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Meteorology is a weather and climate based event designed to test students' understanding of meteorological concepts. Its topic changes every year between Climate, Everyday Weather, and Severe Storms. A basic knowledge of weather and climate, among with other basic Meteorology concepts, is suggested for studying for the Climate topic.

This page refers to the 2009, 2012, 2015, and 2018 topic of Meteorology. See Climate Notes for a general outline of all Climate topics.


The event allows for four front-back note sheets per team and a non-graphing calculator dedicated to computation for each competitor.

Personal resources for studying prior to the competition are not restricted. You should have some sort of Meteorology textbook that has information about all three topics, so you can use it even after the topic changes. Other, more specific and advanced textbooks can also be useful to experienced participants. A useful tactic for studying is looking up topics on Google to get familiar with some subjects before going more specific. Wikipedia and other online encyclopedias are also useful for this purpose.

Topics for Climate

  1. Weather vs. climate
  2. Composition and evolution of Earth's atmosphere
  3. Solar radiation and Earth's radiative energy balance
  4. Climatic zones and classification
  5. Natural climatic variability and recent climate trends
  6. Oceanic and Atmospheric circulation
  7. Earth's celestial cycles
  8. Paleoclimates of Earth's geologic history and pass changes in climate
  9. Human impact on climate change and future changes in climate

These climate and climate change topics are only recommended for studying, so not all questions will fall into any of the above categories. Also, some questions will test your ability to read different forms of charts graphs and tables.

Remember that these topics are what is RECOMMENDED, not necessarily what actually shows up on the test. It is very likely a test will also feature topics from the Everyday Weather.

History of Climate

500 BCE Parmenides classifies world climates
330 BCE Hippocrates writes a treatise on climate
61 Seneca complains of Rome’s Air pollution
1644 Rev Holm makes first weather observation in America
1683 Halley publishes first good map of winds
1714 Fahrenheit introduces a Temperature scale
1735 Halley proposes circulation cells
1827 Fourier proposes possibility of CO2induced global warming
1837 Agassiz used term ice age for a proposed glacial theory
1840 Agassiz publishes “Studies on glaciers”
1842 Adhemer proposes regular variations in orbits which explained ice ages
1853 First international Meteorological Conference held in Brussels
1857 Blodgit publishes “Climatology of the US”
1864 Croll studies astronomical theory of ice ages
1874 Chamblain suggested several ice ages separated by nonglacial epoch
1878 IMO founded
1935 IMO selected 1901-1930 as the basis for calculating climatic normal
1964 Clean Air Act passed

General Weather and Climate

Average Daily Temperature - average of daily high and low

Average Monthly Temperature - average of the ADTs of a month

Yearly Average Temperature - averaging the 12 AMTs

Daily Temperature range - difference between the day’s high and low.

Yearly Temperature Range - difference between the average of the warmest and coldest month.

Climate - a region’s composite or average weather

The Difference Between Weather and Climate

Weather is usually defined as a day-to-day measurement. This includes temperature, precipitation, clouds, fronts, etc. Climate is basically long-term weather, or what causes weather. For example, the statement "today's high temperature is 71 degrees Fahrenheit" refers to weather, while the statement "the average high temperature for August is 82 degrees Fahrenheit" refers to climate.

Climate Change

Also see Ecology#Global Warming for more information

Climate change is defined as the change in weather patterns over an extended period of time. Factors that can determine and affect climate are called forcing mechanisms. Forcing mechanisms can be further classified as either internal or external.

Internal Forcing Mechanisms

Internal forcing mechanisms are factors within Earth's climate system (the atmosphere, hydrosphere, cryosphere, lithosphere, and biosphere) with the lithosphere limited to only surface formations. Examples of internal forcing mechanisms include changes in the oceans (such as El Niño-Southern Oscillation and variation of thermohaline circulation) and biological processes (such as the mass introduction of oxygen into the atmosphere by photosynthetic organisms and the Daisyworld Model).

External Forcing Mechanisms

External forcing mechanisms are factors that are independent from the Earth's climate system or involve the subsurface lithosphere. External forcing mechanisms include changes in Earth's orbit (Milankovitch Cycles), variations in the amount of energy being output by the Sun, volcanic activity, movement of tectonic plates, and human activities.

