On the relationship between ground level enhancement and solar flare

We made an effort to understand the associations and relationships between ground level enhancement (GLE) events and solar flares for the time period of 1986-2006. Our results show that, on average, the GLE event-associated solar flare (similar to 0.2 x 10(-4) W/m(2)) is much stronger than the non-GLE-associated solar flare (similar to 0.3 x 10(-5) W/m(2)). The findings have also been supported by the solar flare indices that, on average, the GLE event-associated solar flare index (similar to 35.01) is much higher than the non-GLE-associated solar flare index (similar to 4.88). However, this association does not seem to precisely imply that GLEs can occur because of a solar flare, so we examined cross correlations between GLE events and simultaneous solar flares. We found that most (similar to 78%) of the highest correlations (r > 0.8) took place during an X class flare. There is no clear indication that the more the time lag, the less or more is the correlation or vice versa. Overall, 50% of the high correlations took place at higher time lag (>= 65 min), and similar to 36% of the high correlations took place at lower time lag (<= 40 min), while the rest (similar to 14%) of the correlations were abruptly high and low at medium time lag (> 40 and < 65 min). On the basis of the results of cross correlations, we suggest that the intensive portions of solar flares should be responsible for causing GLEs and that the direct proportionality of the time-integrated intensive portion of a flare with the impulsive phase of a GLE event seems to be the main property for comprehending the mechanism.