共查询到20条相似文献，搜索用时 15 毫秒
1.
T. N. Woods F. G. Eparvier R. Hock A. R. Jones D. Woodraska D. Judge L. Didkovsky J. Lean J. Mariska H. Warren D. McMullin P. Chamberlin G. Berthiaume S. Bailey T. Fuller-Rowell J. Sojka W. K. Tobiska R. Viereck 《Solar physics》2012,275(1-2):115-143
The highly variable solar extreme ultraviolet (EUV) radiation is the major energy input to the Earth’s upper atmosphere, strongly impacting the geospace environment, affecting satellite operations, communications, and navigation. The Extreme ultraviolet Variability Experiment (EVE) onboard the NASA Solar Dynamics Observatory (SDO) will measure the solar EUV irradiance from 0.1 to 105?nm with unprecedented spectral resolution (0.1?nm), temporal cadence (ten seconds), and accuracy (20%). EVE includes several irradiance instruments: The Multiple EUV Grating Spectrographs (MEGS)-A is a grazing-incidence spectrograph that measures the solar EUV irradiance in the 5 to 37?nm range with 0.1-nm resolution, and the MEGS-B is a normal-incidence, dual-pass spectrograph that measures the solar EUV irradiance in the 35 to 105?nm range with 0.1-nm resolution. To provide MEGS in-flight calibration, the EUV SpectroPhotometer (ESP) measures the solar EUV irradiance in broadbands between 0.1 and 39?nm, and a MEGS-Photometer measures the Sun’s bright hydrogen emission at 121.6?nm. The EVE data products include a near real-time space-weather product (Level?0C), which provides the solar EUV irradiance in specific bands and also spectra in 0.1-nm intervals with a cadence of one minute and with a time delay of less than 15?minutes. The EVE higher-level products are Level?2 with the solar EUV irradiance at higher time cadence (0.25?seconds for photometers and ten seconds for spectrographs) and Level?3 with averages of the solar irradiance over a day and over each one-hour period. The EVE team also plans to advance existing models of solar EUV irradiance and to operationally use the EVE measurements in models of Earth’s ionosphere and thermosphere. Improved understanding of the evolution of solar flares and extending the various models to incorporate solar flare events are high priorities for the EVE team. 相似文献
2.
Jun Nishikawa 《Solar physics》1994,152(1):125-130
Spatially-resolved precise photometric observations of the whole Sun at wavelengths of 545nm (FWHM 40nm) were carried out by using the CCD solar surface photometer. Bright parts of photospheric network have contrast of several tenths of percent, and their contribution to the total irradiance is approximately half that of active region faculae. The solar irradiance variations estimated from sunspots, faculae and active network (contrast>0.3%) agreed with the ACRIM data. The quiet Sun irradiance used in the present results was different from the total irradiance at the solar minimum observed by the ACRIM, which indicates unmeasured components (contrast>0.1%) cause the 11-year cycle irradiance variation. 相似文献
3.
George L. Withbroe 《Solar physics》2009,257(1):71-81
The daily images and magnetograms acquired by MDI are a rich source of information about the contributions of different types
of solar regions to variations in the total solar irradiance (TSI). These data have been used to determine the temporal variation
of the MDI irradiance, the mean intensity of the solar disk in the continuum at 676.8 nm. The short-term (days to weeks) variations
of the MDI irradiance and TSI are in excellent agreement with rms differences of 0.011%. This indicates that MDI irradiance
is an excellent proxy for short-term variations of TSI from the competing irradiance contributions of regions causing irradiance
increases, such as plages and bright network, and regions causing irradiance decreases, such as sunspots. However, the long-term
or solar cycle variation of the MDI proxy and TSI differ over the 11-year period studied. The results indicate that the primary
sources of the long-term (several months or more) variations in TSI are regions with magnetic fields between about 80 and
600 G. The results also suggest that the difference in the long-term variations of the MDI proxy and TSI is due to a component
of TSI associated with sectors of the solar spectrum where the contrast in intensity between plages and the quiet Sun is enhanced
(e.g., the UV) compared to the MDI proxy. This is evidence that the long-term variation of TSI is due primarily to solar cycle
variations of the irradiance from these portions of solar spectrum, a finding consistent with modeling calculations indicating
that approximately 60% of the change in TSI between solar minimum and maximum is produced by the UV part of the spectrum shortward
of 400 nm (Solanki and Krivova, Space Sci. Rev. 125, 53, 2006). 相似文献
4.
