• meteorology

    Hadley cells are the basis for our understanding of global-scale meteorology.

    Illustration courtesy NASA

    Storm Synchronicity
    "Unlike history, meteorology does repeat itself."
    Dr. Mel Goldstein, meteorologist

    Christopher Columbus, Meteorologist
    In 1495, explorer Christopher Columbus recorded what might be the first account of a hurricane. While docked off La Isabela, Hispaniola (now the Dominican Republic), Columbus lost three ships in a violent storm. Modern meteorologists debate whether the storm was an actual hurricane or a tornado and waterspout. Columbus attests that "nothing but the service of God and the extension of the monarchy'' would persuade him to endure another storm like that.

    Humid Curls
    Horace Benedict de Saussure was an amateur alpine climber, physicist, and meteorologist. In 1783, he constructed the first hygrometer, an instrument that measures humidity. The medium he used to measure the amount of moisture in the air? Human hair. The hair Sassure tested relaxed, or lengthened, in moist weather. It tensed, or curled, in dry weather.

    Seal of Approval
    Since 1982, the National Weather Association has promoted quality weather broadcasting by issuing a Weathercaster Seal of Approval to qualified broadcasters. The seal exam is difficult, and only 918 people in the U.S. are certified. Find out if your local weather forecaster has made the list!

    Meteorology is the study of the atmosphere, atmospheric phenomena, and atmospheric effects on our weather. The atmosphere is the gaseous layer of the physical environment that surrounds a planet. Earth’s atmosphere is roughly 100 to 125 kilometers (65-75 miles) thick. Gravity keeps the atmosphere from expanding much farther.

    Meteorology is a subdiscipline of the atmospheric sciences, a term that covers all studies of the atmosphere. A subdiscipline is a specialized field of study within a broader subject or discipline. Climatology and aeronomy are also subdisciplines of the atmospheric sciences. Climatology focuses on how atmospheric changes define and alter the world’s climates. Aeronomy is the study of the upper parts of the atmosphere, where unique chemical and physical processes occur. Meteorology focuses on the lower parts of the atmosphere, primarily the troposphere, where most weather takes place.

    Meteorologists use scientific principles to observe, explain, and forecast our weather. They often focus on atmospheric research or operational weather forecasting. Research meteorologists cover several subdisciplines of meteorology to include: climate modeling, remote sensing, air quality, atmospheric physics, and climate change. They also research the relationship between the atmosphere and Earth’s climates, oceans, and biological life.

    Forecasters use that research, along with atmospheric data, to scientifically assess the current state of the atmosphere and make predictions of its future state. Atmospheric conditions both at the Earth's surface and above are measured from a variety of sources: weather stations, ships, buoys, aircraft, radar, weather balloons, and satellites. This data is transmitted to centers throughout the world that produce computer analyses of global weather. The analyses are passed on to national and regional weather centers, which feed this data into computers that model the future state of the atmosphere. This transfer of information demonstrates how weather and the study of it take place in multiple, interconnected ways.

    Scales of Meteorology

    Weather occurs at different scales of space and time. The four meteorological scales are: microscale, mesoscale, synoptic scale, and global scale. Meteorologists often focus on a specific scale in their work.

    Microscale Meteorology
    Microscale meteorology focuses on phenomena that range in size from a few centimeters to a few kilometers, and that have short life spans (less than a day). These phenomena affect very small geographic areas, and the temperatures and terrains of those areas.

    Microscale meteorologists often study the processes that occur between soil, vegetation, and surface water near ground level. They measure the transfer of heat, gas, and liquid between these surfaces. Microscale meteorology often involves the study of chemistry.

    Tracking air pollutants is an example of microscale meteorology. MIRAGE-Mexico is a collaboration between meteorologists in the United States and Mexico. The program studies the chemical and physical transformations of gases and aerosols in the pollution surrounding Mexico City. MIRAGE-Mexico uses observations from ground stations, aircraft, and satellites to track pollutants.

    Mesoscale Meteorology
    Mesoscale phenomena range in size from a few kilometers to roughly 1,000 kilometers (620 miles). Two important phenomena are mesoscale convective complexes (MCC) and mesoscale convective systems (MCS). Both are caused by convection, an important meteorological principle.

    Convection is a process of circulation. Warmer, less-dense fluid rises, and colder, denser fluid sinks. The fluid that most meteorologists study is air. (Any substance that flows is considered a fluid.) Convection results in a transfer of energy, heat, and moisture—the basic building blocks of weather.

