Sunspots begin as small dark areas known as pores.These pores develop into full-fledged spots in a fewdays, with maximum development occurring in about 1to 2 weeks. When sunspots decay the spot shrinks insize and its magnetic field also decreases in size. Thislife cycle may consist of a few days for small spots tonear 100 days for larger groups. The larger spotsnormally measure about 94,500 miles (120,000 kin)across. Sunspots appear to have cyclic variations inintensity, varying through a period of about 8 to 17years. Variation in number and size occurs throughoutthe sunspot cycle. As a cycle commences, a few spotsare observed at high latitudes of both solarhemispheres, and the spots increase in size and number.They gradually drift equatorward as the cycleprogresses, and the intensity of the spots reach amaximum in about 4 years. After this period, decay setsin and near the end of the cycle only a few spots are leftin the lower latitudes (5° to 10°).PlagesPlages are large irregular bright patches thatsurround sunspot groups. (See fig. 1-2). They normallyappear in conjunction with solar prominences orfilaments and may be systematically arranged in radialor spiral patterns. Plages are features of the lowerchromosphere and often completely or partiallyobscure an underlying sunspot.FlaresSolar flares are perhaps the most spectacular of theeruptive features associated with solar activity. (See fig.1-2). They look like flecks of light that suddenly appearnear activity centers and come on instantaneously asthough a switch were thrown. They rise sharply to peakbrightness in a few minutes, then decline moregradually. The number of flares may increase rapidlyover an area of activity. Small flare-like brighteningsare always in progress during the more active phase ofactivity centers. In some instances flares may take theform of prominences, violently ejecting material intothe solar atmosphere and breaking into smallerhigh-speed blobs or clots. Flare activity appears to varywidely between solar activity centers. The greatest flareproductivity seems to be during the week or 10 dayswhen sunspot activity is at its maximum.Flaresareclassifiedaccordingtosizeandbrightness. In general, the higher the importanceclassification, the stronger the geophysical effects.Some phenomena associated with solar flares haveimmediate effects; others have delayed effects (15minutes to 72 hours after flare).Solar flare activity produces significant disruptionsand phenomena within Earth’s atmosphere. Duringsolar flare activity, solar particle streams (solar winds)are emitted and often intercept Earth. These solarparticles are composed of electromagnetic radiation,which interacts with Earth’s ionosphere. This results inseveralreactionssuchas:increasedionization(electrically charging neutral particles), photo chemicalchanges (absorption of radiation), atmospheric heating,electrically charged particle motions, and an influx ofradiation in a variety of wavelengths and frequencieswhich include radio and radar frequencies.Some of the resulting phenomena include thedisruptionofradiocommunicationsandradardetection. This is due to ionization, incoming radiowaves, and the motion of charged particles. Satelliteorbits can be affected by the atmospheric heating andsatellite transmissions may be affected by all of thereactionspreviouslymentioned.Geomagneticdisturbances like the aurora borealis and auroraAustraliaresultprimarilyfromthemotionofelectrically charged particles within the ionosphere.EARTHOf the nine planets in our solar system, Earth is thethird nearest to (or from) the Sun. Earth varies indistance from the Sun during the year. The Sun is 94million miles (150,400,000 km) in summer and 91million miles (145,600,000 km) in winter.MotionsEarth is subject to four motions in its movementthrough space: rotation about its axis, revolution aroundthe Sun, processional motion (a slow conical movementor wobble) of the axis, and the solar motion (themovement of the whole solar system with space). Ofthe four motions affecting Earth, only two are of anyimportance to meteorology.1-5
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