A coupled thermosphere/ionosphere general circulation model
TL;DR: In this paper, the NCAR TGCM was extended to include a self-consistent aeronomic scheme of the thermosphere and ionosphere and the model now calculates total temperature, instead of perturbation temperature about some specified global mean, global distributions of N(µD), N(4S) and NO, and a global ionosphere with distributions of O+,NO+, O2+, N2+ N2+, n+, electron density, and ion temperature as well as the usual fields of winds, temperature and major composition.
Abstract: The NCAR thermospheric general circulation model (TGCM) is extended to include a self-consistent aeronomic scheme of the thermosphere and ionosphere. The model now calculates total temperature, instead of perturbation temperature about some specified global mean, global distributions of N(²D), N(4S) and NO, and a global ionosphere with distributions of O+,NO+, O2+, N2+, N+, electron density, and ion temperature as well as the usual fields of winds, temperature and major composition. Mutual couplings between the thermospheric neutral gas and ionospheric plasma occur at each model time step and at each point of the geographic grid. Steady state results for this first Eulerian model of the ionosphere, are presented for solar minimum equinox conditions. The calculated thermosphere and ionosphere global structure agrees reasonably well with the structure of these regions obtained from empirical models. This suggests that the major physical and chemical processes that describe the large-scale structure of the thermosphere and ionosphere have been identified and a self-consistent aeronomic scheme, based on first principles, can be used to calculate thermospheric and ionospheric structure considering only external sources.
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TL;DR: In this paper, a new simulation model of upper atmospheric dynamics is presented that includes self-consistent electrodynamic interactions between the thermosphere and ionosphere and uses the resultant electric fields and currents in calculating the neutral and plasma dynamics.
Abstract: A new simulation model of upper atmospheric dynamics is presented that includes self-consistent electrodynamic interactions between the thermosphere and ionosphere. This model calculates the dynamo effects of thermospheric winds, and uses the resultant electric fields and currents in calculating the neutral and plasma dynamics. A realistic geomagnetic field geometry is used. Sample simulations for solar maximum equinox conditions illustrate two previously predicted effects of the feedback. Near the magnetic equator, the afternoon uplift of the ionosphere by an eastward electric field reduces ion drag on the neutral wind, so that relatively strong eastward winds can occur in the evening. In addition, a vertical electric field is generated by the low-latitude wind, which produces east-west plasma drifts in the same direction as the wind, further reducing the ion drag and resulting in stronger zonal winds.
949 citations
TL;DR: A new simulation model of the mesosphere, thermosphere, and ionosphere with coupled electrodynamics has been developed and used to calculate the global circulation, temperature and compositional structure between 30-500 km for equinox, solar cycle minimum, geomagnetic quiet conditions.
Abstract: A new simulation model of the mesosphere, thermosphere, and ionosphere with coupled electrodynamics has been developed and used to calculate the global circulation, temperature and compositional structure between 30-500 km for equinox, solar cycle minimum, geomagnetic quiet conditions. The model incorporates all of the features of the National Center for Atmospheric Research (NCAR) thermosphere-ionosphere- electrodynamics general circulation model (TIE-GCM) but the lower boundary has been extended downward from 97 to 30 km (10 mb) and it includes the physical and chemical processes appropriate for the mesosphere and upper stratosphere. The first simulation used Rayleigh friction to represent gravity wave drag in the middle atmosphere and although it was able to close the mesospheric jets it severely damped the diurnal tide. Reduced Rayleigh friction allowed the tide to penetrate to thermospheric heights but did not close the jets. A gravity wave parameterization developed by Fritts and Lu (1993) allows both features to exist simultaneously with the structure of tides and mean flow dependent upon the strength of the gravity wave source. The model calculates a changing dynamic structure with the mean flow and diurnal tide dominant in the mesosphere, the in-situ generated semi-diurnal tide dominating the lower thermosphere and an in-situ generated diurnal tide in the upper thermosphere. The results also show considerable interaction between dynamics and composition, especially atomic oxygen between 85 and 120 km.
562 citations
TL;DR: The Solar EUV Experiment (SEE) is one of four scientific instruments on the NASA Thermosphere Ionosphere Mesosphere Energetics Dynamics (TIMED) spacecraft, which has been simultaneously observing the Sun and Earth's upper atmosphere since January 2002 as discussed by the authors.
