ISO 16457:2022

INTERNATIONAL ISO
STANDARD 16457
Second edition
2022-02
Space environment (natural and
artificial) — The Earth's ionosphere
model — International reference
ionosphere (IRI) model and
extensions to the plasmasphere
Environnement spatial (naturel et artificiel) — Modèle de
l'ionosphère de la Terre — Modèle de l'ionosphère internationale de
référence (IRI) et extensions à la plasmasphère
Reference number
ISO 16457:2022(E)
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Published in Switzerland
ii
ISO 16457:2022(E)
Contents  Page
Foreword .iv
Introduction .v
1 Scope . 1
2  Normative references . 1
3  Terms and definitions . 1
4  Abbreviated terms . 3
5  General considerations .4
6 Applicability. 4
7  Model description .4
8  Model content and inputs . 5
9  Real-time IRI . 6
10  Plasmasphere extension of the IRI model . 6
10.1 General . 6
10.2 Extrapolation of IRI profiles . 6
10.3 Global core plasma model (GCPM) . 6
10.4 IMAGE/RPI plasmasphere model. 6
10.5 IZMIRAN plasmasphere model . 6
11  Accuracy of the model .7
Annex A (informative) Brief introduction to ionosphere and plasmasphere physics .8
Annex B (informative) Physical models . 9
Bibliography .13
iii
ISO 16457:2022(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to
the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see
www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 20, Aircraft and space vehicles,
Subcommittee SC 14, Space systems and operations.
This second edition cancels and replaces the first edition (ISO 16457:2014), which has been technically
revised.
The main changes are as follows:
— adding a description of the newly developed real-time IRI (Clause 9);
— replacing one of the plasmaspheric extension models (GPID) that is no longer available with the
option to extrapolate the standard IRI to plasmaspheric altitudes;
— providing more detail and newer references for the IMAGE/RPI and IZMIRAN plasmaspheric
extensions of IRI.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
iv
ISO 16457:2022(E)
Introduction
The purpose of this document is to identify a set of management guidelines for dealing with space
systems engineering activities and is intended to define the minimum existing processes on the subject
seeking to reach an international agreement on the topic.
Guided by the knowledge gained from empirical data analysis, this document provides guidelines
for specifying the global distribution of electron density, electron temperature, ion temperature,
ion composition, and total electron content through the Earth’s ionosphere and plasmasphere. The
model recommended for the representation of these parameters in the ionosphere is the international
reference ionosphere (IRI).
IRI is an international project sponsored by the Committee on Space Research (COSPAR) and the
International Union of Radio Science (URSI). These organizations formed a working group in the late
1960s to produce an empirical standard model of the ionosphere based on all available data sources.
The IRI Working Group consists of more than 60 international experts representing different countries
and different measurement techniques and modelling communities. The group meets annually to
discuss improvements and additions to the model. As a result of these activities several steadily
[18],[19],[20],[5],[6],[1],[2],[3],[53],[72],[73]
improved editions of the model have been released . The homepage
of the IRI project at http://irimodel.org/ provides access to the computer code (FORTRAN) of the latest
version of the model and to earlier versions and to links to several related sites that use IRI for various
applications.
For a given location over the globe, time, and date, IRI describes the monthly averages of electron
+ + + + + +
density, electron temperature, ion temperature, and the percentage of O , H , He , N , NO , O , and
cluster ions in the altitude range from 50 km to 1 500 km. In addition, IRI provides the electron content
by numerically integrating over the electron density height profile within user-provided integral
boundaries. IRI is a climatological model describing monthly average conditions. The major data
sources for building the IRI model are the worldwide network of ionosondes, the powerful incoherent
scatter radars, the topside sounders and in situ instruments flown on several satellites and rockets.
This document also presents several empirical and semi-empirical models that can be used to extend
the IRI model to plasmasphere altitudes.
One advantage of the empirical approach is that it solely depends on measurements and not on the
evolving theoretical understanding of the processes that determine the electron and ion densities
and temperatures in the Earth’s ionosphere. A physical model can help to find the best mathematical
functions to represent variations of these parameters with altitude, latitude, longitude, time of day, day
of year, and solar and magnetic activity.
