Weather and Climate

1. Weather and Climate What is the weather like today? Is it like this EVERY day? Why? What is the difference between WEATHER and CLIMATE?

2. Weather and Climate • Weather – The temporary environmental conditions in a localized area over a short period of time. In other words…what it’s like OUTSIDE, right HERE, right NOW • Climate – The long-term environmental conditions across a large area and long time. In other words…the AVERAGE of all the WEATHERS

3. What affects weather and climate? • There are two major factors that affect the overall environment and climate… • The tilt of the Earth in relation to it’s orbit around the Sun • - The direction of that tilt that changes as the Earth travels around the Sun

4. First, some basic vocabulary… • Revolution – one ORBIT, or trip around the Sun. This takes the Earth 365 ¼ days Rotation– one SPIN of the Earth on it’s axis. This takes about 24 hours…one DAY.

5. Earth’s TILT • The Earth is not vertical (straight up-and-down) in relation to it’s orbital path, it’s tilted 23 ½ degrees from vertical.  DRAW THIS ! ! ! This tilt means that the Sun’s energy doesn’t hit the Earth equally.

6. Earth’s TILT • This tilt results in uneven heating of the Earth’s surface. “Direct” sunlight “Indirect” sunlight

7. From TILT to SEASONS • As the Earth travels around the Sun, the tilt changes in relation to the Sun. Sometimes “toward” the Sun, sometimes “away”, and sometimes neither.  DRAW THIS !! This creates a predictable cycle of warmer and cooler periods, or seasons.

8. Seasons • Because the direction of the tilt (“towards” or “away”) is opposite for the Northern and Southern hemispheres, so are the seasons. Here is the rule to remember… Tilted “toward” the Sun means Summer, tilted “away” from the Sun means winter

9. Solstice and Equinox • Solstice – the point at which the Earth is pointed farthest toward / away from the Sun, creating long summer days and short winter days . (Latin root word “sol”) • Summer – around June 21 • Winter – around December 21 • Equinox – the point at which the Earth is not pointed toward OR away from the Sun, creating equal day and night. (“equi-nox”) • Spring (“Vernal”) • around March 21 • - Fall (“autumnal”) around Sept. 21

10. Earth’s tilt affects length of days • Places experiencing summer have “longer” days (more sunlight per 24 hrs.) • Places experiencing winter have “shorter” days (less sunlight per 24 hrs.) Longer Summer days Shorter Winter days 24 hrs. of light from Nov. to Feb. 24 hrs. of dark from May to August • Areas above 66 ½ degrees N or S will experience 24 hr. extremes (light and dark) depending on the season

11. Greenhouse Effect • RULE #1 OF NATURE – Energy can be either absorbed or transferred • Normally, when the Sun’s energy penetrates the atmosphere, some of it is absorbed, and some of it is reflected back to space. • Human and natural events increase pollutants that trap the reflected energy and send it back to the Earth again, increasing the Earth’s heat.

12. Distributing the Sun’s Heat - WIND • RULE #2 OF NATURE – Nature seeks balance (equilibrium) • Wind is the movement of air from High pressure to Low pressure • Air Pressure changes with temp. • “Hot” (more active) molecules need room to move, so they spread apart, meaning LESS molecules in a given space (LOW pressure) • “Cold” (less active) molecules don’t move as much, so they pack closer together, meaning MORE molecules in a given space (HIGH pressure) HOT air RISES COLD air SINKS

13. WIND – Sea Breeze • When the sun shines, land (solid) heats up faster than water (liquid) – remember RULE #1 ? • Only the top 2-3 inches of earth get warm, then the heat is reflected back to the air. (Why do dogs dig in the dirt?) • The warm air rises, creating LOW PRESSURE over the land during the early/mid-morning • This imbalance (RULE #2)creates a COOL wind blowing in from the water, called a SEA BREEZE L H

14. WIND – Land Breeze • When the sun sets, the process reverses and land cools off faster than water (RULE #1) • This creates COOLer air (HIGH pressure) over the land and WARMer air (LOW pressure) over the water at night • The WARM wind blowing out from the land is called a LAND BREEZE L H

15. WIND - Monsoons • On a larger scale, the same factors create monsoons - seasonal winds • Due to the Earth’s tilt, differences in the heating of land and ocean create long term wind patterns that bring seasonal rainy and dry periods.

