Coordinated ground-based and Cluster observations of large amplitude global magnetospheric oscillations during a fast solar wind speed interval

Abstract. We present magnetospheric observations of very large amplitude global scale ULF waves, from 9 and 10 December 2000 when the upstream solar wind speed exceeded 600 km/s. We characterise these ULF waves using ground-based magnetometer, radar and optical instrumentation on both the dawn and dusk flanks; we find evidence to support the hypothesis that discrete frequency field line resonances (FLRs) were being driven by magnetospheric waveguide modes. During the early part of this interval, Cluster was on an outbound pass from the northern dusk side magnetospheric lobe into the magnetosheath, local-time conjugate to the Canadian sector. In situ magnetic fluctuations, observed by Cluster FGM, show evidence of quasi-periodic motion of the magnetosheath boundary layer with the same period as the ULF waves seen on the ground. Our observations represent the first simultaneous magnetometer, radar and optical observations of the characteristics of FLRs, and confirm the potential importance of ULF waves for magnetosphere-ionosphere coupling, particularly via the generation and modulation of electron precipitation into the ionosphere. The in situ Cluster measurements support the hypothesis that, during intervals of fast solar wind speed, the Kelvin-Helmholtz instability (KHI) can excite magnetospheric waveguide modes which bathe the flank magnetosphere with discrete frequency ULF wave power and drive large amplitude FLRs. Paper submitted to the special issue devoted to "Cluster: First scientific results", Ann. Geophysicae, 19, 10/11/12, 2001.Key words. Magnetospheric physics (magnetopause, cusp and boundary layers; MHD waves and instabilities; solar wind-magnetosphere interactions)

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Ground-based magnetometer determination of in situ Pc4-5 ULF electric field wave spectra as a function of solar wind speed

Journal of Geophysical Research Atmospheres ◽

10.1029/2011ja017335 ◽

2012 ◽

Vol 117 (A4) ◽

pp. n/a-n/a ◽

Cited By ~ 39

Author(s):

I. Jonathan Rae ◽

Ian R. Mann ◽

Kyle R. Murphy ◽

Louis G. Ozeke ◽

David K. Milling ◽

...

Keyword(s):

Solar Wind ◽

Wind Speed ◽

Electric Field ◽

Solar Wind Speed ◽

Wave Spectra ◽

Field Wave

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What geometrical factors determine the in situ solar wind speed?

Chinese Science Bulletin ◽

10.1007/s11434-011-4965-2 ◽

2012 ◽

Vol 57 (12) ◽

pp. 1409-1414 ◽

Cited By ~ 1

Author(s):

Bo Li ◽

Yao Chen ◽

LiDong Xia

Keyword(s):

Solar Wind ◽

Wind Speed ◽

Solar Wind Speed ◽

Geometrical Factors

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Quantifying the latitudinal representivity of in situ solar wind observations

Journal of Space Weather and Space Climate ◽

10.1051/swsc/2020009 ◽

2020 ◽

Vol 10 ◽

pp. 8 ◽

Cited By ~ 1

Author(s):

Mathew J. Owens ◽

Matthew Lang ◽

Pete Riley ◽

Mike Lockwood ◽

Amos S. Lawless

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Wind Speed ◽

Solar Minimum ◽

Numerical Models ◽

Solar Wind Speed ◽

Cycle Phase ◽

Model State ◽

Fast Wind

Advanced space-weather forecasting relies on the ability to accurately predict near-Earth solar wind conditions. For this purpose, physics-based, global numerical models of the solar wind are initialized with photospheric magnetic field and coronagraph observations, but no further observation constraints are imposed between the upper corona and Earth orbit. Data assimilation (DA) of the available in situ solar wind observations into the models could potentially provide additional constraints, improving solar wind reconstructions, and forecasts. However, in order to effectively combine the model and observations, it is necessary to quantify the error introduced by assuming point measurements are representative of the model state. In particular, the range of heliographic latitudes over which in situ solar wind speed measurements are representative is of primary importance, but particularly difficult to assess from observations alone. In this study we use 40+ years of observation-driven solar wind model results to assess two related properties: the latitudinal representivity error introduced by assuming the solar wind speed measured at a given latitude is the same as that at the heliographic equator, and the range of latitudes over which a solar wind measurement should influence the model state, referred to as the observational localisation. These values are quantified for future use in solar wind DA schemes as a function of solar cycle phase, measurement latitude, and error tolerance. In general, we find that in situ solar wind speed measurements near the ecliptic plane at solar minimum are extremely localised, being similar over only 1° or 2° of latitude. In the uniform polar fast wind above approximately 40° latitude at solar minimum, the latitudinal representivity error drops. At solar maximum, the increased variability of the solar wind speed at high latitudes means that the latitudinal representivity error increases at the poles, though becomes greater in the ecliptic, as long as moderate speed errors can be tolerated. The heliospheric magnetic field and solar wind density and temperature show very similar behaviour.

