Valida ion o he STORM model used in IRI wi h ionosonde
da a
G. Mi o
´ Ama an e
a,*
, M. Cue o San ama ı
´a
b
, K. Alazo
c
, S.M. Radicella
a
a
Ae omony and Radiop opaga ion Labo a o y, Abdus Salam ICTP, S ada Cos ie a 11, 34014 T ies e, I aly
b
Geophysics and Me eo ology Depa men , Facul y o Physics, Complu ense Uni e si y, A da. Complu ense, S/N 28040, Mad id, Spain
c
Ins i u o de Geo ı´sica y As onomı´a, Calle 212, N. 2906, C. Habana 11600, Cuba
Abs ac
The empi ical ionosphe ic s o m co ec ion model STORM included in he new e sion o he IRI model is d i en by he p e ious
ime-his o y o he ap index and is designed o be dependen on la i ude and season. The beha io o his co ec ion model has been
analyzed compa ing oF2 alues ob ained by he IRI model wi h o wi hou s o m co ec ion and hose measu ed by ionosondes dis-
ibu ed a ound he wo ld. A s a is ical analysis was done using wo geomagne ic s o ms du ing 2003 (medium sola ac i i y).
Keywo ds: Ionosphe ic s o m model; IRI; oF2 alues; Ionosonde da a; Valida ion
1. In oduc ion
The In e na ional Re e ence Ionosphe ic model (IRI)
(Bili za, 1990, 2001) is he esul o an in e na ional p ojec
sponso ed by he Commi ee on Space Resea ch (COSPAR)
and he In e na ional Union o Radio Science (URSI), which
aims a p oducing a e e ence model o he ionosphe e based
on a ailable expe imen al da a sou ces. The IRI model can
be un on-line a : h p://nssdc.gs c.nasa.go /space/model/
models/i i.h ml and he sou ce code is a ailable a : p://
nssdc p.gs c.nasa.go /models/.
One o he majo limi a ions o IRI was ha i p o ided
only mon hly a e ages o magne ically quie condi ions.
The s o m co ec ion model STORM (A aujo-P ade e
e al., 2002) was included in he new e sion o IRI and
was designed o be dependen on he in ensi y o he s o m
(ap index o e he 33 p e ious hou s), la i ude, and season.
The model conside s a h eshold o abou 9 in he ap index
be o e co ec ing he oF2 alue o quie condi ions. The
eal ime e sion o he model is a ailable a : h p://sec.
noaa.go /s o m/.
The pu pose o his pape is o e alua e his s o m co -
ec ions by compa ing he oF2 alues ob ained by he IRI
model, wi h and wi hou s o m co ec ion, wi h hose mea-
su ed by ionosondes. Da a om abou 15 obse ing si es
ha e been analyzed o wo geomagne ic s o ms in 2003.
Simila alida ion s udies ha e ecen ly been done by
A aujo-P ade e and Fulle -Rowell (2002), A aujo-P ade e
e al. (2003, 2004), and Mi o
´Ama an e e al. (2004). The
esul s ob ained by A aujo-P ade e e al. (2004) show ha
he s o m model cap u es e y well he di ec ion and mag-
ni ude o he changes in he summe s a ions whe e he e is
a clea endency o a nega i e phase, his was no he case,
howe e , o win e s a ions likely because o he inc eased
a iabili y in oF2.
2. Da a
Table 1 shows he wo geomagne ic s o ms (ap > 150)
analyzed in his s udy: Oc obe 2003 (smoo hed sunspo
numbe : 58.2) and No embe 2003 (smoo hed sunspo
numbe : 56.7). Ionosonde da a we e ob ained di ec ly om
se e al ionosphe ic g oups (Na ional Obse a o y o
*
Co esponding au ho .
E-mail add esses: [email p o ec ed] (G. Mi o
´Ama an e),
mcs@fis.ucm.es (M. Cue o San ama ı
´a), [email p o ec ed] (K. Alazo).
