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Atmosphere and ionosphere models

Overview

A number of reference atmosphere and ionosphere models are available in SPENVIS: They are implemented in two applications:
  1. positional version: evaluation of densities and temperatures over a grid of points;
  2. orbital version: evaluation of densities and particle fluxes over a spacecraft trajectory.

Atmosphere and ionosphere models

NRLMSISE-00

The MSIS empirical models of Hedin [1987, 1988, 1991] provide thermospheric temperature and density based on in-situ data from seven satellites and numerous rocket probes. These models provide estimates of temperature, and the densities of N2, O, O2, He, Ar, and H. Low-order spherical harmonics are used to describe the major variations throughout the atmosphere including latitude, annual, semiannual, and simplified local time and longitude variations. This model provides a useful format for organizing and making widely available the results of satellite missions which provide large amounts of data, but with limited coverage of relevant geophysical conditions by an individual mission. These models facilitate data comparisons and theoretical calculations requiring a background atmosphere, as well as providing convenient engineering solutions.

The MSIS models use a Bates-Walker temperature profile as a function of geopotential height for the upper thermosphere and an inverse polynomial in geopotential height for the lower thermosphere. Exopsheric temperature and other atmospheric quantities are expressed as functions of geographical and solar/magnetic parameters. The temperature profiles allow for exact integration of the hydrostatic equation for a constant mass to determine the density profile based on a density specified at 120 km as a function of geographic and solar/magnetic parameters.

The model version implemented in SPENVIS is NRLMSISE-00. The MSIS software can be obtained at the Naval Research Lab or at NSSDC.

MET-V 2.0

The MET-V 2.0 model [Owens, 2002] is a semi-empirical model using the static diffusion method with coefficients obtained from satellite drag analyses. It is based on the 1988 version of MET and work done on the 1999 version, developed from the Jacchia series of models. With the proper input parameters, an approximate exospheric temperature can be calculated. With exospheric temperature specified, the temperature can be calculated for any altitude between 90 and 2,500 km from an empirically determined temperature profile. In the original development phase of the Jacchia model, the prime objective was to model the total neutral mass density of the thermosphere by adjusting temperature profiles until agreement between modelled and measured total densities (derived from satellite drag observations) was achieved. Agreement between modelled temperatures and those derived from later satellite drag and in situ measurements was not always achieved. Thomson-scatter radar temperature measurements generally show that the diurnal temperature maximum lags the density maximum by a couple of hours, whereas in the MET-V 2.0 model, the temperature and the density maxima and minimal are in phase.

The essence of the MET-V 2.0 model is the calculation of atmospheric density in two major regions: the lower thermosphere (altitudes between 90 km and 105 km) and the upper thermosphere (above 105 km). Between the base of the thermosphere (assumed to be at 90 km) and 105 km, turbulent mixing is assumed to predominate, and diffusion dominates at higher altitudes. The density for all points on the globe at 90 km altitude is assumed constant and mixing of atmospheric constituents prevails to 105 km. Between these two altitudes, the mean molecular mass varies as a result of dissociation of O2 to O. An empirical process is employed in the determination of the mean molecular mass distribution between 90 and 105 km, such that the ratio of O to O2 is 1.5 at 120 km.

The input parameters required by the model are altitude, latitude, longitude, date (month, day, and year), time (hour and minute), 3 hourly geomagnetic index (linear or logarithmic), and the daily 10.7 cm solar radio flux and its average over six solar rotations referenced to the midpoint.

The model version implemented in SPENVIS is MET-V 2.0. The MET-V 2.0 computer program is available upon request to Jerry K. Owens at Jerry.K.Owens@nasa.gov.

DTMB78

Optical measurements of the width of the 630 nm line of atomic oxygen have led to the construction of a global temperature model independently of any assumption related to the distribution of atmospheric constituents. This model was combined with satellite drag data to construct a new three-dimensional thermospheric model [Barlier et al., 1979] which is represented by the acronym DTM (Drag Temperature Model). The model version implemented in SPENVIS is DTMB78.

Since satellite drag data lead to total density in the vicinity of the perigee, some assumptions must be introduced to obtain concentrations for each atmospheric constituent. The construction of DTM is based on the fact that molecular nitrogen, atomic oxygen and helium are successively the major atmospheric constituents above 120 km as a consequence of diffusion separation in the Earth's gravitational field. Barlier et al. [1979] used an iterative procedure to represent the three major constituents N2, O and He in terms of spherical harmonics at 120 km altitude. Using a thermopause temperature model and an analytical temperature profile it then is possible to compute concentrations for the major atmospheric constituents at a given altitude as a function of local solar time, latitude, day number in the year, solar decimetric flux F10.7 and geomagnetic index Kp. The detailed formalism is given by Barlier et al. [1979].

HWM93

The Horizontal Wind Model (HWM) is an empirical model of the horizontal neutral wind in the upper thermosphere. It is based on wind data obtained from the AE-E and DE-2 satellites. A limited set of vector spherical harmonics is used to describe the zonal and meridional wind components. The first edition of the model released in 1987 (HWM87) [Hedin et al., 1988] was intended for winds above 220 km. With the inclusion of wind data from ground based incoherent scatter radar and Fabry-Perot optical interferometers, HWM90 was extended down to 100 km and using MF/Meteor data, HWM93 was extended down to the ground [Hedin et al., 1991].

