Parameterized Ionospheric Model (PIM)

pim_thumbThe Parameterized Ionospheric Model (PIM) is a fast global ionospheric and plasmaspheric model based on a combination of the parameterized output of several regional theoretical ionosphere models and an empirical plasmaspheric model. It represents the climatological portion of the Parameterized Real-time Ionospheric Specification Model (PRISM), currently the operational model for specifying the current state of the ionospheric weather. The development of PRISM and PIM was funded by the Battlespace Environment Division within the Space Vehicles Directorate of the Air Force Research Laboratory (AFRL).

PIM consists of portable FORTRAN 77 source code and a large database of coefficients for an orthogonal function expansion. For user specified geophysical conditions and spatial coordinates, PIM produces electron density profiles (EDPs) between 90 and 25,000 km altitudes, corresponding critical frequencies and heights for the ionospheric E and F2 regions, and Total Electron Content (TEC).

The ionospheric portion of PIM is a parameterization of the results of several regional theoretical ionospheric models. This allows PIM to be computationally fast while retaining the physics of the theoretical ionospheric models. The parameterization compresses the output from the theoretical ionospheric models while preserving important characteristics such as density peaks and scale heights. The large base of data used by PIM contains coefficients from the parameterization. This constitutes PIM as described in Daniell et al., Radio Sci., 30, 1499-1510, 1995. In 1997 we incorporated the Gallagher plasmaspheric model (Gallagher et al., Adv. Space Res., 8(8), 15-24, 1988), a fast empirical model of plasmaspheric H+, into PIM.

Although the PIM FORTRAN code is fully portable to any system with a FORTRAN 77 compiler (with common extensions), the installation process is slightly different for Microsoft Windows and Unix systems, so there are two different downloadable versions of PIM. If you wish to learn more about PIM before downloading the code itself, you may obtain the PIM 1.7 User Guide separately.

Shown below are animations of the total electron content (TEC), which is the total number of electrons present along a path between two points. TEC is significant in determining the scintillation and group delay of a radio wave through the ionosphere and is strongly affected by solar activity. Ionospheric TEC is characterized by observing carrier phase delays of received radio signals transmitted from satellites located above the ionosphere, often using Global Positioning System (GPS) satellites. The TEC animations are for April 11, 2000 from 00:00 UT to 23:00 UT (Universal Time) for a solar activity index (F10.7) of 164, a sunspot number of ssn = 190, and a magnetic Kp = 3.5. F10.7 is the solar radio flux at a wavelength of 10.7 cm (2800 MHz) in units of 10-22 W/m2/Hz as observed at Penticton, British Columbia, and adjusted to a distance of 1 Astronomical Unit (AU) where the latter is the mean earth-sun distance. The magnetic Kp index provides a measure of solar particle radiation by its magnetic effects. The TEC unit (TECu) is 1016 m-2.

The animation above is a map projection of the TEC onto the Earth's surface showing how intensely the ionosphere is being influenced by solar activity (rollover image for 24 hour view). The large red and yellow features moving through the tropics (equatorial region) are known as the Appleton and Equatorial Anomalies. These are bands of maximum TEC that are caused by uprising plasma that occur prior to midnight and are located about 15 degrees north and south of the geomagnetic equator. The animation below shows the same TEC for a fixed Earth globe with a fluid ionosphere moving in time (rollover image for a 360 degree view).

References

Daniell, R. E., Jr., L. D. Brown, D. N. Anderson, M. W. Fox, P. H. Doherty, D. T. Decker, J. J. Sojka, and R. W. Schunk (1995), Parameterized ionospheric model: A global ionospheric parameterization based on first principles models, Radio Sci., 30(5), 1499–1510, doi:10.1029/95RS01826

Gallagher, D. L., P. D. Craven, R. H. Comfort (1988), An empirical model of the earth's plasmasphere, Adv. Space Res., 8(8), 15-24, doi: 10.1016/0273-1177(88)90258-X.