Trends in Parameters of the Layer and Their Possible Causes

The results of determination of the long-term trends in the parameters of the ionospheric 2 layer (critical frequency, height, total electron content, and slab thickness) are considered. It is shown that the recent results of determination of the 2 trends agree with the results of the detailed analysis of the data of stations in two hemispheres published by the authors. Possible causes of appearance of the negative trends in the parameters of the 2 layer at the cooling and contraction of the thermosphere due to anthropogenic effects. Currently, a decrease in the atoms-to-molecules ratio in the thermospheric gas and an increase in the rate of the ion-molecular reactions at the temperature decrease in the winter conditions are the most probable causes of appearance of the negative trends in 2 in the winter months. A comparison of the trends in various parameters is performed and it is shown that these trends agree with each other.