Landmark values of equational electrojet current and magnetic field along a meridian near noon.

Abstract

Landmark values of the equatorial electrojet: the minimum intensity Jm A.km-1, its distance xm km and ratio to maximum intensity Jm/Jo; the magnetic field constant K nT; the maximum northward magnetic field Xo nT, and the distance of zero northward magnetic field wx km; the minimum northward magnetic field Xm nT, its distance um km and ratio to maximum northward field Xm/Xo; the vertical magnetic field Zo nT at the dip equator and the distance of zero vertical field wz km; the maximum vertical magnetic field ZM nT, its distance uM km and ratio to maximum northward field Zm/Xo; have all been derived from September equinox satellite data and they compare favourably with their values from ground-based data. Our Jm/Jo agrees excellently with MUSMANN and SEILER (1978) and ANANDARAO and RAGHAVARAO (1979); while our xm agrees excellently with the location of CAHILL's (1959) westward current, and the findings of MUSMANN and SEILER (1978). The landmark distances xm, wx, um, uM, wz and the ratios Jm/Jo, Xm/Xo and ZM/ Xo do not vary with longitude but the intensity Jm and magnetic fields, K, Xo, Xm, Zo and

Characteristics of the Equatorial Electrojet determined from an array of magnetometers in N-NE Brazil

“…A negative α causes the current to reverse sign at a certain distance x. The minimum in H as observed at our station NAT is thus expected and it seems appropriate to assume that for the EEJ currents the ratio of the peak westward current at the flanks to the peak eastward current (at the center) is approximately 0.3 as suggested by several previous studies (Musmann and Seiler, 1978;Anandarao and Raghavarao, 1979;Onwumechili et al, 1989). To incorporate this ratio in the model, the parameter α was allowed to vary only slightly around −1.8 in the inversion process.…”

“…Insufficient data at the tails of the EEJ and its transition to the Sq was overcome by making the assumption that the westward current at the flanks of the EEJ is 30% of the central eastward current. While there is some support for this assumption (Musmann and Seiler, 1978;Anandarao and Raghavarao, 1979;Onwumechili et al, 1989) it is not necessarily universally accepted . However, when used as a priori information in a combined Sq and EEJ inversion it constrains the amplitude of the Sq and allowes for its extrapolation to the equatorial region.…”

“…Parameter (b) was set to zero, as if the current was concentrated in an infinitely thin layer. EEJ results have also been computed for b = 9.47 km (Onwumechili et al, 1989). In Eqs.…”

“…Although the minimum in the EEJ's H is based on a single station (NAT40), such a minimum has been observed elsewhere (see references quoted earlier). The minimum in H as observed at station NAT40 is thus expected and it seems appropriate to assume for the EEJ currents that the ratio of the peak westward current (at the flanks) to the peak eastward current (at the centre) is around 30% (Musmann and Seiler, 1978;Anandarao and Raghavarao, 1979;Onwumechili et al, 1989). In order to incorporate this ratio for the EEJ in the modelling, the peak amplitude H of the Sq was constrained to a certain equatorial amplitude that determines the adequate zero level (background) for the EEJ's H .…”

“…In the quiet days of 7 and 11 December 1990 the station NAT40 is not available because its recording started only on 12 December 1990. Table 3 summarises the morphology of the electrojet, in terms of the model parameters using Onwumechili's notation (Onwumechili et al, 1989).…”