On the occurrence and motion of decametre-scale irregularities in the sub-auroral, auroral, and polar cap ionosphere

Abstract. The statistical occurrence of decametre-scale ionospheric irregularities, average line-of-sight (LOS) Doppler velocity, and Doppler spectral width in the sub-auroral, auroral, and polar cap ionosphere ( - 57°L to - 88°L) has been investigated using echoes recorded with the Tasman International Geospace Environment Radar (TIGER), a SuperDARN radar located on Bruny Island, Tasmania (147.2° E, 43.4° S geographic; - 54.6 °L). Results are shown for routine soundings made on the magnetic meridian beam 4 and the near zonal beam 15 during the sunspot maximum interval December 1999 to November 2000. Most echoes were observed in the nightside ionosphere, typically via 1.5-hop propagation near dusk and then via 0.5-hop propagation during pre-midnight to dawn. Peak occurrence rates on beam 4 were often > 60% near magnetic midnight and ~ - 70 °L. They increased and shifted equatorward and toward pre-midnight with increasing Kp (i.e. Bz southward). The occurrence rates remained very high for Kp > 4, de-spite enhanced D-region absorption due to particle precipitation. Average occurrence rates on beam 4 exhibited a relatively weak seasonal variation, consistent with known longitudinal variations in auroral zone magnetic activity (Basu, 1975). The average echo power was greatest between 23 and 07 MLT. Two populations of echoes were identified on both beams, those with low spectral width and a mode value of ~ 9 ms-1 (bin size of 2 ms-1) concentrated in the auroral and sub-auroral ionosphere (population A), and those with high spectral width and a mode value of ~ 70 ms-1 concentrated in the polar cap ionosphere (population B). The occurrence of population A echoes maximised post-midnight because of TIGER’s lower latitude, but the subset of the population A echoes observed near dusk had characteristics reminiscent of "dusk scatter" (Ruohoniemi et al., 1988). There was a dusk "bite out" of large spectral widths between ~ 15 and 21 MLT and poleward of - 67 °L, and a pre-dawn enhancement of large spectral widths between ~ 03 and 07 MLT, centred on ~ - 61 °L. The average LOS Doppler velocities revealed that frequent westward jets of plasma flow occurred equatorward of, but overlapping, the diffuse auroral oval in the pre-midnight sector.Key words. Ionosphere (auroral ionosphere; electric fields and currents, ionospheric irregularities)

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Magnetic local time, substorm, and particle precipitation-related variations in the behaviour of SuperDARN Doppler spectral widths

Annales Geophysicae ◽

10.5194/angeo-22-4103-2004 ◽

2004 ◽

Vol 22 (12) ◽

pp. 4103-4122 ◽

Cited By ~ 3

Author(s):

M. L. Parkinson ◽

G. Chisham ◽

M. Pinnock ◽

P. L. Dyson ◽

J. C. Devlin

Keyword(s):