Ann T. Mecherikunnel 《Solar physics》1998,177(1-2):11-23
Simultaneous solar total irradiance observations performed by absolute radiometers on board satellites during the quiet-Sun period between solar cycles 21 and 22 (1985–1987), are analyzed to determine the solar total irradiance at 1 AU for the solar minimum. During the quiet-Sun period the total solar irradiance, UV irradiance, and the various solar activity indices show very little fluctuation. However, the absolute value of the solar total irradiance derived from the observations differ within the accuracy of the radiometers used in the measurements. Therefore, the question often arises about a reference value of the solar total irradiance for use in climate models and for computation of geophysical, and atmospheric parameters. This research is conducted as a part of the Solar Electromagnetic Radiation Study for Solar Cycle 22 (SOLERS22). On the basis of the study we recommended a reference value of 1367.0 ± 0.04 W m-2 for the solar total irradiance at 1 AU for a truly quiet Sun. We also find that the total solar irradiance data for the quiet-Sun period reveals strong short-term irradiance variations. 相似文献
5.
Thomas N. Woods Phillip C. Chamberlin W. K. Peterson R. R. Meier Phil G. Richards Douglas J. Strickland Gang Lu Liying Qian Stanley C. Solomon B. A. Iijima A. J. Mannucci B. T. Tsurutani 《Solar physics》2008,250(2):235-267
Solar soft X-ray (XUV) radiation is highly variable on all time scales and strongly affects Earth’s ionosphere and upper atmosphere;
consequently, the solar XUV irradiance is important for atmospheric studies and for space weather applications. Although there
have been several recent measurements of the solar XUV irradiance, detailed understanding of the solar XUV irradiance, especially
its variability during flares, has been hampered by the broad bands measured in the XUV range. In particular, the simple conversion
of the XUV photometer signal into irradiance, in which a static solar spectrum is assumed, overestimates the flare variations
by more than a factor of two as compared to the atmospheric response to the flares. To address this deficiency in the simple
conversion, an improved algorithm using CHIANTI spectral models has been developed to process the XUV Photometer System (XPS)
measurements with its broadband photometers. Model spectra representative of quiet Sun, active region, and flares are combined
to match the signals from the XPS and produce spectra from 0.1 to 40 nm in 0.1-nm intervals for the XPS Level 4 data product.
The two XPS instruments are aboard NASA’s Solar Radiation and Climate Experiment (SORCE) and Thermosphere, Ionosphere, Mesosphere, Energetics, and Dynamics (TIMED) satellites. In addition, the XPS responsivities have been updated for the latest XPS data processing version. The
new XPS results are consistent with daily variations from the previous simple conversion technique used for XPS and are also
consistent with spectral measurements made at wavelengths longer than 27 nm. Most importantly, the XPS flare variations are
reduced by factors of 2 – 4 at wavelengths shorter than 14 nm and are more consistent, for the first time, with atmospheric
response to solar flares. Along with the details of the new XPS algorithm, several comparisons to dayglow and photoelectron
measurements and model results are also presented to help verify the accuracy of the new XUV irradiance spectra. 相似文献
6.
We present results from sunspot observations obtained by SUMER on SOHO. In sunspot plumes the EUV spectrum differs from the
quiet Sun; continua are observed with different slopes and intensities; emission lines from molecular hydrogen and many unidentified
species indicate unique plasma conditions above sunspots. Sunspot plumes are sites of systematic downflow. We also discuss
the properties of sunspot oscillations 相似文献
7.
