• A current is the steady, predictable movement of a fluid within a larger body of that fluid. Fluids are materials capable of flowing and easily changing shape. The most familiar natural fluid is water. But air is considered a fluid as well. Electricity can also flow as a current.

    Air currents flow in the atmosphere, the layer of air surrounding the Earth. Water currents flow in rivers, lakes, and, oceans. Electric currents flow through power lines or as lightning.

    Air Currents

    Moving air is called wind. Air currents are winds that move in a riverlike flow in a certain direction. Thermal updrafts are gentle currents caused by warm air rising. Birds like eagles or California condors often ride these updrafts high into the sky. Jet streams are rapidly moving cold currents that circle the Earth high in the atmosphere.

    Air currents are caused by the sun's uneven heating of the Earth. As sunlight beams down on the Earth, it warms some areas, particularly the tropics, more than others. As the Earth's surface is heated, it warms the air just above it. The warmed air expands and becomes lighter than the surrounding air. It rises, creating a warm air current. Cooler, heavier air then pushes in to replace the warm air, forming a cool air current.

    Some air currents are familiar. Santa Ana winds are seasonal (fall) occurrences in southern California. These warm, dry currents blow from the Mojave Desert and the Great Basin toward the Pacific Ocean. Jet streams are familiar to mountaineers who climb Mount Everest, Earths tallest point.

    The summit of Mount Everest actually pierces the jet stream, creating icy winds at the top of the world.

    Water Currents

    A river current is the water moving in a river. Rivers flow from high points to lower ones and eventually down to a larger body of water. The force of gravity, which makes the water flow downward, creates river currents.

    Many factors contribute to the strength of river currents. River currents are influenced by the volume, or amount, of water flowing in a river. A rivers steepness as it flows toward its destination can affect its currents. The steepness of a river is called its stream gradient. A river beds topography also influences its currents. Topography refers to the surface features of an area. A riverbeds topography can include sandbars, basins, and dams.

    The Nile River flows north from the high elevations of sub-Saharan Africa to the low-lying areas of Egypt near the Mediterranean Sea. The Niles currents gain strength as the volume of water increases, especially where the Blue Nile (starting in Ethiopia) and the White Nile (starting in Tanzania) merge. The Aswan Dam, in southern Egypt, severely reduces and controls the flow of Nile River currents.

    Ocean currents are great streams of water flowing both near the oceans surface and far below it. Prevailing winds (air currents) that blow over parts of the ocean push the water along, creating surface currents. Winds can also contribute to upwelling, or currents that move cold, nutrient-rich water from the bottom of the ocean to the surface.

    The spin of the Earth from west to east causes ocean currents to swerve to the right north of the Equator and to the left south of the Equator. This swerving, known as the Coriolis effect, sets surface currents flowing clockwise in a circular pattern in the Northern Hemisphere and counterclockwise in the Southern Hemisphere.

    Differences in seawater density also cause ocean currents. Waters density is affected by its temperature and salinity, or saltiness. The colder and saltier the water is, the denser and heavier it is. Cold, dense water tends to sink and flow under warmer, lighter water, creating a current. The strength of ocean currents is measured in sverdrups (SVAIR-drups), named after a Norwegian oceanographer.

    The Gulf Stream is one of the most well-known ocean currents in the world. This warm current flows from the Gulf of Mexico, around the U.S. state of Florida, up the eastern coast of the U.S. and Canada before crossing the Atlantic Ocean. The Gulf Stream is very powerful. Because of the Gulf Stream, northern Europe is warmer than any other area at its latitude, including Alaska and Russia.

    Electrical Currents

    Electricity is the flow of electrons. Electrons are parts of atoms, of which all things are made. For this reason, almost any surface can be electric under the right conditions.

    Electricity needs a conductor. Metals like copper are good conductors for electricity in homes and businesses. Clothes, carpets, and human beings can be conductors of static electricity currents. The strength of electricity is measured in amperes (amps).

    The vacuum of space can actually be a conductor. The solar wind is a flow of a type of electricity from the sun. The solar wind flows all the way to the edge of the solar system. On Earth, the solar wind is blocked by the atmosphere. We can see the impact of the solar wind as the Northern Lights and the Southern Lights, bright slashes of color that sometimes appear in the sky near the North and South Poles.

    River currents can be influenced by climate, location, and topography.

    Streaming Current
    Parts of the Gulf Stream ocean current are up to 80 kilometers (50 miles) wide and more than a kilometer (half mile) deep.

  • Term Part of Speech Definition Encyclopedic Entry
    air Noun

    layer of gases surrounding Earth.

    Encyclopedic Entry: air
    air current Noun

    flowing movement of air within a larger body of air.

    ampere Noun

    unit measuring electrical current, the amount of electrical charge moving through a conductor in one second. Abbreviated A or amp.

    Aswan Dam Noun

    system of two dams in Egypt that control the flow of the Nile River for agricultural, electrical, and sanitary uses.

    atmosphere Noun

    layers of gases surrounding a planet or other celestial body.

    Encyclopedic Entry: atmosphere
    atom Noun

    the basic unit of an element, composed of three major parts: electrons, protons, and neutrons.

    basin Noun

    a dip or depression in the surface of the land or ocean floor.

    Encyclopedic Entry: basin
    Blue Nile Noun

    tributary of the Nile River flowing from Lake Tana in Ethiopia and meeting the White Nile at Khartoum, Sudan, to form the Nile River.

    coast Noun

    edge of land along the sea or other large body of water.

