In meteorology, an undular bore is a wave disturbance in the Earth's atmosphere and can be seen through unique cloud formations. They normally occur within an area of the atmosphere which is stable in the low levels after an outflow boundary or a cold front moves through.
Undular bores are usually formed when two air masses of different temperatures collide. When a low level boundary such as a cold front or outflow boundary approaches a layer of cold, stable air, it creates a disturbance in the atmosphere producing a wave-like motion, known as a gravity wave. Although the undular bore waves appear as bands of clouds across the sky, they are transverse waves, and are propelled by the transfer of energy from an oncoming storm and are shaped by gravity. The ripple-like appearance of this wave is described as the disturbance in the water when a pebble is dropped into a pond or when a moving boat creates waves in the surrounding water. The object displaces the water or medium the wave is travelling through and the medium moves in an upward motion. However, because of gravity, the water or medium is pulled back down and the repetition of this cycle creates the transverse wave motion.[1]
The undular bore's wavelength can measure 5 miles (8.0 km) peak to peak and can travel 16 kilometres per hour (9.9 mph) to 95 kilometres per hour (59 mph).[1] The medium it travels through is the atmosphere. There are several varying types of ‘‘bores’’ in different layers of the atmosphere, such as the mesospheric bore which occurs in the mesosphere.
Occurrencesedit
Rare but not unknown in a great many locations, the waves appear with some predictability and regularity in the Gulf of Carpentaria during spring. They have been seen as frequently as six days in a row according to reports by the two pilots who have most experience with soaring these sometimes enormous examples of the undular bore, known in Australia as the Morning Glory cloud.
In hydraulicsedit
Undular bore and whelps near the mouth of Araguari River in north-eastern Brazil. View is oblique toward mouth from airplane at approximately 30 m (100 ft) altitude.[2]Undular character of the Severn bore near Over Bridge on 9 March 2005.
The term "bore" is also used to describe positive surges advancing in shallow waters. When the surge's Froude number is less than 1.4 to 1.7 (i.e. above unity and below a number somewhere in the range 1.4 to 1.7), the advancing front is followed by a train of well-defined free-surface undulations (called "whelps").[3] The surge is then called an undular surge or undular bore.
The undulations form a standing wave pattern, relative to the undular bore front. So, the phase velocity (propagation velocity relative to still water) of the undulations is just high enough to keep the undulations stationary relative to the bore front. Now, in water waves, the group velocity (which is also the energy-transport velocity) is less than the phase velocity. Therefore, on average, wave energy of the undulations is transported away from the front, and contributing to the energy loss in the region of the front.[4]
^ abMartin Setvak; Jochen Kerkmann; Alexander Jacob; HansPeter Roesli; Stefano Gallino & Daniel Lindsey (2007-03-19). (PDF). Agenzia Regionale per la Protezione dell'Ambiente Ligure. Archived from the original (PDF) on 25 July 2011. Retrieved 2009-07-03.
^Figure 5 in: Susan Bartsch-Winkler; David K. Lynch (1988), Catalog of worldwide tidal bore occurrences and characteristics (Circular 1022), U. S. Geological Survey
^Chanson, Hubert (2009). "Current Knowledge In Hydraulic Jumps And Related Phenomena. A Survey of Experimental Results". European Journal of Mechanics B/Fluids. 28 (2): 191–210. Bibcode:2009EJMF...28..191C. doi:10.1016/j.euromechflu.2008.06.004. ISSN 0997-7546.
