Weather and Climate Unit Remember, Earth has the only atmosphere that can sustain life as we know it In these next chapters we will look at the following: Characteristics of the atmosphere Moisture, clouds, and precipitation (Ch 18) Air Pressure and wind (Ch 19) Weather and Severe Storms (Ch 20) Climate (Ch 21)

Chapter 17 Notes: The Atmosphere

Section I: Atmosphere Characteristics

Composition of the Atmosphere-Major Components Has changed dramatically through Earth’s History Oxygen started to accumulate about ~2.5 bya Air is a mixture of different gases and particles, each with its own physical properties Composition: Nitrogen-78% Oxygen-21% Other Gases-1% Carbon Dioxide Argon All other gases Carbon dioxide is an active absorber of energy given off by Earth, so it play a significant role in the heating the atmosphere

Composition of the Atmosphere-Variable Components Important materials that vary from time to time and place to place include: Water vapor Dust particles Ozone Amount of Water vapor varies from almost none to about 4% by volume Water vapor is the source of all clouds and precipitation. Like CO2, water vapor absorbs heat given off by earth and also absorbs some solar energy Movements of the atmosphere allow dust particles and other solid particles to be suspended in it. Dust we see in the sky is too heavy to stay in the air for very long. Still, many particles are microscopic and remain suspended for larger amounts of time. Sea salts, fine soil, smoke, soot, pollen, microorganisms, ash & dust from volcanic eruptions

Composition of the Atmosphere-Variable Components Ozone is another variable component of the atmosphere Ozone is a form of oxygen that combines 3 oxygen atoms for every molecule (O3) Oxygen we breathe is O2 There is very little ozone in the atmosphere and it’s not distributed equally, located in the stratosphere The ozone layer is critical to life on Earth Ozone absorbs potentially harmful UV radiation from the sun If ozone did not filter most UV radiation and all of the sun’s UV rays reached the surface of Earth, our planet would be uninhabitable for many living organisms

Human Influence on the Atmosphere Air Pollutants are airborne particles and gases that occur in concentrations large enough to endanger the health of organisms Primary pollutants include carbon monoxide, sulfur oxides, nitrogen oxides, volatile organic compounds (VOCs), and particulates Emission from transportation vehicles account for almost half of all primary pollutants Secondary pollutants are not emitted directly in the air They form when reactions take place among primary pollutants and other substances Ex. Sulfur dioxide enters atmosphere, combines with oxygen to give sulfur trioxide, sulfur trioxide combines with water to create sulfuric acid (acid rain) Reactions triggered by sunlight are called photochemical reactions

Height and Structure of the Atmosphere The atmosphere rapidly thins as you travel away from earth until there are too few gas molecules to detect Pressure Changes Atmospheric pressure is the weight of the air above Atmospheric pressure is higher near sea level, and lower in the mountains

Height and Structure of the Atmosphere Temperature changes The atmosphere can be divided vertically into four layers based on temperature Troposphere Stratosphere Mesosphere Thermosphere

Troposphere The tropopause exists as the top of the troposphere This is where temperature stops decreasing Tropopause keeps water vapor and clouds in the troposphere Though it is generally warmer near the surface, cool air sometimes gets trapped beneath warm air, called a temperature inversion Can cause air pollution Bottom layer of the atmosphere, closest to earth’s surface About 10 miles high into the air Densest layer of the atmosphere Clouds, wind, rain, and snow mostly occur here Gets cooler as you go up in altitude Decreases about 6°C for every km of altitude

The Stratosphere Layer above the troposphere Extends about 31 miles into the air (so about 20 miles thick) Has little water vapor, few clouds, and no storms Gets warmer as you go up in altitude Remains at about -67ºF from the top of tropopause to about 16 mi Then it starts to increase to about 32ºF The ozone layer exists at the top of the stratosphere

The Mesosphere Layer above the stratosphere Extends to about 50 miles into the air, so its about 20 miles thick Temperature decreases as you go up in altitude (like in the troposphere) This is the COLDEST layer in the atmosphere; temperatures fall below -112ºF This layer has no well-defined upper limit This is where we see "falling stars" – meteors burning up as they fall to Earth

The Ionosphere The layer that exists between the lower thermosphere and upper mesosphere In this layer, solar energy is absorbed and electrically charged ions are formed Electrons in the ionosphere reflect radio waves, allowing them to be received over long distances Without the ionosphere, most radio signals would travel directly into space

