  The expansion of coronal loops in the transition region may considerably
influence the diagnostics of the plasma emission measure. The cross sectional
area of the loops is expected to depend on the temperature and pressure, and
might be sensitive to the heating rate. The approach here is to study the area
response to slow changes in the coronal heating rate, and check the current
interpretation in terms of steady heating models. We study the area response
with a time-dependent 2D MHD loop model, including the description of the
expanding magnetic field, coronal heating and losses by thermal conduction and
radiation from optically thin plasma. We run a simulation for a loop 50 Mm long
and quasi-statically heated to about 4 MK. We find that the area can change
substantially with the quasi-steady heating rate, e.g. by ~40% at 0.5 MK as the
loop temperature varies between 1 and 4 MK, and, therefore, affects the
interpretation of DEM(T) curves.
