scholarly journals A Bimodal Model of the Solar Wind Speed

1996 ◽  
Vol 154 ◽  
pp. 87-96
Author(s):  
W.A. Coles
Keyword(s):  
Remote Sensing ◽  
Solar Wind ◽  
Wind Speed ◽  
Solar Wind Velocity ◽  
Solar Wind Speed ◽  
Line Of Sight ◽  
Polar Regions ◽  
The Sun ◽  
High Latitudes ◽  
Bimodal Structure

AbstractUntil the ULYSSES spacecraft reached high latitude, the only means for measuring the solar wind velocity in the polar regions was from radio scattering observations (IPS), and these remain the only way to measure the velocity near the sun. However, IPS, like many remote sensing observations, is a “line-of-sight” integrated measurement. This integration is particularly troublesome when the line-of-sight passes through a fast stream but that stream does not occupy the entire scattering region. Observations from the HELIOS spacecraft have shown that the solar wind has a bimodal character which becomes more pronounced near the sun. Recent observations from ULYSSES have confirmed that this structure is clear at high latitudes even at relatively large solar distances. We have developed a method of separating the fast and slow contributions to an IPS observation which takes advantage of this bimodal structure. In this paper I will describe the technique and its application to IPS observations made using the receiving antennas of the EISCAT incoherent backscatter radar observatory in northern Scandinavia.

scholarly journals The role of aerodynamic drag in dynamics of coronal mass ejections

2008 ◽  
Vol 4 (S257) ◽  
pp. 271-277
Author(s):  
Bojan Vršnak ◽  
Dijana Vrbanec ◽  
Jaša Čalogović ◽  
Tomislav Žic
Keyword(s):  
Solar Wind ◽  
Wind Speed ◽  
Coronal Mass Ejections ◽  
Weather Forecasting ◽  
Aerodynamic Drag ◽  
Interplanetary Space ◽  
Solar Wind Speed ◽  
Standard Form ◽  
The Sun

AbstractDynamics of coronal mass ejections (CMEs) is strongly affected by the interaction of the erupting structure with the ambient magnetoplasma: eruptions that are faster than solar wind transfer the momentum and energy to the wind and generally decelerate, whereas slower ones gain the momentum and accelerate. Such a behavior can be expressed in terms of “aerodynamic” drag. We employ a large sample of CMEs to analyze the relationship between kinematics of CMEs and drag-related parameters, such as ambient solar wind speed and the CME mass. Employing coronagraphic observations it is demonstrated that massive CMEs are less affected by the aerodynamic drag than light ones. On the other hand, in situ measurements are used to inspect the role of the solar wind speed and it is shown that the Sun-Earth transit time is more closely related to the wind speed than to take-off speed of CMEs. These findings are interpreted by analyzing solutions of a simple equation of motion based on the standard form for the drag acceleration. The results show that most of the acceleration/deceleration of CMEs on their way through the interplanetary space takes place close to the Sun, where the ambient plasma density is still high. Implications for the space weather forecasting of CME arrival-times are discussed.

Study of alpha particle properties across rarefaction regions

2021 ◽  
Author(s):  
Tereza Durovcova ◽  
Jana Šafránková ◽  
Zdeněk Němeček
Keyword(s):  
Solar Wind ◽  
Wind Speed ◽  
Alpha Particle ◽  
Solar Wind Speed ◽  
Coronal Holes ◽  
Distribution Functions ◽  
Alpha Particles ◽  
Slow Solar Wind ◽  
The Sun ◽  
Wind Source

<p>Two large-scale interaction regions between the fast solar wind emanating from coronal holes and the slow solar wind coming from streamer belt are usually distinguished. When the fast stream pushes up against the slow solar wind ahead of it, a compressed interaction region that co-rotates with the Sun (CIR) is created. It was already shown that the relative abundance of alpha particles, which usually serve as one of solar wind source identifiers can change within this region. By symmetry, when the fast stream outruns the slow stream, a corotating rarefaction region (CRR) is formed. CRRs are characterized by a monotonic decrease of the solar wind speed, and they are associated with the regions of small longitudinal extent on the Sun. In our study, we use near-Earth measurements complemented by observations at different heliocentric distances, and focus on the behavior of alpha particles in the CRRs because we found that the large variations of the relative helium abundance (AHe) can also be observed there. Unlike in the CIRs, these variations are usually not connected with the solar wind speed and alpha-proton relative drift changes. We thus apply a superposed-epoch analysis of identified CRRs with a motivation to determine the global profile of alpha particle parameters through these regions. Next, we concentrate on the cases with largest AHe variations and investigate whether they can be associated with the changes of the solar wind source region or whether there is a relation between the AHe variations and the non-thermal features in the proton velocity distribution functions like the temperature anisotropy and/or presence of the proton beam.</p>

scholarly journals Forecasting the Ambient Solar Wind with Numerical Models. II. An Adaptive Prediction System for Specifying Solar Wind Speed near the Sun

2020 ◽  
Vol 891 (2) ◽  
pp. 165 ◽  
Author(s):  
Martin A. Reiss ◽  
Peter J. MacNeice ◽  
Karin Muglach ◽  
Charles N. Arge ◽  
Christian Möstl ◽  
...  
Keyword(s):  
Solar Wind ◽  
Wind Speed ◽  
Numerical Models ◽  
Solar Wind Speed ◽  
The Sun ◽  
Prediction System ◽  
Adaptive Prediction ◽  
Ambient Solar Wind

Two-Station Interplanetary Scintillation Measurements of Solar Wind Speed near the Sun Using the X-band Radio Signal of the Nozomi Spacecraft

