HF doppler sounder measurements of the ionospheric signatures of small scale ULF waves

Abstract. An HF Doppler sounder, DOPE (DOppler Pulsation Experiment) with three azimuthally-separated propagation paths is used to provide the first statistical examination of small scale-sized, high m waves where a direct measurement of the azimuthal wavenumber m, is made in the ionosphere. The study presents 27 events, predominantly in the post-noon sector. The majority of events are Pc4 waves with azimuthal m numbers ranging from –100 to –200, representing some of the smallest scale waves ever observed in the ionosphere. 4 Pc5 waves are observed in the post-noon sector. The fact that measurements for the wave azimuthal m number and the wave angular frequency are available allows the drift-bounce resonance condition to be used to hypothesise potential particle populations which could drive the waves through either a drift or drift-bounce resonance interaction mechanism. These results are compared with the statistical study presented by Baddeley et al. (2004) which investigated the statistical likelihood of such driving particle populations occurring in the magnetospheric ring current. The combination of these two studies indicates that any wave which requires a possible drift resonance interaction with particles of energies >60 keV, is statistically unlikely to be generated by such a mechanism. The evidence presented in this paper therefore suggests that in the pre-noon sector the drift-bounce resonance mechanism is statistically more likely implying an anti-symmetric standing wave structure while in the post-noon sector both a drift or drift-bounce resonance interaction is statistically possible, indicating both symmetric and anti-symmetric standing mode structures. A case study is also presented investigating simultaneous observations of a ULF wave in ground magnetometer and DOPE data. The event is in the lower m range of the statistical study and displays giant pulsation (Pg) characteristics. Keywords. Ionosphere (Ionosphere-magnetosphere interactions) – Magnetospheric physics (MHD waves and instabilities) – Space plasma physics (Wave-particle interactions)

Download Full-text

ULF waves with drift resonance and drift-bounce resonance energy sources as observed in artificially-induced HF radar backscatter

Annales Geophysicae ◽

10.5194/angeo-19-159-2001 ◽

2001 ◽

Vol 19 (2) ◽

pp. 159-170 ◽

Cited By ~ 30

Author(s):

T. K. Yeoman ◽

D. M. Wright

Keyword(s):

Large Scale ◽

Phase Evolution ◽

Hf Radar ◽

Mhd Waves ◽

Energy Sources ◽

Small Scale ◽

Particle Interactions ◽

Radar Backscatter ◽

Short Period ◽

Wave Particle Interactions

Abstract. HF radar backscatter which has been artificially-induced by a high power RF facility such as the EISCAT heater at Tromsø has been demonstrated to provide ionospheric electric field data of unprecedented temporal resolution and accuracy. Here such data are used to investigate ULF wave processes observed by the CUTLASS HF radars. Within a short period of time during a single four hour experiment three distinct wave types are observed with differing periods, and latitudinal and longitudinal phase evolution. Combining information from the three waves allows them to be divided into those with a large-scale nature, driven externally to the magnetosphere, and those with small azimuthal scale lengths, driven by wave-particle interactions. Furthermore, the nature of the wave-particle interactions for two distinct small-scale waves is revealed, with one wave interpreted as being driven by a drift resonance process and the other by a drift-bounce resonance interaction. Both of these mechanisms with m ≈ -35 and proton energies of 35–45 keV appear to be viable wave energy sources in the postnoon sector.Key words. Ionosphere (active experiments; wave-particle interactions) – Magnetospheric physics (MHD waves and in-stabilities).

