AEROGRAPHER'S MATE 3 & 2 



LITHOMETEORS 



SAND 



Along with hydrometeors, due consideration 

 must be given to lithometeors, since they affect 

 the state of the atmosphere. Lithometeors com- 

 prise a class of atmospheric phenomena, among 

 which dry haze and smoke are the most common 

 examples. In contrast to a hydrometeor, which 

 consists largely of water, a lithometeor is com- 

 posed of solid dust or sand particles, or the 

 ashy products of combustion. 



HAZE 



Haze is suspended dust or salt particles so 

 small that they cannot be individually felt or 

 seen by the unaided eye. They reduce visibility 

 and lend a characteristic opalescent appearance 

 to the air. Haze resembles a uniform veil over 

 the landscape that subdues its colors. This veil 

 has a bluish tinge when viewed against a dark 

 background and a dirty yellow or orange tinge 

 when viewed against a bright background. 



Irregular differences in air temperature may 

 cause a shimmering veil over the landscape. 

 This is called optical haze. 



SMOKE 



Smoke is fine ash particles suspended in 

 the atmosphere. When smoke is present, the 

 disk of the sun at sunrise and sunset appears 

 very red and during the daytime has an orange 

 tinge. Smoke at a distance, such as from forest 

 fires, usually has a light grayish or bluish color 

 and is evenly distributed in the upper air. 



DUST 



Dust is finely divided solid matter, uniformly 

 distributed in the air. It imparts a tannish or 

 grayish hue to distant objects. The sun's disk 

 is pale and colorless or has a yellow tinge at 

 all periods of the day. 



Blowing Dust 



Blowing Dust consists of dust raised by the 

 wind to moderate heights above the ground and 

 restricting horizontal visibility to less than 

 7 miles. When visibility is reduced to less than 

 5/8 mile but not less than 5/l6 mile it is 

 classed as a duststorm and if less than 5/l6 

 mile, a severe duststorm. 



Fine particles of sand picked up from the 

 surface by the wind and blown about in clouds 

 or sheets constitute a troublesome lithometeor 

 in some regions. 



Blowing Sand 



Blowing sand consists of sand raised by 

 the wind to moderate heights above the ground 

 reducing horizontal visibility to less than 7 

 miles. When the visibility is reduced to less 

 than 5/8 mile but not less than 5/l6 mile, it 

 is classed as a sandstorm and if less than 

 5/l6 of a mile, a severe sandstorm. 



DUST DEVILS 



Dust devils, phenomena of whirling, dust- 

 laden air, are caused by intense solar radiation, 

 which sets up a steep lapse rate near the 

 ground. They are best developed on a calm, 

 hot afternoon with clear skies, and in desert 

 regions. As the intense surface heating sets up 

 a steep lapse rate, a small circulation is formed 

 when the surrounding air rushes in to fill the 

 area of the rising warm air. This warm as- 

 cending air carries dust, leaves, and other 

 small material to a height of a few hundred 

 feet. 



PHOTOMETEORS 



The photometeors are any of a number of 

 atmospheric phenomena which appear as luminous 

 patterns in the sky. They constitute such phe- 

 nomena as solar and lunar halos, solar and 

 lunar coronas, rainbows, and fogbows. Photo- 

 meteors are not active elements; that is, they 

 generally do not cause adverse weather. How- 

 ever, they are related to clouds which do cause 

 adverse weather. Thus, they help in describing 

 the state of the atmosphere. 



HALOS 



A halo is a luminous ring around the sun 

 or moon. When it appears around the sun, it is 

 a solar halo; when it forms around the moon, 

 it is a lunar halo. It usually appears whitish, 

 but it may show the spectral colors (red, 

 orange, yellow, green, blue, indigo, and violet) 

 with the red ring on the inside and the violet 



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