International
Reference Ionosphere 2001 Workshop on the Low Latitude Ionosphere
Report / Dieter Bilitza
The 2001 IRI
Workshop was held at the Instituto Nacional de Pesquisas Espaciais in São José
dos Campos, Brazil in the week from June 25 to 29. It was attend by about 60
scientists including representatives from USA, Russia, India, Peru, South
Africa, Japan,
Spain,
Argentina, U.K., Czech Republic, Chile, and Brazil. The 75 papers were
presented in 8 oral sessions and in 1 poster session. The titles of the oral
sessions were: The Equatorial Anomaly Region, Total Electron Content and
Topside, Description of Ionospheric Variability, Modeling the Low Latitude
Ionosphere, Ion composition, Scintillation and Spread-F, Representation of F
Peak and Bottomside Parameters, New Data and Model Inputs and Applications. The
workshop opened with a welcome address by the INPE Director, V.W.J.H. Kirchhoff
and was followed by an overview talk by D. Bilitza (USA) describing the new
version of the IRI model, IRI-2001. The meeting was well prepared and organized
thanks to the excellent efforts of the Local Organizers: J. H. A. Sobral, M.A.
Abdu, and I.S. Batista. Financial support was provided by the Committee on
Space Research (COSPAR), the International Union of Radio Science (URSI), the
International Center for Theoretical Physics (ICTP), the Instituto Nacional de
Pesquisas Espaciais/ Ministério da Ciência e Tecnologia (INPE/MCT), the
Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP), the Sociedade
Brasileira de Geofísica (SBGf), and the Fundação Coordenação de Aperfeiçoamento
de Pessoal de Nível Superios (CAPES). The papers and posters from this workshop
will be considered for a special issue of Advances of Space Research.
Electron Density: D and E
Region
Two new D-region
options have been introduced with IRI-2001 and now await testing by the user
community. The standard IRI D-region model remains in effect as before. A few
first comparisons have shown good agreement between the three model options as
pointed by Bilitza (USA) in his IRI-2001 overview talk. Pulinets (Russia)
pointed out the existence of a large data base of absorption measurements in
Russia that could be of help in modeling long-term trends of D-region
densities. He will contact the responsible scientists. McKinnell (South Africa)
presented a Neural Network (NN) model for E region parameters based on
ionosonde data from Grahamstown, South Africa.
The E region in
general is well represented by IRI. But some areas of improvement remain: (1)
The correct representation of the depth of the nighttime E valley. Incoherent
scatter measurements and theoretical studies have shown that the current IRI
E-valley is too deep. (2) The enhanced E region ionization due to particle
precipitation at auroral latitudes. Bradley (U.K.) reviewed models for
sporadic-E as a starting point for the future inclusion of a sporadic-E model
in IRI.
Electron Density: F1 Region and
F2 Bottomside
IRI-2001
provides considerably improved profiles in this region and includes the F1
probability as a new parameter. These improvements are a result of the annual
IRI Task Force Activity that is organized by Radicella (Italy) at the Abdus
Salam International Center for Theoretical Physics (ICTP) in Trieste, Italy.
Presentations by Reinisch (USA), Mosert (Argentina), Ezquer (Argentina),
Adeniyi (Nigeria; presented by Bilitza), and Mahajan (India) discussed these
efforts and pointed out areas for future improvements. The IRI group strongly
pursues and encourages the establishment of a data base of F1 and bottomside
parameters from a large number of globally distributed ionosondes. Especially
at high solar activities the current IRI bottomside thickness parameter B0
underestimates Jicamarca incoherent scatter data. The great potential of Jicamarca
incoherent scatter data for IRI modelling was reviewed by Chau (Peru).
Comparisons of Brazilian rocket data with IRI were presented by Sobral (Brazil)
and Muralikrishna (Brazil).
Electron Density: F2 Peak
Parameters
With the 2001
version IRI now includes a model for the description of storm effects. The storm-time updating model of
Fuller-Rowell et al. (USA) describes the changes in F2 peak density in terms of
the of the 3-hourly ap index (13 values prior to observation time). First
comparison with ionosonde and Total Electron Content (TEC) data were presented
by Radicella (Italy). The model predicts the observed trends but the study also
underlines the importance of the next step in storm effects modeling, namely
the description of the
storm-induced
changes in the F2 peak height hmF2.
