Segmentation of temperature microstructure

Chen, Huey Long; Hondzo, Miki; Rao, A. Ramachandra

doi:10.1029/2001jc001009

Cited by 7 publications

(4 citation statements)

References 32 publications

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“…Each profile was split into segments of variable length, following the segmentation method by Chen et al (2002). The method employs a wavelet-based test, sensitive to changes in spectral shape and magnitude, to ensure that…”

Section: Microstructure Measurementsmentioning

confidence: 99%

On biogenic turbulence production and mixing from vertically migrating zooplankton in lakes

2018

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Vertical mixing in lakes is a key driver of transport of ecologically important dissolved constituents, such as oxygen and nutrients. In this study we focus our attention on biomixing, which refers to the contribution of living organisms towards the turbulence and mixing of oceans and lakes. While several studies of biomixing in the ocean have been conducted, no in situ studies exist that assess the turbulence induced by freshwater zooplanktonic organisms under real environmental conditions. Here, turbulence is sampled during three different sampling days during the sunset diel vertical migration of Daphnia spp. in a small man-made lake. This common genus may create hydrodynamic disturbances in the lake interior where the thermal stratification usually suppresses the vertical diffusion. Concurrent biological sampling assessed the zooplankton vertical concentration profile. An acoustic-Doppler current profiler was also used to track zooplankton concentration and migration via the backscatter strength. Our datasets do not show biologically-enhanced dissipation rates of temperature variance and turbulent kinetic energy in the lake interior, despite Daphnia concentrations as high as 60 org. L −1 . No large and significant turbulent patches were created within the migrating layer to generate irreversible mixing. This suggests that Daphnia do not affect the mixing in the lake at the organism concentrations observed here.

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Section: Microstructure Measurementsmentioning

confidence: 99%

On biogenic turbulence production and mixing from vertically migrating zooplankton in lakes

2018

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“…Following the methodology of Simoncelli et al (2018), profiles were denoised and filtered before being trimmed to remove poor-quality data at the start and end. After applying a depth offset between the SCAMP pressure sensor and the CTD sensors, each profile was segmented as per Chen et al (2002); given the SCAMP sinking velocity of 0.1 m/s ( ± 0.05 m/s) and a sampling rate of 1000 scans/m, each profile was divided into segmentation bins of 256 (2 8 ) samples or approximately 25 cm.…”

Section: Turbulence and Mixingmentioning

confidence: 99%

Using convective mixing in mesocosms to study climate-driven shifts in phytoplankton community distributions

et al. 2023

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With climate change predicted to alter water column stability and mixing across the world’s oceans, a mesocosm experiment was designed to ascertain how a natural phytoplankton community would respond to these changes. As a departure from other mesocosm experiments, we used heating and cooling to produce four different climate-inspired mixing scenarios ranging from well-mixed water columns representative of typical open turbulence (ϵ = 3 x 10-8 m2/s3) through to a quiescent water column with stable stratification (ϵ = 5 x 10-10 m2/s3). This method of turbulence generation is an improvement on previous techniques (e.g., grid, shaker, and aeration) which tend to produce excessive dissipation rates inconsistent with oceanic turbulence observations. Profiles of classical physical parameters used to describe turbulence and mixing (turbulent dissipation rate, buoyancy frequency, turbulent eddy diffusivity, Ozmidov scale) were representative of the profiles found in natural waters under similar mixing conditions. Chlorophyll-a profiles and cell enumeration showed a clear biological response to the different turbulence scenarios. However, the responses of specific phytoplankton groups (diatoms and dinoflagellates) did not conform to the usual expectations: diatoms are generally expected to thrive under convective, turbulent regimes, while dinoflagellates are expected to thrive in converse conditions, i.e., in stable, stratified conditions. Our results suggest that responses to mixing regimes are taxon-specific, with no overwhelming physical effect of the turbulence regime. Rather, each taxon seemed to very quickly reach a given vertical distribution that it managed to hold, whether actively or passively, with a high degree of success. Future studies on the effects of climate change on phytoplankton vertical distribution should thus focus on the factors and mechanisms that combine to determine the specific distribution of species within taxa. Our convection-based mesocosm approach, because it uses a primary physical force that generates turbulence in open waters, should prove a valuable tool in this endeavor.

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“…Temperature gradient profiles were divided into 50% overlapping segments of 128, 256, and 512 points for computing the power spectra, corresponding to nominal lengths of ;13, ;26, and ;51 cm, respectively. We note that fixed segment lengths were considered specifically to clarify the role of spectral length in the performance of the processing routines [for discussion of stationary segmentation, see Luketina and Imberger (2001) and Chen et al (2002)]. Segments from the beginning of the profiles were rejected to avoid spectra contaminated by variations in profiler descent rate.…”

Section: Application To Microstructure Measurementsmentioning

confidence: 99%

“…The vertical variability and intermittency of x T and « further underscore the need for highly accurate estimates (Gurvich and Yaglom 1967;Gregg 1987). Recent developments in the Batchelor method have focused on considerations of resolution (Mudge and Lueck 1994), thermistor time response (Gregg and Meagher 1980;Gregg 1999), identification of stationary data segments (Luketina and Imberger 2001;Chen et al 2002), fitting procedures (Ruddick et al 2000;Luketina and Imberger 2001;Jonas et al 2003), and contamination and noise (Kocsis et al 1999;Ruddick et al 2000;Luketina and Imberger 2001).…”

Section: Introductionmentioning

confidence: 98%

An Evaluation of χT Estimation Techniques: Implications for Batchelor Fitting and ɛ

Steinbuck

Stacey

Monismith

2009

Journal of Atmospheric and Oceanic Technology

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Techniques for the accurate estimation of the dissipation rate of temperature variance x T from temperature microstructure measurements are synthesized and evaluated. The techniques focus on the treatment of contamination in the integration of the vertical temperature gradient spectrum. The essential improvements come from estimating x T from the wavenumber domain in which the signal exceeds the noise and from reconstructing unresolved wavenumber contributions using the best-fit Batchelor spectrum. The improvement in the estimates of x T results in better Batchelor fits and more robust estimates of the dissipation rate of turbulent kinetic energy «. High correlations of independent measurements of x T and « from two collocated FP07 thermistors demonstrate the value of the techniques and highlight the improvements at the low end of the resolvable ranges of x T and «.

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Segmentation of temperature microstructure

Cited by 7 publications

References 32 publications

On biogenic turbulence production and mixing from vertically migrating zooplankton in lakes

On biogenic turbulence production and mixing from vertically migrating zooplankton in lakes

Using convective mixing in mesocosms to study climate-driven shifts in phytoplankton community distributions

An Evaluation of χT Estimation Techniques: Implications for Batchelor Fitting and ɛ

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