Modelling the Ionospheric Signatures of Geomagnetic Pulsations.

Sutcliffe, P.

doi:10.5636/jgg.46.1011

Cited by 9 publications

(20 citation statements)

References 24 publications

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“…At Fregion heights the phase of these terms respectively lag and lead the b y component on the ground. Wright et al (1997) have suggested that signatures exhibiting relative phases Du YO in the range 90°±120°(b y leading) were a result of the advection mechanism as proposed by Poole et al (1988) and, later, Sutclie and Poole (1989 and Sutclie (1994). The event presented here has a Du YO of~160°with b y leading which implies that it would also be primarily the result of the advection mechanism.…”

Section: Comparison Of the Data With Modelling Workmentioning

confidence: 65%

“…Poole et al, 1988) which makes it a very good diagnostic for observing the modes of ULF waves. The models of Sutclie and Poole (1989) and Sutclie (1994) demonstrate that although the velocity observed by a HF Doppler sounder varies with altitude, the greatest change occurring over a very narrow altitude range corresponding to the region of peak F-region electron density. However, at these altitudes, the relative phases of the contributions from the various mechanisms are almost height independent although the absolute values are sensitive to pulsation frequency and scale size (see also Wright et al, 1997).…”

Section: Comparison Of the Data With Modelling Workmentioning

confidence: 99%

“…The phase of the mechanisms relative to the magnetic signature on the ground is a critical part of the model (Poole et al, 1988;Sutclie andPoole, 1989, 1990;Sutclie, 1994). The largest contributions to the Doppler velocity are due to the advection and compression terms.…”

Section: Comparison Of the Data With Modelling Workmentioning

confidence: 99%

“…The presence of compressional mode waves in the ionosphere, and also the conversion of the incident AlfveÂ n wave into an evanescent fast mode wave (which is subsequently detected at the ground) in the ionospheric E-region results in compression of the magnetic ®eld, leading to changes in the local plasma density and, hence, the refractive index. This is the``compression'' term, in the nomenclature of Poole et al (1988) and Sutclie andPoole (1989, 1990).…”

Section: Comparison Of the Data With Modelling Workmentioning

confidence: 99%

“…2.1). Models of the mechanisms involved in generating the ionospheric signatures observed by HF Doppler sounders have been described by Poole et al (1988), Sutclie andPoole (1989, 1990) and Sutclie (1994).…”

Section: Introductionmentioning

confidence: 99%

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A comparison of EISCAT and HF Doppler observations of a ULF wave

Wright¹,

Yeoman²,

Davies³

1998

Ann Geophysicae

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Abstract. Since the middle of 1995, an HF Doppler sounder has been running almost continuously in northern Norway, with the receiver at Ramfjordmoen and the transmitter at Seljelvnes. Concurrent operation of the EISCAT UHF radar in common programme (CP-1) mode has made it possible to study the ionospheric signature of a magnetospheric ULF wave. These are the ®rst results of such wave signatures observed simultaneously in both instruments. It has been demonstrated that the observed Doppler signature was mainly due to the vertical bulk motion of the ionosphere caused by the electric ®eld perturbation of the ULF wave and the ®rst direct observational con®rmation of a numerical simulation has been achieved. The wave, which was AlfveÂ nic in nature, was detected by the instruments 8°equatorward of the broad resonance region. The implications for the deduced wave modes in the ionosphere and the mechanism producing the HF Doppler variations are discussed.

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Section: Comparison Of the Data With Modelling Workmentioning

confidence: 65%

Section: Comparison Of the Data With Modelling Workmentioning

confidence: 99%

Section: Comparison Of the Data With Modelling Workmentioning

confidence: 99%

Section: Comparison Of the Data With Modelling Workmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

A comparison of EISCAT and HF Doppler observations of a ULF wave

Wright¹,

Yeoman²,

Davies³

1998

Ann Geophysicae

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The role of the Hermanus Magnetic Observatory in geomagnetic field research

Sutcliffe¹

1995

Astrophys Space Sci

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A b s t r a c t . Geomagnetic field research carried out at the Hermanus Magnetic Observatory over the past decade is reviewed. An important aspect of this research has been the study of geomagnetic field variations, with particular emphasis on ULF geomagnetic pulsations. Features of geomagnetic pulsations which are unique to low latitude locations have been investigated, such as the cavity mode nature of low latitude Pi 2 pulsations and the role played by ionospheric O + ions in the field line resonances responsible for Pc 3 pulsations. A theoretical model has been developed which is able to account for the observed relationships between geomagnetic pulsations and oscillations in the frequency of HF radio waves traversing ionospheric paths. Other facets of the research have been geomagnetic field modelling, aimed at improving the accuracy and resolution of regional geomagnetic field models, and the development of improved geomagnetic activity indices.K e y words: Geophysics, geomagnetic field. IntroductionThe Hermanus Magnetic Observatory (HMO) had its origin during the Second Polar Year 1932-1933, an international cooperative project conceived to gain a better understanding of the Earth and its environment. Thus the HMO began its existence due to man's quest for scientific knowledge and understanding. Over the years, however, the prime objectives and culture of the HMO have changed. Particularly significant changes occurred after 1986 when the CSIR, of which the HMO forms part, was reformed to become a more market oriented organisation with the prime objective that research results should be implemented for the benefit of South African industry and society.Over most of the past decade the HMO has functioned primarily as a service providing and technology development body. The service provision aspect entails the provision of information and data on the geomagnetic field to clients mainly for use in the fields of navigation and geophysical exploration. Notwithstanding these changes, the HMO still finds it essential to carry out fundamental and applied research, albeit at a reduced level compared to earlier years.In this paper research carried out at the HMO since 1986 is reviewed. The work falls into three main categories, namely, the study of geomagnetic variations of various types, geomagnetic field modelling, and geomagnetic activity indices. Geomagnetic Field VariationsA variety of temporal variations, spanning periodicities from fractions of a second up to millions of years, take place in the Earth's magnetic field. Studies at the

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High-latitude HF Doppler observations of ULF waves. 1. Waves with large spatial scale sizes

1997

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Abstract. A quantitative study of observations of the ionospheric signatures of magnetospheric ultra low frequency (ULF) waves by a high-latitude (geographic: 69.6°N 19.2°E) high-frequency Doppler sounder has been undertaken. The signatures, which are clearly correlated with pulsations in ground magnetometer data, exhibit periods in the range 100±400 s and have azimuthal wave numbers in the range 3±8. They are interpreted here as local ®eld line resonances. Phase information provided by O-and X-mode Doppler data support the view that these are associated with ®eld line resonances having large azimuthal scale sizes. The relative phases and amplitudes of the signatures in the Doppler and ground magnetometer data are compared with a model for the generation of Doppler signatures from incident ULF waves. The outcome suggests that the dominant mechanism involved in producing the Doppler signature is the vertical component of an E´B bulk motion of the local plasma caused by the electric ®eld perturbation of the ULF wave.

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Modelling the Ionospheric Signatures of Geomagnetic Pulsations.

Cited by 9 publications

References 24 publications

A comparison of EISCAT and HF Doppler observations of a ULF wave

A comparison of EISCAT and HF Doppler observations of a ULF wave

The role of the Hermanus Magnetic Observatory in geomagnetic field research

High-latitude HF Doppler observations of ULF waves. 1. Waves with large spatial scale sizes

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