78 abstracts: meteorology 



METEOROLOGY. — Levels of maximum and minimum cloudiness. W. J. 

 Humphreys. Bulletin of the Mount Weather Observatory, 

 4. 1911. 



The formation of fogs is caused mainly by the cooling of the surface 

 of the earth through radiation, and hence the surface of the earth itself 

 is one level of maximum condensation. The next level of maximum 

 condensation is that of the cumulus cloud, and is limited in elevation 

 by the vertical temperature gradient of the atmosphere. The decrease 

 of temperature with elevation for the first three kilometers usually is 

 far less than the adiabatic rate. Hence, under these conditions, convec- 

 tion can not extend very high, and therefore cumulus clouds commonly 

 are phenomena of the lower atmosphere and of frequent occurrence. 

 The next and only other level of maximum condensation is just beneath 

 the isothermal region where the cirrus cloud prevails. Since the temper- 

 ature at this elevation ceases to decrease with altitude therefore it is 

 the limit of vertical convection, and any clouds brought to this level by 

 long continued storms must spread out and not go up higher. The 

 limit to convection and the swift winds of the upper cloud region spread 

 the cirri over extensive areas, and hence they are more frequently seen 

 than are those of the next lower levels that are more limited in extent. 



At middle latitudes the levels of maximum condensation are, roughly: 

 (1) Fog level, surface of the earth or water. (2) Cumulus hvel, 1 to 2 

 kilometers above the surface. (3) Cirrus level, 8 to 10 kilometers above 

 the surface. 



The corresponding approximate levels, or, preferably, regions of 

 minimum condensation, are: (1) Scud region, 100 to 300 meters eleva- 

 tion. (2) Alto-stratus region, chiefly 4 to 6 kilometers above the sur- 

 face. (3) Isothermal region, usually 11 kilometers or more above the 

 surface. W. J. H. 



METEOROLOGY. — Origin of the permanent ocean highs. W. J. Hum- 

 phreys. Bulletin of the Mount Weather Observatory, 4. 1911. 



The circulation of the atmosphere between the warm equatorial and 

 the cold polar regions, together with the rotation of the earth, causes 

 the prevailing winds at higher latitudes than about 33° to blow from 

 west to east, and the tropical winds to blow from east to west. The 

 former have an angular velocity about the axis of the earth greater 

 than that of the earth itself, and therefore press up toward the equator, 

 while the latter have a smaller angular velocity than the earth and conse- 



