Conjugate occurrence of the electric field fluctuations in the nighttime midlatitude ionosphere

Abstract

The DE 2 satellite observed electric field fluctuations on the topside of the nighttime midlatitude ionosphere. They extended several hundred kilometers in the latitudinal direction with wavelengths of several tens of kilometers, and their amplitudes were a few millivolts per meter. Such fluctuations were often observed at magnetically conjugate points in the northern and southern hemispheres. These electric field fluctuations are perpendicular to the geomagnetic field. They are not accompanied by any significant plasma depletion or electron temperature v•riations. Magnetic field fluctuations are sometimes observed simultaneously with electric field fluctuations. We interpret that these fluctuations are caused by fieldaligned currents which flow from the ionosphere in one hemisphere to the conjugate point in the other hemisphere. The power spectrum of these midlatitude electric field fluctuations follows a power law of the form Power c• f-•, with the spectral index n of 3.5 to 4.5, which is steeper than that of the electric field fluctuations in the high-latitude ionosphere or in the equatorial ionosphere. This phenomenon may be related to other ionospheric phenomena, for example, the F region field-aligned irregularities or spre•d-F, observed by ground-b•sed methods such •s the MU r•d•r, but the relationship is not clear. (MEFs), which often appear simultaneously at magnetically conjugate points, and discuss the relation between these electric field fluctuations and the F region FAIs. In situ observations of the midlatitude ionospheric electric field by satellites play an important role in understanding the mechanism of the ionospheric irregularities which have been observed by ground-based techniques. Observation The DE 2 satellite flew in polar orbit at about 250-km to 900-km altitudes. It observed the ionospheric electric field at midlatitudes from August 1981 to February 21,439 21,440 SAITO ET AL.' MIDLATITUDE ELECTRIC FIELD FLUCTUATIONS a sampling rate of two samples per second [Krehbiel et al., 1981]. Vector magnetic field data were obtained by dinate (SPC) system, where the x axis is in the direction of the satellite velocity and the y axis is downward, with the z axis completing a right-handed coordinate system.

Global characteristics of Pc1 magnetic pulsations during solar cycle 23 deduced from CHAMP data

“…This difference may be due to the fact that Erlandson and Anderson (1996) used E-field measurements for the Pc1 event detection, while we use B-field fluctuations. Moreover, the local time variation of the DE-2 orbit was locked with the seasonal variation (Saito et al, 1995), which may further contribute to the slight disagreement between our Fig. 4 and Erlandson and Anderson (1996).…”

“…One may argue that these two conditions lead to lower Alfvén velocity, which can be expressed by the ratio of E-field over B-field fluctuations (e.g. Saito et al, 1995). However, this interpretation should lead to a larger number of Pc1 events in the SAA than in the northern conjugate region: B-field is weaker (due to the SAA) and plasma density in local summer is higher (Lee et al, 2011, Fig.…”

“…First, the local time (LT) of Magsat or ST-5 was fixed (dawn/dusk), and in the case of DE-2 the LT cannot be decoupled from seasonal variations (e.g. Saito et al, 1995). Second, none of the previous Pc1 observations by LEO satellites spanned a full solar cycle.…”

Imaging science at El Leoncito, Argentina

“…The single-band structure with its movement towards the northwest in the Southern Hemisphere (as shown in Otsuka et al, 2004 andShiokawa et al, 2005) make it distinct from the ESF and BW patterns seen frequently on other nights. The only global study of MLI occurrence patterns was conducted by Saito et al (1995) using the electric field and plasma density instruments on the Dynamics Explorer (DE) spacecraft. In the American longitude sector, they showed that Arecibo's location was close to the peak occurrence zone in their statistical summary, while that zone in the Southern Hemisphere was somewhat poleward of El Leoncito's location.…”

Magnetic Signatures of Ionospheric and Magnetospheric Current Systems During Geomagnetic Quiet Conditions—An Overview

“…MSTIDs are regionally confined nighttime dynamic plasma density irregularities in the ionospheric E -and F -layers associated with electric field fluctuations that map to both conjugate hemispheres and thus produce significant IHFACs (Shiokawa et al 2003). They have first been found by Saito et al (1995) in electric measurements taken by the DE-2 satellite, and by Park et al (2009) in magnetic field observations taken by the CHAMP satellite. Using data from the Swarm constellation, confirmed that their spatial structure is similar to those of the associated plasma density fluctuations.…”