Subject: initial comparisons..TIEGCM, SUNDIAL, IRI

From: [email-masked]
Date: Thu, 9 Feb 1995 18:11:23 -0500

Dear Gang,

We have completed our initial comparisons (i.e., we have generated the
plots) of the SUNDIAL/ATLAS-1 data with the TIEGCM output sent to us by Ben
(Day 27 March UT = 1-13). We are placing them in an ananomous ftp file
(mclapo.saic.com with a subdirectory called TIEGCM) so that you can review
and comment on the results. All the plots are in GIF format.

You will find 8 files, 4 involving foF2 comparisons and 4 involving hmF2
comparisons at UT = 3, 6, 9, and 12

TIEGCMvsAVG_pppp-UTxx.GIF
compares your 27 March run against our measurements averaged at each UT
over the entire campaign period (24 March - 4 April). pppp is either foF2
or hmF2. We show the TIEGCM isocontours in one color scale, and the
difference between the TIEGCM "predictions" and the observations is shown
using a second color scale. The open circles identify the individual
station locations.  The % differences (model minus data) within the open
circles is absolutely correct in its color representation, while the blend
between stations is the result of using Delauney triangulation. (You and
Barbra have already had an introduction to this plot format at the URSI
meeting.) The color legends are at the bottom of each figure.Note that the
maximum range for foF2 differences is set at +40%, while it is set at +25%
for hmF2. The notations across the top (left-to-right) identify the data
period (if averaged data is used in the comparison the campaign period is
listed...if the data of a single day is used, that day is identified. In
the center the parameter being compared is identified as well as the
model...m92.27 (TIEGCM) means we have used your model run for day 27 in the
campaign period (that's your "background" run). The UT time is on the
right.

TIEGCMvsDAY_ppp.UTxx.GIF
is the same as above except only hourly observations on 27 March are used
for comparison against the TIEGCM background run. Day 27 is the leading
candidate for the quietest day during the campaign.

IRIvsAVG_ppp.UTxx.GIF
compares the campaign averaged data against the IRI. All IRI runs were for
a sunspot number = 108 and month 3.5.

TIEGCMvsIRI.pppp.UTxx.GIF 
compares the TIEGCM directly against the IRI.

I have taken a quick look at the results and offer some brief comments
below. (I have heard from Ben just about an hour ago. He will be sending us
the rest of the TIEGCM runs, and we will continue the comparisons and keep
you posted.). In the nearest term (i.e.,tomorrow) we will begin comparisons
of meridional and zonal winds at 300km. We'll first compare TIEGCM against
the HWM, and then we'll compare the predicted meridional winds aganist
those measured (using the servo analysis on ionosonde data). The second
part is likely to take us a little more time since we do not as yet have
the analysis routine in place and tested.

---------------

COMMENTS ON ATLAS-SUNDIAL COMPARISONS

AV.DATA ....vs.....TIEGCM(27)....UT = 3, 6, 9, 12

foF2

1) In general, the model is in better agreement with the observations in
the daytime rather than at night.  The daytime "agreement" is generally
within +20%, while at night the observations tend to be higher than the
model predictions by 30-40% or more.

hmF2

1) The dominant characteristic of the comparison is general agreement
between the model and observations within +15%, with a few excursions to
+25%.

27 MARCH DATA..........TIEGCM(27)...UT = 3, 6, 9, 12

This comparison was done because there was some question at to whether the
TIEGCM background run (defined as day 27) should be compared with the
averaged observations or a "quiet" day (if there ever is such a thing!). As
it turns out  kp and Ap values suggest that 27 March is one of the leading
candidates for most quiet day...so it was picked for this comparison.

foF2

1) Daytime agreement is better than nighttime but the daytime agreement is
not as good when the model is compared with the averaged data at UT = 3 and
6. Arguably, the quiet-day comparison has the edge at UT = 9 and 12 hrs.

hmF2

1) The agreement is not quite as good as in the case involving model
comparison with the averaged data. In this case the spread tended to be
+20%

 AV. DATA....vs....IRI(M=3.5) UT = 3, 6, 9, 12

foF2

1) In general the data is running higher than the IRI with an estimate and
spread at 10+10%.

hmF2

1) The observed heights tend to run higher than those "predicted" by the
IRI, approximately at 12+12%. With higher heights we would expect higher
densities!

TIEGCM(27)....vs....IRI(M=3.5)

There is some question about the merit of such a comparison. When comparing
one model against another, where is the "fault" placed when there are
disagreements? In general, one might take the IRI as the "more correct"
since it is empirically derived. It however has its own set of flaws. 

foF2

1) The TIEGCM gives higher values than the IRI in the auroral region in the
range of 20 - 40% and higher.

2) Best agreement is in the daytime at mid-to-equatorial latitudes. Where
there is disagreement in the daytime the TIEGCM tends to be higher by as
much as 20%. With the exception of equatorial latititudes, the TIEGCM
values become increasingly larger than those of the IRI with increasing
latitude.

3) At night the TIEGCM has larger values (by 20-40%) than the IRI at
equatorial latitudes, but smaller values (by as much as 40%) at
mid-latitudes.

4) At pre-sunrise, there is a noticable  asymmetry in the disagreemnet
about the magnetic equator.

hmF2

1) The TIEGCM values tend to run from 20% higher to 12% lower than those in
the IRI wth regional or temporal trends difficult to unfold.

3) The worst agreement is at night

-------------------------

Regards,

Ed