scholarly journals On the non-geostrophic appearance of some mean surface velocity observations in the Gulf of Mexico

2021 ◽  
Author(s):  
WILTON STURGES
Keyword(s):  
Gulf Of Mexico ◽  
Surface Flow ◽  
Sea Surface ◽  
Surface Velocity ◽  
Geostrophic Balance ◽  
Sea Surface Heights ◽  
The Mean ◽  
Surface Drifters ◽  
Good Agreement

AbstractA previous study of currents in the Gulf of Mexico by the author used long-term means from three independent data sources. Ship-drift results are in good agreement with surface drifters, but these two do not agree with satellite sea-surface heights (SSH). The agreement between the first two suggested the possibility that there could be errors in the SSH or that the mean surface flow is not in geostrophic balance. The present results, using the addition of a fourth long-term mean from hydrographic data, which agrees with the SSH, resolves the issue. The lack of agreement between different long-term means is from inadequate coverage in space and time in data from ship drifts and drifters.

scholarly journals The Flow through the Gulf of Mexico

2019 ◽  
Vol 49 (6) ◽  
pp. 1381-1401 ◽  
Author(s):  
J. Candela ◽  
J. Ochoa ◽  
J. Sheinbaum ◽  
M. López ◽  
P. Pérez-Brunius ◽  
...  
Keyword(s):  
Gulf Of Mexico ◽  
Straits Of Florida ◽  
The North ◽  
Astronomical Tide ◽  
Flow Through ◽  
Sverdrup Transport ◽  
The Mean ◽  
Yucatan Channel ◽  
Range Variation

AbstractFour years (September 2012 to August 2016) of simultaneous current observations across the Yucatan Channel (~21.5°N) and the Straits of Florida (~81°W) have permitted us to investigate the characteristics of the flow through the Gulf of Mexico. The average transport in both channels is 27.6 Sv (1 Sv = 106 m3 s−1), in accordance with previous estimates. At the Straits of Florida section, the transport related to the astronomical tide explains 55% of the observed variance with a mixed semidiurnal/diurnal character, while in the Yucatan Channel tides contribute 82% of the total variance and present a dominant diurnal character. At periods longer than a week the transports in the Yucatan and Florida sections have a correlation of 0.83 without any appreciable lag. The yearly running means of the transport time series in both channels are well correlated (0.98) and present a 3-Sv range variation in the 4 years analyzed. This long-term variability is well related to the convergence of the Sverdrup transport in the North Atlantic between 14.25° and 18.75°N. Using 2 years (July 2014–July 2016) of simultaneous currents observations in the Florida section, the Florida Cable section (~26.7°N), and a section across the Old Bahama Channel (~78.4°W), a mean northward transport of 28.4, 31.1, and 1.6 Sv, respectively, is obtained, implying that only 1.1 Sv is contributed by the Northwest Providence Channel to the mean transport observed at the Cable section during this 2-yr period.

scholarly journals Short-Term Variation of the Surface Flow Pattern South of Lombok Strait Observed from the Himawari-8 Sea Surface Temperature

2019 ◽  
Vol 11 (12) ◽  
pp. 1491 ◽  
Author(s):  
Naokazu Taniguchi ◽  
Shinichiro Kida ◽  
Yuji Sakuno ◽  
Hidemi Mutsuda ◽  
Fadli Syamsudin
Keyword(s):  
Indian Ocean ◽  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Surface Flow ◽  
Sea Surface ◽  
Surface Velocity ◽  
Thermal Plume ◽  
Short Term ◽  
Flow Variation ◽  
The Indian Ocean

Spatial and temporal information on oceanic flow is fundamental to oceanography and crucial for marine-related social activities. This study attempts to describe the short-term surface flow variation in the area south of the Lombok Strait in the northern summer using the hourly Himawari-8 sea surface temperature (SST). Although the uncertainty of this temperature is relatively high (about 0.6 ∘ C), it could be used to discuss the flow variation with high spatial resolution because sufficient SST differences are found between the areas north and south of the strait. The maximum cross-correlation (MCC) method is used to estimate the surface velocity. The Himawari-8 SST clearly shows Flores Sea water intruding into the Indian Ocean with the high-SST water forming a warm thermal plume on a tidal cycle. This thermal plume flows southward at a speed of about 2 m / s . The Himawari-8 SST indicates a southward flow from the Lombok Strait to the Indian Ocean, which blocks the South Java Current flowing eastward along the southern coast of Nusa Tenggara. Although the satellite data is limited to the surface, we found it useful for understanding the spatial and temporal variations in the surface flow field.

scholarly journals Impacts of mean dynamic topography on a regional ocean assimilation system

Ocean Science ◽  
2015 ◽  
Vol 11 (5) ◽  
pp. 829-837 ◽  
Author(s):  
C. Yan ◽  
J. Zhu ◽  
C. A. S. Tanajura
Keyword(s):  
Data Assimilation ◽  
Sea Surface Height ◽  
Sea Surface ◽  
Dynamic Topography ◽  
Altimetry Data ◽  
Mean Dynamic Topography ◽  
Mean Sea Surface ◽  
The Mean

