Solar active regions at 9 and 3.5 mm wavelengths under disturbed conditions

Some properties of solar active regions at 9 and 3.5 mm wavelengths under disturbed conditions are discussed. New regions develop or weak regions intensify at millimeter wavelengths as a result of flares at distant sites. The spectra of the peak flux density of moderately strong bursts observed at 9 mm show a sharp drop toward the shorter millimeter wavelengths. The weak bursts at 3.5 mm manifest mainly as heating phenomena.     

Differential rotation of the solar atmosphere as determined from millimeter data

Radiospectroheliograms obtained at millimeter wavelengths were used to determine the rotation of the solar atmosphere. Regions observed in both emission as well as absorption (associated with H dark filaments) were followed across the disk. The average sidereal rotation rate deduced from emissive regions is given by (deg day^-1)=14.152(±0.270)-4.194(±3.017)sin² B, where B is the heliographic latitude and the quoted errors are the standard deviations of a least squares fit to the data. The rate deduced from absorption regions is given by =14.729(±0.286)-1.050(±1.611)sin² B. This rate is larger than that of emissive regions at all latitudes and shows smaller differential rotation. This apparent difference in the rotation rates is probably due to the difference in the height of formation of the emissive and absorption regions. This difference could be used to estimate the difference in height between an emissive region and an absorption feature in millimeter radiation.     

Characteristics of the Ca ii K-line profiles in the quiet Sun

Feature-to-feature identification is made on simultaneous Ca ii K-line spectrograms (SG) and K_2v spectroheliograms (SHG). The line profiles in plages and in the network boundary nearly always have double-peaked reversal in the core, while those inside the cells present all possibilities: double-peaked, single-peaked on violet side, single-peaked on red side, and unreversed absorption. Statistics of the profiles in the quiet chromosphere show that 50% are K₂₃₂ double-peaked, 20% are K_2v single-peaked, 10% are K_2r single-peaked, and 20% show only incipient reversal or even totally lack any reversal. We call attention to the nontrivial contribution of these absorption profiles which are formed in dark regions shown on SHG's.The physical conditions inferred from different kinds of profiles are briefly discussed.In part to be included in a dissertation to be submitted to the Graduate School, University of Maryland, by S. Y. Liu in partial fulfillment of the requirements for the Ph. D. degree in Astronomy.Visiting Graduate Student, Solar Division, Kitt Peak National Observatory.Visiting Astronomer, Solar Division, Kitt Peak National Observatory.     

Brightness distributions of the Sun at 33 and 37 GHz

The brightness distributions of the Sun were observed at 33 and 37 GHz. Maximum limb brightening of about 10% was observed at both frequencies.     

Comments on the quiet Sun brightness distribution at 1.2 mm wavelength

A re-analysis of the brightness distribution of the quiet Sun at 1.2 mm wavelength is made. It is concluded that there is no evidence for uniform or limb-brightened distribution at this wave-length.     

Observation of a coronal hole at 85 GHz

A coronal hole was observed at 85 GHz(3.5 mm-) on November 24, 1970, when a spectacular coronal hole was observed in soft X-rays by AS&E. The millimeter counterpart of the hole is much weaker and less widespread than in X-rays. The brightness temperature inside the hole was in most places about 100–200 K lower than the mean brightness temperature of the Sun at 85 GHz.     

White light network in the solar photosphere

Time-averaging technique is performed on a set of white light pictures obtained at μ=0.87. After eliminating short-lived granulations, the time-averaged pictures show some large scale but longlived brightness patterns which are not recognizable in any of the single frame snapshots. The patterns are brighter than the background and are co-spatial with the upper photospheric emissions and magnetic fields. We define these patterns as the white light network.