摘要:

Because of its complex nature, the knowledge of spread F is not commensurate with the long period of its study. Rockets, satellites and radar systems have greatley advanced observational information on spread F. We have outlined some of these observations and presented information on certain morphology and characteristics of both the equatorial and high latitude spread F. Although the study of the equatorial spread F seems more advanced than the study of the high latitude spread F, the causes and mechanisms of spread F are poorly understood.

ISSN:0094-243X    

DOI:10.1063/1.41726

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Global UV‐B flux (sum of direct and diffuse radiations) data at four wavelengths 280, 290, 300 and 310 nm are recorded at several locations in India as part of Indian Middle Atmosphere Programme (IMAP). The stations have been selected considering distinct geographic features and possible influence of atmospheric aerosols and particulates on the ground reaching UV‐B flux. Mysore (12.6°N, 76.6°E) has been selected as a continental station largely free from any industrial pollution and large scale bio‐mass burning.An examination of the ground reaching UV‐B flux at Mysore shows a marked dirunal and seasonal asymmetry. This can be attributed to the seasonally varying atmospheric aerosols and particulates which influence the scattering of UV‐B radiation. The available parameterization models are used to reproduce the experimental UV‐B irradiance by varying the input parameters to the model. These results on the dirunal and seasonal variation of global UV‐B flux from experiment and models are discussed in this paper.

ISSN:0094-243X    

DOI:10.1063/1.41727

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

We briefly discuss some of the currently unanswered problems in solar astronomy which lend themselves to investigations particularly in the Extreme Ultra Violet (EUV) region of the spectrum. In this context, need of high spatial, spectral and temporal resolution is emphasized for such studies. Finally, after a brief discussion of the EUV instrumentation, a high resolution stigmatic EUV spectroheliometer is described which is currently under development for high resolution studies of the solar chromosphere, transition region and corona. The spectroheliometer will be flown aboard a sounding rocket.

ISSN:0094-243X    

DOI:10.1063/1.41728

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Solar physics research is an active and growing discipline. This is so not only because an understanding of solar processes is interesting in itself, but also because of the intimate connection between the Sun and the Earth and its inhabitants. It is for these reasons that studies of solar variability and solar seismology occupy prominent positions in current solar research. Solar seismology and solar variability studies, in particular, are paradigms of multi‐disciplinary efforts. They offer a wide range of educational and research experiences and opportunities to students and researchers in many fields. The fruits of this research are often valuable not only in the solar physics domain, but also in various scientific and technological fields. Solar variability research is many‐faceted, and a variety of techniques are employed to study it. Some of the more prominent efforts are surveyed, ranging from direct solar measurement to observations of planets and stars. Emphasis is given to the SCLERA program, which has detected changes on the Sun which may be relevant to the solar energy output and to the long‐term climate of the Earth. This emphasis is given in part to project an example where education is an important consideration. The future of solar variability research is outlined, and the SCLERA International Network is described. This network is based on the idea that collaboration among scientists is the foundation on which are built opportunities for scientific discoveries, educational development, and technological progress.

ISSN:0094-243X    

DOI:10.1063/1.41729

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

There are a number of interesting aspects of the Sun’s internal and surface structure that can be seen in the observed properties of the Sun’s normal modes of oscillation. Two examples of these are the speed of sound and the internal rotation. There are other manifestations that are reported but not yet confirmed; or predicted but not yet observed. Examples here are the abundance of He in the convection zone and the detection of the internal gravity modes of oscillation. The current situation regarding both classes of works is discussed and exciting opportunities are indicated for the next generation of researchers. These opportunities are open to both space and ground‐level observing programs

ISSN:0094-243X    

DOI:10.1063/1.41730

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The following is shown on the basis of a solution of the integral diffusion equations for radiation in a multilevel helium atom under low‐temperature plasma conditions (Te=5000‐10000°K) in the ‘‘vertical slab’’ model with variable electron densities: (a) Neutral helium is ionized by coronal radiation mainly in the &lgr;&lgr;100‐300A spectral region: the degree of helium ionization is maximum at the boundary planes. (b) The 23S level is destroyed by electron impacts, and the 21S level decays via the escape of the quanta of &lgr;584A through the 21P level. (c) Emission in the resonance line &lgr;584A (21P→11S) occurs due to recombination to 21S with subsequent absorption of quanta of infrared radiation &lgr;20581A. (d) The radiation of helium is generated in the vicinity of the boundary planes in the penetration of radiation with &lgr;=200A, where the density of matter decreases gradually down to the coronal value. In the subordinate lines, the radiation is conditioned by quasi‐resonance scattering of photospheric radiation. (e) The calculated absolute values of the intensities of helium and hydrogen lines are in good agreement with the observations. There was a supposition that the electron density is changed by the definite law as it is given on the Figure 2.

ISSN:0094-243X    

DOI:10.1063/1.41731

出版商:AIP    

年代:1992

数据来源: AIP

ISSN:0094-243X    

DOI:10.1063/1.41732

出版商:AIP    

年代:1992

数据来源: AIP

ISSN:0094-243X    

DOI:10.1063/1.41710

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Since the Earth’s atmosphere is transparent to electromagnetic radiation only in few rather narrow windows, space‐based observations are essential for understanding the nature of various astronomical objects. Present status of research in different portions of electromagnetic spectrum is briefly reviewed and some prospects of the development in the future are mentioned. Although space observations are costly, their impact on astrophysics is so substantial that nobody can ignore this area of research. As a consequence, the very nature of astrophysical research is subject to profound change.

ISSN:0094-243X    

DOI:10.1063/1.41711

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Making an effort with the naked eye to observe the night sky means actually to make observations in a rather small wavelength interval from 300nm to 800nm and, hence temperaturewise in terms of black‐body radiation to deal with temperatures of 3000K to 10000K. How the sky would look if our eyes would be sensitive to neutrino radiation or gravitational waves, respectively? First of all, one would surely encounter the same problem as one encounters in the electromagnetic spectrum: One would be able only to observe some spectral lines in the very broad neutrino spectrum or spectrum of gravitational waves. However, the physics involved in those observations and their interpretation would be completely different, compared to the phenomena one is dealing with in the electromagnetic spectrum. Three astronomies seem to exist simultaneously in the future to expand the horizon of astronomical observation: Photon astronomy, neutrino astronomy, and gravitational wave astronomy. Sources of the radiation, their spectra, and ground‐based and space‐based observations for photons, neutrinos, and gravitational waves will be briefly reviewed.

ISSN:0094-243X    

DOI:10.1063/1.41712

出版商:AIP    

年代:1992

数据来源: AIP