The Red-belly snake (Storeria occipitomaculata) is a relatively small snake that rarely exceeds 12 inches in length. It is native to North America, Mexico and Central America, and it is NOT venomous.
The electromagnetic frequency of a wave is defined as how many times the peak of this oscillation moves past a point each second. This has a major effect on the properties of the wave, including its energy.
The Critical Frequency, the highest frequency at which NVIS propagation can be used, is depicted as the foF2 frequency on the chart at the left of the graph and as the upper frequency limit of the first echo sounding curve.