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At least 541 records · Page 30
All sourcesNASA NTRSDOE OSTI
NASA NTRS2016

A Series of Jets that Drove Streamer-Puff CMEs from Giant Active Region of 2014

We investigate characteristics of solar coronal jets that originated from active region NOAA 12192 and produced coronal mass ejections (CMEs). This active region produced many non­‐jet major flare eruptions (X and M class) that made no CME. A multitude of jets occurred from the southeast edge of the active region, and in contrast to the major-­flare eruptions in the core, six of these jets resulted in CMEs. Our jet observations are from SDO/AIA EUV channels and from Hinode/XRT, and CME observations are from the SOHO/LASCO C2 coronograph. Each jet-­driven CME was relatively slow-­moving (approx. 200 - 300 km/s) compared to most CMEs; had angular width (20deg - 50deg) comparable to that of the streamer base; and was of the "streamer­‐puff" variety, whereby a pre-existing streamer was transiently inflated but not removed (blown out) by the passage of the CME. Much of the chromospheric-­temperature plasma of the jets producing the CMEs escaped from the Sun, whereas relatively more of the chromospheric plasma in the non-CME-producing jets fell back to the solar surface. We also found that the CME-producing jets tended to be faster in speed and longer in duration than the non-CME-­producing jets. We expect that the jets result from eruptions of mini-filaments. We further propose that the CMEs are driven by magnetic twist injected into streamer-­base coronal loops when erupting twisted mini-filament field reconnects with the ambient field at the foot of those loops.

region↗
NASA NTRS2016

A Series of Jets that Drove Streamer-Puff CMEs from Giant Active Region of 2014

We investigate characteristics of solar coronal jets that originated from active region NOAA 12192 and produced coronal mass ejections (CMEs). This active region produced many non‐jet major flare eruptions (X and M class) that made no CME. A multiitude of jets occurred from the southeast edge of the active region, and in contrast to the major‐flare eruptions in the core, six of these jets resulted in CMEs. Our jet observations are from multiple SDO/AIA EUV channels, including 304, 171 and 193 Angstrom, and CME observations are taken from SOHO/LASCO C2 coronograph. Each jet‐driven CME was relatively slow‐moving (approximately 200 ‐ 300 km s(sup‐1) compared to most CMEs; had angular width (20deg - 50deg) comparable to that of the streamer base; and was of the "streamer‐puff" variety, whereby a preexisting streamer was transiently inflated but not removed (blown out) by the passage of the CME. Much of the chromospheric‐temperature plasma of the jets producing the CMEs escaped from the Sun, whereas relatively more of the chromospheric plasma in the non‐CME‐producing jets fell back to the solar surface. We also found that the CME‐producing jets tended to be faster in speed and longer in duration than the non‐CME‐producing jets. We expect that the jets result from eruptions of mini-filaments. We further propose that the CMEs are driven by magnetic twist injected into streamer‐base coronal loops when erupting twisted mini-filament field reconnects with the ambient field at the foot of those loops.

Jets↗
NASA NTRS1985

Broadening of looplike solar coronal transients

The broadening of the tops of nine outwardly expanding looplike coronal mass-ejection transients observed during 1973-1974 and 1980 has been examined. Five of the nine transients exhibit increased breadth with time (height); although the rates vary widely, no event shows an increase which can be fitted by a power-law form with a greater-than-linear increase with height. The breadth of four events decreases with height. When all nine events are considered together, the transient breadth with height is fitted with an expression h varies as R exp 0.48 with large scatter. In addition, measurements of the total observed loop length of the nine transients show that this length L varies as R exp 1.30. Both of these results are contrary to the predictions of one model of loop expulsion as a result of an assumed azimuthal magnetic field gradient. Finally, when combined with the facts that looplike mass ejections are usually associated with the occurrence of eruptive prominences, and that such mass ejections are generally accelerated through the corona, it is found that the observed variation of transient breadth with height contradicts some characteristics of self-similar fluid flow which have been ascribed to mass-ejection transients.

