due to the difficulty of observing this faint region (1.5-3 solar radii). New observations from the GOES Solar Ultraviolet Imager in August and September 2018 provide the first com...
Article
Full-text available
Gaps in space weather observations that can be addressed with small satellites are identified. Potential improvements in solar inputs to space weather models, space radiation control, estimations of energy budget of the upper Earth’s atmosphere, and satellite drag modeling are briefly discussed. Key observables, instruments and observation strategi...
Article
Full-text available
We describe a new algorithm for reconstruction of Differential Emission Measures (DEMs) in the solar corona. Although a number of such algorithms currently exist, they can have difficulty converging for some cases, and can be complex, slow, or idiosyncratic in their output (i.e., their inversions can have features that are a result of the inversion...
Preprint
Full-text available
Gaps in space weather observations that can be addressed with small satellites are identified. Potential improvements in solar inputs to space weather models, space radiation control, estimations of energy budget of the upper Earth's atmosphere, and satellite drag modeling are briefly discussed. Key observables, instruments and observation strategi...
Article
Full-text available
Advances in space weather science and small satellite (SmallSat) technology have proceeded in parallel over the past two decades, but better communication and coordination are needed among the respective worldwide communities contributing to this rapid progress. We identify six areas where improved international coordination is especially desirable...
Article
Full-text available
The Dual-zone Aperture X-ray Solar Spectrometer (DAXSS) was flown on 2018 June18 on the NASA 36.336 sounding rocket flight and obtained the highest resolution to date for solar soft X-ray (SXR) spectra over a broad energy range. This observation was during a time with quiescent (non-flaring) small active regions on the solar disk and when the 10.7...
Preprint
Full-text available
The Dual-zone Aperture X-ray Solar Spectrometer (DAXSS) was flown on 2018 June18 on the NASA 36.336 sounding rocket flight and obtained the highest resolution to date for solar soft X-ray (SXR) spectra over a broad energy range. This observation was during a time with quiescent (non-flaring) small active regions on the solar disk and when the 10.7...
Preprint
Full-text available
Advances in space weather science and small satellite (SmallSat) technology have proceeded in parallel over the past two decades, but better communication and coordination is needed among the respective worldwide communities contributing to this rapid progress. We identify six areas where improved international coordination is especially desirable,...
Article
Full-text available
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...
Preprint
Full-text available
We describe a new algorithm for reconstruction of Differential Emission Measures (DEMs) in the solar corona. Although a number of such algorithms currently exist, they can have difficulty converging for some cases, and can be complex, slow, or idiosyncratic in their output (i.e., their inversions can have features that are a result of the inversion...
Article
Full-text available
NASA's WB-57 High Altitude Research Program provides a deployable, mobile, stratospheric platform for scientific research. Airborne platforms are of particular value for making coronal observations during total solar eclipses because of their ability both to follow the Moon's shadow and to get above most of the atmospheric airmass that can interfer...
Preprint
Full-text available
NASA's WB-57 High Altitude Research Program provides a deployable, mobile, stratospheric platform for scientific research. Airborne platforms are of particular value for making coronal observations during total solar eclipses because of their ability both to follow the Moon's shadow and to get above most of the atmospheric airmass that can interfer...
Article
Full-text available
We present the results from four stellar occultations by (486958) Arrokoth, the flyby target of the New Horizons extended mission. Three of the four efforts led to positive detections of the body, and all constrained the presence of rings and other debris, finding none. Twenty-five mobile stations were deployed for 2017 June 3 and augmented by fixe...
Preprint
Full-text available
We present the results from four stellar occultations by (486958) Arrokoth, the flyby target of the New Horizons extended mission. Three of the four efforts led to positive detections of the body, and all constrained the presence of rings and other debris, finding none. Twenty-five mobile stations were deployed for 2017 June 3 and augmented by fixe...
