Long-Term Trends in the Height of the Ionospheric F2 Layer Peak

Long-term variations (trends) in the height of the ionospheric F2 layer peak hmF2 is analyzed based on the data of Moscow and Juliusruh stations. The near-noon LT hours and two winter months (January and February) and two summer months (June and July) are considered for a period of 1996-2023. Well-pronounced and statistically significant negative hmF2 trends are found both in summer and winter. Overall, the F2 layer height decreased during the analyzed period by 0.5-1 km per year. The "Delta" method developed and published by the authors earlier is applied to the same data. The results confirm a systematic decrease in the hmF2 value in the past two decades. It is found that the F2 layer height has decreased in recent years more rapidly than in the earlier years.