UNITED STA TES DA IL Y A TMOSPHERIC SVIi 1 'K Y :?01 



which, if they form in the nortliern part of the plateau region, 

 move eastward to our hikes and thence to the 8t Lawrence with 

 scant rainfall ; cyclones which, if they have their origin fartlier 

 south on the warmer plains of Colorado, move into the Ohio 

 valley and thence into New England with considerahly more 

 precipitation ; and cyclones which, if they have their inception 

 on the hot and high plains of Arizona and New Mexico, can al- 

 ways be expected to give abundant rainfall when they reach the 

 lower Mississippi valley, and later as they pass over the Middle 

 Atlantic states. All these can be studied during? their incejjtion 

 at an average altitude of 5,000 feet above sea level and under 

 conditions of extreme aridit}' ; they can be viewed later as they 

 come down nearly to sea level in tlie Mississippi valley and 

 reach a more humid atmosj)here 1,000 miles from the place of 

 their birth ; and. finally, they are seen as they reach the ex- 

 tremely humid air of the Atlantic ocean, l,oOO miles farther east. 



The great winter cyclones which originate south of the Jajia- 

 nese islands and cross the Pacific ocean come under our vision 

 as they successfully surmount the formidable Rocky Mountain 

 barriers with but little diminution of energy, sweep across our 

 continent with increasing force and heav}^ precipitation, and 

 within three daj's pass beyond our meteorological horizon at the 

 Atlantic seaboard only to be heard from three days later as 

 borean ravagers of northern Europe. 



The great anti-cyclones or high-pressure eddies, which consti- 

 tute the American cold waves, drift into our territory from the 

 Canadian Northwest provinces and are studied under rapidly 

 changing conditions during 3,000 miles of their course. The 

 high-pressure eddy, with all the convectional principles of the 

 cyclone reversed, may be said not to deiiend upon the land of its 

 birth for the cold it brings, for a strong vortical and anti-cyclonic 

 motion at the center is continually drawing down the cohl air 

 from above. In the cold wave it must be conceded that the loss 

 of heat by radiation to a cloudless sky is much greater than that 

 gained by compression, or else it must l)e assumed that the at- 

 mosphere i)ossesses such intense colil at the elevation from 

 which the air is drawn that, notwithstanding the heat gained by 

 compression in its descent, it is still far below the normal tem- 

 perature at the surface of the earth. 



The West Indian hurricanes, always at .'<ea level and in humid 

 air, which are the most violent of all American storms, intrude 

 themselves into the domain of the United States weather map at 