Article
Full-text available
We investigate the global energetics and energy closure of various physical processes that are energetically important in solar flares and coronal mass ejections (CMEs), which includes: magnetic energies, thermal energies, nonthermal energies (particle acceleration), direct and indirect plasma heating processes, kinetic CME energies, gravitational...
Article
Full-text available
Solar flare X-ray spectra are typically dominated by thermal bremsstrahlung emission in the soft X-ray (≲10 keV) energy range; for hard X-ray energies (≳30 keV), emission is typically non-thermal from beams of electrons. The low-energy extent of non-thermal emission has only been loosely quantified. It has been difficult to obtain a lower limit for...
Preprint
Full-text available
We present the Spectroscopic Time-Resolving Observatory for Broadband Energy X-rays (STROBE-X), a probe-class mission concept selected for study by NASA. It combines huge collecting area, high throughput, broad energy coverage, and excellent spectral and temporal resolution in a single facility. STROBE-X offers an enormous increase in sensitivity f...
Preprint
Full-text available
Solar flare X-ray spectra are typically dominated by thermal bremsstrahlung emission in the soft X-ray (≲10 keV) energy range; for hard X-ray energies (≳30 keV), emission is typically non-thermal from beams of electrons. The low-energy extent of non-thermal emission has only been loosely quantified. It has been difficult to obtain a lower limit for...
Article
Full-text available
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 t...
Presentation
Detection of soft X-rays (sxr) from the Sun provide direct information on coronal plasma at temperatures in excess of ~1 MK, but there have been relatively few solar spectrally resolved measurements from 0.5 – 10. keV. The Miniature X-ray Solar Spectrometer (MinXSS) CubeSat is the first solar science oriented CubeSat mission flown for the NASA Scie...
Article
Full-text available
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...
Presentation
Full-text available
We present FOXSI (Focusing Optics X-ray Solar Imager), a Small Explorer (SMEX) Heliophysics mission that is currently undergoing a Phase A concept study. FOXSI will provide a revolutionary new perspective on energy release and particle acceleration on the Sun. FOXSI is a direct imaging X-ray spectrometer with higher dynamic range and better than 10...
Presentation
Full-text available
While there have been significant advances in our understanding of impulsive energy release at the Sun since the advent of RHESSI observations, there is a clear need for new X-ray observations that can capture the full range of emission in flares (e.g., faint coronal sources near bright chromospheric sources), follow the intricate evolution of ener...
Presentation
Full-text available
Total solar eclipses present rare opportunities to study the complex solar corona, down to altitudes of just a few percent of a solar radius above the surface, using ground-based and airborne observatories that would otherwise be dominated by the intense solar disk and high sky brightness. Studying the corona is critical to gaining a better underst...
Poster
Full-text available
The Great American Eclipse of 2017 provided an excellent opportunity for heliophysics research on the solar corona and dynamics that encompassed a large number of research groups and projects, including projects flown in the air and in space. Two NASA WB-57F Canberra high altitude research aircraft were launched from NASA’s Johnson Space Center, El...
Article
Full-text available
We present the first results of a search for transient hard X-ray (HXR) emission in the quiet solar corona with the Nuclear Spectroscopic Telescope Array (NuSTAR) satellite. While NuSTAR was designed as an astrophysics mission, it can observe the Sun above 2 keV with unprecedented sensitivity due to its pioneering use of focusing optics. NuSTAR fir...
Presentation
Full-text available
Solar soft X-ray (SXR) observations provide important diagnostics of plasma heating, during solar flares and quiescent times. Spectrally- and temporally-resolved measurements are crucial for understanding the dynamics, origins, and evolution of these energetic processes, providing probes both into the temperature distributions and elemental composi...
Poster
Full-text available
Total solar eclipses present rare opportunities to study the complex solar corona, down to altitudes of just a few percent of a solar radius above the surface, using ground-based and airborne observatories that would otherwise be dominated by the intense solar disk and high sky brightness. Studying the corona is critical to gaining a better underst...
