scholarly journals Kinetic and Hydrodynamic Models of the Solar Wind and Polar Wind: A Focus Group of the Solar-Terrestrial Interactions From Microscale to Global Models (STIMM-2) Workshop; Sinaia, Romania, 13 and 15 June 2007

Eos ◽  
2008 ◽  
Vol 89 (9) ◽  
pp. 86-86 ◽  
Author(s):  
J. F. Lemaire ◽  
M. Echim
Keyword(s):  
Solar Wind ◽  
Focus Group ◽  
Polar Wind ◽  
Hydrodynamic Models ◽  
Global Models

scholarly journals Alfvénic fluctuations in "newborn"' polar solar wind

2005 ◽  
Vol 23 (4) ◽  
pp. 1513-1520 ◽  
Author(s):  
B. Bavassano ◽  
E. Pietropaolo ◽  
R. Bruno
Keyword(s):  
Solar Wind ◽  
Solar Activity ◽  
Solar Maximum ◽  
Activity Cycle ◽  
Residual Energy ◽  
Mhd Waves ◽  
Polar Wind ◽  
Interplanetary Physics ◽  
Low Latitudes ◽  
Comparative Statistical Analysis

Abstract. The 3-D structure of the solar wind is strongly dependent upon the Sun's activity cycle. At low solar activity a bimodal structure is dominant, with a fast and uniform flow at the high latitudes, and slow and variable flows at low latitudes. Around solar maximum, in sharp contrast, variable flows are observed at all latitudes. This last kind of pattern, however, is a relatively short-lived feature, and quite soon after solar maximum the polar wind tends to regain its role. The plasma parameter distributions for these newborn polar flows appear very similar to those typically observed in polar wind at low solar activity. The point addressed here is about polar wind fluctuations. As is well known, the low-solar-activity polar wind is characterized by a strong flow of Alfvénic fluctuations. Does this hold for the new polar flows too? An answer to this question is given here through a comparative statistical analysis on parameters such as total energy, cross helicity, and residual energy, that are of general use to describe the Alfvénic character of fluctuations. Our results indicate that the main features of the Alfvénic fluctuations observed in low-solar-activity polar wind have been quickly recovered in the new polar flows developed shortly after solar maximum. Keywords. Interplanetary physics (MHD waves and turbulence; Sources of the solar wind) – Space plasma physics (Turbulence)

scholarly journals Large-scale velocity fluctuations in polar solar wind

2005 ◽  
Vol 23 (3) ◽  
pp. 1025-1031 ◽  
Author(s):  
B. Bavassano ◽  
R. Bruno ◽  
R. D'Amicis
Keyword(s):  
Solar Wind ◽  
Solar Activity ◽  
High Latitude ◽  
Large Scale ◽  
Activity Cycle ◽  
High Solar Activity ◽  
Time Lags ◽  
Polar Wind ◽  
Frequency Distributions ◽  
Long Range Correlations

Abstract. The 3-D structure of the solar wind varies dramatically along the Sun's activity cycle. In the present paper we focus on some properties of the polar solar wind. This is a fast, teneous, and steady flow (as compared to low-latitude conditions) that fills the high-latitude heliosphere at low solar activity. The polar wind has been extensively investigated by Ulysses, the first spacecraft to perform in-situ measurements in the high-latitude heliosphere. Though the polar wind is quite a uniform flow, fluctuations in its velocity do not appear negligible. A simple way to characterize the solar wind structure is that of performing a multi-scale statistical analysis of the wind velocity differences. The occurrence frequency distributions of velocity differences at time lags from 1 to 1024h and the corresponding values of mean, standard deviation, skewness, and kurtosis have been obtained. A comparison with previous results in ecliptic wind at both low and high solar activity has been performed. It comes out that the kind of trend observed in the distributions for changing scale is the same for the different solar wind regimes. Differences between different flows just have an effect on the values of the distribution moments and the scales at which the transition from non-Gaussian to Gaussian-like behaviours occurs. This is typical of systems in which random fluctuations are mixed to coherent structures of some characteristic size, in other words, systems where long-range correlations cannot be neglected.

