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Bohlin, J. D.

Publications and source records attributed to Bohlin, J. D..

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

The Solar Probe mission

The Solar Probe will deliver a 133.5 kg science payload into a 4 R(S) perihelion solar polar orbit to explore in situ one of the last frontiers in the solar system - the solar corona. Using a payload of 12 scientific experiments, it will be possible to answer many long-standing fundamental problems concerning the structure and dynamics of the outer solar atmosphere, including the acceleration, storage, and transport of energetic particles near the sun and in the inner heliosphere.

Anderson, J.↗
NASA NTRS1983

Solar and heliospheric physics space missions for the 1980's

Proposed space missions or observing facilities for the late 1980s and early 1990s that would enable research on specific problems in solar and heliospheric physics are reviewed. For studies of the sun's interior, mission possibilities include the Solar Internal Dynamics Mission (SIDM) or the Solar Beacon to provide continuous monitoring of solar oscillations, and the Starprobe grazing encounter flyby. Visible surface atmospheres of the sun may be studied by the repair of the Solar Maximum Mission, and an Advanced Solar Observatory making observations from the X-ray to the IR. Possible missions investigating the inner corona would involve the proposed Solar Interplanetary Satellite (SIS), which would complement the single-spacecraft International Solar Polar Mission, the Solar Corona Diagnostics Mission (SCDM), and Starprobe. The SIS, Interplanetary Physics Laboratory and SCDM missions would also permit measurement of the solar wind. Experiments of opportunity based on the SMM, SIS, SCDM and SIDM projects may be used for studies of solar-terrestrial interactions, together with dedicated programs such as the Solar Terrestrial Observatory.

Bohlin, J. D.↗
NASA NTRS1980

Solar Maximum Mission

The paper considers the objectives of the Solar Maximum Mission (SMM), and describes its spacecraft, the scientific planning, the observing program, and the guest investigator programs. The SMM observatory will be injected into a circular orbit with an altitude of 574 km and it is designed for a minimum of one year of operational life; its observing program is directed at the physics of solar flares, and includes studies of thermalization, the nature of electron acceleration, the flare energy budget, and the flare decay. Finally, the SMM Guest Investigator program is discussed, including ground-based synoptic and atomic data investigations and SMM data interpretation.

Bohlin, J. D.↗
NASA NTRS1979

Advanced solar space missions

The space missions in solar physics planned for the next decade are similar in that they will have, for the most part, distinct, unifying science objectives in contrast to the more general 'exploratory' nature of the Orbiting Solar Observatory and Skylab/ATM missions of the 1960's and 70's. In particular, the strategy for advanced solar physics space missions will focus on the quantitative understanding of the physical processes that create and control the flow of electromagnetic and particulate energy from the sun and through interplanetary space at all phases of the current sunspot cycle No. 21. Attention is given to the Solar Maximum Mission, the International Solar Polar Mission, solar physics on an early Shuttle mission, principal investigator class experiments for future spacelabs, the Solar Optical Telescope, the Space Science Platform, the Solar Cycle and Dynamics Mission, and an attempt to send a spacecraft to within 4 solar radii of the sun's surface.

Bohlin, J. D.↗
NASA NTRS1978

The solar XUV He I and He II emission lines. I - Intensities and gross center-to-limb behavior

The center-to-limb variation of the He II 304- and 256-A lines and He I 584- and 537-A lines is derived for different solar features, but averaged over the chromospheric supergranulation structure. The general trend is for limb brightening in quiet-sun regions, limb neutrality in unipolar magnetic regions (UMR), and limb darkening in polar coronal holes. The center-to-limb behavior in these optically thick emission lines indicates collisional excitation and decreasing transition-region temperature gradients with respect to optical depth in the sequence quiet sun to UMR to coronal hole.

Mango, S. A.↗
NASA NTRS1978

Extreme ultraviolet observations of coronal holes. II - Association of holes with solar magnetic fields and a model for their formation during the solar cycle

Skylab and ground-based observations in the extreme UV range of the spectrum are used to analyze characteristics of coronal holes, and to correlate their development with variations in the solar cycle. The mergence of bipolar magnetic regions (BMR) during the declining phase of the cycle is held reponsible for the formation of large equatorial holes (M-regions, which cause recurring geomagnetic storms). The BMR mergence model can also be applied to polar cap holes.

