What is Weather? www.ai.mit.edu/people/jimmylin/pictures/2001-12-seattle.htm

Combination of properties of the troposphere at a given time

Includes….. Temperature Pressure Humidity Precipitation Sunshine Cloud cover Wind direction & speed

Air Mass  a section of air that has the same properties (temp & humidity)

Front boundary between two air masses Warm front – when a warmer air mass replaces a cooler one Cold front – when a cooler air mass replaces a warmer one

Why is precipitation normally found along fronts? 1. Front = rising air 2. Rising air = cooling air 3. Cooling air = lower ability to hold H2O

As the air cools, it cannot hold as much water vapor, so the water vapor condenses to clouds and eventually precipitation

Air Pressure - weight of the atmosphere per unit area - gravity has a huge affect on air pressure (pressure is near Earth’s surface)

HIGH pressure areas form when cooler, more dense air sinks towards Earth’s surface. The air warms as it sinks so Highs are usually associated with fair or clear weather.

LOW pressure areas form when warmer, less dense air rises into the atmosphere. Usually associated with fronts and precipitation because of the rising air

Why uneven heating? Winds result from the uneven heating of the atmosphere Why uneven heating?

1. Specific heat of land (soil) and water land and sea breezes

Describe wind direction using High and Low Describe wind direction sinking air and rising air Land Breeze --- air is sinking over land because it cools more quickly when the sun goes down, H over the land and L over the water. Sea Breeze ------ air is rising over the land because it heats more quickly in the daytime

2.

Uneven heating from the sun helps form pressure belts around Earth These pressure belts contribute to the production of three major convection zones in the atmosphere Label pressure belts, discuss why equator is L Equator is L because it receives the most direct sunlight = lots of heating = rising air = low pressure area…… Air cannot rise forever, it will eventually have to sink, this is why the 30N and 30S are H pressure belts = sinking air…. (for this reason, many of the worlds largest deserts are found at this latitude) 60N and 60S are L pressure belts 90S and 90N are H pressure belts

Add winds to the diagram…. Without coriolis… Add winds to the diagram…. Without coriolis….. This would be accurate BUT Earth rotates

Coriolis Effect

Draw winds with coriolis effect LABEL!!!

Hadley Cell animation

Climate Average long term weather of an area 2 Main factors Temperature Precipitation

Temperature & Precipitation are affect by four main factors…..

1. Latitude – determines the amount of solar energy a region receives Only the equator receives direct sunlight year round

Earth’s tilt gives us seasons NOT distance from the sun

2. Atmospheric Circulation Convection currents and prevailing winds created by the heating and cooling of the atmosphere

3. Ocean Circulation Also affected by solar heating and the Coriolis Effect.

Oceans have a great affect on climate b/c H2O holds a lot of heat Oceans/Large bodies of H2O tend to make climates more moderate * Warmer winters & cooler summers than inland areas * Usually more precipitation

4. Topography - shape of the land

What is El Nino?

Normal South Pacific Conditions

Upwelling of nutrient rich water provides lots of food for fish

Surface winds blow westward EQUATOR Warm waters pushed westward SOUTH AMERICA AUSTRALIA Warm water Thermocline Cold water Normal Conditions

During non-El Niño/normal years, the southeast trade winds, drag surface water westward away from shore. As surface water moves away, upwelling brings up colder waters from depths of 40-80 meters or more. This deep sea water is rich in nutrients which can sustain large fish populations.

El Nino (ENSO – El Nino Southern Oscillation)

Prentice Hall Textbook animation link

Winds weaken, causing updrafts and storms Drought in Australia and Southeast Asia EQUATOR Warm water flow stopped or reversed AUSTRALIA SOUTH AMERICA Warm water deepens off South America Warm water Thermocline Cold water El Niño Conditions

During an El Niño event, the southeast trade winds weaken and so does the amount upwelling in the eastern Pacific. The deeper thermocline means that any upwelling that does occur is unable to tap into the rich nutrients found in deeper waters. Consequently, warm nutrient-poor water predominates the region and a decrease in the fish population is observed.