    Encyclopedic Entry: coast
    conductor Noun

    material that transfers heat, light, electricity, or sound.

    copper Noun

    chemical element with the symbol Cu.

    Coriolis effect Noun

    the result of Earth's rotation on weather patterns and ocean currents. The Coriolis effect makes storms swirl clockwise in the Southern hemisphere and counterclockwise in the Northern Hemisphere.

    Encyclopedic Entry: Coriolis effect
    current Noun

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

    Encyclopedic Entry: current
    dam Noun

    structure built across a river or other waterway to control the flow of water.

    density Noun

    number of things of one kind in a given area.

    Encyclopedic Entry: density
    destination Noun

    place where a person or thing is going.

    electric current Noun

    rate of flow of electricity, measured in amperes.

    electricity Noun

    set of physical phenomena associated with the presence and flow of electric charge.

    electron Noun

    negatively charged subatomic particle.

    elevation Noun

    height above or below sea level.

    Encyclopedic Entry: elevation
    Equator Noun

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

    Encyclopedic Entry: equator
    fluid Noun

    material that is able to flow and change shape.

    gravity Noun

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

    Gulf Stream Noun

    warm current that starts in the Gulf of Mexico and travels along the eastern coast of the U.S. and Canada before crossing the North Atlantic Ocean.

    impact Noun

    meaning or effect.

    influence Verb

    to encourage or persuade a person or organization to act a certain way.

    jet stream Noun

    winds speeding through the upper atmosphere.

    Encyclopedic Entry: jet stream
    lake Noun

    body of water surrounded by land.

    Encyclopedic Entry: lake
    latitude Noun

    distance north or south of the Equator, measured in degrees.

    Encyclopedic Entry: latitude
    lightning Noun

    sudden electrical discharge from clouds.

    Encyclopedic Entry: lightning
    merge Verb

    to combine.

    metal Noun

    category of elements that are usually solid and shiny at room temperature.

    mountaineer Noun

    someone who climbs mountains.

    Mount Everest Noun

    highest spot on Earth, 8,850 meters (29,035 feet). Mount Everest is part of the Himalaya range, in Nepal and China.

    Nile River Noun

    (5,592 kilometers/3,473 miles) river in East Africa.

    northern lights Noun

    also known as the aurora borealis. The bright bands of color around the North Pole caused by the solar wind and the Earth's magnetic field.

    nutrient Noun

    substance an organism needs for energy, growth, and life.

    Encyclopedic Entry: nutrient
    ocean Noun

    large body of salt water that covers most of the Earth.

    Encyclopedic Entry: ocean
    oceanographer Noun

    person who studies the ocean.

    power line Noun

    cable or cord used to transfer electricity from a power plant to a population center. Also called a transmission line.

    prevailing wind Noun

    wind that blows from one direction.

    reduce Verb

    to lower or lessen.

    river Noun

    large stream of flowing fresh water.

    Encyclopedic Entry: river
    river bed Noun

    material at the bottom of a river.

    salinity Noun


    sandbar Noun

    underwater or low-lying mound of sand formed by tides, waves, or currents.

    Santa Ana winds Noun

    extremely strong, dry winds flowing from the Mojave Desert or Great Basin through Southern California to the Pacific Ocean.

    seawater Noun

    salty water from an ocean or sea.

    solar system Noun

    the sun and the planets, asteroids, comets, and other bodies that orbit around it.

    solar wind Noun

    flow of charged particles, mainly protons and electrons, from the sun to the edge of the solar system.

    southern lights Noun

    the bright bands of color around the South Pole caused by the solar wind and the Earth's magnetic field. Also known as the aurora australis.

    South Pole Noun

    fixed point that, along with the North Pole, forms the axis on which the Earth spins.

    Encyclopedic Entry: South Pole
    static electricity Noun

    motionless electronic charge that builds up on a material.

    stream Noun

    body of flowing water.

    Encyclopedic Entry: stream
    stream gradient Noun

    measurement of how steep a riverbed is.

    sub-Saharan Africa Noun

    geographic region located south of the Sahara Desert in Africa.

    summit Noun

    highest point of a mountain.

    sverdrup Noun

    measurement of the strength of ocean currents.

    temperature Noun

    degree of hotness or coldness measured by a thermometer with a numerical scale.

    Encyclopedic Entry: temperature
    thermal Noun

    rising current of warm air.

    topography Noun

    study of the shape of the surface features of an area.

    tropics Plural Noun

    region generally located between the Tropic of Cancer (23 1/2 degrees north of the Equator) and the Tropic of Capricorn (23 1/2 degrees south of the Equator).

    Encyclopedic Entry: tropics
    updraft Noun

    rising movement of gas.

    upwelling Noun

    process in which cold, nutrient-rich water from the bottom of an ocean basin or lake is brought to the surface due to atmospheric effects such as the Coriolis force or wind.

    Encyclopedic Entry: upwelling
    vacuum Noun

    area of empty space.

    volume Noun

    space an object occupies.

    White Nile Noun

    tributary of the Nile River flowing from the highland rivers of Burundi to Lake Victoria and meeting the Blue Nile to form the Nile River at Khartoum, Sudan.

    wind Noun

    movement of air (from a high pressure zone to a low pressure zone) caused by the uneven heating of the Earth by the sun.