Macqueen, R. M.↗
NASA NTRS2010

Relation Between Type II Bursts and CMEs Inferred from STEREO Observations

The inner coronagraph (COR1) of the Solar Terrestrial Relations Observatory (STEREO) mission has made it possible to observe coronal mass ejections (CMEs) a in the spatial domain overlapping with that of the metric type II radio bursts. The type II bursts were associated with generally weak flares (mostly B and C class soft X-ray flares), but the CMEs were quite energetic. Using CME data for a set of type II bursts during the declining phase of solar cycle 23, we determine the CME height when the type II bursts start, thus giving an estimate of the heliocentric distance at which CME-driven shocks form. This distance has been determined to be approximately 1.5Rs (solar radii), which coincides with the distance at which the Alfv?n speed profile has a minimum value. We also use type II radio observations from STEREO/WAVES and Wind/WAVES observations to show that CMEs with moderate speed drive either weak shocks or no shock at all when they attain a height where the Alfv?n speed peaks (?3Rs ? 4Rs). Thus the shocks seem to be most efficient in accelerating electrons in the heliocentric distance range of 1.5Rs to 4Rs. By combining the radial variation of the CME speed in the inner corona (CME speed increase) and interplanetary medium (speed decrease) we were able to correctly account for the deviations from the universal drift-rate spectrum of type II bursts, thus confirming the close physical connection between type II bursts and CMEs. The average height (approximately 1.5 Rs) of STEREO CMEs at the time of type II bursts is smaller than that (2.2 Rs) obtained for SOHO (Solar and Heliospheric Observatory) CMEs. We suggest that this may indicate, at least partly, the density reduction in the corona between the maximum and declining phases, so a given plasma level occurs closer to the Sun in the latter phase. In two cases, there was a diffuse shock-like feature ahead of the main body of the CME, indicating a standoff distance of 1Rs - 2Rs by the time the CME left the LASCO field of view.

Gopalswamy, N.↗
NASA NTRS2002

Satellite Observations of Solar Irradiance and Sun-Climate Impacts

Solar activity is now near its maximum, with events such as the 2001 "Bastille Day Event", a Coronal Mass Ejection which merited a full session at AGUs annual meeting - and two major sunspot groupings earlier this year, with associated variations in TSI (Total Solar Irradiance). We discuss recent satellite measurements of TSI by ACRIM 2 and 3 and Virgo, and new precision observations of TSI and SSI (Solar Spectral Irradiance) expected from the SORCE mission, planned to launch in fall 2002. SSI has been added to TSI as a required EOS and NPOESS measurement because different spectral components provide energy inputs to different components of the climate system - UV into upper atmosphere and ozone, IR into lower atmosphere and clouds, and Visible into the biosphere. Succeeding satellite missions being planned for 2006 and 2010 will continue to monitor both TSI and SSI. We summarize current ideas about the potential impact of solar variability on Earth's climate on time scales from days to decades to centuries.

Cahalan, Robert↗
DOE OSTI2020

Superthermal Electron Deposition on the Mars Nightside During ICMEs

Superthermal electron precipitation is one of the main sources supporting the Mars nightside ionosphere. It is expected that solar wind electron fluxes are to increase significantly during interplanetary coronal mass ejections (ICMEs) and therefore an enhanced nightside ionospheric density. This study is to quantify the variation of the precipitating and deposited electron fluxes during five extreme ICMEs encountered by Mars Global Surveyor (MGS). We find that energy fluxes correlate better with the upstream dynamic pressure proxy than number fluxes and electron fluxes increase more at high energies, which means that electrons tend to have a lower peak production altitude during storm times. The precipitating and net/deposited fluxes are increased up to an order of magnitude from low to high dynamic pressures. The estimated total electron content (TEC) is a few times of 10 14 m -2 for quiet times and on the order of 1015 m -2 for storm times, with an enhancement up to an order of magnitude locally near strong crustal fields. Crustal magnetic fields have an effect on the deposited fluxes with more prominent magnetic reflection over strong magnetic fields during quiet periods, which is significantly reduced during storm times. Lastly, we estimate a global energy input from downward fluxes of 1.1 × 10 8 and 5.5 × 10 8 W and the globally deposited energy from net fluxes of 2.0 × 10 7 and 1.6 × 10 8 W for quiet and storm time periods, a factor of 5 and 8 enhancement globally, respectively, but up to an order of magnitude locally near strong crustal fields.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1994

A new class of forward-reverse shock pairs in the solar wind

A new class of forward-reverse shock pairs in the solar wind has been discovered using Ulysses observations at high heliographic latitudes. These shock pairs are produced by expansion of coronal mass ejections, CMEs, that have internal pressures that are higher than, and speeds that are comparable to, that of the surrounding solar wind plasma. Of six certain CMEs observed poleward of S31 deg, three have associated shock pairs of this nature. We suggest that high internal CME pressures may exist primarily for events that have high speeds close to the surface of the Sun.

