"Several times a year an atmospheric river [shown in the image on the right forming over Hawai'i]—a long, narrow conveyor belt of storms that stream in relentlessly from the Pacific Ocean—drops inches of rain or feet of snow on the U.S. west coast. Such a system triggered floods and mudslides in central and southern California this past weekend [2-3 February 2019]."
"Atmospheric rivers flow through the sky about a mile above the ocean surface, and may extend across a thousand miles of ocean to the coast. Some bring routine rain but the more intense systems can carry as much water as 15 Mississippi Rivers. The series of storms striking land can arrive for days or, occasionally, weeks on end. They hit west-facing coastlines worldwide, although the U.S. experiences more than most other national coasts."
The “atmospheric river scale” "ranks severity and impacts, from category 1 (weak) to category 5 (exceptional)."
"Without a scale, we really had no way to objectively communicate what would be a strong storm or a weak one."
"Scientists, the media and the public viewed atmospheric rivers as primarily a hazard, but the weaker ARs are quite beneficial. Water managers made it clear to us that a rating scale would be helpful."
"The scale, published Tuesday in the Bulletin of the American Meteorological Society, ranks atmospheric rivers on five levels:"
- Category 1: Weak—primarily beneficial
- Category 2: Moderate—mostly beneficial, but also somewhat hazardous
- Category 3: Strong—balance of beneficial and hazardous
- Category 4: Extreme—mostly hazardous, but also beneficial (if persistent drought)
- Category 5—Exceptional—primarily hazardous
- 1 Atmospheric rivers
- 2 Anticyclones
- 3 Cyclogenesis
- 4 Cyclones
- 5 Dust devils
- 6 Extratropical cyclones
- 7 Jet streams
- 8 Mesocyclones
- 9 Polar lows
- 10 Polar vortices
- 11 Subtropical cyclones
- 12 Subtropical ridges
- 13 Tornadoes
- 14 Tropical cyclones
- 15 Upper level cyclones
- 16 Warm-core cyclones
- 17 Theoretical aerometeors
- 18 Radars
- 19 Meteorology
- 20 See also
- 21 References
- 22 External links
The particularly intense storm system in the image on the right produced as much as 26 in (66 cm) of precipitation in California and up to 17 ft (520 cm) of snowfall in the Sierra Nevada during December 17–22, 2010.
Atmospheric rivers consist of narrow bands of enhanced water vapor transport, typically along the boundaries between large areas of divergent surface air flow, including some frontal zones in association with extratropical cyclones that form over the oceans.
Pineapple Express storms are the most commonly represented and recognized type of atmospheric rivers; they are given the name due to the warm water vapor plumes originating over the Hawaiian tropics that follow a path towards California.
Atmospheric rivers are typically several thousand kilometers long and only a few hundred kilometers wide, and a single one can carry a greater flux of water than the Earth's largest river, the Amazon River.
Integrated water vapor transport (IVT) is more directly attributed to orographic precipitation, a key factor in the production of intense rainfall and subsequent flooding.
On any given day, atmospheric rivers account for over 90% of the global meridional (north-south) water vapor transport, yet they cover less than 10% of the Earth's circumference. Atmospheric rivers are also known to contribute to about 22% of total global runoff.
They also are the major cause of extreme precipitation events that cause severe flooding in many mid-latitude, westerly coastal regions of the world, including the West Coast of North America, Western Europe, the west coast of North Africa, the Iberian Peninsula, Iran and New Zealand. Equally, the absence of atmospheric rivers has been linked with the occurrence of droughts in several parts of the world including South Africa, Spain and Portugal.
The inconsistency of California's rainfall is due to the variability in strength and quantity of these storms, which can produce strenuous effects on California's water budget, which make California a perfect case study to show the importance of proper water management and prediction of these storms. The significance atmospheric rivers have for the control of coastal water budgets juxtaposed against their creation of detrimental floods can be constructed and studied by looking at California and the surrounding coastal region of the western United States, where atmospheric rivers have contributed 30-50% of total annual rainfall. The Fourth National Climate Assessment (NCA) report, released by the U.S. Global Change Research Program (USGCRP) on November 23, 2018 confirmed that along the U.S. western coast, landfalling atmospheric rivers "account for 30%–40% of precipitation and snowpack. These landfalling atmospheric rivers "are associated with severe flooding events in California and other western states."
