486 abstracts: meteorology 



METEOROLOGY. — Daily changes in temperature up to IfiOO meters. 

 Alfred J. Henry. Bulletin Mount Weather Observatory 5: 

 1-18. 1912. 



This paper is a discussion of the 24-hour accidental changes in temper- 

 ature of the free air from the ground to 4000 meters above sea level as 

 determined by means of kite flights made at Mount Weather, Va. 

 Inasmuch as only nights made on consecutive days and to approximately 

 the same altitude could be used the total number of flights available was 

 less than 100 and for that reason the results reached are perhaps a trifle 

 uncertain. 



The accidental changes in temperature in the free air to warmer and 

 colder, respectively, is a subject about which comparatively little is 

 known. On the earth's surface, however, it is known that in a general 

 way changes to lower temperature are greater in magnitude and occur 

 with greater frequency than those of an opposite character. In a meas- 

 ure this is also true of the free air up to the altitude mentioned. There 

 appears to be a point in the free air above Mount Weather where the 

 accidental changes are at a maximum value. In rising temperature 

 in winter the accidental changes are greatest between the 1 and 1^ 

 kilometer levels above sea where they are several degrees greater than 

 at the ground on the mountain top. This is also true of falling tempera- 

 ture, the greatest change, however, extends thru a deeper stratum, viz., 

 from the first to the second kilometer above sea or from 1553 to 4833 feet 

 above the mountain top. This characteristic is much less pronounced 

 in summer than in winter. 



A comparison between the temperature of the free air in the ascent 

 and the descent of the kites, respectively, shows that the temperature 

 of the air is changing by small amounts practically all the time. Natur- 

 ally the greatest changes are recorded under the influence of a nearby 

 storm-center, as when a warm southerly wind is replaced by a cold 

 northerly one. A typical case was investigated; it showed an hourly fall 

 of 0.9°C. which if continued for 24 hours would amount to 21.6°C. or 

 39.6° F. This amount is believed to closely approximate the true daily 

 fall under extreme weather conditions. 



It was found that changes in the free air temperatures above Mount 

 Weather in the layers below 4000 meters occurred under very definite 

 pressure distribution, that is to say, changes to higher temperatures 

 almost invariably occur when the region to the east and northeast is 

 occupied by an area of high pressure and the Mississippi valley or the 

 upper Lake region is occupied by low pressure. Mount Weather is 



