aerosol: (adj. aerosolized) A tiny solid or liquid particle suspended in air or as a gas. Aerosols can be natural, such as fog or gas from volcanic eruptions, or artificial, such as smoke from burning fossil fuels.
air masses: Large volumes of air, sometimes covering many hundreds or thousands of square kilometers (square miles), that typically have a consistent temperature or water-vapor content. Air masses are often classified by their source, such as continental, arctic or tropical. Air masses and other weather systems are steered across Earth’s surface by jet streams and by differences in atmospheric pressure.
atmosphere: The envelope of gases surrounding Earth, another planet or a moon.
chemical: A substance formed from two or more atoms that unite (bond) in a fixed proportion and structure. For example, water is a chemical made when two hydrogen atoms bond to one oxygen atom. Its chemical formula is H2O. Chemical also can be an adjective to describe properties of materials that are the result of various reactions between different compounds.
chemical reaction: A process that involves the rearrangement of the molecules or structure of a substance, as opposed to a change in physical form (as from a solid to a gas).
circulation: (adj. circulatory) A term that refers to the pumping of some fluid repeatedly throughout a system of vessels.
climate: The weather conditions that typically exist in one area, in general, or over a long period.
climate change: Long-term, significant change in the climate of Earth. It can happen naturally or in response to human activities, including the burning of fossil fuels and clearing of forests.
cloud: A plume of molecules or particles, such as water droplets, that move under the action of an outside force, such as wind, radiation or water currents. (in atmospheric science) A mass of airborne water droplets and ice crystals that travel as a plume, usually high in Earth’s atmosphere. Its movement is driven by winds.
coauthor: One of a group (two or more people) who together had prepared a written work, such as a book, report or research paper. Not all coauthors may have contributed equally.
computer model: A program that runs on a computer that creates a model, or simulation, of a real-world feature, phenomenon or event.
continental United States: Also known as the lower 48 states, these are all U.S. states except Alaska and Hawaii. They all reside below Canada and above Mexico.
current: A fluid — such as of water or air — that moves in a recognizable direction.
develop: To emerge or to make come into being, either naturally or through human intervention, such as by manufacturing.
equator: An imaginary line around Earth that divides Earth into the Northern and Southern Hemispheres.
jet stream: A fast-flowing, high-altitude air current. On Earth, the major jet streams flow from west to east in the mid-latitude regions of the Northern and Southern Hemispheres.
mechanism: The steps or process by which something happens or “works.” It may be the spring that pops something from one hole into another. It could be the squeezing of the heart muscle that pumps blood throughout the body. It could be the friction (with the road and air) that slows down the speed of a coasting car. Researchers often look for the mechanism behind actions and reactions to understand how something functions.
molecule: An electrically neutral group of atoms that represents the smallest possible amount of a chemical compound. Molecules can be made of single types of atoms or of different types. For example, the oxygen in the air is made of two oxygen atoms (O2), but water is made of two hydrogen atoms and one oxygen atom (H2O).
NASA: Short for the National Aeronautics and Space Administration. Created in 1958, this U.S. agency has become a leader in space research and in stimulating public interest in space exploration. It was through NASA that the United States sent people into orbit and ultimately to the moon. It also has sent research craft to study planets and other celestial objects in our solar system.
oxygen: A gas that makes up about 21 percent of Earth’s atmosphere.
ozone: A colorless gas made of molecules that contain three oxygen atoms. It can form high in the atmosphere or at ground level. When it forms at Earth’s surface, ozone is a pollutant that irritates eyes and lungs. It is also a major ingredient of smog.
particle: A minute amount of something, usually in solid form.
poles: (in Earth science and astronomy) The cold regions of the planet that exist farthest from the equator; the upper and lower ends of the virtual axis around which a celestial object rotates.
radical: (in chemistry) A molecule having one or more unpaired outer electrons. Radicals readily take part in chemical reactions. The body is capable of making radicals as one means to kill cells, and thereby rid itself of damaged cells or infectious microbes.
simulate: To deceive in some way by imitating the form or function of something. A simulated dietary fat, for instance, may deceive the mouth that it has tasted a real fat because it has the same feel on the tongue — without having any calories. A simulated sense of touch may fool the brain into thinking a finger has touched something even though a hand may no longer exists and has been replaced by a synthetic limb. (in computing) To try and imitate the conditions, functions or appearance of something. Computer programs that do this are referred to as simulations.
solid: Firm and stable in shape; not liquid or gaseous.
stratosphere: The second layer of the Earth’s atmosphere, just above the troposphere, or ground layer. The stratosphere stretches from roughly 14 to 64 kilometers (9 to about 31 miles) above sea level.
sulfate: A family of chemical compounds that are related to sulfuric acid (H2SO4).
troposphere: The lowest level of Earth’s atmosphere. It runs from the planet’s surface to a height of 8 to 14 kilometers (5 to 9 miles), depending on the latitude. It’s the region where the air is thickest and where most weather occurs. Air currents moving through this region often flow not only horizontally, but often vertically (up and down).
weather: Conditions in the atmosphere at a localized place and a particular time. It is usually described in terms of particular features, such as air pressure, humidity, moisture, any precipitation (rain, snow or ice), temperature and wind speed. Weather constitutes the actual conditions that occur at any time and place. It’s different from climate, which is a description of the conditions that tend to occur in some general region during a particular month or season.