Spectral Width ◽

Auroral Oval ◽

Auroral Zone ◽

Lower Latitude ◽

Velocity Spread ◽

Doppler Velocity ◽

High Time Resolution ◽

Particle Precipitation ◽

Study Interval ◽

Present Case Study

Abstract. Super Dual Auroral Radar Network (DARN) radars often detect a distinct transition in line-of-sight Doppler velocity spread, or spectral width, from <50ms–1 at lower latitude to >200ms–1 at higher latitude. They also detect a similar boundary, namely the range at which ionospheric scatter with large spectral width suddenly commences (i.e. without preceding scatter with low spectral width). The location and behaviour of the spectral width boundary (SWB) (and scatter boundary) and the open-closed magnetic field line boundary (OCB) are thought to be closely related. The location of the nightside OCB can be inferred from the poleward edge of the auroral oval determined using energy spectra of precipitating particles measured on board Defence Meteorology Satellite Program (DMSP) satellites. Observations made with the Halley SuperDARN radar (75.5° S, 26.6° W, geographic; –62.0°Λ) and the Tasman International Geospace Environment Radar (TIGER) (43.4° S, 147.2° E; –54.5°Λ) are used to compare the location of the SWB with the DMSP-inferred OCB during 08:00 to 22:00 UT on 1 April 2000. This study interval was chosen because it includes several moderate substorms, whilst the Halley radar provided almost continuous high-time resolution measurements of the dayside SWB location and shape, and TIGER provided the same in the nightside ionosphere. The behaviour of the day- and nightside SWB can be understood in terms of the expanding/contracting polar cap model of high-latitude convection change, and the behaviour of the nightside SWB can also be organised according to substorm phase. Previous comparisons with DMSP OCBs have proven that the radar SWB is often a reasonable proxy for the OCB from dusk to just past midnight (Chisham et al., 2004). However, the present case study actually suggests that the nightside SWB is often a better proxy for the poleward edge of Pedersen conductance enhanced by hot particle precipitation in the auroral zone. Simple modeling implies that the large spectral widths must be caused by ~10-km scale velocity fluctuations. Key words. Ionosphere (auroral ionosphere; ionospheremagnetosphere interactions) – Magnetospheric physics (storms and substorms)

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On the lifetime and extent of an auroral westward flow channel (AWFC) observed during a magnetospheric substorm

Annales Geophysicae ◽

10.5194/angeo-21-893-2003 ◽

2003 ◽

Vol 21 (4) ◽

pp. 893-913 ◽

Cited By ~ 17

Author(s):

M. L. Parkinson ◽

M. Pinnock ◽

H. Ye ◽

M. R. Hairston ◽

J. C. Devlin ◽

...

Keyword(s):

Electric Fields ◽

Wide Band ◽

Spectral Width ◽

Recovery Phase ◽

Auroral Oval ◽

Flow Channel ◽

Doppler Velocity ◽

Evening Sector ◽

Phase Interval ◽

Electric Fields And Currents

Abstract. A -190-nT negative bay in the geomagnetic X component measured at Macquarie Island ( -65° L) showed that an ionospheric substorm occurred during 09:58 to 11:10 UT on 27 February 2000. Signatures of an auroral westward flow channel (AWFC) were observed nearly simultaneously in the backscatter power, LOS Doppler velocity, and Doppler spectral width measured using the Tasman International Geospace Environment Radar (TIGER), a Southern Hemisphere HF SuperDARN radar. Many of the characteristics of the AWFC were similar to those occurring during a polarisation jet (PJ), or subauroral ion drift (SAID) event, and suggest that it may have been a pre-cursor to a fully developed, intense westward flow channel satisfying all of the criteria defining a PJ/SAID. A beam-swinging analysis showed that the westward drifts (poleward electric field) associated with the flow channel were very structured in time and space, but the smoothed velocities grew to ~ 800 ms-1 (47 mVm-1) during the 22-min substorm onset interval 09:56 to 10:18 UT. Maximum west-ward drifts of >1.3 km s-1 (>77 mVm-1) occurred during a ~ 5-min velocity spike, peaking at 10:40 UT during the expansion phase. The drifts decayed rapidly to ~ 300 ms-1 (18 mVm-1) during the 6-min recovery phase interval, 11:04 to 11:10 UT. Overall, the AWFC had a lifetime of 74 min, and was located near -65° L in the evening sector west of the Harang discontinuity. The large westward drifts were confined to a geographic zonal channel of longitudinal ex-tent >20° (>1.3 h magnetic local time), and latitudinal width ~2° L. Using a half-width of ~ 100 km in latitude, the peak electric potential was >7.7 kV. However, a transient velocity of >3.1 km s-1 with potential >18.4 kV was observed further poleward at the end of the recovery phase. Auroral oval boundaries determined using DMSP measurements suggest the main flow channel overlapped the equatorward boundary of the diffuse auroral oval. During the ~ 2-h interval following the flow channel, an ~ 3° L wide band of scatter was observed drifting slowly toward the west, with speeds gradually decaying to ~ 50 ms-1 (3 mVm -1). The scatter was observed extending past the Harang discontinuity, and had Doppler signatures characteristic of the main ionospheric trough, implicating the flow channel in the further depletion of F-region plasma. The character of this scatter was in contrast with the character of the scatter drifting toward the east at higher latitude.Key words. Ionosphere (auroral ionosphere; electric fields and currents; ionosphere-magnetospehere interactions) Magnetospheric physics (storms and substorms)

