Model scope and corrections — read first

Kp is the planetary geomagnetic activity index (0–9), not an interplanetary magnetic-field index: NOAA's scale associates Kp=5 with G1, Kp=7 with G3, and Kp=9 with G5 storms. Not every solar flare or CME causes a storm at Earth; propagation direction and interplanetary magnetic-field orientation matter. The magnetosphere mainly deflects or traps charged particles, not all cosmic rays; the atmosphere and other geophysical factors also matter. Outside Earth, field lines emerge near the geographic South Pole and enter near the geographic North Pole; distinguish physical magnetic polarity from geographic names; Van Allen belt extents are approximate. Earth textures still load from external sources; complete imagery requires a network connection.

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Magnetosphere andsolar wind
Module 12 · Magnetosphere & Solar Wind
Key concepts
Solar wind intensity
Geomagnetic storm Kp index 3
Kp≥5: geomagnetic storm; Kp≥7: strong storm
Higher Kp pushes auroras toward lower latitudes (potentially into mid-latitudes)
Layers
Parameters
Bow shock: ~10–15 R⊕
Magnetopause: dayside ~10 R⊕
Magnetotail: nightside ~200 R⊕
Auroral oval latitude: approximately 65°–75° (quiet conditions)
During storms, it may reach 45° or lower
Geomagnetic storm status
Kp index3
Storm levelQuiet
Lowest auroral latitude~68°
Magnetopause distance~10 R⊕
Magnetosphere structure
Bow Shock
The solar wind slows abruptly here and is deflected by Earth's magnetic field
Magnetopause
Where magnetic pressure equals solar wind pressure; the magnetosphere boundary
Van Allen radiation belts
Energetic particles trapped by Earth's magnetic field; inner belt (1-2R⊕), outer belt (3-9R⊕)
Auroral Oval
Solar wind particles travel along field lines into the upper atmosphere, exciting oxygen and nitrogen to emit light
Magnetotail
On the nightside, it is stretched into a streamlined tail extending hundreds of R⊕
Counterintuitive insight
Auroras are not "sunlight reaching the poles" — they occur when energetic particles (electrons, protons) from the solar wind follow magnetic field lines into the polar atmosphere, colliding with O, N₂, and other particles and exciting light emission.

Without Earth's magnetic field, the solar wind would directly erode the atmosphere (as on Mars). The magnetic field is a protective umbrella for life.