9. a) What are three characteristics of a continental polar air mass? How does it form? b) What are three characteristics of a maritime polar air mass? How does it form? c) What are the two main characteristics of a continental tropical air mass? How does it form? d) What are three characteristics of a maritime tropical air mass? 10. a) Which of the four types of air mass in Question 9 produces the greatest amounts of daily average precipitation over California? (These events occur in atmospheric rivers.) b) Where is the air mass in (a) located in relation to a cold front? c) Which of the four types of air mass in Question 9 occurs most frequently with rain showers during winter over California? d) Where is the air mass in (c) located in relation to a cold front? 11. a) From what direction is the wind usually when a cold front is approaching San Diego? b) From what direction is the wind usually after a cold front has passed San Diego?