H. P. Jones G. A. Chapman K. L. Harvey J. M. Pap D. G. Preminger M. J. Turmon S. R. Walton 《Solar physics》2008,248(2):323-337
Physical understanding of total and spectral solar irradiance variation depends upon establishing a connection between the
temporal variability of spatially resolved solar structures and spacecraft observations of irradiance. One difficulty in comparing
models derived from different data sets is that the many ways for identifying solar features such as faculae, sunspots, quiet
Sun, and various types of “network” are not necessarily consistent. To learn more about classification differences and how
they affect irradiance models, feature “masks” are compared as derived from five current methods: multidimensional histogram
analysis of NASA/National Solar Observatory/Kitt Peak spectromagnetograph data, statistical pattern recognition applied to
SOHO/Michelson Doppler Imager photograms and magnetograms, threshold masks allowing for influence of spatial surroundings
applied to NSO magnetograms, and “one-trigger” and “three-trigger” algorithms applied to California State University at Northridge
Cartesian Full Disk Telescope intensity observations. In general all of the methods point to the same areas of the Sun for
labeling sunspots and active-region faculae, and available time series of area measurements from the methods correlate well
with each other and with solar irradiance. However, some methods include larger label sets, and there are important differences
in detail, with measurements of sunspot area differing by as much as a factor of two. The methods differ substantially regarding
inclusion of fine spatial scale in the feature definitions. The implications of these differences for modeling solar irradiance
variation are discussed.
K.L. Harvey and S.R. Walton are deseased, to whom this paper is dedicated. 相似文献
8.
Using Hinode EUV Imaging Spectrometer (EIS) spectra recorded daily at Sun center from the end of 2006 to early 2011, we studied the long-term evolution of the quiet corona. The light curves of the higher temperature emission lines exhibit larger variations in sync with the solar activity cycle while the cooler lines show reduced modulation. Our study shows that the high temperature component of the corona changes in quiet regions, even though the coronal electron density remains almost constant there. The results suggest that heat input to the quiet corona varies with the solar activity cycle. 相似文献
9.
Thomas N. Woods Gary J. Rottman Scott M. Bailey Stanley C. Solomon John R. Worden 《Solar physics》1998,177(1-2):133-146
The solar extreme ultraviolet (EUV) irradiance, the dominant global energy source for Earth's atmosphere above 100 km, is not known accurately enough for many studies of the upper atmosphere. During the absence of direct solar EUV irradiance measurements from satellites, the solar EUV irradiance is often estimated at the 30–50% uncertainty level using both proxies of the solar irradiance and earlier solar EUV irradiance measurements, primarily from the Air Force Geophysics Laboratory (now Phillips Laboratory) rockets and Atmospheric Explorer (AE) instruments. Our sounding rocket measurements during solar cycle 22 include solar EUV irradiances below 120 nm with 0.2 nm spectral resolution, far ultraviolet (FUV) airglow spectra below 160 nm, and solar soft X-ray (XUV) images at 17.5 nm. Compared to the earlier observations, these rocket experiments provide a more accurate absolute measurement of the solar EUV irradiance, because these instruments are calibrated at the National Institute of Standards and Technology (NIST) with a radiometric uncertainty of about 8%. These more accurate sounding-rocket measurements suggest revisions of the previous reference AE–E spectra by as much as a factor of 2 at some wavelengths. Our sounding-rocket flights during the past several years (1988–1994) also provide information about solar EUV variability during solar cycle 22. 相似文献
10.
This article describes an update of the physical models that we use to reconstruct the FUV and EUV irradiance spectra and the radiance spectra of the features that at any given point in time may cover the solar disk depending on the state of solar activity. The present update introduces important modifications to the chromosphere–corona transition region of all models. Also, the update introduces improved and extended atomic data. By these changes, the agreement of the computed and observed spectra is largely improved in many EUV lines important for the modeling of the Earth’s upper atmosphere. This article describes the improvements and shows detailed comparisons with EUV/FUV radiance and irradiance measurements. The solar spectral irradiance from these models at wavelengths longer than ≈?200 nm is discussed in a separate article. 相似文献
11.