IRI is recommended for international use by COSPAR and URSI. The IRI model is updated and improved
as new data and new sub-models become available. This document provides a common framework of
the international standard of the Earth’s ionosphere and plasmasphere for the potential users.
v
INTERNATIONAL STANDARD ISO 16457:2022(E)
Space environment (natural and artificial) — The Earth's
ionosphere model — International reference ionosphere
(IRI) model and extensions to the plasmasphere
1 Scope
This document provides guidance to potential users for the specification of the global distribution of
ionosphere densities and temperatures, as well as the total content of electrons in the height interval
from 50 km to 1 500 km. It includes and explains several options for a plasmaspheric extension of the
model, embracing the geographical area between latitudes of 80°S and 80°N and longitudes of 0°E to
360°E, for any time of day, any day of year, and various solar and magnetic activity conditions.
A brief introduction to ionospheric and plasmaspheric physics is given in Annex A. Annex B provides
an overview over physical models, because they are important for understanding and modelling the
physical processes that produce the ionospheric plasma.
2  Normative references
There are no normative references in this document.
3  Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
ionosphere
region of the Earth's atmosphere in the height interval from 50 km to 1 500 km containing weakly
ionized cold plasma
3.2
plasmasphere
−3 +
torus of cold, relatively dense (> 10 cm ) plasma of mostly H in the inner magnetosphere, which is
trapped on the Earth's magnetic field lines and co-rotates with the Earth
Note 1 to entry: Cold plasma is considered to have an energy of between a few electronvolts and a few dozen
electronvolts.
3.3
plasmapause
outward boundary of the plasmasphere (3.2) located at between two and six Earth radii from the centre
of the Earth and formed by geomagnetic field lines where the plasma density drops by a factor of 10 or
more across a range of L-shells of as little as 0,1
Note 1 to entry: The L-shell is a parameter describing a particular set of planetary magnetic field lines, often
describing the set of magnetic field lines which cross the Earth's magnetic equator at a number of Earth-radii
equal to the L-value, e.g. “L = 2” describes the set of the Earth's magnetic field lines which cross the Earth's
magnetic equator two Earth radii from the centre of the Earth.
ISO 16457:2022(E)
3.4
solar activity
series of processes occurring in the Sun’s atmosphere which affect the interplanetary space and the
Earth
Note 1 to entry: The level of solar activity is characterized by indices.
3.5
ionospheric storm
storm lasting about a day, documented by depressions and/or enhancements of the ionospheric electron
density during various phases of the storm
Note 1 to entry: Ionospheric storms are the ultimate result of solar flares or coronal mass ejections, which
produce large variations in the particle and electromagnetic radiation that hit Earth's magnetosphere and
ionosphere (3.1), as well as large-scale changes in the global neutral wind, composition and temperature.
3.6
sunspot number
R
daily index of sunspot activity defined as k(10 g + s) where s is the number of individual spots, g is the
number of sunspot groups, and k is an observatory factor
Note 1 to entry: R is alternatively called Ri or Rz or SSN.
Note 2 to entry: R12 is 12-month running mean of monthly sunspot number.
[68]
Note 3 to entry: In 2014 the calculation scheme for the officially distributed sunspot number was changed
with the result that the new sunspot number (SSN2) is about a factor of 1,45 larger than the old one (SSN1).
3.7
F10.7
solar radio flux at 10,7 cm wavelength measured at the ground daily at noon
Note 1 to entry: Besides this ‘observed’ F10.7 index there is also an ‘adjusted’ F10.7 index that is adjusted to 1AU.
Often used averages are the 81-day (3 solar rotations) running mean and the 12-month running mean.
3.8
Lyman-α index
solar activity (3.4) index based on daily measured solar emission at 121,6 nm (H Lyman-α line)
3.9
MGII index
solar activity (3.4) index based on core-to-wing ratio of the magnesium ion h and k lines at 279,56 nm
and 280,27 nm
3.10
Kp index
planetary three-hour index of geomagnetic activity characterizing the disturbance in the Earth's
[87]
magnetic field over three-hour universal time (UT) intervals
Note 1 to entry: The index scale is uneven quasi-logarithmic and assigned to successive 3 h UT intervals giving
eight values per UT day, and ranges in 28 steps from 0 (quiet) to 9 (disturbed).
