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Fabian Schloesser
,
Peter Cornillon
,
Kathleen Donohue
,
Brahim Boussidi
, and
Emily Iskin

Abstract

Detailed understanding of submesoscale processes and their role in global ocean circulation is constrained, in part, by the lack of global observational datasets of sufficiently high resolution. Here, the potential of thermosalinograph (TSG) and Visible Infrared Imager Radiometer Suite (VIIRS) data is evaluated, to characterize the submesoscale structure of the near-surface temperature fields in the Gulf Stream and Sargasso Sea. In addition to spectral density, the structure function is considered, a statistical measure less susceptible to data gaps, which are common in the satellite-derived fields. The structure function is found to be an unreliable estimator, especially for steep spectral slopes, nominally between 2 and 3, typical of the Gulf Stream and Sargasso regions. A quality-control threshold is developed based on the number and size of gaps to ensure reliable spectral density estimates. Analysis of the impact of gaps in the VIIRS data on the spectra shows that both the number of missing values and the size of gaps affect the results, and that the steeper the spectral slope the more significant the impact. Furthermore, the TSG, with a nominal resolution of 75 m, captures the spectral characteristics of the fields in both regions down to scales substantially smaller than 1 km, while the VIIRS fields, with a nominal resolution of 750 m, reproduce the spectra well down to scales of about 20 km in the Sargasso Sea and 5 km in the Gulf Stream. The scales at which the VIIRS and TSG spectra diverge are thought to be determined by sensor and retrieval noise.

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George R. Halliwell Jr.
,
Peter Cornillon
, and
Deirdre A. Byrne

Abstract

Sea surface temperature (Ts ) maps of the region from 59.5° to 75.5°W, 22.5° to 33.5°N containing the western North Atlantic Subtropical Convergence Zone (STCZ) were derived from AVHRR/2 images. The 7- year mean annual cycle was removed and the maps were filtered in space and time to represent anomaly variability with wavelengths ≥ 220 km and periods ≥ 50 days. Warm and cold anomaly features were observed cast of 71°W between 26° and 32°N that propagated westward at 3–4 km day−1 and that occasionally exceeded ±1°C in amplitude. They are generally strong and persistent from fall to spring and are only marginally detectable during summer. During 1981–82, 1982–83, and 1985–86, individual features could be followed through the entire fall-spring interval. During 1983–84,1986–87,and 1987–88,they could typically be followed for 2–4 months, and during 1984–85, for only 1–2 months. The features were anisotropic during all fall-spring intervals except 1986–87, and they had characteristic wavelengths of ∼800 km in the minor axis direction and periods of ∼200 days. Local forcing by synoptic atmospheric variability alone could not amount for the existence of these features. Anomaly features propagated westward in a manner consistent with theoretical zonal dispersion properties of first-mode baroclinic Rossby waves, suggesting that the anomalies may be coupled to a field of wavelike eddies. Since the anomalies were confined to the zonal hand of large mean meridional Ts gradients associated with the STCZ, where meridional eddy currents are relatively effective at forcing anomalies these eddy currents could be largely responsible for their existence. In one case, however, the influence of eddies an vertical heat flux at the mixed layer base appeared to be important. The relatively strong and persistent 1985–86 anomaly features appeared during a several-day interval at the onset of relatively stormy fall weather and (presumably) rapid mixed-layer deepening.

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George R. Halliwell Jr.
,
Young Jae Ro
, and
Peter Cornillon

Abstract

Previous studies have documented the existence of a zonal band of strong, persistent, westward-propagating sea surface temperature (T s ) anomalies with zonal wavelengths of ≈800 km and periods of ≈200 days that are confined to the subtropical convergence zone (STCZ, roughly 26°–32°N). Two years of satellite-derived sea surface temperature (T s ) and sea surface elevation anomaly (η) maps of the Sargasso Sea (22.5°–33.5°N, 71.5°–59.5°W) are analyzed to determine how these anomalies are forced and why they an confined to the STCZ. A simple anomaly model forced by horizontal eddy currents and damped by a linear feedback mechanism explains many properties of the anomaly response. At wavelengths exceeding several hundred kilometers, forcing by horizontal eddy currents becomes less important relative to atmospheric forcing with increasing wavelength. The anomalies are confined to the STCZ partly because the large mean T s gradient there enables the horizontal eddy currents to be relatively effective at forcing anomalies. Also, the eddies that force these anomalies, wavelike features with wavelengths of ∼800 km and periods of ∼200 days, are themselves confined to the STCZ. These wavelike eddies were not detecting during earlier experiments such as MODE because the domains within which they were conducted were too small. Within the STCZ, zonal dispersion properties of the eddy field are consistent with baroclinic Rossby wave variability. To the north and south of the STCZ, however, zonal dispersion properties differ substantially from the properties observed within the STCZ. The eddy dispersion properties change abruptly across transition zones 1–2 degree wide centered at 32.5° and 25.5°N. A simple linearized reduced-gravity model is used to demonstrate that interaction between eddies and zonal mean currents can qualitatively account for the change is dispersion properties south of the STCZ, but not to the north within the Gulf Stream recirculation region.

