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Publications and source records attributed to Jordan, S. D..
The solar ultraviolet measurement of emitted radiation (SUMER) observational program provides continuous observations of the solar disk and the low corona off-limb since 24 January 1996. The achievements of the observational program to date are reviewed. Examples of results from various researchers are presented and discussed. The SUMER instrument and its performance onboard the Solar and Heliospheric Observatory (SOHO) are summarized.
This paper describes the results of comparing Solar EUV Rocket Telescope and Spectrograph (SERTS-3) images obtained in the transition region line of He II 304 A with chromospheric He I 10830 A absorption; with strong coronal lines of Mg IX 368 A, Fe XV 284 A and 417 A, and Fe XVI 335 A and 31 A; with H-alpha; with Ca II 8542 A; and with magnetograms in Fe I 8688H-alpha. All of the images are illustrated, and the image reconstruction techniques used are described and evaluated. The high correlation of the He II 304 A and He I 10830 A images, originally found by Harvey and Sheeley (1977), is confirmed and is put on a quantitative basis. We find that the supergranulation network has greater contrast, and that filaments appear darker, in 10830 A than in 304 A. In active regions, the 304 A line follows more closely the behavior of H-alpha and Ca II 8542 A than the 10830 A line.
Although a large body of recent work supports the formation of the He II 304 A resonance line by collisional excitation in the quiet sun, the formation mechanism is less clear in strong coronal active regions and flares. The 1989 May 5 flight of the Goddard Solar Extreme Ultraviolet Rocket Telescope and Spectrograph (SERTS-3) provided a data set that is well suited to addressing this question. This paper develops a method of assessment of the line formation mechanism that is based on simple non-LTE theory and is applied to these data. The results support the conclusion of other authors that the 304 A line is formed by collisional excitation in the quiet sun, but that photoionization-recombination (p-r) may play a significant role in coronal active regions, and that p-r is important, and may even be predominant, in many flares.
The experiment Solar Ultraviolet Measurements of Emitted Radiation (SUMER) is designed for the investigations of plasma flow characteristics, turbulence and wave motions, plasma densities and temperatures, structures and events associated with solar magnetic activity in the chromosphere, the transition zone and the corona. Specifically, SUMER will measure profiles and intensities of Extreme Ultraviolet (EUV) lines emitted in the solar atmosphere ranging from the upper chromosphere to the lower corona; determine line broadenings, spectral positions and Doppler shifts with high accuracy, provide stigmatic images of selected areas of the Sun in the EUV with high spatial, temporal and spectral resolution and obtain full images of the Sun and the inner corona in selectable EUV lines, corresponding to a temperature from 10,000 to more than 1,800,000 K.
Use of the Solar Optical Telescope (SOT) to study the energetics and dynamics of the solar atmosphere is described. Studies include the origin and evolution of the Sun's magnetic field, the structure of solar subsurface convection, the heating of the outer solar atmosphere, and sources of the solar wind in the lower lying regions of the outer atmosphere. To achieve the scientific goals of the SOT, it is necessary to observe features in the solar atmosphere on the scale of a typical photon mean-free-path in continuum radiation and also of the hydrodynamic or density scale-height. The 1.3 m telescope, of a Gregorian configuration, achieves close to 0.1 arcsec angular resolution on the Sun in visible and ultraviolet wavelengths.
This paper describes NASA's Solar Optical Telescope (SOT), which is designed to measure the density temperature, magnetic fields, and the nonthermal velocity fields of solar features on a scale at which the basic physical processes are occurring. A series of 7- to 14-day missions carrying a 1.3-meter solar-observing telescope that has a spatial resolution only slightly larger than the photon mean-free-path of about 80 km will be flown as a Spacelab-attached payload aboard the Space Transportation System (STS) in mid-1990. The telescope (Fig. 1) will be built and integrated by the Perkin-Elmer Corporation and is managed by NASA's Goddard Space Flight Center. Coarse pointing to the sun is provided by the Spacelab instrument pointing system (IPS), whereas fine pointing is provided by the Observatory pointing and control system. The science instruments for the first mission, the photometric filtergraph and the coordinated filtergraph/spectrograph, that are integrated into a combined instrument package are also described.