3.11
ap index
three-hour UT amplitude index of geomagnetic variation equivalent to the Kp index (3.10)
Note 1 to entry: It is expressed in 1 nT to 400 nT.
ISO 16457:2022(E)
3.12
total electron content
TEC
integral number of electrons in the unitary area column from a lower altitude boundary to an upper
boundary
Note 1 to entry: Typically, the integral is taken from the lower boundary of the ionosphere (3.1) to the plasmapause
(3.3)
16 −2
Note 2 to entry: It is expressed in units of 10 electrons m (TECU).
3.13
TECg
TEC-based global index
global ionospheric index based on GNSS-derived TEC-noon measurements at the network of IGS stations
Note 1 to entry: See References [70] and [82] for more information on IGS stations.
3.14
GEC
global electron content
integral of TEC (3.12) over the whole globe based on GNSS-derived TEC measurements
3.15
IG
ionosphere global index
[56] [7]
ionosphere-effective sunspot number (3.6) that is obtained by adjusting the CCIR maps to global
ionosonde measurements of the F2 plasma critical frequency foF2
Note 1 to entry: IG12 is 12-month running mean of monthly ionosphere-effective sunspot number.
Note 2 to entry: See Reference [56] for the ionosphere-effective sunspot number and Reference [7] for the CCIR
maps.
4  Abbreviated terms
ELF extremely low frequency (less than 3 kHz)
BeiDou BeiDou Navigation Satellite System
GALILEO European Global Satellite Navigation System
GLONASS Global Orbiting Navigation Satellite System
GNSS Global Navigation Satellite System (e.g. GPS, GLONASS, GALILEO and others)
GPS Global Positioning System
HF high frequency (3 MHz to 30 MHz)
IRI international reference ionosphere
LF low frequency (30 kHz to 300 kHz)
MF medium frequency (300 kHz to 3 MHz)
UHF ultra high frequency (300 MHz to 3 000 MHz)
VHF very high frequency (30 MHz to 300 MHz)
VLF very low frequency (3 kHz to 30 kHz)
ISO 16457:2022(E)
5  General considerations
This model for the representation of the ionospheric and plasmaspheric plasma parameters is important
to a wide spectrum of applications. Electromagnetic waves travelling through the ionized plasma at the
Earth’s environment experience retardation and refraction effects. A remote sensing technique relying
on signals traversing the ionosphere and plasmasphere therefore needs to account for the ionosphere-
plasmasphere influence in its data analysis. Applications can be found in the disciplines of altimetry,
radio astronomy, satellite communication, navigation and orbit determination.
Radio signals, transmitted by modern communication and navigation systems, can be heavily disturbed
by space weather hazards. Thus, severe temporal and spatial changes of the electron density in the
ionosphere and plasmasphere can significantly degrade the signal quality of various radio systems
which even can lead to a complete loss of the signal. Model-based products providing specific space
weather information, in particular now- and fore-cast of the ionospheric state, serve for improvement
of the accuracy and reliability of impacted communication and navigation systems.
For high frequency radio communication, a good knowledge of the heights and plasma frequencies of
the reflective layers of the ionosphere and the plasmasphere is critical for continuous and high-quality
radio reception. High frequency communication remains of great importance in many remote locations
of the globe. The model helps to estimate the effect of charged particles on technical devices in the
Earth's environment and defines the ionosphere-plasmasphere operational environment for existing
and future systems of radio communication, radio navigation, and other relevant radio technologies in
the medium and high frequency ranges.
