Question: Where does Earth's magnetic field point during magnetopause?
About the article "Aurora", section "Frequency of occurrence".

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If the pressure from particles within the magnetosphere is neglected, it is possible to estimate the distance to the part of the magnetosphere that faces the Sun.
The condition governing this position is that the dynamic ram pressure from the solar wind is equal to the magnetic pressure from the Earth's magnetic field.
formula_1 where formula_2 and formula_3 are the density and velocity of the solar wind, and "B"("r") is the Magnetic field strength of the planet in SI units ("B" in T, μ0 in H/m)Since the dipole magnetic field strength varies with distance as formula_4 the magnetic field strength can be written as formula_5.
formula_6.
Solving this equation for r leads to an estimate of the distance formula_7 The distance from Earth to the subsolar magnetopause varies over time due to solar activity, but typical distances range from 6 - 15 Rformula_8.
Empirical models using real-time solar wind data can provide a real-time estimate of the magnetopause location.
A bow shock stands upstream from the magnetopause.
It serves to decelerate and deflect the solar wind flow before it reaches the magnetopause  
Jupiter's internal magnetic field prevents the solar wind, a stream of ionized particles emitted by the Sun, from interacting directly with its atmosphere, and instead diverts it away from the planet, effectively creating a cavity in the solar wind flow, called a magnetosphere, composed of a plasma different from that of the solar wind.
The Jovian (i.e.
pertaining to Jupiter) magnetosphere is so large that the Sun and its visible corona would fit inside it with room to spare.
If one could see it from Earth, it would appear five times larger than the full moon in the sky despite being nearly 1700 times farther away.
As with Earth's magnetosphere, the boundary separating the denser and colder solar wind's plasma from the hotter and less dense one within Jupiter's magnetosphere is called the magnetopause.
The distance from the magnetopause to the center of the planet is from 45 to 100 "R"j (where "R"j=71,492 km is the radius of Jupiter) at the subsolar point—the unfixed point on the surface at which the Sun would appear directly overhead to an observer.
The position of the magnetopause depends on the pressure exerted by the solar wind, which in turn depends on solar activity.
In front of the magnetopause (at a distance from 80 to 130 "R"j from the planet's center) lies the bow shock, a wake-like disturbance in the solar wind caused by its collision with the magnetosphere.
The region between the bow shock and magnetopause is called the magnetosheath.
At the opposite side of the planet, the solar wind stretches Jupiter's magnetic field lines into a long, trailing magnetotail, which sometimes extends well beyond the orbit of Saturn.
The structure of Jupiter's magnetotail is similar to Earth's.
It consists of two lobes (blue areas in the figure), with the magnetic field in the southern lobe pointing toward Jupiter, and that in the northern lobe pointing away from it.
The lobes are separated by a thin layer of plasma called the tail current sheet (orange layer in the middle).
Like Earth's, the Jovian tail is a channel through which solar plasma enters the inner regions of the magnetosphere, where it is heated and forms the radiation belts at distances closer than 10 "R"j from Jupiter.
The shape of Jupiter's magnetosphere described above is sustained by the neutral sheet current (also known as the magnetotail current), which flows with Jupiter's rotation through the tail plasma sheet, the tail currents, which flow against Jupiter's rotation at the outer boundary of the magnetotail, and the magnetopause currents (or Chapman-Ferraro currents), which flow against rotation along the dayside magnetopause.
These currents create the magnetic field that cancels the internal field outside the magnetosphere.
They also interact substantially with the solar wind.
Jupiter's magnetosphere is traditionally divided into three parts: the inner, middle and outer magnetosphere.
The inner magnetosphere is located at distances closer than 10 "R"j from the planet.
The magnetic field within it remains approximately dipole, because contributions from the currents flowing in the magnetospheric equatorial plasma sheet are small.
In the middle (between 10 and 40 "R"j) and outer (further than 40 "R"j) magnetospheres, the magnetic field is not a dipole, and is seriously disturbed by its interaction with the plasma sheet (see magnetodisk below). 
Previous single and two-spacecraft missions were not capable of providing the data required to accurately study the boundaries of the magnetosphere.