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Imaging radar observations of Farley Buneman waves during the JOULE II experiment

Annales Geophysicae ◽

10.5194/angeo-26-1837-2008 ◽

2008 ◽

Vol 26 (7) ◽

pp. 1837-1850 ◽

Cited By ~ 16

Author(s):

D. L. Hysell ◽

G. Michhue ◽

M. F. Larsen ◽

R. Pfaff ◽

M. Nicolls ◽

...

Keyword(s):

Electric Fields ◽

Spectral Width ◽

Auroral Zone ◽

Convection Flow ◽

Coherent Scatter ◽

Flow Angle ◽

Doppler Shifts ◽

Ion Acoustic ◽

The Waves ◽

Acoustic Speed

Abstract. Vector electric fields and associated E×B drifts measured by a sounding rocket in the auroral zone during the NASA JOULE II experiment in January 2007, are compared with coherent scatter spectra measured by a 30 MHz radar imager in a common volume. Radar imaging permits precise collocation of the spectra with the background electric field. The Doppler shifts and spectral widths appear to be governed by the cosine and sine of the convection flow angle, respectively, and also proportional to the presumptive ion acoustic speed. The neutral wind also contributes to the Doppler shifts. These findings are consistent with those from the JOULE I experiment and also with recent numerical simulations of Farley Buneman waves and instabilities carried out by Oppenheim et al. (2008). Simple linear analysis of the waves offers some insights into the spectral moments. A formula relating the spectral width to the flow angle, ion acoustic speed, and other ionospheric parameters is derived.

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Multi-technique investigations of storm-time ionospheric irregularities over the São Luís equatorial station in Brazil

Annales Geophysicae ◽

10.5194/angeo-22-3513-2004 ◽

2004 ◽

Vol 22 (10) ◽

pp. 3513-3522 ◽

Cited By ~ 19

Author(s):

E. R. de Paula ◽

K. N. Iyer ◽

D. L. Hysell ◽

F. S. Rodrigues ◽

E. A. Kherani ◽

...

Keyword(s):

Electric Fields ◽

Power Spectra ◽

Spectral Width ◽

Radar Data ◽

Ionospheric Irregularities ◽

Quiet Time ◽

Vhf Radar ◽

Equatorial Station ◽

Plasma Irregularities ◽

Magnetospheric Convection

Abstract. On 11 April 2001, a large magnetic storm occurred with SSC at 13:43 UT, and Dst reached below -200nT after two southward Bz excursions. The Kp index during this storm reached 8 and remained high (>4) for about 21h, and the São Luís magnetometer H component presented simultaneous oscillations and decreased substantially relative to the previous magnetically quiet days. This storm triggered strong ionospheric irregularities, as observed by a recently installed 30MHz coherent scatter radar, a digisonde, and a GPS scintillation receiver, all operating at the São Luís equatorial station (2.33° S, 44° W, dip latitude 1.3° S). The ionospheric conditions and the characteristics of the ionospheric irregularities observed by these instruments are presented and discussed. The VHF radar RTI (Range Time Intensity) echoes and their power spectra and spectral width for the storm night 11-12 April 2001, were used to analyse the nature and dynamics of the plasma irregularities and revealed the coexistence of many structures in the altitudinal range of 400-1200km, some locally generated and others that drifted from other longitudinal sectors. The radar data also revealed that the plumes had periodic eastward and westward zonal velocities after 22:20 UT, when well-developed quiet-time plumes typically drift eastward. Another interesting new observation is that the F-layer remained anomalously high throughout the 11-12 April 2001 storm night (21:00 UT to 09:00 UT next day) (the LT at São Luís is UT -3h), as indicated by the digisonde parameters hmF2 and h'F, which is a condition favourable for spread F generation and maintenance. The AE auroral index showed enhancements (followed by decreases) that are indicative of magnetospheric convection enhancements at about 15:00 UT, 20:00 UT and 22:00 UT on 11 April 2001 and at 00:20 UT (small amplitude) on 12 April 2001, associated with many Bz fluctuations, including clear two southward incursions that gave rise to large and long lasting Kp values and large negative Dst values. This intense auroral activity generated disturbance dynamo and prompt penetration electric fields that were responsible for the maintenance of the F-layer at a high altitude along the night of 11-12 April 2001. The short-lived F-region height rise seen between 16:00 to 18:00 UT on 11 April 2001 is probably due to the prompt penetration eastward electric fields of magnetospheric origin during the first IMF Bz turning to south around 15:00 UT.

