Model:

          AIMM: Assimilative Ionospheric Model for Mid-latitudes
Principle: 
 
               The electron density and ion species O+, NO+, O2+ and N2+
               are obtained numerically  by solving the equations  of
               continuity for  all  4 ions and of momentum for O+. 21
               chemical reactions are involved, with stable as well as
               meta-stable O+ considered. EUV91/EUVAC, MSIS86, HWM90/HWMMU 
	       and IRI95/Millstone Models are  adopted  in  order to 
	       determine the background  solar radiation  flux and neutral 
	       composition,  temperature and  wind.  Observed  foF2 may be  
	       used  to  fit  the simulated profile to the observed point at 
	       F2 peak.

Inputs: 
               geophysical  location (for  mid-latitudes), 
	       date of  year,
               solar 10.7cm flux, 
	       Ap index, 
	       electron  density at 500km (users can select Millstone 
		Hill model, IRI95 values or observed foF2).

Output:
               number density for electron as well as O+, NO+, O2+ and N2+,
               total contents within 100-500km and below the F2 peak, with
               the minimum time interval of 5  minutes for 24 hours, and
               minimum height interval of 2 km

Online Computations
	      Click here: http://www.haystack.mit.edu/madrigal/Models/mim_form.html 


  For Ionospheric Data Assimilations
 (This part is NEW !) 

It solves the O+ diffusion equation, derived from the continuity and the
momentum equations of O+, and the mass continuity equation for NO+, O2+
and N2+ to compute Ne over 100--500 km altitude. The lower boundary is
assumed to be in photochemical equilibrium. The upper boundary density is
set to the measured electron density. Plasma temperatures are set to
measured values.  Photoelectron impact is considered with a formula for
the ratio of secondary production to photoionization as given by Richards
and Torr [1988].  We allow for the effects of vibrationally excited N2 by
using the rate coefficient for the reaction of O+ with N2 as expressed by
Buonsanto} [1995].

We use an empirical model of meridional ion drifts perpendicular to the
geomagnetic field [ Zhang et al., 2000] to allow for the ExB drift
contribution to the ion vertical motion. We use the MU radar wind
climatology developed by Kawamura et al. [2000] to represent the values of
the meridional wind used in the model. The neutral concentration and
temperature are given by MSIS86 [Hedin, 1987] and the solar flux by EUVAC
[Richards et al., 1994].  

We modify each of these parameters, one or two or three at a time, for
best fit between model and data. Our assimilation system also estimates
the correlation coefficient if there are more than one variable being
fitted. This helps examine the uniquness of the derived variables.

               Zhang S-R, Xin-yu Huang, Yuan-zhi Su and S. M. Radicella,
               A Physical Model for One-dimensional and Time- dependent
               Ionosphere, Part I. Description of the Model,
               Annali di Geofisica, Vol 36, N.5-6, 1993

               Zhang S-R and Huang, A numerical study of ionospheric
               profiles at midlatitudes
               Ann. Geophysocae, 13, 551-557,1995

               Zhang S. R., S. Fukao and W. L. Oliver, Data modeling and
               assimilation studies with the MU radar 
               J. Atmos. Solar-Terr. Phys., 61, 563-583, 1999

               Zhang, S.-R., W. L. Oliver, S. Fukao, Y. Otsuka, A study of 
	       the forenoon ionospheric F2-layer behavior over the middle 
	       and upper atmospheric radar, J. Geophys. Res., 105, 15,823-15,833, 2000

	       Zhang, S.-R., W. L. Oliver, S. Fukao, S. Kawamura,
	       Extraction of Solar and Thermospheric Information from the 
	       Ionospheric Electron Density Profile, J. Geophys. Res.,
	       106, 12,821-12,836, 2001

               Those interested users may contact the model author at the
               address below:

               Dr. Shunrong Zhang
               MIT Haystack Observatory
               Route 40, Westford, MA 01886
               Email: shunrong@haystack.mit.edu