6 Applicability
There are a multitude of operational usages for ionospheric models, of which the most important are
outlined in this clause. Operators of certain navigational satellite systems such as GPS (USA), GLONASS
1)
(Russia), BeiDou (China) and GALILEO (Europe) require ionospheric predictions to mitigate losses of
navigation signal phase and/or amplitude lock, as well as to maintain accurate orbit determination for
all its satellites. Users of global navigation satellite systems need precise ionospheric models to increase
[57][58]
the accuracy and to reduce the precise positioning convergence time . Radio and television
operators using LF, MF, HF, VHF, UHF satellite or ground stations require ionospheric parameters for
efficient communications and for reducing interferences. Space weather forecasters have a great need
for accurate ionospheric models to support their customers with reliable and up-to-the-minute space
weather information. Ionospheric models are also used in the aeronautical and space system industries
and by governmental agencies performing spacecraft design studies. Here the models help to estimate
surface charging, sensor interference and satellite anomaly conditions.
Users also apply ionospheric models to mitigate problems with HF communications, HF direction
finding, radar clutter and disruption to ELF/VLF communications with underwater vehicles. Insurance
companies estimating the cost of protecting human health in space and satellites make use of
ionospheric models. Scientists using remote sensing measurement techniques in astronomy, biology,
geology, geophysics and seismology require parameter estimates for compensating the effects of the
ionosphere on their observations. An ionospheric model can be also used to evaluate tomographic,
radio occultation, and other similar techniques, by providing the ground-truth background model for
test runs. Amateur radio operators, as well as students and teachers in space research and applications,
also use ionosphere parameters. This document may be also applied for ray-path calculations to assess
the performance of a particular ground-based or space-borne system. Monthly medians of ionospheric
parameters are useful for HF circuit and service planning, while maps for individual days and hours aid
frequency management and retrospective studies.
7  Model description
The first version of the IRI model, IRI-1979, and its mathematical build-up is described in References [18],
[19] and [20]. The most detailed description of the model and the mathematical formulas and methods
[2]
used is given in a 155-page report about IRI-1990 . The next significant updates of the model were
ISO 16457:2022(E)
[5] [3] [53],[54] [71],[72] [73]
introduced with IRI-1995 , IRI-2000 , IRI-2007 , IRI-2012 and IRI-2016 . The latest
version of the model is available from http:// irimodel .org.
IRI-related research efforts and applications of the IRI model are presented and discussed during
1)
annual IRI workshops , with each workshop focusing on a specific modelling topic. Papers from these
2)
workshops have been published in dedicated issues of the journal Advances in Space Research .
Reviews of IRI and other ionospheric models can be found in References [4], [51], [52] and [54].
8  Model content and inputs
The IRI model uses a modular approach combining sub-models for the different parameters in different
altitude and/or time regimes. Examples of such sub-models are:
— International Telecommunication Union ITU-R (former CCIR) model for the F2 layer critical
−3
frequency foF2 (directly related with the F2 peak electron density, in m ) and for the propagation
[7]
factor M(3000)F2 (inversely correlated with the peak height, in km) ; IRI recommends use of the
[55]
CCIR model above continental areas and recommends use of the URSI model above ocean areas,
because the URSI model produces better results than the CCIR model in these areas; Instead of the
[56]
CCIR-recommended sunspot number IRI uses the global ionosphere index IG because it gives
better results especially at high solar activities;
[38]
— COSPAR international reference atmosphere (CIRA) model (NRL-MSISE-00 ) for the neutral
temperature;
[9]
— STORM model for storm-time updating of the F2 layer peak density ;
— International geomagnetic reference field (IGRF) model of the International Association of
Geomagnetism and Aeronomy (IAGA) for the magnetic coordinates (https:// www .ngdc .noaa .gov/
IAGA/ vmod/ ).
The IRI model requires the following indices as input parameters:
— R12, the 12-month running mean of sunspot number R;
— F10.7, the daily index and 81-day and 12-month running mean;
— IG12, the 12-month running mean of global ionosphere index IG;
— ap indices, the 3-hourly planetary magnetic indices for the prior 33 hours.
These indices can either be found automatically from the indices files that are included with the IRI
software package and that are updated quarterly, or the user can provide his/her own input values for
these indices. For R12 and IG12, the indices file starts from January 1958 and include indices prediction
for one to two years into the future. For ap index, the values start from January 1960 and include no
predictions.
