DOCSLIB.ORG

OCEAN SURFACE TOPOGRAPHY Definition Introduction

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
OCEAN SURFACE TOPOGRAPHY Definition Introduction OCEAN SURFACE TOPOGRAPHY 455 motion of the ocean has a wide range of spatial and OCEAN SURFACE TOPOGRAPHY temporal scales. We all have the experience of watching ocean surface and being awed by the ever-changing Lee-Lueng Fu waves and their breaking into turbulence and white caps. Jet Propulsion Laboratory, California Institute of In order to measure the velocity of an ocean current, we Technology, Pasadena, CA, USA must average out these wave effects. At longer periods, there are ocean tides. If the timescales of our interests Definition are longer than tides, we must also average out the The deviation of the height of the ocean surface from effects of tides. Fortunately, there is a dynamic property the geoid is known as the ocean surface topography. of large-scale ocean currents called the geostrophic bal- The geoid is a surface on which the Earth’s gravity field ance. This balance occurs when the Rossby number, is uniform. The ocean surface topography is caused by defined as U/fL, is much smaller than unity. In the nota- ocean waves, tides, currents, and the loading of atmo- tion, U is the speed of the current, L is the spatial scale, spheric pressure. The main application of ocean surface and f is the Coriolis parameter defined as f ¼ 2O sinj, topography is for the determination of large-scale ocean where O is the Earth’s rotation rate (7.292 Â 10À5 rad/s) circulation. and j is the latitude. For example, if U ¼ 50 cm/s at 45 latitude, geostrophic balance occurs when L » 5 km. Introduction Then the geostrophic velocity of the current at ocean sur- The determination of global ocean circulation has been face can be computed from the pressure at ocean surface a challenging goal of physical oceanographers. The fluid as follows: Satellite Orbit Instrument Corrections • tracker bias • waveform sampler gain calibration biases • antenna gain pattern • AGC attenuation • Doppler shift Atmospheric Refraction • range acceleration Corrections • oscillator drift • dry gases R • pointing angle/sea state • water vapor • ionospheric electrons H External Geophysical Adjustments • geoid height hg Sea-State Bias • ocean tidal height hT • atmospheric pressure loading h Corrections a • EM bias • skewness bias hd=h-hg-hT-ha h=H-R Sea Surface Reference Ellipsoid Bottom Topography Ocean Surface Topography, Figure 1 Schematic illustration of the measurement system of satellite altimetry (From Chelton et al., 2001). 456 OCEAN SURFACE TOPOGRAPHY 80′N 40′N 0′ 80′S 80′S 160′W 120′W80′W40′W0′ 40′E80′E120′E 160′E −80 −60 −40 −200 20406080100 120 140 160 180 200 220 240 260 cm Ocean Surface Topography, Figure 2 OST derived from a combined analysis of satellite altimeter data, surface drifter data, and a geoid model (From Rio and Hernandez, 2004). @ the Earth’s surface can be computed from the gradient of ¼ 1 p fv r @ (1) the atmospheric surface pressure; similarly, the speed x and direction of large-scale ocean surface currents can be @ computed from the gradient of OST as shown by ¼1 p fu r @ (2) Equations 1 and 2. OST has been traditionally estimated y from the density field of the ocean as follows: where p is the pressure, r is the density of sea water, and 0 1 Z0 Z0 u and v are the zonal and meridional velocity components, @r @r ¼1 @ 0 þ 0 A respectively. The large-scale ocean currents are also in s r @ T dz @ S dz (3) hydrostatic balance, namely, p ¼ g , where is the 0 T S Àh Àh elevation of the ocean surface topography (denoted by OST hereafter), defined as the deviation of the ocean where T’ and S’ are the temperature and salinity deviations surface from the geoid, and g is the Earth’s gravity from their mean values, and r and ro are the density and acceleration. The geoid is defined as the ocean surface its depth average, respectively, and h is the depth of the on which the Earth’s gravity field is uniform. In the ocean. This quantity, s, has been traditionally referred absence of any motions, the ocean surface would be to as the steric sea level, which is an approximation of conformed to the geoid. OST. In most places, the steric sea level is predominantly The role of OST for ocean currents is thus equivalent to determined by temperature, and therefore is a good the role of atmospheric surface pressure for winds. indicator of the heat content of the water column of the The speed and direction of large-scale wind blowing at ocean. OST is also influenced by other factors such as OCEAN SURFACE TOPOGRAPHY 457 70 60 50 40 30 20 10 0 −10 −20 −30 −40 −50 −60 −70 0 30 60 90 120 150 180 210 240 270 300 330 360 −20 −15 −10 −5 0 5 101520 Ocean Surface Topography, Figure 3 A snapshot (May 30, 2007) of the temporal change of OST from its time-mean value. The unit is cm. wind, atmospheric