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Peter Cornillon
,
David Evans
,
Otis B. Brown
,
Robert Evans
,
Paul Eden
, and
James Brown

Abstract

A method for acquisition, processing and analysis of digital, satellite-derived SST fields on a research vessel at sea in near-real-time (within 10 h of the satellite pass) is discussed. Such imagery provides a general view of the SST field over a large area (700 × 900 km) centered on a 128 × 128 pixel, full-resolution view of the study area.

The ability to send these images to the research vessel in a reasonable amount of time (about 1 h using ATS-3) was a result of a three-level approach to data compression. To perform data compression, first, the overall image was decimated by 2 while the central 128 × 128 pixel portion was retained in full resolution. Second, a 1-bit-deep cloud mask was derived from the image. Third, the remaining SST values were encoded as SST steps from the previous pixel on a given scan line. Overall, the data were reduced by 75%–80%. An error-correcting protocol KERMIT, was used to establish low error rate data communications through the ATS-3 VHF links. A moderate capability digital display unit facilitates display and manipulation of the resultant imagery.

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Edward R. Levine
,
D. N. Connors
,
Peter C. Cornillon
, and
H. Thomas Rossby

Abstract

No abstract available.

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Lothar Stramma
,
Peter Cornillon
,
Robert A. Weller
,
James F. Price
, and
Melbourne G. Briscoe

Abstract

Data from a surface mooring located in the Sargasso Sea at 34°N, 70°W between May 1982 and May 1984 were compared with satellite data to investigate large diurnal sea surface temperature changes. Mooring and satellite measurements are in excellent agreement for those days on which no clouds covered the site at the time of the satellite pass. During the summer half-year at this site, there is a 20% charm of diurnal warming of more than 0.5°C, with values of up to 3.5°C observed in the two-year period.

Diurnal warming observed at the mooring has been simulated well by a one-dimensional model driven by local beat and momentum fluxes. Under the conditions of very light wind and strong insolation that produce the Largest surface warming, the surface mixed-layer depth reduces to the convection depth, and wind-mixing becomes unimportant. The thermal response is then limited to depths between 1 and 2 m, making it likely that such events have been underreported in routine ship observations.

In all cases observed, the spatial extent of warming events as determined by satellite data are well correlated with the corresponding atmospheric pressure patterns. Conditions giving rise to the largest diurnal warming events are often associated with a westward-extending ridge of the Bermuda high. In the region studied, 57°–75°W and 29°–43°N, diurnal warming of more than 1°C was found on occasion to cover areas in excess of 300 000 km2, with warming of more than 2°C coveting areas in excess of 130 000 km2.

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C. L. Gentemann
,
Joel P. Scott
,
Piero L. F. Mazzini
,
Cassia Pianca
,
Santha Akella
,
Peter J. Minnett
,
Peter Cornillon
,
Baylor Fox-Kemper
,
Ivona Cetinić
,
T. Mike Chin
,
Jose Gomez-Valdes
,
Jorge Vazquez-Cuervo
,
Vardis Tsontos
,
Lisan Yu
,
Richard Jenkins
,
Sebastien de Halleux
,
Dave Peacock
, and
Nora Cohen
Full access
C. L. Gentemann
,
Joel P. Scott
,
Piero L. F. Mazzini
,
Cassia Pianca
,
Santha Akella
,
Peter J. Minnett
,
Peter Cornillon
,
Baylor Fox-Kemper
,
Ivona Cetinić
,
T. Mike Chin
,
Jose Gomez-Valdes
,
Jorge Vazquez-Cuervo
,
Vardis Tsontos
,
Lisan Yu
,
Richard Jenkins
,
Sebastien De Halleux
,
Dave Peacock
, and
Nora Cohen

Abstract

From 11 April to 11 June 2018 a new type of ocean observing platform, the Saildrone surface vehicle, collected data on a round-trip, 60-day cruise from San Francisco Bay, down the U.S. and Mexican coast to Guadalupe Island. The cruise track was selected to optimize the science team’s validation and science objectives. The validation objectives include establishing the accuracy of these new measurements. The scientific objectives include validation of satellite-derived fluxes, sea surface temperatures, and wind vectors and studies of upwelling dynamics, river plumes, air–sea interactions including frontal regions, and diurnal warming regions. On this deployment, the Saildrone carried 16 atmospheric and oceanographic sensors. Future planned cruises (with open data policies) are focused on improving our understanding of air–sea fluxes in the Arctic Ocean and around North Brazil Current rings.

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