Solar Physics ◽  
2011 ◽  
Vol 276 (1-2) ◽  
pp. 315-336 ◽  
Author(s):  
M. Tokumaru ◽  
S. Fujimaki ◽  
M. Higashiyama ◽  
A. Yokobe ◽  
T. Ohmi ◽  
...  
Keyword(s):  
Solar Wind ◽  
Wind Speed ◽  
Radio Signal ◽  
Solar Wind Speed ◽  
The Sun ◽  
Interplanetary Scintillation ◽  
X Band

Structure in the Solar Corona from Radio Scintillation Measurements

1996 ◽  
Vol 154 ◽  
pp. 97-104
Author(s):  
Richard Woo
Keyword(s):  
Solar Wind ◽  
Wind Speed ◽  
Recent Progress ◽  
Solar Wind Speed ◽  
Source Region ◽  
Density Fluctuations ◽  
The Sun ◽  
Fine Scale ◽  
Radio Scintillation ◽  
Electron Density Fluctuations

AbstractSince the 1950s, a wide variety of radio observations based on scattering by electron density fluctuations in the solar wind has provided much of our information on density fluctuations and solar wind speed near the source region of the solar wind. This paper reviews recent progress in the understanding of the nature of these density fluctuations and their relationship to features on the Sun. The results include the first measurements of fine-scale structure within coronal streamers and evidence for structure in solar wind speed in the inner corona.

Latitudinal distribution of solar-wind speed from magnetic observations of the Sun

Nature ◽  
1990 ◽  
Vol 347 (6292) ◽  
pp. 439-444 ◽  
Author(s):  
Y-M. Wang ◽  
N. R. Sheeley ◽  
A. G. Nash
Keyword(s):  
Solar Wind ◽  
Wind Speed ◽  
Solar Wind Speed ◽  
The Sun ◽  
Latitudinal Distribution

scholarly journals ANALISIS KONDISI FLUKS ELEKTRON DI SABUK RADIASI ELEKTRON LUAR BERDASARKAN MEDAN MAGNET ANTARPLANET (BZ) DAN KECEPATAN ANGIN MATAHARI (ANALYSIS OF ELECTRON FLUX CONDITION IN OUTER ELECTRON RADIATION BELT BASED ON INTERPLANETARY MAGNETIC FIELD (BZ) AND SOL

2018 ◽  
Vol 15 (1) ◽  
pp. 39
Author(s):  
Siska Filawati
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Wind Speed ◽  
Radiation Belt ◽  
Solar Wind Velocity ◽  
Electron Flux ◽  
Interplanetary Space ◽  
Solar Wind Speed ◽  
Electron Radiation ◽  
Outer Electron

Interplanetary space is a hazard precursor for solar eruption toward earth. The solar eruptions enhance electron flux that can lead to anomalies, shifts, and permanent damage to spacecraft, e.g. satellites. The data used in this paper are interplanetary space data represented by interplanetary magnetic field (Bz) and solar wind speed, as well as Dst and AE indexes as comparison indicating disturbance has reached Earth’s poles and equator during 2011-2012. The method used is to determine the value of maximum and minimum Bz in the year 2011-2012 which is taken five days before and after. Analysis and calculation of correlation is done to data of Bz-electron flux and solar wind velocity-electron flux. Clarification of disturbence in interplanetary space and outer electron radiation belt is using index data Dst and AE indexes are used to clarify interplanetary space and outer electron radiation belt disturbances. The aim of this study is to determine the characteristics of interplanetary space that can increase the electron flux so that the space weather early warning can be done. It was found that the period of electron flux enhancement after decrease and increase of Bz was 2 to 3 days. The electron flux would enhance when interplanetary space was in its normal condition at solar wind speed 500 km/sec and Bz is -5 nT to +5 nT. Electron flux correlation with solar wind velocity was better than with Bz. ABSTRAKKondisi ruang antarplanet merupakan prekursor bahaya erupsi matahari terhadap bumi. Erupsi matahari dapat menyebabkan peningkatan fluks elektron. Tingginya fluks elektron dapat menyebabkan anomali, pergeseran, dan kerusakan permanen pada wahana antariksa, misal satelit. Data yang digunakan pada makalah ini adalah data ruang antarplanet yang diwakili oleh kondisi medan magnet antarplanet (Bz) dan kecepatan angin matahari yang merupakan prekursor peningkatan fluks elektron serta data indeks Dst dan indeks AE sebagai pembanding bahwa gangguan telah mencapai kutub dan ekuator bumi selama rentang waktu 2011-2012. Metode yang digunakan adalah menentukan nilai Bz maksimum dan minimum dalam tahun 2011-2012 yang selanjutnya dari penanggalan data tersebut diambil data lima hari sebelum dan sesudah. Analisis dan perhitungan korelasi dilakukan terhadap data Bz-fluks elektron dan kecepatan angin matahari-fluks elektron. Klarifikasi gangguan yang terjadi di ruang antarplanet dan sabuk radiasi elektron luar menggunakan data indeks Dst dan indeks AE. Tujuan ditulisnya makalah ini adalah untuk mengetahui karakteristik kondisi ruang antarplanet yang dapat meningkatkan fluks elektron agar peringatan dini cuaca antariksa dapat dilakukan. Hasil yang didapatkan adalah waktu yang dibutuhkan fluks elektron setelah terjadi penurunan dan peningkatan Bz adalah 2 hingga 3 hari, fluks elektron akan meningkat saat kondisi ruang antarplanet normal yaitu pada kecepatan 500 km/detik dan Bz -5 nT hingga +5 nT, korelasi fluks elektron dengan kecepatan angin matahari lebih baik dibanding fluks elektron dengan Bz.

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