A hens, G eece; Communica ions Resea ch Labo a o y,
Tokyo, Japan; Is i u o Nazionale di Geofisica e Vulcanolo-
gia, Rome, I aly; Ins i u o de Geo ı
´sica y As onomı
´a, La
Habana, Cuba, CASLEO, San Juan, A gen ina, and IPS
Radio and Space Se ices, Aus alia), o downloaded om
he Uni e si y o Massachuse s Lowell DIDBase (h p://
ulca .uml.edu/DIDB/DIDBHome.h ml). In o de o a oid
possible e o s in he au oma ic scaling hose da a we e
manually scaled using he Sao-Explo e so wa e (h p://
ulca .uml.edu/SAO-X/SAO-X.h ml). Ionog ams om 30
ionosonde loca ions we e scaled bu only hose wi h a con-
inuous 5-day pe iod o oF2 alues we e included in he
e alua ion. Geog aphic coo dina es o hese obse ing
si es, as well as hei geomagne ic la i ude and modified
dip la i ude, a e shown in Table 2. Un o una ely, la i udi-
nal dependence canno be discussed because o he sca ci y
o high la i ude da a.
3. Me hodology
Fo each s o m hou ly measu ed oF2 alues ha e been
compa ed wi h model p edic ions using he IRI wi h
STORM and wi hou STORM. The s a is ical analysis
p esen ed he e is based on he me hod de eloped by
A aujo-P ade e e al. (2004). Tha pape e alua es he
empi ical s o m- ime ionosphe ic co ec ion model
Table 2
Geog aphic coo dina es, geomagne ic la i udes, and modified dip la i udes o he obse ing si es used in he s o m IRI model e alua ion
S a ion La . Long. La . geomag. Modip
Oc obe 2003
Midla i ude (40/60) Fai o d (FAI) 51.70 358.50 54.55 56.06
Chil on (CHI) 51.50 359.40 54.18 55.92
Rome (ROM) 41.90 12.50 42.40 49.17
Dyess A b (DYE) 32.50 260.30 42.16 49.61
Midla i ude (20/40) A hens (ATH) 38.00 23.50 36.48 45.96
Wakkanai (WAK) 45.40 141.70 35.42 51.15
Kokubunji (KOK) 35.70 139.60 25.60 43.44
Low la i ude (0/20) Jicama ca (JIC) 12.00 283.20 0.68 0.65
Ascension Is (ASC) 7.95 345.60 1.40 23.24
Midla i ude (20/40) Towns ille (TOW) 19.63 146.85 28.60 41.26
No olk Is. (NOR) 29.03 167.97 34.60 46.45
B isbane (BRI) 27.53 152.92 35.58 46.87
Midla i ude (40/60) Munda ing (MUN) 31.98 116.22 43.31 51.55
No embe 2003
Midla i ude (40/60) Chil on (CHI) 51.50 359.40 54.18 55.92
Mills one H (MIL) 42.60 288.50 53.99 55.90
Rome (ROM) 41.90 12.50 42.40 49.17
Dyess AFB (DYE) 32.50 260.30 42.16 49.61
Eglin AFB (EGL) 30.40 273.20 41.23 49.50
San Vi o (SAV) 40.60 17.80 40.11 48.11
Midla i ude (20/40) A hens (ATH) 38.00 23.50 36.48 45.96
Wakkanai (WAK) 45.40 141.70 35.42 51.15
Ramey (RAM) 18.50 292.90 29.89 42.48
Kokubunji (KOK) 35.70 139.60 25.60 43.44
Low la i ude (0/20) Ascension Is (ASC) 7.95 345.60 1.40 23.24
Midla i ude (20/40) Concepcion (CON) 36.80 286.90 25.42 35.59
Towns ille (TOW) 19.63 146.85 28.60 41.26
Lea mon h (LEA) 21.80 114.00 33.17 45.14
G ahams own (GRA) 33.30 26.50 33.80 50.97
No olk Is. (NOR) 29.03 167.97 34.60 46.45
B isbane (BRI) 27.53 152.92 35.58 46.87
Midla i ude (40/60) Munda ing (MUN) 31.98 116.22 43.31 51.55
The ionosonde s a ions a e so ed in o h ee geomagne ic g oups (0–20, 20–40, 40–60).
