Statistical study of ULF waves in the magnetotail by THEMIS observations

Abstract. Ultra-low-frequency (ULF) waves are ubiquitous in the magnetosphere. Previous studies mostly focused on ULF waves in the dayside or near-Earth region (with radial distance R<12 RE). In this study, using the data of the Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission during the period from 2008 to 2015, the Pc5–6 ULF waves in the tail region with XGSM∗<0, 8 RE<R<32 RE (mostly on the stretched magnetic field lines) are studied statistically. A total of 1089 azimuthal oscillating events and 566 radial oscillating events were found. The statistical results show that both the azimuthal and radial oscillating events in the magnetotail region (12 RE<R<32 RE) are more frequently observed in the post-midnight region. The frequency decreases with increasing radial distance from Earth for both azimuthal oscillating events (8 RE<R<16 RE) and radial oscillating events (8 RE<R<14 RE), which is consistent with the field line resonances theory. About 52 % of events (including the azimuthal and radial oscillating events) are standing waves in the region of 8–16 RE, while only 2 % are standing waves in the region of 16–32 RE. There is no obvious dawn–dusk asymmetry of ULF wave frequency for events in 8 RE<R<32 RE, which contrasts with the obvious dawn–dusk asymmetry found by previous studies in the inner magnetosphere (4 RE<R<9 RE). An examination for possible statistical relationships between the ULF wave parameters and substorm occurrences is carried out. We find that the wave frequency is higher after the substorm onset than before it, and the frequency differences are more obvious in the midnight region than in the flank region.

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ULF wave activity during the 2003 Halloween superstorm: multipoint observations from CHAMP, Cluster and Geotail missions

Annales Geophysicae ◽

10.5194/angeo-30-1751-2012 ◽

2012 ◽

Vol 30 (12) ◽

pp. 1751-1768 ◽

Cited By ~ 24

Author(s):

G. Balasis ◽

I. A. Daglis ◽

E. Zesta ◽

C. Papadimitriou ◽

M. Georgiou ◽

...

Keyword(s):

Low Frequency ◽

Wave Activity ◽

Low Earth Orbit ◽

Topside Ionosphere ◽

Ulf Waves ◽

Satellite Mission ◽

Ulf Wave ◽

Activity Frequency ◽

Field Lines ◽

First Time

Abstract. We examine data from a topside ionosphere and two magnetospheric missions (CHAMP, Cluster and Geotail) for signatures of ultra low frequency (ULF) waves during the exceptional 2003 Halloween geospace magnetic storm, when Dst reached ~−380 nT. We use a suite of wavelet-based algorithms, which are a subset of a tool that is being developed for the analysis of multi-instrument multi-satellite and ground-based observations to identify ULF waves and investigate their properties. Starting from the region of topside ionosphere, we first present three clear and strong signatures of Pc3 ULF wave activity (frequency 15–100 mHz) in CHAMP tracks. We then expand these three time intervals for purposes of comparison between CHAMP, Cluster and Geotail Pc3 observations but also to be able to search for Pc4–5 wave signatures (frequency 1–10 mHz) into Cluster and Geotail measurements in order to have a more complete picture of the ULF wave occurrence during the storm. Due to the fast motion through field lines in a low Earth orbit (LEO) we are able to reliably detect Pc3 (but not Pc4–5) waves from CHAMP. This is the first time, to our knowledge, that ULF wave observations from a topside ionosphere mission are compared to ULF wave observations from magnetospheric missions. Our study provides evidence for the occurrence of a number of prominent ULF wave events in the Pc3 and Pc4–5 bands during the storm and offers a platform to study the wave evolution from high altitudes to LEO. The ULF wave analysis methods presented here can be applied to observations from the upcoming Swarm multi-satellite mission of ESA, which is anticipated to enable joint studies with the Cluster mission.

