The effect of polar magnetic sub-storms on the equatorial sporadic E

It is known that equatorial sporadic E disappears at night when dynamo field is east to west. During some DP₂ type magnetic sub-storms, which cause a depression of the geomagnetic horizontal field at the equator, theq type of sporadic E is found to disappear at the equatorial stations Huancayo and Kodaikanal. This suggests that one of the mechanisms causing the temporary disappearance of E _s —q during daytime in equatorial ionograms is the replacement of the east to west dynamo electric field by a west to east electric field due to the imposition of an electric field opposing the normal daytime S _q field.