Download Full-text

ULF wave occurrence statistics in a high-latitude HF Doppler sounder

Annales Geophysicae ◽

10.1007/s00585-999-0749-2 ◽

1999 ◽

Vol 17 (6) ◽

pp. 749-758 ◽

Cited By ~ 4

Author(s):

D. M. Wright ◽

T. K. Yeoman ◽

T. B. Jones

Keyword(s):

Solar Cycle ◽

Geomagnetic Activity ◽

High Latitude ◽

Statistical Study ◽

Low Frequency ◽

Occurrence Rate ◽

Mhd Waves ◽

Ulf Wave ◽

High Latitude Ionosphere ◽

Mhd Waves And Instabilities

Abstract. Ultra low frequency (ULF) wave activity in the high-latitude ionosphere has been observed by a high frequency (HF) Doppler sounder located at Tromsø, Norway (69.7°N, 19.2°E geographic coordinates). A statistical study of the occurrence of these waves has been undertaken from data collected between 1979 and 1984. The diurnal, seasonal, solar cycle and geomagnetic activity variations in occurrence have been investigated. The findings demonstrate that the ability of the sounder to detect ULF wave signatures maximises at the equinoxes and that there is a peak in occurrence in the morning sector. The occurrence rate is fairly insensitive to changes associated with the solar cycle but increases with the level of geomagnetic activity. As a result, it has been possible to characterise the way in which prevailing ionospheric and magnetospheric conditions affect such observations of ULF waves.Key words. Ionosphere (auroral ionosphere; ionosphere -magnetosphere interactions) · Magnetospheric physics (MHD waves and instabilities)

Download Full-text

Bistatic observations of large and small scale ULF waves in SPEAR-induced HF coherent backscatter

Annales Geophysicae ◽

10.5194/angeo-26-2253-2008 ◽

2008 ◽

Vol 26 (8) ◽

pp. 2253-2263 ◽

Cited By ~ 12

Author(s):

T. K. Yeoman ◽

L. J. Baddeley ◽

R. S. Dhillon ◽

T. R. Robinson ◽

D. M. Wright

Keyword(s):

High Power ◽

High Latitude ◽

Wave Number ◽

Lower Latitude ◽

Small Scale ◽

Particle Interactions ◽

Ulf Wave ◽

Wave Characteristics ◽

Azimuthal Wave ◽

Azimuthal Wave Number

Abstract. HF radar backscatter which has been artificially-induced by a high power RF facility has been demonstrated to provide ionospheric electric field data of unprecedented temporal resolution and accuracy. Here such data, induced by the SPEAR high power radar on Svalbard, are used to investigate ULF wave processes observed by the CUTLASS HF radars. Observations are presented of both waves with a large-scale nature, driven externally to the magnetosphere and those with small azimuthal scale lengths, driven by wave-particle interactions. For ULF wave events with large azimuthal scale lengths an excellent agreement in the observed wave polarisation ellipse is found between the radar observations and ground-based magnetometer data. In contrast, for the small scale events, no ground-based magnetic counterpart is observed. Indeed the data from the two CUTLASS radars seem inconsistent, and each radar must be interpreted separately, as the spatial resolution of the radars is sufficient to resolve the wave characteristics along the radar beams, but insufficient to resolve the wave characteristics across the beams. A high azimuthal wave number (m) wave with a period of 300 s and m~−60 is observed to occur over Svalbard at ~14:00 magnetic local time. This confirms the existence of waves driven by wave-particle interactions with trapped particle populations in the outer magnetosphere. A comparison of the observed wave characteristics with previous, lower latitude, observations suggests that these high latitude waves have a similar azimuthal scale size to those generated in the inner magnetosphere; the azimuthal wave number of −60 observed in the present study is comparable to previous values of −20– −50, but suggests an increase of m with latitude. A similar energy source in drifting proton populations is also suggested, but with lower characteristic proton energies of 10 keV implicated at high latitude, compared to the 20–60 keV energies invoked for previous lower latitude observations.