^Benjamin, T.B.; Lighthill, M.J. (1954), "On cnoidal waves and bores", Proceedings of the Royal Society of London. Series A, Mathematical and Physical Sciences, 224 (1159): 448–460, Bibcode:1954RSPSA.224..448B, doi:10.1098/rspa.1954.0172, S2CID 119869484
External linksedit
LiveScience article
Satellite image of undular bore over Gulf of Mexico
Possible undular bore over Arabian Sea
Strange Storm Shaped by Gravity Wave Live Science, 15 October 2007
Morning Glory Waves of the Gulf of Carpentaria – Articles and Images, 1989 on
January 01, 1970
undular, bore, meteorology, undular, bore, wave, disturbance, earth, atmosphere, seen, through, unique, cloud, formations, they, normally, occur, within, area, atmosphere, which, stable, levels, after, outflow, boundary, cold, front, moves, through, image, lik. In meteorology an undular bore is a wave disturbance in the Earth s atmosphere and can be seen through unique cloud formations They normally occur within an area of the atmosphere which is stable in the low levels after an outflow boundary or a cold front moves through Image of a likely undular bore wave In hydraulics an undular bore is a gentle bore with an undular hydraulic jump pattern at the downstream subcritical side Contents 1 In meteorology 1 1 Overview 1 2 Occurrences 2 In hydraulics 3 See also 4 References 5 External linksIn meteorology edit nbsp NEXRAD radar image of undular bore wave Overview edit nbsp View of a small undular bore from Earth Undular bores are usually formed when two air masses of different temperatures collide When a low level boundary such as a cold front or outflow boundary approaches a layer of cold stable air it creates a disturbance in the atmosphere producing a wave like motion known as a gravity wave Although the undular bore waves appear as bands of clouds across the sky they are transverse waves and are propelled by the transfer of energy from an oncoming storm and are shaped by gravity The ripple like appearance of this wave is described as the disturbance in the water when a pebble is dropped into a pond or when a moving boat creates waves in the surrounding water The object displaces the water or medium the wave is travelling through and the medium moves in an upward motion However because of gravity the water or medium is pulled back down and the repetition of this cycle creates the transverse wave motion 1 The undular bore s wavelength can measure 5 miles 8 0 km peak to peak and can travel 16 kilometres per hour 9 9 mph to 95 kilometres per hour 59 mph 1 The medium it travels through is the atmosphere There are several varying types of bores in different layers of the atmosphere such as the mesospheric bore which occurs in the mesosphere Occurrences edit Rare but not unknown in a great many locations the waves appear with some predictability and regularity in the Gulf of Carpentaria during spring They have been seen as frequently as six days in a row according to reports by the two pilots who have most experience with soaring these sometimes enormous examples of the undular bore known in Australia as the Morning Glory cloud In hydraulics edit nbsp Undular bore and whelps near the mouth of Araguari River in north eastern Brazil View is oblique toward mouth from airplane at approximately 30 m 100 ft altitude 2 nbsp Undular character of the Severn bore near Over Bridge on 9 March 2005 The term bore is also used to describe positive surges advancing in shallow waters When the surge s Froude number is less than 1 4 to 1 7 i e above unity and below a number somewhere in the range 1 4 to 1 7 the advancing front is followed by a train of well defined free surface undulations called whelps 3 The surge is then called an undular surge or undular bore The undulations form a standing wave pattern relative to the undular bore front So the phase velocity propagation velocity relative to still water of the undulations is just high enough to keep the undulations stationary relative to the bore front Now in water waves the group velocity which is also the energy transport velocity is less than the phase velocity Therefore on average wave energy of the undulations is transported away from the front and contributing to the energy loss in the region of the front 4 A related occurrence of positive surges is the tidal bore in estuaries See also editAltostratus undulatus cloud Derecho Gravity wave Haboob Hydraulic jump Morning Glory cloud Tidal boreReferences edit a b Martin Setvak Jochen Kerkmann Alexander Jacob HansPeter Roesli Stefano Gallino amp Daniel Lindsey 2007 03 19 Outflow from convective storm Mauritania and adjacent Atlantic Ocean 13 August 2006 PDF Agenzia Regionale per la Protezione dell Ambiente Ligure Archived from the original PDF on 25 July 2011 Retrieved 2009 07 03 Figure 5 in Susan Bartsch Winkler David K Lynch 1988 Catalog of worldwide tidal bore occurrences and characteristics Circular 1022 U S Geological Survey Chanson Hubert 2009 Current Knowledge In Hydraulic Jumps And Related Phenomena A Survey of Experimental Results European Journal of Mechanics B Fluids 28 2 191 210 Bibcode 2009EJMF 28 191C doi 10 1016 j euromechflu 2008 06 004 ISSN 0997 7546 Benjamin T B Lighthill M J 1954 On cnoidal waves and bores Proceedings of the Royal Society of London Series A Mathematical and Physical Sciences 224 1159 448 460 Bibcode 1954RSPSA 224 448B doi 10 1098 rspa 1954 0172 S2CID 119869484External links editLiveScience article Satellite image of undular bore over Gulf of Mexico Possible undular bore over Arabian Sea One NASA site of undular bore wave over Iowa Another NASA site of undular bore wave over Arabian Sea Strange Storm Shaped by Gravity Wave Live Science 15 October 2007 Hubert Chanson 2007 Hydraulic Jumps Bubbles and Bores In 16th Australasian Fluid Mechanics Conference AFMC Gold Coast Queensland Australia 3 7 Dec 2007 Plenary lecture pp 39 53 Gravity wave over Iowa YouTube video Morning Glory Waves of the Gulf of Carpentaria Articles and Images 1989 on Retrieved from https en wikipedia org w index php title Undular bore amp oldid 1189604082, wikipedia, wiki, book, books, library,
