Electric currents induced in the ionosphere generate magnetic fields (ionospheric dynamo region). Effects on Schumann resonances have been reported following geomagnetic and ionospheric disturbances. Neglecting ionospheric and tropospheric effects, the signal from navigation satellites has a fixed precision. Ground waves "do not" include ionospheric and tropospheric waves. Arecibo also includes several NSF funded radars for ionospheric studies. The spacecraft broadcast ionospheric model parameters, but some errors remain. Stations closer to the magnetic equator are not used due to ionospheric effects. The strength of the signal received can vary with a sudden ionospheric disturbance. LORAN suffers from electronic effects of weather and the ionospheric effects of sunrise and sunset. These traits make precise measurement and compensation of humidity errors more difficult than ionospheric effects. AFGRL developed the Klobuchar model for computing ionospheric corrections to GPS location. Among the slow correction data is the ionospheric delay. All types of wire (line), satellite and ionospheric radio communication are employed. F10.7 and R12 are two indices commonly used in ionospheric modelling. Reflection occurs at the ionospheric E layer or F layers.