WEAKEST SOLAR WIND OF THE SPACE AGE AND THE CURRENT MINI SOLAR MAXIMUM

The last solar minimum, which extended into 2009, was especially deep and prolonged. Since then, sunspot activity has gone through a very small peak while the heliospheric current sheet achieved large tilt angles similar to prior solar maxima. The solar wind fluid properties and interplanetary magnetic field (IMF) have declined through the prolonged solar minimum and continued to be low through the current mini solar maximum. Compared to values typically observed from the mid-1970s through the mid-1990s, the following proton parameters are lower on average from 2009 through day 79 of 2013: solar wind speed and beta (similar to 11%), temperature (similar to 40%), thermal pressure (similar to 55%), mass flux (similar to 34%), momentum flux or dynamic pressure (similar to 41%), energy flux (similar to 48%), IMF magnitude (similar to 31%), and radial component of the IMF (similar to 38%). These results have important implications for the solar wind's interaction with planetary magnetospheres and the heliosphere's interaction with the local interstellar medium, with the proton dynamic pressure remaining near the lowest values observed in the space age: similar to 1.4 nPa, compared to similar to 2.4 nPa typically observed from the mid-1970s through the mid-1990s. The combination of lower magnetic flux emergence from the Sun (carried out in the solar wind as the IMF) and associated low power in the solar wind points to the causal relationship between them. Our results indicate that the low solar wind output is driven by an internal trend in the Sun that is longer than the similar to 11 yr solar cycle, and they suggest that this current weak solar maximum is driven by the same trend.