Solar cycle evolution of ULF wave power in solar wind and on ground

The solar cycle evolution of the ultra-low frequency (ULF) power was studied in solar wind and on ground. We aim finding out how the ULF power in interplanetary and on ground magnetic field evolves over the solar cycle 23 (SC23) and how well do they follow each other in monthly time scales. The hourly power of the ULF waves was computed in the Pc5 frequency range 2–7 mHz for years 1998–2008. The highest wave power in SC23 is found to occur in late 2003 and the lowest at the solar minimum. Ground ULF power follows the IMF power and solar wind speed, particularly well during declining phase. The ULF power in winter exceeds the ULF power in other seasons during the declining phase of SC23, while equinoxes dominate in the ascending phase and the solar maximum. The ground ULF power was found to rise with magnetic latitude from 54° to 73°, after which Pc5 power decreases towards the polar cap. The Pc5 power in the auroral zone is larger in the nightside than the dayside due to substorm activity implying that magnetotail processes are an important contributor to the nightside ULF power.

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Correlations between ULF wave power, solar wind speed, and relativistic electron flux in the magnetosphere: solar cycle dependence

Journal of Atmospheric and Solar-Terrestrial Physics ◽

10.1016/j.jastp.2003.10.002 ◽

2004 ◽

Vol 66 (2) ◽

pp. 187-198 ◽

Cited By ~ 80

Author(s):

I.R. Mann ◽

T.P. O'Brien ◽

D.K. Milling

Keyword(s):

Solar Wind ◽

Solar Cycle ◽

Wind Speed ◽

Relativistic Electron ◽

Electron Flux ◽

Solar Wind Speed ◽

Wave Power ◽

Ulf Wave ◽

Cycle Dependence

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The influence of solar wind variability on magnetospheric ULF wave power

Annales Geophysicae ◽

10.5194/angeo-33-697-2015 ◽

2015 ◽

Vol 33 (6) ◽

pp. 697-701 ◽

Cited By ~ 3

Author(s):

D. Pokhotelov ◽

I. J. Rae ◽

K. R. Murphy ◽

I. R. Mann

Keyword(s):

Solar Wind ◽

Dynamic Properties ◽

Solar Wind Speed ◽

Low Frequency ◽

Wave Power ◽

Ion Temperature ◽

Ulf Wave ◽

Wind Variability ◽

Resonant Interactions ◽

Solar Wind Parameters

Abstract. Magnetospheric ultra-low frequency (ULF) oscillations in the Pc 4–5 frequency range play an important role in the dynamics of Earth's radiation belts, both by enhancing the radial diffusion through incoherent interactions and through the coherent drift-resonant interactions with trapped radiation belt electrons. The statistical distributions of magnetospheric ULF wave power are known to be strongly dependent on solar wind parameters such as solar wind speed and interplanetary magnetic field (IMF) orientation. Statistical characterisation of ULF wave power in the magnetosphere traditionally relies on average solar wind–IMF conditions over a specific time period. In this brief report, we perform an alternative characterisation of the solar wind influence on magnetospheric ULF wave activity through the characterisation of the solar wind driver by its variability using the standard deviation of solar wind parameters rather than a simple time average. We present a statistical study of nearly one solar cycle (1996–2004) of geosynchronous observations of magnetic ULF wave power and find that there is significant variation in ULF wave powers as a function of the dynamic properties of the solar wind. In particular, we find that the variability in IMF vector, rather than variabilities in other parameters (solar wind density, bulk velocity and ion temperature), plays the strongest role in controlling geosynchronous ULF power. We conclude that, although time-averaged bulk properties of the solar wind are a key factor in driving ULF powers in the magnetosphere, the solar wind variability can be an important contributor as well. This highlights the potential importance of including solar wind variability especially in studies of ULF wave dynamics in order to assess the efficiency of solar wind–magnetosphere coupling.

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Low frequency geomagnetic field variations at Dome C (Antarctica)

Annales Geophysicae ◽

10.5194/angeo-21-923-2003 ◽

2003 ◽

Vol 21 (4) ◽

pp. 923-932 ◽

Cited By ~ 5

Author(s):

S. Lepidi ◽

L. Cafarella ◽

P. Francia ◽

A. Meloni ◽

P. Palangio ◽

...