Because the plasma comprising the magnetosphere cannot presently be accessed using remote sensing techniques, satellites must be used to measure it in-situ.
Four spacecraft allow scientists make the 3D, time-resolved measurements needed to create a realistic picture of the complex plasma interactions occurring between regions of the magnetosphere and between the magnetosphere and the solar wind.
Each satellite carries a scientific payload of 11 instruments designed to study the small-scale plasma structures in space and time in the key plasma regions: solar wind, bow shock, magnetopause, polar cusps, magnetotail, plasmapause boundary layer and over the polar caps and the auroral zones.
The bow shock is the region in space between the Earth and the sun where the solar wind decelerates from super- to sub-sonic before being deflected around the Earth.
In traversing this region, the spacecraft make measurements which help characterize processes occurring at the bow shock, such as the origin of hot flow anomalies and the transmission of electromagnetic waves through the bow shock and the magnetosheath from the solar wind.
Behind the bow shock is the thin plasma layer separating the Earth and solar wind magnetic fields known as the magnetopause.
This boundary moves continuously due to the constant variation in solar wind pressure.
Since the plasma and magnetic pressures within the solar wind and the magnetosphere, respectively, should be in equilibrium, the magnetosphere should be an impenetrable boundary.
However, plasma has been observed crossing the magnetopause into the magnetosphere from the solar wind.
Cluster's four-point measurements make it possible to track the motion of the magnetopause as well as elucidate the mechanism for plasma penetration from the solar wind.
In two regions, one in the northern hemisphere and the other in the south, the magnetic field of the Earth is perpendicular rather than tangential to the magnetopause.
These polar cusps allow solar wind particles, consisting of ions and electrons, to flow into the magnetosphere.
Cluster records the particle distributions, which allow the turbulent regions at the exterior cusps to be characterized.
The regions of the Earth's magnetic field that are stretched by the solar wind away from the sun are known collectively as the magnetotail.
Two lobes that reach past the Moon in length form the outer magnetotail while the central plasma sheet forms the inner magnetotail, which is highly active.
Cluster monitors particles from the ionosphere and the solar wind as they pass through the magnetotail lobes.
In the central plasma sheet, Cluster determines the origins of ion beams and disruptions to the magnetic field-aligned currents caused by substorms.
The precipitation of charged particles in the atmosphere creates a ring of light emission around the magnetic pole known as the auroral zone.
Cluster measures the time variations of transient particle flows in the region.  
The magnetosheath is the region of space between the magnetopause and the bow shock of a planet's magnetosphere.
The regularly organized magnetic field generated by the planet becomes weak and irregular in the magnetosheath due to interaction with the incoming solar wind, and is incapable of fully deflecting the highly charged particles.
The density of the particles in this region is considerably lower than what is found beyond the bow shock, but greater than within the magnetopause, and can be considered a transitory state.
Scientific research into the exact nature of the magnetosheath has been limited due to a longstanding misconception that it was a simple byproduct of the bow shock/magnetopause interaction and had no inherently important properties of its own.
Recent studies indicate, however, that the magnetosheath is a dynamic region of turbulent plasma flow that may play an important role in the structure of the bow shock and the magnetopause, and may help to dictate the flow of energetic particles across those boundaries.
The Earth's magnetosheath typically occupies the region of space approximately 10 Earth radii on the upwind (Sun-facing) side of the planet, extending significantly farther out on the downwind side due to the pressure of the solar wind.
The exact location and width of the magnetosheath does depend on variables such as solar activity. 
The solar wind also carries with it the magnetic field of the Sun.
This field will have either a North or South orientation.
If the solar wind has energetic bursts, contracting and expanding the magnetosphere, or if the solar wind takes a southward polarization, geomagnetic storms can be expected.
The southward field causes magnetic reconnection of the dayside magnetopause, rapidly injecting magnetic and particle energy into the Earth's magnetosphere.
During a geomagnetic storm, the ionosphere's F2 layer will become unstable, fragment, and may even disappear.
In the northern and southern pole regions of the Earth, auroras will be observable in the sky.