Table 1
Geomagne ic s o m pe iods selec ed in he s o m model e alua ion
Day Mon h Day yea Yea Ap index Day Mon h Day yea Yea Ap index
27 10 300 2003 11 19 11 323 2003 12
28 10 301 2003 25 20 11 324 2003 150
29 10 302 2003 204 21 11 325 2003 42
30 10 303 2003 191 22 11 326 2003 30
31 10 304 2003 116 23 11 327 2003 22
Fig. 1. Hou ly a ia ion o oF2 du ing he Oc obe 2003 s o m a Munda ing, Rome, A hens, B isbane, and Ascension Island. Ci cles, model p edic ions
o oF2 wi h S o m model; iangles, oF2 p edic ions wi hou S o m model; squa es, oF2 ionosonde alues (measu emen s).
Fig. 2. Hou ly a ia ion o oF2 du ing he No embe 2003 s o m a Lea mon h, Kokubunji, A hens, Mills one Hill and Ascension Island. Ci cles, oF2
alues wi h S o m model; iangles, oF2 p edic ions wi hou S o m model; squa es, oF2 ionosonde alues (measu emen s).
STORM du ing all he significan geomagne ic s o ms in
2000 and 2001 (high sola ac i i y). The esul s ob ained in
he cu en s udy apply o 2003, a middle-low sola ac i i y
pe iod, allowing us o es ablish a possible sola ac i i y
dependence o he s o m model. We calcula ed he daily oo
mean squa e e o (RMSE) o he en i e day (RMSE 24
hou s), o he pe iod om 08 o 16 LT (RMSE day ime),
and o he pe iod om 20 o 04 LT (RMSE nigh ime)
RMSE ¼ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
P
N1
i¼0
oF2modi oF2expi
½
2
N
u
u
u
ð1Þ
we e oF2mod is he model p edic ion and oF2exp he
measu ed alue. We calcula ed RMSE using IRI wi hou
STORM and wi h STORM. Nis he numbe o hou s
o each case. The pe cen age imp o emen (A aujo-
P ade e e al., 2004) is hen gi en as
imp o emen ð%Þ¼RMSEwi hou RMSEwi h
RMSEwi hou 100:
ð2Þ
Nega i e alues o ‘‘imp o emen ’’ indica e ha he
STORM model is wo se han he quie day model.
4. Resul s
Fig. 1 compa es he measu ed oF2 alues wi h he model
p edic ions using he S o m and no S o m e sions o he IRI
model. The plo s show he esul s o some o he s a ions o
a 5-day pe iod (120 h, DOY 300–304) in Oc obe 2003. I can
be seen ha s o m effec s appea o DOY 302, 303, and 304.
The STORM model shows mixed success. Fo nega i e ion-
osphe ic esponses on days 303 and 304 i cap u es he di ec-
ion o he changes a Munda ing, B isbane, Towns ille, and
No olk Is. (summe ), as well as a Fai o d and Chil on
(win e ). Howe e , STORM does no cap u e he di ec ion
o he changes a Rome and A hens (win e ). Fo posi i e
ionosphe ic esponse on day 302, STORM cap u es he
di ec ion o he changes a A hens, Kokubunji, and Rome
(win e ), bu does no cap u e he di ec ion o he changes
a B isbane, Munda ing, and Towns ille (summe ). The
STORM model p edic ion o days 303 and 304 a Ascen-
sion Island and Jicama ca (summe ) and Dyess and Wakka-
nai (win e ) a e no imp o ing he quie -day IRI p edic ions.