Gosling, J. T.↗
NASA NTRS2007

On the Origin of Near-Radial Magnetic Fields in the Heliosphere: Numerical Simulations

Deviations from the direction of the "Parker spiral" can be found in in situ measurements of the interplanetary magnetic field on essentially all scales. One intriguing subset is the intervals of near-radial magnetic field, lasting for many hours. Some such intervals are obviously associated with coronal mass ejections, while others appear to be embedded within the ambient solar wind. Most occur on declining speed profiles, such that, when mapped back to the Sun, an entire radial field interval appears to have been launched at approximately the same time. It has been proposed that these events are the result of abrupt, semipermanent speed decreases on these field lines close to the Sun, and that such speed changes might be due to interchange reconnection. In this study, we use a three-dimensional, time-dependent magnetohydrodynamic model to assess to what extent this can account for near-radial magnetic fields observed relatively far out in the heliosphere. We find that sudden speed drops on the trailing portions of high-speed flows can produce strongly underwound (that is near radial) field lines in the heliosphere, although significantly larger speed gradients are required than are typically observed. Moreover, the simulations also reproduce the decreases in density, temperature, and magnetic field strength that are also commonly observed within these events. The question of what produces the abrupt speed drops remains to be answered.

Mikic, Zoran↗
NASA NTRS2011

Geoeffectiveness (D (sub st) and K (sub p)) of Interplanetary Coronal Mass Ejections During 1995-2009 and Implications for Storm Forecasting

We summarize the geoeffectiveness (based on the Dst and Kp indices) of the more than 300 interplanetary coronal mass ejections (ICMEs) that passed the Earth during 1996-2009, encompassing solar cycle 23. We subsequently estimate the probability that an ICME will generate geomagnetic activity that exceeds certain thresholds of Dst or Kp, including the NOAA "G" storm scale, based on maximum values of the southward magnetic field component (Bs), the solar wind speed (V), and the y component (Ey) of the solar wind convective electric field E = -V x B, in the ICME or sheath ahead of the ICME. Consistent with previous studies, the geoeffectiveness of an ICME is correlated with Bs or Ey approx.= VBs in the ICME or sheath, indicating that observations from a solar wind monitor upstream of the Earth are likely to provide the most reliable forecasts of the activity associated with an approaching ICME. There is also a general increase in geoeffectiveness with ICME speed, though the overall event-to-event correlation is weaker than for Bs and Ey. Nevertheless, using these results, we suggest that the speed of an ICME approaching the Earth inferred, for example, from routine remote sensing by coronagraphs on spacecraft well separated from the Earth or by all-sky imagers, could be used to estimate the likely geoeffectiveness of the ICME (our "comprehensive" ICME database provides a proxy for ICMEs identified in this way) with a longer lead time than may be possible using an upstream monitor

Richardson, I. G.↗
NASA NTRS2009

Relation Between Type II Bursts and CMEs Inferred from STEREO Observations

The inner coronagraph (COR1) of the Solar Terrestrial Relations Observatory (STEREO) mission has made it possible to observe CMEs in the spatial domain overlapping with that of the metric type II radio bursts. The type II bursts were associated with generally weak flares (mostly B and C class soft X-ray flares), but the CMEs were quite energetic. Using CME data for a set of type II bursts during the declining phase of solar cycle 23, we determine the CME height when the type II bursts start, thus giving an estimate of the heliocentric distance at which CME-driven shocks form. This distance has been determined to be approx. 1.5Rs (solar radii), which coincides with the distance at which the Alfven speed profile has a minimum value.We also use type II radio observations from STEREO/WAVES and Wind/WAVES observations to show that CMEs with moderate speed drive either weak shocks or no shock at all when they attain a height where the Alfven speed peaks (approx. 3Rs - 4Rs). Thus the shocks seem to be most efficient in accelerating electrons in the heliocentric distance range of 1.5Rs to 4Rs. By combining the radial variation of the CME speed in the inner corona (CME speed increase) and interplanetary medium (speed decrease) we were able to correctly account for the deviations from the universal drift-rate spectrum of type II bursts, thus confirming the close physical connection between type II bursts and CMEs. The average height (approx 1.5Rs) of STEREO CMEs at the time of type II bursts is smaller than that (2.2Rs) obtained for SOHO (Solar and Heliospheric Observatory) CMEs. We suggest that this may indicate, at least partly, the density reduction in the corona between the maximum and declining phases, so a given plasma level occurs closer to the Sun in the latter phase. In two cases, there was a diffuse shock-like feature ahead of the main body of the CME, indicating a standoff distance of 1Rs - 2Rs by the time the CME left the LASCO field of view.