Bohlin, J. D.↗
NASA NTRS1977

H-alpha macrospicules - Identification with EUV macrospicules and with flares in X-ray bright points

The paper presents observational evidence that two newly observed transient solar phenomena, EUV macrospicules and X-ray bright-point flares, are closely related. Time-lapse H-alpha filtergram observations of the limb in quiet regions show small surgelike eruptions called H-alpha macrospicules. From the similarity of H-alpha macrospicules and EUV macrospicules, and from comparison of simultaneous H-alpha and He II 304 A observations, we conclude that H-alpha macrospicules are EUV macrospicules viewed in H-alpha, although most EUV macrospicules are too faint in H-alpha to appear on H-alpha filtergrams of normal exposure. From comparison of simultaneous X-ray and H-alpha observations of flares in X-ray bright points situated on the limb, we show that flares in X-ray bright points often produce H-alpha macrospicules.

Moore, R. L.↗
NASA NTRS1977

Extreme-ultraviolet observations of coronal holes. I - Locations, sizes and evolution of coronal holes, June 1973-January 1974

The disk boundaries of coronal holes have been systematically determined from XUV observations taken during the manned Skylab missions (June 1973-January 1974). The resulting atlas was used to find the sizes, global distributions, differential rotation rates, growth/decay rates and lifetimes of holes during this period. The polar cap holes together covered 15% of the sun's total surface area, a number which remained surprisingly constant throughout Skylab despite the fact that each pole was independently evolving in time. Lower latitude holes contributed another 2 to 5%.

Bohlin, J. D.↗
NASA NTRS1976

Doppler wavelength shifts of transition zone lines measured in Skylab solar spectra

Wavelengths of lines of the transition-zone ions Si IV, C IV, O IV, N V, and O V are observed to be redshifted relative to the wavelengths of chromospheric lines in XUV spectra obtained from the normal-incidence spectrograph on Skylab. The spectra cover the wavelength range from 1200 to 1565 A and were obtained with the slit positioned over chromospheric network and cell regions, on coronal holes, and above the limb. The network-area and coronal-hole spectra were obtained near the disk center. Only some of the spectra show redshifted transition-zone lines. The observed shifts are between 0.03 and 0.08 A, implying velocities of 15 km/s or less. The amount of wavelength shift does not always appear to be the same for lines of different ions. The shifts imply that descending plasma in the solar atmosphere produces more emission than ascending plasma at temperatures between approximately 70,000 and 200,000 K.

Doschek, G. A.↗
NASA NTRS1976

The physical properties of coronal holes

Coronal hole data obtained by Skylab during the period May 1973 to February 1974 are reviewed for the region from the photosphere out through the low corona. Coronal holes have a significantly lower density and temperature than the typical background corona, possess an open divergent magnetic field structure, and are the source of the high-speed solar wind stream which give rise to recurrent geomagnetic storms. The photospheric, chromospheric, and coronal signatures of coronal holes are described, and the evolution of coronal holes is examined, with attention to the lifetimes, the differential rotation, and the areas covered by the holes. The association of coronal holes to large-scale magnetic fields and to disk activity is considered.

Bohlin, J. D.↗
NASA NTRS1975

The sources of material comprising a mass ejection coronal transient

The origin of the material ejected during a white-light coronal transient on August 26 and 27, 1973, is investigated using simultaneous observations of a slowly ascending prominence and the more rapid accompanying coronal transient. Nearly identical simultaneous images of the prominence were obtained over a six-hour period in the H-alpha and He II (304 A) emission lines; contemporaneous Skylab coronograph observations over approximately 1.5 hours showed that the mass-ejection coronal transient rose above the ascending prominence. Based on analysis of these observations, it is concluded that: (1) the bulk of the ejected material originated in the lower corona, despite the lack of an observed depletion there; (2) the material in the transient was at coronal temperature and was visible in polarized radiation due to Thomson scattering of photospheric light by free electrons; and (3) the total event was far larger, more energetic, and longer lasting than would have been inferred from the prominence observations alone.

