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.

scholarly journals A Puzzling Disagreement between Observations and Numerical Models in the Central Gulf of Mexico

2013 ◽  
Vol 43 (12) ◽  
pp. 2673-2681 ◽  
Author(s):  
Wilton Sturges ◽  
Alexandra Bozec
Keyword(s):  
Gulf Of Mexico ◽  
Numerical Models ◽  
Surface Flow ◽  
Return Flow ◽  
Mean Flow ◽  
The West ◽  
Near Surface ◽  
Direct Observations ◽  
Order Of Magnitude ◽  
The Difference

Abstract Two large, independent sets of direct observations in the central Gulf of Mexico show a mean near-surface flow of ~10 cm s−1 to the west, concentrated in the northern and southern Gulf. Numerical models that the authors have examined do not produce this mean westward flow. The observed speeds appear to be almost an order of magnitude larger than the estimated errors; this paper studies the observations to estimate carefully the possible errors involved and compares the observations with model results. The flow to the west in the southern Gulf is presumably wind driven on the shallow parts of the shelf, and, in slightly deeper water at the outer edges of the shelf, is possibly the result of southward Sverdrup interior flow driven by the negative curl of the wind stress. In another possibly related issue, long-term deep current-meter observations in the northern Gulf at ~1000 m and below find flow to the west, whereas some models find flow to the east. The flow proposed here assumes a mean flow to the west above roughly 300 m, with a required return flow in deep water. The difference between the deep observations and the models will produce a slope of pressure surfaces of the opposite sign below 1000 m, reversing the direction of upper-layer geostrophic flow in the models.

scholarly journals The Mean Upper-Layer Flow in the Central Gulf of Mexico by a New Method

2016 ◽  
Vol 46 (10) ◽  
pp. 2915-2924 ◽  
Author(s):  
Wilton Sturges
Keyword(s):  
Gulf Of Mexico ◽  
Numerical Models ◽  
Independent Set ◽  
Sea Surface ◽  
Return Flow ◽  
Mean Flow ◽  
The Mean ◽  
Layer Flow ◽  
A New Technique ◽  
Height Data

AbstractPrevious studies have found a puzzling disagreement between two large datasets and the results of numerical models in the central Gulf of Mexico. The observations suggest an upper-layer mean flow to the west of order 10 cm s−1, while the numerical models find no such mean flow. A new technique is used here, using 23 yr of satellite-derived sea surface height data, to estimate the mean flow. This third, independent set of data yields the same westward flow found in previous studies. These findings require that there be sinking in the western Gulf. The details of the return flow remain an intriguing problem.

scholarly journals Deep Cyclonic Circulation in the Gulf of Mexico

2005 ◽  
Vol 35 (10) ◽  
pp. 1801-1812 ◽  
Author(s):  
Christopher J. DeHaan ◽  
Wilton Sturges
Keyword(s):  
Gulf Of Mexico ◽  
Accurate Result ◽  
Sea Water ◽  
Cyclonic Circulation ◽  
Loop Current ◽  
Mean Flow ◽  
Eastern Gulf Of Mexico ◽  
Geostrophic Shear ◽  
Layer Flow ◽  
Yucatan Channel

Abstract The anticyclonic Loop Current dominates the upper-layer flow in the eastern Gulf of Mexico, with a weaker mean anticyclonic pattern in the western gulf. There are reasons, however, to suspect that the deep mean flow should actually be cyclonic. Topographic wave rectification and vortex stretching contribute to this cyclonic tendency, as will the supply of cold incoming deep water at the edges of the basin. The authors find that the deep mean flow is cyclonic both in the eastern and western gulf, with speeds on the order of 1–2 cm s−1 at 2000 m. Historical current-meter mooring data, as well as profiling autonomous Lagrangian circulation explorer (PALACE) floats (at 900 m), suggest that vertical geostrophic shear relative to 1000 m gives a surprisingly accurate result in the interior of the basin. The temperature around the edges of the basin at 2000 m is coldest near the Yucatan Channel, where Caribbean Sea water is colder by ∼0.1°C. The temperature increases steadily with distance in the counterclockwise direction from the Yucatan, consistent with a deep mean cyclonic boundary flow.