Abstract. An ocean data assimilation system was developed for the Pacific–Indian oceans with the aim of assimilating altimetry data, sea surface temperature, and in situ measurements from Argo (Array for Real-time Geostrophic Oceanography), XBT (expendable bathythermographs), CTD (conductivity temperature depth), and TAO (Tropical Atmosphere Ocean). The altimetry data assimilation requires the addition of the mean dynamic topography to the altimetric sea level anomaly to match the model sea surface height. The mean dynamic topography is usually computed from the model long-term mean sea surface height, and is also available from gravimetric satellite data. In this study, the impact of different mean dynamic topographies on the sea level anomaly assimilation is examined. Results show that impacts of the mean dynamic topography cannot be neglected. The mean dynamic topography from the model long-term mean sea surface height without assimilating in situ observations results in worsened subsurface temperature and salinity estimates. Even if all available observations including in situ measurements, sea surface temperature measurements, and altimetry data are assimilated, the estimates are still not improved. This proves the significant impact of the MDT (mean dynamic topography) on the analysis system, as the other types of observations do not compensate for the shortcoming due to the altimetry data assimilation. The gravimeter-based mean dynamic topography results in a good estimate compared with that of the experiment without assimilation. The mean dynamic topography computed from the model long-term mean sea surface height after assimilating in situ observations presents better results.

Incipient Wind-Generation of Ocean Waves by a Norther1

1957 ◽  
Vol 38 (7) ◽  
pp. 399-404
Author(s):  
Basil W. Wilson
Keyword(s):  
Gulf Of Mexico ◽  
Ocean Waves ◽  
Sea Surface ◽  
Wind Generation ◽  
The South ◽  
The North ◽  
Good Agreement

Details are presented of observations and photographs of the sea surface in the Gulf of Mexico, near Galveston, obtained during a south-north run on a formal cruise of the A. A. Jakkula, oceanographic vessel of the Texas A. & M. Research Foundation. The occasion was highlighted by the advent of a norther which provided an example of incipient wind-generation of waves from ripples. The first stage of the run had following winds and swells from the south. After a period of calm the wind backed to the north and wavelets from the north developed against the southerly swell. Good agreement is obtained between the observed heights and periods of waves and those determind by forecasting procedures which make suitable allowance for the moving fetch and the variability of the wind within it.

scholarly journals Toward Estimating Climatic Trends in SST. Part I: Methods of Measurement

2006 ◽  
Vol 23 (3) ◽  
pp. 464-475 ◽  
Author(s):  
Elizabeth C. Kent ◽  
Peter K. Taylor
Keyword(s):  
Measurement Method ◽  
Early Period ◽  
Sea Surface ◽  
Data Set ◽  
Climatic Trends ◽  
The Pacific ◽  
The Mean ◽  
Seasonal Signal ◽  
Long Term Trend

Abstract To assess climatic changes in sea surface temperature (SST), changes in the measurement method with time and the effect of these changes on the mean SST must be quantified. Observations from the International Comprehensive Ocean–Atmosphere Data Set (ICOADS) have been analyzed for the period from 1970 to 1997 using both SST measurement metadata contained within the dataset and a World Meteorological Organization (WMO) catalog of observing ships. The WMO metadata were particularly important in identifying engine-intake SSTs during the 1970s, but increased method identification over the entire period. There are strong regional variations in the preferred SST measurement method, with engine-intake SST most common in the Pacific and bucket SST preferred by countries bordering the Atlantic. The number of engine-intake SSTs increases over time and becomes more numerous than buckets by the early 1980s. There are significant differences between SST observations made by different methods. The rounding of reports is more common for engine-intake SST than for either bucket or hull sensor SST, which degrades its quality. Significant time-varying biases exist between SST derived from buckets and from engine intakes. The SST difference has a strong seasonal signal with bucket SST being relatively cold in winter, probably resulting from heat loss from the buckets, and warm in summer, probably resulting from solar warming or the sampling of a shallow warm layer. There is also a long-term trend with engine-intake SST being relatively warm in the early period but with a small annual mean difference between the two methods by 1990.

On the propagation of the Lg phase

1960 ◽  
Vol 50 (2) ◽  
pp. 197-210
Author(s):  
Eugene Herrin ◽  
Jean Richmond
Keyword(s):  
Gulf Of Mexico ◽  
Continental Crust ◽  
East Coast ◽  
Shear Waves ◽  
Surface Velocity ◽  
Upper Crust ◽  
Ray Theory ◽  
The Mean ◽  
Bodies Of Water ◽  
Sedimentary Layer

ABSTRACT Empirical determinations of the mean surface velocity of Lg indicate a range from 3.47 to 3.54 km/sec., with one set of velocities off the east coast of Mexico as low as 3.20 km/sec. Computations based on ray theory show that Lg with these velocities may be shear waves guided in the upper crust by an alternation of refractions and surface reflections. The slower velocities would result from shear waves traveling almost entirely in the sedimentary layer. Polarization of Lg is related to the angle at which the guided shear waves are incident at the surface. Calculations show that Lg would travel in a continental crust covered by a considerable thickness of water, thus supporting the hypothesis that the absence of Lg indicates that an oceanic crust underlies such bodies of water as the Gulf of Mexico. All computations were run on the Univac 1103 at Southern Methodist University.

