Lee-Lueng Fu's research while affiliated with California Institute of Technology and other places
What is this page?
This page lists the scientific contributions of an author, who either does not have a ResearchGate profile, or has not yet added these contributions to their profile.
It was automatically created by ResearchGate to create a record of this author's body of work. We create such pages to advance our goal of creating and maintaining the most comprehensive scientific repository possible. In doing so, we process publicly available (personal) data relating to the author as a member of the scientific community.
If you're a ResearchGate member, you can follow this page to keep up with this author's work.
If you are this author, and you don't want us to display this page anymore, please let us know.
It was automatically created by ResearchGate to create a record of this author's body of work. We create such pages to advance our goal of creating and maintaining the most comprehensive scientific repository possible. In doing so, we process publicly available (personal) data relating to the author as a member of the scientific community.
If you're a ResearchGate member, you can follow this page to keep up with this author's work.
If you are this author, and you don't want us to display this page anymore, please let us know.
Publications (130)
A data assimilation system for a high-resolution model has been developed to address the opportunities and challenges posed by the upcoming Surface Water and Ocean Topography (SWOT) satellite mission. This developed system is based on a three-dimensional variational data assimilation scheme (3DVAR), which is computationally highly efficient and thu...
The future Surface Water and Ocean Topography (SWOT) mission aims to map sea surface height (SSH) in wide swaths with an unprecedented spatial resolution and subcentimeter accuracy. The instrument performance needs to be verified using independent measurements in a process known as calibration and validation (Cal/Val). The SWOT Cal/Val needs in sit...
After the surface water and ocean topography (SWOT) satellite launches in 2022, an in‐situ field campaign will be conducted to estimate the ocean state for calibration and validation (CalVal) purposes. It is demonstrably difficult to capture the sea surface height (SSH) features that are the focus of SWOT, with short time periods (<20 days) and fin...
A state-of-the-art data assimilation system for a high-resolution model has been developed to address the opportunities and challenges posed by the upcoming Surface Water and Ocean Topography (SWOT) satellite mission. A new ‘extended’ three-dimensional variational data assimilation scheme (extended-3DVAR) is formulated to assimilate observations ov...
We present a mapping methodology to improve the resolution of gridded sea surface height (SSH) from multisatellite along‐track measurements, and apply it in the California Current system. This is motivated by the upcoming Surface Water and Ocean Topography (SWOT) satellite mission, which will collect novel high‐resolution wide‐swath SSH measurement...
Reconstructability of upper ocean vertical velocity ( w) and vorticity ( ζ) fields from high-resolution sea surface height (SSH) data is explored using the global 1/48° horizontal-resolution MITgcm output in the context of the forth-coming Surface Water and Ocean Topography (SWOT) mission. By decomposing w with an omega equation of the primitive-eq...
Monitoring and Predicting Regional to Coastal Sea Level: Towards Comprehensive Observing and Modeling Systems
High-resolution satellite images of ocean color and sea surface temperature reveal an abundance of ocean fronts, vortices and filaments at scales below 10 km but measurements of ocean surface dynamics at these scales are rare. There is increasing recognition of the role played by small scale ocean processes in ocean-atmosphere coupling, upper-ocean...
A major challenge for managing impacts and implementing effective mitigation measures and adaptation strategies for coastal zones affected by future sea level (SL) rise is our limited capacity to predict SL change at the coast on relevant spatial and temporal scales. Predicting coastal SL requires the ability to monitor and simulate a multitude of...
Satellite observations of the last two decades have led to a major breakthrough emphasizing the existence of a strongly energetic mesoscale turbulent eddy field in all the oceans. This ocean mesoscale turbulence is characterized by cyclonic and anticyclonic eddies (with a 100‐ to 300‐km size and depth scales of ∼500–1,000 m) that capture approximat...
The M 2 internal tide field contains waves of various baroclinic modes and various horizontal propagation directions. This paper presents a technique for decomposing the sea surface height (SSH) field of the multimodal multidirectional internal tide. The technique consists of two steps: first, different baroclinic modes are decomposed by two-dimens...
The future international Surface Water and Ocean Topography (SWOT) Mission, planned for launch in 2021, will make high-resolution 2D observations of sea-surface height using SAR radar interferometric techniques. SWOT will map the global and coastal oceans up to 77.6° latitude every 21 days over a swath of 120 km (20 km nadir gap). Today’s 2D mapped...