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Quasiperiodic ULF-pulsations in Saturn's magnetosphere

Annales Geophysicae ◽

10.5194/angeo-27-885-2009 ◽

2009 ◽

Vol 27 (2) ◽

pp. 885-894 ◽

Cited By ~ 5

Author(s):

G. Kleindienst ◽

K.-H. Glassmeier ◽

S. Simon ◽

M. K. Dougherty ◽

N. Krupp

Keyword(s):

Magnetic Field ◽

Local Time ◽

Large Scale ◽

Rotation Period ◽

Low Frequency ◽

Radial Distance ◽

Main Magnetic Field ◽

Ulf Wave ◽

Field Investigations ◽

Magnetosphere Of Saturn

Abstract. Recent magnetic field investigations made onboard the Cassini spacecraft in the magnetosphere of Saturn show the existence of a variety of ultra low frequency plasma waves. Their frequencies suggest that they are presumably not eigenoscillations of the entire magnetospheric system, but excitations confined to selected regions of the magnetosphere. While the main magnetic field of Saturn shows a distinct large scale modulation of approximately 2 nT with a periodicity close to Saturn's rotation period, these ULF pulsations are less obvious superimposed oscillations with an amplitude generally not larger than 3 nT and show a package-like structure. We have analyzed these wave packages and found that they are correlated to a certain extent with the large scale modulation of the main magnetic field. The spatial localization of the ULF wave activity is represented with respect to local time and Kronographic coordinates. For this purpose we introduce a method to correct the Kronographic longitude with respect to a rotation period different from its IAU definition. The observed wave packages occur in all magnetospheric regions independent of local time, elevation, or radial distance. Independent of the longitude correction applied the wave packages do not occur in an accentuated Kronographic longitude range, which implies that the waves are not excited or confined in the same selected longitude ranges at all times or that their lifetime leads to a variable phase with respect to the longitudes where they have been exited.

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The Pulsating Magnetosphere at Jupiter

10.5194/egusphere-egu2020-3651 ◽

2020 ◽

Author(s):

Harry Manners ◽

Adam Masters

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Dynamic Pressure ◽

Wave Spectrum ◽

Low Frequency ◽

Global Scale ◽

Wave Activity ◽

Ulf Waves ◽

Ulf Wave ◽

Wide Range

The magnetosphere of Jupiter is the largest planetary magnetosphere in the solar system, and plays host to internal dynamics that remain, in many ways, mysterious. Prominent among these mysteries are the ultra-low-frequency (ULF) pulses ubiquitous in this system. Pulsations in the electromagnetic emissions, magnetic field and flux of energetic particles have been observed for decades, with little to indicate the source mechanism. While ULF waves have been observed in the magnetospheres of all the magnetized planets, the magnetospheric environment at Jupiter seems particularly conducive to the emergence of ULF waves over a wide range of periods (1-100+ minutes). This is mainly due to the high variability of the system on a global scale: internal plasma sources and a powerful intrinsic magnetic field produce a highly-compressible magnetospheric cavity, which can be reduced to a size significantly smaller than its nominal expanded state by variations in the dynamic pressure of the solar wind. Compressive fronts in the solar wind, turbulent surface interactions on the magnetopause and internal plasma processes can also all lead to ULF wave activity inside the magnetosphere.To gain the first comprehensive view of ULF waves in the Jovian system, we have performed a heritage survey of magnetic field data measured by six spacecraft that visited the magnetosphere (Galileo, Ulysses, Voyager 1 & 2 and Pioneer 10 & 11). We found several-hundred wave events consisting of wave packets parallel or transverse to the mean magnetic field, interpreted as fast-mode or Alfv&#233;nic MHD wave activity, respectively. Parallel and transverse events were often coincident in space and time, which may be evidence of global Alfv&#233;nic resonances of the magnetic field known as field-line-resonances. We found that 15-, 30- and 40-minute periods dominate the Jovian ULF wave spectrum, in agreement with the dominant &#8220;magic frequencies&#8221; often reported in existing literature.We will discuss potential driving mechanisms as informed by the results of the heritage survey, how this in turn affects our understanding of energy transfer in the magnetosphere, and potential investigations to be made using data from the JUNO spacecraft. We will also discuss the potential for multiple resonant cavities, and how the resonance modes of the Jovian magnetosphere may differ from those of the other magnetized planets.

