ANALYTICAL EXPRESSION OF O+-H+ ION TRANSITION SURFACE FOR USE IN IRI

A global surface of O+-H+ transition level is constructed, based on published data from OGO-6, Intercosmos-2, Alouette-l, ISS-b, and TAIYO satellites. This surface covers +/-60 degrees dipole latitude, all longitudes, two levels of solar activity, summer and winter solstices, and 00 and 12 hours local time. The surface is used as input data to a mathematical model which calculates transition levels in 5-dimensional space: sunspot number (R), month (M), local time (LT), dipole latitude (DL), and longitude (LONG). This model is based on a generalized multivariable polynomial, using a system of linearly independent functions. Model transition levels are compared with averaged data from AE-E and AE-C, as well as rocket measurements from Vertical-6 and Vertical-10. The obtained analytical expression can be directly used in IRI.