Solar wind

Katya GeorgievaBoian Kirov

Simeon Asenovski

The solar wind carries plasma with embedded The solar wind carries plasma with embedded magnetic fields to the Earthmagnetic fields to the Earth

The interaction of the solar wind with the Earth’s The interaction of the solar wind with the Earth’s magnetic field leads to geomagnetic disturbancesmagnetic field leads to geomagnetic disturbances

Solar wind – expansion of the solar corona

The solar corona is not in hydrostatic equilibruim

The corona ( the solar atmosphere) is expanding until it encounters the interstellar matter

Eugene Parker (1956)

3 types of solar windSlow solar wind: max in sunspot min

• background geomagnetic activity• galactic cosmic rays modulation• solar wind electric field

High speed solar wind: max during sunspot declining phase

• recurrent geomagnetic storms• galactic cosmic rays modulation• energetic particles precipitation• solar wind electric field

Coronal mass ejections: max during sunspot max• Sporadic geomagnetic storms• galactic cosmic rays modulation• energetic particles precipitation, solar proton events• solar wind electric field

3 components of geomagnetic activity corresponding to the 3 types of solar wind

• FloorFloor – background geomagnetic activity due to the slow solar windslow solar wind

• Sunspot-relatedSunspot-related geomagnetic activity due to CMEsCMEs proportional in number and intensity to the sunspot number

• Additional geomagnetic activity due to high-speed solar wind

low “floor” of geomagnetic high “floor” of geomagneticactivity activitywell expressed dependence of small to vanishing dependence geomagnetic activity on geomagnetic activity onsunspot-related solar activity sunspot –related solar activitysmall impact of non sunspot- high impact of non sunspot- related solar activity related solar activity

Different relative importance of the 3 components Different relative importance of the 3 components of geomagnetic activity in different periods of geomagnetic activity in different periods

The time the Earth spends in slow solar wind from the equatorial streamer belt depends on the solar cycle solar cycle

phasephase

Distribution of slow and fast solar windDistribution of slow and fast solar wind

• In sunspot min: slow solar wind confined to the In sunspot min: slow solar wind confined to the ecliptic, fast wind at higher latitudesecliptic, fast wind at higher latitudes

• In sunspot max slow and fast streams at all latitudesIn sunspot max slow and fast streams at all latitudes • Cycle to cycle variationsCycle to cycle variations

Variations of the thickness of the heliospheric current sheet

The thicker the sheet (bigger gamma) – the

higher the geomagnetic activity

“floor”

Are solar wind parameters also changing from cycle to cycle?

• We look at sunspot min periods• Divide the days into 4 groups:• - slow background solar wind (V<450

km/s)• - faster background solar wind (V>450

km/s)• - coronal mass ejections• - high speed solar wind

% of time during sunspot min

Variations from min to min – slow wind

Variations from min to min – fast wind

What is fast solar wind

By variations

Solar polarity changes from cycle to cycle

Solar rotation axis tilted by 7o

Seasonal variations of IMF direction

By variations in positive and negative polarity cycles

NAM and SAM indices

NAM index in positive and negative polarity cycles

SAM index in positive and negative polarity cycles