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Dynamical critical scaling of electric field fluctuations in the greater cusp and magnetotail implied by HF radar observations of F-region Doppler velocity

Annales Geophysicae ◽

10.5194/angeo-24-689-2006 ◽

2006 ◽

Vol 24 (2) ◽

pp. 689-705 ◽

Cited By ~ 17

Author(s):

M. L. Parkinson

Keyword(s):

Solar Wind ◽

Open Field ◽

Electric Fields ◽

Spectral Width ◽

Hf Radar ◽

Doppler Velocity ◽

Closed Field ◽

Scaling Exponent ◽

Central Plasma ◽

Field Lines

Abstract. Akasofu's solar wind ε parameter describes the coupling of solar wind energy to the magnetosphere and ionosphere. Analysis of fluctuations in ε using model independent scaling techniques including the peaks of probability density functions (PDFs) and generalised structure function (GSF) analysis show the fluctuations were self-affine (mono-fractal, single exponent scaling) over 9 octaves of time scale from ~46 s to ~9.1 h. However, the peak scaling exponent α0 was a function of the fluctuation bin size, so caution is required when comparing the exponents for different data sets sampled in different ways. The same generic scaling techniques revealed the organisation and functional form of concurrent fluctuations in azimuthal magnetospheric electric fields implied by SuperDARN HF radar measurements of line-of-sight Doppler velocity, vLOS, made in the high-latitude austral ionosphere. The PDFs of vLOS fluctuation were calculated for time scales between 1 min and 256 min, and were sorted into noon sector results obtained with the Halley radar, and midnight sector results obtained with the TIGER radar. The PDFs were further sorted according to the orientation of the interplanetary magnetic field, as well as ionospheric regions of high and low Doppler spectral width. High spectral widths tend to occur at higher latitude, mostly on open field lines but also on closed field lines just equatorward of the open-closed boundary, whereas low spectral widths are concentrated on closed field lines deeper inside the magnetosphere. The vLOS fluctuations were most self-affine (i.e. like the solar wind ε parameter) on the high spectral width field lines in the noon sector ionosphere (i.e. the greater cusp), but suggested multi-fractal behaviour on closed field lines in the midnight sector (i.e. the central plasma sheet). Long tails in the PDFs imply that "microbursts" in ionospheric convection occur far more frequently, especially on open field lines, than can be captured using the effective Nyquist frequency and volume resolution of SuperDARN radars.

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On the apparent equatorward propagation of auroral substorm absorption events at low auroral latitudes

Canadian Journal of Physics ◽

10.1139/p78-187 ◽

1978 ◽

Vol 56 (11) ◽

pp. 1412-1416 ◽

Cited By ~ 1

Author(s):

Syed Ziauddin ◽

M. A. Abdu

Keyword(s):

Time Dependence ◽

Local Time ◽

Electric Fields ◽

Auroral Zone ◽

Lower Latitude ◽

Precipitation Region ◽

Auroral Substorm ◽

Strong Electric Fields ◽

Local Time Dependence ◽

Consistent Tendency

Auroral substorm absorption events observed at two stations. Val d'Or, P.Q. and Ottawa, Ont., located on the lower latitude side of the auroral zone (around L = 4) show a consistent tendency for an apparent equatorward propagation of the events. The observed velocities of propagation do not show any local time dependence or other trends expected from a pure gradient B drift of substorm electrons from the midnight precipitation region to the day side. Though a limited number of events are analysed the results indicate the possible influence of strong electric fields on the drift velocities of the substorm electrons.