scholarly journals Mean Flow in the Gulf of Mexico

2008 ◽  
Vol 38 (7) ◽  
pp. 1501-1514 ◽  
Author(s):  
Wilton Sturges ◽  
Kern E. Kenyon
Keyword(s):  
Gulf Of Mexico ◽  
Data Sources ◽  
Loop Current ◽  
Independent Data ◽  
Ekman Pumping ◽  
Mean Flow ◽  
The West ◽  
Net Flux ◽  
Yucatan Channel ◽  
Current Potential

Abstract Several independent data sources suggest that there is a net upper-layer mass flux O(3 Sv) (Sv ≡ 106 m3 s−1) to the west in the central Gulf of Mexico, even though the western gulf is a closed basin. A plausible explanation is that this net flux is pumped downward by the convergent wind-driven Ekman pumping, as is typical of all midlatitude anticlyclonic gyres. The downward flux can follow isopycnals to depths O(500–600 m) and deeper by eddy mixing; a mechanism for forcing deep water to the south through the Yucatan Channel is provided by the intrusion and ring-shedding cycle of the Loop Current. Potential vorticity maps show that a deep flow from the western gulf back to the Yucatan Channel is likely.

scholarly journals Near-Surface and Deep Circulation Coupling in the Western Gulf of Mexico

2018 ◽  
Vol 48 (1) ◽  
pp. 145-161 ◽  
Author(s):  
M. Tenreiro ◽  
Julio Candela ◽  
Enric Pallàs Sanz ◽  
Julio Sheinbaum ◽  
José Ochoa
Keyword(s):  
Gulf Of Mexico ◽  
Surface Currents ◽  
Loop Current ◽  
Cyclonic Gyre ◽  
Cyclonic Vorticity ◽  
Near Surface ◽  
Deep Circulation ◽  
Rear Part ◽  
The Mean ◽  
Mean Circulation

AbstractThe coupling between the upper (z < 1000-m depth) and deep (z > 1500 m) circulation in the western Gulf of Mexico (WGoM) driven by the arrival of Loop Current eddies (LCEs) is analyzed from moorings measuring horizontal velocity in the full water column during a 5-yr period (October 2008–October 2013). Nine LCEs crossing the mooring array are documented. A composite of these events shows that strong northward currents at depth having speeds of 0.1–0.2 m s−1 precede (~10–20 days) the strong northward near-surface currents (~0.5 m s−1) characteristic of the western rim of the LCEs. These deep northward flow intensifications are followed by southward deep flows coupled with the surface-intensified southward current of the eastern (rear) part of the LCEs crossing the array. These results are consistent with the existence of a deep anticyclone leading and a cyclone trailing the upper-layer LCEs. Objectively interpolated regional maps of velocities and vertical vorticity obtained from up to 30 moorings indicate the mean circulation at 100-m depth in the northern WGoM is mostly anticyclonic and enhanced by the arrival of the westward-propagating LCEs, while the southern part is dominated by the presence of a semipermanent cyclonic structure (Bay of Campeche cyclonic gyre). At 1500-m depth, the mean circulation follows the slope in a cyclonic sense and shows a cyclonic vorticity maximum on the abyssal plane consistent with the LCE deep flow composites. This suggests the LCEs strongly modulate not only the upper-layer circulation but also impact the deep flow.

