Precipitation

Question 1

What are 3 ways air may be caused to rise?

Answer 1

1. As it cross an area of higher elevation – causes relief (or orographic) precipitation.
2. It absorbs heat from the ground and rises – causes convectional precipitation.
3. Cooler, denser air flows underneath it forcing air aloft – causes cyclonic precipitation.

Question 2

Describe orographic precipitation.

Answer 2

• warm moist air moving across the ocean is forced to rise by mountains
• as the air rises, it cools
• As air cools, the water vapour in the air condenses and water droplets form, until it precipitates on the windward side of the mountain [the side with clouds]
• As the air moves back down the mountain, it collects moisture from the ground via evaporation. (This side of the mountain is called the leeward side. It receives very little precipitation)

Question 3

Describe convectional precipitation.

Answer 3

• sun heats the ground
• Hot ground hearts the lowest air, and water from the ground is evaporated
• Water vapour rises rapidly
• as it rises it cools and condenses

Question 4

How do air masses move preceeding cyclonic/frontal precipitation?

Answer 4

• warm air mass comes into contact wtih cold air mass
• warm air [less dense] rises above cooler mass
• Moist air condenses and forms clouds

Question 5

What is a hyetograph?

Answer 5

is a graphical representation of the distribution of rainfall over time, where the “rainfall amount” or “depth” is plotted on the y-axis, and the “time” is plotted on the x-axis

Question 6

What is a rainfall mass curve?

Answer 6

a plot of summation of rainfall increments as a function of time, where cumulative rainfall amounts are indicated on the y-axis and time is indicated on the x-axis

Question 7

Which methods of modelling rain guage data are weighted?

Answer 7

The Theissen polygon method and the Isohyetal method