The development of the technologies of remote sensing of the ocean was initiated in the 1970s, while the ideas of observing the ocean from space were conceived in the late 1960s. The first global view from space revealed the expanse and complexity of the state of the ocean that had perplexed and inspired oceanographers ever since. This paper presen...
The Surface Water and Ocean Topography (SWOT) mission aims to measure the sea surface height (SSH) at a high spatial resolution using a Ka-band radar interferometer (KaRIn). The primary oceanographic objective is to characterize the ocean eddies at a spatial resolution of 15 km for 68% of the ocean surface. This resolution is derived from the ratio...
The Surface Water and Ocean Topography mission will begin by scanning Earth’s surface once a day. We invite ocean scientists to contribute ground-based measurements to compare with the satellite data.
![Figure 3. Frequency-wave number spectra of KE (KE [m 2 /s 2 ])...](profile/Hector-Torres-13/publication/328547024/figure/fig3/AS:817414421893121@1571898193512/Frequency-wave-number-spectra-of-KE-KE-m-2-s-2-corresponding-to-the_Q320.jpg)
Internal gravity waves (IGWs) and balanced motions (BMs) with scales <100-km capture most of the vertical velocity field in the upper ocean. They have, however, different impacts on the ocean energy budget, which explains the need to partition motions into BMs and IGWs. One way is to exploit the synergy of using different satellite observations, th...
The transition scale Lt from balanced geostrophic motions to unbalanced wave motions, including nearinertial flows, internal tides, and inertia-gravity wave continuum, is explored using the output from a global 1/488 horizontal resolution Massachusetts Institute of Technology general circulation model (MITgcm) simulation. Defined as the wavelength...
The wavenumber spectrum of sea surface height (SSH) is an important indicator of the dynamics of the ocean interior. While the SSH wavenumber spectrum has been well studied at mesoscale wavelengths and longer, using both in situ oceanographic measurements and satellite altimetry, it remains largely unknown for wavelengths less than ~70 km. The Surf...
Simulated along-track ocean altimetry data were used to implement the use of a nonlinear dynamic propagator to perform three-dimensional (time and 2D space) interpolation of mesoscale sea surface height (SSH). The method is an inverse approach to processing altimetry data unevenly sampled in time and space into high-level gridded altimetry maps. Th...
Utilizing the framework of effective surface quasigeostrophic (eSQG) theory, this study explores the potential of reconstructing the 3D upper-ocean circulation structures, including the balanced vertical velocity w field, from high-resolution sea surface height (SSH) data of the planned Surface Water and Ocean Topography (SWOT) satellite mission. S...
Conventional altimetry measures a one-dimensional profile of sea surface height (SSH) along the satellite track. Two-dimensional SSH can be reconstructed using mapping techniques; however, the spatial resolution is quite coarse even when data from several altimeters are analyzed. A new satellite mission based on radar interferometry is scheduled to...
In 2009, Thales Alenia Space and Suds-Concepts issued a book called “Climate Change and Satellites”, bringing together an international network of scientists, users, and representatives of major space agencies. With a circulation of over 15,000, mainly in the scientific, governmental and CC community, it was recognized as a leading publication in i...
Many issues may challenge standard interpolation techniques to produce high-resolution gridded maps of sea surface height in the context of future missions like Surface Water and Ocean Topography (SWOT). The present study proposes a new method to address these challenges. Based on the conservation of potential vorticity, the method provides a simpl...
Measurement of sea surface height (SSH) over a finite swath along satellite tracks has been planned for future space missions. The effect of water vapor in the troposphere on the delay of radar signal must be corrected for in the SSH measurement. The efficacy of a nadir-looking radiometer that has been the approach for conventional altimetry is exa...
Conventional radar altimeter makes measurement of sea surface height (SSH) in one-dimensional profiles along the ground tracks of a satellite. Such profiles are combined via various mapping techniques to construct two-dimensional SSH maps, providing a valuable data record over the past two decades for studying the global ocean circulation and sea l...
The past decade has seen tremendous progress in the application of ocean remote sensing to the study of the global ocean circulation. This chapter provides a summary of the resultant advances in our understanding of the key processes of the ocean that affect climate variability. Many of the advances result from the combined usage of remote sensing...
The Argentine Basin in the South Atlantic Ocean is one of the most energetic regions in the ocean with complicated dynamics, which plays an important role in the global climate. A number of observations have discovered an intense anticyclonic gyre of barotropic circulation around the Zapiola Rise in the center of the basin. Theoretical studies have...