In addition, model users have the options to use measured peak parameters to update the IRI profile,
including the F2, F1, and E layer critical frequencies (or electron densities), the F2 peak height (or
M(3000)F2 propagation factor), the E peak height, and the bottomside thickness and shape parameters
B0 and B1. In this way, real-time IRI predictions can be obtained if the real-time peak parameters are
available.
The total electron content (TEC) is obtained by numerical integration from the model’s lower boundary
(65 km during daytime and 80 km during night time) to the user-specified upper boundary.
1) Information about past and future workshops can be found on the IRI homepage (http:// irimodel .org), which
also provides access to the final report from each workshop and to a bibliography of IRI-related papers and issues
of Advances in Space Research.
2) A list of IRI issues of Advances in Space Research is available at http:// irimodel .org/ docs/ asr _list .html.
ISO 16457:2022(E)
9  Real-time IRI
Various data-assimilation techniques and indices-updating algorithms have been used to bring IRI
[74]-[81]
closer to the observed conditions in either real-time or retrospective mode . The most advanced
[79]
system developed by Galkin et al. uses the global database of ionosonde measurements of the Global
Ionospheric Radio Observatory (GIRO) to provide real-time inputs of foF2, hmF2, B0 and B1 for IRI.
10 Plasmasphere extension of the IRI model
10.1 General
The models described in 10.2 to 10.5 have been proposed as plasmasphere extension of the IRI model.
10.2 Extrapolation of IRI profiles
With the version of the IRI model available at http:// irimodel .org, a user is given the option to increase
the upper boundary for TEC computations to up to 20 000 km (GPS satellite altitude). Above 2 000 km a
simple extrapolation is used employing the IRI topside function.
10.3 Global core plasma model (GCPM)
[10]
GCPM-2000 is an empirical description of thermal plasma densities in the plasmasphere,
plasmapause, magnetospheric trough and polar cap. GCPM-2000 uses the Kp index and is coupled to IRI
3)
in the transition region 500 km to 600 km .
10.4 IMAGE/RPI plasmasphere model
[15]
The IMAGE/RPI plasmasphere model is based on more than 700 density profiles along field lines
[21]
derived from active sounding measurements made by the radio plasma imager (RPI) on the
IMAGE satellite between June 2000 and July 2005. The measurements cover all magnetic local times
and vary from L = 1,6 to L = 4 spatially. The resulting model depends not only on L-shell but also on
magnetic latitude and can be applied to specify the electron densities in the plasmasphere between
2 000 km altitude and the plasmapause (the plasmapause location itself is not included in this model).
A comparison of this model with other diffusive equilibrium models was published in Reference [22]. A
power profile model as function of magnetic activity was developed from RPI observations for the polar
[17]
cap region .
10.5 IZMIRAN plasmasphere model
4) [8],[11],[13]
The IZMIRAN plasmasphere model is an empirical model based on whistler and satellite
observations. IRI-Plas model presents global vertical analytical profiles of electron density and
temperature in the plasmasphere smoothly fitted to the IRI Ne(h) and Te(h) profiles at the altitude of the
topside half peak density (400 km to 600 km for electron density and 400 km for electron temperature)
and extended towards the plasmapause (up to 36 000 km). For the smooth fitting of the two models,
5)
the shape of the IRI topside electron density profile is modified using ISIS-1, ISIS-2 and IK-19 satellite
[12]
inputs . The plasmasphere model depends on solar activity and magnetic activity. The latest version
of IRI-Plas model includes dependence on eight solar and ionospheric proxy indices (SSN, R12, F10.7,
3) A FORTRAN code implementation of GCPM that includes all regions except the polar cap is available at https://
plasmasphere .nasa .gov/ models/ .
4) IZMIRAN: Institute of Terrestrial Magnetism, Ionosphere and Radio Waves Propagation, Russian Academy of
Sciences.
5) ISIS: International Satellites for Ionospheric Studies; IK-19: Intercosmos-19 satellite.
ISO 16457:2022(E)
[69],[70],[81]-[84]6)
Lyman-α index, MGII index, TECg, GEC and IG) . IRI-Plas applies the new global model
[86]
GMF2 that provides foF2 and hmF2 global maps based on the re-calibrated sunspot numbers SSN .