Abstract: [1] The Solar EUV Experiment (SEE) is one of four scientific instruments on the NASA Thermosphere Ionosphere Mesosphere Energetics Dynamics (TIMED) spacecraft, which has been simultaneously observing the Sun and Earth's upper atmosphere since January 2002. The SEE instrument measures the irradiance of the highly variable, solar extreme ultraviolet (EUV) radiation, one of the major energy sources for the upper atmosphere. The primary SEE data product is the solar spectral irradiances from 0.1 to 194 nm in 1 nm intervals that are fundamental for the TIMED mission's investigation of the energetics in the tenuous, but highly variable, layers of the Earth's atmosphere above 60 km. The TIMED mission began normal operations on 22 January 2002, a time when the Sun displayed maximum levels of activity for solar cycle 23, and has provided daily measurements as solar activity has declined to moderate levels. Solar irradiance variability observed by SEE during the 2 years of the TIMED prime mission includes a variety of moderate and large flares over periods of seconds to hours and dozens of solar rotational cycles over a typical period of 27 days. The SEE flare measurements provide important, new results because of the simultaneous spectral coverage from 0.1 to 194 nm, albeit limited temporal coverage due to its 3% duty cycle. In addition, the SEE measurements reveal important, new results concerning phase shifts of 2–7 days in the intermediate-term variations between different UV wavelengths that appear to be related to their different center-to-limb variations. The new solar EUV irradiance time series from SEE are also important in filling the “EUV Hole,” which is the gap in irradiance measurements in the EUV spectrum since the 1980s. The solar irradiances measured by SEE (Version 7, released July 2004) are compared with other measurements and predictions from models of the solar EUV irradiance. While the measurement comparisons show reasonable agreement, there are significant differences between SEE and some of the models in the EUV range. The data processing algorithms and calibrations are also discussed.
525 citations
Cites methods from "A coupled thermosphere/ionosphere g..."
...The primary atmospheric models for the SEE investigation are the Thermosphere Ionosphere Mesosphere Electrodynamics General Circulation Model (TIME-GCM) [Roble et al., 1988], the MSISE-90 model [Hedin, 1991], and the NRLMSISE-00 model [Picone et al., 2002]....
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...The primary atmospheric models for the SEE investigation are the Thermosphere Ionosphere Mesosphere Electrodynamics General Circulation Model (TIME-GCM) [ Roble et al., 1988 ], the MSISE-90 model [Hedin, 1991], and the NRLMSISE-00 model [Picone et al., 2002]....
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...These solar-terrestrial interactions will be studied using the TIME-GCM [ Roble et al., 1988 ], which is a model of the upper atmosphere that has an option to use the SEE solar irradiance daily measurements as an input....
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TL;DR: A low-latitude ionospheric model has been developed at the Naval Research Laboratory: Sami2 is Another Model of the Ionosphere (SAMI2) as discussed by the authors, which treats the dynamic plasma and chemical evolution of seven ion species in the altitude range ∼ 100 km to several thousand kilometers.
Abstract: A new low-latitude ionospheric model has been developed at the Naval Research Laboratory: Sami2 is Another Model of the Ionosphere (SAMI2). SAMI2 treats the dynamic plasma and chemical evolution of seven ion species (H + , He + , N + , O + , N + 2 , NO + , and O + 2 ) in the altitude range ∼ 100 km to several thousand kilometers. The ion continuity and momentum equations are solved for all seven species; the temperature equation is solved for H + , He + , O + , and the electrons. SAMI2 models the plasma along the Earth's dipole field from hemisphere to hemisphere, includes the E x B drift of a flux tube (both in altitude and in longitude), and includes ion inertia in the ion momentum equation for motion along the dipole field line. The final point is relevant for plasma dynamics at very high altitudes where ion inertia can be important. For example, we have found that ion sound waves, which are supported by ion inertia, may be generated in the topside ionosphere (> 1000 km) at sunrise and sunset [Huba et al., 2000b]. The neutral species are specified using tile Mass Spectrometer Incoherent Scatter model (MSIS86) and the Horizontal Wind Model (HWM93). In this paper we describe in detail the SAMI2 model and present representative results from the model.
503 citations
United States Naval Research Laboratory1, York University2, University of Michigan3, Clemson University4, Colorado State University5, University of Washington6, British Antarctic Survey7, Massachusetts Institute of Technology8, Arecibo Observatory9, Science Applications International Corporation10, National Center for Atmospheric Research11, National Institute of Information and Communications Technology12, University of Adelaide13
TL;DR: The Horizontal Wind Model (HWM07) as mentioned in this paper provides a statistical representation of the horizontal wind fields of the Earth's atmosphere from the ground to the exosphere (0-500 km).
Abstract: [1] The new Horizontal Wind Model (HWM07) provides a statistical representation of the horizontal wind fields of the Earth's atmosphere from the ground to the exosphere (0–500 km). It represents over 50 years of satellite, rocket, and ground-based wind measurements via a compact Fortran 90 subroutine. The computer model is a function of geographic location, altitude, day of the year, solar local time, and geomagnetic activity. It includes representations of the zonal mean circulation, stationary planetary waves, migrating tides, and the seasonal modulation thereof. HWM07 is composed of two components, a quiet time component for the background state described in this paper and a geomagnetic storm time component (DWM07) described in a companion paper.
490 citations
References
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TL;DR: The MSIS-86 empirical model of thermospheric temperature, density and composition as discussed by the authors uses new temperature and composition data from the Dynamics Explorer satellite to improve the representation of polar region morphology over that in theMSIS-83 model.