Long-term change of the global sea level resulting from climate change has become an issue of great societal interest. The advent of the technology of satellite altimetry has modernized the study of sea level on both global and regional scales. In combination with in situ observations of the ocean density and space observations of Earth’s gravity v...
A new satellite mission called Surface Water and Ocean Topography (SWOT)
has been developed jointly by the U.S. National Aeronautics and Space
Administration and France's Centre National d'Etudes Spatiales. Based
on the success of nadir-looking altimetry missions in the past, SWOT
will use the technique of radar interferometry to make wide-swath
al...
The wavenumber spectrum of sea surface height (SSH) observed by satellite altimetry was analyzed by Xu and Fu. The spectral shape in the wavelength range of 70-250 km was approximated by a power law, representing a regime governed by geostrophic turbulence theories. The effects of altimeter instrument noise were assumed insignificant at wavelengths...
The Surface Water Ocean Topography (SWOT) mission was recommended in
2007 by the National Research Council's Decadal Survey, "Earth Science
and Applications from Space: National Imperatives for the Next Decade
and Beyond", for implementation by NASA. The SWOT mission is a
partnership between two communities, the physical oceanography and the
hydrol...
The Southern Ocean (SO) transports heat towards Antarctica and plays an important role in determining the heat budget of the
Antarctic climate system. A global ocean data synthesis product at eddy-permitting resolution from the Estimating the Circulation
and Climate of the Ocean, Phase II (ECCO2) project is used to estimate the meridional heat tran...
Sea surface temperature images and surface drifter observations are
compared to the results from a high resolution numerical simulation to
study the properties of cyclonic eddies generated at the density front
of the tropical instability waves in the Pacific. These cyclonic eddies,
of which the diameter is about 50-150km and the vertical extent is...
Spaceborne observations of sea surface topography have revealed a significant interannual variability of the Azores Current strength and eddy energy. The objective of this paper is to establish the relationship between these variations and atmospheric forcing over the subtropical North Atlantic. Based on satellite altimetry, hydrography, and atmosp...
The wavenumber spectra of wind kinetic energy over the ocean from Quick Scatterometer (QuikSCAT) observations have revealed complex spatial variability in the wavelength range of 1000–3000 km, with spectral slopes varying from −1.6 to −2.9. Here the authors performed a spectral analysis of QuikSCAT winds over the global ocean and found that (i) the...
The small-scale variability of the tropical Pacific is studied with the simulations from a numerical model in terms of vorticity structures. ALagrangian method based on theOkubo-Weiss parameter is used to identify the structures and track their main characteristics. Between 8°S and 8°N, the structure characteristics are spatially inhomogeneous comp...
Over the last two decades, satellite altimetry has provided one of the most important tools for global monitoring and understanding of ocean dynamics, ranging from large-scale to smaller mesoscale processes. This paper will present some recent results using altimetry to detect smaller ocean processes in the open ocean and in coastal regions. The sp...
The wavenumber spectra of sea surface height from satellite altimeter observations have revealed complex spatial variability that cannot be explained by a universal theory of mesoscale turbulence. Near the edge of the core regions of high eddy energy, agreement is observed with the prediction of the surface quasigeostrophic (SQG) turbulence theory,...
Over the last two decades, several nadir profiling radar altimeters have provided our first global look at the ocean basinscale circulation and the ocean mesoscale at wavelengths longer than 100 km. Due to sampling limitations, nadir altimetry is unable to resolve the small wavelength ocean mesoscale and sub-mesoscale that are responsible for the v...
The primary objective of the National Research Council (NRC) Decadal Survey recommended SWOT (Surface Water and Ocean Topography) Mission is to measure the water elevation of the global oceans, as well as terrestrial water bodies (such as rivers, lakes, reservoirs, and wetlands), to answer key scientific questions on the kinetic energy of ocean cir...
The Ocean Surface Topography Mission/Jason-2 (OSTM/Jason-2) satellite altimetry mission was successfully launched on June 20, 2008, as a cooperative mission between CNES, EUMETSAT, NASA, and NOAA. OSTM/Jason-2 will continue to precisely measure the surface topography of the oceans and continental surface waters, following on the same orbit as its p...
IntroductionSustained, Systematic Observing Systems (Existing Capabilities)Development of Improved Observing Systems (New Capabilities)SummaryReferences
In 1992, NASA and the French space agency launched the first high-precision satellite altimeter to measure changes in sea surface height. With it began a new era in oceanography. Data from satellite altimeters continues to be used to estimate global sea level rise, sea surface height, geostrophic velocity, significant wave height and atmospheric wa...