Field measurement of near-surface typhoon characteristics using a smart monitoring system on a long-span arch bridge site

2019 ◽  
Vol 22 (8) ◽  
pp. 1977-1987
Author(s):  
Xu Wang ◽  
Huaqiang Li ◽  
Zengshun Chen ◽  
Yuanhao Qian ◽  
Yanru Wang ◽  
...  
Keyword(s):  
Monitoring System ◽  
Wind Velocity ◽  
Turbulence Intensity ◽  
Eastern China ◽  
Mean Flow ◽  
Time Duration ◽  
Lateral Direction ◽  
Near Surface ◽  
Gust Factor ◽  
The Mean

During landfall of Typhoon Haikui in Eastern China in 2012, ground level wind data were recorded using a smart monitoring system installed on JiuBao Bridge in Hangzhou, China. This article documents the mean flow and turbulence characteristics from data recorded during the storm. The results show that both turbulence intensity and gust factor decrease with the increase in the mean wind velocity. However, as the mean wind velocity increases, this trend gradually attenuates. The peak factor distribution with gust averaging time duration derived with the Typhoon Haikui data agrees well with the Durst curve. However, the longitudinal gust factor derived from the typhoon wind-speed record in this study is higher compared with the curves proposed by Durst and Krayer-Marshall. Analyses of the gust factor distribution with the turbulence intensity during the passage of the storm reveal a similarity to the empirical curves of Ishizaki and Choi. Results show that the relationship between lateral turbulence and gust factors can be well represented by a quadratic polynomial. Turbulence scale increased with mean wind velocity. The values of autocorrelation coefficients in longitudinal direction are larger than those in lateral direction. There has no obvious dependency of cross-correlation coefficients with mean wind velocity. In general, the wind characteristics in this study are shown to be very similar to those of winds under normal circumstance.

scholarly journals Near-Surface Transport Properties and Lagrangian Statistics during Two Contrasting Years in the Adriatic Sea

2020 ◽  
Vol 8 (9) ◽  
pp. 681
Author(s):  
Saeed Hariri
Keyword(s):  
Transport Properties ◽  
General Circulation Model ◽  
General Circulation ◽  
Circulation Model ◽  
Mean Flow ◽  
Near Surface ◽  
Surface Transport ◽  
The Real ◽  
Lagrangian Statistics ◽  
The Mean

This paper describes the near-surface transport properties and Lagrangian statistics in the Adriatic semi-enclosed basin using synthetic drifters. Lagrangian transport models were used to simulate synthetic trajectories from the mean flow fields obtained by the Massachusetts Institute of Technology general circulation model (MITgcm), implemented in the Adriatic from October 2006 until December 2008. In particular, the surface circulation properties in two contrasting years (2007 had a mild winter and cold fall, while 2008 had a normal winter and hot summer) are compared here. In addition, the Lagrangian statistics for the entire Adriatic Basin after removing the Eulerian mean circulation for numerical particles were calculated. The results indicate that the numerical particles were slower in this simulation when compared with the real drifters. This is because of the reduced energetic flow field generated by the MIT general circulation model during the selected years. The numerical results showed that the balanced effects of the wind-driven recirculation in the northernmost area(which would be a sea response to the Bora wind field) and the Po River discharge cause the residence times to be similar during the two selected years (182 and 185 days in 2007 and 2008, respectively). Furthermore, the mean angular momentum, diffusivity, and Lagrangian velocity covariance values are smaller than in the real drifter observations, while the maximum Lagrangian integral time scale is the same.

scholarly journals Convective self–aggregation in a mean flow

2021 ◽  
Vol 21 (13) ◽  
pp. 10337-10345
Author(s):  
Hyunju Jung ◽  
Ann Kristin Naumann ◽  
Bjorn Stevens
Keyword(s):  
Momentum Flux ◽  
Surface Flux ◽  
Surface Heat ◽  
Horizontal Wind ◽  
Convective System ◽  
Mean Flow ◽  
Near Surface ◽  
Surface Heat Exchange ◽  
The Mean ◽  
Self Aggregation

