Identifications of some highly-ionized iron and nickel lines in the 200–400 Å region of the solar spectrum

A number of previously unclassified multiplets of Fexiv, xiii, xii, and xi produced by transitions of the type 3s ²3p ⁿ -3s3p ⁿ⁺¹ are identified in the XUV spectrum of the Sun. The iron lines account for most of the previously unidentified strong lines between 330 and 370 Å. Solar observations of especial value for the investigation of the 300–400 Å region were the slitless spectroheliograms of September 22, 1968 (Purcell and Tousey, 1969) and November 4, 1969 (Tousey, 1971) — on which the image of a flare was recorded. Other solar identifications in the same spectral region include the resonance lines of Nixvii and Nixviii, and one 3p-3d multiplet of Fexiii. The solar blend at 417 Å involving the Fexv inter-combination line and Sxiv is resolved.     

The interpretation of the XUV solar spectrum

This paper reviews (a) the earth's ionosphere, and (b) the solar atmosphere, in relation to the recent observations of solar XUV. The expected ionospheric characteristics are derived as directly as possible from the XUV observations and then compared with the well-known D-, E-, and F-layer formations. The comparison leads to (1) a high ionospheric recombination coefficient decreasing rapidly with height, (2) contributions to the E-layer from both UV and X-rays, and (3) very little difference in the solar cycle variations from the D-, E-, and F-layers although intensity variations are greater from high than low ions. The flux measurements of the identified XUV solar emission lines give information on the numbers of ions in the solar atmosphere. This makes it possible to derive (1) the amount of solar material in each temperature range, (2) the chemical abundances, and (3) the physical differences between quiet solar atmosphere, centres of activity, and flares. When the new dielectronic recombination coefficients are well investigated it should be possible to redetermine the distribution of solar material with temperature. The fitting of such results to chromospheric and coronal models provides many problems.     

Observations of the profiles of solar UV emission lines and their analysis in terms of the heating and production of the corona

Observations of the solar spectrum have been made between 1200–2200 with high spectral resolution. The results were obtained with an all-reflecting echelle spectrograph carried by a stabilized Skylark rocket launched in April 1970. Measurements of the profiles of a number of emission lines due to Siii, Cii, Siiii and Civ formed in the temperature range 10⁴-10⁵ K, indicate ion energies which are considerably in excess of the electron temperatures derived from the ionization balance. Since the ion/electron relaxation time is very short the observed ion energies cannot correspond to an ion temperature and hence a non-thermal mechanical energy component exists in the transition zone.It is postulated that the non-thermal energy component represents the actual mechanical energy responsible for the heating of the corona, and, that, it is propagated as an acoustic wave. On this basis and with a preliminary estimate of the reflection from the transition zone, a flux of 3 × 10⁵ erg cm ^-2 s ^-1 is established as entering the corona. This value is in agreement with estimates of the total energy loss from the corona due to conduction, radiation and the solar wind, thus establishing a gross energy balance.Theoretical calculations are currently underway to establish the physical nature of the atmosphere which would result from such a propagating flux. At the present time this has been carried out for an atmosphere in hydrostatic equilibrium and the energy balance equation solved. A preliminary temperature structure which results is shown in Figure 1, together with the derived distribution in electron density. This gives a corona of the right temperature and density but the observed structure deviates in detail from those derived from an analysis of the solar XUV spectrum.     

