The electrical conductivity
The interaction of the terminal ions with aerosol particles is probably a significant sink for Ions in the polar aerosol layers near the summer mesopause where noctiluccnt clouds are commonly observed. The electrical conductivity of the mesosphere is important because it governs the clcctrical properties of the equalization layer in the global circuit. Below about 60 km. the Juicy Couture Sale terminal small ions are the main charge carriers; but above 60 km, free electrons can exist and their high mobility is responsible for the abrupt increase in electrical conductivity observed in the mesosphere. Furthermore, above 70 km. collisions be-tween electrons and air molecules become infrequent enough so that electrons arc con-fined to spiral about a magnetic field line and the motion perpendicular to the field becomes more difficult than motion along the field. The electrical conductivity be-comes anisotropic, and this anisotropy has a dominant Juicy Couture Outlet influence on the electrical prop-erties of the global circuit above 70 km. Rocket l>orne measurements of the upper atmosphere conductivity and electric field indicate some Juicy Couture Outlet Online puzzling features. There appear to be regions in the upper stratosphere and mesosphere that have abrupt increases and decreases in vertical conductivity pro-files. The decreases arc probably associated with aerosol layers, but the increases are difficult to interpret. On occasion, the electric field near 50- to 70-km altitude has been observed to increase enormously from what Ls exported if the mesosphere is a passive element in the global circuit. The mesosphere may not be electrically passive but may. in fact, contain active electrical generators that are not currently known. The major sources of ionization above about 85 km are extreme-ultraviolet (EUV) radiation and auroral particle precipitation (see Chapter 14). The ionizing portion of the solar spectrum (i.e., wavelengths below 102.7 nin) is absorbed in the thermosphere and creates an ionosphere that consists of positive molecular and atomic ions (e.g., N J, NO *, O j. O') and negative electrons. The solar EUV radiation and the electron and ion densities throughout the ionosphere are highly dependent on solar activity; there are known variations with the 11-yr sunspot cycle, the 27-day rotation of the Sun, and solar flares.