Another
prominent feature still missing in the IRI hmF2 model, is the characteristic
peak shortly after sunset at equatorial latitudes. With the introduction of the
Scherliess-Fejer equatorial ion drift model in IRI-2001, one could now try to
include this feature by exploiting the strong correlation between hmF2 and
vertical ion drift at the equator especially during nighttime. Obrou (Ivory
Coast) and Bilitza (USA) studied this correlation with ionosonde data from Korhogo
(Ivory Coast). Batista (Brazil) plans to investigate this aspect further with
South American data. The current hmF2 model in IRI is based on the CCIR model
for the propagation factor M(3000)F2. Adeniyi (Nigeria) and Bilitza (USA)
showed that by using measured values of M(3000)F2, instead of the CCIR model,
the evening peak in hmF2 could quite often be reproduced. Their study is based
on ionosonde data from Ougadougou,
Burkina Faso, an African station close to the magnetic equator. A better
representation of hmF2 during quiet as well as storm time will be an important
future goal of the IRI group.
Intercosmos 19
topside sounder data were used to study the equator anomaly region and the
longitudinal distribution of F peak and topside parameters (Deminova and
Karpachev (Russia). Torres (Chile presented a systematic comparative study of
ionosonde data from Brazil and Chile and found in general good agreement
between the foF2 and hmF2 measurements and the IRI predictions for low solar
activity and discrepancies during high solar activity especially during
nighttime. Lazo and Calzadilla (Cuba; presented by Radicella) showed how
spherical harmonic analysis can be used for regional foF2 mapping for the
European and American sector. Ways to fully access the large amount of
ionosonde data stored on microfilm were discussed by Wright (USA)
Electron Density: Topside,
Plasmasphere and TEC
The times and
frequency of occurrence of an additional layer (the so-called F3 layer) above
the F2 peak were discussed by Batista (Brazil) based on data from ionosondes
and topside sounders. Such a layer develops when the equatorial vertical drift
pushes the F2 peak upward while simultaneously a new F2 peak develops at lower
altitudes due to the standard F layer forming processes. This equatorial
phenomenon is most often found during daytime summer and high solar activity.
More statistical studies are needed before this feature can be included in IRI.
Shortcomings of
the current IRI topside model were discussed by Ezquer (Argentina) based on
comparisons with insitu data from the Japanese Taiyo satellite. Efforts to
improve the IRI topside model continue with topside sounder data from Alouette
and ISIS (Bilitza, USA), and Intercosmos 19 (Pulinets, Russia). Bilitza (USA)
proposed a correction factor to better represent the upper topside. Iwamoto (Japan) discussed ways of correcting
the current IRI topside formulas to better represent ISS-b measurements.
Argentine IRI
studies with topside and TEC data were discussed by Ezquer Argentina) and
Mosert (Argentina). A TEC model for the Brazilian region was compared with IRI
and discrepancies were found during sunrise (1-hour shift) and midnight (IRI
does not include the observed peak near midnight) (Souza, Brazil). An effort
was initiated during the workshop to develop a TEC model for the whole South
American continent. The validation of GPS deduced TEC maps from several groups
with TOPEX data revealed shortcomings of several of the map algorithms (Orus
and Garcia-Fernandez, Spain). An overview of the activities of the
International GPS Service (IGS) Ionosphere Working Group was provided by
Feltens (Germany; presented by Bilitza). The Barcelona, Spain UPC group will continue to pursue the
updating of IRI with GPS data as a promising way to get better IRI predictions.
Efforts to
combine IRI with a plasmaspheric model continue. Gallagher’s GCPM and
Chasovitin’s SIM have been proposed as candidate models. Triskova (Czech
Republic) pointed out Magion satellite data as potential data source and Oyama
(Japan) the Akebono data.
Electron Density: Spread-F and
Variability
A model
describing the occurrence probability of Spread-F in the American longitude
sector was presented by Abdu (Brazil). The model describes the probability in
terms of local time, season, solar flux, and latitude (dip=+/- 25). The
dominant features of spread-F occurrence in the Indian sector were discussed by
Chandra (India) highlighting the strong correlation with solar activity.
