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

Abstract

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).

Effect of Disturbance Electric Fields on Equatorial Electrojet Over Indian Longitudes

“…We find that although PP signature remained the same throughout, Ddyn signature showed a longitude dependence for all the three storms. This spectral technique is also suggested by Amory- Mazaudier et al (2017).…”

“…In the late recovery phase, auroral indices were quiet (24 and 25 March 2015) in the first 12 hr and there were no fluctuation in E y component. This demonstrates that at this stage the Ddyn process becomes the dominant mechanism that restructures the ionospheric parameters (Amory‐Mazaudier et al, ). Similar observations of Ddyn were reported in the late recovery phase of the storm (Fathy et al, ).…”

The Response of African Equatorial/Low‐Latitude Ionosphere to 2015 St. Patrick's Day Geomagnetic Storm

“…This reversed electrojet (Mayaud, ) sometimes occurs during cases of rapid decrease in magnetospheric penetrating electric field during sudden northward turning (Kikuchi et al, ). Amory‐Mazaudier et al () have, however, warned that such reversed electrojet are related to Ddyn and should not be confused with quiet time CEJ.…”

“…DP2 and Ddyn signals can be extracted from Diono using appropriate filters and taken into consideration the characteristics of each signals. It has been shown that short‐term oscillations of about 3‐hr periods are characteristics of the DP2, while diurnal oscillations producing a reversal in the daily variation of the Earth's magnetic field are associated to Ddyn (Amory‐Mazaudier et al, ; Nava et al, ). Nava et al () further used a high‐pass filter to extract periods lower than 4 h from Diono and a band‐pass filter to separate diurnal periods corresponding to Ddyn.…”

Critical Evaluation of the Impact of Disturbance Dynamo on Equatorial Ionosphere During Daytime

“…The equatorward vortex resembles an anti‐Sq current system (Le Huy & Amory‐Mazaudier, ; Zaka et al, ), flowing essentially opposite to the quiet day currents and, therefore, driving westward electric field perturbations during daytime. The DD causes global scale magnetic disturbances (Fambitakoye et al, ) which have been characterized by latitudinal profile of D dyn (Amory‐Mazaudier et al, ; Le Huy & Amory‐Mazaudier, ) that is defined as follows, wherein Δ H , S R , and SYMH are overall fluctuations in the horizontal geomagnetic field above various components of Earth's internal magnetic field magnetic field, magnetic field fluctuations due to quiet time ionospheric dynamo, and magnetic field induced by the ring current (and corrected for magnetic latitude), respectively. In this mathematical relationship, the contributions from the other ionospheric (DP2) and magnetospheric currents (e.g., Chapman‐Ferraro and Tail currents) are assumed to be negligible during the recovery phase of the storm.…”