"As the world warms, the "landfalling atmospheric rivers on the West Coast are likely to increase" in "frequency and severity" because of "increasing evaporation and higher atmospheric water vapor levels in the atmosphere."
Landfalling ARs were "responsible for nearly all the annual peak daily flow (APDF)s in western Washington" from 1998 through 2009.
This AR in the image on the left brought a "stunning" end to the American West's 5-year drought with "some parts of California received nearly twice as much rain in a single deluge as normally falls in the preceding 5 months (October–February)".
The Great Red Spot on Jupiter is, in fact, the inverse phenomenon, an anticyclone.
An anticyclone is a weather phenomenon defined by the United States National Weather Service's glossary as "a large-scale circulation of winds around a central region of high atmospheric pressure, clockwise in the Northern Hemisphere, counterclockwise in the Southern Hemisphere".
Def. "a system of winds that spiral out from a centre of high pressure" is called an anticyclone.
"High-pressure weather systems often bring fair weather and relatively clear skies. In early June 2012, a high off the coast of Tasmania did just that...and in spectacular fashion."
"The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite acquired this view of a hole in a cloud formation [in the image on the left] at 3:00 p.m. local time (05:00 Universal Time) on June 5, 2012. The weather system over the Great Australian Bight cut out the oval-shaped hole from a blanket of marine stratocumulus clouds."
"The cloud hole, with a diameter that stretched as far as 1,000 kilometers (620 miles) across, was caused by sinking air associated with an area of high pressure near the surface. Globally, the average sea-level pressure is about 1013 millibars; at the center of this high, pressures topped 1,040 millibars."
"Sea-level pressure maps published by the Australian Bureau of Meteorology on June 5 showed that the shape of the cloud hole matched the shape of the high-pressure area. However, the center of high pressure and the cloud hole didn't match precisely; the center of the high was near the western edge of the clear area, about 100 kilometers from the cloud edge."
"In general, winds blow outward and away from areas of high pressure. As a result, areas of high pressure pull air downward. As the air sinks, it also warms, increasing the rate of evaporation and making it difficult for the air to sustain clouds. Areas of low pressure, by contrast, pull air upward and generate clouds and stormy weather."
"While low-pressure systems often produce circular cyclonic storms and clouds, high-pressure systems (which are sometimes called anticyclones) can yield large circular areas of clear skies."
"You could call it an anti-storm."
"Weather models simulated the cloud formation quite accurately. We checked the Global Modeling and Assimilation Office (GMAO) forecast, and it really nailed the system."
The evolution of an anticyclone depends on a few variables such as its size, intensity, moist-convection, Coriolis force etc.
Surface anticyclones form due to downward motion through the troposphere, in areas within a synoptic flow pattern in higher levels of the troposphere, beneath the western side of troughs, on weather maps, these show converging winds (isotachs), also known as confluence, or converging height lines near or above the level of non-divergence, which is near the 500 hPa pressure surface about midway up the troposphere.
Cyclogenesis is the process of cyclone formation and intensification.
Cyclogenesis is the development or strengthening of cyclonic circulation in the atmosphere (a low-pressure area).
The anticyclonic equivalent, the process of formation of high pressure systems, dealing with surface systems is anticyclogenesis.
Cyclogenesis is the opposite of cyclolysis, which concerns the weakening of surface cyclones. The term has an anticyclonic () equivalent—Anticyclogenesis.
Def. a system of winds rotating around a center of low atmospheric pressure, the more or less violent small-scale circulations such as tornadoes, waterspouts, and dust devils is called a cyclone.
The largest low-pressure systems are polar vortices and extratropical cyclones of the largest scale (the synoptic scale), which includes warm-core cyclones such as tropical cyclones and subtropical cyclones.
Mesocyclones, tornadoes and dust devils lie within the smaller mesoscale.
Upper level cyclones can exist without the presence of a surface low, and can pinch off from the base of the tropical upper tropospheric trough during the summer months in the Northern Hemisphere.
A beautifully-formed low-pressure system swirls off the southwestern coast of Iceland, illustrating the maxim that "nature abhors a vacuum." The vacuum in this case would be a region of low atmospheric pressure. In order to fill this void, air from a nearby high-pressure system moves in, in this case bringing clouds along for the ride. And because this low-pressure system occurred in the Northern Hemisphere, the winds spun in toward the center of the low-pressure system in a counter-clockwise direction; a phenomenon known as the Coriolis force (in the Southern Hemisphere, the Coriolis force would be manifested in a clockwise direction of movement).
