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

2012 ◽  
Vol 117 (A4) ◽  
pp. n/a-n/a ◽  
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

scholarly journals What geometrical factors determine the in situ solar wind speed?

2012 ◽  
Vol 57 (12) ◽  
pp. 1409-1414 ◽  
Author(s):  
Bo Li ◽  
Yao Chen ◽  
LiDong Xia
Keyword(s):  
Solar Wind ◽  
Wind Speed ◽  
Solar Wind Speed ◽  
Geometrical Factors

scholarly journals Quantifying the latitudinal representivity of in situ solar wind observations

2020 ◽  
Vol 10 ◽  
pp. 8 ◽  
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.

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

2018 ◽  
Vol 8 ◽  
pp. A18 ◽  
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.

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

2002 ◽  
Vol 20 (4) ◽  
pp. 405-426 ◽  
Author(s):  
I. R. Mann ◽  
I. Voronkov ◽  
M. Dunlop ◽  
E. Donovan ◽  
T. K. Yeoman ◽  
...  
Keyword(s):  
Solar Wind ◽  
Wind Speed ◽  
Large Amplitude ◽  
Solar Wind Speed ◽  
Mhd Waves ◽  
Ulf Waves ◽  
Fast Solar Wind ◽  
Discrete Frequency ◽  
Waveguide Modes

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)

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

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.

Solar wind speed within 20RSof the Sun estimated from limb coronal mass ejections

2006 ◽  
Vol 111 (A1) ◽  
Author(s):  
Tomoko Nakagawa ◽  
Nat Gopalswamy ◽  
Seiji Yashiro
Keyword(s):  
Solar Wind ◽  
Wind Speed ◽  
Coronal Mass Ejections ◽  
Solar Wind Speed ◽  
The Sun

Determination of the Internal Electric Field in the Electrooptic Active Layer of Multilayer Polymer Stacks

1997 ◽  
Vol 488 ◽  
Author(s):  
S. Grossmann ◽  
T. Weyrauch ◽  
W. Haase
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Time Dependent ◽  
Polymer Interfaces ◽  
Internal Electric Field ◽  
Inhomogeneous Distribution ◽  
Time Dependent Behaviour ◽  
Dependent Behaviour

AbstractWe report on a method to investigate the inhomogeneous distribution of an electric dc field in multilayer polymer stacks. In situ electroabsorption (EA) measurements are applied in order to estimate the local electric fields in double layer polymer films. The observed time dependent behaviour is compared with a model equivalent circuit. The results indicate that besides the relation of ohmic resistivities and capacities of the different polymer layers in the investigated systems also the influence of the electric properties of polymer/electrode and polymer/polymer interfaces must be considered.

Coronal density and the solar wind speed at all latitudes

1981 ◽  
Vol 86 (A11) ◽  
pp. 8869 ◽  
Author(s):  
D. G. Sime ◽  
B. J. Rickett
Keyword(s):  
Solar Wind ◽  
Wind Speed ◽  
Solar Wind Speed ◽  
Coronal Density
Sign in / Sign up

Export Citation Format

Share Document