pressure, and tides. However, our oceanography community. Oceanographers began to knowledge of OST has primarily been obtained through realize the potential of observing the global ocean circula- shipboard measurement of ocean temperature and salinity tion from OST determined from space. using Equation 3 until the recent development of satellite The challenges of determining OST from satellite altimetry (Fu and Cazenave, 2001). altimetry were the measurement accuracies. For example, an error of 1 cm in OST is capable of producing an error in the mass transport by ocean current of the magnitude Satellite altimetry of several million tons per second, which is a significant The concept of using a radar altimeter for measuring fraction of the transport of major ocean currents. The the height of sea surface was developed in the 1960s. technique of satellite altimetry is conceptually straightfor- The measurement of the round-trip travel time of a radar ward, but there are numerous sources for measurement pulse from a satellite to the surface of the ocean allows errors as illustrated in Figure 1. Corrections for these the determination of the distance between the satellite errors constitute the enterprise of precision altimetry and the ocean surface. If the location of the satellite in beginning with the TOPEX/Poseidon Mission. The reader orbit is also known in an Earth-fixed coordinate, then the is referred to Chelton et al. (2001) for a treatise of the height of the sea surface is determined in this coordinate details. Only the major components of the measurement and so is the OST if the knowledge of the geoid is system are briefly described in this entry. available as well. The first satellite altimeter was carried First,thefreeelectronsintheEarth’s ionosphere slow by Skylab launched in the early 1970s. The first satellite down the radar signals and have a net effect of more than altimeter with sufficient precision for detecting OST was 20 cm in error if not corrected. To correct for this error, radar onboard Seasat, which was launched in 1978 returning altimeter must transmit in two channels, for example, the Ku only about 100 days of data. However, the first image of band (13.6 GHz) and the C band (5.3 GHz) as the TOPEX/ the ocean reflecting the variability of OST caused by Poseidon altimeter. The signal delays are different for the ocean currents provided a revolutionary impact on the measurements made at the two channels, which are used 458 OCEAN SURFACE TOPOGRAPHY 65 55 45 35 25 15 5 −5 −15 −25 −35 −45 −55 −65 0306090 120 150 180 210 240 270 300 330 360 0 5 10 15 20 25 30 Ocean Surface Topography, Figure 4 The standard deviation of the temporal change of OST in unit of centimeters. to determine the total electron content and the signal delay. to continue the precision altimetry data record. In the Second, the water vapor in the Earth’s troposphere also mean time, the other satellite altimeters from the ERS, has the effect of delaying radar signals by more than ENVISAT, and Geosat Follow-On (GFO) missions have 40 cm in the tropics. The approach of the TOPEX/Poseidon contributed to the measurement of sea surface height Mission was to carry a three-frequency microwave and OST by providing enhanced spatial and temporal radiometer for making measurement of the water vapor con- resolutions. These missions have, however, benefited tent and the corresponding signal delay of the altimeter. from the cross-calibration with the precision missions for Third, the precise location of the satellite in orbit must be correcting for large-scale errors such as orbit errors determined. This requires onboard precision tracking and tidal effects. It has been recognized by the altimetry systems and well-maintained geodetic ground systems. For community that the continuation of precision missions example, the TOPEX/Poseidon Mission carries three (e.g., Jason) in combination with other missions independent orbit tracking systems: laser retroreflectors, (e.g., ENVISAT) is essential for the measurement of GPS receivers, and a Doppler system called DORIS. OST for a variety of applications. After Seasat, there were two satellite altimeters flown without the full suite of capabilities of error corrections: the US Geosat and the European Remote-Sensing Satellite Ocean general circulation (ERS). The first satellite altimeter mission that was dedi- The measurement of sea surface height from satellite altim- cated to optimal measurement of OST was the joint Amer- etry is not sufficient for the determination of OST. The ican/French TOPEX/Poseidon Mission, launched in 1992. missing link is the geoid. Direct measurement of the Earth’s Aside from the complete measurement system, the 66 gravity field for geoid determination is limited to orbit inclination was chosen for the determination of a resolution of 300 km at present (Jayne, 2000).