    In both an MCC and MCS, a large area of air and moisture is warmed during the middle of the day—when the sun angle is at its highest. As this warm air mass rises into the colder atmosphere, it condenses into clouds, turning water vapor into precipitation.

    An MCC is a single system of clouds that can reach the size of the state of Ohio and produce heavy rainfall and flooding. An MCS is a smaller cluster of thunderstorms that lasts for several hours. Both react to unique transfers of energy, heat, and moisture caused by convection.

    The Deep Convective Clouds and Chemistry (DC3) field campaign is a program that will study storms and thunderclouds in Colorado, Alabama, and Oklahoma. This project will consider how convection influences the formation and movement of storms, including the development of lightning. It will also study their impact on aircraft and flight patterns. The DC3 program will use data gathered from research aircraft able to fly over the tops of storms.

    Synoptic Scale Meteorology
    Synoptic-scale phenomena cover an area of several hundred or even thousands of kilometers. High- and low-pressure systems seen on local weather forecasts, are synoptic in scale. Pressure, much like convection, is an important meteorological principle that is at the root of large-scale weather systems as diverse as hurricanes and bitter cold outbreaks.

    Low-pressure systems occur where the atmospheric pressure at the surface of the Earth is less than its surrounding environment. Wind and moisture from areas with higher pressure seek low-pressure systems. This movement, in conjunction with the Coriolis force and friction, causes the system to rotate counter-clockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere, creating a cyclone. Cyclones have a tendency for upward vertical motion. This allows moist air from the surrounding area to rise, expand and condense into water vapor, forming clouds. This movement of moisture and air causes the majority of our weather events.

    Hurricanes are a result of low-pressure systems (cyclones) developing over tropical waters in the Western Hemisphere. The system sucks up massive amounts of warm moisture from the sea, causing convection to take place, which in turn causes wind speeds to increase and pressure to fall. When these winds reach speeds over 119 kilometers per hour (74 miles per hour), the cyclone is classified as a hurricane.

    Hurricanes can be one of the most devastating natural disasters in the Western Hemisphere. The National Hurricane Center, in Miami, Florida, regularly issues forecasts and reports on all tropical weather systems. During hurricane season, hurricane specialists issue forecasts and warnings for every tropical storm in the western tropical Atlantic and eastern tropical Pacific. Businesses and government officials from the United States, the Caribbean, Central America, and South America rely on forecasts from the National Hurricane Center.

    High-pressure systems occur where the atmospheric pressure at the surface of the Earth is greater than its surrounding environment. This pressure has a tendency for downward vertical motion, allowing for dry air and clear skies.

    Extremely cold temperatures are a result of high-pressure systems that develop over the Arctic and move over the Northern Hemisphere. Arctic air is very cold because it develops over ice and snow-covered ground. This cold air is so dense that it pushes against Earth’s surface with extreme pressure, preventing any moisture or heat from staying within the system.

    Meteorologists have identified many semi-permanent areas of high-pressure. The Azores high, for instance, is a relatively stable region of high pressure around the Azores, an archipelago in the mid-Atlantic Ocean. The Azores high is responsible for arid temperatures of the Mediterranean basin, as well as summer heat waves in Western Europe.

    Global Scale Meteorology
    Global scale phenomena are weather patterns related to the transport of heat, wind, and moisture from the tropics to the poles. An important pattern is global atmospheric circulation, the large-scale movement of air that helps distribute thermal energy (heat) across the surface of the Earth.

    Global atmospheric circulation is the fairly constant movement of winds across the globe. Winds develop as air masses move from areas of high pressure to areas of low pressure. Global atmospheric circulation is largely driven by Hadley cells. Hadley cells are tropical and equatorial convection patterns. Convection drives warm air high in the atmosphere, while cool, dense air pushes lower in a constant loop. Each loop is a Hadley cell.

    Hadley cells determine the flow of trade winds, which meteorologists forecast. Businesses, especially those exporting products across oceans, pay close attention to the strength of trade winds because they help ships travel faster. Westerlies are winds that blow from the west in the midlatitudes. Closer to the Equator, trade winds blow from the northeast (north of the Equator) and the southeast (south of the Equator).

    Meteorologists study long-term climate patterns that disrupt global atmospheric circulation. Meteorologists discovered the pattern of El Nino, for instance. El Niño involves ocean currents and trade winds across the Pacific Ocean. El Niño occurs roughly every five years, disrupting global atmospheric circulation and affecting local weather and economies from Australia to Peru.

