The book "Orta Enlem E-Yogunlugu Çukurunun yonosferik Kritik Frekanslardaki zi" offers a comprehensive analysis of electronic density in the ionosphere, particularly in the mid-latitudes. It examines the critical frequencies captured by ionospheric probes in the Northern Hemisphere between 30 and 70 degrees magnetic latitude. The collected data, based on statistical analyses, are investigated in terms of their temporal and seasonal variations as well as the constant magnetic latitude. The results show that the electronic density values measured by the satellites Ariel 3 and Ariel 4 at an altitude of about 550 km exhibit similar changes across different local times and seasons. This work is aimed at professionals and students engaged in ionospheric research and related physical phenomena.