Characteristics of 150 km echoes linked with solar eclipse and their implications to the echoing phenomenon

Abstract

This paper presents a study based on Gadanki radar observations of 150 km echoes made during the solar eclipse of 15 January 2010 that occurred during 1122-1515 IST. Radar echoes were observed only during 1150-1215 IST and 1344-1356 IST linked with the entry and recovery phases of the eclipse, respectively. The most striking observation found is the unusual ascending and descending features of the echoing regions observed during these two time periods. Although these echoes occurred at higher altitudes than those of control days, SNR and spectral width of these echoes are similar to those of the lower echoing region observed on the control days. Further, Doppler velocities suggest the presence of westward electric field unlike those of the control days. Concurrent ionosonde observations showed ascent and descent of the F₁ layer very similar to those observed in the 150 km echoes. These observations and related analysis suggest that the observed echoes were due to the combined action of the electron density gradients and the reduced recombination rate linked with the solar eclipse effect. These observations are first of its kind and elucidate the role of density gradient and recombination rate in the 150 km echoing process.