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

1998 ◽  
Vol 16 (10) ◽  
pp. 1190-1199 ◽  
Author(s):  
D. M. Wright ◽  
T. K. Yeoman ◽  
J. A. Davies
Keyword(s):  
Resonance Region ◽  
Mhd Waves ◽  
Broad Resonance ◽  
Radio Science ◽  
Ionospheric Physics ◽  
Ulf Wave ◽  
Bulk Motion ◽  
First Results ◽  
Mhd Waves And Instabilities ◽  
Uhf Radar

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 first 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 field perturbation of the ULF wave and the first direct observational confirmation of a numerical simulation has been achieved. The wave, which was Alfvénic 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.Key words. Magnetosphere-ionosphere interactions · MHD waves and instabilities · Radio science · Ionospheric physics

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

1999 ◽  
Vol 17 (6) ◽  
pp. 749-758 ◽  
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)

scholarly journals Interaction of Pc4 ULF waves with solar wind velocity and its dependence on Kp values

2021 ◽  
Vol 14 (12) ◽  
pp. 1013-1020
Author(s):  
M T Khan ◽  
◽  
K A Nafees ◽  
A K Singh
Keyword(s):  
Solar Wind ◽  
Solar Wind Speed ◽  
Mhd Waves ◽  
Ulf Waves ◽  
Ulf Wave ◽  
Magnetic Pulsations ◽  
Recorded Data ◽  
Mhd Waves And Instabilities ◽  
Field Lines ◽  
East West

Background/Objectives: Magnetic Pulsations recorded on the ground in the earth are produced by processes inside the magnetosphere and solar wind. These processes produce a wide variety of ULF hydromagnetic wave type which can be categorized on the ground as either Pi or Pc pulsations (irregular or continuous). Methods: Distinctive regions of the magnetosphere originate different frequencies of waves. Digital Dynamic Spectra (DDS) for the northsouth (X), east-west (Y) and vertical (Z) components of the recorded data were constructed for every day for 365 days (January 1 to December 31, 2005) in the station order PON, HAN and NAG respectively. Pc4 geomagnetic pulsations are quasi-sinusoidal fluctuations in the earth’s magnetic field in the length range 45-150 seconds. The magnitude of these pulsations ranges from fraction of a Nano Tesla (nT) to several nT. The monthly variation of Pc4 occurrence has a Kp dependence range of 0 to 9-. However, Pc4 occurrence was reported for Kp values, yet the major Pc4 events occurred for rage 5+ <Kp< 8+. The magnitudes of intervals of Pc4 occurrence decreased in the station order PON, HAN and NAG respectively. Analysis of the data for the whole year 2005 provided similar patterns of Pc4 occurrence for Vsw at all the three stations. Although Pc4 ULF wave occurrence become reported for Vsw ranging from 250 to 1000 Km/s, yet the major Pc4 event recorded for a Vsw range of 300-700 Km/sec. Findings: The current study is undertaken for describing the interaction of Pc4 ULF waves with solar wind speed and its dependence on Kp values. The results suggest that the solar wind control Pc4 occurrence through a mechanism in which Pc4 wave energy is convected through the magnetosheath and coupled to the standing oscillations of the magnetospheric field lines. PACS Nos: 94.30.cq; 96.50.Tf Keywords: Geomagnetic micropulsations; MHD waves and instabilities; Solar wind-control of Pc4 pulsation

scholarly journals The effects of high-frequency ULF wave activity on the spectral characteristics of coherent HF radar returns: a case study

2004 ◽  
Vol 22 (5) ◽  
pp. 1843-1849
Author(s):  
D. M. Wright ◽  
T. K. Yeoman ◽  
E. E. Woodfield
Keyword(s):  
High Frequency ◽  
Spectral Power ◽  
Spectral Characteristics ◽  
Wave Activity ◽  
Hf Radar ◽  
Mhd Waves ◽  
Closed Field ◽  
Radio Science ◽  
Ionospheric Physics ◽  
Field Lines

Abstract. It is now a common practice to employ ground-based radars in an attempt to distinguish between those regions of the Earth's upper atmosphere which are magnetically conjugate to open and closed magnetic field lines. Radar returns from ionospheric irregularities inside the polar cap and cusp regions generally exhibit large spectral widths in contrast to those which exist on closed field lines at lower latitudes. It has been suggested that the so-called Spectral Width Boundary (SWB) might act as a proxy for the open-closed field line boundary (OCFLB), which would then be an invaluable tool for investigating reconnection rates in the magnetosphere. The exact cause of the increased spectral widths observed at very high latitudes is still subject to considerable debate. Several mechanisms have been proposed. This paper compares a dusk-sector interval of coherent HF radar data with measurements made by an induction coil magnetometer located at Tromsø, Norway (66° N geomagnetic). On this occasion, a number of equatorward excursions of the SWB in the radar backscatter are accompanied by increases in spectral power of ULF waves in the Pc1-2 frequency band as the SWB passes overhead. Thus, these observations support the possibility that high-frequency magnetospheric wave activity at least contribute to the observed spectral characteristics and that such wave activity might play a significant role in the nightside ionosphere. Key words. Ionosphere (auroral ionosphere) – Magnetospheric physics (MHD waves and instabilities) – Radio science (ionospheric physics)

