The correlations between the typhoon and th f(0)F(2) of ionosphere

The effect of a typhoon on the critical frequency of the F(2) region has been studied using observations made in 1969, 1970, 1972, 1973. Twenty-one observations of typhoon crossings or passings by Hainan are compared with simultaneous ionospheric data from the same area. It is found that there are evident correlations between the passage of the typhoon and the number density of electrons in the F(2) region, or f(0)F(2). It is indicated that f(0)F(2) decreases in the area immediately above the typhoon center, but increases in the surrounding area. It is suggested that the strong vertical convection in the troposphere caused by the typhoon can change the local circulation system in the stratosphere and mesosphere, and this would influence f(0)F(2) through the change in turbopause height and in the ratio of the atmospheric composition of the F(2) region. Typhoon effects in the upper atmosphere can thus be used to study the coupling between the upper and lower atmospheres.