"WEATHER" IN THE UPPER ATMOSPHERE

Internet Resources

Space Weather Advisories
NOAA Space Weather Scales
Solar Proton Events since 1976
Earth-orbiting satellite positions
Space weather victims

List of Affected Systems

• Radio Communications
• Military Defense
• Search-and-Rescue Operations
• Navigational Systems (For info on GPS, the Global Positioning System; more detail yet)
• Satellites
• Astronauts
• Geologic Exploration
• Electric Power
• Pipelines
• Auroral Displays
• Animals
• Climate

• Magnetospheric Storm which causes a (Geo)magnetic Storm on Earth's surface is the result of significant changes is the speed of the solar wind (i.e. gusts) due to a Coronal Mass Ejection (CME) or Coronal Hole, for instance. CME's produce the most intense storms while coronal holes are responsible for 27-day recurrent storms. Descriptions of the April 6, 2000 Geomagnetic Storm and the May 1998 Magnetic Storms
• Magnetospheric Substorm which is evident as an Auroral Substorm or Magnetic Substorm was identified in 1963 by Sydney Chapman and Syun-Ichi Akusofu and is triggered by a solar wind disturbance when the Interplanetary Magnetic Field (IMF) has a southward polarity. The link of magnetic activity to a southward IMF was established by Don Fairfield in 1966.
• Sudden Ionospheric Disturbance (SID) produces Shortwave Fadeout (first identified by Dellinger in 1937) on the dayside of the Earth as the result of enhanced X-rays from a solar flare
• F-region Ionospheric Storm usually lasts a day or so and is the result of altered circulation globally caused by enhanced flux of energetic electrons (electron precipitation) into Earth's ionosphere. Usually (but not always) associated with magnetospheric storms
• D-region Ionospheric Storm (aka Post-Storm Effect) of enhanced electron density lasts a week or so after the F-region ionospheric storm
• Polar Cap Absorption (PCA) Event, first observed on Feb 23, 1956, usually lasts several days over the polar regions and is the result of a solar proton flare
• Travelling Ionospheric Disturbance (TID) is a ripple or wave in the electron density structure that propagates horizontally which affects the refraction of radiowaves and so degrades directional finders. There are two main types:
  • large-scale TID with 1000 km or more between wave crests usually moving from pole to equator and generated by auroral activity
  • medium-scale TID with hundreds of km wavelengths thought to be generated by thunderstorm activity
• Scintillation is the random amplitude and phase shifts of radio waves due to propagation through small-scale inhomogeneities in electron densities. Spread F in an ionogram is indicative of ionospheric inhomogeneities. The twinkling of stars is the same effect on visible light due to inhomgeneities in air density. Several features contribute to scintillation including:
  • Ionospheric Blob which is a "blob of air" near the pole that has broken from the dayside F-region (with high electron density) and migrated to the nightside region (where the electron density is otherwise low).
  • Ionospheric Bubble which is a "bubble" of air (with low electron density) that rises into the F-region (where electron densities are otherwise high). These bubbles most frequently form in equatorial regions just after sunset. The effect on radio communication was called the "London Lunchtime Effect".
  • Localized electron precipitation that also produces auroral displays.
• Sporadic E layer (E_s layer) is a thin layer (usually less than 1 mile thick) with limited horizontal extent (tens of miles) in the E-region having enhanced electron density similar to that of the F-region and hence causes reflection at lower altitude of radio waves normally reflected by the F-region. One source of sporadic E is the ionized trail of a meteor. Sporadic E layers also have differing characteristics and causes depending on latitude:
  • equatorial: occur at day with no seasonal preference; cause thought to be turbulence induced by atmospheric tides, gravity waves and the equatorial electrojet
  • mid-latitude: relatively rare occurring around noon in summers; cause thought to be wind shear
  • polar: occur late p.m./early a.m. with no seasonal preference; cause thought to be electric fields associated with auroral activity
• D-region Bite-Out is a daytime depletion of electron density as the result of electrons attaching to polar mesopheric cloud ice particles
• D-region Winter Anomaly is a period of enhanced radio wave absorption usually occurring in late winter and thought to be associated with a sudden stratospheric warming