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Modulation of radio frequency signals by ULF waves

Annales Geophysicae ◽

10.5194/angeo-25-1113-2007 ◽

2007 ◽

Vol 25 (5) ◽

pp. 1113-1124 ◽

Cited By ~ 10

Author(s):

C. L. Waters ◽

T. K. Yeoman ◽

M. D. Sciffer ◽

P. Ponomarenko ◽

D. M. Wright

Keyword(s):

Spatial Structure ◽

Radio Frequency ◽

Wave Energy ◽

Ionospheric Plasma ◽

Low Frequency ◽

Radar Data ◽

Hf Radar ◽

Ulf Waves ◽

Ulf Wave ◽

Magnetometer Arrays

Abstract. The ionospheric plasma is continually perturbed by ultra-low frequency (ULF; 1–100 mHz) plasma waves that are incident from the magnetosphere. In this paper we present a combined experimental and modeling study of the variation in radio frequency of signals propagating in the ionosphere due to the interaction of ULF wave energy with the ionospheric plasma. Modeling the interaction shows that the magnitude of the ULF wave electric field, e, and the geomagnetic field, B0, giving an e×B0 drift, is the dominant mechanism for changing the radio frequency. We also show how data from high frequency (HF) Doppler sounders can be combined with HF radar data to provide details of the spatial structure of ULF wave energy in the ionosphere. Due to spatial averaging effects, the spatial structure of ULF waves measured in the ionosphere may be quite different to that obtained using ground based magnetometer arrays. The ULF wave spatial structure is shown to be a critical parameter that determines how ULF wave effects alter the frequency of HF signals propagating through the ionosphere.

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A numerical model to investigate the polarisation azimuth of ULF waves through an ionosphere with oblique magnetic fields

Annales Geophysicae ◽

10.5194/angeo-23-3457-2005 ◽

2005 ◽

Vol 23 (11) ◽

pp. 3457-3471 ◽

Cited By ~ 23

Author(s):

M. D. Sciffer ◽

C. L. Waters ◽

F. W. Menk

Keyword(s):

Magnetic Fields ◽

Low Frequency ◽

Wave Mode ◽

Ulf Waves ◽

High Latitudes ◽

Wave Fields ◽

One Dimensional ◽

Ulf Wave ◽

Dip Angle ◽

Ground Wave

Abstract. A one dimensional, computational model for the propagation of ultra low frequency (ULF; 1-100 mHz) wave fields from the Earth's magnetosphere through the ionosphere, atmosphere and into the ground is presented. The model is formulated to include solutions for high latitudes where the Earth's magnetic field, (B0), is near vertical and for oblique magnetic fields applicable at lower latitudes. The model is used to investigate the wave polarisation azimuth in the magnetosphere compared with the ground wave fields, as a function of the dip angle of B0. We find that for typical ULF wave scale sizes, a 90° rotation of the wave polarisation azimuth from the magnetosphere to the ground occurs at high latitudes. However, this effect does not necessarily occur at lower latitudes in all cases. We show that the degree to which the wave polarisation azimuth rotates critically depends on the properties of the compressional ULF wave mode.

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

Indian Journal of Science and Technology ◽

10.17485/ijst/v14i12.2317 ◽

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

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The magnetospheric interactions of predicted ULF wave power

10.5194/egusphere-egu21-15528 ◽

2021 ◽

Author(s):

Sarah Bentley ◽

Rhys Thompson ◽

Clare Watt ◽

Jennifer Stout ◽

Teo Bloch

Keyword(s):

Solar Wind ◽

Radiation Belt ◽

Internal State ◽

Low Frequency ◽

Ulf Waves ◽

Wave Power ◽

Ulf Wave ◽

Radiation Belt Electrons ◽

Spatial Parameters ◽

The Given

We present and analyse a freely-available model of the power found in ultra-low frequency waves (ULF, 1-15 mHz) throughout Earth&#8217;s magnetosphere. Predictions can be used to test our understanding of magnetospheric dynamics, while accurate models of these waves are required to characterise the energisation and transport of radiation belt electrons in space weather.This model is constructed using decision tree ensembles, which iteratively partition the given parameter space into variable size bins. Wave power is determined by physical driving parameters (e.g. solar wind properties) and spatial parameters of interest (magnetic local time MLT, magnetic latitude and frequency). As a parameterised model, there is no guarantee that individual physical processes can be extracted and analysed. However, by iteratively considering smaller scale driving processes, we identify predominant wave drivers and find that solar wind driving of ULF waves are moderated by internal magnetospheric conditions. Significant remaining uncertainty occurs with mild solar wind driving, suggesting that the internal state of the magnetosphere should be included in future.Models such as this may be used to create global magnetospheric &#8220;maps&#8221; of predicted wave power which may then be used to create radial diffusion coefficients determining the effect of ULF waves on radiation belt electrons.

