What is Space Weather
What is space weather? Space weather has become very important in the satellite communications and navigation age, and therefore maritime communications and navigation systems on our sailboats are affected. The underlying factor ruling space weather, at least in this end of the galaxy is the sun.
The Sun - Earth Environment is the region extending from the surface of the sun to the earths ionosphere and magnetic field. It is dominated by electromagnetic radiation and electrically charged particles emanating from the sun. The sun is by its' violent nature prone to dramatic and violent changes, with events such as solar flares, and the resultant blast streams of radiation and energized particles that stream towards earth. The effects of space weather are dramatic on our communications systems.
What is Space Weather
Space weather is due to changes in the speed or density of the solar wind, and this is the continuous flow of charged particles that flow from the sun past the earth and out into the voids of space. This particle flow has the effect of distorting the earth's magnetic field, compressing it in the direction of the sun and stretching it out in the opposite direction of the sun. The solar wind fluctuations cause variation in the strength and direction of the magnetic field measured near the earths' surface. Any abrupt changes in this dynamic medium are called geomagnetic disturbances. The electrical layers of the upper atmosphere (ionosphere) are disturbed during these events, in conjunction with normal changes, due to flows of charged particles into the various layers and regions. This impacts on HF communications as the ionosphere acts as a mirror bouncing and reflecting signals back down to earth. This bounce or skip effect is the foundation for long distance communication for those of us that have Ham or SSB/HF radio equipment installed, so space weather prediction is important as that meteorological forecast for your next offshore cruising or ocean passage. Space weather real time situation and forecasts are available at Space Weather Live.
What is Space Weather - Solar
Cycles
Space weather solar activity occurs on an 11-year solar cycle. Cycles vary in both intensity and length, and the solar activity is characterized by the appearance of sunspots on the sun. Sunspots are regions of stronger magnetic field. The solar maximum is the time when maximum spot numbers are visible. Sunspot numbers is that quoted for average number over a 12-month period, and is the traditional measure of solar cycle status. Peak sunspot like highest rainfall is that for recorded worst cases, and 5 of the last 6 have been high magnitudes. Cycle 19 in 1957 peak had a sunspot number of 201, and the largest on record, Cycle 21 in 1979 had a peak sunspot number of 165 was the second largest, Cycle 22 in 1989 was equal third largest. At present cycle 25 has peaked and is declining in its 11 year cycle. Solar Cycle 26 is expected to commence at some time between January 2029 and December 2032. Read more about this in my book The Marine Electrical and Electronics Bible 4th Edition.
What is Space Weather
– Solar Flares
Solar flares are strong outbursts of energy monitored over a wide wavelength spectrum from visible light to the radio spectrum. This is due to the release of energy generated as sunspot magnetic fields distort and twist due to the effects of differential rotation of the sun. Solar flares are also associated with ejection of clouds of charged particles into the solar wind stream. This is termed a coronal mass ejection and often occurs with flare activity. The result is a geomagnetic and ionosphere storm back at us on the Third rock, Earth. Coronal holes are yet another space weather phenomena, and these are large regions in the solar corona or the suns outer atmosphere. The regions are typified by lower temperatures and density, and are the locations of magnetic field lines, which open into outer space. The coronal holes contribute high speed streams to the solar wind which if reaching earth produce space weather disturbances.
What is Space Weather
– HF Radio
The ionosphere exists at a height of 50km to 500km above earth, and is formed by ionization of air atoms by incoming UV ionizing radiation from the sun. The ionosphere is a weakly ionized plasma, or gas, which effects radio wave propagation. The atmospheric chemistry determines the structure, which is divided in to layers D, E, F1 and F2 in order of increasing height. The F layer is of key importance to HF communications. This is present both day and night, the strongest height at night reflects highest radio frequencies in HF bands. Extreme ultraviolet (EUV) radiation is responsible for forming and maintaining the ionosphere. This radiates from hot bright regions overlying sunspots, so this is also dependant on solar sunspot activity. At lows in the sun solar cycle EUV radiation is weak and density of charged particles in the F region is lowest. This means only lower frequency HF signals can be reflected. At cycle peaks the EUV and ionosphere density are both large and higher frequencies in the HF band can be reflected. Other factors for HF radio communications are the season, time of day, and the latitude.
What is Space Weather
Solar flares produce a great deal of electromagnetic radiation. The x-ray component increases the D layer ionisation. HF communications use the F layer above so they must transit the D layer twice during any signal skips. The increased ionization with higher density of neutral particles results in the absorption of signal in the D layer during a major solar flare. This is termed Sudden Ionosphere Disturbance (SID) and is observed as increased attenuation of HF signals in particular at lower frequencies. This is also called SWF or short wave fadeout. SSWF for sudden and GSWF for gradual. This follows closely with solar flare patterns, and is observed in conjunction with solar flares. They characteristically have rapid onsets of several minutes and decline periods up to an hour or more. SWF affects lower frequencies in HF band and higher frequencies may remain unaffected or be the first to recover. SWF features are that HF circuit is disturbed only when there is an ionosphere reflection point for the signal located in the sunlit hemisphere. What is space weather? It is weather that affects almost our whole technological world.