On the historical origins of the CEJ, DP2, and Ddyn current systems and their roles in the predictions of ionospheric responses to geomagnetic storms at equatorial latitudes

In this short letter, we recall the differences between the counter electrojet (CEJ), which is a phenomenon observed on the magnetically quiet days and the disturbance dynamo (Ddyn), which can be observed during and after a geomagnetic storm. The CEJ is well known to occur near the geomagnetic dip equator. It can be identified by a reversal in the horizontal component (H) of the geomagnetic field daily regular variations. In contrast to equatorial electrojet (EEJ) that flows eastward in the daytime, the CEJ is considered to flow westward. The magnetic signatures of the reversed solar quiet (Sq) current at the low latitude during magnetic storms are due to the Ddyn. This disturbance (Ddyn) is produced by current systems that are driven by thermospheric storm winds originating from the Joule heating of enhanced high‐latitude currents. The DP2 is the magnetic effect of current systems at high latitudes. These currents are associated with the coupling of magnetosphere and ionosphere through geomagnetic field lines. They are associated to the magnetospheric convection. During intense magnetic storms these high‐latitude currents are enhanced and their magnetic effects can extend toward the low latitudes. This work shows that the study of magnetic perturbations makes it possible to understand the disturbances of the ionospheric electric currents. The use of an efficient treatment of the magnetic signals makes it possible to separate the magnetic effects of the different perturbations prompt penetration of the magnetospheric convection electric field and disturbance dynamo electric field. This was performed in the paper Nava et al. (2016). A similar variation of the Earth's magnetic field can result from different physical mechanisms. In this paper we want to underline the fact that a negative variation of the Hcomponent of the geomagnetic field at the equator is not necessary, a counter electrojet as defined by Gouin (1962). Another mechanism is that the disturbance dynamo can also produce a negative variation of the Hcomponent of the Earth's magnetic field at the magnetic equator. It is also important to understand that the magnetic variations can be used to know the physical processes acting in the Sun‐Earth system. Now the model as thermosphere‐ionosphere‐electrodynamics general circulation model can reproduce magnetic variations so it is important to work with the magnetic data to improve the models. The counter electrojet is a magnetic quiet day phenomenonThe disturbance dynamo is a disturbed day magnetic phenomenonThe counter electrojet and the disturbance dynamo exhibit the same magnetic signature, but there are different physical processes