Chapter 14 — AIR MASSES AND FRONTS 



5°N 



IO°N 



15°N 



Figure 14-25.— Weather conditions in an active portion of the ITCZ. 



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Seasonal Variation 



The use of mapped digital satellite data has 

 improved the information of the seasonal 

 meridional displacement of the cloud band 

 associated with the ITCZ. 



The cloud pictures revealed that the cloud 

 band has somewhat different characteristics in 

 different parts of the world. In the Atlantic, 

 it is centered about 3 degrees north in the 

 winter season and moves to about 8 degrees 

 north by late summer. In the Pacific, the 

 seasonal fluctuations of the cloud band are not 

 readily apparent east of 150 degrees west. 

 Seasonal pressure changes over North America 

 may be responsible for what seasonal shift of 

 the ITCZ cloud band there is in the eastern 

 Pacific. West of 150 degrees the movements 

 are not well defined. The large area of 

 relatively cloud-free skies during the winter 

 season southwest of Central America and 

 Mexico suggests that dry wintertime continental 



outflow pushes the ITCZ cloud band to the south 

 in this area. There is some evidence of a 

 weak second cloud band associated with the 

 ITCZ along 5 degrees south, during the period 

 January through March. It varies in strength 

 from year to year, occasionally failing to 

 develop at all. The ITCZ band of clouds in 

 the Indian Ocean during the Southern Hemisphere 

 summer is much broader in extent than either 

 of the cloud bands found in the Atlantic or 

 Pacific Oceans. 



TROPICAL CYCLONES 



The most widespread destructive weather 

 phenomenon is the tropical cyclone, which each 

 year claims lives and causes extensive damage. 

 While a tornado exceeds the severity of a full- 

 fledged tropical cyclone it is generally confined 

 to a smaller area and has a comparatively short 

 path and life duration. The tropical cyclone due 

 to its greater horizontal extent and longer life, 



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