Ionization in the Upper Atmosphere Variation with Longitude

Continuing a former paper (Phys. Rev. 34 1167 1929 ) the present paper gives theoretical calculations of the changes in the ionization in the upper atmosphere with longitude. The electrical conductivity of the upper atmosphere is about 1.4 × ${10}^{-5\mathrm{}}$ at noon equinox at the equator and an order of magnitude less at night. The maximum density of electrons $y_m$ varies with the latitude $\theta$ and longitude $\psi$, measured from noon equinox at the equator according to $y_m=3.14\mathrm{}\times {10}^{5}cos \theta (0.18\mathrm{} sin \psi +cos \psi )$ for the daylight hours. At night the expression is more complex. The values of $y_m$ yield skip distances of short wireless waves roughly in accord with observation in the day but somewhat too great at night. The theory puts the shortest skip distance at 40 minutes past noon and observation in temperate zones gives 2 p.m.; the agreement is good, but not perfect.