IRBEM wraps three generations of the COSPAR/NRLMSISE neutral atmosphere model family. Each routine computes number densities for the major atmospheric species plus the total mass density and temperature profile at a given location and time, driven by solar flux and geomagnetic activity indices. All three models share an identical input/output structure, differing in the underlying physics and data coverage.Documentation Index
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All three IRBEM atmospheric routines require altitude inputs greater than 85 km. While MSISE-90 and NRLMSISE-00 describe the atmosphere from ground level to exospheric heights as physical models, IRBEM’s wrappers enforce the same >85 km lower bound for all three routines.
Common Input Structure
All three routines accept the same parameter set. ThewhichAp switch controls how the geomagnetic Ap index is provided — either as a single daily value or as the full 7-element time history required for the most accurate results.
Ap Array Structure
WhenwhichAp = 2, the Ap input is a [7, ntime] array with the following element definitions:
| Index | Description |
|---|---|
| 1 | Daily Ap |
| 2 | 3-hour Ap index for current time |
| 3 | 3-hour Ap index for 3 hours before current time |
| 4 | 3-hour Ap index for 6 hours before current time |
| 5 | 3-hour Ap index for 9 hours before current time |
| 6 | Average of eight 3-hour Ap indices from 12 to 33 hours before current time |
| 7 | Average of eight 3-hour Ap indices from 36 to 59 hours before current time |
whichAp = 1, only element 1 (daily Ap) is used; the remaining elements are ignored.
MSIS86
The Mass-Spectrometer-Incoherent-Scatter 1986 (MSIS-86) neutral atmosphere model, based on Hedin et al. [1977, 1983, 1987], constitutes the upper portion of the COSPAR International Reference Atmosphere CIRA-86. It describes neutral temperature and the densities of He, O, N₂, O₂, Ar, H, and N from approximately the mesosphere to exospheric heights. Data sources include rocket, satellite (OGO-6, AE-C/D/E, ESRO-4, DE-2), and incoherent scatter radar measurements.Parameters
Number of time points.
Ap input mode:
1— only the daily Ap value is used2— the full 7-element Ap time history is used
Day of year for each time point (January 1st = 1).
Universal time in seconds for each time point.
Altitude in km. Must be greater than 85 km for MSIS-86.
Geodetic latitude in degrees.
Geodetic longitude in degrees.
3-month average of the F10.7 solar radio flux index.
Daily F10.7 solar radio flux for the previous day.
Geomagnetic Ap index array. See the Ap array structure above.
Output
Atmospheric number densities (and total mass density):
| Index | Species | Units |
|---|---|---|
| 1 | He number density | cm⁻³ |
| 2 | O number density | cm⁻³ |
| 3 | N₂ number density | cm⁻³ |
| 4 | O₂ number density | cm⁻³ |
| 5 | Ar number density | cm⁻³ |
| 6 | Total mass density | g cm⁻³ |
| 7 | H number density | cm⁻³ |
| 8 | N number density | cm⁻³ |
Atmospheric temperatures:
| Index | Quantity | Units |
|---|---|---|
| 1 | Exospheric temperature | K |
| 2 | Temperature at altitude | K |
Call Sequences
MSISE90
MSISE-90 is an updated MSIS model that extends coverage from ground level to thermospheric heights. Below 72.5 km it is based primarily on the MAP Handbook tabulation of zonal-average temperature and pressure (CIRA-86), supplemented by National Meteorological Center data below 20 km and rocket measurements from 1947–1972. Above 72.5 km it is a revised MSIS-86 incorporating Space Shuttle and newer incoherent scatter data.For studies focused solely on the thermosphere (above 120 km), the MSIS-86 model is recommended by the original author. MSISE-90 is best suited for research that spans multiple atmospheric regions.
Parameters
MSISE-90 accepts the identical parameter set as MSIS-86. See the MSIS86 parameters section above.Output
MSISE-90 produces the same 8-element density and 2-element temperature arrays as MSIS-86. See MSIS86 output.Call Sequences
NRLMSISE00
NRLMSISE-00 (Picone et al., 2002) is the most recent model in the MSIS family, developed by Mike Picone, Alan Hedin, and Doug Drob at NRL. Key improvements over MSISE-90 include:- Extensive use of drag and accelerometer data on total mass density
- Addition of an O⁺ and hot oxygen component to total mass density above 500 km
- SMM UV occultation data on O₂ concentration
Parameters
NRLMSISE-00 accepts the identical input parameter set as MSIS-86 and MSISE-90. See the MSIS86 parameters section above.Output
Atmospheric densities — the first 8 elements are identical to MSIS-86/MSISE-90; the 9th is unique to NRLMSISE-00:
| Index | Species | Units |
|---|---|---|
| 1 | He number density | cm⁻³ |
| 2 | O number density | cm⁻³ |
| 3 | N₂ number density | cm⁻³ |
| 4 | O₂ number density | cm⁻³ |
| 5 | Ar number density | cm⁻³ |
| 6 | Total mass density | g cm⁻³ |
| 7 | H number density | cm⁻³ |
| 8 | N number density | cm⁻³ |
| 9 | Anomalous oxygen number density | cm⁻³ |
Temperatures (same as MSIS-86 and MSISE-90):
| Index | Quantity | Units |
|---|---|---|
| 1 | Exospheric temperature | K |
| 2 | Temperature at altitude | K |
Call Sequences
Model Comparison
| Feature | MSIS-86 | MSISE-90 | NRLMSISE-00 |
|---|---|---|---|
| Altitude range | ~85 km – exosphere | Ground – exosphere | Ground – exosphere |
| Best domain | Thermosphere (>120 km) | Multi-region studies | All altitudes (recommended) |
| Species output | 8 (He, O, N₂, O₂, Ar, ρ, H, N) | 8 (same) | 9 (adds anomalous O) |
| Total mass density | Yes | Yes | Yes (improved above 500 km) |
| Solar drag data | No | Partial | Extensive |