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A climatological study of Clear Air Turbulence over the North Atlantic
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
2013 (English)Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesisAlternative title
En klimatologisk studie av Clear Air Turbulence över Nordatlanten (Swedish)
Abstract [en]

Clear Air Turbulence (CAT) is the turbulence experienced at high altitude on board an aircraft. The main mechanisms for its generation are often said to be Kelvin-Helmholtz instability and mountain waves. CAT is an issue to the aviation industry in the sense that it is hard to predict its magnitude and exact location. Mostly, it is just a nuisance for the crew and passengers, but occasionally it causes serious injuries and aircraft damage. It also prevents air-to-air refuelling to be conducted in a safe manner. The micro scale nature of CAT makes it necessary to describe it with turbulence indices.

The first part of this study presents a verification of the two commonly used turbulence indices, TI1 and TI2, developed by Ellrod and Knapp in 1992. The verification is done with AMDAR (Aircraft Meteorological Data Relay) reports and computed indices from ERA-Interim data. The second part presents a 33-year climatology of the indices for describing CAT. Results show that the index TI1 is generally the better of the two indices based on hit rate, but TI2 performs better based on false alarm rate. The climatology suggests that CAT is more frequent at the northern east coast of the U.S., over the island of Newfoundland and east of Greenland. In the vertical, CAT seems to occur most frequently at the 225 hPa level but also occur frequently at the 300 hPa level at the aforementioned areas. Based on AMDAR reports from 2011, only 0.014% of the reports were positive turbulence observations. The low amount of reports suggests that CAT can be avoided effectively with current CAT predicting skills and flight planning.

Abstract [sv]

Clear Air Turbulence (CAT) är den turbulens på hög höjd som upplevs ombord på flygplan och orsaken till denna turbulens sägs ofta vara Kelvin-Helmholtz-instabilitet och lävågor. På grund av svårigheten att förutsäga dess styrka och exakta position är CAT ett problem inom flygbranschen. Ofta är CAT bara ett irritationsmoment för besättning och passagerare, men kan ibland orsaka personskador och flygplansskador. Den mikroskaliga strukturen som CAT har gör det nödvändigt att beskriva den med turbulensindex.

Den första delen av denna studie tar upp pålitligheten av två ofta använda turbulensindex, TI1 och TI2, utvecklade av Ellrod och Knapp år 1992. Verifikationen görs med hjälp av AMDAR-rapporter (Aircraft Meteorological Data Relay) och turbulensindex beräknade med data från ERA-Interim. Den andra delen består av en 33-års klimatologisk studie av CAT baserat på dessa index. Baserat på träffgrad presterar TI1 generellt bättre än TI2, men TI2 presterar bättre än TI1 vad gäller falsklarmsgrad. Den klimatologiska studien tyder på att CAT är mer frekvent över USAs norra ostkust, över Newfoundland och öster om Grönland. I vertikalled verkar CAT förekomma mest frekvent omkring 225 hPa-nivån, men även runt 300 hPa-nivån över de geografiska områden som nämnts ovan. AMDARrapporter från 2011 visar att endast 0.014% av rapporterna observerade turbulens. Den låga andelen antyder att man effektivt kan undvika CAT över nordatlanten med branschens nuvarande förmåga att förutse CAT och god färdplanering.

Place, publisher, year, edition, pages
2013. , 38 p.
Series
Examensarbete vid Institutionen för geovetenskaper, ISSN 1650-6553 ; 264
Keyword [en]
CAT, clear air turbulence, turbulence indices, climatology, North Atlantic, ERA-Interim, AMDAR
Keyword [sv]
CAT, clear air turbulence, klarluftsturbulens, turbulensindex, klimatologi, nordatlanten, ERA-Interim, AMDAR
National Category
Meteorology and Atmospheric Sciences
Identifiers
URN: urn:nbn:se:uu:diva-201732OAI: oai:DiVA.org:uu-201732DiVA: diva2:628916
External cooperation
Totalförsvarets forskningsinstitut, FOI
Subject / course
Meteorology
Educational program
Master Programme in Physics
Supervisors
Examiners
Projects
Research on a CRuiser Enabled Air Transport Environment, RECREATE
Available from: 2013-06-19 Created: 2013-06-14 Last updated: 2013-06-19Bibliographically approved

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