Keyword(s):

Solar Wind ◽

Wind Speed ◽

Geomagnetic Field ◽

Solar Wind Speed ◽

Low Frequency ◽

Mhd Waves ◽

Polar Cap ◽

Ionospheric Currents ◽

Terra Nova Bay ◽

Terra Nova

Abstract. We conduct an analysis of the geomagnetic field variations recorded at the new Antarctic station Dome C, located very close to the geomagnetic pole, which has been operating for approximately one month during the 1999–2000 campaign. We also perform a comparison with simultaneous measurements at the Italian Antarctic station Terra Nova Bay, in order to investigate the spatial extension of the phenomena observed at very high latitude. Our results show that between the two stations the daily variation is similar and the fluctuations with f ~ 1 mHz are coherent, provided that in both cases the comparison is made between geographically oriented components, suggesting that ionospheric currents related to the geographic position, more than field-aligned currents, are responsible for the lowest frequency variations; conversely, higher frequency (Pc5) fluctuations are substantially decoupled between the two stations. We also found that at Dome C the fluctuation power in the 0.55–6.7 mHz frequency band is well related with the solar wind speed during the whole day and that at Terra Nova Bay the correlation is also high, except around local geomagnetic noon, when the station approaches the polar cusp. These results indicate that the solar wind speed control of the geomagnetic field fluctuation power is very strict in the polar cap and less important close to the polar cusp.Key words. Magnetospheric physics (MHD waves and instabilities; Polar cap phenomena; Solar wind-magnetosphere interactions)

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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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Ground-based Pc5 ULF wave power: Solar wind speed and MLT dependence

Journal of Atmospheric and Solar-Terrestrial Physics ◽

10.1016/j.jastp.2008.12.004 ◽

2009 ◽

Vol 71 (10-11) ◽

pp. 1082-1092 ◽

Cited By ~ 33

Author(s):

D.M. Pahud ◽

I.J. Rae ◽

I.R. Mann ◽

K.R. Murphy ◽

V. Amalraj

Keyword(s):

Solar Wind ◽

Wind Speed ◽

Solar Wind Speed ◽

Wave Power ◽

Ulf Wave

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Understanding the controlling factors of Ultra-Low Frequency waves and their penetration during geomagnetic storms

10.5194/egusphere-egu2020-11063 ◽

2020 ◽

Author(s):

Jonathan Rae ◽

Kyle Murphy ◽

Clare Watt ◽

Jasmine Sandhu ◽

Samuel Wharton ◽

...

Keyword(s):

Solar Wind ◽

Radiation Belt ◽

Ring Current ◽

Geomagnetic Storms ◽

Particle Interaction ◽

Low Frequency ◽

Controlling Factors ◽

Wave Power ◽

Inner Magnetosphere ◽

Ulf Wave

Wave-particle interactions play a key role in radiation belt dynamics. Traditionally, Ultra-Low Frequency (ULF) wave-particle interaction is parameterised statistically by a small number of controlling factors for given solar wind driving conditions or geomagnetic activity levels. Here, we investigate solar wind driving of ultra-low frequency (ULF) wave power and the role of the magnetosphere in screening that power from penetrating deep into the inner magnetosphere. We demonstrate that, during enhanced ring current intensity, the Alfv&#233;n continuum plummets, allowing lower frequency waves to penetrate deeper into the magnetosphere than during quiet periods. With this penetration, ULF wave power is able to accumulate closer to the Earth than characterised by statistical models. During periods of enhanced solar wind driving such as coronal mass ejection driven storms, where ring current intensities maximise, the observed penetration provides a simple physics-based reason for why storm-time ULF wave power is different compared to non-storm time waves. We demonstrate statistically that the ring current plays a pivotal role in allowing ULF wave energy to access the inner magnetosphere and show a new parameterisation of ULF wave power for radiation belt research purposes that is specifically tuned for geomagnetic storms.

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Semiannual variation of Pc5 ultra-low frequency (ULF) waves and relativistic electrons over two solar cycles of observations: comparison with predictions of the classical hypotheses

Annales Geophysicae ◽

10.5194/angeo-38-953-2020 ◽

2020 ◽

Vol 38 (5) ◽

pp. 953-968

Author(s):

Facundo L. Poblet ◽

Francisco Azpilicueta ◽

Hing-Lan Lam

Keyword(s):