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Statistical study of ULF waves in the magnetotail by THEMIS observations

10.5194/angeo-2018-39 ◽

2018 ◽

Author(s):

Shuai Zhang ◽

Anmin Tian ◽

Quanqi Shi ◽

Hanlin Li ◽

Alexander W. Degeling ◽

...

Keyword(s):

Statistical Study ◽

Low Frequency ◽

Radial Distance ◽

Ulf Waves

Abstract. Ultra-low frequency (ULF) waves are ubiquitous in the magnetosphere. Previous studies mostly focused on ULF waves in the dayside or near-earth region (with radial distance R

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Resonant ULF absorption at storm time conditions

Solnechno-Zemnaya Fizika ◽

10.12737/21428 ◽

2017 ◽

Vol 3 (1) ◽

pp. 79-87 ◽

Cited By ~ 1

Author(s):

Владимир Бадин ◽

Vladimir Badin

Keyword(s):

Magnetic Field ◽

Variational Analysis ◽

Spectral Power ◽

Low Frequency ◽

Resonant Absorption ◽

Ulf Waves ◽

Doppler Signals ◽

Doppler Data ◽

High Latitude Ionosphere ◽

Field Lines

The work deals with ULF radar observations of the high-latitude ionosphere. Doppler data from the Norwegian STARE instrument are analyzed for the moderate magnetic storm observed on December 31, 1999–January 01, 2000. Upon averaging the Doppler signals along radar beams, the spectral power of signals is determined for each beam as a function of frequency ranging from 1 to 10 mHz. Sharp drops (about 10 dB) of spectral powers with frequency are found for all radar beams. A variational analysis of spectral powers is carried out by least squares, with power drops being modeled by stepwise profiles constructed of mean spectral powers preceding and succeeding the drops. Using this variational analysis, the frequency of the power drop is determined for each radar beam. Being averaged over all beams, this frequency is 4.8±0.5 mHz. The results obtained are interpreted as resonant absorption of ultra-low-frequency (ULF) waves occurring on eigenfrequencies of magnetic field lines over wave propagation from the magnetopause deep into the magnetosphere.

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ULF wave transmission across collisionless shocks: 2.5D local hybrid simulations

10.5194/egusphere-egu21-7970 ◽

2021 ◽

Author(s):

Primož Kajdič ◽

Yann Pfau-Kempf ◽

Lucile Turc ◽

Andrew Dimmock ◽

Minna Palmroth

Keyword(s):

Magnetic Field ◽

Low Frequency ◽

Simulation Models ◽

Ulf Waves ◽

Collisionless Shocks ◽

Ulf Wave ◽

Field Fluctuations ◽

Fourier Spectra ◽

The Waves ◽

Upstream Waves

We study the interaction of upstream ultra-low frequency (ULF) waves with collisionless shocks by analyzing the outputs of eleven 2.5D local hybrid simulation models. Our simulated shocks have Alfv&#233;nic Mach numbers between 4.29-7.42 and their &#952;BN angles are 15&#186;, 30&#186;, 45&#186; and 50&#186;. Thus all are quasi-parallel or marginally quasi-perpendicular shocks. Upstream of all of the shocks the ULF wave foreshock develops. It is populated by transverse and compressive ULF magnetic field fluctuations that propagate upstream in the rest frame of upstream plasma. We show that the properties of the upstream waves reflect on the properties of the shock ripples. We also show that due to these ripples, as different portions of upstream waves reach the shocks, they encounter shock sections with different properties, such as the downstream magnetic field and the orientation of the local shock normals. This means that the waves are not simply transmitted into the downstream region but are heavily processed by the shocks. The identity of upstream fluctuations is largely lost, since the downstream fluctuations do not resemble the upstream waves in their shape, waveform extension, orientation nor in their wavelength. However some features are conserved. For example, the Fourier spectra of upstream waves present a bump or flattening at wavelengths corresponding to those of the upstream ULF waves. Most of the corresponding compressive downstream spectra also exhibit these features, while transverse downstream spectra are largely featureless.

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