Charles J. Garcia

BRIGHTNESS VARIATIONS OF THE WHITE-LIGHT CORONA DURING THE YEARS 1964--67.

Observations of the white light corona were made on over 900 days during the years 1964–67 at heights between 1.125 and 2.0 R⊙ with the K-coronameter at Mount Haleakala and Mauna Loa, Hawaii. The brightness distribution of the minimum corona was elliptical with average equatorial intensities three times the polar. Coronal features of the new cycle at 1.125 R⊙ occurred predominantly in the sunspot zones at 25–30° latitude and in a high latitude zone which migrated toward the North pole before solar maximum. The brightness of the inner corona doubled over this period and a close association is found between the average corona and 10.7-cm solar radio flux. Electron densities in the equatorial regions were nearly twice those of Van de Hulsts model corona, in agreement with the results of recent eclipse observations.

Abrupt depletions of the inner corona

During the time period 1970-early 1973, 13 instances of major abrupt depletions of localized regions of the inner solar corona (1.1-2 R0) were detected at Mauna Loa, Hawaii. Because of their almost invariable association with the ascending Ha prominence material (most generally flare sprays and, in one instance the disparition brusque of a large filament near the solar limb) and close correlation in time and position with outward moving Type IV radio sources, we surmise that the coronal material was expelled from the sun. In several of these cases plasma clouds were tracked to 10 R0 by Naval Research Laboratory with a coronagraph aboard 0S0-7. Limited evidence suggests that some aspects of a coronal disturbance, including trajectory of flare spray and depletion of the inner corona, are homologous within 24 hours, so the overall coronal magnetic field configuration is not necessarily permanently altered. Key words: sun - corona - prominences

EVOLUTION OF CORONAL HELMETS DURING THE ASCENDING PHASE OF SOLAR CYCLE 20.

The principal polar-crown coronal helmet structures were selected from nearly three years (May, 1965–January, 1968) of K-coronameter observations made at Haleakala and Mauna Loa, Hawaii. Six isolated and long-lived helmet systems were found at latitudes of 45° and above. Their developments are compared with underlying chromospheric and photospheric activity and a simple phenomenological model is presented showing that a coronal system is formed over an active region. Thereafter the center of gravity of the system gradually drifts poleward with the trailing unipolar magnetic region (UMR), and it becomes a high latitude coronal helmet, arched over a polar crown filament.By comparison of these coronal helmets with observations of the outer corona (to circa 4 R⊙) made at solar eclipse, lunar sunset, and with balloon and rocket-borne externally occulted corona-graphs, it appears that ground-based K-coronameter measurements to a distance of 1.5–2.0 R⊙ are sufficient to detect the coronal streamers.

K-coronal enhancements and chromospheric plages

A systematic investigation was made of the K-corona immediately overlying the positions of the brightest and most isolated chromospheric plages during the years 1964–1967. In all cases, the corona was found to be enhanced with peak brightness proportional to the plage area. In the absence of plages, the K-coronal brightness remained at a quiet level which was essentially the same thoughout this part of the solar cycle.

Solar Radiation: Effects of Atmospheric Water Vapor and Volcanic Aerosols

Abstract Atmospheric water vapor attenuates normal incidence solar radiation received on Mauna Loa, Hawaii, by up to 10%. During periods of active fountaining, aerosols from Kilauea Volcano at times obscure global trends in atmospheric turbidity. Corollary measurements such as precipitable water and the aureole are necessary in order to evaluate the effects upon solar radiation of global trends in atmospheric turbidity.

Mauna loa coronagraph observations around the 7 March 1970 eclipse

The locations of seven principal coronal features observed in projection at the 7 March 1970 eclipse are established from synoptic coronagraphic measurements.

Mauna Loa sky conditions, bench mark and present

Sky conditions at the Mauna Loa Solar Observatory (MLSO) were measured during a period of uncontaminated skies in July 1981, and during the presence of volcanic dust clouds in 1982 using MLSO instrument systems. A six-fold increase in scattering due to aerosols, is accompanied by a 25 percent direct incident radiation decrease, and sky polarization/intensity perturbations were detected after the onset of volcanic clouds.