Surprisingly few solar coronal loops have been observed simultaneously with TRACE and SOHO/CDS , and even fewer analyses of these loops have been conducted and published .
The SOHO Joint Observing Program 146 was designed in part to provide the simultaneous observations required for in-depth temperature analysis of active region loops and determine whether these loops are isothermal or multithermal .
The data analyzed in this paper were taken on 2003 January 17 of AR 10250 .
We used TRACE filter ratios , emission measure loci , and two methods of differential emission measure analysis to examine the temperature structure of three different loops .
TRACE and CDS observations agree that Loop 1 is isothermal with Log T = 5.85 , both along the line of sight as well as along the length of the loop leg that is visible in the CDS field of view .
Loop 2 is hotter than Loop 1 .
It is multithermal along the line of sight , with significant emission between 6.2 < Log T < 6.4 , but the loop apex region is out of the CDS field of view so it is not possible to determine the temperature distribution as a function of loop height .
Loop 3 also appears to be multithermal , but a blended loop that is just barely resolved with CDS may be adding cool emission to the Loop 3 intensities and complicating our results .
So , are coronal loops isothermal or multithermal ?
The answer appears to be yes !