Solar cycle variations are included (since HWM90), but they are found to be small and not always very clearly delineated by the current data. Variations with magnetic activity index (Ap) are included. Mid- and low-latitude data are reproduced quite well by the model. The polar vortices are present, but not to full detail. The model describes the transition from predominantly diurnal variations in the upper thermosphere to semidiurnal variations in the lower thermosphere and a transition from summer to winter flow above 140 km to winter to summer flow below. Significant altitude gradients in the wind extend up to 300 km at some local times.

The model software provides zonal and meridional winds for specified latitude, longitude, time, and Ap index. A comparison of the HWM values with winds derived from IRI parameters and from ionosonde measurements have shown in general good agreement [Miller et al., 1990]. The model version implemented in SPENVIS is HWM93.

The HWM93 software can be obtained at NSSDC.

IRI2001

The International Reference Ionosphere (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 sixties to produce an empirical standard model of the ionosphere, based on all available data sources. Several steadily improved editions of the model have been released. For given location, time and date, IRI describes the electron density, electron temperature, ion temperature, and ion composition in the altitude range from about 50 km to about 2000 km, and also the electron content. It provides monthly averages in the non-auroral ionosphere for magnetically quiet conditions. The major data sources are the worldwide network of ionosondes, the powerful incoherent scatter radars (Jicamarca, Arecibo, Millstone Hill, Malvern, St. Santin), the ISIS and Alouette topside sounders, and in situ instruments on several satellites and rockets.

IRI is updated yearly during special IRI Workshops (e.g., during COSPAR general assembly). Several extensions are planned, including models for the ion drift, description of the auroral and polar ionosphere, and consideration of magnetic storm effects. The model version implemented in SPENVIS is IRI2001 [Bilitza, 2001].

The IRI software can be obtained at NSSDC.

NeQuick v2.0

NeQuick is a 3D and time dependent ionospheric electron density model. More specifically, it is a quick-run model customised for trans-ionospheric applications that allows one to calculate the electron concentration at any given location in the ionosphere and subsequently the total electron content (TEC) along any ground-to-satellite ray-path by means of numerical integration. NeQuick has been developed at the Aeronomy and Radiopropagation Laboratory of the Abdus Salam International Centre for Theoretical Physics(ICTP) in Trieste, Italy and at the Institute for Geophysics, Astrophysics and Meteorology of the University of Graz in Austria.

Following the increasing amount of available data, the model formulation has been updated in order to improve its capabilities to provide representations of the ionosphere at global scales. In particular, major changes have been introduced in the model topside and bottomside formulation. In addition, specific revisions have been applied to the computer package associated to NeQuick in order to improve its computational efficiency. As a result, a new version of the model, NeQuick v2.0, has been made available [Nava, Coïsson & Radicella, 2008].

The model version implemented in SPENVIS is NeQuick v2.0. The original NeQuick source code can be obtained at the International Telecommunication Union, Radiocommunication Sector ( ITU-R).

References

Bilitza, D., International Reference Ionosphere 2000, Radio Science, 36, 261-275, 2001.

Barlier, F., C. Berger, J. L. Falin, G. Kockarts, and G. Thuillier, J. Atmosph. Terr. Phys., 41, 527-541, 1979.

Hedin, A. E., A Revised Thermospheric Model Based on Mass Spectrometer and Incoherent Scatter Data: MSIS-83, J. Geophys. Res., 88, 10170, 1983.

Hedin, A. E., MSIS-86 Thermospheric Model, J. Geophys. Res., 92, 4649, 1987.

Hedin, A. E., Extension of the MSIS Thermosphere Model into the Middle and Lower Atmosphere, J. Geophys. Res., 96, 1159, 1991.

Hedin, A. E., N. W. Spencer, and T. L. Killeen, Empirical Global Model of Upper Thermosphere Winds Based on Atmosphere and Dynamics Explorer Satellite Data, J. Geophys. Res., 93, 9959-9978, 1988.

Hedin, A. E., et al., Revised Global Model of Thermosphere Winds Using Satellite and Ground-Based Observations, J. Geophys. Res., 96, 7657-7688, 1991.

Miller, K. L., A. E. Hedin, P. J. Wilkinson, D. G. Torr, and P. G. Richards, Neutral Winds Derived from IRI Parameters and from the HWM87 Wind Model for the SUNDIAL Campaign of September, 1986, Adv. Space Res., 10, 99, 1990.

Nava, B., Coïsson, P. & Radicella, S. M., A new version of the NeQuick ionosphere electron density model, Journal of Atmospheric and Solar-Terrestrial Physics, 70, 1856-1862, 2008.

Owens, J. K., NASA Marshall Engineering Thermosphere Model-Version 2.0, NASA/TM—2002-211786, 2002.

Last update: Mon, 12 Mar 2018