SANSA Space Science FAQ

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What is 'space weather'?

'Space weather' is a concept that is growing in importance as mankind becomes increasingly dependent on technological systems. The Sun is the source of the solar wind; a flow of gases from the Sun that streams past Earth at speeds of more than 500 kilometres per second. Disturbances in the solar wind shake Earth's magnetic field and pump energy into the radiation belts. Regions on the surface of the Sun often flare and give off ultraviolet light and X-rays that heat up the Earth's upper atmosphere.

Does the Sun itself spin? If so, how fast?

The rotation period of the Sun varies from about 25 days at the equator to over 30 days at the poles, so it takes roughly two weeks for a feature to cross the solar disc.

What is the role of a Space Weather Centre?

To deliver space weather products and services that meet the evolving needs of the nation.  A Space Weather Centre gathers, in real time, the available data that describes the state of the Sun, Heliosphere, Magnetosphere, and Ionosphere to form a picture of the environment from the Sun to the Earth.  With this information, forecasts, watches, warnings and alerts are prepared by the Space Weather Centre and issued to anyone affected by space weather.

How do you monitor events on the sun?

SWC forecasters utilize a variety of ground and space-based sensors and imaging systems to view activity at various depths in the solar atmosphere.

What is a solar flare?

A solar flare is an intense burst of radiation coming from the release of magnetic energy associated with sunspots. Solar flares are seen by the photons (or light) released across the spectrum. X-rays are the primary wavelength monitored in the classification of solar flares. Flares also contribute to the acceleration of protons and other charged particles that may accompany a significant event.

Does ALL solar activity impact Earth? Why or why not?

We can divide solar activity into four main components.  Solar flares, coronal mass ejections, high speed solar wind, and solar energetic particles.

Solar flares impact Earth only when they occur on the side of the Sun facing Earth.  Because flares are made of photons, these travel out directly from the flare site, so if we can see the flare, we can be impacted by it.
Coronal mass ejections, also called CMEs, are large clouds of plasma and magnetic field that erupt from the Sun.  These clouds can erupt in any direction, and then continue on in that direction, plowing right through the solar wind.  Only when the cloud is aimed at Earth will the CME hit Earth and therefore cause impacts.

High speed solar wind streams coming from the Sun come from special areas on the Sun known as coronal holes.  These holes can form anywhere on the Sun and usually only when they are closer to the equator than to the solar poles do the winds they produce impact Earth.
Solar energetic particles are high energy charged particles, thought to primarily be released by coronal mass ejections.  Where the cloud of a CME plows through the solar wind, the solar energetic particles are travelling much faster and because they are charged, must follow the magnetic field lines that pervade the space between the Sun and the Earth.  Therefore, only the charged particles that follow magnetic field lines that intersect the Earth will have an impact on Earth.

Have scientists seen changes in the intensity of space weather?

On a short time scale, the intensity of space weather is always changing.  Conditions can be mild one minute and stormy the next.  On longer time scales, space weather varies with the solar cycle.  The solar cycle is an average 11 year cycle where the number of sunspots goes from very few per month, to many, and back to very few.  At solar minimum, we might see no sunspots where at solar maximum, we can have 200 sunspots in a month.  Solar flares, coronal mass ejections and solar energetic particles all increase in frequency as we get closer to solar maximum.  High speed wind streams are more frequent at solar minimum, thus ensuring that space weather is something to watch for no matter where we are in the solar cycle.

What are sunspots and how do they relate to space weather?

The magnetic field in sunspots stores energy that is released in solar flares. As a result, flares usually occur in a cycle that mimics the eleven-year sunspot cycle. Other forms of space weather such as geomagnetic storms and proton radiation showers follow a similar cycle. Sunspots usually occur in groups-usually as simple pairs-but at times in complicated arrangements with many spots and complex shapes. These unusual regions most often produce solar flares. Space weather forecasters use the complexity and shapes of sunspots to make flare forecasts-the more complex the groups of spots, the more likely a flare will occur.

What is the solar max and solar min?

At solar minimum, the sun may go many days with no spots visible. At maximum, there may be several hundred spots on any day.

What are the northern lights and are they related to space weather?

When the sun is active, it often produces mass ejections that interact with Earth's magnetic field. Electric currents begin to flow in the upper atmosphere, and these currents produce the aurora borealis, which occurs almost simultaneously around both the north and south poles.

How do you forecast space weather?

A good space weather forecast begins with a thorough analysis. SWC forecasters analyze near-real-time grounda nd space-based observations to assess the current state of the solar-geophysical environment (from the Sun to the Earth and points in between). Space weather forecasters also analyze the 27-day recurrent pattern of solar activity. Based on a thorough analysis of current conditions, comparing these conditions to past situations, and using numerical models similar to weather models, forecasters are able to predict space weather on times scales of hours to weeks.

Why is forecasting space weather important?

Some of the specific effects of space weather on Earth systems include interference with short wave radio propagation, problems with electric power grids, the decay of satellite orbits, and radiation hazard for satellites and for astronauts during some phases of space missions.

How does the "South Atlantic Anomaly" affect satellites?

The South Atlantic Anomaly is a dip in the Earth's magnetic field which allows cosmic rays, and charged particles to reach lower into the atmosphere. The anomaly is always there, but it does change in intensity. The SAA is populated with high energy particles that can penetrate the skin of the spacecraft and cause upsets in spacecraft electronics.

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