Combining the Brazilian and Indian efforts should produce a first global
spread-F model for IRI. Ezquer (Argentina) reported about first GPS
scintillation measurements at Tucuman, Argentina. Iyer (India) compared the
scintillation indices (SI, S4) derived from data of the anomaly crest station
Rajkot with the models of Aerons and Secan. Wright (USA) discussed the
monitoring of Spread-F with digital ionosondes and pointed to the IGY-era
“f-plots” as a data source.
Quantitative
description of ionopsheric variability
(i.e. standard deviation from a
monthly mean) are now the primary goal of the IRI Taks Force Activity at
ICTP. At this workshop first results were presented by Mosert (Argentina)
regarding the variability of TEC based on data from two Argentine stations.
Electron and Ion Temperatures
IRI now includes
the Truhlik-Triskova-Smilauer model as a new option for the electron
temperature. This new model includes the early morning peak in temperature that
is currently represented by the standard IRI model only in the F region not in
the topside. An important next step is now a correct representation of solar
cycle variations. The effect of geomagnetic inclination of electron density and
temperature was discussed by Oyama (Japan) based on his Hinotori satellite
data. Truhlik (Czech Republic) intends to use the formalism developed for his
electron temperature model to also produce a global ion temperature model.
Incoherent scatter data could play an important role in improving the IRI
plasma temperature models, especially the variation with season and solar
activity as was pointed out by Mahajan (India) and Chau (Peru).
Ion Composition and Drift
Triskova and
Truhlik (Czech Republic) presented a
new model for the ion composition (O+, H+, He+,
and N+) in the altitude range 500 to 3000 km based on data from
Intercosmos 24 (ACTIVE) and from the Atmosphere Explorer satellites. The model
describes the ion densities in terms of local time and a specially introduced
magnetic field coordinate. The authors plan to also use ion composition data
from ISIS 1, ISS-b, AE-B and AEROS to extend their model particularly in terms
of the description of solar cycle variations. An effort at the National Space
Science Data Center (NSSDC) to make older ionospheric satellite data (like ISIS
1, AEROS and AE) available online was described by Bilitza (USA). Truhlik
(Czech Republic) introduced a new model for the light ion density ratio based
on ISIS 2, ISS-b, and Intercosmos 24 data. Currently IRI use a constant value
of 0.1 for this ratio. It was decided to include the new model in the next
version of IRI.
Anderson and
Reinisch (USA) pointed to the potential for deducing the daytime electrojet
current and vertical ExB ion drift from equatorial magnetometer
measurements.
Applications, New Members, and
Future Mettings
A 3-D
visualization of the Earth globe with surrounding IRI ionosphere nicely
illustrated the great educational capabilities of IRI in conjunction with
graphics tools (Watari and Iwamoto, Japan).
Lee-Anne
McKinnell (Rhodes University, Grahamstown, South Africa), Vladimir Truhlik
(Institute of Atmospheric Physics, Prague, Czech Republic), and V. K. Depuev
(IZMIRAN, Moscow, Russia) were elected as new members of the IRI Working Group.
In 2002 there
will be a number of meetings with IRI involvement. Most importantly the
next IRI
workshop will be held as a session C4.3, entitled "The Path toward
Improved Ionosphere Specification and Forecast Models", during the World
Space Congress 2002 (34th COSPAR Scientific Assembly) in Houston, Texas (10-19
October, 2002). Session C0.1 (Standard Space Environment Models for ISO) during
the same congress will discuss models that are proposed to the International
Standardization Organization (ISO) including the IRI model for the ionosphere.
During the URSI General Assembly in Maastricht, Netherlands (18-24 August 2002)
session G2, entitled "Operational Ionospheric Models Including Data
Ingest" is of special interest for the IRI group.
For the 2003 IRI Workshop the IRI Working Group has been presented with two proposals: (1) Rhodes University, Grahamstown, South Africa; (2) Polytechnical University of Catalonia, Barcelona, Spain. The local organizers were tasked with exploring local funding possibilities to support the workshop logistics and maybe also local travel for participants from the region.
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