Download Full-text

<i>Letter to the editor</i>CUTLASS observations of a high-m ULF wave and its consequences for the DOPE HF Doppler sounder

Annales Geophysicae ◽

10.1007/s00585-999-1493-3 ◽

1999 ◽

Vol 17 (11) ◽

pp. 1493-1497 ◽

Cited By ~ 10

Author(s):

D. M. Wright ◽

T. K. Yeoman

Keyword(s):

Spatial Information ◽

Hf Radar ◽

Mhd Waves ◽

Small Scale ◽

M Wave ◽

Ulf Wave ◽

Naturally Occurring ◽

Mhd Waves And Instabilities ◽

Independent Confirmation ◽

Heated Volume

Abstract. The CUTLASS (Co-operative UK Twin Located Auroral Sounding System) Finland HF radar, whilst operating in a high spatial and temporal resolution mode, has measured the ionospheric signature of a naturally occurring ULF wave in scatter artificially generated by the Tromsù Heater. The wave had a period of 100 s and exhibited curved phase fronts across the heated volume (about 180 km along a single radar beam). Spatial information provided by CUTLASS has enabled an m-number for the wave of about 38 to be determined. This high-m wave was not detected by the IMAGE (International Monitor for Auroral Geomagnetic Efects) network of ground magnetometers, as expected for a wave of a small spatial scale size. These observations over the first independent confirmation of the existence of the ground uncorrelated ULF wave signatures previously reported in measurements recorded from an HF Doppler sounder located in the vicinity of Tromsö. These results both demonstrate a new capability for geophysical exploration from the combined CUTLASS-EISCAT ionospheric Heater experiment, and provide a verification of the HF Doppler technique for the investigation of small scale ULF waves.Key words. Ionosphere (ionosphere – magnetosphere interactions) . Magnetospheric physics (magnetosphere – ionosphere interactions; MHD waves and instabilities)

Download Full-text

SPATIAL STRUCTURE OF AZIMUTHALLY SMALL-SCALE MHD WAVES IN ONE-DIMENSIONALLY INHOMOGENEOUS FINITE PRESSURE PLASMA WITH CURVED FIELD LINES

Solnechno-Zemnaya Fizika ◽

10.12737/szf-61202006 ◽

2020 ◽

Vol 6 (1) ◽

pp. 63-74

Author(s):

Aleksandr Petrashchuk ◽

Dmitriy Klimushkin

Keyword(s):

Spatial Structure ◽

Field Line ◽

Wave Structure ◽

Plasma Pressure ◽

Mhd Waves ◽

Small Scale ◽

Radial Coordinate ◽

Pressure Plasma ◽

Transparent Region ◽

Field Lines

We have studied propagation of hydromagnetic (MHD) waves in one-dimensionally inhomogeneous finite pressure plasma with curved field lines. Magnetic surfaces are considered to be concentric cylinders, where the cylinder’s radius models the radial coordinate in Earth’s magnetosphere. The waves are supposed to be azimuthally small-scale. In this approximation there are only two MHD modes — Alfvén and slow magnetosonic (SMS). We have derived an ordinary differential equation for the spatial structure of the wave field in this model. We have examined the character of the singularity on the surface of Alfvén and SMS resonances and the influence of field line curvature on them. We have determined wave transparent regions. The SMS transparent region was found to essentially broaden as compared to the straight field line case. The very existence of the Alfvén transparent region is caused by the field line curvature and finite plasma pressure; otherwise, the wave structure is represented by a localized resonance.

Download Full-text

SPATIAL STRUCTURE OF AZIMUTHALLY SMALL-SCALE MHD WAVES IN ONE-DIMENSIONALLY INHOMOGENEOUS FINITE PRESSURE PLASMA WITH CURVED FIELD LINES

Solar-Terrestrial Physics ◽

10.12737/stp-61202006 ◽

2020 ◽

Vol 6 (1) ◽

pp. 50-59

Author(s):

Aleksandr Petrashchuk ◽

Dmitriy Klimushkin

Keyword(s):

Spatial Structure ◽

Field Line ◽

Wave Structure ◽

Plasma Pressure ◽

Mhd Waves ◽

Small Scale ◽

Radial Coordinate ◽

Pressure Plasma ◽

Transparent Region ◽

Field Lines

Download Full-text

A statistical study of unstable particle populations in the global ringcurrent and their relation to the generation of high <i>m</i> ULF waves