Electromagnetic radiation from the Sun is Earths primary energy source. Space-based radiometric measurements in the past two decades have begun to establish the nature, magnitude and origins of its variability. An 11-year cycle with peak-to-peak amplitude of order 0.1 % is now well established in recent total solar irradiance observations, as are larger variations of order 0.2 % associated with the Suns 27-day rotation period. The ultraviolet, visible and infrared spectral regions all participate in these variations, with larger changes at shorter wavelengths. Linkages of solar radiative output variations with solar magnetism are clearly identified. Active regions alter the local radiance, and their wavelength-dependent contrasts relative to the quiet Sun control the relative spectrum of irradiance variability. Solar radiative output also responds to sub-surface convection and to eruptive events on the Sun. On the shortest time scales, total irradiance exhibits five minute fluctuations of amplitude
%, and can increase to as much as 0.015 % during the very largest solar flares. Unknown is whether multi-decadal changes in solar activity produce longer-term irradiance variations larger than observed thus far in the contemporary epoch. Empirical associations with solar activity proxies suggest reduced total solar irradiance during the anomalously low activity in the seventeenth century Maunder Minimum relative to the present. Uncertainties in understanding the physical relationships between direct magnetic modulation of solar radiative output and heliospheric modulation of cosmogenic proxies preclude definitive historical irradiance estimates, as yet.Received: 26 August 2004, Published online: 16 November 2004
Correspondence to: Claus Fröhlich 相似文献
12.
As part of a program to estimate the solar spectrum back to the early twentieth century, we have generated fits to UV spectral
irradiance measurements from 1 – 410 nm. The longer wavelength spectra (150 – 410 nm) were fit as a function of two solar
activity proxies, the Mg ii core-to-wing ratio, or Mg ii index, and the total Ca ii K disk activity derived from ground based observations. Irradiance spectra at shorter wavelengths (1 – 150 nm) where used
to generate fits to the Mg ii core-to-wing ratio alone. Two sets of spectra were used in these fitting procedures. The fits at longer wavelengths (150
to 410 nm) were derived from the high-resolution spectra taken by the Solar Ultraviolet Spectral Irradiance Monitor (SUSIM)
on the Upper Atmospheric Research Satellite (UARS). Spectra measured by the Solar EUV Experiment (SEE) instrument on the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite were used for the fits at wavelengths from 1 to 150 nm. To generate fits between solar irradiance and solar
proxies, this study uses the above irradiance data, the NOAA composite Mg ii index, and daily Ca ii K disk activity determined from images measured by Big Bear Solar Observatory (BBSO). In addition to the fitting coefficients
between irradiance and solar proxies, other results from this study include an estimated relationship between the fraction
of the disk with enhanced Ca ii K activity and the Mg ii index, an upper bound of the average solar UV spectral irradiance during periods where the solar disk contains only regions
of the quiet Sun, as was believed to be present during the Maunder Minimum, as well as results indicating that slightly more
than 60% of the total solar irradiance (TSI) variability occurs between 150 and 400 nm. 相似文献
13.
We investigate the coronal imaging capabilities of the Solar UltraViolet Imager (SUVI) on board the Geostationary Operational Environmental Satellite-R series spacecraft. Nominally Sun-pointed, SUVI provides solar images in six extreme ultraviolet (EUV) wavelengths. On-orbit data indicated that SUVI had sufficient dynamic range and sensitivity to image the corona to the largest heights above the Sun to date while simultaneously imaging the Sun. We undertook a campaign to investigate the existence of the EUV signal well beyond the nominal Sun-centered imaging area of the solar EUV imagers. We off-pointed the SUVI line of sight by almost one imaging area around the Sun. We present the details of the campaign we conducted when the solar cycle was at near the minimum and some results that confirm that EUV emission is present to beyond three solar radii.
相似文献14.