    El Niño is linked with changes in air pressure in the Pacific Ocean known as the Southern Oscillation. Air pressure drops over the eastern Pacific, near the coast of the Americas, while air pressure rises over the western Pacific, near the coasts of Australia and Indonesia. Trade winds weaken. Eastern Pacific nations experience extreme rainfall. Warm ocean currents reduce fish stocks, which depend on nutrient-rich upwelling of cold water to thrive. Western Pacific nations experience drought, devastating agricultural production.

    Understanding the meteorological processes of El Niño helps farmers, fishers, and coastal residents prepare for the climate pattern.

    History of Meteorology

    The development of meteorology is deeply connected to developments in science, math, and technology. The Greek philosopher Aristotle wrote the first major study of the atmosphere around 340 BCE. Many of Aristotle’s ideas were incorrect, however, because he did not believe it was necessary to make scientific observations.

    A growing belief in the scientific method profoundly changed the study of meteorology in the 17th and 18th centuries. Evangelista Torricelli, an Italian physicist, observed that changes in air pressure were connected to changes in weather. In 1643, Torricelli invented the barometer, to accurately measure the pressure of air. The barometer is still a key instrument in understanding and forecasting weather systems. In 1714, Daniel Fahrenheit, a German physicist, developed the mercury thermometer. These instruments made it possible to accurately measure two important atmospheric variables.

    There was no way to quickly transfer weather data until the invention of the telegraph by American inventor Samuel Morse in the mid-1800s. Using this new technology, meteorological offices were able to share information and produce the first modern weather maps. These maps combined and displayed more complex sets of information such as isobars (lines of equal air pressure) and isotherms (lines of equal temperature). With these large-scale weather maps, meteorologists could examine a broader geographic picture of weather and make more accurate forecasts.

    In the 1920s, a group of Norwegian meteorologists developed the concepts of air masses and fronts that are the building blocks of modern weather forecasting. Using basic laws of physics, these meteorologists discovered that huge cold and warm air masses move and meet in patterns that are the root of many weather systems.

    Military operations during World War I and World War II brought great advances to meteorology. The success of these operations was highly dependent on weather over vast regions of the globe. The military invested heavily in training, research, and new technologies to improve their understanding of weather. The most important of these new technologies was radar, which was developed to detect the presence, direction, and speed of aircraft and ships. Since the end of World War II, radar has been used and improved to detect the presence, direction, and speed of precipitation and wind patterns.

    The technological developments of the 1950s and 1960s made it easier and faster for meteorologists to observe and predict weather systems on a massive scale. During the 1950s, computers created the first models of atmospheric conditions by running hundreds of data points through complex equations. These models were able to predict large-scale weather, such as the series of high- and low-pressure systems that circle our planet.

    TIROS I, the first meteorological satellite, provided the first accurate weather forecast from space in 1962. The success of TIROS I prompted the creation of more sophisticated satellites. Their ability to collect and transmit data with extreme accuracy and speed has made them indispensable to meteorologists. Advanced satellites and the computers that process their data are the primary tools used in meteorology today.

    Meteorology Today

    Today’s meteorologists have a variety of tools that help them examine, describe, model, and predict weather systems. These technologies are being applied at different meteorological scales, improving forecast accuracy and efficiency.

    Radar is an important remote sensing technology used in forecasting. A radar dish is an active sensor in that it sends out radio waves that bounce off particles in the atmosphere and return to the dish. A computer processes these pulses and determines the horizontal dimension of clouds and precipitation, and the speed and direction in which these clouds are moving.

    A new technology, known as dual-polarization radar, transmits both horizontal and vertical radio wave pulses. With this additional pulse, dual-polarization radar is better able to estimate precipitation. It is also better able to differentiate types of precipitation—rain, snow, sleet, or hail. Dual-polarization radar will greatly improve flash-flood and winter-weather forecasts.

    Tornado research is another important component of meteorology. Starting in 2009, the National Oceanic and Atmospheric Administration (NOAA) and the National Science Foundation conducted the largest tornado research project in history, known as VORTEX2. The VORTEX2 team, consisting of about 200 people and more than 80 weather instruments, traveled more than 16,000 kilometers (10,000 miles) across the Great Plains of the United States to collect data on how, when, and why tornadoes form. The team made history by collecting extremely detailed data before, during, and after a specific tornado. This tornado is the most intensely examined in history and will provide key insights into tornado dynamics.

    Satellites are extremely important to our understanding of global scale weather phenomena. The National Aeronautics and Space Administration (NASA) and NOAA operate three Geostationary Operational Environmental Satellites (GOES) that provide weather observations for more than 50 percent of the Earth’s surface.

