On acceleration of &lt;1 MeV/n He ions in the corotating compression regions near 1 AU: STEREO observations

Abstract. Observations of multi-MeV corotating interaction region (CIR) ions are in general consistent with models of CIR shock acceleration and transport. The presence of suprathermal particles near 1 AU in unshocked compression regions is not adequately explained. Nonetheless, more recent works demonstrate that unshocked compression regions associated with CIRs near 1 AU could energize particles. In the energy range from ~0.1 to ~1 MeV/n we investigate CIR events observed in 2007–2008 by the STEREO A and B spacecraft. We treat the predictions of compression acceleration by comparing the observed ion intensities with the model parameters. These observations show that the ion intensity in CIR events with in-situ reverse shock is well organized by the parameters which characterize the compression region itself, like compression width, solar wind speed gradients and the total pressure. In turn, for CIR events with the absence of the shocks the model predictions are not fulfilled.

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Deriving CME volume and density from remote sensing data

10.5194/egusphere-egu21-2535 ◽

2021 ◽

Author(s):

Manuela Temmer ◽

Lukas Holzknecht ◽

Mateja Dumbovic ◽

Bojan Vrsnak ◽

Nishtha Sachdeva ◽

...

Keyword(s):

Solar Wind ◽

Solar Wind Speed ◽

Remote Sensing Data ◽

Propagation Speed ◽

Solar Wind Density ◽

Sheath Region ◽

Pile Up ◽

Mass Ejection ◽

Interplanetary Propagation

Using combined STEREO-SOHO white-light data, we present a method to determine the&#160;volume and density of a coronal mass ejection (CME) by applying the graduated cylindrical&#160;shell model (GCS) and deprojected mass derivation. Under the assumption that the CME &#160;mass is roughly equally distributed within a specific volume, we expand the CME self-similarly and calculate the CME density for distances close to the Sun (15&#8211;30 Rs) and at 1 AU.&#160;The procedure is applied on a sample of 29 well-observed CMEs and compared to their&#160;interplanetary counterparts (ICMEs). Specific trends are derived comparing calculated and&#160;in-situ measured proton densities at 1 AU, though large uncertainties are revealed due to&#160;the unknown mass and geometry evolution: i) a moderate correlation for the magnetic&#160;structure having a mass that stays rather constant and ii) a weak&#160;correlation for the sheath density by assuming the sheath region is an extra mass&#160;- as expected for a mass pile-up process - that is in its amount comparable to the initial CME&#160;deprojected mass. High correlations are derived between in-situ measured sheath density&#160;and the solar wind density and solar wind speed as measured 24&#160;hours ahead of the arrival of the disturbance. This gives additional confirmation that the&#160;sheath-plasma indeed stems from piled-up solar wind material. While the CME&#160;interplanetary propagation speed is not related to the sheath density, the size of the CME&#160;may play some role in how much material is piled up.

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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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Large-scale electron solar wind parameters of the inner heliosphere with Parker Solar Probe/FIELDS

10.5194/egusphere-egu2020-18573 ◽

2020 ◽

Author(s):

Karine Issautier ◽

Mingzhe Liu ◽

Michel Moncuquet ◽

Nicole Meyer-Vernet ◽

Milan Maksimovic ◽

...

Keyword(s):