Recent studies have shown that the formation of the well-defined, zonally oriented Azores Current may be the result of water mass transformation associated with the Mediterranean outflow in the Gulf of Cadiz. As the denser Mediterranean water descends down the continental slope, it entrains overlying North Atlantic Central Water. It is believed tha...
The elevation of the ocean surface has been measured for over two decades from spaceborne altimeters. However, existing altimeter measurements are not adequate to characterize the dynamic variations of most inland water bodies, nor of ocean eddies at scales of less than about 100 km, notwithstanding that such eddies play a key role in ocean circula...
Satellite altimetry has revolutionized oceanography since the early 1990s after the launch of the TOPEX/Poseidon and ERS-1 missions. The progress made in the past 20 years is reviewed in the paper with a focus on the most recent advances. Precision altimetry measurements from TOPEX/Poseidon and its follow-ons have provided continuous global view of...
Satellite altimeter data are used to study the characteristics of the horizontal propagation of eddy variability of the global oceans. Decade-long time series of sea surface height is analyzed for finding the maximum cross correlation with neighboring time series within a window of space and time lags. The space and time lags corresponding to the m...
The advent of high accuracy satellite altimetry in the 1990's brought the first global view of ocean dynamics, which together with a global network of supporting observations brought a revolution in understanding of how the ocean works (Fu and Cazenave, 2001). At present a constellation of flying satellite missions routinely provides sea level anom...
Abstract Satellite altimetry has revolutionized the study of the global oceans for the past two
A new technique is presented for estimating time-averaged, upper ocean geostrophic velocity from a combination of altimeter data and subsurface float data. The technique makes uses of the strong relationship between sea-surface height anomaly and anomalous velocity at depth to reduce mesoscale eddy variability in subsurface float displacements. The...
Observations made by satellite altimeters since the 1980s have provided progressively improved views of the global ocean mesoscale eddy field, which contains most of the kinetic energy of the ocean circulation. Along with these improved views, ocean models have progressed from coarse-resolution, highly dissipative mesh grids to higher resolutions w...
A global ocean data synthesis product at eddy-permitting resolution from Estimating the Circulation and Climate of the Ocean, Phase II (ECCO2) project are used to estimate the oceanic eddy heat transport. We show that in a number of locations the time-mean eddy heat transport constitutes a considerable portion of the total time-mean heat transport,...
The nature of the interannual variability of the meridional overturning
circulation (MOC) of the North Atlantic Ocean is studied using an ECCO
(http://www.ecco-group.org) assimilation product for the period of
1993-2003. The time series of the 1st Empirical Orthogonal Function
(EOF) of the MOC is found to be correlated with the North Atlantic
Oscil...
Radar altimetry has revolutionized oceanography by providing global measurements of ocean surface topography (OST [e.g., Fu and Cazenave, 2001]). Long-term measurements of large-scale circulation and heat storage of the global oceans have led to discoveries such as the effects of changes in ocean circulation on climate (e.g., El Ni~o and La Niña)....
The Argentine Basin of the South Atlantic Ocean is a region of complicated ocean dynamics involving a wide range of spatial and temporal scales. Previous studies reported the existence of a basin mode of topographic barotropic Rossby waves with a period close to 25 days in the region. Using observations of sea level anomalies from satellite altimet...
The forcing of the equatorial Indian Ocean by the highly periodic monsoon wind cycle creates many interesting intraseasonal variabilities. The frequency spectrum of the wind stress observations from the European Remote Sensing Satellite scatterometers reveals peaks at the seasonal cycle and its higher harmonics at 180, 120, 90, and 75 days. The obs...
Carl Wunsch was awarded the 2006 William Bowie Medal at the AGU Fall Meeting Honors Ceremony, which was held on 13 December 2006, in San Francisco, Calif. The medal recognizes outstanding contributions to fundamental geophysics and for unselfish cooperation in research.
We propose to apply the technique of synthetic aperture radar
interferometry to the measurement of ocean surface topography at spatial
resolution approaching 1 km. The measurement will have wide ranging
applications in oceanography, hydrology, and marine geophysics. The
oceanographic and related societal applications are briefly discussed in
the pa...
We propose to apply the technique of synthetic aperture radar interferometry to the measurement of ocean surface topography at spatial resolution approaching 1 km. The measurement will have wide ranging applications in oceanography, hydrology, and marine geophysics. The oceanographic and related societal applications are briefly discussed in the pa...
