Anomalously low proton temperatures in the solar wind following interplanetary shock waves-evidence for magnetic bottles?

Abstract

Occasionally, anomalously low values of the solar wind proton temperature Tp are observed when the solar wind velocity v is high. A large fraction of such measurements by the Vela 3 satellites follow the passage of interplanetary shocks by some 20-60 hours. Of 24 postshock events in which v exceeded 400 km sec -x and for which Vela 3 measurements are available, 12 exhibited plasma states of anomalously low Tp, high v. The proton density at the time of these observations typically was depressed below normal, and the velocity tended to be constant or falling. A very strong association with abnormally high (_• 15%) concentrations of He++/H + in the solar wind is noted for these anomalous proton temperatures, the usual temporal sequence of events at 1 AU being: (1) shock wave, (2) helium enrichment, and (3) low Tp, high v. It is suggested that these observations are consistent with a model for some shock wave disturbances that includes the ejection of new material (distinguished by the helium enrichment at 1 AU) into the solar wind at the time of large solar flares and the formation of a magnetic bottle configuration in the solar wind behind and within the ejecta. The anomalo.usly low proton temperatures then result from the adiabatic cooling of the plasma within the magnetic bottle. The positive correlation between solar wind flow speed v and proton tempei•ature T• is. well documented in the literature [Strong et al., 1966; Hundhausen e,t al., 1967; Burlaga and Ogilvie, 1970]. A demonstration of this correlation is provided by Figure 1, which is a scatter plot in the v, T• plane of the 3-hour averages of the Vela 3 solar wind data obtained between July 1965 and December 1967. Several recent papers [Burlaga and Ogilvie, 1970; Hartle and Barnes, 1970; Hundhause.n, 1973] have concentrated on an understanding of the general increase in proton temperature with increasing flow s.peed. Although differences in interpretation exist, there is agreement that the average increase in proton temperature with increasing flow speed probably represents a mapping outward from the corona of increasingly high coronal proton temperatures. One of our concerns recently has been the interpretation of the relatively large scatter of plasma states evident in Figure I particularly at high flow speeds. That is, we have been concerned with the deviations from the average flow speed-proton temperature relationship. It is now clear that compressional heating caused by high-speed streams overtaking slower-moving plasma is responsible for a major part of the plasma states of excessively high proton temperature at moderate and high flow speeds [Burlaga and Ogilvie, 1970; Burlaga et al., 1971; Gosling et al., 1972; V. Pizzo, J. T. Gosling, and A. J. Hundhausen, unpublished manuscript, 1972; Hundhausen, 1973]. On the other hand, rarefactional cooling in the trailing part of high-speed streams does not appear to be a major factor in explaining the anomalously low proton temperature states sometimes observed at high flow speeds [Gosling et al., 1972; V....

Small Solar Wind Transients and Their Connection to the Large-Scale Coronal Structure

“…However, temperature depressions are considered one of the best indicators of the CME related material in the solar wind (e.g. Gosling, Pizzo, and Bame, 1973;Richardson and Cane, 1995). An example of a temperature depression event observed by Wind is given in Figure 6 (Event E11).…”

“…We searched for the intervals with decreased magnetic field variability, smooth rotation of the magnetic field and clear decreases in the proton temperature (T p ) and proton beta. Solar wind temperature depressions are considered as one of the most reliably ICME identifiers (Gosling, Pizzo, and Bame, 1973;Richardson and Cane, 1995). Using the empirical correlation between solar wind speed and proton temperature (Lopez, 1987) to calculate the "expected proton temperature" (T ex ) Richardson and Cane (1995) found that ICMEs typically have T p /T ex < 0.5.…”

Coronal mass ejections and their sheath regions in interplanetary space

“…These speculations stemmed from the attempts to explain geomagnetic disturbances (e.g., Lindeman 1911;Chapman and Ferraro 1929;Bartels 1932) and so-called Forbush decreases in cosmic ray intensities (Forbush 1937;Morrison 1956;Cocconi et al 1958;Piddington 1958). The first ICME observations emerged in the 1970s suggesting loop-or bubble-like structures behind interplanetary shocks (e.g., Hirshberg et al 1970;Gosling et al 1973;Palmer et al 1978). For a more detailed historical review on ICMEs, and their role in understanding solar-terrestrial relationships, we guide the reader to Gopalswamy (2016).…”

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

“…ICMEs are identified by several characteristic features in the interplanetary medium, as reviewed by Gosling (1990) and Neugebauer and Goldstein (1997). Solar wind signatures of ICMEs include the increase of He ++ (Hirshberg et al, 1972;Borrini et al, 1982), the abnormally low proton temperature (Gosling et al, 1973;Richardson and Cane, 1995), the bidirectional electron heat flow (Gosling et al, 1987), and the magnetic cloud (Burlaga et al, 1981;Marubashi, 2000;Lepping et al, 2006), though the regions of these ICME signatures do not necessarily coincide with each other.…”