Solar Wind ◽

Large Scale ◽

Statistical Study ◽

Solar Wind Speed ◽

The Sun ◽

Solar Wind Parameters ◽

Power Law Index ◽

Probe Mission ◽

Inner Heliosphere

We present in situ properties of electron density and temperature in the inner heliosphere obtained during the three first solar encounters at 35 solar radii of the Parker Solar Probe mission. These preliminary results, recently shown by Moncuquet et al., ApJS, 2020, are obtained from the analysis of the plasma quasi-thermal noise (QTN) spectrum measured by the radio RFS/FIELDS instrument along the trajectories extending between 0.5 and 0.17 UA from the Sun, revealing different states of the emerging solar wind, five months apart. The temperature of the weakly collisional core population varies radially with a power law index of about -0.8, much slower than adiabatic, whereas the temperature of the supra-thermal population exhibits a much flatter radial variation, as expected from its nearly collisionless state. These measured temperatures are close to extrapolations towards the Sun of Helios measurements.We also present a statistical study from these in situ electron solar wind parameters, deduced by QTN spectroscopy, and compare the data to other onboard measurements. In addition, we focus on the large-scale solar wind properties. In particular, from the invariance of the energy flux, a direct relation between the solar wind speed and its density can be deduced, as we have already obtained based on Wind continuous in situ measurements (Le Chat et al., Solar Phys., 2012). We study this anti-correlation during the three first solar encounters of PSP.

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On the Drag parameter of ICME propagation models

10.5194/egusphere-egu2020-21007 ◽

2020 ◽

Author(s):

Gianluca Napoletano ◽

Raffaello Foldes ◽

Dario Del Moro ◽

Francesco Berrilli ◽

Luca Giovannelli ◽

...

Keyword(s):

Solar Wind ◽

Travel Time ◽

Initial Conditions ◽

Solar Wind Speed ◽

Distribution Functions ◽

Model Parameters ◽

Wind Condition ◽

The Sun ◽

The Earth ◽

External Fluid

ICME (Interplanetary Coronal Mass Ejection) are violent phenomena of solar activity that affect the whole heliosphere and the prediction of their impact on different solar system bodies is one of the primary goals of the planetary space weather forecasting. The travel time of an ICME from the Sun to the Earth can be computed through the Drag-Based Model (DBM), which is based on a simple equation of motion for the ICME defining its acceleration as a=-&#915;(v-w)v-w, where a and v are the CME acceleration and speed, w is the ambient solar-wind speed and &#915; is the so-called drag parameter (Vrs&#780;nak et al., 2013). In this framework, &#915; depends on the ICME mass and cross-section, on the solar-wind density and, to a lesser degree, on other parameters. The typical working hypothesis for DBM implies that both &#915; and w are constant far from the Sun. To run the codes, forecasters use empirical input values for &#915; and w, derived by pre-existent knowledge of solar-wind condition and by solving the &#8220;inverted problem&#8221; (where the ICME travel time is known and the unknowns are &#915; and/or w). In the 'Ensemble' approaches (Dumbovich et al., 2018; Napoletano et al. 2018), the uncertainty about the actual values of such inputs are rendered by Probability Distribution Functions (PDFs), accounting for the values variability and our lack of knowledge. Among those PDFs, that of &#915; is poorly defined due to the relatively scarce statistics of recorded values.&#160;Employing a list of past ICME events, for which initial conditions when leaving the Sun and arrival conditions at the Earth are known, we employ a statistical approach to the Drag-Based Model to determine a measure of &#915; and w for each case. This allows to obtain distributions for the model parameters on experimental basis and, more importantly, to test whether different conditions of relative velocity to the solar wind influence the value of the drag efficiency, as it must be expected for solid objects moving into an external fluid. In addition, we perform numerical simulations of a solid ICME-shaped structure moving into the solar-wind modelled as an external fluid. Outcomes from these simulations are compared with our experimental results, and thus employed to interpret them on physical basis.

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Understanding Solar Wind Formation by Identifying the Origins of In Situ Observations

10.5194/egusphere-egu21-6200 ◽

2021 ◽

Author(s):

Samantha Wallace ◽

Nicholeen M. Viall ◽

Charles N. Arge

Keyword(s):

