Time series of temperature in Fram Strait determined from the 2008–2009 DAMOCLES acoustic tomography measurements and an ocean model

A pilot acoustic tomography program in Fram Strait during 2008–2009 measured a year‐long record of acoustic travel times along a 130 km range acoustic path crossing the West Spitsbergen Current. Individual ray arrivals were not observed. Rather, the arrival patterns consisted of a single, stable, br...

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Bibliographic Details
Published in:Journal of geophysical research. Oceans 2016-07, Vol.121 (7), p.4601-4617
Main Authors: Sagen, Hanne, Dushaw, Brian D., Skarsoulis, Emmanuel K., Dumont, Dany, Dzieciuch, Matthew A., Beszczynska‐Möller, Agnieszka
Format: Article
Language:English
Subjects:
Acoustic measurement
Acoustic tomography
Acoustics
Arrivals
average ocean temperature
Brackish
Circulation
Climate
Computer simulation
Constraint modelling
Data assimilation
Data collection
Duration
Estimates
Fram Strait circulation
Geophysics
High resolution
Hydrographic sections
Inverse
Marine
Markov chains
Monte Carlo simulation
numerical ocean model
Ocean models
Ocean temperature
Oceans
Seasonal variation
Statistical methods
Straits
Temperature
Temperature effects
Tomography
Travel time
Variability
West Spitsbergen Current
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Summary:A pilot acoustic tomography program in Fram Strait during 2008–2009 measured a year‐long record of acoustic travel times along a 130 km range acoustic path crossing the West Spitsbergen Current. Individual ray arrivals were not observed. Rather, the arrival patterns consisted of a single, stable, broad arrival pulse of about 100 ms duration. Travel time variations of ±0.15 s recorded the vigorous mesoscale environment of the region and the seasonal cycle. To estimate ocean temperature from the tomography data an inverse scheme employed a high‐resolution ocean model for Fram Strait as the reference ocean. The information from the tomographic measurements is primarily average temperature. Estimated temperatures, averaged over 0–1000 m depth and over range, had a mean of 1.11°C and variations of ±0.33°C; the uncertainty of the tomography estimates was about 60m°C. Agreement with an alternate inverse approach based on EOFs and a Markov Chain Monte Carlo inversion scheme relying on a matched‐peak approach was excellent, indicating a robust estimate for ocean temperature. The inverse estimates for average temperature agreed with the equivalent estimates from hydrographic sections obtained along the acoustic path at the start and end of the program. Among other deficiencies, the ocean model greatly underestimated the intensity of the mesoscale fluctuations and exhibited a warm bias of about 0.38°C in section‐averaged temperature. Tomographic measurements in Fram Strait offer unique large‐scale temperature constraints for ocean models through data assimilation. It is anticipated that these constraints will lead to more accurate estimates of the circulation and transports in Fram Strait. Key Points Tomography accurately measures path‐averaged temperature in Fram Strait An ocean model misrepresents both mean and variability compared to data Tomographic data can be used to correct ocean models through data assimilation
ISSN:2169-9275
2169-9291
DOI:10.1002/2015JC011591