The clouds in the image resembled pulled cotton and lace as they spun in a lazy hurricane-like pattern. This huge system swirled over the Denmark Strait in between Greenland and Iceland.
The process in which an extratropical cyclone undergoes a rapid drop in atmospheric pressure (24 millibars or more) in a 24-hour period is referred to as explosive cyclogenesis, and is usually present during the formation of a nor'easter.
Def. any of the high-speed, high-altitude air currents that circle the Earth in a westerly direction is called a jet stream.
Jet streams are fast flowing, narrow air currents found in the atmospheres of some planets, including Earth. The main jet streams are located near the tropopause, the transition between the troposphere (where temperature decreases with altitude) and the stratosphere (where temperature increases with altitude). The major jet streams on Earth are westerly winds (flowing west to east). Their paths typically have a meandering shape; jet streams may start, stop, split into two or more parts, combine into one stream, or flow in various directions including the opposite direction of most of the jet. The strongest jet streams are the polar jets, at around 7–12 km (23,000–39,000 ft) above sea level, and the higher and somewhat weaker subtropical jets at around 10–16 km (33,000–52,000 ft). The Northern Hemisphere and the Southern Hemisphere each have both a polar jet and a subtropical jet. The northern hemisphere polar jet flows over the middle to northern latitudes of North America, Europe, and Asia and their intervening oceans, while the southern hemisphere polar jet mostly circles Antarctica all year round.
Heating of the earth near the equator forces upward motion and convection along the monsoon trough or intertropical convergence zone, then divergence over the near-equatorial trough leads to air rising aloft and moving away from the equator: as air moves towards the mid-latitudes, it cools and sinks leading to subsidence near the 30° parallel of both hemispheres, resulting in circulation known as the Hadley cell which forms the subtropical ridge.
Many of the world's deserts are caused by these climatological high-pressure areas.
Because these anticyclones strengthen with height, they are known as warm core ridges.
Upper level cyclones
Def. "movement of [atmospheric] air usually caused by convection or [subtle] differences in air pressure" is called wind.
Def. a discrete unit of air, wind, or mist traveling or falling through or partially through an atmosphere is called an aerometeor.
Def. a "wind whose direction and speed are determined by a balance of the horizontal pressure gradient force and the force due to the earth's rotation to the left in the northern hemisphere and to the right in the southern hemisphere" is called a geostrophic wind.
Def. a "warm dry wind blowing down the side of a mountain" is called a foehn, or foehn wind, or chinook.
The chinook generally blows from the southwest, but its direction may be modified by topography. When it sets in after a spell of intense cold, the temperature may rise by 20–40°F in 15 minutes due to replacement of a cold air mass with a much warmer air mass in minutes."
"Wind shear is a change in wind direction, wind speed, or both, along a given direction in space (e.g., along a horizontal or vertical distance)."
Def. a "strong, abrupt rush of wind" is called a gust.
On the right is a composite of hourly radar images. These wind gusts averaged ~75 mph over about 450 miles. This is referred to as the Derecho event.
There are four main scales, or sizes of systems, dealt with in meteorology: the macroscale, the synoptic scale, the mesoscale, and the microscale.
The macroscale deals with systems with global size, such as the Madden–Julian oscillation.
Synoptic scale systems cover a portion of a continent, such as extratropical cyclones, with dimensions of 1,000–2,500 km (620–1,550 mi) across.
The mesoscale is the next smaller scale, and often is divided into two ranges: meso-alpha phenomena range from 200–2,000 km (120–1,240 mi) across (the realm of the tropical cyclone), while meso-beta phenomena range from 20–200 km (12–124 mi) across (the scale of the mesocyclone).
The microscale is the smallest of the meteorological scales, with a size under 2 kilometres (1.2 miles) (the scale of tornadoes and waterspouts).
- Mark Fischetti (February 5, 2019). Warning Scale Unveiled for Dangerous Rivers in the Sky. Scientific American. Retrieved 8 February 2019.
- Martin Ralph (February 5, 2019). Warning Scale Unveiled for Dangerous Rivers in the Sky. Scientific American. Retrieved 8 February 2019.