Feedback Forcing mechanisms often set feedback systems into motion, one of which being the Sea Ice-Albedo Loop. The Sea Ice-Albedo feedback is a positive feedback climate process where a change in the area of snow-covered land, ice caps, glaciers or sea ice alters the albedo. This change in albedo acts to reinforce the initial alteration in ice area. Cooling tends to increase ice cover and hence the albedo, reducing the amount of solar energy absorbed and leading to more cooling. Conversely, warming tends to decrease ice cover and hence the albedo, increasing the amount of solar energy absorbed, leading to more warming.

Earth's Atmosphere

The atmosphere is one of the three major spheres: the biosphere and the geosphere being the other two.


The composition of gases in the Earth's atmosphere is as follows:

  • Nitrogen-78.08%
  • Oxygen-20.95%
  • Argon-0.93%
  • Carbon Dioxide-0.038%
  • trace amounts of other gases such as neon, helium, and methane
  • water vapor, on average around 1%


The modern atmosphere is sometimes referred to as Earth's "third atmosphere", in order to distinguish the current chemical composition from previous compositions. The original atmosphere (about 4.6 billion years ago) was primarily helium and hydrogen. Heat from the still-molten crust, the sun, and a probably enhanced solar wind, dissipated this atmosphere. About 4.4 billion years ago, the surface had cooled enough to form a crust. It was heavily populated with volcanoes, which released steam, carbon dioxide, and ammonia. This led to the early "second atmosphere", which was primarily carbon dioxide and water vapor, with some nitrogen but virtually no oxygen. This second atmosphere had approximately 100 times as much gas as the current atmosphere, but as it cooled much of the carbon dioxide was dissolved in the seas and precipitated out as carbonates. The later "second atmosphere" contained largely nitrogen and carbon dioxide. However, simulations run at the University of Waterloo and University of Colorado in 2005 suggest that it may have had up to 40% hydrogen. It is generally believed that the greenhouse effect, caused by high levels of carbon dioxide and methane, kept the Earth from freezing. The oxygen-nitrogen atmosphere that we have now is the "third atmosphere". Between 200 and 250 million years ago, up to 35% of the atmosphere was oxygen (as found in bubbles of ancient atmosphere preserved in amber), but this percentage has dropped to what it is today. Currently, half of the atmosphere’s mass in within 5500 m of the earth’s surface.

Greenhouse Gases

The greenhouse effect occurs when gases in the atmosphere trap the Sun's radiation, thereby making the Earth warmer. These gases are called "greenhouse gases" for their direct role in it. When these gases are ranked by their contribution to the greenhouse effect, the most important are:

  • Water vapor, which contributes 36–70%
  • Carbon dioxide, which contributes 9–26%
  • Methane, which contributes 4–9%
  • Ozone, which contributes 3–7%
  • Nitrous oxide, which contributes 2–4%

Greenhouse effect.JPG

Volcanic Particulates

Large eruptions eject particles and gases such as water, carbon dioxide, sulfur dioxide, hydrochloric acid, and hydrofluoric acid. The finest volcanic particles remain in the stratosphere for only a few months, and they have only minor climatic effects. The only major effect on climate occurs when sulfur dioxide reacts with hydroxide and water to form sulfur aerosols which can last in the stratosphere for 2-3 years. These sulfur aerosols absorb and scatter solar radiation and therefore prevent sunlight from reaching the Earth, making the Earth colder and cooler. Also, hydrochloric acid and hydrofluoric acid can dissolve in water droplets and fall as acid rain.

Volcanic injection.png

Solar Radiation and Earth’s Radiative Energy Balance

Sunlight is the source of energy for the Earth’s oceans, atmosphere, land, and biosphere. The Earth absorbs some sunlight as energy.This energy serves to heat the Earth to temperatures far above the minus 454 degrees Fahrenheit (3 degrees Kelvin) of deep space. Averaged over an entire year and the entire Earth, the sun deposits 342 Watts of energy into every square meter of the Earth. This energy is output form the sun in the form of short-wave radiation, and is absorbed and reflected by earth as long-wave radiation. Albedo is the ratio of radiation reflected back over the amount of radiation received in the first place.

Daisyworld Model

The Daisyworld Model is a hypothetical idea in which a planet is covered in black and white daisies. The daisies have different albedos, so the growth of both daisies affect the planet's temperature and overall population. The Daisyworld Model is a demonstration of the Gaia Theory.


