The most relevant innovation of the new version of the code is that we can now reliably synthesize the emission from the transition region, mostly in the EUV band, as well as that from the corona. The high resolution of the temperature structure in the transition region now allows a proper sampling in the temperature range of many EUV lines of the transition region.
We derive the predicted emission from temperature and density profiles
obtained along the loop at different times during the flare evolution. The flux
in a particular line, at a distance R from the sun (
AU), is
calculated as:
where 
is the electronic density, T is the plasma temperature, V is
the plasma volume, and G(T) is the emission function which has been
tabulated for most observed lines by several authors. We use Landini &
Monsignori Fossi (1990) tables as G(T).
Figure 4: Same flare as in Fig. 2 (click here): predicted
light curves of the
flare in ten important EUV and X-ray spectral lines which sample
different temperatures of the transition region and corona synthesized
with the results of the new code (solid lines). We also show for
comparison, five of the light curves (Fe XXV, Ca XIX, S XV, Fe XV, Mg X)
obtained with the previous PH code (dashed lines);
the others were by far too noisy to be reported
As a test we have synthesized 10 spectral lines which are frequently
observable by many satellites such as SMM (XRP), Yohkoh (BCS), and SOHO
(EIT, CDS, SUMER). They form in a wide range of temperatures, spanning from
the upper chromosphere to the high corona. They are:
Fe XXV (1.85 Å, 
K), Ca XIX (
3.17 Å, 
K), S XV (
5.04 Å, 
K), Fe XV (284.15 Å
, 
K), Mg X (609.80 Å, 
K), Ne VIII (780.32 Å, 
K), O VI (1031.90 Å, 
K), N V (
1238.80 Å, 
K), C IV (
1548.20 Å, 
K), Si IV (1402.77 Å, 
K).
We show the light curves in these lines in
Fig. 4 (click here). The inadequate resolution of the previous PH code has
not crucially affected the predictions for the X-ray spectral emission which
originate at the highest temperatures, such as
the Fe XXV, Ca XIX and S XV lines. These predicted curves successfully
fitted the observed light curves of the November 12 flare.
Differences due to the numerical noise become more evident in the light
curves of spectral lines, such as Fe XV and Mg X, which form at the lowest
coronal temperatures, next to the transition region (see Fig. 4 (click here)).
As for the emission of the plasma at temperature below 
K
(principally UV), we can synthesize it only by using the new version of the
Palermo-Harvard code and therefore we have no other results to compare with.