Date of Award

Winter 1994

Project Type


Program or Major


Degree Name

Doctor of Philosophy

First Advisor

James Ryan


This dissertation is an investigation of solar flare and microflare occurrence rates, times, and sizes in the context of solar flare occurrence models and periods, and coronal heating. Solar flares, explosive releases of energy with effects observed at earth, are not fully understood. Microflares, smaller versions of typical solar flares, were previously only observed during a short balloon experiment. They may provide clues to understanding solar flares by allowing us to test what we already know about large solar flares.

The Compton Gamma-Ray Observatory's (GRO) Burst and Transient Source Experiment (BATSE) is used to search for solar flares. This study differs from others because it is the most sensitive with a long observing time. We have used an automated algorithm to search thirteen months of BATSE discriminator data. This algorithm enabled us to detect flares at the instrumental threshold.

In this work we extend the flare size frequency distribution down to sizes smaller than previously observed in long-term experiments and find that the observed flares are not a significant heat source for the corona. We find that the power-law shape previously measured applies to flares as small as the instrumental threshold. We test the data for systematic variations in power-law index of the flare size frequency distribution. There is only evidence for variation of the power-law index with the phase of a 51-day period.

Time series analyses are used to uncover periodic features in the daily flare occurrence rate. There is evidence for a flare size threshold effect in periodic activity. There are also characteristic activity time scales evident in the daily flare rate.

We test for randomness of solar flare occurrence and find no apparent correlation between times of flare occurrence. We also find no correlation between flare size and the time interval between flares. These findings support the avalanche flare model of Lu and Hamilton (1991) but are inconsistent with the occurrence model of Rosner and Vaiana (1978).