- Zhu, Yong; Reginald E. Newell (1994). "Atmospheric rivers and bombs". Geophysical Research Letters 21 (18): 1999–2002. doi:10.1029/94GL01710. https://web.archive.org/web/20100610063041/http://paos.colorado.edu/~dcn/ATOC6020/papers/AtmosphericRivers_94GL01710.pdf.
- Zhu, Yong; Reginald E. Newell (1998). "A Proposed Algorithm for Moisture Fluxes from Atmospheric Rivers". Monthly Weather Review 126 (3): 725–735. doi:10.1175/1520-0493(1998)126<0725:APAFMF>2.0.CO;2. ISSN 1520-0493.
- Kerr, Richard A. (28 July 2006). "Rivers in the Sky Are Flooding The World With Tropical Waters". Science 313 (5786): 435. doi:10.1126/science.313.5786.435. PMID 16873624. http://tenaya.ucsd.edu/~dettinge/atmos_rivers.science.pdf.
- White, Allen B.; et al. (2009-10-08). The NOAA coastal atmospheric river observatory. 34th Conference on Radar Meteorology.
- Dettinger, Michael (2011-06-01). "Climate Change, Atmospheric Rivers, and Floods in California – A Multimodel Analysis of Storm Frequency and Magnitude Changes1". JAWRA Journal of the American Water Resources Association 47 (3): 514–523. doi:10.1111/j.1752-1688.2011.00546.x. ISSN 1752-1688.
- Dettinger, Michael D.; Ralph, Fred Martin; Das, Tapash; Neiman, Paul J.; Cayan, Daniel R. (2011-03-24). "Atmospheric Rivers, Floods and the Water Resources of California". Water 3 (2): 445–478. doi:10.3390/w3020445. http://www.mdpi.com/2073-4441/3/2/445.
- Ralph, F. Martin (2006). "Flooding on California's Russian River: Role of atmospheric rivers". Geophys. Res. Lett. 33 (13): L13801. doi:10.1029/2006GL026689. http://tenaya.ucsd.edu/~dettinge/atmos_rivers.pdf.
- Guan, Bin; Waliser, Duane E.; Molotch, Noah P.; Fetzer, Eric J.; Neiman, Paul J. (2011-08-24). "Does the Madden–Julian Oscillation Influence Wintertime Atmospheric Rivers and Snowpack in the Sierra Nevada?". Monthly Weather Review 140 (2): 325–342. doi:10.1175/MWR-D-11-00087.1. ISSN 0027-0644.
- Guan, Bin; Waliser, Duane E. (2015-12-27). "Detection of atmospheric rivers: Evaluation and application of an algorithm for global studies". Journal of Geophysical Research: Atmospheres 120 (24): 2015JD024257. doi:10.1002/2015JD024257. ISSN 2169-8996.
- Paltan, Homero; Waliser, Duane; Lim, Wee Ho; Guan, Bin; Yamazaki, Dai; Pant, Raghav; Dadson, Simon (2017-10-25). "Global Floods and Water Availability Driven by Atmospheric Rivers". Geophysical Research Letters 44 (20): 10,387–10,395. doi:10.1002/2017gl074882. ISSN 0094-8276.
- Neiman, Paul J.; et al. (2009-06-08). Landfalling Impacts of Atmospheric Rivers: From Extreme Events to Long-term Consequences (PDF). The 2010 Mountain Climate Research Conference.
- Neiman, Paul J. (2008). "Diagnosis of an Intense Atmospheric River Impacting the Pacific Northwest: Storm Summary and Offshore Vertical Structure Observed with COSMIC Satellite Retrievals". Monthly Weather Review 136 (11): 4398–4420. doi:10.1175/2008MWR2550.1. http://tenaya.ucsd.edu/~dettinge/neiman_cosmic08.pdf.
- Neiman, Paul J. (2008). "Meteorological Characteristics and Overland Precipitation Impacts of Atmospheric Rivers Affecting the West Coast of North America Based on Eight Years of SSM/I Satellite Observations". Journal of Hydrometeorology 9 (1): 22–47. doi:10.1175/2007JHM855.1. http://tenaya.ucsd.edu/~dettinge/Neiman_Ar-JHM08.pdf.
