Temperature and composition of the equatorial ionosphere

Values of temperature and composition obtained from incoherent scattering measurements in December 1965 and March–May 1966 at Jicamarca are presented. These values are derived from the autocorrelation function of the scattered signal, and the method by which this function is measured and analyzed is discussed in some detail. The temperature results differ considerably from those of temperate latitudes. During the day, the electron temperature reached a maximum value of the order of 1500–2000°K near 220–250 km, then decreased, arriving at equilibrium with the ion temperature somewhat above 300 km. Above 400–500 km, both the ion and electron temperatures increased, sometimes reaching values of the order of 2000°K at the highest heights observed (800–1000 km). During sunrise, the electron temperatures often exceeded 3000°K near 400 km. At sunset, the electrons and ions quickly reached equilibrium, and the ionosphere became isothermal at temperatures that sometimes fell slightly below 600°K. The altitude at which the O+ concentration fell to 50% of the total varied between 600 and 800 km in December 1965, and between 650 and 1100 km in March–April 1966.