According to Buys Ballot’s law，when an observer in the Northern Hemisphere experiences a northwest wind，the center of low pressure is located to the（）.

单项选择题A warm air mass is characterized by（）.

A.stability
B.instability
C.gusty winds
D.good visibility

单项选择题A series of brief showers accompanied by strong，shifting winds may occur along or some distance ahead of a(n)（）.

A.upper front aloft
B.cyclone
C.occluded front
D.cold front

单项选择题A sea breeze is a wind（）.

A.that blows towards the sea at night
B.that blows towards an island during the day
C.caused by cold air descending a coastal incline
D.caused by the distant approach of a hurricane

单项选择题A line of clouds，sharp changes in wind direction，and squalls are most frequently associated with a(n)（）.

A.occluded front
B.warm front
C.cold front
D.warm sector

单项选择题A hygrometer is a device used for determining（）.

A.the absolute temperature
B.atmospheric pressure
C.wind velocity
D.relative humidity