CLIMATE and WEATHER Part II

PRECIPITATION

Precipitation Three types of precipitation: RELIEF PRECIPITATION CONVECTIONAL PRECIPITATION CYCLONIC PRECIPITATION Three types of precipitation: RELIEF PRECIPITATION CONVECTIONAL PRECIPITATION CYCLONIC PRECIPITATION

Why does precipitation occur? Air cools as it rises As air cools, water vapour condenses more than it evaporates Air cools as it rises As air cools, water vapour condenses more than it evaporates

Why does air rise? 1.It rises to cross an area of high elevation. This causes RELIEF PRECIPITATION 2.It rises because it has absorbed heat from the earth’s surface. This causes CONVECTIONAL PRECIPITATION 3.It rises because there is a cooler, denser air mass flowing beneath it that forces it up. This causes CYCLONIC PRECIPITATION. 1.It rises to cross an area of high elevation. This causes RELIEF PRECIPITATION 2.It rises because it has absorbed heat from the earth’s surface. This causes CONVECTIONAL PRECIPITATION 3.It rises because there is a cooler, denser air mass flowing beneath it that forces it up. This causes CYCLONIC PRECIPITATION.

RELIEF PRECIPITATION Mountain barriers create relief precipitation As the moist air rises up the slope of a mountain, it expands and cools As the air cools, the rate of evaporation decreases while the rate of condensation increases The result is water droplets in the air The heavier and more condense the droplets become, rain falls In colder temperatures, water vapour condenses to snow Mountain barriers create relief precipitation As the moist air rises up the slope of a mountain, it expands and cools As the air cools, the rate of evaporation decreases while the rate of condensation increases The result is water droplets in the air The heavier and more condense the droplets become, rain falls In colder temperatures, water vapour condenses to snow

RELIEF PRECIPITATION

CONVECTIONAL PRECIPITATION Very common in summer Common in location such as the Prairie provinces, Ontario and Qu é bec The land is subject to intense heating As the ground heats up, the air above it rises As it rises it expands and cools The water vapour within it condenses, forming puffy white clouds As more water vapour condenses into these clouds, the clouds develop vertically and water droplets get larger and larger Very common in summer Common in location such as the Prairie provinces, Ontario and Qu é bec The land is subject to intense heating As the ground heats up, the air above it rises As it rises it expands and cools The water vapour within it condenses, forming puffy white clouds As more water vapour condenses into these clouds, the clouds develop vertically and water droplets get larger and larger

CONVECTIONAL PRECIPITATION At high altitudes, the water droplets may even freeze, forming ice pellets (hailstones) The weight of the water droplets or hailstones cause them to fall to the ground, often violent downpours At high altitudes, the water droplets may even freeze, forming ice pellets (hailstones) The weight of the water droplets or hailstones cause them to fall to the ground, often violent downpours

CONVECTIONAL PRECIPITATION

CYCLONIC PRECIPITATION A cyclonic storm (also known as a front) is a large, low-pressure system that forms when a warm air mass and a cold air mass collide This often occurs under the polar-front jet stream which separates cold dry arctic air from warm, moist tropical air The rotation of the earth causes the air to circulate in a counterclockwise direction A cyclonic storm (also known as a front) is a large, low-pressure system that forms when a warm air mass and a cold air mass collide This often occurs under the polar-front jet stream which separates cold dry arctic air from warm, moist tropical air The rotation of the earth causes the air to circulate in a counterclockwise direction

CYCLONIC PRECIPITATION

Homework Textbook - page 139 #1-10 a), 11