Abstract: The MSIS-86 empirical model of thermospheric temperature, density and composition uses new temperature and composition data from the Dynamics Explorer satellite to improve the representation of polar region morphology over that in the MSIS-83 model. Terms were added or changed to better represent seasonal variations in the polar regions under both quiet and magnetically disturbed conditions. Local time variations in the magnetic activity effect were added. In addition a new species, atomic nitrogen, was added to the previous list of N2, O2, He, O, H, and Ar covered by the model.
1,699 citations
TL;DR: In this paper, a model for large-scale global convection characteristics of the high-latitude ionosphere has been constructed that allows the largescale Global Convection Model (GCM) to be used in F region chemical models.
Abstract: Mathematical expressions have been constructed that allow the large-scale global convection characteristics of the high-latitude ionosphere to be reproduced. The model contains no discontinuities in the ion convection velocity and as such should be useful in F region chemical models. The number of variables in the model allow such features as the dayside throat and the Harang discontinuity to be modeled. The applicability of the model to magnetospheric physics is limited by the exclusion of large-magnitude small-scale flow features associated with discrete arcs and by the inability of the model to produce separate flow cells at the same local time.
586 citations
TL;DR: In this article, a global, three-dimensional, time-dependent numerical model of the thermosphere has been created to simulate the dynamical behavior of the earth's thermospheres under a wide variety of geophysical conditions.
Abstract: A global, three-dimensional, time-dependent numerical model of the thermosphere has been created to simulate the dynamical behavior of the earth's thermosphere under a wide variety of geophysical conditions. Comparison of the model's predictions with the available data from ground-based, rocket and satellite techniques has shown that thermospheric dynamics can be realistically simulated by considering only three processes which deposit energy, or energy and momentum, in the thermosphere. Comparisons between the simulations and available data allow assessment of the magnitudes of the various processes as functions, particularly, of solar and geomagnetic activity. The model is fully self-consistent in solving the neutral gas equations of momentum, energy and continuity, including all the Coriolis, inertial, viscosity and nonlinear terms, but assumes that the thermosphere contains a single species whose mean molecular weight varies only with the pressure. At times when the mean meridional wind is la...
430 citations
TL;DR: The global neutral gas temperature distribution and circulation of the thermosphere are calculated for equinox and solstice conditions by using NCAR's thermospheric general circulation model (TGCM) as discussed by the authors.
Abstract: The global neutral gas temperature distribution and circulation of the thermosphere are calculated for equinox and solstice conditions by using NCAR's thermospheric general circulation model (TGCM) The variables are determined on a 5° grid in latitude and longitude at 24 constant pressure surface layers in the vertical from about 90 to 500 km Global empirical models of electron density and neutral composition are used to specify ion drag and the neutral gas background properties The energy sources that drive the thermosphere include heating caused by the absorption of solar EUV and UV radiation and a high-latitude heat source associated with auroral processes Starting from a global average state, the TGCM reached a diurnal reproducible pattern in approximately 5 days and showed no apparent instabilities in the basic flow The calculated motion patterns indicate that the observed day-to-day variability in the thermosphere is likely because of variations in the heat and momentum sources such as the result of neutral plasma interactions and waves coming from the lower atmosphere The calculated horizontal structure of wind and temperature is qualitatively different between the upper and lower thermosphere This difference occurs because the diurnal and semidiurnal forcing are in phase in the optically thick lower thermosphere but out of phase in the optically thin upper thermosphere Using the latest calculated heating efficiencies and measured fluxes of EUV, the calculated diurnal temperature amplitude is 250 K, compared to 320 K predicted by the MSIS empirical model, indicating that solar heating is primarily responsible for maintaining the structure of the thermosphere The zonally averaged properties of the TGCM essentially agree with previous results obtained from a two-dimensional model of the zonally symmetric thermosphere However, for reasons discussed, the latitudinal variations of temperatures is somewhat larger than previously calculated Our previously estimated auroral heating terms need to be reduced by 30%–40% to get best agreement with observations
398 citations
Journal Article•
TL;DR: In this article, an analytical prescription of particle precipitation in the auroral oval is developed that enables rapid numerical evaluation of auroral ionization rates and global aurora power input, and an ion chemical scheme is used to calculate the electron density enhancements and ion density distributions caused by auroral particle precipitation.
Abstract: A model of high latitude auroral processes has been developed for use in the NCAR TGCM. The ion drift pattern associated with magnetospheric convection is specified by the empirical model of Heelis et al. (1982) considering offset geographic and geomagnetic poles. An analytic prescription of particle precipitation in the auroral oval is developed that enables rapid numerical evaluation of auroral ionization rates and global aurora power input. An analytic expression has been derived for the total ionization rate and an ion chemical scheme is used to calculate the electron density enhancements and ion density distributions caused by auroral particle precipitation. The results of TGCM runs with and without auroral particle precipitation show the importance of auroral ionization in determining the dynamic structure of the winter hemisphere lower thermosphere.
332 citations