Connecting the dots: Multi-point observations for solar wind science and forecasting

2020 ◽  
Author(s):  
Mathew Owens
Keyword(s):  
Remote Sensing ◽  
Solar Wind ◽  
Atmospheric Science ◽  
Dimensional Structure ◽  
Earth Orbit ◽  
Global Models ◽  
3 Dimensional ◽  
Wind Measurements ◽  
Vantage Points ◽  
Connecting The Dots

<p>Atmospheric science and forecasting, concerned with a volume ~10<sup>13</sup> m<sup>3</sup>, is underpinned by an extensive observational network; point measurements at 10k land-based stations, 4k ships and buoys, and around 1k dedicated balloon launches and aircraft; remote sensing from hundreds of radars and 10 dedicated operational satellites providing independent “look directions” through the atmosphere. By comparison, the heliosphere is a vastly under-sampled system. In the ~10<sup>28</sup> m<sup>3</sup> volume contained within Earth orbit, there has been a maximum of 5 simultaneous point measurements and remote sensing from (at most) 3 simultaneous vantage points. This makes it difficult to reliably interpret observations in terms of the 3-dimensional structure and extent of solar wind transients. Solar Orbiter, Parker Solar Probe, STEREO-A and L1 monitors (and a possible future L5 monitor), as well as more limited solar wind measurements from planetary/cometary missions, will shortly provide unprecedented observational coverage and thus a unique opportunity to better understand solar wind transients. Nevertheless, sampling will remain sparse and connecting point observations and interpreting remote sensing observations will remain ambiguous. Global models of the solar wind can aid greatly in this regard. This talk will summarise how observations and models can be best combined to exploit the strengths of both, and what we can learn about solar wind transients.</p>

scholarly journals Compressive fluctuations in high-latitude solar wind

2004 ◽  
Vol 22 (2) ◽  
pp. 689-696 ◽  
Author(s):  
B. Bavassano ◽  
E. Pietropaolo ◽  
R. Bruno
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
High Latitude ◽  
Correlation Coefficients ◽  
Field Measurements ◽  
Solar Wind Plasma ◽  
Ecliptic Plane ◽  
Mhd Waves ◽  
Polar Wind ◽  
Interplanetary Physics

Abstract. Solar wind compressive fluctuations at MHD scales have been extensively studied in the past using data from spacecraft on the ecliptic plane. In the present study, based on plasma and magnetic field measurements by Ulysses, a statistical analysis of the compressive fluctuations observed in the high-latitude solar wind is performed. Data are from the first out-of-ecliptic orbit of Ulysses, when the Sun's activity is low and the high-latitude heliosphere is characterized by the presence of a fast and relatively steady solar wind, the polar wind. Our analysis is based on the computation of hourly-scale correlation coefficients for several pairs of solar wind parameters such as velocity, density, temperature, magnetic field magnitude, and plasma pressures (thermal, magnetic, and total). The behaviour of the fluctuations in terms of their amplitude has been examined, too, and comparisons with the predictions of existing models have been performed. The results support the view that the compressive fluctuations in the polar solar wind are mainly a superposition of MHD compressive modes and of pressure-balanced structures. Nearly-incompressible effects do not seem to play a relevant role. In conclusion, our results about compressive fluctuations in the polar wind do not appear as a break with respect to previous low-latitude observations. However, our study clearly indicates that in a homogeneous environment, as the polar wind, the pressure-balanced fluctuations tend to play a major role. Key words. Interplanetary physics (MHD waves and turbulence; solar wind plasma) – Space plasma physics (turbulence)

scholarly journals The Key Role of Cold Ionospheric Ions As a Source of Hot Magnetospheric Plasma and As a Driver of the Dynamics of Substorms and Storms

2021 ◽  
Vol 8 ◽  
Author(s):  
C. R. Chappell ◽  
A. Glocer ◽  
B. L. Giles ◽  
T. E. Moore ◽  
M. M. Huddleston ◽  
...  
Keyword(s):  
Solar Wind ◽  
Magnetospheric Plasma ◽  
Direct Access ◽  
Polar Wind ◽  
Polar Cusp ◽  
Reconnection Region ◽  
Mhd Modeling ◽  
Warm Plasma ◽  
Gain Access

The solar wind has been seen as the major source of hot magnetospheric plasma since the early 1960’s. More recent theoretical and observational studies have shown that the cold (few eV) polar wind and warmer polar cusp plasma that flow continuously upward from the ionosphere can be a very significant source of ions in the magnetosphere and can become accelerated to the energies characteristic of the plasma sheet, ring current, and warm plasma cloak. Previous studies have also shown the presence of solar wind ions in these magnetospheric regions. These studies are based principally on proxy measurements of the ratios of He++/H+ and the high charge states of O+/H+. The resultant admixture of ionospheric ions and solar wind ions that results has been difficult to quantify, since the dominant H+ ions originating in the ionosphere and solar wind are indistinguishable. The ionospheric ions are already inside the magnetosphere and are filling it from the inside out with direct access from the ionosphere to the center of the magnetotail. The solar wind ions on the other hand must gain access through the outer boundaries of the magnetosphere, filling the magnetosphere from the outside in. These solar wind particles must then diffuse or drift from the flanks of the magnetosphere to the near-midnight reconnection region of the tail which takes more time to reach (hours) than the continuously large outflowing ionospheric polar wind (10’s of min). In this paper we examine the magnetospheric filling using the trajectories of the different ion sources to unravel the intermixing process rather than trying to interpret only the proxy ratios. We compare the timing of the access of the ionospheric and solar wind sources and we use new merged ionosphere-magnetosphere multi-fluid MHD modeling to separate and compare the ionospheric and solar wind H+ source strengths. The rapid access of the initially cold polar wind and warm polar cusp ions flowing down-tail in the lobes into the mid-plane of the magnetotail, suggests that, coupled with a southward turning of the IMF Bz, these ions can play a key triggering role in the onset of substorms and subsequent large storms.

