WINDS AND WEATHER 187 



Land and Sea Effects on Wind. You have learned that 

 land absorbs heat more readily than water, and also gives 

 it off more readily. So, other things being equal, land is 

 warmer than water in summer and cooler than water in 

 winter. This may produce a considerable effect upon air 

 movements. Its tendency is to cause air to move land- 

 ward in summer (to replace the ascending hot air there) 

 and waterward in winter. The most striking case of this 

 is the relation between the great tropical peninsula of 

 India and the Indian Ocean which surrounds it. Here 

 the prevailing winds change with the seasons in the manner 

 just indicated. In this region these seasonal winds are 

 called the monsoons. (The winds previously discussed, 

 being affected by the rotation of the planet, are called 

 planetary winds.) 



Change hi wind direction may also be effected by the 

 temperature change of night and day between water and 

 land. This effect is, of course, not so wide-spread as the 

 seasonal change in such a case as India, but it is enough 

 to give us along the shores of lakes and oceans frequent 

 fluctuations in the direction of wind. It gives us what 

 we call lake or sea breezes, or land-breezes. During a 

 hot day and evening the air may move in from water to 

 land (sea-breeze), and then, toward morning, if the land 

 has cooled off more than the water, it may move water- 

 ward again (land-breeze). 



QUESTIONS 



1. Why do we study the weather? 



2. How are weather-maps made and what do they tell us? 



3. What causes low pressure and high pressure in the atmosphere? 



4. What are the trade- winds? 



5. What are isotherms and isobars? 



