In addition to its main role of archiving and disseminating data from space science spacecraft, NSSDC has for many years held and disseminated empirical models of special interest to the space plasma physics community. Traditionally, this has involved both coefficient sets and software code for atmospheric and ionospheric composition/temperature models and magnetospheric magnetic field and trapped particle models. In recent years NSSDC has also provided the ability for users to actually execute these models through its captive NODIS account.
As a new service NSSDC is now providing World Wide Web-based accessibility to information about a wide range of models as well as to the ability to execute the International Reference Ionosphere (IRI) model, the Mass Spectrometer and Incoherent Scatter neutral atmosphere model Extended version 1990 (MSISE90), the International Geomagnetic Reference Field (IGRF) model, and the external-source magnetospheric magnetic field model of N. Tsyganenko (T89C).
For the most part these models execute in either of two modes. In one mode users interactively specify a time and spatial point of interest and are provided all the model parameters for that time and place. In the other mode users interactively specify for which independent variable they want profiles of model parameters, then specify values for the remaining independent variables, and are then provided the profiles requested.
Both the IRI and MSIS models require values of certain solar/geomagnetic activity indices. Time series of these indices are built into the NSSDC system, so users do not have to find historical values of such parameters themselves.
The IRI model has a special feature that enables users to generate profiles of peak parameters (D, E, F1, F2 heights, density, critical frequency). NSSDC's T89C code provides parameters not only at the point specified but also at the point of magnetic conjugacy to the specified point and at the equatorial crossing point of the model magnetic field line that passes through the specified location.
Much of the model output at this point is numeric. Providing additional graphical display output is intended for 1996. Also, it is anticipated that additional models will become WWW-accessible and -executable. The presently available models are all accessible from URL http://nssdc.gsfc.nasa.gov/space/model/models_home.html .