N. Brice Orange Hakeem M. Oluseyi David L. Chesny Maulik Patel Katie Hesterly Lauren Preuss Chantale Neira Niescja E. Turner 《Solar physics》2014,289(5):1557-1584
Since their discovery 20 year ago, transition region bright points have never been observed spectroscopically. Bright point properties have not been compared with similar transition region and coronal structures. In this work we have investigated three transient quiet Sun brightenings including a transition region bright point (TR BP), a coronal bright point (CBP) and a blinker. We use time-series observations of the extreme-ultraviolet emission lines of a wide range of temperature T (logT=5.3?–?6.4) from the EUV Imaging Spectrometer (EIS) onboard the Hinode satellite. We present the EIS temperature maps and Doppler maps, which are compared with magnetograms from the Michelson Doppler Imager (MDI) onboard the SOHO satellite. Doppler velocities of the TR BP and blinker are ≤?25 km?s?1, which is typical of transient TR phenomena. The Doppler velocities of the CBP were found to be ≤?20 km?s?1 with exception of those measured at logT=6.2 where a distinct bi-directional jet is observed. From an EM loci analysis we find evidence of single and double isothermal components in the TR BP and CBP, respectively. TR BP and CBP loci curves are characterized by broad distributions suggesting the existence of unresolved structure. By comparing and contrasting the physical characteristics of the events we find that the BP phenomena are an indication of multi-scaled self-similarity, given the similarities in both their underlying magnetic field configuration and evolution in relation to EUV flux changes. In contrast, the blinker phenomena and the TR BP are sufficiently dissimilar in their observed properties as to constitute different event classes. Our work is an indication that the measurement of similar characteristics across multiple event types holds class-predictive power, and is a significant step towards automated solar atmospheric multi-class classification of unresolved transient EUV sources. Finally, the analysis performed here establishes a connection between solar quiet region CBPs and jets. 相似文献
15.
J. Sánchez Almeida 《Astrophysics and Space Science》2009,320(1-3):121-127
The changes in the Sun occurring at human time-scales can be pinned down to the presence of magnetic fields. These fields determine the structure of the outer solar atmosphere and, therefore, they are responsible for all the energetic part of the solar spectrum, including the UV. Our understanding of the magnetic fields existing at the base of the atmosphere has changed during the last years. The new spectro-polarimeters reveal an ubiquitous magnetic field, present even in the quiet regions. They are widespread and of complex topology, containing far more (unsigned) magnetic flux and magnetic energy that all traditional manifestations of solar activity. These so-called quiet Sun magnetic fields are the subject of the contribution. I summarize their main observational properties, as well as the models put forward to explain them. According to the common wisdom, they may be generated by a turbulent dynamo driven by convective motions. Their true physical role is not understood yet, but it may be consequential both for the Sun (e.g., in determining the structure of the quiet corona), and for other astronomical objects (e.g., if a turbulent dynamo operates in the Sun, the same mechanism provides a very efficient mean of creating surface magnetic fields in all stars with convective envelopes). I discuss the impact of the quiet Sun fields on the transition region and corona, trying to point out the UV signatures of those fields. 相似文献
16.
George L. Withbroe 《Solar physics》2006,235(1-2):369-386
An analysis of spatially-resolved measurements of the intensity of the photospheric continuum by the Michelson Doppler Imager
(MDI) on the SOHO spacecraft indicates that these data can be used to study variations of the Total Solar Irradiance (TSI).
Since the techniques employed depend upon ratios of intensities measured by MDI, they are independent of the absolute photometric
calibration of the instrument. The results suggest that, while it is possible to account for short-term (weeks to months)
variation in TSI by variations in the irradiance contributions of regions with enhanced magnetic fields (larger than ten G
as measured by MDI), the longer-term variations are influenced significantly by variations in the brightness of the quiet
Sun, defined here as regions with magnetic field magnitudes smaller than ten G. The latter regions cover a substantial fraction
of the solar surface, ranging from approximately 90% of the Sun near solar minimum to 70% near solar maximum. The results
provide evidence that a substantial fraction, 50% or more, of the longer term (≥one year) variation in TSI is due to changes
in the brightness of the quiet Sun. 相似文献
17.
The density dependence of solar EUV line intensity ratios from Mg VIII, Si VII, S IX and Si IX ions have been used to determine electron densities in the quiet Sun and coronal holes. The line intensity values have been computed using a model atmosphere of Kopp and Orrall (1976) in order to emphasize the utility of the lines studied which could be compared with observational data that future missions might provide. 相似文献
18.
