Local time distribution of HF Doppler frequency deviations associated with storm sudden commencements

Kikuchi, Takashi; Ishimine, T.; Sugiuchi, H.

doi:10.1029/ja090ia05p04389

Cited by 38 publications

(60 citation statements)

References 13 publications

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“…That is con®rmed by the test calculation by making all conductivity equal from 30°l atitude to the equator. The pro®le of the east-west component of electric ®eld (E u ) at 30°is consistent with the local time pro®le of the polarity of MFD of SCF in the observations of HF Doppler frequencies associated SC as shown by Kikuchi et al (1985).…”

Section: Comparison Of Dierent Models Of S Humentioning

confidence: 54%

Numerical analysis of global ionospheric current system including the effect of equatorial enhancement

Tsunomura¹

1999

Ann Geophysicae

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Abstract. A modeling method is proposed to derive a two-dimensional ionospheric layer conductivity, which is appropriate to obtain a realistic solution of the polar-originating ionospheric current system including equatorial enhancement. The model can be obtained by modifying the conventional, thin shell conductivity model. It is shown that the modi®cation for one of the non-diagonal terms (S hu ) in the conductivity tensor near the equatorial region is very important; the term in¯uences the pro®le of the ionospheric electric ®eld around the equator drastically. The proposed model can reproduce well the results representing the observed electric and magnetic ®eld signatures of geomagnetic sudden commencement. The new model is applied to two factors concerning polar-originating ionospheric current systems. First, the latitudinal pro®le of the DP2 amplitude in the daytime is examined, changing the canceling rate for the dawnto-dusk electric ®eld by the region 2 ®eld-aligned current. It is shown that the equatorial enhancement would not appear when the ratio of the total amount of the region 2 ®eld-aligned current to that of region 1 exceeds 0.5. Second, the north-south asymmetry of the magnetic ®elds in the summer solstice condition of the ionospheric conductivity is examined by calculating the global ionospheric current system covering both hemispheres simultaneously. It is shown that the positive relationship between the magnitudes of high latitude magnetic ®elds and the conductivity is clearly seen if a voltage generator is given as the source, while the relationship is vague or even reversed for a current generator. The new model, based on the International Reference Ionosphere (IRI) model, can be applied to further investigations in the quantitative analysis of the magnetosphere-ionosphere coupling problems.

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Section: Comparison Of Dierent Models Of S Humentioning

confidence: 54%

Numerical analysis of global ionospheric current system including the effect of equatorial enhancement

Tsunomura¹

1999

Ann Geophysicae

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“…The electric field/current associated with the preliminary impulse penetrates to low latitudes and causes similar perturbations there [ Kikuchi and Araki , 1985; Kikuchi et al , 2001]. The short‐lived preliminary impulse is often detected with ground magnetometers, and the associated electric field perturbations are identified with HF Doppler observations [ Kikuchi et al , 1985; Sastri et al , 1993].…”

Section: Introductionmentioning

confidence: 99%

Low‐latitude ionospheric electric and magnetic field disturbances in response to solar wind pressure enhancements

et al. 2008

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[1] We study the characteristics of the low-latitude ionospheric electric field and geomagnetic field in response to a sudden enhancement of the solar wind pressure. When the magnetosphere is compressed by an interplanetary shock, a significant enhancement in the dayside equatorial ionospheric ion vertical velocity occurs over 30-40 min and is measured by the Jicamarca incoherent scatter radar. A similar enhancement occurs in the high-latitude ionospheric convection and is detected by the SuperDRAN HF radars. The simultaneous enhancements of the ionospheric ion velocity at high and low latitudes provide strong evidence of the occurrence of penetration electric fields produced by solar wind pressure enhancements. The geomagnetic field first increases rapidly over 2-3 min and then falls over 30-40 min to an asymptotic value. The enhanced magnetic field occurs from the subauroral region to the equator at all local times. The time scale of 30-40 min is much longer than the conventional preliminary and main impulses of geomagnetic response to interplanetary shocks. There are two possible mechanisms that may be responsible for the generation of the enhanced ionospheric electric and magnetic fields. One mechanism is that the solar wind shock causes an over-compression of the magnetosphere, and the other is that the field-aligned and ionospheric currents driven by the solar wind shock cause the enhancements of the ionospheric electric and magnetic fields. However, neither of the mechanisms appears to be able to provide a complete explanation of all observed features.Citation: Huang, C.-S., K. Yumoto, S. Abe, and G. Sofko (2008), Low-latitude ionospheric electric and magnetic field disturbances in response to solar wind pressure enhancements,

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“…From previous studies on the ionospheric plasma motion by using the HF Doppler measurement, the main frequency deviation following the preliminary one is negative in the daytime and evening sectors (06:00-21:00 MLT) and positive in the nighttime sector (21-06 MLT) (Kikuchi et al, 1985). The signature of the main frequency deviation indicates the penetration of the dawn-to-dusk convection electric field into the lowlatitude regions during the MI phase of SC.…”

Section: Confirmation Of Global Nature Of the Enhanced Convection Elementioning

confidence: 92%

Enhancements of magnetospheric convection electric field associated with sudden commencements in the inner magnetosphere and plasmasphere regions

Shinbori

Ono

Iizima

et al. 2006

Advances in Space Research

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Local time distribution of HF Doppler frequency deviations associated with storm sudden commencements

Cited by 38 publications

References 13 publications

Numerical analysis of global ionospheric current system including the effect of equatorial enhancement

Numerical analysis of global ionospheric current system including the effect of equatorial enhancement

Low‐latitude ionospheric electric and magnetic field disturbances in response to solar wind pressure enhancements

Enhancements of magnetospheric convection electric field associated with sudden commencements in the inner magnetosphere and plasmasphere regions

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