Charge, Element, And Isotope Analysis System Research Articles

A Change in the Solar He ii EUV Global Network Structure as an Indicator of the Geo-Effectiveness of Solar Minima

Solar activity during 2007--2009 was very low, causing anomalously low thermospheric density. A comparison of solar extreme ultraviolet (EUV) irradiance in the He II spectral band (26 to 34 nm) from the Solar Extreme ultraviolet Monitor (SEM), one of instruments on the Charge Element and Isotope Analysis System (CELIAS) onboard of the Solar and Heliospheric Observatory (SOHO) for the two latest solar minima showed a decrease of the absolute irradiance of about 15 +- 6 % during the solar minimum between Cycles 23 and 24 compared with the Cycles 22/23 minimum when a yearly running mean filter was used. We found that some local, shorter-term minima including those with the same absolute EUV flux in the SEM spectral band show a larger concentration of spatial power in the global network structure from the 30.4 nm SOHO Extreme ultraviolet Imaging Telescope (EIT) images for the local minimum of 1996 compared with the minima of 2008--2011. We interpret this larger concentration of spatial power in the transition region's global network structure as a larger number of larger area features on the solar disk. Such changes in the global network structure during solar minima may characterize, in part, the geo-effectiveness of the solar He II EUV irradiance in addition to the estimations based on its absolute levels.

A possible way of understanding the differential motion of minor ions in the solar wind

Measurements with Solar and Heliospheric Observatory (SOHO)/Charge, Element, and Isotope Analysis System (CELIAS) in high‐speed solar wind show that some minor ions such as O6+ have a relatively high drift velocity; however, other ions such as Fe9+ tend to lag behind oxygen by a few tens of km/s [Hefti et al., 1998]. This subtle observational feature has not yet been understood. A possible way, based on the quasi‐linear theory of cyclotron resonance, of understanding this phenomenon is presented in this paper. The charge per mass of the ion O6+ and Fe9+ are different, a fact which results in different features of the ion‐cyclotron resonance with waves. In plasma with protons, drifting alpha particles, and electrons, the dispersion relation of cyclotron waves has two branches. The oxygen ions tend to resonate with the inward propagating waves of the left‐hand‐polarized (LHP) first branch and the outward propagating waves of the LHP second branch. These resonances may together lead to a velocity distribution with a central velocity higher than the proton (solar wind) bulk velocity by about 50 km/s at 1 AU. The Fe9+ ions tend to resonate with both the inward and outward propagating waves of the first branch and may thus form a velocity distribution with a central velocity very near the proton bulk velocity. These analytical results are shown to be supported by numerical results from a two‐dimensional simulation based on the quasi‐linear diffusion equation. The limitations of the present analysis and further work, which should be done to support the ideas proposed here, are also discussed.

Effect of the 14 July 2000 solar flare on Earth's FUV emissions

An X‐class solar flare occurring on 14 July 2000 (Bastille Day) marked the initiation of events which led to a powerful geomagnetic storm on 15 July. At the time of the flare the NASA‐IMAGE spacecraft was near apogee and observed a global‐scale transient increase in far ultraviolet (FUV) emissions of the thermosphere in both the N2 Lyman‐Birge‐Hopfield (LBH) band and the O I 135.6‐nm line and also in geocoronal emissions of H I at 121.6‐nm. Comparison with the solar x‐ray flux measured by GOES 10 shows the delayed response of the FUV emissions compared to the peak in x‐rays. This lag is attributed to a later peak in EUV emissions, which drive the photoelectron flux in the energy range which is, in turn, most effective in producing N2 LBH and O I 135.6‐nm emissions. Measurements of solar EUV input by Solar and Heliospheric Observatory (SOHO) Charge, Element, and Isotope Analysis System (CELIAS)/Solar Extreme‐Ultra‐Violet Monitor (SEM) confirm the close correlation between solar EUV and terrestrial FUV emissions. A comparison of the flare‐time variation in the signal in each channel of the instrument allows one to (1) determine the variation in resonantly scattered solar emissions and (2) differentiate between emissions created through photodissociation by solar EUV and those driven by terrestrial photoelectron impact. The latter provides a means for positively identifying the dayglow emissions observed in the SI‐12 instrument.