A simila analysis was made o he No embe 2003
s o m. Fig. 2 shows some examples o he compa ison
be ween measu ed and p edic ed oF2 alues o DOY
323–327 (No embe 19–23). Fo he nega i e ionosphe ic
esponse on day 325, STORM cap u es he di ec ion o
he changes a Lea mon h, B isbane, G ahams own, Mun-
da ing, Towns ille, No olk Is., and Concepcion (summe ),
bu does no cap u e he di ec ion o he changes a Kok-
ubunji (win e ). Fo he posi i e ionosphe ic esponse,
STORM cap u es he di ec ion o he changes a A hens,
Ramey, San Vi o and Rome (win e ), bu does no cap u e
he di ec ion o he changes a Mills one Hill and Chil on
Table 3
Pe cen age imp o emen (% Imp) du ing he 5-day pe iod o he Oc obe 2003 (le panel) and No embe 2003 ( igh panel) s o ms a each ionosonde s a ion
Oc obe 2003 No embe 2003
Name La . geomg 300 % Imp 301 % Imp 302 % Imp 303 % Imp 304 % Imp Name La . geomg 323 % Imp 324 % Imp 325 % Imp 326 % Imp 327 % Imp
FAI 54.55 3.8 11.7 27.1 50.0 48.9 CHI 54.18 1.3 2.1 100.0 4.3 7.3
CHI 54.18 10.9 26.7 45.6 40.7 MIL 53.99 11.5 9.5 52.9 10.1 4.5
ROM 42.40 6.8 9.0 17.3 41.2 37.1 ROM 42.40 5.2 8.0 9.6 6.5 24.2
DYE 42.16 3.6 10.7 2.4 1.4 2.7 DYE 42.16 0.0 4.8 0.3 15.2 15.3
ATH 36.48 3.4 8.9 22.6 108.2 70.8 EGL 41.23 5.6 4.8 2.6 12.0 15.0
WAK 35.42 4.3 9.7 4.0 1.8 0.0 SAV 40.11 2.5 8.9 5.1 3.4 13.0
KOK 25.60 2.2 4.3 15.5 29.4 27.5 ATH 36.48 2.0 15.0 13.4 2.2 19.5
JIC 0.68 2.6 5.1 2.8 0.5 10.0 WAK 35.42 11.7 10.3 7.0 34.2 0.0
ASC 1.40 1.9 3.0 1.0 3.3 2.5 RAM 29.89 10.0 17.9 13.2 16.0 20.1
TOW 28.60 0.0 1.0 23.5 50.7 16.1 KOK 25.60 15.9 27.6 66.7 7.5 5.1
NOR 34.60 0.0 4.4 8.1 61.5 48.0 ASC 1.40 0.0 2.6 1.8 11.6 6.3
BRI 35.58 1.6 1.2 6.4 38.3 63.4 CON 25.42 0.5 28.7 28.8 4.9 2.6
MUN 43.31 0.0 2.5 15.6 39.4 59.9 TOW 28.60 0.7 11.7 58.6 13.8 16.5
LEA 33.17 1.0 1.2 51.9 17.5 8.8
GRA 33.80 2.2 10.9 58.8 9.0 24.3
NOR 34.60 1.6 36.6 54.4 38.0 7.0
BRI 35.58 0.9 28.2 46.0 17.8 12.0
MUN 43.31 0.0 15.2 73.9 6.3 11.1
(win e ). STORM does no imp o e he p edic ions on day
325 a Ascension Island (summe ), Wakkanai, Dyess, and
Eglin (win e ).
Clea ly, STORM does no imp o e he p edic ions he
wo low la i ude s a ions analyzed, Ascension Island and
Jicama ca, du ing he s o m pe iods. This is o be expec ed
because o he sca ci y o da a ha we e a ailable o he
de elopmen o STORM and he s ill poo unde s anding
o he diffe en low la i ude physical p ocesses in ol ed
(A aujo-P ade e e al., 2002).
Table 3 shows he pe cen age imp o emen s, as defined
abo e o he 5-day s o m pe iods in Oc obe (le panel)
and No embe ( igh panel) 2003. The RMSE was calcu-
la ed conside ing he p e ious 24 h. Table 3 is so ed by
geomagne ic la i ude since he STORM model was
designed wi h a la i udinal dependence. Nega i e alues
Table 4
RMSE o No he n and Sou he n Hemisphe es o each o he 5 days in Oc obe 2003 s o m
Day Ap RMSE 24 hou s RMSE day ime RMSE nigh ime
Coun S o m No S o m Coun S o m No S o m Coun S o m No s o m
No h hemisphe e (Oc 2003)
300 11 142 1.34 1.39 52 1.81 1.89 54 0.62 0.64
301 25 165 1.36 1.50 61 2.06 2.28 62 0.51 0.56
302 204 139 1.70 2.02 56 2.26 2.71 48 1.12 1.30
303 191 123 2.90 2.91 55 2.18 2.20 34 4.18 4.15
304 116 154 2.02 1.94 62 2.45 2.34 52 1.86 1.82
A e age s o m pe iod 1.86 1.95 2.15 2.28 1.66 1.69
A e age s o m days 2.21 2.29 2.30 2.42 2.39 2.42
% imp o emen 3.5% 4.9 % 1.2%
Sou h hemisphe e (Oc 2003)
300 11 135 1.52 1.55 51 1.37 1.42 52 1.75 1.76
301 25 131 1.96 2.01 48 1.74 1.82 47 2.18 2.21
302 204 108 2.38 2.25 41 2.20 2.05 42 2.69 2.62
303 191 97 2.09 2.58 19 2.31 2.77 45 2.02 2.26
304 116 105 2.00 2.46 21 2.39 2.99 52 1.79 2.04
A e age s o m pe iod 1.99 2.17 2.00 2.21 2.09 2.18
A e age s o m days 2.16 2.43 2.30 2.60 2.17 2.31
% imp o emen 11.1% 11.5% 6.1%
A e ages o he en i e s o m pe iod and o he specific s o m days (in bold) a e also shown. The pe cen age o imp o emen is calcula ed o he s o m
days. Resul s a e also shown o day ime (08–16 LT) and nigh ime (20–04 LT).
