The QBO modulation of the occurrence of the counter electrojet

Abstract

Continuous hourly measurements of horizontal component of geomagnetic field obtained at Trivandrum, India, have been used to study the occurrence of the Counter Electrojet (CEJ). Because the data cover nearly three solar activity cycles, they can be used to investigate long‐term variations of the CEJ. After the data have been processed and detrented to reduce the influence of solar cycles and annual variations, they reveal a quasi‐biennial oscillation (QBO) of the occurrence of the CEJ. When compared with the QBO wind phase in the stratosphere, the occurrence of the CEJ is found to increase in east phase and to decrease in west one. This relationship suggests a possible mechanism for the production of the CEJ. Under certain conditions the interaction between the upward propagating planetary waves and the solar or lunar semidiurnal tides may cause the semidiurnal tides to be increased in amplitude and shifted in phase, which ultimately results in the occurrence of the CEJ.