摘要:

For more than 90 years, solar extreme ultraviolet (EUV) irradiance modeling has progressed from empirical blackbody radiation formulations, through fudge factors, to typically measured irradiances and reference spectra as well as time‐dependent empirical models representing continua and line emissions. A summary of recent EUV measurements by five rockets and three satellites during the 1980s is presented along with the major modeling efforts. The most significant reference spectra are reviewed and three independently derived empirical models are described. These include Hinteregger's 1981 SERF1, Nusinov's 1984 two‐component, and Tobiska's 1990/1991 SERF2/EUV91 flux models. They each provide daily full‐disk broad spectrum flux values from 2 to 105 nm at 1 AU. All the models depend to one degree or another on the long time series of the Atmosphere Explorer E (AE‐E) EUV database. Each model uses ground‐ and/or space‐based proxies to create emissions from solar atmospheric regions. Future challenges in EUV modeling are summarized including the basic requirements of models, the task of incorporating new observations and theory into the models, the task of comparing models with solar‐terrestrial data sets, and long‐term goals and modeling objectives. By the late 1990s, empirical models will potentially be improved through the use of proposed solar EUV irradiance measurements and images at selected wavelengths that will greatly enhance modeling and predicti

ISSN:0148-0227    

DOI:10.1029/93JA01943

年代:1993

数据来源: WILEY

摘要:

From satellite observations the solar total irradiance is known to vary. Sunspot blocking, facular emission, and network emission are three identified causes for the variations. In this paper we examine several different solar indices measured over the past century that are potential proxy measures for the Sun's irradiance. These indices are (1) the equatorial solar rotation rate, (2) the sunspot structure, the decay rate of individual sunspots, and the number of sunspots without umbrae, and (3) the length and decay rate of the sunspot cycle. Each index can be used to develop a model for the Sun's total irradiance as seen at the Earth. Three solar indices allow the irradiance to be modeled back to the mid‐1700s. The indices are (1) the length of the solar cycle, (2) the normalized decay rate of the solar cycle, and (3) the mean level of solar activity. All the indices are well correlated, and one possible explanation for their nearly simultaneous variations is changes in the Sun's convective energy transport. Although changes in the Sun's convective energy transport are outside the realm of normal stellar structure theory (e.g., mixing length theory), one can imagine variations arising from even the simplest view of sunspots as vertical tubes of magnetic flux, which would serve as rigid pillars affecting the energy flow patterns by ensuring larger‐scale eddies. A composite solar irradiance model, based upon these proxies, is compared to the northern hemisphere temperature departures for 1700‐1992. Approximately 71% of the decadal variance in the last century can be modeled with these solar indices, although this analysis does not include anthropogenic or other variations which would affect the results. Over the entire three centuries, ∼50% of the variance is modeled. Both this analysis and previous similar analyses have correlations of model solar irradiances and measured Earth surface temperatures that are significant at better than the 95% confidence level. To understand our present climate variations, we must place the anthropogenic variations in the context of natural variability from solar, volcanic, oceanic, and other

ISSN:0148-0227    

DOI:10.1029/93JA01944

年代:1993

数据来源: WILEY

摘要:

It has recently been reported that the total radiative emission variations from solar type stars exceeds the currently observed solar constant variations (from spacecraft over the last decade) by a factor near 4. Aside from other remote alternatives, this suggests three clear possibilities: (1) the Sun may undergo irradiance variations several times larger than any we have seen; (2) our Sun is highly unusual with regard to its radiative output; or (3) our terrestrial position in the heliosphere provides a special vantage point which reduces the observed solar irradiance variations. We investigate the last possibility by considering the influence of observer latitude upon calculated irradiance variations using a simple model for emission from solar contrast features. We consider modeled sunspots, faculae, and network structures. As the latitude angle of the observer rises relative to the heliographic equator, sunspot deficit contributions diminish and facular plus network contributions escalate. We find that the observing latitude can influence the irradiance variations by a factor near 6. When we integrate the irradiance variations, over the celestial sphere, they average to 3 times the terrestrial effect, suggesting that the solar cycle luminosity variations are proportionally, 3 times larger than the solar constant variations. Thus we suggest the Sun's luminosity output varies even more strongly with the solar cycle than is apparent in the solar constant variations. The influence of the observer viewing angle relative to stellar spin axis, studied here, may be possible to investigate with a thorough statistical examination of other solar type stars. Additionally, the rotational modulation due to active regions (as a function of observer viewing angle) may also be a valuable area for future investigation.

