Atmospheric physics

Atmospheric physics is the application of physics to the study of the atmosphere. Atmospheric physicists attempt to model Earth's atmosphere and 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 mechanics and spatial statistics which 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 sensing instruments.

Radiation

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 infrared portion 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

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

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 electron densities 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.]

Atmospheric tide

The largest-amplitude atmospheric tides are mostly generated in the troposphere and stratosphere when 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 mesosphere and 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 2008-04-15.]

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 2008-07-08.]

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 Council and the Science and Technology Facilities Council. Divisions of the U.S. National Oceanic and Atmospheric Administration (NOAA) oversee research projects and weather modeling 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 Aeronomy studies the atmosphere and outer space.

See also

*Adiabatic lapse rate
*Atmospheric thermodynamics
*Baroclinic instability
*Barotropic instability
*Barotropic vorticity equation
*David Bates (physicist)
*Convective instability
*Coriolis effect
*Euler equations
*Geostrophic wind
*Gravity wave
*Hydrostatic balance
*Kelvin-Helmholtz instability
*Madden-Julian oscillation
*Navier–Stokes equations
*Potential vorticity
*Pressure gradient force
*Primitive equations
*Rossby number
*Rossby radius of deformation
*Space weather
*Thermal wind
*Vorticity equation

References