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CUTLASS HF radar observations of high-velocity E-region echoes

Annales Geophysicae ◽

10.5194/angeo-19-411-2001 ◽

2001 ◽

Vol 19 (4) ◽

pp. 411-424 ◽

Cited By ~ 10

Author(s):

M. V. Uspensky ◽

A. V. Koustov ◽

P. Eglitis ◽

A. Huuskonen ◽

S. E. Milan ◽

...

Keyword(s):

Electric Fields ◽

High Velocity ◽

Power Doppler ◽

Spectral Width ◽

Plasma Instability ◽

Hf Radar ◽

Doppler Velocity ◽

Classical Type ◽

E Region

Abstract. A short event of high-velocity E-region echo observations by the Pykkvibaer HF radar is analysed to study echo parameters and the echo relation to the Farley-Buneman plasma instability. The echoes were detected in several beams aligned closely to the magnetic L-shell direction. Two echo groups were identified: one group corresponded to the classical type 1 echoes with velocities close to the nominal ion-acoustic speed of 400 ms–1 , while the other group had significantly larger velocities, of the order of 700 ms–1 . The mutual relationship between the echo power, Doppler velocity, spectral width and elevation angles for these two groups was studied. Plotting of echo parameters versus slant range showed that all ~700 ms–1 echoes originated from larger heights and distances of 500–700 km, while all ~400 ms–1 echoes came from lower heights and from farther distances; 700–1000 km. We argue that both observed groups of echoes occurred due to the Farley-Buneman plasma instability excited by strong ( ~70 mVm–1 ) and uniformly distributed electric fields. We show that the echo velocities for the two groups were different because the echoes were received from different heights. Such a separation of echo heights occurred due to the differing amounts of ionospheric refraction at short and large ranges. Thus, the ionospheric refraction and related altitude modulation of ionospheric parameters are the most important factors to consider, when various characteristics of E-region decametre irregularities are derived from HF radar measurements.Key words. Ionosphere (ionospheric irregularities; plasma waves and instabilities; polar ionosphere)

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<i>Letter to the Editor:</i> First complementary observations by ionospheric tomography, the EISCAT Svalbard radar and the CUTLASS HF radar

Annales Geophysicae ◽

10.1007/s00585-998-1519-2 ◽

1998 ◽

Vol 16 (11) ◽

pp. 1519-1522 ◽

Cited By ~ 1

Author(s):

C. N. Mitchell ◽

I. K. Walker ◽

S. E. Pryse ◽

I. Kersley ◽

I. W. McCrea ◽

...

Keyword(s):

Auroral Zone ◽

Hf Radar ◽

Auroral Ionosphere ◽

Polar Cap ◽

Low Velocity ◽

Radio Science ◽

Ionospheric Tomography ◽

Ionospheric Physics ◽

Incoherent Scatter ◽

Complementary Nature

Abstract. Experimental results are presented from ionospheric tomography, the EISCAT Svalbard radar and the CUTLASS HF radar. Tomographic measurements on 10 October 1996, showing a narrow, field-aligned enhancement in electron density in the post-noon sector of the dayside auroral zone, are related to a temporal increase in the plasma concentration observed by the incoherent scatter radar in the region where the HF radar indicated a low velocity sunwards convection. The results demonstrate the complementary nature of these three instruments for polar-cap ionospheric studies.Key words. Ionosphere · Auroral ionosphere · Polar ionosphere · Radio science (ionospheric physics)

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Energy–latitude dispersion patterns near the isotropy boundaries of energetic protons