    GOES-15, launched in 2010, includes a solar X-ray imager that monitors the sun’s X-rays for the early detection of solar phenomena, such as solar flares. Solar flares can affect military and commercial satellite communications around the globe. A highly accurate imager produces visible and infrared images of Earth’s surface, oceans, cloud cover, and severe storm developments. Infrared imagery detects the movement and transfer of heat, improving our understanding of the global energy balance and processes such as global warming, convection, and severe weather.

  • Term Part of Speech Definition Encyclopedic Entry
    aeronomy Noun

    study of the characteristics of the upper part of the atmosphere.

    aerosol adjective, noun

    liquid substance sealed in an air-tight container with a gas, and released under pressure as a spray or foam.

    air mass Noun

    a large volume of air that is mostly consistent, horizontally, in temperature and humidity.

    Encyclopedic Entry: air mass
    air pressure Noun

    force pressed on an object by air or atmosphere.

    alter Verb

    to change.

    arid Adjective

    dry.

    atmospheric science Noun

    study of the atmosphere's physical characteristics, motions, and processes, and the way in which these factors affect the rest of our environment.

    barometer Noun

    an instrument that measures atmospheric pressure.

    Encyclopedic Entry: barometer
    circulation Noun

    moving in a circular motion.

    climate Noun

    all weather conditions for a given location over a period of time.

    Encyclopedic Entry: climate
    cloud Noun

    visible mass of tiny water droplets or ice crystals in Earth's atmosphere.

    Encyclopedic Entry: cloud
    commercial Adjective

    having to do with the buying and selling of goods and services.

    concept Noun

    idea.

    condense Verb

    to turn from gas to liquid.

    convection Noun

    transfer of heat by the movement of the heated parts of a liquid or gas.

    current Noun

    steady, predictable flow of fluid within a larger body of that fluid.

    Encyclopedic Entry: current
    cyclone Noun

    weather system that rotates around a center of low pressure and includes thunderstorms and rain. Usually, hurricanes refer to cyclones that form over the Atlantic Ocean.

    dense Adjective

    having parts or molecules that are packed closely together.

    differentiate Verb

    to distinguish or mark as different.

    dimension Noun

    extension or measurement in any given direction.

    discipline Noun

    field of study.

    drought Noun

    period of greatly reduced precipitation.

    Encyclopedic Entry: drought
    dual-polarization radar Noun

    instruments and software that collect data on the horizontal and vertical properties of weather (rain, hail) and non-weather (insect, ground clutter) targets.

    El Nino Noun

    irregular, recurring weather system that features a warm, eastern-flowing ocean current in the eastern Pacific Ocean.

    Encyclopedic Entry: El Niño
    Equator Noun

    imaginary line around the Earth, another planet, or star running east-west, 0 degrees latitude.

    Encyclopedic Entry: equator
    estimate Verb

    to guess based on knowledge of the situation or object.

    export Verb

    to transport goods to another place for trade.

    fish stock Noun

    amount of fish available to be harvested in a specific area at a specific time.

    fluid Noun

    material that is able to flow and change shape.

    forecast Verb

    to predict, especially the weather.

    front Noun

    boundary between air masses of different temperatures and humidities.

    Encyclopedic Entry: front
    gas Noun

    state of matter with no fixed shape that will fill any container uniformly. Gas molecules are in constant, random motion.

    geostationary orbit Noun

    orbit around the Earth directly above the Equator.

    global atmospheric circulation Noun

    constant movement of winds across the globe. Also called atmospheric circulation and general circulation.

    global scale meteorology Noun

    study of weather patterns--related to the transport of heat, wind, and moisture--from the tropics to the poles.

    global warming Noun

    increase in the average temperature of the Earth's air and oceans.

    Encyclopedic Entry: global warming
    gravity Noun

    physical force by which objects attract, or pull toward, each other.

    Great Plains Noun

    grassland region of North America, between the Rocky Mountains and the Mississippi River.

    ground station Noun

    research site where data is collected on the ground (not in the atmosphere).