Solar Wind ◽

Solar Wind Speed ◽

Source Region ◽

Heliospheric Current Sheet ◽

Slow Solar Wind ◽

The Sun ◽

Flux Transport ◽

Model Driven ◽

In Situ Observations

Solar wind formation can be separated into three physical steps &#8211; source, release, and acceleration &#8211; that each leave distinct observational signatures on plasma parcels.&#160; The Wang-Sheeley-Arge (WSA) model driven by Air Force Data Assimilative Photospheric Flux Transport (ADAPT) time-dependent photospheric field maps now has the ability to connect in situ observations more rigorously to their precise source at the Sun, allowing us to investigate the physical processes involved in solar wind formation. &#160;&#160;In this talk, I will highlight my PhD dissertation research in which we use the ADAPT-WSA model to either characterize the solar wind emerging from specific sources, or investigate the formation process of various solar wind populations. &#160;In the first study, we test the well-known inverse relationship between expansion factor (fs) and observed solar wind speed (vobs) for solar wind that emerges from a large sampling of pseudostreamers, to investigate if field line expansion plays a physical role in accelerating the solar wind from this source region.&#160; We find that there is no correlation between fs and vobs at pseudostreamer cusps. In the second study, we determine the source locations of the first identified quasiperiodic density structures (PDSs) inside 0.6 au. Our modeling provides confirmation of these events forming via magnetic reconnection both near to and far from the heliospheric current sheet (HCS) &#8211; a direct test of the Separatrix-web (S-web) theory of slow solar wind formation.&#160; In the final study, we use our methodology to identify the source regions of the first observations from the Parker Solar Probe (PSP) mission.&#160; Our modeling enabled us to characterize the closest to the Sun observed coronal mass ejection (CME) to date as a streamer blowout.&#160; We close with future ways that ADAPT-WSA can be used to test outstanding questions of solar wind formation.

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

Annales Geophysicae ◽

10.5194/angeo-20-405-2002 ◽

2002 ◽

Vol 20 (4) ◽

pp. 405-426 ◽

Cited By ~ 33

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)

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CME arrival prediction and its dependency on input data and model parameters

10.5194/egusphere-egu2020-4703 ◽

2020 ◽

Author(s):

Tanja Amerstorfer ◽

Jürgen Hinterreiter ◽

Martin A. Reiss ◽

Maike Bauer ◽

Christian Möstl ◽

...

Keyword(s):

Solar Wind ◽

Wind Speed ◽

Real Time ◽

Arrival Time ◽

Solar Wind Speed ◽

Model Parameters ◽

The Sun ◽

Model Set ◽

Different Sources ◽

Ambient Solar Wind

During the last years, we focused on developing a prediction tool that utilizes the wide-angle observations of STEREO's heliospheric imagers. The unsurpassable advantage of these imagers is the possibility to observe the evolution and propagation of a coronal mass ejection (CME) from close to the Sun up to 1 AU and beyond. We believe that using this advantage instead of relying on coronagraph observations that are limited to observe only 14% of the Sun-Earth line, it is possible to improve today's CME arrival time predictions. The ELlipse Evolution model based on HI observations (ELEvoHI) assumes an elliptic frontal shape within the ecliptic plane and allows the CME to adjust to the ambient solar wind speed, i.e. it is drag-based. ELEvoHI is used as an ensemble simulation by varying the CME frontal shape within given boundary values. The results include a frequency distrubution of predicted arrival time and arrival speed and an estimation of the arrival probability. ELEvoHI can be operated using several kinds of inputs. In this study we investigate 15 well-defined single CMEs when STEREO was around L4/5 between the end of 2009 and the beginning of 2011. Three different sources of input propagation directions (and shapes) are used together with three different sources of ambient solar wind speed and two different ways of defining the most appropriate fit to the HI data. The combination of these different approaches and inputs leads to 18 different model set-ups used to predict each of the 15 events in our list leading to 270 ELEvoHI ensemble predictions and all in all to almost 60000 runs. To identify the most suitable and most accurate model set-up to run ELEvoHI, we compare the predictions to the actual in situ arrival of the CMEs. This model is specified for using data from future space weather missions carrying HIs located at L5 or L1 and can also directly be used together with STEREO-A near real-time HI beacon data to provide real-time CME arrival predictions during the next 7 years when STEREO-A is observing the Sun-Earth space.

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