GEOSTROPHIC CURRENTS AND THEIR COMPUTATIONS

1965 ◽  
pp. 66-72
Author(s):  
HUGH J. McLELLAN
Keyword(s):  
Geostrophic Currents

scholarly journals Use of recent geoid models to estimate mean dynamic topography and geostrophic currents in South Atlantic and Brazil Malvinas confluence

2012 ◽  
Vol 60 (1) ◽  
pp. 41-48
Author(s):  
Alexandre Bernardino Lopes ◽  
Joseph Harari
Keyword(s):  
Numerical Model ◽  
Large Scale ◽  
Singular Spectrum Analysis ◽  
Satellite System ◽  
South Atlantic ◽  
Dynamic Topography ◽  
Geostrophic Currents ◽  
Mean Dynamic Topography ◽  
Level Model

The use of geoid models to estimate the Mean Dynamic Topography was stimulated with the launching of the GRACE satellite system, since its models present unprecedented precision and space-time resolution. In the present study, besides the DNSC08 mean sea level model, the following geoid models were used with the objective of computing the MDTs: EGM96, EIGEN-5C and EGM2008. In the method adopted, geostrophic currents for the South Atlantic were computed based on the MDTs. In this study it was found that the degree and order of the geoid models affect the determination of TDM and currents directly. The presence of noise in the MDT requires the use of efficient filtering techniques, such as the filter based on Singular Spectrum Analysis, which presents significant advantages in relation to conventional filters. Geostrophic currents resulting from geoid models were compared with the HYCOM hydrodynamic numerical model. In conclusion, results show that MDTs and respective geostrophic currents calculated with EIGEN-5C and EGM2008 models are similar to the results of the numerical model, especially regarding the main large scale features such as boundary currents and the retroflection at the Brazil-Malvinas Confluence.

scholarly journals 4DVAR HF radar assimilation South of Africa

2020 ◽  
Author(s):  
Xavier Couvelard ◽  
Christophe Messager ◽  
Pierrick Penven ◽  
Phillipe Lattes
Keyword(s):  
Complex Dynamics ◽  
Surface Current ◽  
Hf Radar ◽  
Detailed Knowledge ◽  
Oceanic Circulation ◽  
Geostrophic Currents ◽  
Area Of Interest ◽  
Covered Area ◽  
The One ◽  
Gas Fields

Abstract The oceanic circulation south of Africa is characterized by a complex dynamics with a strong variability due to the presence of the Agulhas current and numerous eddies. The area of interest of this paper, is also the location of several natural gas fields under seafloor which are targeted for drilling and exploitation.The complex and powerful ocean currents induce significant issues for ship operations at the surface as well as under the surface for deep sea operations. Therefore, the knowledge of the state of the currents and the ability to forecast them in a realistic manner could greatly enforce the safety of various marine operation. Following this objective an array of HF radar systems was deployed to allow a detailed knowledge of the Agulhas currents and its associated eddy activity. It is shown in this study that 4DVAR assimilation of HF radar allow to represent the surface circulation more realistically. Two kind of experiments have been performed, a one-month analysis and two days forecast. The one-month 4DVAR experiment have been compared to geostrophic currents issued from altimeters and highlight an important improvement of the geostrophic currents. Furthermore, despite the restricted size of the area covered with HF radar, we show that the solution is improved almost in the whole domain, mainly upstream and downstream of the HF radar's covered area. We also show that while benefits of the assimilation on the surface current intensity is significantly reduced in the first 6 hours of the forecast, the correction in direction persists after 48 hours.

Synergistic Use of Satellite and In-Situ Current Data to Improve the Characterisation of Seasonal Trends

2009 ◽  
Author(s):  
Liam Harrington-Missin ◽  
Mark Calverley ◽  
Gus Jeans
Keyword(s):  
Current Data ◽  
Seasonal Trend ◽  
Measured Signal ◽  
Geostrophic Current ◽  
Geostrophic Currents ◽  
Current Regime ◽  
Long Period ◽  
In Situ Data ◽  
One Year

The synergistic use of measured in-situ current data and altimetry derived geostrophic current data provides improved seasonal characterisation of the current regime, West of Shetland. In September 2007, considerable downtime was experienced by an offshore operator, West of Shetland, as a result of unexpectedly high currents persisting for a number of days. This downtime was unanticipated following conclusions derived from one year of in-situ measured data, which suggested a most favourable current regime during the months August to October. Ten years of altimetry derived geostrophic currents were utilised in conjunction with approximately 3 years of in-situ data to assess the validity of the reported seasonal trend. The altimetry derived geostrophic currents correlated well with the dominating long period signal extracted from the in-situ data. Seasonal comparison between the altimetry derived geostrophic currents and the total measured signal showed the previously available measurement year had a relatively benign September. Based on the 10 years of satellite data, the inter-annual variability of the current regime West of Shetland does not show any clear seasonal trend.

The importance of including sea surface current when estimating air-sea turbulent heat fluxes and wind stress in the Gulf Stream region

2020 ◽  
Author(s):  
Xiangzhou Song
Keyword(s):  
Heat Flux ◽  
Wind Stress ◽  
Gulf Stream ◽  
Turbulent Heat Flux ◽  
Heat Fluxes ◽  
Turbulent Heat ◽  
Surface Currents ◽  
Mean Flow ◽  
Geostrophic Currents ◽  
Turbulent Heat Fluxes

AbstractUsing buoy observations from 2004 to 2010 and newly released atmospheric reanalysis and satellite altimetry-derived geostrophic currents from 1993 to 2017, the quantitative contribution of daily mean surface currents to air-sea turbulent heat flux and wind stress uncertainties in the Gulf Stream (GS) region is investigated based on bulk formulas. At four buoy stations, the daily mean latent (sensible) heat flux difference between the estimates with and without surface currents ranges from -18 (-4) to 20 (4) Wm-2, while the daily mean wind stress difference ranges from -0.04 to 0.02 Nm-2. The positive values indicate higher estimates with opposite directions between surface currents and absolute winds. The transition between positive and negative differences is significantly associated with synoptic-scale weather variations. The uncertainties based on buoy observations are approximately 7% and 3% for wind stress and turbulent heat fluxes, respectively. The new reanalysis and satellite geostrophic currents confirm the uncertainties identified by buoy observations with acceptable discrepancies and provide a spatial view of the uncertainty fields. The mean geostrophic currents are aligned with the surface wind along the GS; therefore, the turbulent heat fluxes and wind stress will be ‘underestimated’ with surface currents included. However, on both sides of the GS, the surface flow can be upwind due to possible mechanisms of eddy-mean flow interactions and recirculations, resulting in higher turbulent heat flux estimations. The wind stress and turbulent heat flux uncertainties experience significant seasonal variations and show long-term trends.

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