Solar Energetic Particles↗
NASA NTRS2015

Wind Magnetic Clouds for 2010-2012: Model Parameter Fittings, Associated Shock Waves, and Comparisons to Earlier Periods

We fitted the parameters of magnetic clouds (MCs) as identified in the Wind spacecraft data from early 2010 to the end of 2012 using the model of Lepping, Jones, and Burlaga (J. Geophys. Res. 95, 1195, 1990). The interval contains 48 MCs and 39 magnetic cloud-like (MCL) events. This work is a continuation of MC model fittings of the earlier Wind sets, including those in a recent publication, which covers 2007 to 2009. This period (2010 - 2012) mainly covers the maximum portion of Solar Cycle 24. Between the previous and current interval, we document 5.7 years of MCs observations. For this interval, the occurrence frequency of MCs markedly increased in the last third of the time. In addition, over approximately the last six years, the MC type (i.e. the profile of the magnetic-field direction within an MC, such as North-to-South, South-to-North, all South) dramatically evolved to mainly North-to-South types when compared to earlier years. Furthermore, this evolution of MC type is consistent with global solar magnetic-field changes predicted by Bothmer and Rust (Coronal Mass Ejections, 139, 1997). Model fit parameters for the MCs are listed for 2010 - 2012. For the 5.7 year interval, the observed MCs are found to be slower, weaker in estimated axial magnetic-field intensity, and shorter in duration than those of the earlier 12.3 years, yielding much lower axial magnetic-field fluxes. For about the first half of this 5.7 year period, i.e. up to the end of 2009, there were very few associated MC-driven shock waves (distinctly fewer than the long-term average of about 50 % of MCs). But since 2010, such driven shocks have increased markedly, reflecting similar statistics as the long-term averages. We estimate that 56 % of the total observed MCs have upstream shocks when the full interval of 1995 - 2012 is considered. However, only 28 % of the total number of MCLs have driven shocks over the same period. Some interplanetary shocks during the 2010 - 2012 interval are seen to apparently occur without an obvious MC-driver, probably indicating an encounter with a distant flank of a MC-driven shock. Some of these may be driven by a different kind of structure, however.

Magnetic clouds↗
NASA NTRS2002

Satellite Observations of Solar Irradiance and Sun-Climate Impacts

Solar activity is now near its maximum, with events such as the 2001 "Bastille Day Event", a Coronal Mass Ejection which merited a full session at AGO'S annual meeting - and two major sunspot groupings earlier this year, with associated variations in TSI (Total Solar Irradiance). We discuss recent satellite measurements of TSI by ACRIM 2 and 3 And Virgo, and new precision observations of TSI and SSI (Solar Spectral Irradiance) expected from the SORCE mission, planned to launch in fall 2002. SSG has been added to TSI as a required EOS and NPOESS measurement because different spectral components provide energy inputs to different components of the climate system - UV into upper atmosphere and ozone, IR into lower atmosphere and clouds, and Visible into the biosphere. Succeeding satellite missions being planned for 2006 and 2010 will continue to monitor both TSI and SSI. We summarize current ideas about the potential impact of solar variability on Earth's climate on time scales from days to decades to centuries.

Cahalan, R.↗
NASA NTRS2010

Two Types of Magnetic Flux Cancellation in the Solar Eruption of 2007 May 20

We study a solar eruption of 2007 May 20, in an effort to understand the cause of the eruption's onset. The event produced a GOES class B6.7 flare peaking at 05:56 UT, while ejecting a surge/filament and producing a coronal mass ejection (CME). We examine several data sets, including H-alpha images from the Solar Optical Telescope (SOT) on Hinode, EUV images from TRACE, and line-of-sight magnetograms from SOHO/MDI. Flux cancelation occurs among two different sets of flux elements inside of the erupting active region: First, for several days prior to eruption, opposite-polarity sunspot groups inside the region move toward each other, leading to the cancelation of approximately 10^{21} Mx of flux over three days. Second, within hours prior to the eruption, positive-polarity moving magnetic features (MMFs) flowing out of the positive-flux spots at approximately 1 kilometer per second repeatedly cancel with field inside a patch of negative-polarity flux located north of the sunspots. The filament erupts as a surge whose base is rooted in the location where the MMF cancelation occurs, while during the eruption that filament flows out along the polarity inversion line between the converging spot groups. We conclude that a plausible scenario is that the converging spot fields brought the magnetic region to the brink of instability, and the MMF cancelation pushed the system "over the edge." triggering the eruption.