Elemental Abundances for the 1996 Streamer Belt

The purpose of this paper is to explore the observed physical characteristics of the solar corona streamer belt from 1996 June 1 to August 5. The UV spectral data was collected by the Ultraviolet Coronagraph Spectrometer (UVCS) instrument on board the Solar and Heliospheric Observatory (SOHO) spacecraft. From this data the abundances of oxygen, silicon, and magnesium were determined on an almost daily basis during this time period at both the west and east limbs. The streamer belt was composed of both active and quiescent streamers, which allows for the comparison of these two categories of magnetic field structures. The depletion of these three elemental abundances in the core of quiescent streamers was found, as in previous observations. The variance in abundance with solar rotation was investigated as a consequence of the long time frame considered here. The first ionization potential (FIP) effect was present in the data, and the danger of exploring this phenomena by the traditional FIP bias was also covered. A comparison with in situ elemental abundance data from the Charge, Element, and Isotope Analysis System (CELIAS) instrument on SOHO provides evidence suggesting that active-region streamers and the outer ‘‘ leg ’’ structural component of quiescent streamers are definite contributors to the slow solar wind. Subject headings: solar wind — Sun: abundances — Sun: corona

Calcium Abundance in the Solar Wind

We report on the calcium abundance in the solar wind for an extended time period around the 1996 solar minimum. Data were recorded with the Mass Time-of-Flight (MTOF) sensor of the Charge, Element, and Isotope Analysis System (CELIAS) instrument on the SOHO spacecraft. The Ca/O abundance is 0.017 ± 0.003 for slow solar wind (VSW 500 km s-1). Compared to the photospheric Ca/O abundance ratio of (Ca/O)PS = 0.00421 ± 0.00079, the solar wind clearly shows strong first ionization potential (FIP) fractionation as is expected for a low-FIP element. The Ca/H abundance is ACa = 6.63 ± 0.05 and ACa = 6.21 ± 0.10 for slow and fast solar winds, respectively. For comparison, the photospheric Ca abundance is ACa = 6.36 ± 0.02.

Space weather observations using the SOHO CELIAS complement of instruments

The Solar and Heliospheric Observatory (SOHO) spacecraft located at Ll is well outside the Earth's magnetosphere and has been observing the Sun continuously since December 1995, except for relatively brief periods due to spacecraft operational interruptions. While a variety of instruments on the SOHO spacecraft investigate the solar properties important to an improved understanding of the Sun and its effect on space weather, the present work is limited to the observations provided by the Charge, Element, and Isotope Analysis System (CELIAS) proton monitor (PM) and Solar Extreme Ultraviolet Monitor (SEM) instruments and their relationship to other space weather observations. The CELIAS observations consist of particle and EUV/soft X‐ray solar flux measurements. A brief description of the CELIAS instrumentation and examples of the precursor information signaling the possibility of coronal mass ejection events observed by the CELIAS/SEM are presented. In addition, the entire SEM database since commissioning is presented on both expanded and compressed timescales in order to provide both the long‐term weather trends and short‐term storm data. The SEM data presented are full‐disk observations and have a 15 s sampling rate.

Determination of the 36Ar/38Ar isotopic abundance ratio of the solar wind using SOHO/CELIAS/MTOF

This study is on the first direct measurements of the 36Ar/38Ar isotopic ratio in both the interstream (IS)-associated and coronal hole (CH)-associated solar wind. Two summed mass spectra are compiled for each solar wind region using the Mass Time-Of-Flight (MTOF) sensor of the Charge, Element, and Isotope Analysis System (CELIAS) instrument on the Solar and Heliospheric Observatory (SOHO) spacecraft. A detailed analysis of over 9.2 d of nonconsecutive IS-associated solar wind speed (395 ± 25 km/s) places the 36Ar/38Ar ratio at 5.6 ± 0.7. A similar analysis for a CH-associated solar wind speed (525 ± 25 km/s), with ∼22.8 nonconsecutive days of CH-associated solar wind speed data, derived a similar 36Ar/38Ar ratio of 5.5 ± 0.6. The error associated with these measurements is essentially the instrumental uncertainty. Both the solar wind 36Ar/38Ar isotopic ratios found in this study are consistent with the terrestrial 36Ar/38Ar ratio as well as previous reported ratios for solar wind examined in this study. A comparison of these results suggests little or no isotopic fractionation occurring between the two solar wind regimes. This study presents the results in the context of solar wind fractionation models and in relation to experimental evidence derived from in situ observations on refractory elements.

Model for the mass fractionation in the January 6, 1997, coronal mass ejection

For the coronal mass ejection (CME) of January 6, 1997, strong element fractionation of the heavy ions was observed at 1 AU with the Mass Time‐of‐Flight (MTOF) sensor of the Charge, Element, and Isotope Analysis System (CELIAS) on the Solar and Heliospheric Observatory (SOHO). During the passage of the CME plasma and the passage of the erupted filament, which followed the CME, a mass‐dependent element fractionation was found with an enhancement of heavy elements, increasing monotonically with atomic mass. Si/O and Fe/O ratios around 0.5 were observed, which corresponds to an increase of about a factor of 4 compared to regular slow solar wind. We present a theoretical model with which we can reproduce the observed element fractionation. The model assumes hot coronal loops with non‐Maxwellian electron distributions as the precursor structure of the CME on the solar surface. Diffusion perpendicular to the magnetic field results in the preferential loss of lighter ions from the loop, leading to mass fractionation. To quantitatively reproduce the fractionation process, the loops must have existed for ∼ 28 hours before they became part of the CME plasma, a time that is commensurate with optical observations of loops in the active region from which the CME was launched.