Load more

Recommended publications
  • Ocean Surface Topography Altimetry by Large Baseline Cross-Interferometry from Satellite Formation
    remote sensing Article Ocean Surface Topography Altimetry by Large Baseline Cross-Interferometry from Satellite Formation Weiya Kong 1,2, Bo Liu 2,*, Xiaohong Sui 2, Running Zhang 3 and Jinping Sun 1 1 School of Electronic and Information Engineering, Beihang University, Beijing 100191, China; [email protected] (W.K.); [email protected] (J.S.) 2 Qian Xuesen Laboratory of Space and Technology, Beijing 100094, China; [email protected] 3 Beijing Institute of Spacecraft System Engineering, Beijing 100094, China; [email protected] * Correspondence: [email protected]; Tel.: +86-010-6811-3401 Received: 21 September 2020; Accepted: 26 October 2020; Published: 27 October 2020 Abstract: Imaging Radar Altimeter (IRA) is the current development tendency for ocean surface topography (OST) altimetry,which utilizes Synthetic Aperture Radar (SAR) and interferometry to improve the spatial resolution of OST to several kilometers or even better. Meanwhile, centimetric altimetry accuracy should be guaranteed for applications such as geostrophic currents or marine gravity anomaly inversion. However, the baseline length of IRA which determines the altimetric sensitivity is confined by the satellite platform, in consideration of baseline vibration and payload capability. Therefore, the baseline length from a single satellite can extend to only tens of meters, making it difficult to achieve centimetric accuracy. Referring to the successful experience from TerraSAR-X/TanDEM-X, satellite formation can easily extend the baseline length to hundreds or thousands of meters, depending on the helix orbit. Therefore, we propose the large baseline IRA (LB-IRA) from satellite formation for OST altimetry: the carrier frequency shift (CFS) is brought in to compensate for the severe baseline decorrelation, and the helix orbit is carefully selected to prevent severe time decorrelation from along-track baseline.
    [Show full text]
  • Assessment of DUACS Sentinel-3A Altimetry Data in the Coastal Band of the European Seas: Comparison with Tide Gauge Measurements
    remote sensing Article Assessment of DUACS Sentinel-3A Altimetry Data in the Coastal Band of the European Seas: Comparison with Tide Gauge Measurements Antonio Sánchez-Román 1,* , Ananda Pascual 1, Marie-Isabelle Pujol 2, Guillaume Taburet 2, Marta Marcos 1,3 and Yannice Faugère 2 1 Instituto Mediterráneo de Estudios Avanzados, C/Miquel Marquès, 21, 07190 Esporles, Spain; [email protected] (A.P.); [email protected] (M.M.) 2 Collecte Localisation Satellites, Parc Technologique du Canal, 8-10 rue Hermès, 31520 Ramonville-Saint-Agne, France; [email protected] (M.-I.P.); [email protected] (G.T.); [email protected] (Y.F.) 3 Departament de Física, Universitat de les Illes Balears, Cra. de Valldemossa, km 7.5, 07122 Palma, Spain * Correspondence: [email protected]; Tel.: +34-971-61-0906 Received: 26 October 2020; Accepted: 1 December 2020; Published: 4 December 2020 Abstract: The quality of the Data Unification and Altimeter Combination System (DUACS) Sentinel-3A altimeter data in the coastal area of the European seas is investigated through a comparison with in situ tide gauge measurements. The comparison was also conducted using altimetry data from Jason-3 for inter-comparison purposes. We found that Sentinel-3A improved the root mean square differences (RMSD) by 13% with respect to the Jason-3 mission. In addition, the variance in the differences between the two datasets was reduced by 25%. To explain the improved capture of Sea Level Anomaly by Sentinel-3A in the coastal band, the impact of the measurement noise on the synthetic aperture radar altimeter, the distance to the coast, and Long Wave Error correction applied on altimetry data were checked.