- "Atmospheric river of moisture targets Britain and Ireland". CIMSS Satellite Blog. November 19, 2009.
- Stohl, A.; Forster, C.; Sodermann, H. (March 2008). "Remote sources of water vapor forming precipitation on the Norwegian west coast at 60°N–a tale of hurricanes and an atmospheric river". Journal of Geophysical Research 113 (D5): n/a. doi:10.1029/2007jd009006.
- Lavers, David A; R. P. Allan; E. F. Wood; G. Villarini; D. J. Brayshaw; A. J. Wade (6 December 2011). "Winter floods in Britain are connected to atmospheric rivers". Geophysical Research Letters 38 (23): n/a. doi:10.1029/2011GL049783. http://www.met.reading.ac.uk/~sgs02rpa/PAPERS/Lavers11GRL.pdf. Retrieved 12 August 2012.
- Dettinger, Michael D. (2013-06-28). "Atmospheric Rivers as Drought Busters on the U.S. West Coast". Journal of Hydrometeorology 14 (6): 1721–1732. doi:10.1175/JHM-D-13-02.1. ISSN 1525-755X.
- Christensen, Jen; Nedelman, Michael (November 23, 2018). "Climate change will shrink US economy and kill thousands, government report warns". CNN. Retrieved November 23, 2018.
- Chapter 2: Our Changing Climate. National Climate Assessment (NCA). Washington, DC: USGCRP. November 23, 2018. Retrieved November 23, 2018.
- Wehner, M. F.; Arnold, J. R.; Knutson, T.; Kunkel, K. E.; LeGrande, A. N. (2017). Wuebbles, D. J.; Fahey, D. W.; Hibbard, K. A.; Dokken, D. J.; Stewart, B. C.; Maycock, T. K., eds. Droughts, Floods, and Wildfires (Report). Climate Science Special Report: Fourth National Climate Assessment. 1. Washington, DC: U.S. Global Change Research Program. pp. 231–256. doi:10.7930/J0CJ8BNN.
- Dettinger, M., 2011: Climate change, atmospheric rivers, and floods in California–a multimodel analysis of storm frequency and magnitude changes. Journal of the American Water Resources Association, 47 (3), 514–523. doi:10.1111/j.1752-1688.2011.00546.x.
- Warner, M. D., C. F. Mass, and E. P. Salathé Jr., 2015: Changes in winter atmospheric rivers along the North American West Coast in CMIP5 climate models. Journal of Hydrometeorology, 16 (1), 118–128. doi:10.1175/JHM-D-14-0080.1.
- Gao, Y., J. Lu, L. R. Leung, Q. Yang, S. Hagos, and Y. Qian, 2015: Dynamical and thermodynamical modulations on future changes of landfalling atmospheric rivers over western North America. Geophysical Research Letters, 42 (17), 7179–7186. doi:10.1002/2015GL065435.
- Neiman, Paul. J.; Schick, L. J.; Ralph, F. M.; Hughes, M.; Wick, G. A. (December 2011). "Flooding in western Washington: The connection to atmospheric rivers". American Meteorological Society (AMS) 12 (6): 1337–1358. doi:10.1175/2011JHM1358.1.
- Wuebbles, D. J.; Fahey, D. W.; Hibbard, K. A.; Dokken, D. J.; Stewart, B. C.; Maycock, T. K., eds. (October 2017). Climate Science Special Report (CSSR) (PDF) (Report). Fourth National Climate Assessment. 1. Washington, DC: U.S. Global Change Research Program. p. 470. doi:10.7930/J0J964J6.
- Ellen Cohen (2009). "Jupiter's Great Red Spot". Hayden Planetarium. Retrieved 2007-11-16.
- "Glossary: Anticyclone". National Weather Service. Retrieved January 19, 2010.
- SemperBlotto (15 August 2005). anticyclone. San Francisco, California: Wikimedia Foundation, Inc. Retrieved 9 February 2019.
- Adam Voiland, Patrick Minnis, Joanna Joiner, Steve Lang and Heather Hyre (June 5, 2012). An Australian “Anti-storm”. Washington, DC USA: NASA. Retrieved 9 February 2019.CS1 maint: Multiple names: authors list (link)
- Patrick Minnis (June 5, 2012). An Australian “Anti-storm”. Washington, DC USA: NASA. Retrieved 9 February 2019.
