Radio astronomical studies with 1500-meter diameter low-frequency telescope

Radio astronomical studies with 1500 meter diameter low frequency telescop

Large scale structure of the corona

This is an introduction to this section of the proceedings. In this section is a brief description of some radio results obtained with meter-decameter radioheliograph. An optical study based upon synoptic data of polarized brightness (pB), H alpha line filtergrams and large scale B-fields is presented. This is followed by two papers on the interpretation of coronal mass ejection (CME) and modeling of three dimensional coronas

Ground based solar radio observations during solar maximum mission

The Very Large Array (VLA) and the Westerbork Synthesis Radio Telescope (WSRT) were used for making aperture synthesis maps of solar active and flaring regions. Observations of the Flare buildup in the form of increased intensity and polarization were made. Ring structure associated with sunspots were interpreted as due to the existence of cool material above the spot. Model computations were performed to explain the total intensity and polarization structures of a continuous set of active region maps

Three dimensional structures of solar active regions

Three dimensional structure of an active region is determined from observations with the Very Large Array (VLA) at 2, 6, and 20 cm. This region exhibits a single magnetic loop of length approx. 10 to the 10th power cm. The 2 cm radiation is mostly thermal bremsstrahlung and originates from the footpoints of the loop. The 6 and 20 cm radiation is dominated by the low harmonic gyroresonance radiation and originates from the upper portion of the legs or the top of the loop. The loop broadens toward the apex. The top of the loop is not found to be the hottest point, but two temperature maxima on either side of the loop apex are observed, which is consistent with the model proposed for long loops. From 2 and 6 cm observations it can be concluded that the electron density and temperature cannot be uniform in a plane perpendicular to the axis of the loop; the density should decrease away from the axis of the loop

VLA observations of coronal bright points at 6 and 20 cm wavelengths

Prior to and during the Spacelab-2 operation, observations were made at 6 and 20 cm of solar coronal bright points, using the Very Large Array (VLA) in the C-configuration. The ultraviolet coverage ranged from 200 to 18,000 wavelengths. The maps were convolved with beams of 18 x 18 inches at 20 km and 4 x 4 inches at 6 cm. Only the preliminary results from July 15 and July 31, 1985 observations

The Height Structure of the Solar Atmosphere from the EUV Perspective

We investigate the structure of the solar chromosphere and transition region using full Sun images obtained with the Extreme Ultraviolet Imaging Telescope (EIT) aboard the Solar and Heliospheric Observatory (SOHO) spacecraft. The limb seen in the EIT coronal images (taken in lines of Fe IX/X at 171 \AA, Fe XII at 195 \AA and Fe XV at 284 \AA) is an absorption limb predicted by models to occur at the top of the chromosphere where the density of neutral hydrogen becomes significant ($\sim10^{10}$ cm$^{-3}$). The transition-region limb seen in He II 304 \AA images is an emission limb. We find: (1) the limb is higher at the poles than at the equator both in the coronal images (by 1300 $\pm$ 650 km) and the 304 \AA images (by 3500 $\pm$ 120 0 km); and (2) the 304 \AA limb is significantly higher than the limb in the coronal images. The height difference is 3100 $\pm$ 1200 km at the equator, and 6600 $\pm$ 1200 km at the poles. We suggest that the elevation of the 304 \AA limb above the limb in the coronal images may be due to the upper surface of the chromosphere being bumpy, possibly because of the presence of spicules. The polar extension is consistent with a reduced heat input to the chromosphere in the polar coronal holes compared with the quiet--Sun atmosphere at the equator.Comment: 6 pages, 2 figure

Two dimensional imaging observations of meter-decameter bursts associated with the February 1986 flare activity

An analysis is presented of the two dimensional imaging observations of a flare observed on 3 Feb. l986 using the Clark Lake Multifrequency Radioheliograph. The flare produced almost all types of Meter-decimeter radio emission: enhanced storm radiation, type III/V bursts, II and IV and flare continuum. The flare continuum had early (FCE) and late (FC II) components and the type II occurred during the period between these two components. Comparing the source positions of type III/V and FCE it was found that these bursts must have occurred along adjacent open and closed field lines, respectively. The positional analysis of type II and FC II implies that the nonthermal electrons responsible for FC II need not be accelerated by type II shock and this conclusion is further supported by the close association of FC II with a microwave peak. Using the positional and temporal analysis of all these bursts and the associated hard X-ray and microwave emissions, a schematic model is developed for the magnetic field configuration in the flaring region in which the nonthermal particles responsible for these bursts are confined or along which they propagate