    [Show full text]
  • Coriolis Quality Control Manual
    direction de la technologie marine et des systèmes d'information département informatique et données marines Christine Coatanoan Loïc Petit De La Villéon March 2005 – COR-DO/DTI-RAP/04-047 Coriolis data centre Coriolis-données In-situ data quality control Contrôle qualité des données in-situ Coriolis data center In-situ data quality control procedures Contrôle qualité des données in-situ © IFREMER-CORIOLIS Tous droits réservés. La loi du 11 mars 1957 interdit les copies ou reproductions destinées à une utilisation collective. Toute représentation ou reproduction intégrale ou partielle faite par quelque procédé que ce soit (machine électronique, mécanique, à photocopier, à enregistrer ou tout autre) sans le consentement de l'auteur ou de ses ayants cause, est illicite et constitue une contrefaçon sanctionnée par les articles 425 et suivants du Code Pénal. © IFREMER-CORIOLIS All rights reserved. No part of this work covered by the copyrights herein may be reproduced or copied in any form or by any means – electronic, graphic or mechanical, including photocopying, recording, taping or information and retrieval systems - without written permission. COR-DO/DTI-RAP/04-047 25/03/2005 Coriolis-données Titre/ Title : In-situ data quality control procedures Contrôle qualité des données in-situ Titre traduit : Reference : COR-DO/DTI-RAP/04-047 nombre de pages 15 Date : 25/03/2005 bibliographie (Oui / Non) Version : 1.3 illustration(s) (Oui / Non) langue du rapport Diffusion : libre restreinte interdite Nom Date Signature Diffusion Attribution Nb ex. Préparé par : Christine Coatanoan 15/05/2004 Loïc Petit De La Villéon Vérifié par : Thierry Carval 04/06/2004 COR-DO/DTI-RAP/04-047 25/03/2005 Résumé : Ce document décrit l’ensemble des tests de contrôle qualité appliqués aux données gérées par le centre de données Coriolis Abstract : This document describes the quality control tests applied on the in situ data processed at the Coriolis Data Centre Mots-clés : Contrôle qualité.
    [Show full text]
  • Global Observations of Fine-Scale Ocean Surface Topography with the Surface Water and Ocean Topography (SWOT) Mission
    fmars-06-00232 May 13, 2019 Time: 15:5 # 1 REVIEW published: 15 May 2019 doi: 10.3389/fmars.2019.00232 Global Observations of Fine-Scale Ocean Surface Topography With the Surface Water and Ocean Topography (SWOT) Mission Rosemary Morrow1*, Lee-Lueng Fu2, Fabrice Ardhuin3, Mounir Benkiran4, Bertrand Chapron3, Emmanuel Cosme5, Francesco d’Ovidio6, J. Thomas Farrar7, Sarah T. Gille8, Guillaume Lapeyre9, Pierre-Yves Le Traon4, Ananda Pascual10, Aurélien Ponte3, Bo Qiu11, Nicolas Rascle12, Clement Ubelmann13, Jinbo Wang2 and Edward D. Zaron14 1 Centre de Topographie des Océans et de l’Hydrosphère, Laboratoire d’Etudes en Géophysique et Océanographie Spatiale, CNRS, CNES, IRD, Université Toulouse III, Toulouse, France, 2 Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, United States, 3 Laboratoire d’Océanographie Physique et Spatiale, Centre National de la Edited by: Recherche Scientifique – Ifremer, Plouzané, France, 4 Mercator Ocean, Ramonville-Saint-Agne, France, 5 Institut des Fei Chai, Géosciences de l’Environnement, Université Grenoble Alpes, Grenoble, France, 6 Sorbonne Université, CNRS, IRD, MNHN, Second Institute of Oceanography, Laboratoire d’Océanographie et du Climat: Expérimentations et Approches Numériques (LOCEAN-IPSL), Paris, France, State Oceanic Administration, China 7 Woods Hole Oceanographic Institution, Woods Hole, MA, United States, 8 Scripps Institution of Oceanography, University 9 Reviewed by: of California, San Diego, La Jolla, CA, United States, Laboratoire de Météorologie Dynamique (LMD-IPSL),
    [Show full text]
  • Coriolis Effect
    Project ATMOSPHERE This guide is one of a series produced by Project ATMOSPHERE, an initiative of the American Meteorological Society. Project ATMOSPHERE has created and trained a network of resource agents who provide nationwide leadership in precollege atmospheric environment education. To support these agents in their teacher training, Project ATMOSPHERE develops and produces teacher’s guides and other educational materials. For further information, and additional background on the American Meteorological Society’s Education Program, please contact: American Meteorological Society Education Program 1200 New York Ave., NW, Ste. 500 Washington, DC 20005-3928 www.ametsoc.org/amsedu This material is based upon work initially supported by the National Science Foundation under Grant No. TPE-9340055. Any opinions, findings, and conclusions or recommendations expressed in this publication are those of the authors and do not necessarily reflect the views of the National Science Foundation. © 2012 American Meteorological Society (Permission is hereby granted for the reproduction of materials contained in this publication for non-commercial use in schools on the condition their source is acknowledged.) 2 Foreword This guide has been prepared to introduce fundamental understandings about the guide topic. This guide is organized as follows: Introduction This is a narrative summary of background information to introduce the topic. Basic Understandings Basic understandings are statements of principles, concepts, and information. The basic understandings represent material to be mastered by the learner, and can be especially helpful in devising learning activities in writing learning objectives and test items. They are numbered so they can be keyed with activities, objectives and test items. Activities These are related investigations.
