We present a first systematic study on the cross-sectional temperature structure of coronal loops using the six coronal temperature filters of the Atmospheric Imaging Assembly ( AIA ) instrument on the Solar Dynamics Observatory ( SDO ) .
We analyze a sample of 100 loop snapshots measured at 10 different locations and 10 different times in active region NOAA 11089 on 2010 July 24 , 21:00-22:00 UT .
The cross-sectional flux profiles are measured and a cospatial background is subtracted in 6 filters in a temperature range of T \approx 0.5 - 16 MK , and 4 different parameterizations of differential emission measure ( DEM ) distributions are fitted .
We find that the reconstructed DEMs consist predominantly of narrowband peak temperature components with a thermal width of \sigma _ { log ( T ) } \leq 0.11 \pm 0.02 , close to the temperature resolution limit of the instrument , consistent with earlier triple-filter analysis from TRACE by Aschwanden and Nightingale ( 2005 ) and from EIS/Hinode by Warren et al .
( 2008 ) or Tripathi et al .
( 2009 ) .
We find that 66 % of the loops could be fitted with a narrowband single-Gaussian DEM model , and 19 % with a DEM consisting of two narrowband Gaussians ( which mostly result from pairs of intersecting loops along the same line-of-sight ) .
The mostly isothermal loop DEMs allow us also to derive an improved empirical response function of the AIA 94 Å filter , which needs to be boosted by a factor of q _ { 94 } = 6.7 \pm 1.7 for temperatures at log ( T ) \lower 1.72 pt \hbox { $ \buildrel < \over { \scriptstyle \sim } $ } 6.3 .
The main result of near-isothermal loop cross-sections is not consistent with the predictions of standard nanoflare scenarios , but can be explained by flare-like heating mechanisms that drive chromospheric evaporation and upflows of heated plasma coherently over loop cross-sections of w \approx 2 - 4 Mm .