CHAPTER 15 



METEOROLOGICAL ELEMENTS 



When the term "meteorological elements" 

 is used, it is in reference to those elements 

 which are responsible for the formation of weather 

 within the atmosphere. 



Most weather, as it is known and as it has 

 a bearing on naval operations, occurs in that 

 portion of the atmosphere referred to as the 

 troposphere. The meteorological elements that 

 comprise this weather are temperature, atmos- 

 pheric pressure, humidity, hydrometeors, litho- 

 meteors, photometeors, electrometeors, and 

 wind. Temperature, atmospheric pressure, wind 

 and humidity were discussed in previous chapters 

 of this training manual. 



This chapter will be confined to discussing 

 hydrometeors, lithometeors, photometeors, and 

 electrometeors occurring below the tropopause 

 (within the troposphere). Above the tropopause, 

 little or no weather occurs, except for the 

 aurora, because water vapor is present only 

 in very small quantities. The presence of water 

 vapor in the air is the most important factor 

 controlling the type and intensity of weather. 



forms of precipitation, although they are hy- 

 drometeors. Precipitation is classified accord- 

 ing to both its form (liquid, freezing, and solid) 

 and size (and rate of fall). The size of pre- 

 cipitation drops determines their rate of fall 

 to a large extent. Also, the size determines 

 some of the different types of precipitation. 



Rain 



Precipitation which reaches the earth's sur- 

 face as water droplets with a diameter of 0.02 

 inch (0.5 mm) or more is classified as rain. 

 If the droplets freeze on contact with the ground 

 or other objects, the precipitation is classified 

 as freezing rain. Rain emanating from convective 

 clouds is referred to as rain showers. Showers 

 usually start and stop rather suddenly; they are 

 quite intermittent in character; and the drops 

 of which they are composed are usually larger 

 and the impact (therefore the intensity) of the 

 drops is greater than with other types of rain. 



Drizzle 



HYDROMETEORS 



Hydrometeors consist of liquid or solid water 

 particles which are either falling through or sus- 

 pended in the atmosphere, blown from the sur- 

 face by wind , or deposited on objects. Hydro- 

 meteors comprise all forms of precipitation, such 

 as rain, drizzle, snow, and hail, and such el- 

 ements as clouds, fogs, blowing snow, and dew. 



Drizzle consists of very small and uniformly 

 dispersed droplets that may appear to float 

 while following air currents. Sometimes drizzle 

 is referred to as mist. Unlike fog droplets, 

 drizzle falls to the ground. However, the rate 

 of fall is very slow. The slow rate of fall and the 

 small size of the droplets distinguish drizzle 

 from rain. When the droplets freeze on contact 

 with the ground or other objects, they are called 

 freezing drizzle. Drizzle usually restricts visi- 

 bility. 



PRECIPITATION 



Snow 



Precipitation includes all forms of moisture Snow consists of white or translucent ice 



that fall to the earth's surface, such as rain, crystals. In their pure form the ice crystals 

 snow, hail, drizzle, etc. Dew and frost are not are highly complex, hexagonally branched forms. 



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