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

1999 ◽  
Vol 17 (11) ◽  
pp. 1493-1497 ◽  
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)

scholarly journals Cluster as a wave telescope – first results from the fluxgate magnetometer

2001 ◽  
Vol 19 (10/12) ◽  
pp. 1439-1447 ◽  
Author(s):  
K.-H. Glassmeier ◽  
U. Motschmann ◽  
M. Dunlop ◽  
A. Balogh ◽  
M. H. Acuña ◽  
...  
Keyword(s):  
Wave Vector ◽  
Low Frequency ◽  
Plasma Waves ◽  
Minimum Variance ◽  
Mhd Waves ◽  
Fluxgate Magnetometer ◽  
Propagating Waves ◽  
First Results ◽  
Mhd Waves And Instabilities ◽  
First Time

Abstract. The four Cluster spacecraft provide an excellent opportunity to study spatial structures in the magnetosphere and adjacent regions. Propagating waves are amongst the interesting structures and for the first time, Cluster will allow one to measure the wave vector of low-frequency fluctuations in a space plasma. Based on a generalized minimum variance analysis wave vector estimates will be determined in the terrestrial magnetosheath and the near-Earth solar wind. The virtue and weakness of the wave telescope technique used is discussed in detail.Key words. Electromagnetics (wave propagation) – Magnetospheric physics (MHD waves and instabilities; plasma waves and instabilities)

scholarly journals Evaluation of neutron induced reactions on 56Fe with CONRAD

2020 ◽  
Vol 239 ◽  
pp. 11005 ◽  
Author(s):  
M. Diakaki ◽  
S. Chen ◽  
G. Noguere ◽  
D. Bernard ◽  
P. Tamagno ◽  
...  
Keyword(s):  
Statistical Model ◽  
Energy Range ◽  
Fast Neutron ◽  
Neutron Energy ◽  
Resonance Region ◽  
Covariance Matrices ◽  
Neutron Energy Range ◽  
Model Calculations ◽  
First Results ◽  
The Continuum

The evaluation of the 56Fe neutron induced reactions is currently ongoing at the CEA-Cadarache using the code CONRAD, with the goal to cover the whole energy range from the Resolved Resonance Region to the continuum and estimate the corresponding uncertainties and covariance matrices. Some first results and issues occurred from this work are presented and discussed here, more specifically on the analysed transmission and capture data in the Resolved Resonance Region, as well as the optical and statistical model calculations in the fast neutron energy range.

scholarly journals Magnetospheric lion roars

2000 ◽  
Vol 18 (4) ◽  
pp. 406-410 ◽  
Author(s):  
W. Baumjohann ◽  
E. Georgescu ◽  
K.-H. Fornacon ◽  
H. U. Auster ◽  
R. A. Treumann ◽  
...  
Keyword(s):  
Sampling Rate ◽  
Cone Angle ◽  
Mhd Waves ◽  
Lower Hybrid ◽  
High Sampling Rate ◽  
Polarized Waves ◽  
Magnetospheric Configuration And Dynamics ◽  
Mhd Waves And Instabilities ◽  
Electron Gyrofrequency ◽  
First Time

Abstract. The Equator-S magnetometer is very sensitive and has a sampling rate normally of 128 Hz. The high sampling rate for the first time allows detection of ELF waves between the ion cyclotron and the lower hybrid frequencies in the equatorial dawnside magnetosphere. The characteristics of these waves are virtually identical to the lion roars typically seen at the bottom of the magnetic troughs of magnetosheath mirror waves. The magnetospheric lion roars are near-monochromatic packets of electron whistler waves lasting for a few wave cycles only, typically 0.2 s. They are right-hand circularly polarized waves with typical amplitudes of 0.5 nT at around one tenth of the electron gyrofrequency. The cone angle between wave vector and ambient field is nearly always smaller than 1°.Key words: Magnetospheric physics (magnetospheric configuration and dynamics; MHD waves and instabilities; plasma waves and instabilities)

scholarly journals Case studies on the dynamics of Pi3 geomagnetic and riometer pulsations during auroral activations

2002 ◽  
Vol 20 (2) ◽  
pp. 151-159 ◽  
Author(s):  
N. G. Kleimenova ◽  
O. V. Kozyreva ◽  
K. Kauristie ◽  
J. Manninen ◽  
A. Ranta
Keyword(s):  
Mhd Waves ◽  
Geomagnetic Pulsations ◽  
Tight Coupling ◽  
Ionospheric Currents ◽  
Particle Precipitation ◽  
Mhd Waves And Instabilities ◽  
Energetic Particle Precipitation ◽  
Particle Intensity ◽  
Auroral Phenomena ◽  
Current Signatures