A great explanation of the Dasiyworld Model can be found here: [1]

Koppen Climate Classification

  • Köppen Climate Classification-
    • GROUP A: Tropical/megathermal climates- Tropical rain forest climate (Af), Tropical monsoon climate (Am), Tropical wet and dry or savanna climate (Aw)
    • GROUP B: Dry (arid and semiarid) (climate’s precipitation is less than potential evapotranspiration)- Subtropical desert (Bwh), Subtropical steppe (Bsh), Mid-Latitude desert (Bwk), Mid-Latitude Steppe (Bsk)
    • GROUP C: Temperate/mesothermal climates- Mediterranean climates (Csa, Csb), Humid subtropical climates (Cfa, Cwa), Maritime Temperate climates or Oceanic climates (Cfb, Cwb, Cfc), temperate climate with dry winters (Cwb), Maritime Subarctic climates or Subpolar Oceanic climates (Cfc)
    • GROUP D: Continental/microthermal climate- Hot Summer Continental climates (Dfa, Dwa, Dsa), Warm Summer Continental or Hemiboreal climates (Dfb, Dwb, Dsb), Continental Subarctic or Boreal (taiga) climates (Dfc, Dwc, Dsc)
    • GROUP E: Polar climates- Tundra climate (ET), Ice Cap climate (EF)
    • GROUP H: Highland climates, in which altitude plays a role in determining climate classification


Natural Climatic Variability

Temperature controls:

  • Latitude- main factor, higher the latitude, the lower the average yearly temperature and larger the yearly temperature range.
  • Altitude- average rate of decrease is 6.5 °C per kilometer.
  • Land/sea boundary- areas in close proximity to a large bodies of water will tend to have a smaller range of temperatures (less extreme temperatures) than areas at similar latitudes and elevation that are far from large bodies of water (known as continentality)
  • Prevailing winds- moderates temperature; effect doesn't extend past the first high mountain range. Warm or cold ocean currents can affect the temperature of an area.

Rainfall controls:

  • Latitude- wet belt or dry belt
  • Mountains- windward sides are rainy, leeward sides have dry, descending winds called chinooks and foehns (known as the rain shadow effect)
  • Distance from the sea- drier near interior of continent (not a guarantee)

Koppen vs Thornthwaite The Köppen classification depends on average monthly values of temperature and precipitation. Koppen's rival system was modified/developed by an American climatologist and geographer C. W. Thornthwaite. Thornthwaite's classification system utilizes the monitoring of the soil water budget using evapotranspiration.

Three-Cell Model of Atmospheric Circulation

For more information about the three-cell model, see Meteorology/Everyday Weather#Three Cell Model.

The Three-Cell Model explains air circulation around the earth. It consists of the Hadley, Ferrel, and Polar Cells. 3cell.JPG

Semi-Permanent Highs and Lows

Semi-permanent highs and lows are pressure systems that last over a certain location throughout the year. They affect the climate by steering weather systems and hurricanes.

Jan sfc press.jpg July sfc pres.jpg

Aleutian Low

The Aleutian low is located west of Alaska in the Bering sea, near the Aleutian islands. The Aleutian low is most intense during the winter and weakens drastically in the summer. It intensifies cyclones and steers them into the Pacific Northwest.

Icelandic Low

The Icelandic low is located near Iceland and Greenland. It is similar to the Aleutian low. It is strongest in the winter and weak in the summer. It also intensifies cyclones.

Bermuda High

The Bermuda high is located in the Atlantic Ocean in the northern hemisphere around 30N. It is close to the east coast in the summer and drifts further east in the winter. It directs moist air onto the east coast during the summer. It also has a major impact on the path of hurricanes in the Atlantic and where it will make landfall. It allows the gulf stream to dip in winter and helps drive the Gulf Stream. Europeans often refer to the Bermuda High as the Azores High

Siberian High

The Siberian high is located over Russia in Siberia. It forms during the winter and is the strongest semi-permanent high in the northern hemisphere. It consists of very cold air.

North Pacific High

The North Pacific High is located in the northeast Pacific, northeast of Hawaii but west of California. It is usually strongest in the summer and shifts towards equator in the winter. The North Pacific High is responsible for dry summer in California and year round trade winds in Hawaii

South Pacific High

The South Pacific high is located in the south Pacific ocean off the coast of South America. It causes the west coast of South America to be very dry.

Thermal Low

A thermal low is not one specific pressure system, but is a type of semi-permanent pressure system. They usually occur over deserts where there is intense daytime heating, which causes the heated air to rise, creating a low. They occur during the summer. They have little to no precipitation and weak cyclonic circulation.