Abstract. Convective self-aggregation is an atmospheric phenomenon seen in numerical simulations in a radiative convective equilibrium framework thought to be informative of some aspects of the behavior of real-world convection in the deep tropics. We impose a background mean wind flow on convection-permitting simulations through the surface flux calculation in an effort to understand how the asymmetry imposed by a mean wind influences the propagation of aggregated structures in convection. The simulations show that, with imposing mean flow, the organized convective system propagates in the direction of the flow but slows down compared to what pure advection would suggest, and it eventually becomes stationary relative to the surface after 15 simulation days. The termination of the propagation arises from momentum flux, which acts as a drag on the near-surface horizontal wind. In contrast, the thermodynamic response through the wind-induced surface heat exchange feedback is a relatively small effect, which slightly retards the propagation of the convection relative to the mean wind.

Subinertial Slope-Trapped Waves in the Northeastern Gulf of Mexico

2009 ◽  
Vol 39 (6) ◽  
pp. 1475-1485 ◽  
Author(s):  
Z. R. Hallock ◽  
W. J. Teague ◽  
E. Jarosz
Keyword(s):  
Gulf Of Mexico ◽  
Current Velocity ◽  
Kelvin Waves ◽  
Loop Current ◽  
Mobile Bay ◽  
The West ◽  
Direct Forcing ◽  
Northeastern Gulf Of Mexico ◽  
The Waves ◽  
Acoustic Doppler Current Profilers

Abstract Current velocity from moored arrays of acoustic Doppler current profilers (ADCPs) deployed on the outer shelf and slope, south of Mobile Bay in the northeastern Gulf of Mexico, shows evidence of alongslope, generally westward-propagating subinertial baroclinic Kelvin waves with periods of about 16 and 21 days, amplitudes of 5–10 cm s−1, and wavelengths of about 500 km. The observed waves were highly coherent over the slope between about 200 and 500 m and accounted for a significant amount of the current variability below 200 m. The source of the waves could be attributed to effects of the Loop Current on the west Florida slope but is more likely due to direct forcing by Loop Current–generated eddies impacting the experimental area.

Near-surface particle image velocimetry measurements in a transitionally rough-wall atmospheric boundary layer

2007 ◽  
Vol 580 ◽  
pp. 319-338 ◽  
Author(s):  
SCOTT C. MORRIS ◽  
SCOTT R. STOLPA ◽  
PAUL E. SLABOCH ◽  
JOSEPH C. KLEWICKI
Keyword(s):  
Reynolds Number ◽  
Particle Image Velocimetry ◽  
Environmental Science ◽  
Particle Image ◽  
Shear Velocity ◽  
Mean Flow ◽  
Mean Velocity ◽  
Near Surface ◽  
Image Velocimetry ◽  
The Mean

The Reynolds number dependence of the structure and statistics of wall-layer turbulence remains an open topic of research. This issue is considered in the present work using two-component planar particle image velocimetry (PIV) measurements acquired at the Surface Layer Turbulence and Environmental Science Test (SLTEST) facility in western Utah. The Reynolds number (δuτ/ν) was of the order 106. The surface was flat with an equivalent sand grain roughness k+ = 18. The domain of the measurements was 500 < yuτ/ν < 3000 in viscous units, 0.00081 < y/δ < 0.005 in outer units, with a streamwise extent of 6000ν/uτ. The mean velocity was fitted by a logarithmic equation with a von Kármán constant of 0.41. The profile of u′v′ indicated that the entire measurement domain was within a region of essentially constant stress, from which the wall shear velocity was estimated. The stochastic measurements discussed include mean and RMS profiles as well as two-point velocity correlations. Examination of the instantaneous vector maps indicated that approximately 60% of the realizations could be characterized as having a nearly uniform velocity. The remaining 40% of the images indicated two regions of nearly uniform momentum separated by a thin region of high shear. This shear layer was typically found to be inclined to the mean flow, with an average positive angle of 14.9°.

Sign in / Sign up

Export Citation Format

Share Document