Three-Dimensional Evolution of Solar Wind During Solar Cycles 22–24

Abstract

This paper presents the analysis of three-dimensional evolution of solar wind density turbulence and speed at various levels of solar activity between solar cycles 22 and 24. The solar wind data used in this study has been obtained from interplanetary scintillation (IPS) measurements made at the Ooty Radio Telescope, operating at 327 MHz. Results show that (i) on the average, there was a downward trend in density turbulence from the maximum of cycle 22 to the deep minimum phase of cycle 23; (2) the scattering diameter of the corona around the Sun shrunk steadily towards the Sun, starting from 2003 to the smallest size at the deepest minimum, and it corresponded to a reduction of ∼50% in density turbulence between maximum and minimum phases of cycle 23; (3) The latitudinal distribution of solar wind speed was significantly different between minima of cycles 22 and 23. At the minimum phase of solar cycle 22, when the underlying solar magnetic field was simple and nearly dipole in nature, the high-speed streams were observed from poles to ∼30 • latitudes in both hemispheres. In contrast, in the long-decay phase of cycle 23, the sources of high-speed wind at both poles, in accordance with the weak polar fields, occupied narrow latitude belts from poles to ∼60 • latitudes. Moreover, in agreement with the large amplitude of heliospheric current sheet, the low-speed wind prevailed the low-and mid-latitude regions of the heliosphere. (4) At the transition phase between cycles 23 and 24, the high levels of density and density turbulence were observed close to the heliospheric equator and the low-speed speed wind extended from equatorial-to mid-latitude regions. The above results in comparison with Ulysses and other in-situ measurements suggest that the source of solar wind has changed globally, with the important implication that the supply of mass and energy from the Sun to the interplanetary space has significantly reduced in the prolonged period of low level of solar activity. The IPS results are consistent with the onset and growth of the current solar cycle 24, starting from middle of 2009. However, the width of the high-speed wind at the northern high latitudes has almost disappeared and indicates that the ascending phase of the current cycle has almost reached near to the maximum phase at the northern hemisphere of the Sun. But, in the southern part of the hemisphere, the solar activity has yet to develop and/or increase.

Magnetism, dynamo action and the solar-stellar connection

“…As shown in Fig. 28(left panel) these coupled dynamo-wind models reproduce qualitatively well the variations seen in IPS radio maps of Tokumaru et al (2010) and Manoharan (2012), and with the estimations by Wang and Sheeley (2006) using ULYSSES data and semi-empirical methods. A recent analysis of 5 years of IBEX satellite data also indicates that solar wind speed variation with respect to the heliographic latitude are compatible with the change of solar magnetic field geometry generated by dynamo action along the 11-year cycle (McComas et al 2014).…”

Stellar wind interaction and pick-up ion escape of the Kepler-11 “super-Earths”

“…These are reasonable values for the slow solar wind, as measured by the ACE satellite (e.g. Wargelin et al 2004;Vršnak et al 2007;Manoharan 2012). The mass density, velocity, and pressure of the wind as a function of radial distance from the star are shown in Fig.…”

Dynamics of Coronal Hole Boundaries

“…It appears to be associated with streamers (Raymond et al 1997), being limited to low latitudes during the minimum of solar cycle 23 (Manoharan 2012), when the streamers were also found only at low latitudes. The slow wind extended further during the more complex solar minimum of cycle 24 (Tokumaru et al 2010), when streamer structures also extended to higher latitudes.…”