Chapter 12 — THE GOVERNING FUNDAMENTALS OF METEOROLOGY 



The main body of the sun, although composed 

 of gases, is opaque and has a well-defined 

 visible surface referred to as the photosphere. 

 This is the source we see from which all light 

 and heat of the sun is radiated. Above the 

 photosphere is a more transparent gaseous layer 

 referred to as the chromosphere with a thick- 

 ness of about 10,000 km. Above the chromo- 

 sphere is the corona, which may extend outward 

 a distance of several solar diameters. As 

 illustrated in figure 12-1, the photosphere, 

 chromosphere, and the corona, comprise what 

 may be referred to as the solar atmosphere. 



Within the solar atmosphere certain more 



transient phenomena (referred to as solar 

 activity) occur similar to the systems occuring 



within the earth's atmosphere. This activity 



consists of the phenomena in the following 



paragraphs which collectively describe the 

 features of the solar disc. 



Solar Prominences 



Solar prominences are perhaps the most 

 beautifully colored appendages of the sun. They 

 appear as great clouds of gas, sometimes 

 resting on the sun's surface and at other times 

 floating free with no visible connection. When 

 viewed against the solar disc, they appear as 

 long dark filaments. They display a variety of 

 shapes, sizes, and activity which defy general 

 description. 



The more active types appear hotter than 

 the surrounding atmosphere with temperatures 

 near 10,000,000° K. 



Sunspots 



Sunspots appear as relatively dark areas 

 on the surface of the sun. They may appear 

 singly or in more complicated groups dominated 

 by large spots near the center. 



Sunspots begin as small dark areas known 

 as pores. These pores develop into full-fledged 

 spots in a few days, with maximum development 

 occurring in about 1 to 2 weeks. Decaying of 

 the sunspots consists of the spot shrinking in 

 size. This life cycle may consist of a few days 

 for small spots to nearly 100 days for larger 

 groups. The larger spots normally measure 

 about 120,000 km. Sunspots appear to have 

 cyclic variations in intensity, varying through 

 a period of about 8 to 17 years. 



Plages 



Plages are large irregular bright patches 

 which surround sunspot groups. They normally ap- 

 pear in conjunction with solar prom '.nences or fila- 

 ments and may be systematically arranged in 

 radial or spiral patterns. Plages are features 

 of the lower chromosphere and are often 

 completely or partially obscured by an under- 

 lying sunspot. 



Flares 



Solar flares are perhaps the most spectacular 

 of the eruptive features associated with solar 

 activity. They appear as flecks of light which 

 suddenly appear near activity centers, appearing 

 instantaneously as though a switch were thrown. 

 They rise sharply to peak brightness in a few 

 minutes, then decline gradually. The number 

 of flares may increase rapidly over an area 

 of activity. Small flarelike brightenings are 

 always in progress during the more active 

 phase of activity centers. The smaller flares 

 may be classified as subflares. In some 

 instances flares may take the form of prom- 

 inences, violently ejecting material into the 

 solar atmosphere and breaking into smaller 

 high-speed blobs or clots. Flare activity varies 

 widely between solar activity centers and appears 

 to be a function of the complexity of the 

 magnetic field. 



The greatest flare productivity seems to be 

 during the week or 10 days when sunspot activity 

 is at its maximum. 



As mentioned in an earlier chapter, solar 

 flare activity causes communication problems 

 affecting all modes of radio transmission. 



EARTH 



Of the nine planets of our solar system, 

 the earth is third in distance from the sun. 

 Its maximum distance from the sun is 94 

 million miles in summer; its minimum distance 

 from the sun is 91 million miles in winter. 

 It has an atmosphere more than 600 miles 

 thick. 



Motions 



The earth is subject to four motions in its 

 movement through space. Only two of these 



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