Seasonal features that are not related in a simple way to solar declination occur in the daily variation of the horizontal intensity of the earth's magnetic field at Tucson, as at Honolulu studied previously. They are studied here in quiet-day data averaged over 11 years. The nature of these features suggests that they may arise from the seasonal variation of the large-scale air circulation in the lower ionosphere, and that they may offer the possibility of utilizing regular geomagnetic observations in meteorological research