Sterlin, Alphonse C.↗
NASA NTRS1991

Shuffling foot points and magnetohydrodynamic discontinuities in the solar wind

ISEE three-field and plasma data are used to investigate the frequency of occurrence of isolated, large-amplitude rotational (RD) and tangential (TD) discontinuities in different types of solar wind flow. It is found that there are relatively more TDs in solar wind that originates in closed field regions and is ejected into interplanetary space by coronal transients than in the solar wind that originates in open field regions. The speed of the wind from open field regions is approximately linearly related to the number of RDs per hour; such a relation does not exist for the wind associated with coronal mass ejections. These results are consistent with the hypothesis that the convection-driven shuffling of magnetic foot points at the solar surface leads to TDs, magnetic reconnection, and heating of the corona on closed field lines, while in the open field regions the disturbances created by the shuffling are carried off by waves which contribute to the acceleration of the solar wind.

Neugebauer, M.↗
NASA NTRS2005

Microsat and Lunar-Based Imaging of Radio Bursts

No present or approved spacecraft mission has the capability to provide high angular resolution imaging of solar or magnetospheric radio bursts or of the celestial sphere at frequencies below the ionospheric cutoff. Here, we describe a MIDEX-class mission to perform such imaging in the frequency range approx. 30 kHz to 15 MHz. This mission, the Solar Imaging Radio Array (SIRA), is solar and exploration-oriented, with emphasis on improved understanding and application of radio bursts associated with solar energetic particle (SEP) events and on tracking shocks and other components of coronal mass ejections (CMEs). SIRA will require 12 to 16 micro-satellites to establish a sufficient number of baselines with separations on the order of kilometers. The constellation consists of microsats located quasi-randomly on a spherical shell, initially of approx. 10 km diameter. The baseline microsat is 3-axis stabilized with body-mounted solar arrays and an articulated, earth pointing high gain antenna. The constellation will likely be placed at L1, which is the preferred location for full-time solar observations. We also discuss briefly follow-on missions that would be lunar-based with of order 10,000 dipole antennas.

interferometry↗
NASA NTRS1989

The role of eruption in solar flares

This article focuses on two problems involved in the development of models of solar flares. The first concerns the mechanism responsible for eruptions, such as erupting filaments or coronal mass ejections, that are sometimes involved in the flare process. The concept of 'loss of equilibrium' is considered and it is argued that the concept typically arises in thought-experiments that do not represent acceptable physical behavior of the solar atmosphere. It is proposed instead that such eruptions are probably caused by an instability of a plasma configuration. The instability may be purely MHD, or it may combine both MHD and resistive processes. The second problem concerns the mechanism of energy release of the impulsive (or gradual) phase. It is proposed that this phase of flares may be due to current interruption, as was originally proposed by Alfven and Carlqvist. However, in order for this process to be viable, it seems necessary to change one's ideas about the heating and structure of the corona in ways that are outlined briefly.

Sturrock, Peter A.↗
NASA NTRS1985

Shock and statistical acceleration of energetic particles in the interplanetary medium

Definite evidence for particle acceleration in the solar wind came around a decade ago. Two likely sources are known to exist: particles may be accelerated by the turbulence resulting from the superposition of Alfven and Magnetosonic waves (Statistical Acceleration) or they may be accelerated directly at shock fronts formed by the interaction of fast and slow solar wind (CIR's) or by traveling shocks due to sporadic coronal mass ejections. Naurally both mechanisms may be operative. In this work the acceleration problem was tackled numerically using Helios 1 and 2 data to create a realistic representation of the Heliospheric plasma. Two 24 hour samples were used: one where there are only wave like fluctuations of the field (Day 90 Helios 1) and another with a shock present in it (Day 92 of Helios 2) both in 1976 during the STIP 2 interval. Transport coefficients in energy space have been calculated for particles injected in each sample and the effect of the shock studied in detail.

Valdes-Galicia, J. F.↗