El Niño and La Niña

El Niño and La Niña are officially defined as sustained sea surface temperature anomalies of magnitude greater than 0.5 °C across the central tropical Pacific Ocean. When the condition is met for a period of less than five months, it is classified as El Niño or La Niña conditions; if the anomaly persists for five months or longer, it is classified as an El Niño or La Niña episode. Historically, it has occurred at irregular intervals of 2-7 years and has usually lasted one or two years.

El Niño

The first signs of an El Niño are:

1. Rise in air pressure over the Indian Ocean, Indonesia, and Australia 2. Fall in air pressure over Tahiti and the rest of the central and eastern Pacific Ocean 3. Trade winds in the south Pacific weaken or head east 4. Warm air rises near Peru, causing rain in the northern Peruvian deserts 5. Warm water spreads from the west Pacific and the Indian Ocean to the east Pacific. It takes the rain with it, causing extensive drought in the western Pacific and rainfall in the normally dry eastern Pacific.

El Niño's warm current of nutrient-poor tropical water, heated by its eastward passage in the Equatorial Current, replaces the cold, nutrient-rich surface water of the Humboldt Current, also known as the Peru Current, which support great populations of food fish. In most years the warming lasts only a few weeks or a month, after which the weather patterns return to normal and fishing improves. However, when El Niño conditions last for many months, more extensive ocean warming occurs and its economic impact to local fishing for an international market can be serious. During non-El Niño conditions, the Walker circulation is seen at the surface as easterly trade winds, which move water and air warmed by the sun towards the west. This also creates ocean upwelling off the coasts of Peru and Ecuador and brings nutrient-rich cold water to the surface, increasing fishing stocks. The western side of the equatorial Pacific is characterized by warm, wet low-pressure weather as the collected moisture is dumped in the form of typhoons and thunderstorms. The ocean is some 60 cm higher in the western Pacific as the result of this motion. Also refer to Walker Circulation model and how it relates to ENSO.


La Niña

In the Pacific, La Niña is characterized by unusually cold ocean temperatures in the eastern equatorial Pacific, compared to El Niño, which is characterized by unusually warm ocean temperatures in the same area. Atlantic tropical cyclone activity is generally enhanced during La Niña. The La Niña condition often follows the El Niño, especially when the latter is strong.

Table with La Niña and El Niño Effects

La Niña and El Niño Effects
El Niño La Niña
Strong Equatorial Counter-Current Strong Peruvian Current
Wetter than Average Winter over Florida Higher Sea Level in the West Pacific
Pronounced Ridge in Polar Jet over Western North America Stronger than Normal Subtropical Highs in Pacific
Drier than Average over Indonesia and Australia Increased Snowfall in the North Western U.S.
Large-Scale Warming of Pacific Oceanic Cooling of the Pacific

Thermohaline Circulation

The term thermohaline circulation (THC) refers to the part of the large-scale ocean circulation that is thought to be driven by global density gradients created by surface heat and freshwater fluxes. The adjective thermohaline derives from "thermo-", referring to temperature, and "-haline", referring to salt content. These factors together determine the density of sea water. The thermohaline circulation is sometimes called the ocean conveyor belt, the great ocean conveyor, or the global conveyor belt. On occasion, it is used to refer to the meridional overturning circulation (often abbreviated as MOC).

Oceanic Circulation Path

Wind-driven surface currents (such as the Gulf Stream) head polewards from the equatorial Atlantic Ocean, cooling all the while and eventually sinking at high latitudes (forming North Atlantic Deep Water). The formation and movement of the deep water masses at North Atlantic Ocean creates sinking water masses that fills the ocean basins and flows very slowly into the deep abyssal plains of the Atlantic. This high latitude cooling and the low latitude heating drives the movement of the deep water in a polar southward flow. The deep water flows through the Antarctic Ocean Basin around South Africa where it is split into two routes: one into the Indian Ocean and one past Australia into the Pacific. While the bulk of it upwells in the Southern Ocean, the oldest waters (with a transit time of around 1000 years) upwell in the North Pacific. At the Indian Ocean, some of the cold and salty water from Atlantic -- drawn by the flow of warmer and fresher upper ocean water from the tropical Pacific -- causes a vertical exchange of dense, sinking water with lighter water above.