Abstract. A sequence of three subsequent auroral activations (at 18:10, 19:48 and 20:00 UT) on 9 February 1997 is analysed. The brightenings of optical auroras were collocated with latitudinally localized bursts of pulsating riometer absorption and Pi3 geomagnetic pulsations. In two of the cases, the strongest westward directed electrojet currents and the footpoint of the upward directed field-aligned currents related to the auroral brightening were observed in the same region as the largest amplitude of the pulsations and their polarization changed. In the third case, field-aligned current signatures were present, but not so pronounced that their accurate location could not be defined. In all cases, the spectra of geomagnetic and absorption pulsations were similar. Based on ground-based observations alone, it is difficult to say whether the energetic particle precipitation (riometer absorption) was modulated by the geomagnetic pulsations or whether the geomagnetic pulsations were caused by varying ionospheric currents controlled by the precipitating particle intensity. However, the localized nature of both pulsations of the two different phenomena and their tight coupling with each other seem to support the latter option.Key words. Ionosphere (Particle precipitation) – Magnetospheric physics (auroral phenomena; MHD waves and instabilities)

scholarly journals Modelling the main ionospheric trough using the Electron Density Assimilative Model (EDAM) with assimilated GPS TEC

2018 ◽  
Vol 36 (1) ◽  
pp. 125-138 ◽  
Author(s):  
James A. D. Parker ◽  
S. Eleri Pryse ◽  
Natasha Jackson-Booth ◽  
Rachel A. Buckland
Keyword(s):  
Electron Density ◽  
Large Scale ◽  
Western Europe ◽  
Global Scale ◽  
Electron Content ◽  
Total Electron ◽  
Radio Science ◽  
Ionospheric Physics ◽  
Main Ionospheric Trough ◽  
Plasma Distribution

Abstract. The main ionospheric trough is a large-scale spatial depletion in the electron density distribution at the interface between the high- and mid-latitude ionosphere. In western Europe it appears in early evening, progresses equatorward during the night, and retreats rapidly poleward at dawn. It exhibits substantial day-to-day variability and under conditions of increased geomagnetic activity it moves progressively to lower latitudes. Steep gradients on the trough-walls on either side of the trough minimum, and their variability, can cause problems for radio applications. Numerous studies have sought to characterize and quantify the trough behaviour. The Electron Density Assimilative Model (EDAM) models the ionosphere on a global scale. It assimilates observations into a background ionosphere, the International Reference Ionosphere 2007 (IRI2007), to provide a full 3-D representation of the ionospheric plasma distribution at specified times and days. This current investigation studied the capability of EDAM to model the ionosphere in the region of the main trough. Total electron content (TEC) measurements from 46 GPS stations in western Europe from September to December 2002 were assimilated into EDAM to provide a model of the ionosphere in the trough region. Vertical electron content profiles through the model revealed the trough and the detail of its structure. Statistical results are presented of the latitude of the trough minimum, TEC at the minimum and of other defined parameters that characterize the trough structure. The results are compared with previous observations made with the Navy Ionospheric Monitoring System (NIMS), and reveal the potential of EDAM to model the large-scale structure of the ionosphere. Keywords. Ionosphere (midlatitude ionosphere; modelling and forecasting) – radio science (ionospheric physics)

scholarly journals Ground clutter cancellation in incoherent radars: solutions for EISCAT Svalbard radar

2000 ◽  
Vol 18 (9) ◽  
pp. 1242-1247 ◽  
Author(s):  
T. Turunen ◽  
J. Markkanen ◽  
A. P. van Eyken
Keyword(s):  
Subtraction Method ◽  
Free Electrons ◽  
Simple Manner ◽  
Radio Science ◽  
Ionospheric Physics ◽  
Incoherent Scatter ◽  
Ground Clutter ◽  
Incoherent Scatter Radars ◽  
Instruments And Techniques ◽  
Physics Signal

Abstract. Incoherent scatter radars measure ionosphere parameters using modified Thomson scatter from free electrons in the target (see e.g. Hagfors, 1997). The integrated cross section of the ionospheric scatterers is extremely small and the measurements can easily be disturbed by signals returned by unwanted targets. Ground clutter signals, entering via the antenna side lobes, can render measurements at the nearest target ranges totally impossible. The EISCAT Svalbard Radar (ESR), which started measurements in 1996, suffers from severe ground clutter and the ionosphere cannot be measured in any simple manner at ranges less than about 120–150 km, depending on the modulation employed. If the target and clutter signals have different, and clearly identifiable, properties then, in principle, there are always ways to eliminate the clutter. In incoherent scatter measurements, differences in the coherence times of the wanted and unwanted signals can be used for clutter cancellation. The clutter cancellation must be applied to all modulations, usually alternating codes in modern experiments, used for shorter ranges. Excellent results have been obtained at the ESR using a simple pulse-to-pulse clutter subtraction method, but there are also other possibilities.Key words: Radio science (ionospheric physics; signal processing; instruments and techniques)

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