Table 5
RMSE o No h and Sou h Hemisphe es o each o he 5 days in No embe 2003
Day Ap RMSE 24 hou s RMSE day ime RMSE nigh ime
Coun S o m No s o m Coun S o m No s o m Coun S o m No s o m
No h hemisphe e (No 2003)
323 12 237 0.86 0.85 89 0.86 0.94 88 0.82 0.75
324 150 203 1.97 2.13 82 2.37 2.63 66 0.95 0.88
325 42 213 2.43 2.38 81 2.35 2.02 80 3.06 3.16
326 30 202 1.17 1.26 73 1.51 1.73 76 0.75 0.66
327 22 214 1.23 1.40 90 1.42 1.74 67 1.01 0.98
A e age s o m pe iod 1.53 1.60 1.70 1.81 1.32 1.29
A e age s o m days 2.20 2.26 2.36 2.32 2.00 2.02
% imp o emen 2.6% 1.7% 1.0%
Sou h hemisphe e (No 2003)
323 12 179 1.31 1.30 64 1.27 1.26 71 1.37 1.36
324 150 161 1.54 1.89 63 1.52 1.93 59 1.40 1.61
325 42 107 1.79 2.80 16 2.93 4.02 57 1.56 2.52
326 30 146 1.36 1.28 55 1.45 1.34 52 1.36 1.31
327 22 161 1.28 1.28 61 1.53 1.46 61 1.14 1.22
A e age s o m pe iod 1.46 1.71 1.74 2.00 1.37 1.60
A e age s o m days 1.66 2.34 2.22 2.97 1.48 2.06
% imp o emen 29.0% 25.2% 28.1%
A e ages o he en i e s o m pe iod and o he specific s o m days (in bold) a e also shown. The pe cen age imp o emen is calcula ed o he s o m days.
Resul s a e also shown o day ime (08–16 LT) and nigh ime (20–04 LT).

mean ha STORM wo sens he p edic ions (shadowed
cells).
The p edic ed alues o he nega i e effec s obse ed in
he Aus alian egion and a wo Eu opean s a ions
(Chil on and Fai o d) du ing Oc obe 2003 (days 303
and 304) a e imp o ed by up o 63%. In he case o No em-
be 2003 (day 325), he imp o emen eaches alues o 74%
in he Aus alian egion. I is impo an o poin ou ha
Chil on and he Aus alian s a ions ha e been included in
he 75 ionosonde s a ions used in he de elopmen o he
STORM model (A aujo-P ade e e al., 2002). The model
imp o emen is mode a e o posi i e effec s p edic ions,
up o 23% in Oc obe 2003 and 13% in No embe 2003,
bo h o hem in A hens s a ion.
Table 4 shows he RMSE o he No he n and Sou h-
e n Hemisphe es o each o he 5 days in Oc obe 2003.
S o m days a e ma ke in bold. The a e age o he en i e
s o m pe iod and o he specific s o m days (bold) a e also
shown. The pe cen age o imp o emen is calcula ed o
he s o m days. As i has been no iced be o e, he bes
esul s a e ound o he Sou he n Hemisphe e (summe
s a ions) whe e he pe cen age imp o emen is mo e han
10%. In o de o find a possible hou ly dependence, RMSE
and he pe cen age imp o emen has been sepa a ely calcu-
la ed o day- and nigh ime pe iods. The esul s ob ained
clea ly show ha he model wo ks be e be ween 08:00
and 16:00 LT.