11 Accuracy of the model
The IRI model has been built to represent the monthly average behavior of space plasma. Efforts are
underway to also include a quantitative description of the monthly variability in IRI. As variability
measure, either the relative standard deviation or upper/lower quartiles and deciles will be used.
The accuracy of the IRI electron density model is typically (given here as standard deviation divided by
[88]
monthly median in %) :
— 50 % to 80 % at heights from 65 km to 95 km;
— 5 % to 15 % at heights from 100 km to 200 km during daytime;
— 15 % to 30 % at heights from 100 km to 200 km during night time;
— 15 % to 25 % at heights from 200 km to 1 000 km at low and middle dip latitudes (< 60°);
— 50 % to 80 % at heights from 200 km to 1 000 km at high dip latitudes (> 60°).
6) Source code for this IRI-Plas ionosphere-plasmasphere version is available from the IZMIRAN web site https://
ftp .izmiran .ru/ pub/ izmiran/ SPIM/ and IRI-Plas online is available at http:// www .ionolab .org/ .
ISO 16457:2022(E)
Annex A
(informative)
Brief introduction to ionosphere and plasmasphere physics
The ionosphere and plasmasphere are conductive, ionized regions of the Earth’s atmosphere consisting
of free electrons and ions. The ionosphere and plasmasphere are embedded within the Earth’s magnetic
field and thus are constrained by interactions of the ionized particles with the magnetic field. The
ionization levels in this near-Earth space plasma are controlled by solar extreme ultraviolet (EUV)
radiation and particle precipitation. The dynamics of the neutral atmosphere plays a significant role
in causing movement of the ionized particles by collisions with neutral atoms and molecules from the
surrounding thermosphere. The ionosphere extends in altitude from about 65 km to about 1 500 km
and exhibits significant variations with local time, altitude, latitude, longitude, solar cycle, season,
and geomagnetic activity. At middle and low latitudes, the ionosphere is contained within a region of
closed field lines, whereas at high latitudes the geomagnetic field can reconnect with the interplanetary
magnetic field and thus open the ionosphere to the driving force of the solar wind.
Plasma flowing upwards from the oxygen-dominated ionosphere is constrained to move along
the Earth’s magnetic field lines co-rotating with Earth and comprising the hydrogen-dominated
[25],[26] + +
plasmasphere extended up to a few Earth radii . The O /H transition height where the ion gas
consists of an equal percentage of both ions is often taken as the boundary between the ionosphere and
plasmasphere. These two regions of the upper atmosphere are strongly coupled through diffusion and
+ + +
resonant charge exchange reactions between O and H . At quiet conditions, H in the plasmasphere
typically diffuses down to the topside ionosphere at night and undergoes resonant charge exchange
+ +
reactions with atomic oxygen to produce O (downward flux). The O produced in this way can make a
significant contribution to the maintenance of the night-time ionosphere, and works in combination with
the meridional component of the neutral wind. The depleted night-time plasmasphere can be refilled
+
during the day through the reverse process; that is, the O ions flow up from the ionosphere, exchange
charges with the neutral hydrogen atoms to produce protons, and the protons are then stored in the
plasmasphere (upward flux). During geomagnetically disturbed conditions the plasmaspheric plasma
can be eroded by the enhanced magnetospheric electric fields, and consequently, the flux becomes
upward both during the day and night, due to the reduced plasmaspheric pressure, to refill the empty
plasmaspheric flux tubes. While the low-latitude flux tubes refill relatively quickly due to their small
volumes, most of the mid-latitude flux tubes are always in a partially depleted state, since the average
time between consecutive geomagnetic storms is not long enough for the upflowing ionospheric flux to
completely refill the flux tubes.
Terrestrial HF communications rely entirely on reflections from the ionized layers in the upper
atmosphere, but the ionosphere acts also as a hindrance because it distorts ground-to-space and
spacecraft-to-spacecraft radio links. Although empirical models of the ionosphere are now accessible
via electronic networking, most of them are far from reliable in predicting the average ionospheric
conditions, not to mention their limitations in forecasting the ionospheric "space weather". In particular,
a reliable and standard ionosphere-plasmasphere model is required for calibration of trans-ionospheric
signals of the high-altitude GPS and GLONASS satellites at 20 200 km above the Earth. On the other
hand, GNSS are also benefiting ionospheric modelling because they provide measurements of TEC
between ground receiver and satellite transmitter if the system operates on two or more frequencies.