ISSN:0148-0227    

DOI:10.1029/93JA01941

年代:1993

数据来源: WILEY

摘要:

We analyze simultaneous, or near‐simultaneous, coregistered, digital, photometric images of solar photospheric intensity and line‐of‐sight magnetic field. Images were made with the Lockheed tunable filter instrument at the Swedish Solar Observatory, La Palma, with the video spectra‐spectroheliograph system at the San Fernando Observatory and with the new NASA spectromagnetograph at the National Solar Observatory at Kitt Peak. We study the disk center contrasts of small magnetic elements. While active region faculae are dark at disk center quiet Sun network features are bright. The populations of magnetic field elements that make up these two kinds of features are quite different. Different contrast center‐limb functions must be used when estimating their irradiance or luminosity contributions. The disk center contrasts of active region faculae are color dependent and indicate a depth effect related to the H−opacity of the facular atmosphere. This result is important for calibration of monochromatic observations of faculae to bolometric irradiance fluctuations. We emphasize the value of cooperative observations among installations whose differing strengths are co

ISSN:0148-0227    

DOI:10.1029/93JA01942

年代:1993

数据来源: WILEY

摘要:

The decadal oscillation of the temperature and geopotential height in the lower stratosphere of the northern hemisphere can be followed back to the early 1950s. During this time it was in phase with the 11‐year sunspot cycle. The correlation with the solar cycle is positive and largest in the stratospheric geopotential heights of the subtropics below 10 mbar (∼31 km, which is as high as the grid point data reach), especially on the western, ocean‐dominated side of the hemisphere. As expected from the hydrostatic equation, it is also evident in the temperatures of the upper troposphere in the same region. There is no large correlation at high latitudes. The correlation with the sunspot cycle is weakest in January‐February, but if the data in these months are grouped according to the wind direction in the quasi‐biennial oscillation (QBO) of the lower equatorial stratosphere, the positive subtropical correlations in the east years are as high as in all other months. There are, in addition large negative correlations in the Arctic in agreement with the strong teleconnection (negative correlation) between lower and higher latitudes in winter. There is no consistent sign in the weak correlations at middle and lower latitudes in the west years, but in the Arctic the correlation with the solar cycle is highly positive, because those major midwinter warmings that occur in west years of the QBO take place in solar maxima, whereas the years without major warmings are found in solar minima. There is not yet an explanation of the 10‐12 year oscillation in the s

ISSN:0148-0227    

DOI:10.1029/92JA02736

年代:1993

数据来源: WILEY

摘要:

Among the various uncertainties present in climate modeling, the variability of total solar irradiance is not one of the least. For lack of any direct measure of the solar irradiance in the past, substitutes are needed. However, the difficulties are twofold: (1) the reliability of the proxies and (2) the need for some physical mechanism relating these proxies to the solar luminosity. On the basis of a better understanding of the solar machinery we can now propose a plausible scenario connecting the exchanges of energy between the various reservoirs: magnetic, thermal, gravitational, and kinetic. In the present paper we discuss the available proxies and suggest a way to reconstruct total solar irradiance over the past four centuries. The response of the Laboratoire de Météorologie Dynamique atmospheric general circulation model to magnetoconvective solar forcing during the Maunder minimum is discussed. The simulated cooling appears to be compatible with temperature data from the Little Ice Age; in addition, it is found that variations of globally homogeneous external forcing parameters, like incoming solar flux or greenhouse gas loading, yield climate responses with very similar geographical pattern

ISSN:0148-0227    

DOI:10.1029/93JA00305

年代:1993

数据来源: WILEY

摘要:

Many years of research have demonstrated that large, nonrecurrent geomagnetic storms, shock wave disturbances in the solar wind, and energetic particle events in interplanetary space often occur in close association with large solar flares. This result has led to a paradigm of cause and effect ‐ that large solar flares are the fundamental cause of these events in the near‐Earth space environment. This paradigm, which I call “the solar flare myth,” dominates the popular perception of the relationship between solar activity and interplanetary and geomagnetic events and has provided much of the pragmatic rationale for the study of the solar flare phenomenon. Yet there is good evidence that this paradigm is wrong and that flares do not generally play a central role in producing major transient disturbances in the near‐Earth space environment. In this paper I outline a different paradigm of cause and effect that removes solar flares from their central position in the chain of events leading from the Sun to near‐Earth space. Instead, this central role is given to events known as coronal mas

ISSN:0148-0227    

DOI:10.1029/93JA01896

年代:1993

数据来源: WILEY

摘要:

This paper will list, investigate, and evaluate the various spin mechanisms for cosmic dust particles that have been suggested in the literature. This evaluation will concentrate on the possibility of particle fragmentation (rotational bursting) of cosmic dust. The importance of particle fragmentation is manifested by the fact that dust particle size distribution will be changed. More importantly, repeated fragmentation of interplanetary dust particles will give rise to some of the observed “β meteoroids.” Some of these particles are driven out of the solar system and into interstellar space by solar radiation pressure. If this mass loss mechanism is taking place in stellar systems, then it becomes a source for interstellar dust. This paper also addresses the possibility that massive rotational bursting by circumsolar dust particles is taking place in the F corona region. This rotational bursting of F coronal dust could be taking place because of the classical “Paddack effect,” along with a similar spin mechanism suggested by the author, and caused by coronal mass e

ISSN:0148-0227    

DOI:10.1029/93JA01521

年代:1993

数据来源: WILEY

摘要:

Systematic discrepancies have been observed between ion density measurements taken by the electrostatic analyzers on ISEE 3 and the Faraday cup and electrostatic analyzer on board the IMP 8 spacecraft during the International Magnetospheric Study. We have quantified these discrepancies as a function of solar wind bulk velocity and ion temperature, and have developed correction algorithms that should bring all density measurements to a common base. The electron densities from ISEE 3 are used as the intercalibrating base, since these measurements of the solar wind density should not depend on the ion velocity or temperature.

ISSN:0148-0227    

DOI:10.1029/93JA01747

年代:1993

数据来源: WILEY

摘要:

Two‐dimensional hybrid (particle ions, massless fluid electrons) simulations of quasi‐parallel collisionless shocks are carried out in order to investigate the upstream wave properties, the shock re‐formation process, and the downstream turbulence. The two‐dimensional simulations confirm the results of earlier one‐dimensional simulations. When backstreaming diffuse ions are retained re‐formation of a shock with an upstream magnetic field ‐ shock normal angle of ΘBno= 30° occurs as a result of upstream low‐frequency waves which steepen, become pulsationlike structures and take over as the re‐formed shock. The upstream waves are initially aligned with the shock normal; later in the run the waves become more and more aligned with the upstream magnetic field. However, when approaching the shock, the wave vectors are refracted in the region of increasing diffuse ion density into the shock normal direction so that shock re‐formation is again coherent along the shock surface. In addition, re‐formation on a smaller scale and out of phase along the shock front is due to more or less specularly reflected ions. Re‐formation of a ΘBno= 10° shock is due to locally at the shock ramp emerging waves. These are attributed to the so‐called interface instability in the region of partial overlap between the incident cold solar wind and part of the hot downstream distribution. These waves emerge in phase along the shock surface and thus re‐formation is in this more parallel case also coherent along the shock. At medium Alfvén Mach number (MA∼ 5) shocks, upstream waves which are aligned with the upstream magnetic field are convected into the shock and produce ripples on the shock surface. At higher Mach number (MA∼ 9) the shock surface becomes less coherent and the local value of the shock normal ‐ magnetic field angle varies greatly. The re‐formation length scale is larger than in the lower Mach number case. The turbulence downstream reflects the two mechanisms of shock reformation: in the ΘBno= 30° case the upstream pulsations are mode converted when convected through the shock layer. In the ΘBno= 10° case the downstream turbulence results f

ISSN:0148-0227    

DOI:10.1029/93JA01647

年代:1993

数据来源: WILEY