Low Frequency ◽

Auroral Zone ◽

Least Square ◽

Wave Power ◽

Relativistic Electrons ◽

Functional Dependencies ◽

Solar Cycles ◽

Superposed Epoch Analysis ◽

Ulf Wave ◽

Semiannual Variation

Abstract. Pc5 ULF (ultra-low frequency) waves can energize electrons to relativistic energies of >2 MeV in geostationary orbits. Enhanced fluxes of such electrons can induce operational anomalies in geostationary satellites. The variations of the two quantities in timescales ranging from days to solar cycles are thus of interest in gauging their space weather effects over different time frames. In this study, we present a statistical analysis of two 11-year solar cycles (cycles 22 and 23) of data comprising the daily relativistic electron fluence observed by Geostationary Environment Satellites (GOESs) and daily Pc5 ULF wave power derived from auroral zone magnetic observatories in Canada. First, an autocorrelation analysis is carried out, which indicates a 27 d periodicity in both parameters for all solar phases, and such a periodicity is most pronounced in the declining and late declining phase. Also, a 9 and 13 d periodicity are seen in some years. Then, a superposed epoch analysis is performed to scrutinize semiannual variation (SAV), which shows that fluence near the equinoxes is 1 order of magnitude higher than near solstices, and Pc5 ULF wave power is 0.5 orders of magnitude higher near the equinoxes than near the solstices. We then evaluate three possible SAV mechanisms (which are based on the axial, equinoctial, and Russell and McPherron effect) to determine which one can best explain the observations. Correlation of the profiles of the observational curves with those of the angles that control each of the SAV mechanisms suggests that the equinoctial mechanism may be responsible for the SAV of electron fluence, while both the equinoctial and the Russell and McPherron mechanisms are important for the SAV of Pc5 ULF wave power. Comparable results are obtained when using functional dependencies of the main angles instead of the angles mentioned above. Lastly, superposed curves of fluence and Pc5 ULF wave power were used to calculate least-square fits with a fixed semiannual period. Comparison of the maxima and minima of the fits with those predicted by the three mechanisms shows that the equinoctial effect better estimates the maxima and minima of the SAV in fluence while for the SAV in Pc5 ULF wave power the equinoctial and Russell and McPherron mechanisms predict one maximum and one minimum each.

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Foreshock wave transmission into the magnetosheath and magnetosphere: results from global hybrid-Vlasov simulations

10.5194/egusphere-egu21-7255 ◽

2021 ◽

Author(s):

Lucile Turc ◽

Markus Battarbee ◽

Urs Ganse ◽

Andreas Johlander ◽

Yann Pfau-Kempf ◽

...

Keyword(s):

Solar Wind ◽

Mach Number ◽

Cone Angle ◽

Low Frequency ◽

Compressional Wave ◽

Wave Transmission ◽

Wave Power ◽

Solar Wind Flow ◽

Magnetic Pulsations ◽

Wave Properties

The foreshock, extending upstream of the quasi-parallel shock and populated with shock-reflected particles, is home to intense wave activity in the ultra-low frequency range. The most commonly observed of these waves are the &#8220;30 s&#8221; waves, fast magnetosonic waves propagating sunward in the plasma rest frame, but carried earthward by the faster solar wind flow. These waves are thought to be the main source of Pc3 magnetic pulsations (10 &#8211; 45 s) in the dayside magnetosphere. A handful of case studies with suitable spacecraft conjunctions have allowed simultaneous investigations of the wave properties in different geophysical regions, but the global picture of the wave transmission from the foreshock through the magnetosheath into the magnetosphere is still not known. In this work, we use global simulations performed with the hybrid-Vlasov model Vlasiator to study the Pc3 wave properties in the foreshock, magnetosheath and magnetosphere for different solar wind conditions. We find that in all three regions the wave power peaks at higher frequencies when the interplanetary magnetic field strength is larger, consistent with previous studies. While the transverse wave power decreases with decreasing Alfv&#233;n Mach number in the foreshock, the compressional wave power shows little variation. In contrast, in the magnetosheath and the magnetosphere, the compressional wave power decreases with decreasing Mach number. Inside the magnetosphere, the distribution of wave power varies with the IMF cone angle. We discuss the implications of these results for the propagation of foreshock waves across the different geophysical regions, and in particular their transmission through the bow shock.

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Extremely low geomagnetic activity during the recent deep solar cycle minimum

Proceedings of the International Astronomical Union ◽

10.1017/s174392131200484x ◽

2011 ◽

Vol 7 (S286) ◽

pp. 200-209 ◽

Cited By ~ 12

Author(s):

E. Echer ◽

B. T. Tsurutani ◽

W. D. Gonzalez

Keyword(s):

Solar Wind ◽

Solar Cycle ◽

Geomagnetic Activity ◽

Solar Minimum ◽

Solar Wind Speed ◽

Sunspot Cycle ◽

Cycle Minimum ◽

Current Minimum ◽

Solar Wind Parameters ◽

Xix Century

AbstractThe recent solar minimum (2008-2009) was extreme in several aspects: the sunspot number, Rz, interplanetary magnetic field (IMF) magnitude Bo and solar wind speed Vsw were the lowest during the space era. Furthermore, the variance of the IMF southward Bz component was low. As a consequence of these exceedingly low solar wind parameters, there was a minimum in the energy transfer from solar wind to the magnetosphere, and the geomagnetic activity ap index reached extremely low levels. The minimum in geomagnetic activity was delayed in relation to sunspot cycle minimum. We compare the solar wind and geomagnetic activity observed in this recent minimum with previous solar cycle values during the space era (1964-2010). Moreover, the geomagnetic activity conditions during the current minimum are compared with long term variability during the period of available geomagnetic observations. The extremely low geomagnetic activity observed in this solar minimum was previously recorded only at the end of XIX century and at the beginning of the XX century, and this might be related to the Gleissberg (80-100 years) solar cycle.

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