This is the case because TEC can be deduced from the difference in delay at the different frequencies.
Due to the high temporal and spatial variability of the space plasma surrounding the Earth and due
to the requirements of its specification for the design and operation of space vehicles, remote sensing,
reliable communication and navigation, modelling of the ionosphere and plasmasphere is an important
research focus within the worldwide space science communities. Among these efforts the IRI plays an
outstanding part and is widely used by space agencies and scientists and engineers worldwide. It is
recommended for international use by COSPAR and URSI.
ISO 16457:2022(E)
Annex B
(informative)
Physical models
Physical models typically use a numerical iterative scheme to solve the Boltzmann equations for the
[53]
ionospheric gas including the continuity, energy, and momentum equations . They are solved along
field-lines of the Earth magnetic field where the field is represented either by a simple tilted dipole or
a multipole model like the IGRF. The equations are either solved self-consistently along a full flux tube
or the plasmaspheric flux is provided as a top boundary condition. The effects of the geomagnetic field
on the transport of the ionospheric plasma are introduced by the magnetic dip (I) and declination (D)
angles from IGRF.
The ionosphere is strongly coupled with the neutral atmosphere, chemically as well as dynamically. In
addition to the effects of the neutral wind, the neutral atmosphere significantly affects the ionospheric
plasma density distribution through neutral composition and temperature. The neutral composition
is a crucial factor not only for the production and loss of the plasma, but also for the diffusion of the
ionospheric plasma through the neutral atmosphere. The neutral temperature effect on the ionosphere
usually comes from the changes of the neutral densities caused by the neutral temperature change.
Below the F-region peak, chemical equilibrium prevails and the plasma density profile is largely
controlled by the neutral composition through the production and loss. As altitude increases, plasma
diffusion becomes important and well above the F-region peak, the plasma density profile is primarily
determined by diffusion. However, the diffusion of the plasma through the neutral atmosphere strongly
depends on the neutral densities, mainly the O density in the topside ionosphere, via collisions between
the plasma and the neutrals.
A physical model requires several input parameters, including the neutral densities and temperature,
neutral wind, and plasma temperatures. For these inputs, empirical models are adopted. In assimilative
mode of operation, up to six free model parameters should be adjusted to measurements within
physically reasonable ranges, and this cannot be reached straightforward under certain conditions.
Utah State University has been developing the global assimilation of ionospheric measurements (GAIM)
models that specify and forecast the state of the ionosphere. There are two models; the Gauss Markov
[27],[29],[59]-[63]
(GAIM-GM) and full physics (GAIM-FP) models . GAIM-GM uses a physics-based ionosphere
model and a Kalman filter as a basis for assimilating a diverse set of measurements. The physics-based
model is the ionosphere forecast model (IFM), which is global, covers altitudes from 90 km to 1 400 km,
and takes account of five ion species (NO+, O2+, N2+, O+, H+). However, the main output of the model is a
3-D electron density distribution. GAIM-FP uses a physics-based model of the ionosphere-plasmasphere
system and an ensemble Kalman filter as a basis for assimilating the measurements. The physics-
based model is the ionosphere plasmasphere model (IPM), which is global, covers the ionosphere and
plasmasphere from 90 km to 30 000 km, and takes account of six ion species (NO+, O2+, N2+, O+, H+,
He+). The primary output of GAIM-FP is a 3-D plasma density distribution. However, the model also
provides the self-consistent drivers of the ionosphere-plasmasphere system (e.g. neutral winds and
composition and electric fields).
The University of Southern California and the Jet Propulsion Laboratory (USC/JPL) physics
[30],[31],[28] [32]
model is derived from the Sheffield University Plasmasphere Ionosphere Model, SUPIM .