16. Global Wind Patterns • RULE # 3 OF NATURE – Nature obeys the stronger force • The Earth gets the most direct sunlight in the tropics, so HOT air RISES at the Equator. • The least sunlight hits the polar region, so the COLD air sinks at the poles • These two extremes force the middle latitude winds to flow “backwards”, rising at 60 deg. and sinking at 30 deg., even though that is warmer air.

17. Coriolis Effect • Because the Earth spins (rotates) under the winds as they travel N and S, they appear to curve because of the Coriolis effect. (see it) • The result is curved wind patterns across the Earth surface. • All winds are named for where they come FROM. • Areas of no major wind pattern are called “doldrums” or “horse latitudes” (Spanish explorers)

18. Water Currents • Most ocean currents are affected by global wind patterns blowing across the oceans. Most COOL currents flow EAST Most WARM currents flow WEST

19. Precipitation – Nature’s Thermostat • There are 3 basic causes for rain. They are: • Convection – due to evaporation and cooling • Sun’s energy causes surface water to evaporate and become humidity • As the day cools off, the air cools and condenses, causing storms and rain • Usually in tropical environments • Frontal – due to changes in temperature • Starts with warm, moist air at the surface and above • As a cold front approaches, it stays low, forcing the moist air aloft • This cools and condenses the air, creating rain on the “leading edge” of the front • Usually in mid-latitudes where warm and cold air systems collide

20. Precipitation, Part II • Orographic – due to changes in elevation • Moist air travels over land and approaches a steep rise in elevation • As the air is forced up the side of the rise, the air cools, causing precip. on the “windward” side of the mountain • As the (now dry) air continues over and down the “leeward” side of the mountain, it warms up and absorbs any available moisture, creating a “rain shadow desert” • Found in areas of mountains or other rapid elevation change

21. CLIMATES • The world is divides into three large climate zones, based on latitude.  DRAW THIS !!! Low Latitude (“Tropical”) climates – always hot Mid Latitude (“Temperate”) climates – hot/cold seasons High Latitude (“Polar”) climates – seasons either mild or extreme cold

22. Climate Zones • Climate zones are divided into regions with differences in two key characteristics: • Amount of moisture (rain), and • Typical temperature range through the year • These two characteristics are affected by balancing the effects of four factors: • Latitude • Altitude • Nearness to water • Direction of atmosphere and ocean currents  WRITE THESE DOWN !

23. Latitude • Due to the Earth’s tilt, the amount of sun energy changes over the earth’s surface… Polar (High Latitude) zone – either mild temps. or extreme cold Temperate (Mid-Latitude) zone – seasonal, most varied climates Tropical (Low Latitude) zone – year-round direct sunlight, always hot RULE: The HIGHER the latitude, the COLDER the temps.

24. Altitude (Elevation) • Higher elevation = thinner air, therefore less air to hold heat makes it colder. RULE – The HIGHER the elevation, the COLDER the temperatures.

25. Nearness to Water • Land heats up and cools down QUICKLY. • Water heats up and cools down SLOWLY. • Therefore, water acts like a blanket… holding heat and releasing it slowly. • This results in smaller daily and seasonal temperature changes near large bodies of water. • “Coastal” areas are humid, “continental” areas are dry 30 degree change in Houston 45 degree change in Denver

26. Direction of Currents • Global wind and ocean currents transfer heat and moisture around the world, and help carry moisture from the oceans to the land • Warm water moving toward the land brings moisture (H2O) • Warm water moving parallel to the coast brings heat, no H2O • Cool water brings cool, dry air -> mild or desert climates

27. How it Works...Tropical Wet Climate • Latitude – in the tropics HOT • Altitude – low land doesn’t stop air flow until mtns. in the west • Nearness – flat land “acts coastal”, allows moisture inland • Direction – air flow brings in warm, moist air from the ocean which then hits the mountain and rains