Dependence of the Lunar Modulation of Geomagnetic Activity on the Celestial Latitude of the Moon

Evidence is presented indicating that two factors play a part in the lunar modulation of geomagnetic activity: (1) Phase of the moon: the average level of geomagnetic activity is diminished for several days before full moon and enhanced for several days after full moon. (2) Celestial latitude of the moon: activity is diminished when the moon is more than 4° from the plane of the ecliptic and enhanced when the moon is closer to the plane. Approximately from first quarter to last quarter, when these two factors work together the greatest amplitude of modulation occurs; when they work against each other no significant modulation of geomagnetic activity is detected. There is no evidence of any significant lunar influence on geomagnetic activity over the new-moon half of the orbit. These results are discussed in terms of recent observations of the earth's magnetic tail.