Solar cycle invariance in solar wind proton temperature relationships

López, Ramón

doi:10.1029/ja092ia10p11189

Cited by 200 publications

(165 citation statements)

References 20 publications

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“…This approach compares, point by point, the observed proton temperature T p with the ''expected'' temperature T ex appropriate for ''normally expanding'' solar wind with the observed solar wind speed V sw . The expected temperature is essentially the typical temperature found in normal solar wind with speed V sw and is inferred using the well-established correlation between the solar wind speed and T p [Lopez, 1987]. To calculate T ex between 0.3 and 1 AU from the observed solar wind speed, we use the relationship derived by Lopez and Freeman [1986] based on Helios plasma data,…”

Section: Discussionmentioning

confidence: 99%

Characteristics of the interplanetary coronal mass ejections in the heliosphere between 0.3 and 5.4 AU

Wang

Richardson

2005

J. Geophys. Res.

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[1] We identify and characterize interplanetary coronal mass ejections (ICMEs) observed by spacecraft in the solar wind, namely Helios 1 and 2, PVO, ACE, and Ulysses, which together cover heliocentric distances from 0.3 to 5.4 AU. The primary identification signature used to look for ICMEs is abnormally low proton temperatures. About 600 probable ICMEs were identified from the solar wind plasma and magnetic field data from these spacecraft. We use these events to study the radial evolution of ICMEs between 0.3 and 5.4 AU, mainly in a statistical sense. The occurrence rate of ICME approximately follows the solar activity cycle. ICMEs expand as they move outward since the internal pressure is generally larger than the external pressure. The average radial width of ICMEs increases with distance. ICMEs expand by a factor of 2.7 in radial width between 1 and 5 AU. The radial expansion speed of ICMEs decreases with distance and is of the order of the Alfvén speed. The density and magnetic field magnitude decrease faster in ICMEs, which fall off with distance R as R À2.4 and R À1.5 , respectively, than in the ambient solar wind; however, the temperature decreases as R À0.7 , slightly less rapid than in the ambient solar wind. These results are consistent with previous findings with relatively limited data coverage. We also use a one-dimensional MHD model to investigate the radial expansion of the ICMEs and find that the radial expansion speed is of the order of the Alfvén speed, consistent with the observations.

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Section: Discussionmentioning

confidence: 99%

Characteristics of the interplanetary coronal mass ejections in the heliosphere between 0.3 and 5.4 AU

Wang

Richardson

2005

J. Geophys. Res.

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“…Event 6 was the only exceptional case in that it exhibits no enhancement in this composition ratio. Column 10 shows the averages within the MCs of the ratio of observed proton temperature, T p , to the proton temperature statistically expected from the solar wind speed, T ex (Lopez, 1987). It is seen that the proton temperature ratios are appreciably lower than those for the background solar wind, except for two cases (Events 3 and 10).…”

Section: Event Selectionmentioning

confidence: 99%

“…While many studies have been made to analyze an MC's geometry with cylindrical flux rope models Bothmer and Schwenn, 1998;Shimazu and Marubashi, 2000;Mulligan et al, 1998Mulligan et al, , 2001Lynch et al, 2003;Lepping et al, 2006), only a few studies were made with torus models (Marubashi, 1997(Marubashi, , 2000Romashets and Vandas, 2003), or with other different models (Vandas and Geranios, 2001;Vandas and Romashets, 2003). Judging from the proposed global configuration of MCs, there should be more encounters with MCs near the flank than identified thus far.…”

Section: Introductionmentioning

confidence: 99%

Long-duration magnetic clouds: a comparison of analyses using torus- and cylinder-shaped flux rope models

2007

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Abstract. We identified 17 magnetic clouds (MCs) with durations longer than 30 h, surveying the solar wind data obtained by the WIND and ACE spacecraft during 10 years from 1995 through 2004. Then, the magnetic field structures of these 17 MCs were analyzed by the technique of the least-squares fitting to force-free flux rope models. The analysis was made with both the cylinder and torus models when possible, and the results from the two models are compared. The torus model was used in order to approximate the curved portion of the MCs near the flanks of the MC loops. As a result, we classified the 17 MCs into 4 groups. They are (1) 5 MC events exhibiting magnetic field rotations through angles substantially larger than 180 • which can be interpreted only by the torus model; (2) 3 other MC events that can be interpreted only by the torus model as well, though the rotation angles of magnetic fields are less than 180 • ; (3) 3 MC events for which similar geometries are obtained from both the torus and cylinder models; and (4) 6 MC events for which the resultant geometries obtained from both models are substantially different from each other, even though the observed magnetic field variations can be interpreted by either of the torus model or the cylinder model. It is concluded that the MC events in the first and second groups correspond to those cases where the spacecraft traversed the MCs near the flanks of the MC loops, the difference between the two being attributed to the difference in distance between the torus axis and the spacecraft trajectory. The MC events in the third group are interpreted as the cases where the spacecraft traversed near the apexes of the MC loops. For the MC events in the fourth group, the real geometry cannot be determined from the model fitting technique alone. Though an attempt was made to determine which model is more plausible for each of the MCs in this group by comparing the characteristics of associated bidirectional electron heat flows, the results Correspondence to: K. Marubashi (k.marubashi@eos.ocn.ne.jp)were not very definitive. It was also found that the radii of the flux ropes obtained from the torus fitting tend to be generally smaller than those obtained from the cylinder fitting. This result raises a possible problem in estimating the magnetic flux and helicity carried away from the Sun by the MCs.

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“…2 indicate the start and end times of the geomagnetic storm. The dashed curve plotted in the temperature panel shows the temperature calculated from the solar wind speed by using the correlation between solar wind speed and proton temperature (Lopez, 1987). The abnormally depressed proton temperature compared with the calculated temperature has often been observed in the case of interplanetary magnetic flux ropes or ejecta (Richardson and Cane, 1993).…”

Section: Southward Imfs Associated With Magnetic Flux Ropesmentioning

confidence: 99%

Formation of a strong southward IMF near the solar maximum of cycle 23

Watari¹,

Vandas

Watanabe

2004

Ann. Geophys.

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Abstract. We analyzed observations of the solar activities and the solar wind parameters associated with large geomagnetic storms near the maximum of solar cycle 23. This analysis showed that strong southward interplanetary magnetic fields (IMFs), formed through interaction between an interplanetary disturbance, and background solar wind or between interplanetary disturbances are an important factor in the occurrence of intense geomagnetic storms. Based on our analysis, we seek to improve our understanding of the physical processes in which large negative B z 's are created which will lead to improving predictions of space weather.

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Solar cycle invariance in solar wind proton temperature relationships

Cited by 200 publications

References 20 publications

Characteristics of the interplanetary coronal mass ejections in the heliosphere between 0.3 and 5.4 AU

Characteristics of the interplanetary coronal mass ejections in the heliosphere between 0.3 and 5.4 AU

Long-duration magnetic clouds: a comparison of analyses using torus- and cylinder-shaped flux rope models

Formation of a strong southward IMF near the solar maximum of cycle 23

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