Ionospheric Winds and Viscous Dissipation

Analysis of frequency distribution of vertical shear of horizontal winds is reported for 2000 samples obtained between 90 and 136 km. The distribution is independent of altitude when shears are normalized by dividing by limiting shears of .075 sec−1 below 110 km, decreasing to .035 sec−1 at 128 km. Associated vertical wavelengths are also altitude independent when normalized, with shortest wavelengths increasing from 3 km at 90 km to 10 km at 136 km. The Richardson number, as a criterion of turbulence, shows that 7% of space/time samples below 110 km will permit turbulence to initiate, while no samples above 115 km will permit onset of turbulence. Viscosities (computed by Hines equation relating viscosity and limiting wavelength) are 30‐fold greater than molecular at 90 km, approaching molecular above 115 km. The rate of deposition through viscous shear is 2000–4000 erg g−1 sec−1, but 10% of the samples have a five‐fold higher rate, which will significantly affect temperature profiles. The shears found are capable of increasing molecular ion and electron density to about 4×103 cm−3 from background ionization levels below 103 cm−3, and to 2×104 cm−3 from backgrounds of 104 cm−3. They cannot significantly enhance 105 cm−3 backgrounds.