The Atmosphere: Structure and Temperature STURDIVANT

Atmospheric Basics The atmosphere is a sea of gases, many of which are vital to our existence What the atmosphere is doing in a particular location at a particular time is WEATHER What the atmosphere does in general over a region is the CLIMATE Weather and Climate include air temperature, humidity, type and amount of precipitation, air pressure, and wind speed/direction

Atmospheric Composition The composition of the atmosphere has changed throughout Earth’s 4.6 billion year history It is thought to have been created by gases released during volcanic eruptions Data suggests that Oxygen did not appear in the atmosphere until 2.5 billion years ago

Atmospheric Composition - Major The vast majority of the atmosphere is very constant – with 99% of its composition being Nitrogen and Oxygen Of the remaining 1%, 0.93% is Argon Despite their abundance, Nitrogen, Oxygen, and Argon play a limited role in weather Carbon Dioxide makes up roughly 0.039% of the atmosphere

Atmospheric Composition - Variable Some components of atmospheric air that vary with time and place are water vapor, dust, and ozone These variable components significantly affect weather and climate Water vapor varies from 0-4% of atmospheric volume, and is the source of clouds and precipitation Ozone exists where sunlight energizes Oxygen molecules enough to combine into O3. Ozone absorbs UV rays that would make our planet uninhabitable

Atmospheric Structure Unlike the ocean boundary, there is no “sharp” boundary to the atmosphere, as it slowly dissipates with height Atmospheric Pressure depends on the weight of the atmosphere above Because the atmosphere dissipates with height, atmospheric pressure drops quickly near the surface Atmospheric Temperature, however, is more complex

Atmospheric Temperature For relatively low elevations in the atmosphere – where humans live – we see temperatures dropping with elevation This is why we see snow on mountain tops and not in low valleys We divide the atmosphere into layers of increasing / decreasing temperature These are the troposphere, stratosphere, mesosphere, and thermosphere

Earth-Sun Relationships The Sun provides all the energy that drives weather patterns on Earth The amount of time and angle at which light hits the Earth from the Sun determines weather and seasons Earth both rotates and revolves, creating not only day and night, but seasons as well Areas more directly facing the Sun see smaller seasonal changes (equator)

Heating the Atmosphere To understand how heat and temperature changes within the atmosphere, we need to first understand HEAT Heat – transfer of energy due to a temperature difference Heat can be transferred in THREE ways – Conduction (direct molecule-to- molecule contact), Convection (fluid flow), and Radiation (electromagnetic waves)

Solar Radiation Most atmospheric energy is derived from solar radiation, so it’s important to understand what solar radiation does When INSOLATION (incoming solar radiation) hits an object, THREE things can happen Absorption – light is stopped, heats the object Transmission – light travels through, doesn’t interact with object Reflection – object bounces radiation back. Some objects absorb radiation then re-emit (reflect) in all directions. This is called Scattering

What happens to Solar Radiation?

Greenhouse Effect Gases in the atmosphere that absorb insolation create a Greenhouse Effect This effect is important to keep our planet warm, but it can also over- warm the planet Water Vapor and Carbon Dioxide both absorb infrared light, while allowing visible light to pass through

What else controls Temperature? Temperature Control – any factor that causes temperature to vary Latitude plays the biggest role, in general Other controls are land vs water cover, altitude, geographic position, cloud cover, and ocean currents

Land/Water and Temperature Land (rock, soil, etc) heats up and cools down much more easily than water. Thus, we notice areas with more water have smaller daily and seasonal temperature changes This is why, for example, temperatures in Vancouver, BC are more mild than temperatures in Winnipeg, Manitoba

Location and Temperature Simply being near water doesn’t necessarily affect the temperature significantly For example, the easterly wind through the United States causes water’s effect to be significant on the West coast, but not so much on the East coast

Altitude and Temperature Within the troposphere, temperature decreases with elevation This means areas similar in latitude but at different elevations have different annual temperature ranges Guayaquil and Quito, Ecuador are both near the equation, but Quito lies within the Andes mountains

Other Factors There are a variety of other factors that can affect surface temperatures outside of these Albedo – fraction of insolation reflected Areas covered in snow reflect a large amount of light away Similarly, areas frequented with cloud cover reflect a large amount of light away