Improved Surface Velocity and Trajectory Estimates in the Gulf of Mexico from Blended Satellite Altimetry and Drifter Data

2015 ◽  
Vol 32 (10) ◽  
pp. 1880-1901 ◽  
Author(s):  
Maristella Berta ◽  
Annalisa Griffa ◽  
Marcello G. Magaldi ◽  
Tamay M. Özgökmen ◽  
Andrew C. Poje ◽  
...  
Keyword(s):  
Gulf Of Mexico ◽  
Skill Score ◽  
Velocity Fields ◽  
Ocean Dynamics ◽  
Surface Velocity ◽  
Skill Scores ◽  
Dynamical Regimes ◽  
Surface Drifters ◽  
Average Dispersion ◽  
And Control

AbstractThis study investigates the results of blending altimetry-based surface currents in the Gulf of Mexico with available drifter observations. Here, subsets of trajectories obtained from the near-simultaneous deployment of about 300 Coastal Ocean Dynamics Experiment (CODE) surface drifters provide both input and control data. The fidelity of surface velocity fields are measured in the Lagrangian frame by a skill score that compares the separation between observed and hindcast trajectories to the observed absolute dispersion. Trajectories estimated from altimetry-based velocities provide satisfactory average results (skill score > 0.4) in large (~100 km) open-ocean structures. However, the distribution of skill score values within these structures is quite variable. In the DeSoto Canyon and on the shelf where smaller-scale structures are present, the overall altimeter skill score is typically reduced to less than 0.2. After 3 days, the dataset-averaged distance between hindcast and drifter trajectories, , is about 45 km—only slightly less than the average dispersion of the observations, km. Blending information from a subset of drifters via a variational method leads to significant improvements in all dynamical regimes. Skill scores typically increase to 0.8 with reduced to less than half of . Blending available drifter information with altimetry data restores velocity field variability at scales not directly sampled by the altimeter and introduces ageostrophic components that cannot be described by simple Ekman superposition. The proposed method provides a means to improve the fidelity of near-real-time synoptic estimates of ocean surface velocity fields by combining altimetric data with modest numbers of in situ drifter observations.

Analysis of Numerical Simulation on Near Surface Beneath Clean and Contaminated Small-Scale Wind-Driven Water Waves

2007 ◽  
Author(s):  
Xiaoxia Hu ◽  
Ali Dolatabadi ◽  
Kamran Siddiqul
Keyword(s):  
Numerical Model ◽  
Water Waves ◽  
Numerical Study ◽  
Surface Region ◽  
Surface Flow ◽  
Small Scale ◽  
Mean Velocity ◽  
Near Surface ◽  
The Mean ◽  
Good Agreement

We report on a numerical study conducted to investigate the near-surface flow beneath clean and contaminated small-scale wind-driven water surfaces. The numerical model is validated in terms of the velocity and surface wave characteristics. A good agreement is observed between the experimental and numerical values. The results from the numerical model show that the mean velocity in the near-surface region is 25–50% higher beneath the contaminated surface as compared to the clear surface. The present trend is also in agreement with the previous experimental observations.

On the Mean Flow in the Western Gulf of Mexico and a Reappraisal of Errors in Ship-Drift Data

2020 ◽  
Vol 50 (7) ◽  
pp. 1983-1988
Author(s):  
Wilton Sturges
Keyword(s):  
Gulf Of Mexico ◽  
Surface Flow ◽  
Return Flow ◽  
Loop Current ◽  
Mean Flow ◽  
The West ◽  
Near Surface ◽  
Southern Half ◽  
The Mean ◽  
Layer Flow

AbstractShip-drift data in the Gulf of Mexico have led to a perplexing result, that the near-surface flow in the west has a north–south mean, of the east–west flow, ~5–10 cm s−1 into a closed basin. Ship-drift data have been used in the past hundred years under the assumption that they are reasonably accurate; the present study examines that assumption carefully, finding that the standard deviation of individual observations is typically ~20 cm s−1. In a monthly mean composed of order 400 observations or more, as examined here, the standard error of the mean will be reduced accordingly. In the southern part of the western Gulf of Mexico, the observed upper-layer flow is clearly to the west and is consistent with our expectations. In the northern part, however, the apparent flow as reported by ship drift in deep water is not significantly different from zero. Thus, the puzzling result remains: three different datasets in the southern half of the basin clearly show flow to the west, with speeds of 10 cm s−1 or more, yet there is no clear evidence of a near-surface return flow back to the east. The convergent wind stress forces downwelling of the upper layer; its return flow could be at some intermediate depth. The transport to the west from Loop Current rings is possibly returned in a deep boundary flow driven by the rectification of deep topographic Rossby waves.

Sign in / Sign up

Export Citation Format

Share Document