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This page covers both the solar wind and the interplanetary magnetic field (IMF) it carries with it.

 

Introduction

The concept of continuous solar wind developed in 1950's. First, Biermann (1951, 1957) observed comet tails as they passed close to the Sun, and explained the observed tail deflection by a continuous flux of protons from the Sun. Then Parker (1959) showed that the solar corona must expand, and called the outward streaming coronal gas 'solar wind'.

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The solar wind originating from the streamers (closed field lines) is slow, while that originating from the coronal holes is fast. This creates the so-called "corotating interaction regions" (CIR) in the interplanetary space. As the solar wind moves away from the Sun, tangential discontinuities and interplanetary (fast) shocks are formed, creating pressure variations.

In addition, the variables shown in the table are functions of solar latitude: for example, density is at maximum, speed at minimum around the equator (Kojima and Kakinuma, 1990; Rickett and Coles, 1991; see also the Ulysses results here). However, the hemispheres are not exactly symmetric (see the annual variability of geomagnetic activity).

Typical periodicities in the solar wind can be divided into those that reflect the time scales of the solar processes themselves, those that reflect the rotation of the Sun, and those that reflect the orientation of Earth (the most typical observation point) with respect to the Sun. The first include the 11- and 22-year solar cycles and the 1.3 year and 154 day cycles. Others will be discussed in the geomagnetic activity section (see also below).

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Because of these effects, the changes in the solar wind plasma parameters (density, velocity, etc.) and IMF (especially direction in relation to Earth's own field) are very important for magnetospheric and ionospheric physics, and the scientific community tries to have continuous monitoring of these parameters via satellites like IMP-8, ISEE, and Wind. However, there are difficulties, because there is - at any given time - at most two or three satellite within the solar wind (quite often none at all), and the solar wind/IMF system is not homogenoushomogeneous, as discussed above. See also the discussion about substorm triggering.

Solar wind event categories

Solar wind event categories:

Code

Description

BzN

Strong northward Bz for extended period

BzS

Strong southward Bz for extended period

CME

Coronal Mass Ejections

EyC

Change in Ey=VxBz

HSS

Very high speed stream for extended period

IMC

Interplanetary magnetic cloud

IR

Interaction Region

IS

Interplanetary shock

LSS

Very low speed stream for extended period

MISC

Miscallaneous

PC

Pressure change

SBC

Interplanetary sector boundary crossings

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