Space weather

Each day, we consciously experience atmospheric weather, driven by radiation from the Sun. In addition, we are mostly unknowingly subjected to space weather driven primarily by streams of high-energy particles bursting out from the surface of the Sun.

Space weather defined

Just as weather on Earth is the set of ever-changing conditions in our atmosphere, space weather is the set of ever-changing conditions in the region from the Sun’s outer atmosphere to near-Earth space.

Earth weather’s component parts are measures like air temperature and pressure, wind speed and direction, humidity and precipitation. By contrast, space weather is measured by the speed, pressure and density of the solar wind, the types of electromagnetic radiation bombarding the Earth’s upper atmosphere and the extent and interaction of the Earth’s magnetic field with that of the solar wind.

Space weather origins

Although cosmic rays from outside the Solar System do play a part, the primary driver of space weather is the Sun.

In addition to the continuous output of electromagnetic radiation ranging from high energy X-rays to radio noise, the upper atmosphere of the Sun outwardly boils off, in all directions, a continuous stream of charged particles. These are mostly electrons and protons, and this continuous stream is referred to as the solar wind.

Depending on the activity within the Sun’s outer regions, the density and speed of this solar wind can vary from 5–100 protons per cubic centimetre (p/cm3) with speeds between 200–800 km/s. On a typically average day, the speed of the solar wind is about 400 km/s and its density about 10 p/cm3. (Pause for a moment to come to terms with a speed of 400 km/s – an Airbus A380 jet airliner has a cruising speed of about 960 km/h, which is 0.267 km/s.)

The Earth’s atmosphere and magnetic field play crucial roles in subduing the damaging effects of both the electromagnetic radiation and solar wind that continually stream out from the Sun.

Space weather storms

Earth weather storms such as hurricanes and tornadoes can result in severe damage to property and people’s lives. Similarly, space weather storms such as solar flares and coronal mass ejections (also known as solar particle events) can cause electromagnetic and radiation damage to satellites, power transmission lines and communication networks. Although not as frequent as Earth weather storms, most industrialised nations carefully monitor the Sun’s activity so that, in the event of major solar activity, warnings and precautionary measures can be put in place.

A solar flare is a sudden, explosive release of high-energy particles and radiation from the solar atmosphere. It increases the amount of X-rays and UV light reaching Earth. The X-rays can interfere with high-frequency radio communications, and the UV can result in heating of the upper atmosphere, causing it to expand further out into space. Satellites in low-Earth orbit now experience increased drag due to a denser concentration of plasma particles. This alters the orbit of the satellite. If appropriate alterations to the orbital path cannot be made, the lifetime of the satellite could be substantially reduced. Read about how in 2012 two solar flares hurled charged particles at Earth.

Coronal mass ejection

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The SOHO satellite (Solar Heliospheric Observatory) captured these images of the Sun spitting out a coronal mass ejection (CME) on 15 March 2013. This type of image is known as a coronagraph.

Rights: ESA&NASA/SOHO

A coronal mass ejection (CME) can release huge amounts of matter and electromagnetic radiation into space above the Sun’s surface. The ejected material is plasma consisting mainly of electrons and protons moving at speeds in the region of 600 km/s. When this interacts with the Earth’s magnetic field, it can cause magnetic field fluctuations that generate rogue electric currents in power transmission lines, submarine communication cables and cross-country pipelines. If large enough, these electric currents can have damaging effects.

Space weather and human society

Space weather does impact life on Earth in many ways.

Many aspects of our modern technology such as communications, transportation and electrical power systems can be disrupted by space weather storms. Exposure to radiation can threaten astronauts and commercial air travellers and, in the long term, has influenced the evolution of life on Earth. Recent scientific research has indicated that space weather has an influence on the weather and climate that we experience.

Industrialised countries, particularly those with investment in satellite technologies, monitor space weather through a number of agencies such as NOAA, NWS Space Weather Prediction Centre, NASA and European Space Agency. Several New Zealand internet sites take real-time feeds from these agencies.