The out-flowing undersea of cold and salty water makes the sea level of the Atlantic slightly lower than the Pacific and salinity or halinity of water at the Atlantic higher than the Pacific. These characteristics of the Pacific generate a large but slow flow of warmer and fresher upper ocean water from the tropical Pacific to the Indian Ocean through the Indonesian Archipelago to replace the cold and salty Antarctic Bottom Water. This is also known as Haline forcing (net high latitude freshwater gain and low latitude evaporation). This warmer, fresher water from the Pacific also flows up through the South Atlantic to Greenland, where it cools off and undergoes evaporative cooling and sinks to the ocean floor, providing a continuous thermohaline circulation. It is known as overturning. Hence, a recent and popular name for the thermohaline circulation, emphasizing the vertical nature and pole-to-pole character of this kind of ocean circulation, is the meridional overturning circulation.

Thermohaline Circulation.png

Impact on Earth's Climate

As such, the state of the circulation has a large impact on the climate of the Earth. Because of this massive circulation, extensive mixing takes place between the ocean basins, reducing differences between them and making the Earth's ocean a global system. On their journey, the water masses transport both energy (in the form of heat) and matter (solids, dissolved substances and gases) around the globe. If this system were to shut down, this changed flow would alter the climates of the entire Earth, and there would be no more circulation of salt or water. This would change the ocean habitats as well, and would affect marine life.

Milankovitch Cycles


The angle of the Earth's axial tilt (obliquity) varies with respect to the plane of the Earth's orbit. These slow 2.4° obliquity variations are roughly periodic, taking approximately 41,000 years to shift between a tilt of 22.1° and 24.5° and back again. When the obliquity increases, the amplitude of the seasonal cycle in insolation (INcoming SOLar radiATION) increases, with summers in both hemispheres receiving more radiative flux from the Sun, and the winters less radiative flux. As a result, it is assumed that the winters become colder and summers warmer. But these changes of opposite sign in the summer and winter are not of the same magnitude. The annual mean insolation increases in high latitudes with increasing obliquity, while lower latitudes experience a reduction in insolation. Cooler summers are suspected of encouraging the start of an ice age by melting less of the previous winter's ice and snow. So it can be argued that lower obliquity favors ice ages both because of the mean insolation reduction in high latitudes as well as the additional reduction in summer insolation. We are presently in a period of decreasing obliquity.


The Earth's orbit is an ellipse. The eccentricity is a measure of the departure of this ellipse from circularity. The shape of the Earth's orbit varies from being nearly circular (low eccentricity of 0.005) to being mildly elliptical (high eccentricity of 0.058) and has a mean eccentricity of 0.028 (or 0.017 which is current value). The major component of these variations occurs on a period of 413,000 years (eccentricity variation of ±0.012). A number of other terms vary between 95,000 and 136,000 years, and loosely combine into a 100,000-year cycle. The present eccentricity is 0.017.


Precession is the change in the direction of the Earth's axis of rotation relative to the fixed stars, with a period of roughly 26,000 years. This gyroscopic motion is due to the tidal forces exerted by the sun and the moon on the solid Earth, associated with the fact that the Earth is not a perfect sphere but has an equatorial bulge. The sun and moon contribute roughly equally to this effect. In addition, the orbital ellipse itself precesses in space (anomalistic precession), primarily as a result of interactions with Jupiter and Saturn. This orbital precession is in the opposite sense to the gyroscopic motion of the axis of rotation, shortening the period of the precession of the equinoxes with respect to the perihelion from 25,771.5 to ~21,636 years.

Representative Concentration Pathways (RCP)

Four greenhouse gas concentration (not emission) trajectory adopted by the IPCC (Intergovernmental Panel on Climate Change) for its 5th assessment report.The four RCPs, RCP2.6, RCP4.5, RCP6, and RCP8.5, are named after a possible range of radiative forcing values in the year 2100 relative to pre-industrial values (+2.6, +4.5, +6.0, and +8.5 W/m2, respectively).

Station Models


This image is a station model. It can tell you many different things, like wind speed, wind direction, temperature, dew point, current weather, cloud cover, and pressure, given that you know how to read and interpret it. Some symbols have more information than others on them, but here is a basic overview:

  • The 48 is the current temperature (in degrees Fahrenheit)
  • The 45 is the dew point (in degrees Fahrenheit)
  • The symbol in between the two numbers is the current weather. In this example, it is a light rain


This is what tells you information about the wind. The direction the stick faces shows the wind direction, and how many lines on the end of it show the wind speed. A half line signifies five knots, a full line ten knots, and a bold line fifty knots.

Here is a key to making and reading station models. It is highly recommended to add this on to your note sheet.