The Ionosphere (cont) Because the ions require solar energy, the ionosphere is larger (thicker) during the day This means radio waves can travel farther into the atmosphere at night before being reflected. The radio waves return to Earth’s surface farther from their source than they do in the daytime

The Ionosphere (cont) The ionosphere is also where auroras take place Auroras form when energetic ions from the sun hit atoms and molecules in the ionosphere Are seen encircling Earth’s Magnetic poles

The Thermosphere Layer above the mesosphere, extends to about 298 miles into the air, so it is about 250 miles thick This is the THICKEST layer of the atmosphere Temperatures start to rise Temperatures in this layer average around 1796ºF The outermost portion of the thermosphere at about 298 miles up, is known as the exosphere Some gases escape the gravitational pull of the Earth and escape into space. Some gases are pulled in by gravity from space and add to the Earth’s atmosphere

The Magnetosphere Region in space (so not really a part of the atmosphere) whose shape is determined by Earth’s internal magnetic field, the solar wind plasma, and the interplanetary magnetic field Here, a mix of free ions and electrons from solar wind and the ionosphere is confined by electromagnetic forces Provides protection to earth’s water

Section II: Heating the Atmosphere

Energy Transfer as Heat Heat is the energy transferred from one object to another because of difference in the object’s temperature Temperature is a measure of the average kinetic energy of the individual atoms or molecules in a substance

Electromagnetic waves The sun is the ultimate source of energy that creates our weather The sun emits heat, light, UV rays, and other EM radiation

Three mechanisms Three mechanisms of energy transfer are conduction, convection, and radiation Conduction the transfer of heat through matter by molecular activity. Energy is transferred through collisions from one molecule to another Heat flows from the higher temperature matter to the lower temperature matter Metals are good conductors, gases are not good conductors This is the LEAST important mechanism of heat transfer for the atmosphere

Convection Much of the heat transfer that occurs in the atmosphere is carried on by convection Transfer of heat by mass movement or circulation within a substance Takes place in fluids, like the ocean and air, and solids, like the mantle

Radiation Radiation is the transfer of heat through space by electromagnetic waves that travel out in all directions Unlike convection and conduction, which need material to travel through, radiant energy can travel through the vacuum of space There are 4 laws governing radiation

4 Laws Governing Radiation All objects, at any temperature, emit radiation energy Hotter objects radiate more total energy per unit area than colder objects do The hottest radiating bodies produce the shortest wavelengths of maximum radiation Objects that are good absorbers of radiation are good emitters as well The atmosphere does not absorb certain wavelengths of radiation, but it is a good absorber of other wavelengths

What happens to solar radiation? Usually there are three different results Some energy is absorbed by the object Substances such as water and air are transparent to certain wavelengths of radiation Some radiation may bounce off the object without being absorbed or transmitted

What happens to solar radiation? Reflection and Scattering Reflection occurs when light bounces off an object. Reflection radiation has the same intensity as incident radiation Scattering produces a larger number of weaker rays that travel in different directions

What happens to solar radiation? Absorption About 50% of the solar energy that strikes the top of the atmosphere reaches Earth’s surface and is absorbed The greenhouse effect is the heating of Earth’s surface and atmosphere from solar radiation being absorbed and emitted by the atmosphere, mainly by water vapor and carbon dioxide

Section III: Temperature Controls

Temperature Controls A temperature control is any factor that causes temperature to vary from place to place and from time to time. Factors other than latitude that exert a strong influence on temperature include heating of land and water, altitude, geographic position, cloud cover, and ocean currents

Land vs Water Land heats more rapidly and to higher temperatures than water Land cools more rapidly and to lower temperatures than water

Geographic Position Geographic setting can greatly influence temperatures experienced at a specific location Terms to look at the next graph: Leeward-wind blows from land toward ocean Windward-winds blows from ocean toward land

Geographic Positions Influence of mountains- Mountains act like barriers Seattle shows marine influence Spokane’s is more continental

Altitude Altitude can greatly influence temperatures at a specific location Higher altitude=colder temperatures

Cloud Cover and Albedo Albedo is the fraction of total radiation that is reflected by any surface Many clouds have high albedo and therefore reflect back to space a significant portion of the sunlight that strikes them When have more cloud cover=lower maximum temperature

During daylight hours, clouds reflect solar radiation back to space During daylight hours, clouds reflect solar radiation back to space. At night, clouds absorb radiation from the land and reradiate some of it back to Earth, increasing nighttime temperatures

World Distribution of Temperature Isotherms are lines that connect points that have the same temperature Isotherms generally trend east to west and show a decrease in temperatures from the tropics towards the poles.