Article
Full-text available
In this study we synthesize the results of four previous studies on the global energetics of solar flares and associated coronal mass ejections (CMEs), which include magnetic, thermal, nonthermal, and CME energies in 399 solar M and X-class flare events observed during the first 3.5 years of the Solar Dynamics Observatory (SDO) mission. Our finding...
Article
Full-text available
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 to 10 keV) can vary by more than a factor of...
Technical Report
Full-text available
Decades of astrophysical observations have convincingly shown that soft X-ray (SXR; ~0.1– 10 keV) emission provides unique diagnostics for the high temperature plasmas observed in solar flares and active regions. SXR observations critical for constraining models of energy release in these phenomena can be provided using instruments that have alread...
Technical Report
Full-text available
How impulsive magnetic energy release leads to solar eruptions and how those eruptions are energized and evolve are vital unsolved problems in Heliophysics. The standard model for solar eruptions summarizes our current understanding of these events. Magnetic energy in the corona is released through drastic restructuring of the magnetic field via re...
Technical Report
Full-text available
Even in the absence of resolved flares, the corona is heated to several million degrees. However, despite its importance for the structure, dynamics, and evolution of the solar atmosphere, the origin of this heating remains poorly understood. Several observational and theoretical considerations suggest that the heating is driven by small, impulsive...
Presentation
Full-text available
The balloon-borne Gamma-Ray Imager/Polarimeter for Solar flares (GRIPS) instrument flew over Antarctica in January 2016 to study particle acceleration and energy release at the Sun. GRIPS is designed to provide a near-optimal combination of high-resolution imaging, spectroscopy, and polarimetry of solar-flare gamma-ray/hard X-ray emissions from ~20...
Poster
Full-text available
The Miniature X-ray Solar Spectrometer (MinXSS) CubeSat (Mason et al., 2016) was deployed from the International Space Station on 2016 May 16 and has been taking routine soft x-ray (SXR) measurements of the sun since 2016 June 9. Since that time, >386 flares have occurred (see histogram). Using the methods outlined in Woods, et al. (2016), we can e...
Poster
Full-text available
Solar flares explosively release large amounts of magnetic energy, a significant fraction of which goes into transient heating of coronal plasma to temperatures up to tens of MK. Decades of observations have shown that flares are multi-thermal, exhibiting broad temperature distributions or "differential emission measures" (DEMs). Recent studies sug...
Poster
Full-text available
We combine observations of solar flares from the EUV Variability Experiment (EVE) on-board the Solar Dynamics Observatory (SDO) with X-ray data from the Reuven Ramaty High Energy Spectroscopic Imager (RHESSI) to calculate the Differential Emission Measure (DEM). This improvement over the isothermal approximation is intended to help to resolve ambig...
Poster
Full-text available
We present FOXSI (Focusing Optics X-ray Solar Imager), a recently proposed Small Explorer (SMEX) mission that will provide a revolutionary new perspective on energy release and particle acceleration on the Sun. FOXSI is a direct imaging X-ray spectrometer with higher dynamic range and better than 10x the sensitivity of previous instruments. Flown o...
Presentation
Soft X-rays serve as an important diagnostic tool for hot (T > 10^6 K) solar coronal plasma elemental composition, elemental ionization states, density of emitting plasma and dynamical events triggered by magnetic field structures. Spectrally resolved, solar disc averaged, soft X-ray spectra from the Miniature X-ray Solar Spectrometer (MinXSS) Cube...
Poster
Full-text available
There are four decades of broadband soft X-ray (SXR) measurements, but these measurements cannot directly quantify the varying contributions of emission lines (bound-bound) amongst the thermal radiative recombination (free-bound) and thermal and non-thermal bremsstrahlung (free-free) continua. The Miniature X-ray Solar Spectrometer (MinXSS) CubeSat...