The relation of temporal variations of soft X‐ray emission from comet Hyakutake to variations of ion fluxes in the solar wind

Both the Röntgen X‐Ray Satellite (ROSAT) and the Extreme Ultraviolet Explorer (EUVE) have detected soft X‐ray emission from comet C/Hyakutake 1996 B2. This emission varied by a factor of about 2 over a few hours and by a factor of 4 from day to day. One explanation for the excitation of cometary X rays is the charge transfer mechanism suggested by Cravens. This process involves charge exchange collisions between highly charged heavy ions in the solar wind and neutral gas in the cometary coma. Oxygen ion fluxes observed by the Charge, Element, and Isotope Analysis System (CELIAS) Mass Time‐of‐Flight (MTOF) instrument on the SOHO spacecraft and proton fluxes measured by near‐Earth spacecraft are mapped to the location of the comet to demonstrate that the comet X‐ray variability can be explained on the basis of variability in the solar wind. There is a good correlation between cometary X‐ray emission and oxygen ion fluxes and a poorer correlation with proton flux. The correlation between the solar wind oxygen flux and cometary X rays degrades with increasing latitudinal separation of SOHO from the comet. Cometary X‐ray emission is not sensitive to variations in solar X‐ray fluxes and is unlikely to be caused by crossing of the heliospheric current sheet. The charge transfer mechanism appears to be supported by all the data examined to date. Cometary X rays have some shortcomings as remote sensors of the solar wind, however, because of variations in cometary gas production rates and in the charge states and abundances of heavy solar wind ions.

Oxygen freeze‐in temperatures measured with SOHO/CELIAS/CTOF

We use the charge time‐of‐flight (CTOF) mass and charge spectrometer of the charge, element, and isotope analysis system (CELIAS) on board the Solar and Heliospheric Observatory (SOHO) to determine the solar wind oxygen freeze‐in temperature T76 from the O7+ and O6+ abundance ratios in the period from days 92 to 229 of 1996 (Carrington Rotations 1908 to 1912). The freeze‐in temperature is a conserved property of the solar wind because the charge states do not change after a distance of a few solar radii. Therefore it is an ideal in situ diagnostic for remote sensing of the inner solar corona. We determine the mean freeze‐in temperature during the selected period to be 1.6 × 106 K. We use it to map coronal regions of different temperatures and to determine the separation between such regions based on our observation of abrupt transitions of the freeze‐in temperature. We find a upper limit for the separation in the inner corona of 1000 km.

The Fe/O elemental abundance ratio in the solar wind as observed with SOHO CELIAS CTOF

Using data of the Charge Time‐of‐Flight (CTOF) mass spectrometer of the Charge, Element, and Isotope Analysis System (CELIAS) on board the Solar and Heliospheric Observatory (SOHO) from ∼80 days of observation around solar minimum we derive a value for the Fe/O abundance ratio for the inecliptic solar wind of 0.11 ± 0.03. Since Fe has a low first ionization potential (FIP) and O is a high‐FIP element, their relative abundance is diagnostic for the FIP fractionation process. The unprecedented time resolution of the CELIAS CTOF sensor allows a fine‐scaled study of the Fe/O ratio as a function of the solar wind bulk speed. On average, the Fe/O abundance ratio shows a continuous decrease by a factor of 2 with increasing solar wind speed between 350 and 500 km/s. This corresponds to the well‐known FIP effect dependence. Our value at ∼500 km/s agrees with the previously observed Fe/O ratio in the fast solar wind emerging from polar coronal holes whereas the value for speeds below 350 km/s is consistent with a remote abundance determination in the leg of a coronal streamer. The variability of the Fe/O abundance ratio is much larger in the slow than in the fast solar wind.

Kinetic properties of solar wind minor ions and protons measured with SOHO/CELIAS

Using observations of the Charge Time‐of‐Flight(CTOF) charge and mass spectrometer of the Charge, Element and Isotope Analysis System (CELIAS), and of CELIAS/proton monitor on board the Solar and Heliospheric Observatory (SOHO), we present an overview of speeds and kinetic temperatures of minor ions and protons in the solar wind near solar minimum, covering the Carrington Rotations 1908 to 1912. In the case of a collision‐dominated solar wind the speed of minor ions is expected to be lower or equal to the speed of the protons, and all species are expected to have equal temperatures. On the other hand, minor ions can be accelerated and heated by wave‐particle interaction. In this case, equal thermal speeds of all species are expected. CTOF data allow the determination of the kinetic parameters of various ions with high accuracy and with high time resolution. The mean O6+ speed of the observed period is 390 km s−1. The speeds of Si7+ and Fe9+ correlate well with O6+, the linear correlation coefficient being 0.96 or higher. Our results also indicate that silicon and iron tend to lag behind oxygen with a speed difference of ∼20 km s−1 at 500 km s−1. At the same time, the kinetic temperature of the ions under investigation exhibit the well‐known mass proportionality, which is attributed to wave‐particle interactions. During the period of low solar activity in consideration, many cases are observed where the kinetic temperature is extraordinarily low (104 K for O6+).

