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The Naval Research Laboratory prepared three instruments for ATM and also a series of rocket payloads for purposes of calibration, under the overall direction of R. Tousey, the Principal Investigator. In this preliminary report a summary of results from operations during the first mission (SL/2) and sample results are presented.
(Solar Phys.). A very bright coronal streamer was observed on December 13, 1971 by the Naval Research Laboratory's coronagraph on board of OSO-7. The next day, the streamer had changed it's brightness and configuration considerably. Three subsequent coronagraph images, taken on December 14 at 0407, 0418 and 0430 UT show a large plasma cloud moving outward from the Sun between 3 and 10 solar radii. They also show distinct smaller clouds moving outward with projected velocities between 950 and 1100 km s−1. Traced back in time to the lower solar corona, these clouds coincide with discrete type II radiobursts observed from Culgoora between 0241 and 0256 UT. Each single cloud shows it's signature in the radio recording between 100 and 20 MHz. The drift velocity of the radio bursts can be determined to be 1600 km s−1 using Newkirk's coronal streamer model. Assuming, that the plasma clouds are ejected from an active region 30° behind the east limb vertically, their true velocities close to the surface of the Sun would be approximately 1400 km s−1, which is in good agreement with the drift velocities determined from the type II bursts, considering all uncertainties. Therefore, the type II burst disturbance moves with the same velocity as the driving material.
Skylab has demonstrated the dominant role of magnetic fields in the solar atmosphere. The solar wind is not a necessary consequence of the pressure imbalance between the hot corona and the interplanetary medium. High speed solar windstreams are originating in coronal holes where coronal density and temperature are less than in the quiet sun. Older models of the solar wind invoke heat conduction from the hot corona as the prime energy source for the solar wind. However in coronal holes the energy supplied by heat conduction is less than in the ordinary sun while the high speed windstreams require an amount of energy which cannot be supplied by conduction alone.
The optics and electronics of a new filter magnetograph will be described. The instrument uses a Zeiss 0.13 Å birefringent filter to isolate magnetic sensitive lines. All four Stokes parameters can be measured. A Westinghouse SEC vidicon WX 30 654 serves as the detector. The data are completely digitized and transmitted in real time into a Univac 1108 computer.
A preliminary description of ultraviolet spectra of active regions and flares, photographed from Skylab by the Naval Research Laboratory's UV Spectrograph is given. The findings can be summarized as follows: (1) Line profiles of medium ionized lines (transition zone lines) show the most pronounced broadenings and shifts in flares and flare like events. (2) Typical full width at half maximum of these lines correspond to Doppler-velocities of 70 km s-1. (3) Shifts of the same magnitude can be observed. (4) Intersystem lines are not broadened nor shifted. (5) Forbidden coronal lines and intersystem lines become enhanced in the flare spectrum at the moment, when the turbulence seen in the allowed transitions, disappears. (6) A very broad line at 1354.2 Å which appears only in flare spectra, seems to be the forbidden transition 3P1 – 3P0 of Fe XXI.
The combined operations of the Large Angle Spectrometric Coronagraph (LASCO) and the Extreme Ultraviolet Imaging Telescope (EIT) on the Solar and Heliospheric Observatory (SOHO), launched in December 1995, have provided an unprecedented opportunity for observing essentially all coronal phenomena that are not hidden behind the disk of the Sun. Consequently, observations with these instrument are providing information on coronal mass ejections (CMEs) from their initiation through their development over 30 ⊙. They reveal a coronal that never reaches a steady state. The corona is the site of continuous, time-dependent outflows, both within the coronal holes and the high speed streams and in the streamer belts and their mid-latitude sources. The spatial scales of these outflows range from 10s of arc-seconds through about a solar radius in large CMEs.
Some characteristic features of UV spectra which can be seen in flares (Brueckner, this Symposium, p. 135) can also be detected in active regions without the presence of typical other flare phenomena like X-ray enhancement. Another distinct difference between these ‘flare-like’ spectra and flare spectra is the absence of very high temperature ions like Fe XXI in the ‘flare-like’ spectra. They occur in small areas and can be detected as ‘fluctuating Hα bright points’ in broad band Hα. Simultaneously, a strong UV brightening can be seen. As reported by the Skylab crews, these brightenings occur more frequently and quasi-periodic prior to flares. Their spectra show the very broad transition zone lines and often strong line shifts toward the blue or red. Figure 1 shows a selection of typical spectra. One notices a very asymmetric Lα profile in one case. Spectra prior to, during, and after a flare are reproduced in Figure 2. One recognizes that the transition zone instability started intermittently prior to the flare and could be seen during short time intervals long after the flare had ceased.