- Joanna Joiner and Arlindo da Silva (June 5, 2012). An Australian “Anti-storm”. Washington, DC USA: NASA. Retrieved 9 February 2019.
- Masoud Rostami & Vladimir Zeitlin (2017) Influence of condensation and latent heat release upon barotropic and baroclinic instabilities of vortices in a rotating shallow water f-plane model, Geophysical & Astrophysical Fluid Dynamics, 111:1, 1-31, DOI: 10.1080/03091929.2016.1269897 https://doi.org/10.1080/03091929.2016.1269897
- "Glossary of Meteorology". American Meteorological Society. 2009. Retrieved 2009-02-17.
- Konstantin Matchev (2009-02-25). Middle-Latitude Cyclones - II. University of Florida. Retrieved 2009-02-16.CS1 maint: Date and year (link)
- Nina A. Zaitseva (2006). "Cyclogenesis". National Snow and Ice Data Center. Retrieved 2006-12-04.
- Arctic Climatology and Meteorology (2006). "Cyclogenesis". National Snow and Ice Data Center. Retrieved 2006-12-04.
- "Cyclogenesis". Glossary of Meteorology. American Meteorological Society. 26 January 2012. Retrieved 2016-07-23.
- Glossary of Meteorology (June 2000). "Cyclonic circulation". American Meteorological Society. Retrieved 2008-09-17.
- Glossary of Meteorology (June 2000). "Cyclone". American Meteorological Society. Retrieved 2008-09-17.
- BBC Weather Glossary (July 2006). "Cyclone". British Broadcasting Corporation. Retrieved 2006-10-24.
- "UCAR Glossary — Cyclone". University Corporation for Atmospheric Research. Retrieved 2006-10-24.
- National Hurricane Center (2012). Glossary of NHC terms. Retrieved on 2012-08-13.
- I. Orlanski (1975). "A rational subdivision of scales for atmospheric processes". Bulletin of the American Meteorological Society 56 (5): 527–530. doi:10.1175/1520-0477-56.5.527.
- David Brand (1999-05-19). "Colossal cyclone swirling near Martian north pole is observed by Cornell-led team on Hubble telescope". Cornell University. Retrieved 2008-06-15.
- Samantha Harvey (2006-10-02). "Historic Hurricanes". NASA. Retrieved 2008-06-14.
- Sanders, F.; J. R. Gyakum (1980-06-12). "Synoptic-dynamic climatology of the "Bomb"" (PDF). Massachusetts Institute of Technology, Cambridge. Retrieved 2012-01-21.
- United States Department of Energy (26 June 2002). Ask a Scientist. Retrieved 5 May 2008.
- Owen E. Thompson (1996). "Hadley cell". Channel Video Productions. Retrieved 2007-02-11.
- ThinkQuest team 26634 (1999). "The Formation of Deserts". Oracle ThinkQuest Education Foundation. Retrieved 2009-02-16.
- Emperorbma (8 December 2003). wind. San Francisco, California: Wikimedia Foundation, Inc. Retrieved 9 February 2019.
- geostrophic wind. San Francisco, California: Wikimedia Foundation, Inc. July 11, 2011. Retrieved 2013-02-17.
- foehn. San Francisco, California: Wikimedia Foundation, Inc. January 19, 2013. Retrieved 2013-02-17.
- chinook. San Francisco, California: Wikimedia Foundation, Inc. October 17, 2012. Retrieved 2013-02-17.
- Mark R. Mireles, Kirth L. Pederson, Charles H. Elford (February 21, 2007). Meteorologial Techniques. 106 Peacekeeper Drive, Suite 2N3, Offutt Air Force Base, Nebraska USA: Air Force Weather Agency/DNT. Retrieved 2013-02-17.CS1 maint: Multiple names: authors list (link)
- gust. San Francisco, California: Wikimedia Foundation, Inc. January 14, 2013. Retrieved 2013-02-17.
- Mesoscale Dynamics and Modeling Laboratory (2006-09-08). "Part I: Introduction to Mesoscale Dynamics". Retrieved 2006-12-04.
- Arctic Climatology and Meteorology (2006). "Synoptic Scale". Retrieved 2006-10-25.
- University Corporation for Atmospheric Research. Definition of Mesoscale. Retrieved on 2006-10-25.