Type IV solar radio emission

Conclusion We have got a reasonably clear idea of the various forms under which the type IV continuum emission may appear. Also we can imagine what kind of processes come into play during a type IV event. But the insight gained so far applies to the general case. Individual cases are widely different, and we are still far from understanding why a given event behaves as it does. For instance, why are metric responses lacking at a certain big microwave outburst, or why is the decimetric component particularly strong or prolonged on certain occasions? One can imagine that such questions would receive an answer if one were allowed to see the configuration of magnetic lines of force above the activity region !Does the type IV event tell us a fine story of the interplay of energetic particles and streams of particles with coronal magnetic fields ? Maybe the story would be a fine one if the language could be understood. At present we know only a few words of it; for this reason to us the story is very fragmentary. First of all, however, the message should be recorded far more completely than has been done so far. The number of observations that should be made of one and the same event is tremendous; the program comprises:1) spectral observations from 1000 Mc/s down to the lowest frequencies; 2) single frequency observations at a great many wavelengths covering the whole radio spectrum; 3) measurements of polarization and 4) determinations of position and angular extent in at least every octave of the whole radio spectrum.Especially as regards the latter two points, the present situation is still very unsatisfactory, though good work has been done already in Japan. The realization of a complete recording of phenomena during a type IV event calls for a combined effort of several observatories.Very encouraging are the established relations between solar type IV events and terrestrial phenomena. From an analysis of solar cosmic ray events as recorded on several places on the earth, interesting inferences have been drawn regarding the travelling conditions of particles in interplanetary space (cf. Carmichael, 1962). Likewise, one may expect interesting information on the behaviour of interplanetary particle clouds of solar origin from (interferometric) observations of decametric radio emission on the occasion of type IV events.The occurrence of a major type IV event enables forecasters to predict successfully geomagnetic and ionospheric storms. Type IV events will determine at what times certain space research experiments will be launched in the next solar cycle. One should like to be able to indicate the probability for the occurrence of type IV solar radio flares themselves. It is known that these flares generally occur in complex sunspot groups; but a complex sunspot group does not of necessity imply the occurrence of a type IV flare. Observations of coronal condensations at microwave frequencies with a high resolution interferometer may help sorting out those centres of activity that are most likely to produce type IV flares.     

Laboratory-produced radiation related to the solar flare emission

A review is given of continuing efforts to generate laboratory spectra at photon energies above 1 keV from highly ionized atoms. Emphasis is placed on the most easily-interpreted highest ion stages such as the hydrogenic, helium-like and lithium-like species. The close similarities to solar flare observations of certain signatures, such as the line and continuum X-ray spectra and microwave emission as well as their sequence of occurrence, are pointed out and scaling factors are given.     

Absolute intensity measurements in the extreme ultraviolet spectrum of solar radiation

Experimental results and problems of absolute intensity measurements of solar electromagnetic radiation in the extreme ultraviolet (EUV) and soft X-ray region of the spectrum (designated cumulatively as XUV for brevity) are reviewed. The numerous practical problems are divided in two major areas, (a) general problems of heterochromatic absolute XUV spectrophotometry in the laboratory and (b) specific problems characteristic of requirements of solar physics, the physics of planetary atmospheres, and existing restrictions of space technology. Within the first area (a) emphasis is placed on recent progress toward justified reliance on ionization detectors without necessary connection to source standards. For the second area (b), emphasis is placed on the immediate need to have existing exploratory observations followed by a new phase of more systematic experiments of increased accuracy.     

The emission mechanisms for solar radio bursts

Emission mechanisms for meter- solar radio bursts are reviewed with emphasis on fundamental plasma emission.The standard version of fundamental plasma emission is due to scattering of Langmuir waves into transverse waves by thermal ions. It may be treated semi-quantitatively by analogy with Thomson scattering provided induced scattering is unimportant. A physical interpretation of induced scattering is given and used to derive the transfer equation in a semi-quantitative way. Solutions of the transfer equation are presented and it is emphasized that standard fundamental emission with brightness temperatures 10⁹ K can be explained only under seemingly exceptional circumstances.Two alternative fundamental emission mechanisms are discussed: coalescence of Langmuir waves with low-frequency waves and direct conversion due to a density inhomogeneity. It is pointed out for the first time that the coalescence process (actually a related decay process) can lead to amplified transverse waves. The coalescence process saturates when the effective temperature T ^t of the transverse waves reaches the effective temperature T ^l of the Langmuir waves. This saturation occurs provided the energy density in the low-frequency waves exceeds a specific value which is about 10^-9 of the thermal energy density for emission from the corona at 100 MHz. It is suggested that direct emission has been dismissed as a possible alternative without adequate justification.Second harmonic plasma emission is discussed and compared with fundamental plasma emission. It also saturates at T ^t T ^l , and this saturation should occur in the corona roughly for T ^l 10¹⁵ K. If fundamental plasma emission is attributed to coalescence with low-frequency waves, then for T ^l 10¹⁵ K the brightness temperatures at the two harmonics should be equal and equal to T ^l . This offers a natural explanation for the approximate equality of the two brightness temperature often found in type II and type III bursts.Analytic treatments of gyro-synchrotron emission are reviewed. The application of the mechanism to moving type IV bursts is discussed in view of bursts with 10¹⁰ K at 43 MHz.     

