Featured observations of high frequency (HF) heating experiments are first introduced; the uniqueness of each observation is presented; the likely cause and physical process of each observed phenomenon instigated by the HF heating are discussed. A special point in the observations. revealed through the ionograms. is the competition between the Langmuir parametric instability and upper... https://lecoureures.shop/product-category/ski-de-fond-homme-bottes/