Meter and decameter wavelength positions of solar bursts of July 31?August 7, 1972

Abstract

The positional analysis of solar bursts at meter and decameter wavelengths during the period July 31-August 7, 1972 is presented. The observations were taken with two arrays — a log periodic array of 16 elements situated on an E-W base line of 3.3 km and portions of the new Clark Lake array in the form of a Tee (an E-W arm of 32 log spiral antennas and a N-S arm of 16 similar antennas). The new array operates over the frequency range 10–120 MHz and has angular resolutions of approximately 3.′5 at 100 MHz and 8.′5 at 40 MHz in the E-W direction. In the N-S direction the instrument has a resolution of 6′ at 100 MHz and 15′ at 40 MHz. During this period the activity was often so complex that we represent it only by ‘snapshots’ taken at representative times at three representative frequency ranges 90–110 MHz, 60–80 MHz and 30–50 MHz. Most of the activity during this period was associated with the active regions McMath 11976 and 11970. The radio-emissive regions were also closely associated with the Fe xv (284 A) coronal maps produced by NASA-GSFC from OSO-7 observations (Figures 1, 2 and 3). Except near the CMP of the region 11976, two regions of continuum emission were often observed — one a relatively smooth continuum and the other a continuum superimposed with many type Ill’s and other fine structure. It seems possible to interpret these continua in terms of plasma waves originating from two sources located at different heights or with different electron density gradients. The angular size of type III sources seems to increase with decreasing frequency. This implies that the open field lines along which the type III electrons travel have larger angular extent at greater height.