Isotopic Composition of Solar Wind Nitrogen: First In Situ Determination with the CELIAS/MTOF Spectrometer on board [ITAL]SOHO[/ITAL

Using the high-resolution Mass Time-of-Flight (MTOF) spectrometer of the Charge, Element, and Isotope Analysis System (CELIAS) experiment on board the Solar and Heliospheric Observatory (SOHO), we have determined the solar wind isotope abundance ratio 14N/15N = 200±55 (1 σ error), suggesting that the relative abundance of 15N in the terrestrial atmosphere is lower than in solar matter. This result is compatible with the hypothesis that terrestrial N (14N/15N = 272) and also N found in lunar surface material are a mixture of a heavy component that is identical to solar N and an unspecified light component. The large variations of 14N/15N in solar system matter is caused by special isotope enrichment processes, as in the case of Mars, as well as by varying contributions of isotopically different components.

Magnesium isotopic composition as observed with the CELIAS/MTOF experiment on the SOHO spacecraft

Solar wind abundance ratios of magnesium isotopes measured with the high resolution Mass Time‐of‐Flight spectrometer (MTOF) of the Charge, Element, and Isotope Analysis System (CELIAS) experiment on board the Solar and Heliospheric Observatory (SOHO) are presented. MTOF, as part of CELIAS, is, because of its high time and mass resolution, an excellent tool for isotope abundance measurements in the solar wind. From the data analysis we have found that the isotopic composition of magnesium in the solar wind agrees with the terrestrial composition within the experimental uncertainty. We have obtained isotopic ratios of 24Mg/25Mg = 7.7 ± 0.4 and 24Mg/26Mg = 7.0 ± 0.5. These values are consistent with the terrestrial values of 24Mg/25Mg = 7.90 ± 0.01 and 24Mg/26Mg = 7.17 ± 0.03. Furthermore, these investigations also show that with the given uncertainties the abundance ratios do not vary significantly within a solar wind velocity range from 375 km/s to 530 km/s.

Detection of 55–80 keV Hydrogen Atoms of Heliospheric Origin by CELIAS/HSTOF onSOHO

The High-Energy Suprathermal Time-of-Flight sensor (HSTOF) of the Charge, Element, and Isotope Analysis System (CELIAS) on the Solar and Heliospheric Observatory (SOHO) near the Lagrangian point L1 is capable of identifying energetic hydrogen atoms (EHAs) between 55 and 80 keV. Between 1996 February 13 and 1997 August 31, near solar minimum, there were 285 "quiet" days when the interplanetary charged-particle flux was low. During these quiet times, HSTOF scanned the apex of the heliosphere once and the antiapex twice. The flux level and time profile, and hence the arrival direction, of the EHAs accumulated during these quiet times are best interpreted as fluxes of EHAs coming from the heliosheath.

Isotopic Composition of Solar Wind Calcium: First in Situ Measurementby CELIAS/MTOF on board [ITAL]SOHO[/ITAL

We present the first results of the Ca isotopic abundances derived from the high-resolution Mass Time-of-Flight (MTOF) spectrometer of the Charge, Element, and Isotope Analysis System (CELIAS) experiment on board the Solar and Heliospheric Observatory (SOHO). We obtain the isotopic ratios 40Ca/42Ca =128±47 and 40Ca/44Ca =50±8, consistent with terrestrial values. This is the first in situ determination of the solar wind calcium isotopic composition and is important for studies of stellar modeling and solar system formation since the present-day solar Ca isotopic abundances are unchanged from their original isotopic composition in the solar nebula.

Isotopic composition of solar wind neon measured by CELIAS/MTOF on board SOHO

We present first results taken from the high‐resolution mass time‐of‐flight spectrometer (MTOF) of the charge, element, and isotope analysis system (CELIAS) experiment on board the Solar and Heliospheric Observatory (SOHO) spacecraft launched in December 1995, concerning the abundance ratios of neon isotopes in the solar wind. We obtain the isotopic ratios 20Ne/22Ne = (13.8 ± 0.7) and 20Ne/21Ne = (440 ± 110), which agree with the values obtained from the Apollo foil solar wind experiments and which have been derived from measurements of solar particles implanted in lunar and meteoritic samples.