Weather & Climate Chapter 6

Weather & Climate Weather:  Refers to the current, day-to-day, short term conditions of the atmosphere.

Weather & Climate Weather:  Wind speed  Wind direction  Temperature  Type of precipitation  Amount of precipitation  Cloud cover  Humidity  Air pressure  Hours of sunshine.

Weather & Climate Climate:  Refers to the long term trends / patterns in the weather for a certain area.  Different areas experience different climate.  Monthly, seasonal, yearly.

Climate OR Weather?? Do the following phrases refer to weather or climate?  Annual precipitation of 200 mm.  Rain forecasted for tomorrow Tuesday.  Normal July temperature averages 22˚ C  Temperatures this week will range between 20 & 30˚C

Climate OR Weather?? Do the following phrases refer to weather or climate?  It was unusually hot this summer.  Grand Falls-Windsor had 15 cm of snow this past weekend.  Vancouver has an annual frost free period of 233 days.  Residents in Florida are preparing to take shelter from a hurricane.

Factors that Affect Climate  Latitude  Ocean Currents  Winds / Air Masses  Elevation / Altitude  Relief (Mountain barriers)  Nearness to water

Scattergraphs

1.Latitude  The further you move away from the equator the colder it gets.  As latitude INCREASES – temperature decreases!  The closer you go towards the equator the warmer it gets.  As latitude DECREASES – temperature increases!

1.Latitude (cont’d) The reason for this is:  The sun’s energy is concentrated in small areas near the equator.  Over larger areas further from the equator…the earth’s shape!  Therefore the farther from the equator the sun’s energy spreads over a larger area.

Intensity and Duration!!

2.Ocean Currents  Pages Q 1-3.  Warm versus cold ocean currents.  Areas near warm ocean currents have temperatures warmer than areas near colder ocean currents.

2.Ocean Currents (cont’d)  Pages Q 1-3.  Warm air over warm ocean currents colliding with cold air over cold ocean currents result in precipitation such as FOG!  Ie. St. John’s, NL where the COLD Labrador current collides with the warmer Gulf Stream (See p. 60)

3.Wind  Understand the cause of wind and how they affect climate

What is Wind? A wind is a horizontal movement of air across a surface. Vertical movements are currents or updrafts and downdrafts Caused by what???? Heat versus cold!! This can be related to convection cells.

What causes wind?  Unequal heating  Unequal heating causes pressure differences  Cold, heavy air sinks = high pressure  Warm, expanding air rises = low pressure  Winds blow from high to low

Know that air blows from areas of high pressure to areas of low pressure.  The statement is fact.  Think: 1. Air inside a balloon  High and low pressures in the earth’s atmosphere are responsible for wind

Define the terms wind & prevailing wind.  Wind:  Is a horizontal movement of air across a surface.  It results from air masses of different temperatures and humidity lying next to each other.  The resulting pressure variation causes “wind” to blow from high pressure areas to low pressure areas.

Prevailing Wind:  Is regular, predictable, normal wind direction for a given area or region.  Caused by global convection cells.  Named after the direction from which it comes

Prevailing Winds

Prevailing Winds

Summary of Prevailing Wind  Global highs and lows are due to uneven heating of the earth  Air moves FROM HIGH pressure TO LOW pressure creating winds.

Describe Orographic rainfall  A relatively warm, moist air blows off the sea  It is forced up by mountains (high relief) Windward Leeward Chinook

Orographic rainfall  Air cools at higher altitude  Cool air holds less moisture  Consequently clouds condense and rain falls  Most rain falls on the windward side of the relief  Leeward side is often in a dry rain shadow because the moisture has all been lost

Definitions  Windward  The side of the mountain receiving the wind of the water/ocean  (consequently more precipitation as well)  Leeward  The side of the mountain sheltered from the wind  (consequently receives less precipitation)  Rain Shadow  The area located on the leeward side of a mountain that receives low amounts of precipitation.  Mainly due to the air that descends on the leeward side has “dumped” on the windward side.

Frontal rainfall / Cyclonic Warm, moist air FRONT Weather Front-2 fronts meet Hence the name frontal rain Warm Moisture laden air meets cold air Warm air is less dense & is forced up over the cooler, more dense air

Frontal rainfall Warm Moisture laden air cools at higher altitude Cool air holds less moisture Consequently clouds condense and rain falls

Describe Convectional rainfall  Usually occurs in hot areas like tropics or continental summer  Sun heats the earth causing large amounts of water to evaporate  Hot air rises forming convection currents (hence the name)  Warm Moisture laden air cools at higher altitude  Cool air holds less moisture  Consequently clouds condense and rain falls Often associated with thunder storms. Air heated from the earth