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  • 1
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    Solar cosmic ray 'square wave' of August 1972 (1975)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: Three Rice University suprathermal ion detector experiments (sides) were deployed on the lunar surface during the Apollo 12, 14, and 15 missions. During the exceptional period of solar activity in August 1972, penetrating particles were observed by all side detectors on the night side of the moon. The penetrating particles are tentatively identified as solar protons with energies (approximately 25 MeV or greater) that were able to penetrate the shielding of all detectors. Of particular interest is the occurrence on August 5 of a 'square wave' flux enhancement of 2-hour duration. Data from a variety of ground-based and space experiments are examined in relation to the square wave. Based on the results of this investigation a model relating the square wave to the flare plasma propagation is proposed. This model hypothesizes transport of energetic particles along a 'corridor' formed by the tangential discontinuity produced by the driver gas of a flare-induced shock wave. This model could explain other frequently observed delayed particle events.
    Keywords: SOLAR PHYSICS
    Type: Journal of Geophysical Research; 80; May 1
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  • 2
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    An empirical determination of the polytropic index for the free-streaming solar wind using Helios 1 data (1995)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: Observations of solar wind proton temperatures indicate that the solar wind is heated as it moves outward toward the orbit of Earth. This heating, which may be the results of electron heat conduction and perhaps MHD waves, has proven difficult to quantify and hence is often neglected in MHD models of the solar wind. An alternate approach to finding explicit heating terms for the MHD energy equation is to use a polytropic approximation. This paper discusses the properties of the polytropic approximation and its application to the solar wind plasma. By using data from the Helios 1 spacecraft, an empirical value for the polytropic index of the free-streaming solar wind is determined. Various corrections to the data are made to account for velocity, nonuniformity in radial sampling, and stream interaction regions. The polytropic index, as derived from proton data, is found to indepedent of speed state, within statistical error, and has an average value of 1.46. If magnetic pressure is included, the polytropic index has an average value of 1.58.
    Keywords: SOLAR PHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 100; A1; p. 13-17
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  • 3
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    Solar wind and extreme ultraviolet modulation of the lunar ionosphere/exosphere (1976)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: The ALSEP/SIDE detectors routinely monitor the dayside lunar ionosphere. Variations in the ionosphere are found to correlate with both the 2800 MHz radio index which can be related to solar EUV and with the solar wind proton flux. For the solar wind, the ionospheric variation is proportionately greater than that of the solar wind. This suggests an amplification effect on the lunar atmosphere due perhaps to sputtering of the surface or, less probably, an inordinate enhancement of noble gases in the solar wind. The surface neutral number density is calculated under the assumption of neon gas. During a quiet solar wind this number agrees with or is slightly above that expected for neon accreted from the solar wind. During an enhanced solar wind the neutral number density is much higher.
    Keywords: SOLAR PHYSICS
    Type: Geophysical Research Letters; 3; Nov. 197
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  • 4
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    The cold solar wind (1985)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: From 3 to 10 percent of the time, the solar wind has a radial proton temperature between 15,000 K and 3500 K (the lowest recorded temperature). This 'cold' component shows some very important features that make it worthy of special study. It shows a temperature dependence on helicentric distance that is nearly adiabatic. When extrapolated back to 3 R(s), assuming adiabatic cooling, the resulting temperature for this cold component is in good agreement with coronal temperatures near the sonic point. Most importantly, the proton velocities and densities associated with this cold component match those predicted by solar wind models that do not incorporate significant wave heating. It is concluded that this is one solar wind component that fits well with appropriate models.
    Keywords: SOLAR PHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 90; 9885-988
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  • 5
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    The relationship between proton temperature and momentum flux density in the solar wind (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: The relationship between proton temperature and momentum flux density/unit mass at 1 AU is examined using Helios 1 solar wind data from 1974 to 1980. In high-speed plasma (V greater than 500 km/s) T(p) increases with increasing n(0) V-squared, where n(0) and T(p) are the density and proton temperature at 1 AU and V is the flow speed. In lowspeed plasma (V less than 500 km/s), T(p) does not increase with increasing n(0) V-squared, and perhaps tends to decrease slightly. These basic relationships between T(p) and n(0) V-squared are not significantly affected by stream interactions. A qualitative explanation of these results is offered in the context of a solar wind model that includes deposition of momentum and energy extending well outward into the interplanetary medium.
    Keywords: SOLAR PHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 13; 640-643
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  • 6
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    Solar wind proton temperature-velocity relationship (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Helios 1 data are analyzed to find an experimental fit for the temperature-velocity relationship at 1 AU. It is shown that the proton temperature-velocity changes at a velocity of approximately 500 km/s. Interplanetary dynamic processes, i.e., stream interactions, are shown to affect the temperature-velocity relationships less than 22 percent; the functional form of these relationships appears to be preserved throughout the solar cycle. It is pointed out that any comprehensive model of the solar wind will have to address the difference in the temperature-velocity relationship between the low- and high-speed wind, since this is a product of the acceleration and subsequent heating process generating the solar wind.
    Keywords: SOLAR PHYSICS
    Type: (ISSN 0148-0227)
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