发射光谱测量电弧加热发动机羽流温度

为了研究玻耳兹曼图法和谱线绝对强度法对测量结果的影响，讨论了电弧加热发动机羽流的光谱诊断方法，并建立了一套光谱诊断系统。以氩气为工质，利用此系统在真空室中进行了光谱诊断．分别用玻耳兹曼图法和谱线的绝对强度法得到了羽流的温度，这两种方法测得的结果有20％～30％的偏差。实验中氩气流量为42．1mg／s，功率约为200W。试验结果表明，在试验工况下，由于羽流处在热力学非平衡态，采用玻耳兹曼图法和谱线的绝对强度法得到的结果是不同的，应该根据具体的工况选择测量方法。     

Microwave spectrum analysis as solar energy release diagnostics

The possibilities of using spectrographic observations of microwave radio emission as a solar flare plasma diagnostic are discussed. The spectral fine structure of the emission is interpreted in the context of plasma emission mechanisms. The balance equations for particles and plasma turbulence together with the transfer equations for electromagnetic waves in a plasma are solved for a model containing a diverging magnetic loop. As a result of the analysis of the blip-type spectral feature, the structure of energy release region and the unperturbed plasma concentration in the preflare loop are evaluated. The number of accelerated electrons and the intensity of the plasma turbulence in the source region are estimated using the properties of the weak continuum emission following the blip. Based on the degree of circular polarization of both the narrow band and the continuum emission, estimates for the external magnetic field strength and the angular width of the radiating plasma turbulence have been obtained.     

Transport of energetic solar particles on closed magnetospheric field lines

Whereas the entry mechanism of energetic solar particles into the open field line region of the magnetosphere is now a rather well understood process, transport processes of solar particles in the closed field line region are still unclear and under dispute. The main difficulty lies not only in the fact that different field models predict different behavior of the particles in the quasi-trapping region (e.g. cut-off latitude), but that dynamic changes of the magnetosphere as geomagnetic storms and substorms greatly influence the particle distribution. The present review tries to summarize the status of knowledge regarding solar proton behavior on closed magnetospheric field lines. Together with a presentation of recent measurements in the closed field line region relevant theoretical problems are discussed. They fall either under the study of single particle motion in different static magnetospheric configurations (due to different field models or due to real, e.g. ring current induced changes), or under the study of resonant interaction processes as pitch angle scattering and radial diffusion.Invited Lecture, Second Meeting of the European Geophysical Society, September 1974, Trieste, Italy.     

Design and Performance of the ICON EUV Spectrograph

We present the design, implementation, and on-ground performance measurements of the Ionospheric Connection Explorer EUV spectrometer, ICON EUV, a wide field (\(17^{\circ}\times 12^{\circ}\)) extreme ultraviolet (EUV) imaging spectrograph designed to observe the lower ionosphere at tangent altitudes between 100 and 500 km. The primary targets of the spectrometer, which has a spectral range of 54–88 nm, are the Oii emission lines at 61.6 nm and 83.4 nm. Its design, using a single optical element, permits a $0\stackrel{{}^{°}}{.}26$ imaging resolution perpendicular to the spectral dispersion direction with a large (\(12^{\circ} \)) acceptance parallel to the dispersion direction while providing a slit-width dominated spectral resolution of \(R\sim25\) at 58.4 nm. Pre-flight calibration shows that the instrument has met all of the science performance requirements.     

Hectometric and kilometric solar radio emission observed from satellites in August 1972

Type II, III, and continuum solar radio events, as well as intense terrestrial magnetospheric radio emissions, were observed at low frequencies (10 MHz to 30 kHz) by the IMP-6 satellite during the period of high solar activity in August 1972. This review covers briefly the unique direction finding capability of the experiment, as well as a detailed chronology of the low frequency radio events, and, where possible, their association with both groundbased radio observations and solar flares. The attempted observation of solar bursts in the presence of intense magnetospheric noise may, as illustrated, lead to erroneous results in the absence of directional information. The problem of assigning an electron density scale and its influence on determining burst trajectories is reviewed. However, for the disturbed conditions existing during the period in question, we feel that such trajectories cannot be determined accurately by this method. In conclusion, the capabilities, limitations, and observing programs of present and future satellite experiments are briefly discussed.