The Arecibo incoherent scatter radar in Puerto Rico is located at 18.3N, 66.7W with an operating frequency of 430 MHz. Data for Arecibo is archived in the CEDAR database and imported into the MADRIGAL database for the years 1970 until 2002.

In the database parameters Ne, Ti, Te, and line-of-sight ion velocity are available. Experimental data with CEDAR "kind of data" codes 2010, 30001, 30002, 30003, 30009, and 300015 are used in an attempt to secure a proper amount of data for modeling.

The data is extracted for each month and stored into individual directories for the next-step binning and fitting. Each month of data for the seasonal bin contains three months worth of data. The electron density, ion temperature, electron temperature, and line-of-sight ion velocity variables are separated into local time hourly bins, and the altitude variations are modeled using a piecewise linear function at different altitude nodes. There are fifteen nodes. Each one is determined according to the height points for one of the main experiments modes (or "kind of data"), and they are 145, 182, 219, 256, 293, 330, 367, 405, 442, 479, 516, 553, 590, and 627 km. (since Oct 21, 2004, these are 100, 110, 120, 130, 140, 160, 180, 200, 225, 250, 300, 350, 400, 450, 500, 550, and 600 km.) The Arecibo model uses a least-square-fit method to determine the altitude dependence, as well as solar activity and magnetic activity dependences assuming linear to F10.7 index for the previous day and ap index for the previous three hours, as indicated below:

P = a0 + a1 × f + a2 × a (1)P is one of the measured parameters (Nel, Ti, Te, or parallel ion velocity), f ((F10.7-135) / 100) is the normalized F10.7 index, a0, a1, and a2 are the fitting coefficients, and a ((ap - 15) / 10) is the normalized ap index. This bin-fit technique was used for the Millstone Hill, St Santin and Shigaraki ISR models. The model error is obtained by calculating the model and data difference for each point of the data and finding the root of the mean of the squared difference (r.m.s.).

The model can be provided to interested users with recovery FORTRAN codes and coefficient data files. It is also available for online interactive calculations and plots; the URL is http://madrigal.haystack.edu/models/ARisrm_form.html. Based on near realtime solar geophysical indices, a Virtual Arecibo Radar (VARR) is created which predicts the ionospheric conditions for Ne, Te, Ti and V// at current local time as well as for the whole day at Arecibo. The VARR is at http://madrigal.haystack.edu/models/varr/. Please contact Shunrong Zhang or John Holt for more details about the model.