In physical models, such as SUPIM, the time-dependent equations of continuity, momentum (ignoring
the time variation and inertial terms in the momentum equation), and energy balance are solved along
eccentric-dipole magnetic field lines for the densities, field-aligned fluxes and temperatures of the
ions and the electrons. Its application relies on accurate estimates of the solar EUV, E x B drift, neutral
wind, and neutral densities. The ion momentum equation is further broken into a field-parallel and field
perpendicular component. The velocity component perpendicular to the magnetic field is considered to
be due entirely to E x B and is an input driver. The parallel component of velocity also has input drivers
ISO 16457:2022(E)
due to neutral winds and electron and ion temperatures. Thus, in the USC/JPL system the only state
+
variable solved for is the O density; the rest are input drivers to the system.
[33]
The coupled thermosphere ionosphere model (CTIM) was developed by coupling a self-consistent
[64]
thermosphere physical model with the Sheffield University high latitude ionospheric model . As
with many of the theoretical models, the global atmosphere is divided into a series of elements in
geographic latitude, longitude, and pressure (or altitude). Each grid point rotates with Earth to define
a non-inertial frame of reference in an Earth-centred coordinate system. The magnetospheric input
[34] [35],[65]
is provided by statistical models of auroral precipitation and electric fields . Both inputs are
keyed to a hemispheric power index (PI), based on the TIROS/NOAA auroral particle measurements
or use solar wind density and magnetic field measurements. A recent upgrade of this model included
[32]
a self-consistent plasmasphere and low latitude ionosphere models in the coupled thermosphere-
[36]
ionosphere-plasmasphere model (CTIP) . The effects of E × B drift at lower latitudes are incorporated
[66]
by the inclusion of a low-latitude physical electric field dynamo model . The new ionosphere-
plasmasphere component of CTIP solves the coupled equations of continuity, momentum and energy to
calculate the densities, field-aligned velocities and temperatures of the ions O+ and H+ and the electrons,
along a total of 800 independent flux-tubes arranged in magnetic longitude and L value (20 longitudes
and 40 L values). CTIPe includes a more fully coupling of electrodynamics into the model. It is used
at NOAA’s Space Weather Prediction Center (SWPC) to study thermosphere-ionosphere phenomena in
order to develop nowcasting and forecasting algorithms for space weather (https:// www .swpc .noaa
.gov/ products/ ctipe -total -electron -content -forecast).
[37],[67]
The field line interhemispheric plasma (FLIP) model is a first-principles, one-dimensional, time-
dependent, chemical, and physical model of the ionosphere and plasmasphere. It couples the local
ionosphere to the overlying plasmasphere and conjugate ionosphere by solving the ion continuity
and momentum, ion and electron energy, and photoelectron equations along entire magnetic flux
+ + + +
tubes. The interhemispheric solutions yield densities and fluxes of H , O , He , and N as well as the
electron and ion temperatures. The neutral densities, temperature, and wind are supplied by the
[38] [39],[89]
empirical NRLMSISE-00 and HWM models. During quiet times the error in the inputs for the
solar EUV flux, MSIS neutral parameters, reaction rates, and cross sections are typically about 20 %.
During ionospheric storms uncertainties can be much larger. The set of nonlinear, second-order, partial
differential equations for continuity, momentum, and energy is transformed into finite difference
equations and solved by a Newton-Raphson iterative scheme. The current FLIP model is primarily a
mid-latitude model but it can include convection electric fields, which are important at equatorial and
auroral latitudes.
As described in the previous paragraphs driver inputs must be obtained from empirical models
[38]
including the following: thermospheric densities from the NRLMSISE-00 model , neutral winds from
[39],[89] [40] [35],[41]-[43],[65]
the horizontal wind model (HWM) , solar EUV , electric fields , and electron
[34]
energy precipitation flux . The interested reader can refer to Reference [30] and references therein.
In this 2003 model validation experiment, only vertical drift at the geomagnetic equator was simulated
and estimated, while all the other inputs were held at their empirical values. The vertical drift was
parameterized by nine coefficients at different local times
The open geospace general circulation model (OpenGGCM) is a global model of the magnetosphe
...