Annales Geophysicae ◽

10.5194/angeo-33-1059-2015 ◽

2015 ◽

Vol 33 (8) ◽

pp. 1059-1070 ◽

Cited By ~ 13

Author(s):

V. A. Sergeev ◽

S. A. Chernyaeva ◽

S. V. Apatenkov ◽

N. Y. Ganushkina ◽

S. V. Dubyagin

Keyword(s):

Flux Ratio ◽

Auroral Oval ◽

Auroral Zone ◽

Frequent Pattern ◽

Lower Latitude ◽

Dispersion Pattern ◽

Mesoscale Structures ◽

Angle Scattering ◽

Dispersion Patterns ◽

Wave Induced

Abstract. Non-adiabatic motion of plasma sheet protons causes pitch-angle scattering and isotropic precipitation to the ionosphere, which forms the proton auroral oval. This mechanism related to current sheet scattering (CSS) provides a specific energy–latitude dispersion pattern near the equatorward boundary of proton isotropic precipitation (isotropy boundary, IB), with precipitation sharply decreasing at higher (lower) latitude for protons with lower (higher) energy. However, this boundary maps to the inner magnetosphere, where wave-induced scattering may provide different dispersion patterns as recently demonstrated by Liang et al. (2014). Motivated by the potential usage of the IBs for the magnetotail monitoring as well as by the need to better understand the mechanisms forming the proton IB, we investigate statistically the details of particle flux patterns near the proton IB using NOAA-POES polar spacecraft observations made during September 2009. By comparing precipitated-to-trapped flux ratio (J0/J90) at >30 and >80 keV proton energies, we found a relatively small number of simple CSS-type dispersion events (only 31 %). The clear reversed (wave-induced) dispersion patterns were very rare (5 %). The most frequent pattern had nearly coinciding IBs at two energies (63 %). The structured precipitation with multiple IBs was very frequent (60 %), that is, with two or more significant J0/J90 dropouts. The average latitudinal width of multiple IB structures was about 1°. Investigation of dozens of paired auroral zone crossings of POES satellites showed that the IB pattern is stable on a timescale of less than 2 min (a few proton bounce periods) but can evolve on a longer (several minutes) scale, suggesting temporal changes in some mesoscale structures in the equatorial magnetosphere. We discuss the possible role of CSS-related and wave-induced mechanisms and their possible coupling to interpret the emerging complicated patterns of proton isotropy boundaries.

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SuperDARN E-region backscatter boundary in the dusk-midnight sector – tracer of equatorward boundary of the auroral oval

Annales Geophysicae ◽

10.5194/angeo-20-1899-2002 ◽

2002 ◽

Vol 20 (12) ◽

pp. 1899-1904 ◽

Cited By ~ 10

Author(s):

P. T. Jayachandran ◽

E. F. Donovan ◽

J. W. MacDougall ◽

D. R. Moorcroft ◽

J.-P. St. Maurice ◽

...

Keyword(s):

Energy Flux ◽

Proton Energy ◽

Auroral Oval ◽

Ionospheric Irregularities ◽

Auroral Ionosphere ◽

Particle Precipitation ◽

Equatorward Boundary ◽

E Region ◽

Proton Aurora

Abstract. We compare the locations of the equatorward boundaries of SuperDARN E-region backscatter and Hb emissions, focusing on the dusk-midnight sector of the auroral oval where the proton aurora is statistically located equatorward of the discrete electron aurora. We show that, whenever both boundaries can be simultaneously identified, they are coincident. Our result complements earlier studies, which demonstrated the correspondence between the DMSP b2i boundary and both the equatorward boundary of the proton auroral oval (Donovan et al., 2002), and the equatorward boundary of SuperDARN E-region echoes (Jayachandran et al., 2002). Further, our result shows that, provided there is sufficient precipitating proton energy flux, the SuperDARN radars can be used to monitor the equatorward edge of the proton auroral oval.Key words. Ionosphere (auroral ionosphere; particle precipitation; ionospheric irregularities)

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