Equatorial E region electric fields at the dip equator: 1. Variabilities in eastern Brazil and Peru

Abstract

The equatorial electrojet (EEJ) is an intense eastward ionospheric electric current centered at about 105 km of altitude along the dip equator, set up by the global neutral wind dynamo that generates the eastward zonal (Ey) and the daytime vertical (Ez) electric fields. The temporal variation of the EEJ is believed to be well understood. However, the longitudinal variability of the Ey and Ez between 100 and 110 km is still quite scarce. Due to their importance overall phenomenology of the equatorial ionosphere, we investigate the variabilities of the Ey and Ez inferred from measurements of the Doppler frequency of Type II echoes provided by coherent backscatter radars installed in locations close to the magnetic equator in the eastern Brazil (2.33°S, 44.20°W) and Peru (11.95°S, 76.87°W). This study is based on long‐term (609 days for both systems) radar soundings collected from 2001 to 2010. The variabilities of the electric fields are studied in terms of the position of the soundings with respect to the dip equator and the magnetic declination angle. Among the results, Ey and Ez show longitudinal dependence, being higher in Peru than east Brazil. Under quiet geomagnetic activity, the mean diurnal variations of Ey ranged from 0.21 to 0.35 mV/m between 8 and 18 h (LT) in Brazil and from 0.23 mV/m to 0.45 mV/m in Peru, while the mean diurnal variations of the Ez ranges from 7.09 to 8.80 mV/m in Brazil and from 9.00 to 11.18 mV/m in Peru.

Equatorial E Region Electric Fields and Sporadic E Layer Responses to the Recovery Phase of the November 2004 Geomagnetic Storm

“…The ion motion, V i (essentially due to neutral wind), can be neglected while deriving V e from the observed Doppler velocity above 100 km (Devasia et al, ). Therefore, we neglected in this work the last term in equation in order to derive the E z component at 105.1 km by equation (Cohen, ; Denardini et al, ; Moro et al, ): where Θ is the zenith angle of the radar beam, B is the Earth's magnetic field flux density, and H is its horizontal component. Finally, the E y component is obtained by equation : where r is the position of the magnetic field line element considering dipole geometry, θ is the magnetic latitude, dθ is the differential magnetic latitude element vector, and the integrals are the well‐known field line‐integrated Pedersen and Hall conductivities, usually represented by Σ P and Σ H , respectively.…”

“…The equatorial electrojet (EEJ) consists of a small Pedersen current driven by the zonal ( E y ) electric field generated by tidal neutral winds and a large Hall current driven by the vertical ( E z ) polarization electric field. The E z component, in turn, is produced by an impeded Hall current driven by the primary E y (Denardini et al, ; Forbes, ; Moro et al, , and references therein). The E y component, eastward during the daytime, controls the vertical plasma transport in the low‐latitude ionosphere and forms a critical input to models that predict ionospheric disturbances in real time (Maruyama et al, ; Scherliess et al, ).…”

“…The E y and the E z components of the E region electric fields (EEFs) in Brazil have been studied in terms of the Doppler shifts of Type II echoes detected with the 50 MHz backscatter coherent (RESCO) radar installed at São Luís (SLZ, 2.3°S, 44.2°W, ~−7° dip angle). Moro et al () investigated the variability of the EEF components based on long‐term RESCO soundings collected during the geomagnetic quiet days ( Kp ≤ 3 + ) between 2001 and 2010 and compared the results with the electric field components inferred at the Jicamarca Radio Observatory (JRO, 11.9°S, 76.8°W, ~2° dip angle). The mean diurnal variations of E y range from 0.21 to 0.35 mV/m between 8 and 18 h (LT) in the Brazilian sector, while the mean diurnal variations of the E z range from 7.09 to 8.80 mV/m.…”

“…The mean diurnal variations of E y range from 0.21 to 0.35 mV/m between 8 and 18 h (LT) in the Brazilian sector, while the mean diurnal variations of the E z range from 7.09 to 8.80 mV/m. However, the electric field components presented an interesting dependence with the dip equator secular displacement effect at SLZ (see Figure 1 in Moro et al, 2016a), which causes different variations in E y and E z at JRO. This result led to a study on the seasonal dependence of E y and E z by Moro et al (2016b), which revealed for the first time the impact of the secular variation of the geomagnetic field on the EEJ in terms of electric fields.…”

On the Sources of the Ionospheric Variability in the South American Magnetic Anomaly During Solar Minimum

“…Therefore, there exists a gap in proper understanding the ionospheric variability in South America, especially in the Brazilian sector where there are some unique geophysical characteristics. One of them is the high magnetic declination angle that reaches approximately −20° in the equatorial region due to the dip equator secular displacement effect causing considerable changes in the Equatorial Electrojet and consequently in sporadic E (Es) layers (Denardini et al, ; Moro et al, , ; Moro et al, ; Resende et al, ). There is also a more pronounced energetic particle precipitation in the SAMA region (Moro et al, , ) when compared with other regions having the same latitudinal range, due to the global minimum in the intensity of the geomagnetic field.…”