Velocity and density
Near the Earth's orbit at 1 astronomical unit (AU) the plasma flows at speeds ranging from 250 to 750 km/s with a density ranging between 3 and 10 particles per cubic centimeter and temperature ranging from 104 to 106 Kelvin.[45]
On average, the plasma density decreases with the square of the distance from the Sun, see Section 4.2,[46] while the velocity decreases and flattens out at 1 AU, see Figure 5.[46]
Voyager 1 and Voyager 2 reported plasma density n between 0.001 and 0.005 particles/cm3 at distances of 80 to 120 AU, increasing rapidy beyond 120 AU at Heliopause to between 0.05 and 0.2 particles/cm3.[47]
Pressure
At 1 AU, the wind exerts a pressure typically in the range of 1–6 nPa ((1–6)×10−9 N/m2),[48] although it can readily vary outside that range.
The ram pressure is a function of wind speed and density. The formula is
P = m p ⋅ n ⋅ V 2 = 1.6726 × 10 − 27 k g ⋅ n ⋅ V 2 {\displaystyle P=m_{\text{p}}\cdot n\cdot V^{2}=\mathrm {1.6726\times 10^{-27}\,kg} \cdot n\cdot V^{2}}
where mp is the proton mass, pressure P is in Pa (pascals), n is the density in particles/cm3 and V is the speed in km/s of the solar wind.[49]
