Passage VI

Air at its dew point temperature (or dew point) is saturated with water vapor. Air temperature usually decreases with increasing altitude. When air cools to its dew point, the water vapor in the air can begin to condense and form clouds.

Air temperatures and dew points were measured every 600 m from the surface (0 m) to an altitude of 3,000 m at 4 cities (A-D). Data, including the altitude of the cloud base over each city, were taken at 2 P. M. on every summer day that clouds were present. Figures 1-4 show the average air temperatures, the average dew points, and the average cloud-base altitudes at each city.

34. The table below shows the average July air temperatures and dew points at 0 m altitude for Miami, Florida, and for Phoenix, Arizona.

Based on this information and the data in Figures 1-4, which of these 2 cities, on average, would have lower cloud bases in July?

Answer and Explanation

Your Answer is

Correct Answer is J

Explanation

From figures 1-4, it can be seen that the dew point decreases slowly with the increase of height, and the height of dew point=air temperature is the average cloud-base altitude, as can be seen from the table given in the title, The difference between the air temperature over Miami and the dew point is smaller, so the air temperature of the city will first drop to the dew point with altitude. So Miami's lower cloud base will be lower