We present a model for the reconstruction of spectral solar irradiance between 200 and 400?nm. This model is an extension of the total solar irradiance (TSI) model of Crouch et al. (Astrophys.?J. 677, 723, 2008) which is based on a data-driven Monte Carlo simulation of sunspot emergence, fragmentation, and erosion. The resulting time-evolving daily area distribution of magnetic structures of all sizes is used as input to a four-component irradiance model including contributions from the quiet Sun, sunspots, faculae, and network. In extending the model to spectral irradiance in the near- and mid-ultraviolet, the quiet Sun and sunspot emissivities are calculated from synthetic spectra at T eff=5750?K and 5250?K, respectively. Facular emissivities are calculated using a simple synthesis procedure proposed by Solanki and Unruh (Astron. Astrophys. 329, 747, 1998). The resulting time series of ultraviolet flux is calibrated against the data from the SOLSTICE instrument on the Upper Atmospheric Research Satellite (UARS). Using a genetic algorithm, we invert quiet Sun corrections, profile of facular temperature variations with height, and network model parameters which yield the best fit to these data. The resulting best-fit time series reproduces quite well the solar-cycle timescale variations of UARS ultraviolet observations, as well as the short-timescale fluctuations about the 81 day running mean. We synthesize full spectra between 200 and 400?nm, and validate these against the spectra obtained by the ATLAS-1 and ATLAS-3 missions, finding good agreement, to better than 3?% at most wavelengths. We also compare the UV variability predicted by our reconstructions in the descending phase of sunspot cycle 23 to SORCE/SIM data as well as to other reconstructions. Finally, we use the model to reconstruct the time series of spectral irradiance starting in 1874, and investigate temporal correlations between pairs of wavelengths in the bands of interest for stratospheric chemistry and dynamics. 相似文献
19.
K. Wilhelm W. Curdt E. Marsch U. Schühle P. Lemaire A. Gabriel J. -C. Vial M. Grewing M. C. E. Huber S. D. Jordan A. I. Poland R. J. Thomas M. Kühne J. G. Timothy D. M. Hassler O. H. W. Siegmund 《Solar physics》1995,162(1-2):189-231
The instrument SUMER - Solar Ultraviolet Measurements of Emitted Radiation is designed to investigate structures and associated dynamical processes occurring in the solar atmosphere, from the chromosphere through the transition region to the inner corona, over a temperature range from 104 to 2 × 106
K and above. These observations will permit detailed spectroscopic diagnostics of plasma densities and temperatures in many solar features, and will support penetrating studies of underlying physical processes, including plasma flows, turbulence and wave motions, diffusion transport processes, events associated with solar magnetic activity, atmospheric heating, and solar wind acceleration in the inner corona. Specifically, SUMER will measure profiles and intensities of EUV lines; determine Doppler shifts and line broadenings with high accuracy; provide stigmatic images of the Sun in the EUV with high spatial, spectral, and temporal resolution; and obtain monochromatic maps of the full Sun and the inner corona or selected areas thereof. SUMER will be flown on the Solar and Heliospheric Observatory (SOHO), scheduled for launch in November, 1995. This paper has been written to familiarize solar physicists with SUMER and to demonstrate some command procedures for achieving certain scientific observations. 相似文献
20.
D. L. Judge D. R. McMullin H. S. Ogawa D. Hovestadt B. Klecker M. Hilchenbach E. Möbius L. R. Canfield R. E. Vest R. Watts C. Tarrio M. Kühne P. Wurz 《Solar physics》1998,177(1-2):161-173
The first results obtained with the Solar EUV Monitor (SEM), part of the Charge, Element, and Isotope Analysis System (CELIAS) instrument, aboard the SOlar and Heliospheric Observatory (SOHO) satellite are presented. The instrument monitors the full-disk absolute value of the solar Heii irradiance at 30.4 nm, and the full-disk absolute solar irradiance integrated between 0.1 nm and 77 nm. The SEM was first turned on December 15, 1995 and obtained ‘first light’ on December 16, 1995. At this time the SOHO spacecraft was close to the L-1 Lagrange point, 1.5 × 106 km from the Earth towards the Sun. The data obtained by the SEM during the first four and a half months of operation will be presented. Although the period of observation is near solar minimum, the SEM data reveal strong short-term solar irradiance variations in the broad-band, central image channel, which includes solar X-ray emissions. 相似文献