The analysis esul s o he No embe 2003 s o m a e
shown in Table 5. In his case, he STORM model
imp o es he p edic ions up o 29% o summe s a ions.
Fo his pa icula s o m, esul s do no show diffe ences
be ween day ime and nigh ime beha io .
The pe cen ages o imp o emen ound by A aujo-P a-
de e e al. (2004) o Oc obe and No embe 2001 s o ms
a e calcula ed wi h he p e ious 24 h and in gene al, hey
a e la ge han he co esponding alues ob ained in his
pape . These diffe ences could be ela ed o he highe
sola ac i i y in 2001, he sunspo numbe was a ound
115, double ha in 2003.
5. Conclusions
Two geomagne ic s o ms (ap > 150) ha e been analyzed:
Oc obe 2003 (13 ionosonde s a ions; smoo hed sunspo
numbe : 58.2), and No embe 2003 (18 ionosonde s a ions;
smoo hed sunspo numbe : 56.7). Measu ed oF2 da a
we e compa ed wi h IRI model p edic ions using he
STORM o no-STORM e sions. STORM cap u es qui e
well he di ec ion o he changes o nega i e effec s du ing
summe condi ions. The imp o emen eaches alues up o
63% du ing Oc obe 2003 and 74% o No embe 2003.
Fo posi i e effec s du ing win e condi ions STORM, in
gene al, imp o es he p edic ions in Eu ope and Japan
wi h imp o emen s eaching 23% o Oc obe 2003 and
13% o No embe 2003. Fo low la i udes (Ascension
Island and Jicama ca) no clea imp o emen is achie ed.
In he case o he Oc obe 2003 s o m he model wo ks be -
e du ing day ime wi h imp o emen o 11% a sou he n
loca ions.
Fu he s udies including high la i ude da a a e equi ed
o es ablish a possible la i udinal dependence o he accu-
acy in oF2 p edic ions.
Acknowledgemen s
The au ho s hank he Uni e si y o Massachuse s
Lowell o p o iding access o he digi al ionog am da a
base (DIDBase), and he ionosphe ic g oups (Na ional
Obse a o y o A hens (G eece), Communica ions
Resea ch Labo a o y (Tokyo, Japan), Is i u o Nazionale
di Geofisica e Vulcanologia (Rome, I aly), he AF DISS
ne wo k (USA), Ins i u o de Geo ı
´sica y As onomı
´a (La
Habana, Cuba), CASLEO (San Juan, A gen ina), and
he IPS Radio and Space Se ices (Aus alia)), whose da a
we e used in his s udy.
Re e ences
A aujo-P ade e, E.A., Fulle -Rowell, T.J., Cod escu, M.V. STORM: an
empi ical s o m- ime ionosphe ic co ec ion model, 1, Model desc ip-
ion. Radio Sci. 37 (5), 1070, doi:10.1029/2001RS00246, 2002.
A aujo-P ade e, E.A., Fulle -Rowell, T.J. STORM: an empi ical s o m-
ime ionosphe ic co ec ion model, 2, Valida ion. Radio Sci. 37 (5),
1071, doi:10.1029/2002RS00262, 2002.
A aujo-P ade e, E.A., Fulle -Rowell, T.J., Bili za, D. Valida ion o he
STORM esponse in IRI2000. J. Geophys. Res. 108 (A3), 1120,
doi:10.1029/2002JA00972, 2003.
A aujo-P ade e, E.A., Fulle -Rowell, T.J., Cod escu, M.V., Anghel, A.
E alua ion and p ospec s o s o m- ime co ec ions in he In e na-
ional Re e ence Ionosphe e. Ad . Space Res. 33, 902–909, 2004.
Bili za, D. In e na ional Re e ence Ionosphe e 1990. NSSDC 90-22,
G eenbel , Ma yland, 1990.
Bili za, D. In e na ional e e ence ionosphe e 2000. Radio Science 36 (2),
261–275, 2001.
Mi o
´Ama an e, G., Alazo, K., Cue o, M., Radicella. S.M. Compa ison
be ween expe imen al and IRI oF2 alues unde quie and s o m
condi ions. P oceedings IRI TFA 2004. in p ess.