Atmospheric science

• 1. Introduction

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  Atmospheric science studies the Earth's atmosphere and the physical processes working inside it. The instruments it relies on read like a list of ways to reach toward the sky. Satellites, rocketsondes, radiosondes, weather balloons, radars, and lasers all gather what the air refuses to tell us directly. The Greek word aēr, meaning air, gives the field its older name, aerology, though some use that term only for the free atmosphere above the planetary boundary layer. Early in the field stood two pioneers, Léon Teisserenc de Bort and Richard Assmann. What follows asks how a single envelope of gas splits into so many distinct sciences. It asks why the chemistry of the air now carries the weight of human choices. And it asks what Earth's atmosphere shares, and does not share, with the worlds beyond it.

• 2. Chemistry Of The Air

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  Acid rain, photochemical smog, and global warming are the kinds of problems atmospheric chemistry was built to confront. The field studies the chemistry of Earth's atmosphere and that of other planets, drawing on environmental chemistry, physics, meteorology, computer modeling, oceanography, geology, and volcanology. Its central concern is the interaction between the atmosphere and living organisms.

  Human activity has changed the composition of the Earth's atmosphere, and some of those changes harm human health, crops, and ecosystems. By building a theoretical understanding of these problems, researchers can test possible solutions and judge the effects of shifts in government policy. The work shows how the chemistry of the air binds itself to social and political decisions.

  Greenhouse gases sit at the heart of this. Combined with atmospheric physics and biogeochemistry, atmospheric chemistry helps study how such gases shape Earth's radiative balance. According to UNEP, emissions reached a record of 57.1 GtCO2e, up 1.3 percent from the previous year. That jump stands out against the growth between 2010 and 2019, which averaged only 0.8 percent each year.

  The Global Nitrous Oxide Budget reported that atmospheric levels rose by roughly 25 percent between 1750 and 2022, with the fastest annual growth in 2020 and 2021. Warming continues as long as emissions stay above a 0 percent increase. To halt the rise in temperatures, emissions must reach zero.

  Tracing emissions back to their sources is part of the discipline's value. About 26 percent of the 2023 total went to power, 15 percent to transportation, 11 percent to industry, and 11 percent to agriculture. To reverse the human-driven damage, cuts of nearly 42 percent are needed by 2030, to be carried out through government intervention.

• 3. Motion Of The Sky

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  Thunderstorms, tornadoes, gravity waves, tropical cyclones, extratropical cyclones, jet streams, and global-scale circulations all fall under atmospheric dynamics. The field studies motion systems of meteorological importance, weaving together observations taken at many locations and times with theory. Its aim is to explain the circulations we observe using fundamental principles from physics.

  Weather forecasting is one objective these studies serve. Others include developing methods to predict seasonal and interannual climate fluctuations. The work also seeks to understand how human-induced perturbations affect the global climate, such as increased carbon dioxide concentrations or depletion of the ozone layer.

• 4. Physics Of The Atmosphere

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  Fluid flow equations, chemical models, radiation balancing, and energy transfer processes are the tools atmospheric physicists use to model Earth's atmosphere and those of other planets. Their work reaches into the underlying oceans and land as well. To model weather systems they draw on scattering theory, wave propagation models, cloud physics, statistical mechanics, and spatial statistics, each carrying high levels of mathematics and physics. The discipline also covers the design and construction of instruments, including remote sensing tools, and the interpretation of the data those instruments provide.

  The Meteorological Office underpins atmospheric studies in the United Kingdom. In the United States, divisions of the National Oceanic and Atmospheric Administration oversee research projects and weather modeling tied to atmospheric physics. The U.S. National Astronomy and Ionosphere Center carries out studies of the high atmosphere.

  The Earth's magnetic field and the solar wind interact with the atmosphere, producing the ionosphere, the Van Allen radiation belts, telluric currents, and radiant energy. This is the upper reach where the planet meets space.

  Satellite-based observation drives much recent work. One example is CALIPSO, the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation. Engineered by NASA and the Centre National d'Etudes Spatiales, the CALIPSO mission studies how clouds and airborne particles help regulate the weather, climate, and quality of Earth's atmosphere. According to NASA, it leans on retrieval algorithm development, climatology development, spectroscopy, weather and climate model evaluation, and cloudy radiative transfer models.

• 5. Reading The Long Record

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  Glacial periods and interglacials leave traces that climatology uses to predict future changes in climate. The science draws knowledge from meteorology, oceanography, geology, biology, and astronomy to study climate itself. Where meteorology studies short-term weather systems lasting up to a few weeks, climatology studies the frequency and trends of those systems over years to millennia. Climatologists examine the nature of climates, local, regional, or global, and the natural or human-induced factors behind climate variability and ongoing global warming.

  One recent study draws on climatology, oceanology, and economics under the title Concerns about El Nino-Southern Oscillation and the Atlantic Meridional Overturning Circulation with an Increasingly Warm Ocean. Scientists under New Insights in Climate Science found that Earth faces El Nino events of greater extremes and broader climate instability. ENSO describes a recurring pattern in which the temperature of waters in the central and eastern tropical Pacific Ocean changes periodically. AMOC, described by NOAA, is a system of ocean currents that circulates water within the Atlantic Ocean, bringing warm water north and cold water south.

  The collapse of the AMOC appears to be arriving sooner than earlier models predicted. The research also shows that economic and social systems are more vulnerable to El Nino impacts than once thought. Stronger knowledge in this realm helps prepare for amplified droughts, floods, and heat extremes.

  The phenomena of climatological interest span the atmospheric boundary layer, circulation patterns, and heat transfer that is radiative, convective, and latent. They include interactions between the atmosphere, the oceans, and the land surface, especially vegetation, land use, and topography. Related disciplines reach from astrophysics and glaciology to hydrology and volcanology.

• 6. The Upper Reaches

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  Above the stratopause lies the territory of aeronomy, the scientific study of Earth's upper atmosphere and the corresponding regions of other planets. On some worlds the entire atmosphere may match the Earth's upper atmosphere or only a portion of it. A branch of both atmospheric chemistry and atmospheric physics, aeronomy stands in contrast to meteorology, which focuses on the layers below the stratopause. In the regions aeronomers study, chemical dissociation and ionization become important phenomena.

• 7. Atmospheres Of Other Worlds

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  Mercury has had much of its atmosphere blasted away by the solar wind. Every planet in the Solar System holds an atmosphere, because each has gravity strong enough to keep gaseous particles near its surface. The larger gas giants are massive enough to retain great amounts of the light gases hydrogen and helium, while smaller planets lose those gases into space. Earth's atmosphere differs from the rest because life processes here introduced free molecular oxygen. Among the moons, only Titan has kept a dense atmosphere, while Triton holds a thin one and the Moon only a trace.

  The energy a planet receives, from the Sun or from its own interior, drives dynamic weather. Mars produces planet-wide dust storms. Jupiter carries an Earth-sized anticyclone called the Great Red Spot. Neptune shows holes in its atmosphere. At least one planet beyond the Solar System, HD 189733 b, has been claimed to hold a weather system like the Great Red Spot but twice as large.

  Hot Jupiters lose their atmospheres into space through stellar radiation, trailing off much like the tails of comets. Such planets can show vast temperature differences between their day and night sides, producing supersonic winds. Yet the day and night sides of HD 189733b appear to share very similar temperatures, a sign that the planet's atmosphere spreads the star's energy effectively around the whole world.