    [Show full text]
  • Climate-Change–Driven Accelerated Sea-Level Rise Detected in the Altimeter Era
    Climate-change–driven accelerated sea-level rise detected in the altimeter era R. S. Nerema,1, B. D. Beckleyb, J. T. Fasulloc, B. D. Hamlingtond, D. Mastersa, and G. T. Mitchume aColorado Center for Astrodynamics Research, Ann and H. J. Smead Aerospace Engineering Sciences, Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO 80309; bStinger Ghaffarian Technologies Inc., NASA Goddard Space Flight Center, Greenbelt, MD 20771; cNational Center for Atmospheric Research, Boulder, CO 80305; dOld Dominion University, Norfolk, VA 23529; and eCollege of Marine Science, University of South Florida, St. Petersburg, FL 33701 Edited by Anny Cazenave, Centre National d’Etudes Spatiales, Toulouse, France, and approved January 9, 2018 (received for review October 2, 2017) Using a 25-y time series of precision satellite altimeter data from acceleration estimate by 0.033 mm/y2, resulting in a final “climate- TOPEX/Poseidon, Jason-1, Jason-2, and Jason-3, we estimate the change–driven” acceleration of 0.084 mm/y2. Climate-change–driven climate-change–driven acceleration of global mean sea level over in this case means we have tried to adjust the GMSL measurements the last 25 y to be 0.084 ± 0.025 mm/y2. Coupled with the average for as many natural interannual and decadal effects as we can to try climate-change–driven rate of sea level rise over these same 25 y of to isolate the longer-term, potentially anthropogenic, acceleration–– 2.9 mm/y, simple extrapolation of the quadratic implies global mean any remaining effects are considered in the error analysis. sea level could rise 65 ± 12 cm by 2100 compared with 2005, roughly We also must consider the impact of errors in the altimeter in agreement with the Intergovernmental Panel on Climate Change measurements, especially instrument drift.
    [Show full text]
  • Coriolis, a French Project for Operational Oceanography
    Coriolis, a French project for operational oceanography S Pouliquen*1,T Carval*1,L Petit de la Villéon*1, L Gourmelen*2, Y Gouriou*3 1 Ifremer Brest France 2 Shom Brest France 3IRD Brest France Abstract The seven French agencies concerned by ocean research are developing together a strong capability in operational oceanography based on a triad including satellite altimetry (JASON), numerical modelling with assimilation (MERCATOR), and in-situ data (CORIOLIS). The CORIOLIS project aims to build a pre-operational structure to collect, validate and distribute ocean data (temperature/salinity profiles and currents) to the scientific community and modellers. The four goals of CORIOLIS are: • To build up a data management centre, part of the ARGO network for the GODAE experiment, able to provide quality-controlled data in real time and delay modes; • To contribute to ARGO floats deployment mainly in the Atlantic with about 300 floats during the 2001-2005 period; • To develop and improve the technology of the profiling Provor floats as a contribution to Argo; • To integrate into CORIOLIS other data presently collected at sea by French agencies from surface drifting buoys, PIRATA deep sea moorings, oceanographic research vessels (XBT, thermosalinograph and ADCP transmitted on a daily basis). By the end of 2005, recommendations will be done to transform the CORIOLIS activity into a permanent, routine contribution to ocean measurement, in accordance with international plans that will follow the ARGO/GODAE experiment. Keywords: In-Situ, Operational Oceanography, Argo, Data Exchange, Mersea * Corresponding author, email: [email protected] * Corresponding author, email: [email protected] * Corresponding author, email: [email protected] * Corresponding author, email: [email protected] * Corresponding author, email: [email protected] 1 1.
