Vertical winds as a plausible cause for equatorial counter electrojet

Abstract

The signatures of the counter‐electrojet that occurs in the afternoon hours as recorded on the ground and satellite‐borne magnetometers during the magnetically quiet days, clearly indicate reversal of the jet current in a narrow latitude region centered around the dip equator. The latitudinal variation of the vertical (Z) and northward (H) components of the earth's magnetic field reveal that the decrease and reversal of the eastward toroidal current of the jet is maximum around the dip equator. By numerically solving the equations governing the electrojet including the terms due to local winds it is shown that vertically upward winds of 15 ‐ 20 m/s are most effective in producing the counter‐electrojet. The profile of vertical winds adopted in the model calculations was actually measured during twilight hours. It is shown that the latitudinal variations of H and Z observed during the counter‐electrojet can be reproduced satisfactorily by the vertical wind hypothesis. A rocket experiment is suggested to verify the presence of vertical winds during the counter‐electrojet.

Longitudinal Difference in Magnetic Field Variations Associated with Quiet Day Counter Electrojet.

“…According to MAYAUD (1977) it would not seem that the CEJ could occur in a very narrow longitude band of less than 30 to 45°. Evidently, apart from the lunar control, other parameters like local vertical winds (RAGHAVA RAO and ANAND RAO, 1980), internal gravity waves (RAGHAVARAO,1976)ortidalwinds(HANUISEetal.,1983couldplaysignificantroles.KANEandTRIVEDI (1981) gave instances of confinement of the CEJ to less than 30° in longitudinal extent from a comparison of H variations at two nearby locations in the South American Sector. Abnormal neutral wind shears in the dip equatorial region were suggested as a possible mechanism by them.…”

Sq and EEJ—A Review on the Daily Variation of the Geomagnetic Field Caused by Ionospheric Dynamo Currents

“…Modeling studies have shown that a particular combination of tidal modes can result in a counter electrojet (Forbes and Lindzen 1976b;Takeda and Maeda 1981;Hanuise et al 1983). The study performed by Raghavarao and Anandarao (1980) showed that an upward wind with a sufficiently large magnitude (15-20 m/s) can also cause a counter electrojet. Observational studies have found that the occurrence of CEJ is dependent on the phase of the moon, suggesting that lunar tides play a role (Bartels and Johnston 1940;Rastogi 1974;Sastri and Arora 1981).…”

Equatorial counter electrojets and polar stratospheric sudden warmings – a classical example of high latitude-low latitude coupling?

“…Though many theories have been proposed for the reversal of the EEJ currents, the exact causative mechanism still remains unexplainable. The local effect within the EEJ region such as gravity wave associated vertical winds (Raghavarao and Anandarao, 1980;Aanadarao and Raghavarao, 1987) and the changes in the tidal components (Somayajulu et al, 1993) are some of the earlier suggestions for CEJs. On the other hand, contributions of the global wind and current systems to the occurrence of CEJs have also been brought out (Stening et al, 1996;Gurubaran et al, 2002).…”