Chapter 13 Atmosphere and Climate

“Climate is what we expect; weather is what we get” Weather and Climate Weather is a short-term atmospheric condition in an area. They include: Temperature Humidity Precipitation Cloud cover What is the weather today here? What is the climate for here? Climate is a region atmospheric condition ’s general pattern of over a long period of time (at least 30 years). The two major factors contributing to a region’s climate: average temperature average precipitation “Climate is what we expect; weather is what we get” Mark Twain

Climate Factors that determine climate: latitude atmospheric circulation patterns oceanic circulation patterns local geography of the area solar activity volcanic activity distance from the equator (most important)

How does latitude influence climate? Equator is a 0o latitude. The amount of solar energy that reaches Earth depends on latitude. Areas near the equator receive more solar energy.

What causes the seasons? Seasons are the direct result the tilt of Earth’s axis. Because of the tilt, the angle at which the sun’s rays strike the Earth change as the Earth orbits the sun.

Reason for Seasons Latitude is the distance north or south of the equator. Measured in degrees. Equator is 0 degrees, the poles are 90 degrees Low Latitudes – get the strongest, most concentrated sunlight. Night and Day are 12 hours, all year round High temps all year round High Latitudes – sunlight is spread over a greater area, weaker, less energy Daylight hours vary At the poles the sun sets for only a few hours during the summer Dark almost all day during winter Average annual temperatures lower than at equator.

How does air circulation influence climate? 3 properties of air help it influence climate: (1) cold air sinks. (2) warm air rises. (3) warm air can hold more water vapor.

Convection cells Three basic rules: 1. Cold air sinks – but pressure is stronger at lower levels so cold air gets compressed and thus warms. 2. Warm Air Rises – lower pressure lets it expand and it cools down 3. Warm Air holds more water vapor than cold air – so as it rises the water vapor cools and condenses How do we get wind? 1. Sun heats the earth surface. 2. Hot Air Rises 3.Cold Air replaces it………wind! High pressure zones in the subtropical regions are where many deserts are located, around 30 degrees north and 30 degrees south latitudes. These zones are created by Hadley Cells (see figure below), a convection pattern resulting from solar energy. The process is such that:   1. Air is heated in greater amounts at the equator because the angle of light hitting the Earth is closer to perpendicular. That is there is less surface area exposed to higher amounts of radiation, and increased warming results. 2. This warm air expands and rises at the equator, creating low pressure zones. 3. These low pressure zones suck in moisture-bearing masses, or rain-clouds, while the equatorial air masses travel towards the poles. Also, these rising masses cannot retain as much water as they continue to rise because they are cooling, which results in high rainfall at the equator, i.e. equatorial rainforests. 4. As these equatorial air masses travel away from the equator, they cool in temperature, and descend closer to the surface of the globe. 5. High air pressure and increased dryness results as the air masses nears the surface. 6. Moisture is sucked from the surface at 30 degrees north and 30 degrees south because the air masses are increasing in temperature and are able to hold more water (Ricklefs 1993).

How do ocean currents affect climate? Water holds large amounts of heat. Surface currents redistribute warm and cool masses of water around the planet. Some surface currents warm or cool coastal areas year- round. El Niño (moves warm waters from the western Pacific Ocean) La Niña (moves cold waters from eastern Pacific Ocean)

Ocean currents Currents also help mix ocean waters to distribute nutrients and dissolved oxygen needed for aquatic organisms Winds moving away from coastal regions result in upwelling of cold, nutrient-rich bottom waters as surface water moves offshore. These nutrients support large populations of phytoplankton, zooplankton, fish, and fish-eating sea birds. El Niño and La Niña are changes in climate patterns that can trigger mild to extreme weather changes over at least ⅔ of the globe.

ENSO El Niño/Southern Oscillation (ENSO) results from a change in direction of tropical winds. Trade winds blowing west are weakened or reversed. Surface water warms along the North and South American coasts, and upwelling of nutrients is suppressed, which reduces primary productivity that results in sharp decline of fish population. Jet stream above North America is also distorted, changing weather patterns. leads to increased clouds and rainfall in SW US Simulation El Niño Animation

La Nina La Niña cools some coastal surface waters and brings back coastal upwelling. This results in warmer, drier winters in the southeastern and southwestern U.S., wetter winters in the Northwest. Typically a La Niña causes more destruction in the U.S. because there are more Atlantic coast hurricanes and tornadoes. Similar to normal conditions, just enhanced.

How does topography affect climate? Elevation (height above sea level) affects climate due to decreasing temps. Temperatures fall by 6oC for every 1,000 m increase in elevation. Mountain ranges may affect precipitation distribution.

Rain Shadow Rain Shadow Dry area on the eastern side of mountains The smaller the mountains, the weaker the rain shadow effect, and vice versa.

Other influences on Earth’s climate: The Sun and Volcanic Eruptions At a solar maximum, the sun emits an increased amount of ultraviolet (UV) radiation. UV radiation produces more ozone, which warms the stratosphere. The increased solar radiation can also warm the lower atmosphere and surface of the Earth a little.

In large-scale volcanic eruptions, sulfur dioxide gas can reach the upper atmosphere. The sulfur dioxide, which can remain in the atmosphere for up to 3 years, reacts with smaller amounts of water vapor and dust in the stratosphere. This reaction forms a bright layer of haze that reflects enough sunlight to cause the global temperature to decrease.