    [Show full text]
  • 2019 Ocean Surface Topography Science Team Meeting Convene
    2019 Ocean Surface Topography Science Team Meeting Convene Chicago 16 West Adams Street, Chicago, IL 60603 Monday, October 21 2019 - Friday, October 25 2019 The 2019 Ocean Surface Topography Meeting will occur 21-25 October 2019 and will include a variety of science and technical splinters. These will include a special splinter on the Future of Altimetry (chaired by the Project Scientists), a splinter on Coastal Altimetry, and a splinter on the recently launched CFOSAT. In anticipation of the launch of Jason-CS/Sentinel-6A approximately 1 year after this meeting, abstracts that support this upcoming mission are highly encouraged. Abstracts Book 1 / 259 Abstract list 2 / 259 Keynote/invited OSTST Opening Plenary Session Mon, Oct 21 2019, 09:00 - 12:35 - The Forum 12:00 - 12:20: How accurate is accurate enough?: Benoit Meyssignac 12:20 - 12:35: Engaging the Public in Addressing Climate Change: Patricia Ward Science Keynotes Session Mon, Oct 21 2019, 14:00 - 15:45 - The Forum 14:00 - 14:25: Does the large-scale ocean circulation drive coastal sea level changes in the North Atlantic?: Denis Volkov et al. 14:25 - 14:50: Marine heat waves in eastern boundary upwelling systems: the roles of oceanic advection, wind, and air-sea heat fluxes in the Benguela system, and contrasts to other systems: Melanie R. Fewings et al. 14:50 - 15:15: Surface Films: Is it possible to detect them using Ku/C band sigmaO relationship: Jean Tournadre et al. 15:15 - 15:40: Sea Level Anomaly from a multi-altimeter combination in the ice covered Southern Ocean: Matthis Auger et al.
    [Show full text]
  • The Difference of Sea Level Variability by Steric Height and Altimetry In
    remote sensing Letter The Difference of Sea Level Variability by Steric Height and Altimetry in the North Pacific Qianran Zhang 1, Fangjie Yu 1,2,* and Ge Chen 1,2 1 College of Information Science and Engineering, Ocean University of China, Qingdao 266100, China; [email protected] (Q.Z.); [email protected] (G.C.) 2 Laboratory for Regional Oceanography and Numerical Modeling, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266200, China * Correspondence: [email protected]; Tel.: +86-0532-66782155 Received: 4 December 2019; Accepted: 22 January 2020; Published: 24 January 2020 Abstract: Sea level variability, which is less than ~100 km in scale, is important in upper-ocean circulation dynamics and is difficult to observe by existing altimetry observations; thus, interferometric altimetry, which effectively provides high-resolution observations over two swaths, was developed. However, validating the sea level variability in two dimensions is a difficult task. In theory, using the steric method to validate height variability in different pixels is feasible and has already been proven by modelled and altimetry gridded data. In this paper, we use Argo data around a typical mesoscale eddy and altimetry along-track data in the North Pacific to analyze the relationship between steric data and along-track data (SD-AD) at two points, which indicates the feasibility of the steric method. We also analyzed the result of SD-AD by the relationship of the distance of the Argo and the satellite in Point 1 (P1) and Point 2 (P2), the relationship of two Argo positions, the relationship of the distance between Argo positions and the eddy center and the relationship of the wind.
