- Atmospheric physics
Atmospheric physics is the application of
physicsto the study of the atmosphere. Atmospheric physicists attempt to model Earth's atmosphereand the atmospheres of the other planets using fluid flow equations, chemical models, radiation balancing, and energy transfer processes in the atmosphere (as well as how these tie in to other systems such as the oceans). In order to model weather systems, atmospheric physicists employ elements of scattering theory, wave propagation models, cloud physics, statistical mechanicsand spatial statisticswhich are highly mathematical and related to physics. It has close links to meteorology and climatology and also covers the design and construction of instruments for studying the atmosphere and the interpretation of the data they provide, including remote sensinginstruments.
The sun emits radiation as a variety of wavelengths. Visible light has wavelengths between 0.4 and 0.7 micrometers. [Atmospheric Science Data Center. [http://eosweb.larc.nasa.gov/EDDOCS/Wavelengths_for_Colors.html What Wavelength Goes With a Color?] Retrieved on
2008-04-15.] Shorter wavelengths are known as the ultraviolet(UV) part of the spectrum, while longer wavelengths are grouped into the infraredportion of the spectrum. [Windows to the Universe. [http://www.windows.ucar.edu/tour/link=/earth/Atmosphere/earth_atmosph_radiation_budget.html Solar Energy in Earth's Atmosphere.] Retrieved on 2008-04-15.] Ozone is most effective in absorbing radiation around 0.25 micrometers, University of Delaware. [http://www.udel.edu/Geography/DeLiberty/Geog474/geog474_energy_interact.html Geog 474: Energy Interactions with the Atmosphere and at the Surface.] Retrieved on 2008-04-15.] where UV-c rays lie in the spectrum. This increases the temperature of the nearby stratosphere. Snow reflects 88% of UV rays, University of Delaware. [http://www.udel.edu/Geography/DeLiberty/Geog474/geog474_energy_interact.html Geog 474: Energy Interactions with the Atmosphere and at the Surface.] Retrieved on 2008-04-15.] while sand reflects 12%, and water reflects only 4% of incoming UV radiation. University of Delaware. [http://www.udel.edu/Geography/DeLiberty/Geog474/geog474_energy_interact.html Geog 474: Energy Interactions with the Atmosphere and at the Surface.] Retrieved on 2008-04-15.] The more glancing the angle is between the atmosphere and the sun's rays, the more likely that energy will be reflected or absorbed by the atmosphere. [Wheeling Jesuit University. [http://www.cet.edu/ete/modules/ozone/ozatmo.html Exploring the Environment: UV Menace.] Retrieved on 2007-06-01.]
Cloud physics is the study of the physical processes that lead to the formation, growth and precipitation of
clouds. Clouds are composed of microscopic droplets of water (warm clouds), tiny crystals of ice, or both (mixed phase clouds). Under suitable conditions, the droplets combine to form precipitation, where they may fall to the earth. [Oklahoma Weather Modification Demonstration Program. [http://www.evac.ou.edu/okwmdp/physics.html CLOUD PHYSICS.] Retrieved on 2008-04-15.] The precise mechanics of how a cloud forms and grows is not completely understood, but scientists have developed theories explaining the structure of clouds by studying the microphysics of individual droplets. Advances in radar and satellite technology have also allowed the precise study of clouds on a large scale.
Atmospheric electricity is the regular diurnal variations of the
Earth's atmospheric electromagnetic network (or, more broadly, any planet's electrical system in its layer of gases). The Earth’s surface, the ionosphere, and the atmosphere is known as the global atmospheric electrical circuit. [Dr. Hugh J. Christian and Melanie A. McCook. [http://thunder.msfc.nasa.gov/primer/primer3.html Lightning Detection From Space: A Lightning Primer.] Retrieved on 2008-04-17.] Lightning discharges 30,000 amperes, at up to 100 million volts, and emits light, radio waves, x-rays and even gamma rays. [NASA. [http://www.nasa.gov/vision/universe/solarsystem/rhessi_tgf.html Flashes in the Sky: Earth's Gamma-Ray Bursts Triggered by Lightning.] Retrieved on 2007-06-01.] Plasma temperatures in lightning can approach 28,000 kelvins and electrondensities may exceed 1024/m³. [Fusion Energy Education. [http://fusedweb.llnl.gov/CPEP/Chart_Pages/5.Plasmas/Lightning.html Lightning! Sound and Fury.] Retrieved on 2008-04-17.]
The largest-amplitude atmospheric tides are mostly generated in the
troposphereand stratospherewhen the atmosphere is periodically heated as water vapour and ozone absorb solar radiation during the day. The tides generated are then able to propagate away from these source regions and ascend into the mesosphereand thermosphere. Atmospheric tides can be measured as regular fluctuations in wind, temperature, density and pressure. Although atmospheric tides share much in common with ocean tides they have two key distinguishing features:
i) Atmospheric tides are primarily excited by the Sun's heating of the atmosphere whereas ocean tides are primarily excited by the Moon's gravitational field. This means that most atmospheric tides have periods of oscillation related to the 24-hour length of the solar day whereas ocean tides have longer periods of oscillation related to the lunar day (time between successive lunar transits) of about 24 hours 51 minutes. [Glossary of Meteorology. [http://amsglossary.allenpress.com/glossary/search?id=atmospheric-tide1 Atmospheric Tide.] Retrieved on
ii) Atmospheric tides propagate in an atmosphere where density varies significantly with height. A consequence of this is that their amplitudes naturally increase exponentially as the tide ascends into progressively more rarefied regions of the atmosphere (for an explanation of this phenomenon, see below). In contrast, the density of the oceans varies only slightly with depth and so there the tides do not necessarily vary in amplitude with depth.
Note that although solar heating is responsible for the largest-amplitude atmospheric tides, the gravitational fields of the Sun and Moon also raise tides in the atmosphere, with the lunar gravitational atmospheric tidal effect being significantly greater than its solar counterpart. [Scientific American. [http://www.sciam.com/article.cfm?id=does-the-moon-have-a-tida Does the Moon have a tidal effect on the atmosphere as well as the oceans?.] Retrieved on
At ground level, atmospheric tides can be detected as regular but small oscillations in surface pressure with periods of 24 and 12 hours. Daily pressure maxima occur at 10 a.m. and 10 p.m. local time, while minima occur at 4 a.m. and 4 p.m. local time. The absolute maximum occurs at 10 a.m. while the absolute minimum occurs at 4 p.m. [Dr James B. Calvert. [http://mysite.du.edu/~jcalvert/geol/tides.htm Tidal Observations.] Retrieved on
2008-04-15.] However, at greater heights the amplitudes of the tides can become very large. In the mesosphere(heights of ~ 50 - 100 km) atmospheric tides can reach amplitudes of more than 50 m/s and are often the most significant part of the motion of the atmosphere.
Centers of research
In the UK, atmospheric studies are underpinned by the
Met Office, the Natural Environment Research Counciland the Science and Technology Facilities Council. Divisions of the U.S. National Oceanic and Atmospheric Administration (NOAA) oversee research projects and weathermodeling involving atmospheric physics. The US National Astronomy and Ionosphere Center also carries out studies of the high atmosphere. In Belgium, the Belgian Institute for Space Aeronomystudies the atmosphere and outer space.
Adiabatic lapse rate
Barotropic vorticity equation
David Bates (physicist)
Pressure gradient force
Rossby radius of deformation
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