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Coronal hole evolution from multi-viewpoint data as input for a STEREO solar wind speed persistence model

Journal of Space Weather and Space Climate ◽

10.1051/swsc/2018007 ◽

2018 ◽

Vol 8 ◽

pp. A18 ◽

Cited By ~ 10

Author(s):

Manuela Temmer ◽

Jürgen Hinterreiter ◽

Martin A. Reiss

Keyword(s):

Solar Wind ◽

Wind Speed ◽

High Speed ◽

Solar Wind Speed ◽

Coronal Holes ◽

In Situ Measurements ◽

False Alarms ◽

Wind Speed Profile ◽

Persistence Model

We present a concept study of a solar wind forecasting method for Earth, based on persistence modeling from STEREO in situ measurements combined with multi-viewpoint EUV observational data. By comparing the fractional areas of coronal holes (CHs) extracted from EUV data of STEREO and SoHO/SDO, we perform an uncertainty assessment derived from changes in the CHs and apply those changes to the predicted solar wind speed profile at 1 AU. We evaluate the method for the time period 2008–2012, and compare the results to a persistence model based on ACE in situ measurements and to the STEREO persistence model without implementing the information on CH evolution. Compared to an ACE based persistence model, the performance of the STEREO persistence model which takes into account the evolution of CHs, is able to increase the number of correctly predicted high-speed streams by about 12%, and to decrease the number of missed streams by about 23%, and the number of false alarms by about 19%. However, the added information on CH evolution is not able to deliver more accurate speed values for the forecast than using the STEREO persistence model without CH information which performs better than an ACE based persistence model. Investigating the CH evolution between STEREO and Earth view for varying separation angles over ∼25–140° East of Earth, we derive some relation between expanding CHs and increasing solar wind speed, but a less clear relation for decaying CHs and decreasing solar wind speed. This fact most likely prevents the method from making more precise forecasts. The obtained results support a future L5 mission and show the importance and valuable contribution using multi-viewpoint data.

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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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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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Global Distribution of the Solar Wind Speed Reconstructed from Improved Tomographic Analysis of Interplanetary Scintillation Observations between 1985 and 2019

The Astrophysical Journal ◽

10.3847/1538-4357/ac1862 ◽

2021 ◽

Vol 922 (1) ◽

pp. 73

Author(s):

Munetoshi Tokumaru ◽

Ken’ichi Fujiki ◽

Masayoshi Kojima ◽

Kazumasa Iwai

Keyword(s):

Solar Wind ◽

Wind Speed ◽

Power Index ◽

Solar Wind Speed ◽

Global Distribution ◽

Interplanetary Scintillation ◽

Wind Speeds ◽

In Situ Observations

Abstract Computer-assisted tomography (CAT) for interplanetary scintillation (IPS) observations enables the determination of the global distribution of solar wind speed. We compared solar wind speeds derived from the CAT analysis of IPS observations between 1985 and 2019 with in situ observations conducted by the near-Earth and Ulysses spacecraft. From this comparison, we found that solar wind speeds from the IPS observations for 2009–2019 were systematically higher than the in situ observations, whereas those for the period until 2008 were in good agreement with the in situ observations. Further, we found that the discrepancy between IPS and the in situ observations is improved by changing the power index of the empirical relation between the solar wind speed and density fluctuations. The CAT analysis using an optimal value for the power index determined from the comparison between IPS and in situ observations revealed long-term variations in the solar wind speed distribution over three cycles, leading to a better understanding of the time-varying global heliosphere. We found that polar solar winds become highly anisotropic at the Cycle 24/25 minimum, which is a peculiar aspect of this minimum. The IPS observations showed general agreement with the Parker Solar Probe observations around the perihelion of Orbit 1; this supports the reliability of the CAT analysis. The results of this study suggest that the physical properties of solar wind microturbulence may vary with a long-term decline in the solar activity, which provides important implication on the solar wind acceleration.

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