A high-latitude investigation of the natural very-low-frequency electromagnetic radiation known as chorus

Data from several Alaskan stations observing the natural VLF electromagnetic radiation known as chorus permit a number of statistical investigations, especially of latitudinal variations of the phenomenon. Maximum occurrence lies at 60° to 70° geomagnetic latitude. Seasonal variations at individual stations depend intricately on latitude. Below, but not above, the auroral zone the diurnal maximum depends on an ‘eccentric geomagnetic latitude.’ Chorus correlates with other phenomena, such as geomagnetic activity, the correlation varying seasonally and diurnally. Correlations between stations show a diurnal behavior consistent with the possibility of the existence of isochronic lines for chorus. Temporal variations in the highest frequency (kilocycles per second) of chorus for each sample show a diurnal minimum near noon and seasonal peaks near equinoxes; temporal variations in the rate of change of frequency of chorus show similar patterns.