    Hadley cell Noun

    air circulation pattern extending from the Equator to the tropics, with warm equatorial air rising and cooler air from the mid-latitudes falling in looped pattern.

    high-pressure system Noun

    weather pattern characterized by high air pressure, usually as a result of cooling. High-pressure systems are usually associated with clear weather.

    hurricane Noun

    tropical storm with wind speeds of at least 119 kilometers (74 miles) per hour. Hurricanes are the same thing as typhoons, but usually located in the Atlantic Ocean region.

    indispensable Adjective

    necessary or needed.

    infrared radiation Noun

    part of the electromagnetic spectrum with wavelengths longer than visible light but shorter than microwaves.

    inhibit Verb

    to slow or prevent.

    isobar Noun

    lines on a weather map connecting areas of equal atmospheric pressure.

    isotherm Noun

    line that unites points of equal temperature.

    low-pressure system Noun

    weather pattern characterized by low air pressure, usually as a result of warming. Low-pressure systems are often associated with storms.

    Mediterranean basin Noun

    land that surrounds the Mediterranean Sea.

    mercury Noun

    chemical element with the symbol Hg.

    mesoscale convective complex Noun

    collection of thunderclouds in two categories: 1.) no more than -32 degrees Celsius and at least 100,000 square kilometers (38,610 square miles), or 2.) no more than -52 degrees Celsius and at least 50,000 square kilometers (19,305 square miles).

    mesoscale convective system Noun

    collection of thunderstorms that normally persists for several hours or more.

    mesoscale meteorology Noun

    study of weather phenomena, such as squalls, usually smaller than 1,000 kilometers (620 miles).

    meteorology Noun

    study of weather and atmosphere.

    Encyclopedic Entry: meteorology
    microscale meteorology Noun

    study of weather phenomena, such as wind circulations or cloud patterns, that are less than 2 kilometers (1.2 miles).

    midlatitudes Noun

    geographic regions between the Equator and the poles.

    model Noun

    image or impression of an object used to represent the object or system.

    National Hurricane Center Noun

    branch of the National Weather Service responsible for tracking and predicting tropical storms.

    natural disaster Noun

    an event occurring naturally that has large-scale effects on the environment and people, such as a volcano, earthquake, or hurricane.

    phenomena Plural Noun

    (singular: phenomenon) any observable occurrence or feature.

    philosopher Noun

    person who studies knowledge and the way people use it.

    physicist Noun

    person who studies the relationship between matter, energy, motion, and force.

    precipitation Noun

    all forms in which water falls to Earth from the atmosphere.

    Encyclopedic Entry: precipitation
    primary Adjective

    first or most important.

    principal Adjective

    leading or dominant.

    radar Noun

    (RAdio Detection And Ranging) method of determining the presence and location of an object using radio waves.

    radio wave Noun

    electromagnetic wave with a wavelength between 1 millimeter and 30,000 meters, or a frequency between 10 kilohertz and 300,000 megahertz.

    satellite Noun

    object that orbits around something else. Satellites can be natural, like moons, or made by people.

    scientific method Noun

    method of research in which a question is asked, data are gathered, a hypothesis is made, and the hypothesis is tested.

    solar flare Noun

    explosion in the sun's atmosphere, which releases a burst of energy and charged particles into the solar system.

    Southern Oscillation Noun

    decrease in the air pressure over the tropical eastern and western Pacific Ocean, linked to El Nino.

    specialize Verb

    to study, work, or take an interest in one area of a larger field of ideas.

    synoptic scale meteorology Noun

    study of weather occurring over a wide region on time scales exceeding 12 hours.

    terrain Noun

    topographic features of an area.

    thermal energy Noun

    heat, measured in joules or calories.

    tornado Noun

    a violently rotating column of air that forms at the bottom of a cloud and touches the ground.

    trade wind Noun

    winds that blow toward the Equator, from northeast to southwest in the Northern Hemisphere and from southeast to northwest in the Southern Hemisphere.

    transmit Verb

    to pass along information or communicate.

    tropical storm Noun

    weather pattern of swirling winds over a center of low pressure above warm ocean waters. Tropical storms are less powerful than cyclones and hurricanes.

    troposphere Noun

    lowest layer of the Earth's atmosphere, extending from the surface to about 16 kilometers (10 miles) above.

    upwelling Noun

    process by which currents bring cold, nutrient-rich water to the ocean surface.

    Encyclopedic Entry: upwelling
    vapor Noun

    visible liquid suspended in the air, such as fog.

    vegetation Noun

    all the plant life of a specific place.

    weather Noun

    state of the atmosphere, including temperature, atmospheric pressure, wind, humidity, precipitation, and cloudiness.

    Encyclopedic Entry: weather
    weather pattern Noun

    repeating or predictable changes in the Earth's atmosphere, such as winds, precipitation, and temperatures.

    Westerlies Plural Noun

    winds blowing from the west across the mid-latitudes.

    X-ray Noun

    radiation in the electromagnetic spectrum with a very short wavelength and very high energy.

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