Studies have been made over a two-year period from April 1981 to March 1983 on an approximately east-west propagation of a long distant (5100 km) radio wave at 40 kHz from Sanwa, Japan to Calcutta. Besides ionospheric effects, the seasonal variations of the amplitude of the received signal have been carefully examined in this paper. The regular amplitude of the signal shows that the sunrise fade minimum lags well behind the ionospheric sunrise and it varies from season to season. Along the path of propagation which is very close to the tropic of cancer, the four important meteorological seasons are pre-monsoon (March–June), monsoon (July–September), post-monsoon (October–November) and winter (December–February), and the meteorological parameters of these seasons have been found to impress the signal amplitude. The signal amplitude has been found to be remarkably related to the product of the temperature and relative humidity. The correlation lies on the fact that humid air possesses a finite conductivity which controls the attenuation of the long wave while passing through the tropospheric regions in multiple paths.