Measuring surface currents with Surface Velocity Program drifters: the instrument, its data, and some recent results

Lumpkin, Rick; Pazos, M. C.

doi:10.1017/cbo9780511535901.003

Cited by 294 publications

(291 citation statements)

References 62 publications

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“…The surface float contains batteries, a satellite transmitter, a thermistor for sub-skin SST and sometimes other instruments measuring barometric pressure, wind speed and direction, salinity or ocean colour. The immersed drogue is centred at 15 m depth, and it is of the holey-sock type; this design reduces the wind slip maximizing the nearsurface current drag (Lumpkin & Pazos 2007). Drifters that have lost their drogue were not considered in our analysis.…”

Section: Methodsmentioning

confidence: 99%

Near-surface eddy dynamics in the Southern Ocean

2011

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The Antarctic Circumpolar Current (ACC) is a crucial component of the global ocean conveyor belt, acting as a zonal link among the major ocean basins but, to some extent, limiting meridional exchange and tending to isolate the ocean south of it from momentum and heat income. In this work we investigate one of the most important mechanisms contributing to the poleward transfer of properties in the Southern Ocean, that is the eddy component of the dynamics. For this particular purpose, observations obtained from near-surface drifters have been used: they represent a very useful data set to analyse the eddy field because of their ability to catch a large number of scales of motion while providing a quasi-synoptic coverage of the investigated area. Estimates of the eddy heat and momentum fluxes are carried out using data taken from the Global Drifter Program databank; they refer to Surface Velocity Program drifter trajectories collected in the area south of 35°S between 1995 and 2006. Eddy kinetic energies, variance ellipses, momentum and heat fluxes have been calculated using the pseudo-Eulerian method, showing patterns in good agreement with those present in the literature based on observational and model data, although there are some quantitative differences. The eddy fluxes have been separated into their rotational and divergent portions, the latter being responsible for the meridional transports. The associated zonal and depth-exponentially integrated meridional heat transport exhibits values spanning over a range between -0.4 PW and -1.1 PW in the ACC region, consistent with previous estimate

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Section: Methodsmentioning

confidence: 99%

Near-surface eddy dynamics in the Southern Ocean

2011

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“…Twelve SVP-B (Surface Velocity Program, with barometer port) drifters (Lumpkin and Pazos 2007) were deployed in the Baltic Sea in 2010-2011 (Kjellsson and Döös 2012). Their drift was tracked over the time interval of 14 July 2010-19 November 2011.…”

Section: Surface Drifters In the Baltic Seamentioning

confidence: 99%

“…Depth <18 m is indicated by cyan shading mostly follow subsurface currents at these depths. A schematic picture of the SVP drifters can be found in Lumpkin and Pazos (2007). Data-including the state of the drifter-are transmitted once an hour.…”

Section: Surface Drifters In the Baltic Seamentioning

confidence: 99%

Evaluation and Tuning of Model Trajectories and Spreading Rates in the Baltic Sea Using Surface Drifter Observations

Kjellsson

Döös

Soomere

2013

Preventive Methods for Coastal Protection

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Results from experiments with surface drifters in the Baltic Sea in 2010-2011 are presented and discussed. In a first experiment, 12 SVP-B (Surface Velocity Program, with Barometer) drifters with a drogue at 12-18 m depth were deployed in the Baltic Sea. In a second experiment, shallow drifters extending to a depth of 1.5 m were deployed in the Gulf of Finland. Results from the SVP-B drifter experiment are compared to results from a regional ocean model and a trajectory code. Differences between the observed SVP-B drifters and simulated drifters are found for absolute dispersion (i.e., squared displacement from initial position) and relative dispersion (i.e., squared distance between two initially paired drifters). The former is somewhat underestimated since the simulated currents are neither as fast nor as variable as those observed. The latter is underestimated both due to the abovementioned reasons and due to the resolution of the ocean model.For the shallower drifters, spreading in the upper 1-2 m of the Gulf of Finland is investigated. The spreading rate is about 200 m/day for separations <0.5 km, 500 m/day for separations below 1 km and in the range of 0.5-3 km/day for separations in the range of 1-4 km. The spreading rate does not follow Richardson's law. The initial spreading, up to a distance of about d = 100-150 m, is governed by the power law d ∼ t 0.27 whereas for larger separations the distance increases as d ∼ t 2.5 .

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“…For illustration, Figure 1 is a schematic of the crossover time calculated using the separation distance To quantify and test the concept of the T c , the global 1/12 ∘ resolution MERCATOR ocean model forecast and analysis (http://www.mercator-ocean.fr) are assessed for July 2015 and January 2016 using Surface Velocity Program (SVP) drifters maintained by the Global Drifter Program's (GDP) Drifter Data Assembly Centre (Lumpkin & Pazos, 2007). The model forecast is run out 7 days, so we compare four model forecast and analysis cycles 7 days apart in each month.…”

Section: Methodsologymentioning

confidence: 99%

The Crossover Time as an Evaluation of Ocean Models Against Persistence

Phillipson

Toumi

2018

Geophysical Research Letters

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A new ocean evaluation metric, the crossover time, is defined as the time it takes for a numerical model to equal the performance of persistence. As an example, the average crossover time calculated using the Lagrangian separation distance (the distance between simulated trajectories and observed drifters) for the global MERCATOR ocean model analysis is found to be about 6 days. Conversely, the model forecast has an average crossover time longer than 6 days, suggesting limited skill in Lagrangian predictability by the current generation of global ocean models. The crossover time of the velocity error is less than 3 days, which is similar to the average decorrelation time of the observed drifters. The crossover time is a useful measure to quantify future ocean model improvements.

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Measuring surface currents with Surface Velocity Program drifters: the instrument, its data, and some recent results

Cited by 294 publications

References 62 publications

Near-surface eddy dynamics in the Southern Ocean

Near-surface eddy dynamics in the Southern Ocean

Evaluation and Tuning of Model Trajectories and Spreading Rates in the Baltic Sea Using Surface Drifter Observations

The Crossover Time as an Evaluation of Ocean Models Against Persistence

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