The Solar Optical Telescope (SOT) is designed to provide the solar physics community with the data necessary for solving several fundamental problems in the energetics and dynamics of the solar atmosphere. Among these problems are questions on the origin and evolution of the sun's magnetic field, heating of the outer solar atmosphere, and sources of the solar wind in the lower lying regions of the outer atmosphere. The SOT will be built under the management of NASA's Goddard Space Flight Center, with science instruments provided by teams led by Principal Investigators. The telescope will be built by the Perkin-Elmer Corporation, and the science instruments selected for the first flight will be provided by the Lockheed Palo Alto Research Laboratory (LPARL) and the California Institute of Technology, with actual construction of a combined science instrument taking place at the LPARL. The SOT has a 1.3-meter-diameter primary mirror that will be capable of achieving diffraction-limited viewing in the visible of 0.1 arc-second. This dimension is less than a hydrodynamic scale-height or a mean-free-path of a continuum photon in the solar atmosphere. Image stability will be achieved by a control system in the telescope, which moves both the primary and tertiary mirrors in tandem, and will be further enhanced by a correlation tracker in the combined science instrument. The SOT Facility is currently scheduled for its first flight on Spacelab at the beginning of the 1990's.
Nonthermal physical processes in the solar atmosphere are discussed. The solar atmospheric regions are defined, and solar convection and its phenomena are explained. The relationship of the solar dynamo, magnetic field, and flares is explored. The solar atmospheric velocity fields are discussed, and the unresolved problem of the nature of atmospheric heating is detailed. The solar wind heating and acceleration are discussed and the need for global solar atmospheric models is emphasized. The application of these solar nonthermal processes to the stars in general is then taken up, employing the same categories as were applied to the solar atmosphere.
Solar physics was reviewed in the context of the solar atmoshere. The understanding of the solar atmosphere is linked to stellar atmospheric research. Topics covered include: the existence of the chromosphere, the corona, and the solar wind; the interactive complex of convection, differential rotation, magnetic field generation and concentration, and the activity cycle; phenomena such as granulation, supergranulation, the 5 minute oscillation, filigree, faculae, sunspots, spicules, prominences, surges, and the spectacular flares.
General features of the solar chromospheric heating problem, which also apply to many stellar chromospheres, are reviewed. Current theories are discussed, including: heating by short period sound waves; the weak shock theory; and the time-dependent approach.
The Solar Optical Telescope (SOT) is a 1-m class, high resolution solar telescope which NASA plans to operate on the Shuttle Spacelab during the mid and late 1980's. SOT will provide resolution down to 0.1 arcsec, and can therefore be used to solve many problems of solar atmosphere structure and dynamics. In particular, SOT should provide definite data on (1) the source of the sun's magnetic field, (2) the amount of power in waves generated in the photosphere, (3) the heating of the chromosphere, and (4) the local and global mass and energy balance in the solar transition region. The SOT Scientific Working Group will help plan, develop, and update the overall scientific plan for the SOT, as well as make recommendations with regard to the SOT project, instrumentation optimization, and scientific data management.
It is demonstrated that short period acoustic waves appear adequate to heat the low chromosphere in the region just above the temperature minimum, these waves are unlikely to provide sufficient energy to heat the chromosphere above tau-5000 A(normal) less than 10 to the -6th. Calculations also show that the electron density to H density ratio from chromospheric models is too low for the H2 molecule to affect the population of H(-).
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The low chromosphere now seems definitely to require mechanical heating, and dissipation of initially acoustic waves by shocking is one of the most promising possibilities. Results of recent calculations indicate that the weak shock theory may be applicable in this case, but discrepancies exist among various applications of this theory, and the explanations offered to date are not completely satisfactory. It is shown that the different approximations used by different authors to evaluate the mechanical flux integral play an important role in producing these discrepancies, in addition to the already well-known effects of the density scale heights and the wave periods. Arguments are presented favoring Ulmschneider's (1970, 1971) method for evaluation of this flux integral.
The results of observations of the sun performed at 3.71 and 11.1 cm on Jan. 14, 1972, using the NRAO three-element interferometer in the 2.7-1.8-0.9 km configuration, are reported. A flare of importance 1 N observed in the active region 693 near the east limb at about 1530 UT is discussed.
The shock dissipation hypothesis for solar atmospheric heating is extended to stellar chromospheres of late type stars which have significant convective envelopes. Principle wave modes are studied for their generation, propagation, and heating properties in the presence of a magnetic field, and various approximations on when a sound wave becomes strong enough to produce heating in the atmosphere are presented.
The detection and significance of 300-second oscillations in extreme-ultraviolet lines formed in the solar transition region are discussed. Detection was accomplished with the Goddard extreme-ultraviolet spectroheliograph and the Wolter type II grazing-incidence telescope. The Cooley-Tukey algorithm was used to compute the required Fourier transform of the discrete data. Presence of significant power in the observed lines around 262 sec seems to be the first observational evidence that periodic waves in this frequency range persist at heights where local kinetic temperatures are close to one million degrees K. The observed horizontal extent of the wave fronts appears to be much greater than the extent of coherent oscillating elements at chromospheric heights. Several implications are stated for the problem of heating of the transition region and low corona.