Diurnal double maxima patterns in the F region ionosphere: Substorm‐related aspects

Abstract

Daytime double maxima (twin peaks or bite-outs) in the ionospheric total electron content (TEC) at middle and lower latitudes are found to be related to substorm signatures shown in both auroral electrojet and ring current variations. Case studies reveal that during substorm onset and recovery phases, the penetration of magnetospheric convection electric fields and their subsequent "overshielding" effects may be the major dynamical sources of these events. A theoretical lowlatitude ionospheric model is used to simulate the dynamical effects of electric field disturbances on F region electron density and TEC. It is demonstrated that the diurnal double maxima in TEC can be created by a combined effect of E x B drift and altitude-dependent F region chemical loss. The required zonal electric fields are found to have greater penetration efficiency in the early evening sector and their latitudinal requirements appear to change with local time. The time scales for the modeled penetration and overshielding effects are 2-3 hours. Modeling results also show that considerable structuring in the local time variation of the ionospheric "equatorial anomaly" can occur due to the interplay of convection electric field penetration and overshielding effects. The possible cause of the midday bite-out ionospheric disturbances by the meridional winds associated with traveling atmospheric disturbances (TADs) is also addressed in modeling studies, but the specialized nature of the required TADs makes this a less well understood substorm-related mechanism.1. Sources of Ionospheric DisturbanceAt middle latitudes, the ionospheric total electron content has been shown to exhibit a major response to geomagnetic storms and substorms [e.g., Mendillo, 1971; Lanzerotti et al., 1975; Mendillo and Klobuchar, 1975; Essex et al., 1981; Titheridge and Buonsanto, 1988; PrSlss et al., 1991; Huang and Gheng, 1991]. This response is believed to be mainly due to a combined effect of dynamical and chemical processes. Thermospheric circulation variations due to Joule heating and energetic particle precipitations in the auroral zone [Rishbeth, 1975; Volland, 1979; Fuller-Rowell and Rees, 1981; Robie et al., 1982, 1987], and electric field perturbations caused by penetration processes [e.g., Vasyliunas, 1972; Jaggi and Wolf, 1973; Testud et al., 1975; Nopper and C'arovillano, 1978; Kamide and Matsushita, 1981; Senior and Blanc, 1984; Earle and Kelley, 1987; Spiro et al., 1988; Fejer et al., 1990a, 1990b] as well as disturbance dynamo processes [Blanc and Richmond, 1980; Fejer et al., 1983], are thought to be major sources of the dynamical disturbances in the middle-and lower-latitude ionosphere. During substorms, traveling atmospheric disturbances (TADs), also triggered by high-latitude Joule heating and particle precipitations, can cause traveling ionospheric disturbances (TIDs) on a global scale [e.g., Yeh and Liu, 1974; Testud et al.Paper number 93JA00502. 0148-0227193193JA-00502$05.00 et al., 1991]. As F region charged particles move upward or downward, ...

Pre-storm electron density enhancements at middle latitudes

“…The observations also indicate that the hmF2 rise or drop is positively correlated with NmF2 variation during daytime. Such a correlation, however, does not apply at post-midnight times (Pi et al, 1993(Pi et al, , 1995. In the absence of production, chemical loss mechanisms dominate in the determination of NmF2 values, particularly at times close to the dawn.…”

An upgrade of the solar-wind-driven empirical model for the middle latitude ionospheric storm-time response

“…Mikhailov et al, 1995;FullerRowell et al, 1996;Field et al, 1998) and electric fields (e.g. Jakowski et al, 1992;Pi et al, 1993). The significance of electric fields for generating storm effects at middle latitudes and also their origin are still hotly debated topics in the literature (Prö lss, 2005).…”

Harmonic analysis of total electron contents time series: methodology and results

“…The evening anomaly explains that midlatitude summer NmF2 attains its highest values several hours beyond midday (Papagiannis and Mullaney 1971). This is in connection with the daytime double maxima (Pi et al 1993), which explains that twin peaks in the ionospheric TEC at middle and lower latitudes are due to substorm signatures in both auroral electrojet and ring current variations. There exists another double maxima phenomenon on the latitude profile near the maximum ionospheric effect (latitude profile at zero longitude in the sun-fixed frame) that is due to equatorial anomaly (Anderson 1973;Oliveira and Walter 2005).…”