In Situ Observations of Solar Wind Stream Interface Evolution

Simunac, K. D. C.; Kistler, L. M.; Galvin, A. B.; Lee, M. A.; Popecki, M. A.; Farrugia, Charles J.; Möbius, E.; Blush, L. M.; Bochsler, P.; Würz, Peter; Klecker, B.; Wimmer‐Schweingruber, R. F.; Thompson, B. J.; Luhmann, J. G.; Russell, C. T.; Howard, R. A.

doi:10.1007/s11207-009-9393-y

Cited by 24 publications

(33 citation statements)

References 23 publications

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“…If we assume that there is a significant distance between the fastto-slow and the slow-to-fast transitions, then the slow distribution functions also need to be taken into account, resulting in the additional contribution This interestingly enough reflects the well-established finding in observational data that the spectral intensities of ion distributions are inversely proportional to the bulk velocity of the solar wind (Hill et al 2009;Dayeh et al 2009b;Simunac et al 2009). …”

Section: Distribution Functions In the Presence Of Continuous Reinjecmentioning

confidence: 96%

Isotropic ion distribution functions triggered by consecutive solar wind bulk velocity jumps: a new equilibrium state

Fahr

Siewert

2011

A&A

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Context. Throughout the heliosphere, ion power spectra have been found in observations to exhibit suprathermal tails that follow power laws. Ion power-law spectra, though having a broad range of spectral indices 4.4 ≤ γ v ≤ 6.6, perhaps favourably seem to have velocity power indices of γ v (−5), a phenomenon that can more or less ubiquitously be found in heliospheric space plasmas. This is probably indicative of an as yet unidentified quasi-equilibrium state of collisionless space plasmas. Aims. We develop the idea that these forms of ion spectra could be produced by a continuous back-and forth-shuffling of wind convected ions in consecutive jumps from fast to slow, and vice-versa, bulk velocity regimes. Methods. The appearance of a quasi-equilibrium state due to this shuffling and re-shuffling, as we show, naturally results in ion distribution functions that are superpositions of a series of weighted Maxwellians resulting into power laws beyond a critical velocity border. Spectral intensities thereby anticorrelate with bulk velocities, but power indices depend only slightly on bulk velocity. Results. The fully developed equilibrium state is shown here, however, to be characterized by a power law with power index γ v = (−3), instead of 4.4 ≤ γ v ≤ 6.6. These latter states, which generally show up in observations, thus may characterize an off-equilibrium state as we discuss in this paper.

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Section: Distribution Functions In the Presence Of Continuous Reinjecmentioning

confidence: 96%

Isotropic ion distribution functions triggered by consecutive solar wind bulk velocity jumps: a new equilibrium state

Fahr

Siewert

2011

A&A

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“…Because the Sun's heliographic equator is tilted about 7 degrees with respect to the ecliptic plane, the separation in heliographic latitude between L5 and Earth can be more than 5 degrees. This relatively small latitude separation is potentially enough to result in substantially different stream structures at the two points of observation (Schwenn, 1990;Leske et al, 2008;Mason et al, 2009;Simunac et al, 2009). Simunac et al (2009) compared the expected and observed time delay between the observations of stream interfaces on STEREO/B and STEREO/A over heliographic longitude separations ranging from 2 to 48 degrees.…”

Section: Introductionmentioning

confidence: 99%

“…This relatively small latitude separation is potentially enough to result in substantially different stream structures at the two points of observation (Schwenn, 1990;Leske et al, 2008;Mason et al, 2009;Simunac et al, 2009). Simunac et al (2009) compared the expected and observed time delay between the observations of stream interfaces on STEREO/B and STEREO/A over heliographic longitude separations ranging from 2 to 48 degrees. They found significant deviations from the expected time-of-arrival when the spacecraft were separated by more than 20 degrees of longitude.…”

Section: Introductionmentioning

confidence: 99%

In situ observations from STEREO/PLASTIC: a test for L5 space weather monitors

et al. 2009

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Abstract. Stream interaction regions (SIRs) that corotate with the Sun (corotating interaction regions, or CIRs) are known to cause recurrent geomagnetic storms. The Earth's L5 Lagrange point, separated from the Earth by 60 degrees in heliographic longitude, is a logical location for a solar wind monitor -nearly all SIRs/CIRs will be observed at L5 several days prior to their arrival at Earth. Because the Sun's heliographic equator is tilted about 7 degrees with respect to the ecliptic plane, the separation in heliographic latitude between L5 and Earth can be more than 5 degrees. In July 2008, during the period of minimal solar activity at the end of solar cycle 23, the two STEREO observatories were separated by about 60 degrees in longitude and more than 4 degrees in heliographic latitude. This time period affords a timely test for the practical application of a solar wind monitor at L5. We compare in situ observations from PLASTIC/AHEAD and PLASTIC/BEHIND, and report on how well the BEHIND data can be used as a forecasting tool for in situ conditions at the AHEAD spacecraft with the assumptions of ideal corotation and minimal source evolution. Preliminary results show the bulk proton parameters (density and bulk speed) are not in quantitative agreement from one observatory to the next, but the qualitative profiles are similar.

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“…Several weak CMEs were seen by LASCO (reported on the CDAW CME catalogue) and at least four CIRs were reported in more-detailed analyses of STEREO/PLASTIC in situ data by Simunac et al (2008).…”

Section: Discussion and Summarymentioning

confidence: 96%

“…We do not know exactly why this is, given that at both other spacecraft locations (Wind and STEREO-B) the density compares well, but clearly the density peak does not appear to be manifest from STEREO-B to Wind to STEREO-A as one might expect for a co-rotating dense structure. Simunac et al (2008) note that there are some CIRs during this interval where the estimated time of arrival from one STEREO spacecraft to the other (under the assumption of radial flow) is not consistent with actual arrival times. This discrepancy could result from potential changes in the solar wind speed/make-up or motion (or changes) of the coronal hole on the solar surface responsible for generating the CIR feature.…”

Section: Comparison With Stereo/plasticmentioning

confidence: 91%

Low-Resolution STELab IPS 3D Reconstructions of the Whole Heliosphere Interval and Comparison with in-Ecliptic Solar Wind Measurements from STEREO and Wind Instrumentation

et al. 2009

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We present initial 3D tomographic reconstructions of the inner heliosphere during the Whole Heliosphere Interval (WHI) -Carrington Rotation 2068 (CR2068) -using Solar-Terrestrial Environment Laboratory (STELab) Interplanetary Scintillation (IPS) observations. Such observations have been used for over a decade to visualise and investigate the structure of the solar wind and to study in detail its various features. These features include co-rotating structures as well as transient structures moving out from the Sun. We present global reconstructions of the structure of the inner heliosphere during this time, and compare density and radial velocity with multi-point in situ spacecraft measurements in the ecliptic; namely STEREO and Wind data, as the interplanetary medium passes over the spacecraft locations.

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In Situ Observations of Solar Wind Stream Interface Evolution

Cited by 24 publications

References 23 publications

Isotropic ion distribution functions triggered by consecutive solar wind bulk velocity jumps: a new equilibrium state

Isotropic ion distribution functions triggered by consecutive solar wind bulk velocity jumps: a new equilibrium state

In situ observations from STEREO/PLASTIC: a test for L5 space weather monitors

Low-Resolution STELab IPS 3D Reconstructions of the Whole Heliosphere Interval and Comparison with in-Ecliptic Solar Wind Measurements from STEREO and Wind Instrumentation

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