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E-region(Also called Heaviside layer, Kennelly–Heaviside layer.) The region of the ionosphere usually found at an altitude between 100 and 120 km. It exhibits one or more distinct maxima and sharp gradients of free electron density. It is most pronounced in the daytime but does not entirely disappear at night. Ionosonde recordings show that the E-region is often subdivided into two or more “E-layers,” while localized and intermittent regions of fairly high ionization, known as sporadic E-layers, are also frequently observed. The E- region is produced by absorption of solar radiation at a variety of extreme ultraviolet (EUV) and x-ray wavelengths.
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8D technique(Also called frost point technique.) A technique for using the radiosonde observation to determine the presence of liquid water droplets in supercooled clouds in saturated or nearly saturated layers of air. For each reported level in the sounding, the negative value of eight times the dewpoint spread (−8D) is plotted on the pseudoadiabatic chart (or equivalent chart). Where the temperature sounding lies to the left of the −8D curve, liquid droplet clouds are considered to be present, and icing is possible on aircraft flying in the cloud layer.
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earth-current storm(Rarely, electrical storm.) Irregular fluctuations in an earth current, often associated with electric field strengths as large as several volts per kilometer, in the earth's crust, superimposed on the normal diurnal variation of the earth currents. Such storms are closely related to magnetic storms.
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earth currentA large-scale surge of electric charge within the conductive earth, associated with a disturbance of the ionosphere. Current patterns of quasi-circular form and extending over areas the size of whole continents have been identified and are known to be closely related to solar-induced variations in the extreme upper atmosphere.
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