How does a source region influence the type of air mass that forms over it? Give specific examples of each basic classification.

First, understand what an air mass is and what a source region means. An air mass can be defined as a large body of air that has similar temperature and moisture properties throughout. A source region is the area over which an air mass forms and gets its characteristics from. This could be bodies of water, polar regions, or land surfaces.

Next, explain how the source region influences the type of air mass. The characteristics of an air mass (such as temperature and moisture content) are strongly influenced by the characteristics of its source region. For instance, air masses that form over oceans will have higher moisture content compared to those that form over land.

Finally, give specific examples for each basic classification of air masses. There are generally four basic classifications of air masses, defined by the type of source region they form over: \n1. Maritime Tropical (mT): Forming over warm ocean waters, these air masses are warm and moist. Example: The Gulf of Mexico, and the western part of the Pacific Ocean near the Philippines. \n2. Continental Tropical (cT): These air masses form over hot, dry desert regions, and are therefore hot and dry. Example: The Sahara Desert, the Middle East, and southwestern United States. \n3. Maritime Polar (mP): Forming over cold ocean waters, these air masses are cold and moist. Example: The North Atlantic and the northern Pacific near Alaska. \n4. Continental Polar (cP) and Continental Arctic (cA): These air masses form over cold surface regions and are therefore cold and dry. Example: Northern Canada, Siberia, and polar regions.

To summarize, the characteristics of a source region (like temperature and moisture level) greatly influence the type of air mass that forms over it. This is why air masses are classified based on the nature of their source regions.