Dynamics of solar active region loops

It has been frequently observed that in solar active regions the measured l ine widths are larger than those based on thermal equilibrium widths. This excess width (characterised as non-thermal velocity, V-nt) has been propose d as a signature of the heating mechanism. The behaviour of the V-nt at cor onal temperatures has not produced consistent results with values ranging f rom 0 to 100 km s(-1). We investigate this problem by using joint observati ons from Norikura Solar Observatory, Japan and the Coronal Diagnostic Spect rometer (CDS) on SOHO. With CDS we determine temperatures, and with Norikur a we obtain accurate line widths for Fe XIV (approximate to 2 MK). We find that values of V-nt range between 10-20 km s(-1). We analyse the dynamical behaviour of different temperature loops and find that for loops with Log T -e < 5.8, the variability oc T-e(0.39). This is comparable to the dependenc e of non-thermal velocity on temperature which we have determined to be V-n t proportional to T-e(0.35). This suggests that the excess line broadening is caused by highly dynamical behaviour in the transition region for active regions. These results have significant implications for potential heating mechanisms and these are discussed.