Chapter 4 — TEMPERATURE, HUMIDITY, AND PRECIPITATION 



8. Precipitation. Precipitation is any and all 

 forms of water particles, whether liquid or 

 solid, that fall from the atmosphere and reach 

 the ground. It is distinguished from clouds, 

 fog, dew, etc., in that it must "fall"; and 

 from clouds and virga, in that it must reach 

 the ground. The amount of fall is usually ex- 

 pressed in inches of liquid water depth of the 

 substance that has fallen at a given point over 

 a specified period of time. 



9. Precipitation gage. A general term for 

 any device that measures the amount of pre- 

 cipitation. 



10. Hygrothermometer. An instrumental sys- 

 tem for obtaining dew point and ambient air 

 temperatures from dial indicators or recorder 

 traces and the use of remoted sensors as ther- 

 mometers. The hygrothermometer, for the Navy, 

 is the temperature/humidity portion of Semi- 

 automatic Meteorological Station AN/GMQ-14. 

 The Automatic Weather Station AN/GMQ-29 is 

 an equivalent system. 



11. Station standard system. For the Navy, 

 the station standard system is the AN/GMQ-14 

 or AN/GMQ-29. (Liquid-in-glass thermometers 

 are the station standard system for those sta- 

 tions not equipped with an AN/GMQ-14 or AN/ 

 GMQ-29.) 



12. Station standby system. The station stand- 

 by system, for the Navy, consists of the various 

 liquid-in-glass thermometers or psychrometers. 



DETERMINING TEMPERATURE, HUMIDITY, 

 AND PRECIPITATION 



Throughout the Naval Weather Service today 

 various assortments of temperature, humidity, 

 and precipitation devices exist; they are com- 

 pletely automatic, semiautomatic, or manually 

 operated. 



The order of precedence for use of the 

 various sensing instruments depends on the 

 elements being sensed. For temperature and 

 humidity, the first order of priority is the 

 hygrothermometer or equivalent system which 

 is the Semiautomatic Meteorological Station 

 AN/GMQ-14 ( ), and the temperature/dew point 

 temperature sensing system of the Automatic 

 Weather Station AN/GMQ-29, respectively. If 

 these systems are not available or properly 

 operating, the next choice will be the psychro- 

 meters , the hand-held electric psychrometer AN/ 

 ML-450A/UM or the manual sling and rotor 



psychrometers, which utilize the liquid-in-glass 

 type of thermometers. 



Remoted Sensor Reading 



When the AN/GMQ-29( ) is used to obtain 

 psychrometric values, the dry-bulb and dew- 

 point temperatures are read to the nearest 

 whole degree directly from the digital win- 

 dows. When the AN/GMQ-14( ) is used, these 

 values are obtained from the left-hand edge 

 of the recorder traces. These values are then 

 used to determine the remaining psychrometric 

 data that is required. 



Psychrometers 



SLING AND ROTOR PSYCHROMETERS.— 

 Procedures for exposure, moistening the wet- 

 bulb, aspiration, and reading the thermometers 

 are detailed in FMH-1. 



ELECTRIC PSYCHROMETER. — Procedures 

 for this instrument vary from those outlined 

 in FMH-1 for psychrometers. 



1. Place the instrument on a flat surface with 

 the graduations of the thermometer facing up- 

 ward and the air intake positioned into the 

 wind and to the left of the operator, or 



2. Grasp the instrument in the left hand 

 with the fingers fitting the curved portion of 

 the case, the graduations of the thermometers 

 facing the operator, and the air intake point- 

 ing to the left and into the wind. 



CAUTION: In either position, the air in- 

 take and both exhaust ports must be entirely 

 free of obstructions and far enough away from 

 the operator's body or any other source of 

 moist air or temperature that may cause a 

 false reading. 



Turn the switch knob clockwise to start 

 aspiration. If thermometer illumination is de- 

 sired, continue turning the knob clockwise un- 

 til sufficient light intensity is obtained. 



When the wet-bulb temperature stabilizes' 

 at a m'nlmum value, note the readings of both 

 thermometers and turn off the switch by turn- 

 ing the knob counterclockwise. 



Expose the psychrometer to the free air 

 for at least 5 minutes before using it for read- 

 ings. 



Exposure of this instrument is dependent 

 on the outside air temperature. If it is 50° F 



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