Hildner, E.↗
NASA NTRS1975

Coronal changes associated with a disappearing filament

Skylab/ATM observations of a disappearing filament near the center of the solar disk are described using XUV and H-alpha spectroheliograms, X-ray filterheliograms, and photospheric magnetograms. The temperature of the coronal plasma as the filament disappeared is estimated to have been in excess of 6 million K, and it is noted that the time history of the soft X-ray and microwave fluxes displayed the gradual-rise-and-fall (GRF) signature, suggesting that the present event may have properties that are characteristic of a wide class of long-duration X-ray and radio events. A comparison with other spatially resolved long-duration X-ray events indicates that all such long-lived bursts involve transients in the outer corona and that some two-thirds of them involve either the eruption or the major activation of a prominence. It is also found that long-lived events are characterized by the appearance of new emission loops in the lower corona during the declining phase of the X-ray emission and that these loops sometimes disappear after the X-ray events and sometimes remain indefinitely.

Sheeley, N. R., Jr.↗
NASA NTRS1975

Synoptic maps of solar coronal hole boundaries derived from He 2 304 A spectroheliograms from the manned skylab missions

The disk boundaries of coronal holes have been determined from He II 304 A spectroheliograms which were taken with the Naval Research Laboratory slitless XUV spectrograph during the manned Skylab missions. These boundaries are plotted by Carrington rotation as synoptic charts in both the standard rectangular as well as polar-view projections. The periods of time for which boundaries were determined are 24 May through 28 June 1973 (first manned Skylab mission), 2 August through 24 September 1973 (second manned mission), and 21 November 1973 through 2 February 1974 (third manned mission); the Carrington rotations covered (in part or totally) are 1601 and 02; 160r, 1604, 05 and 06; and 1608, 09 and 10, respectively.

Bohlin, J. D.↗
NASA NTRS1975

A newly observed solar feature - Macrospicules in He II 304 A

He II 304 A spectroheliograms, obtained with the NRL extreme-ultraviolet slitless spectrograph during the Skylab mission, show spikelike structures at the sun's polar limb which resemble the familiar H-alpha spicules. However, the relatively large size and long life of these He II features has led to distinguishing them by the name 'macrospicules'. The macrospicules appear as protuberances or jets, ranging from 5 to over 60 sec in length, from 5 to 30 sec in width, and from 5 to over 40 minutes in lifetime. Perhaps the most radical departure from H-alpha spicules is that macrospicules occur only within the chromospheric boundaries of coronal holes. Thus macrospicules are most easily visible over the solar poles due to the coronal holes normally present there, and much less frequently at lower latitudes during limb passage of relatively rare, low-latitude coronal holes.

Bohlin, J. D.↗
NASA NTRS1975

The reconnection of magnetic field lines in the solar corona

Skylab XUV coronal spectroheliograms and photospheric magnetograms are compared. This comparison shows that, as new bipolar magnetic fields emerge through the solar surface into the corona, the new coronal fields interact with the old ones in a manner that suggests the reconnection of the field lines.

Sheeley, N. R., Jr.↗
NASA NTRS1975

High resolution Lyman alpha observations of comet Kohoutek /1973f/ near perihelion

The hydrogen Lyman-alpha emission line of comet Kohoutek (1973f) was observed and resolved by the high-dispersion Skylab/ATM S082B spectrograph shortly after the comet's perihelion passage (29-31 December 1973). The Lyman-alpha line width was determined from three different exposures of the comet nuclear region. A simplified analysis of the optical thickness effects showed that this line width is consistent with the established hydrogen outflow velocity of 8 to 10 km/sec.

Keller, H. U.↗
NASA NTRS1975

XUV observations of coronal magnetic fields

Spectroheliograms obtained with the Naval Research Laboratory's Extreme Ultraviolet Spectrograph (S082A) on Skylab are compared with Kitt Peak National Observatory magnetograms. A principal result is the characteristic reconnection of flux from an emerging bipolar magnetic region to previously existing flux in its vicinity. Examples of the disappearance of magnetic flux from the solar atmosphere are also shown. The results of a particularly simple, potential field calculation are shown for comparison with the Skylab observations.

Sheeley, N. R., Jr.↗