    [Show full text]
  • Quarterly Newsletter – Special Issue with Coriolis
    Mercator Ocean - CORIOLIS #37 – April 2010 – Page 1/55 Quarterly Newsletter - Special Issue Mercator Océan – Coriolis Special Issue Quarterly Newsletter – Special Issue with Coriolis This special issue introduces a new editorial line with a common newsletter between the Mercator Ocean Forecasting Center in Toulouse and the Coriolis Infrastructure in Brest. Some papers are dedicated to observations only, when others display collaborations between the 2 aspects: Observations and Modelling/Data assimilation. The idea is to wider and complete the subjects treated in our newsletter, as well as to trigger interactions between observations and modelling communities Laurence Crosnier, Sylvie Pouliquen, Editor Editor Editorial – April 2010 Greetings all, Over the past 10 years, Mercator Ocean and Coriolis have been working together both at French, European and international level for the development of global ocean monitoring and forecasting capabilities. For the first time, this Newsletter is jointly coordinated by Mercator Ocean and Coriolis teams. The first goal is to foster interactions between the french Mercator Ocean Modelling/Data Asssimilation and Coriolis Observations communities, and to a larger extent, enhance communication at european and international levels. The second objective is to broaden the themes of the scientific papers to Operational Oceanography in general, hence reaching a wider audience within both Modelling/Data Asssimilation and Observations groups. Once a year in April, Mercator Ocean and Coriolis will publish a common newsletter merging the Mercator Ocean Newsletter on the one side and the Coriolis one on the other side. Mercator Ocean will still publish 3 other issues per year of its Newsletter in July, October and January each year, more focused on Ocean Modeling and Data Assimilation aspects.
    [Show full text]
  • Ocean Surface Circulation
    Ocean surface circulation Recall from Last Time The three drivers of atmospheric circulation we discussed: • Differential heating • Pressure gradients • Earth’s rotation (Coriolis) Last two show up as direct forcing of ocean surface circulation, the first indirectly (it drives the winds, also transport of heat is an important consequence). Coriolis In northern hemisphere wind or currents deflect to the right. Equator In the Southern hemisphere they deflect to the left. Major surfaceA schematic currents of them anyway Surface salinity A reasonable indicator of the gyres 31.0 30.0 32.0 31.0 31.030.0 33.0 33.0 28.0 28.029.0 29.0 34.0 35.0 33.0 33.0 33.034.035.0 36.0 34.0 35.0 37.0 35.036.0 36.0 34.0 35.0 35.0 35.0 34.0 35.0 37.0 35.0 36.0 36.0 35.0 35.0 35.0 34.0 34.0 34.0 34.0 34.0 34.0 Ocean Gyres Surface currents are shallow (a few hundred meters thick) Driving factors • Wind friction on surface of the ocean • Coriolis effect • Gravity (Pressure gradient force) • Shape of the ocean basins Surface currents Driven by Wind Gyres are beneath and driven by the wind bands . Most of wind energy in Trade wind or Westerlies Again with the rotating Earth: is a major factor in ocean and Coriolisatmospheric circulation. • It is negligible on small scales. • Varies with latitude. Ekman spiral Consider the ocean as a Wind series of thin layers. Friction Direction of Wind friction pushes on motion the top layers.
    [Show full text]
  • Lesson Plans Graphing Sea Level Slopes and Surface Currents
    My NASA Data - Lesson Plans Graphing Sea Level Slopes and Surface Currents Purpose Students analyze the relationship between sea surface height and ocean surface currents by graphing sea height using satellite data. Note: This lesson is modified from NASA's TOPEX/Poseidon lesson plan. Learning Objectives Describe the use of a radar altimeter to measure sea surface height. Plot sea surface height data. Describe the relationship between the slope of the sea surface and the direction and speed of ocean surface currents. Why Does NASA Study This Phenomenon? The ocean surface is not level but has broad, gradual hills and valleys created by surface winds and density differences. Surface currents flow around the sides of these hills and valleys. Measuring this sea surface topography is a challenging task. One measuring device is the TOPEX/Poseidon radar altimeter mounted on an Earth-orbiting satellite. This device sends radar beams down to the sea surface, where they are reflected back to the satellite. The round-trip travel times for the beams allow 1 / 7 scientists to measure the satellite to sea surface distance to within a few centimeters. The satellite- derived sea surface elevations are then compared to those that the sea surface would have if the oceans were still (no currents, waves, etc.). Specifically, the elevations of the imaginary still ocean are subtracted from those calculated from the satellite's data. The height differences show where the ocean's hills and valleys are and the slope of the surface between them. The following activity uses some of these sea height differences, calculated from TOPEX/Poseidon data to investigate the relationship between sea surface topography and ocean surface currents.
    [Show full text]