scholarly journals Velocity fluctuations in polar solar wind: a comparison between different solar cycles

2009 ◽  
Vol 27 (2) ◽  
pp. 877-883 ◽  
Author(s):  
B. Bavassano ◽  
R. Bruno ◽  
R. D'Amicis
Keyword(s):  
Solar Wind ◽  
Wind Velocity ◽  
High Latitude ◽  
Coronal Holes ◽  
Dimensional Structure ◽  
Time Lags ◽  
Solar Cycles ◽  
Polar Wind ◽  
Activity Maximum ◽  
Velocity Fluctuations

Abstract. The polar solar wind is a fast, tenuous and steady flow that, with the exception of a relatively short phase around the Sun's activity maximum, fills the high-latitude heliosphere. The polar wind properties have been extensively investigated by Ulysses, the first spacecraft able to perform in-situ measurements in the high-latitude heliosphere. The out-of-ecliptic phases of Ulysses cover about seventeen years. This makes possible to study heliospheric properties at high latitudes in different solar cycles. In the present investigation we focus on hourly- to daily-scale fluctuations of the polar wind velocity. Though the polar wind is a quite uniform flow, fluctuations in its velocity do not appear negligible. A simple way to characterize wind velocity variations is that of performing a multi-scale statistical analysis of the wind velocity differences. Our analysis is based on the computation of velocity differences at different time lags and the evaluation of statistical quantities (mean, standard deviation, skewness, and kurtosis) for the different ensembles. The results clearly show that, though differences exist in the three-dimensional structure of the heliosphere between the investigated solar cycles, the velocity fluctuations in the core of polar coronal holes exhibit essentially unchanged statistical properties.

A comparison of global models for the solar wind interaction with Mars

Icarus ◽  
2010 ◽  
Vol 206 (1) ◽  
pp. 139-151 ◽  
Author(s):  
D. Brain ◽  
S. Barabash ◽  
A. Boesswetter ◽  
S. Bougher ◽  
S. Brecht ◽  
...  
Keyword(s):  
Solar Wind ◽  
Solar Wind Interaction ◽  
Global Models

scholarly journals Cluster observations of near-Earth magnetospheric lobe plasma densities – a statistical study

2008 ◽  
Vol 26 (9) ◽  
pp. 2845-2852 ◽  
Author(s):  
K. R. Svenes ◽  
B. Lybekk ◽  
A. Pedersen ◽  
S. Haaland
Keyword(s):  
Solar Wind ◽  
Solar Cycle ◽  
Geomagnetic Activity ◽  
Source Region ◽  
Wind Condition ◽  
Quiet Time ◽  
Polar Wind ◽  
Spacecraft Potential ◽  
Solar Uv ◽  
Two Parameters

Abstract. The Cluster-mission has enabled a study of the near-Earth magnetospheric lobes throughout the waning part of solar cycle 23. During the first seven years of the mission the satellites crossed this region of space regularly from about July to October. We have obtained new and more accurate plasma densities in this region based on spacecraft potential measurements from the EFW-instrument. The plasma density measurements are found by converting the potential measurements using a functional relationship between these two parameters. Our observations have shown that throughout this period a full two thirds of the measurements were contained in the range 0.007–0.092 cm−3 irrespective of solar wind conditions or geomagnetic activity. In fact, the most probable density encountered was 0.047 cm−3, staying roughly constant throughout the entire observation period. The plasma population in this region seems to reflect an equilibrium situation in which the density is independent of the solar wind condition or geomagnetic activity. However, the high density tail of the population (ne>0.2 cm−3) seemed to decrease with the waning solar cycle. This points to a source region influenced by the diminishing solar UV/EUV-intensity. Noting that the quiet time polar wind has just such a development and that it is magnetically coupled to the lobes, it seems likely to assume that this is a prominent source for the lobe plasma.

Sign in / Sign up

Export Citation Format

Share Document