Annales Geophysicae ◽

10.5194/angeo-22-4229-2004 ◽

2004 ◽

Vol 22 (12) ◽

pp. 4229-4241 ◽

Cited By ~ 17

Author(s):

L. J. Baddeley ◽

T. K. Yeoman ◽

D. M. Wright ◽

K. J. Trattner ◽

B. J. Kellet

Keyword(s):

Free Energy ◽

Statistical Study ◽

Wave Mode ◽

Particle Energy ◽

Distribution Functions ◽

Mhd Waves ◽

Small Scale ◽

Ulf Waves ◽

Ion Distribution ◽

Resonant Wave

Abstract. The first statistical study of the unstable proton populations which contain "free energy" required to drive small-scale poloidal mode ULF waves in the magnetosphere between L-shell locations of 6 and 9 is presented. The data examined are all in the form of Ion Distribution Functions (IDFs) covering a particle energy range of 0.025keV to 328keV, amassed over 2.5 years from the TIMAS and CAMMICE (MICS) instruments on-board the Polar spacecraft. Any free energy which is available to drive a resonant wave mode manifests itself as a positive gradient region in the IDF. A new analysis technique applied to the data, allows for the first time, the amount of free energy contained in each IDF to be quantified. The results show that IDFs are a common occurrence in the magnetosphere at these L-shells, although they are most common in the dawn/pre-noon sector. Lower energy (10–45keV) protons are the most commonly observed unstable populations and also contain the largest amounts of free energy (>1010J). Positive gradient regions at higher energies (>100keV) are rarely observed and also contain greatly reduced free energies (<109J). Key words. Magnetospheric physics (Energetic particles, trapped; MHD waves and instabilities) – Space plasma physics (wave-particle interactions)

Download Full-text

Non-Linear Interaction of MHD Waves with Small-Scale Ionospheric Irregularities

Telecommunications and Radio Engineering ◽

10.1615/telecomradeng.v61.i12.60 ◽

2004 ◽

Vol 61 (7-12) ◽

pp. 1055-1071

Author(s):

N. N. Gerasimova ◽

V. G. Sinitsin ◽

Yu. M. Yampolski

Keyword(s):

Ionospheric Irregularities ◽

Mhd Waves ◽

Small Scale ◽

Linear Interaction ◽

Non Linear

Download Full-text

High resolution observations of spectral width features associatedwith ULF wave signatures in artificial HF radar backscatter

Annales Geophysicae ◽

10.5194/angeo-22-169-2004 ◽

2004 ◽

Vol 22 (1) ◽

pp. 169-182 ◽

Cited By ~ 4

Author(s):

D. M. Wright ◽

T. K. Yeoman ◽

L. J. Baddeley ◽

J. A. Davies ◽

R. S. Dhillon ◽

...

Keyword(s):

High Resolution ◽

Plasma Source ◽

Spectral Width ◽

Hf Radar ◽

Mhd Waves ◽

Small Scale ◽

Ulf Waves ◽

Source Population ◽

Radar Backscatter ◽

Field Lines

Abstract. The EISCAT high power heating facility at Tromsø, northern Norway, has been utilised to generate artificial radar backscatter in the fields of view of the CUTLASS HF radars. It has been demonstrated that this technique offers a means of making very accurate and high resolution observations of naturally occurring ULF waves. During such experiments, the usually narrow radar spectral widths associated with artificial irregularities increase at times when small scale-sized (high m-number) ULF waves are observed. Possible mechanisms by which these particle-driven high-m waves may modify the observed spectral widths have been investigated. The results are found to be consistent with Pc1 (ion-cyclotron) wave activity, causing aliasing of the radar spectra, in agreement with previous modelling work. The observations also support recent suggestions that Pc1 waves may be modulated by the action of longer period ULF standing waves, which are simultaneously detected on the magnetospheric field lines. Drifting ring current protons with energies of ∼ 10keV are indicated as a common plasma source population for both wave types. Key words. Magnetospheric physics (MHD waves and instabilities) – Space plasma physics (wave-particle interactions) – Ionosphere (active experiments)

Download Full-text