The majority of the kinetic energy of ocean currents is contained in the mesoscale eddies. The pathways of ocean eddies, which are the ``weather'' of ocean circulation, are mapped from space using a decade-long record of sea surface height measured by two simultaneously flying satellite radar altimeters. The speed and direction of the propagation o...
Effects of atmospheric intraseasonal oscillations (ISOs) on the Indian Ocean zonal dipole mode (IOZDM) are investigated by analyzing available observations and a suite of solutions to an ocean general circulation model, namely, the Hybrid Coordinate Ocean Model (HYCOM). Data and model solutions for the period 1991-2000 are analyzed, a period that i...
From sea surface height measurements made by the Ocean Topography Experiment (TOPEX)/Poseidon satellite, Fu et al. found and described large-scale oscillations at the period of 25 days in the Argentine Basin of the South Atlantic Ocean. These oscillations were previously hinted at by in situ observations. Only the extensive space-time sampling capa...
A decade-long record of sea surface height from combined altimeter data taken by the TOPEX/Poseidon and Jason satellites was analyzed for studying the interannual variability of the North Atlantic Ocean. On time scales of 5-6 years, variations of sea surface height have maximum amplitudes in three areas: the subpolar gyre, the Gulf Stream gyre (the...
In the open ocean away from the equator, westward propagation is a ubiquitous characteristic of oceanic variability. A large number of studies have documented the westward propagation of large-scale thermal variability of the ocean and interpreted the findings in terms of baroclinic Rossby waves. Eddy-like features such as Gulf Stream rings and Agu...
This paper describes a new approach to making altimeter measurements
from off-nadir radar signal returns and its oceanographic and
geophysical applications. The approach is based on the technique of
radar interferomety and the new instrument is called the Wide-Swath
Ocean Altimeter (WSOA). WSOA is designed to be flown with a Jason class
conventiona...
On 7 December 2001, the French/U.S. altimetric satellite Jason-1 was launched as a follow-on to the TOPEX/Poseidon Mission (hereafter referred to as T/P). The two satellites are now flying in tandem with a track separation half that of the T/P mission, offering a much improved sampling capability for the study of ocean circulation and tides.Since 1...
On December 7, 2001, the Jason-1 satellite was successfully launched by a Boeing Delta II rocket from the Vandenberg site in California, USA. Its main mission was to maintain the high accuracy altimeter measurements, provided since 1992 by TOPEX/Poseidon (T/P), ensuring continuity in observing and monitoring the ocean for intraseasonal to interannu...
Seven years' worth of wind observations from the ERS-1/2 scatterometers were used to investigate the dynamics of large-scale intraseasonal sea level variability at mid and high latitudes revealed in satellite altimetry data. Significant coherence was found between wind stress curl and sea level at periods from 20 days to a year in three particular...
The effects of the sea level variability along the eastern boundary of the North Pacific Ocean, including those associated with El Niño Southern Oscillation, have been considered an important factor in determining the low-frequency large-scale variability of the ocean interior through Rossby waves generated at the eastern boundary. This hypothesis...
1] Published claims that the reflectivity of the western boundary of the equatorial Pacific is near 100% are examined by using TOPEX/Poseidon data from October 1992 to February 2000. We perform a Fourier analysis of sea surface height measurements and define the variability consistent with the Rossby wave and Kelvin wave dispersion relationship as...
Effects of the Indonesian Throughflow (ITF) on the circulation and thermal structure of the Pacific and Indian Oceans are studied by comparing solutions of a near-global ocean general circulation model with open and closed Indonesian passages from 1981 to 1997. The ITF contributes to the maintenance of the model circulation system around eastern Au...
The basic concept of satellite altimetry is to measure the range from the satellite to the sea surface. The altimeter transmits a short pulse of microwave radiation with known power toward the sea surface. The pulse interacts with the rough sea surface and a part of the incident radiation reflects back to the altimeter. The chapter emphasizes on th...
Satellite altimetry has provided the first direct measurement of the global ocean topography. This chapter discusses the utility of such measurement for the determination of the oceanic general circulation. Because of the lack of detailed knowledge of the geoid, satellite-altimeter data have primarily been used to study the temporal variability of...
The upper Pacific Ocean Current and temperature have been simulated by a three-dimensional ocean general circulation model (OGCM) with two different vertical-mixing schemes. One corresponds to the modified Richardson number-dependent scheme of Pacanowski and Philander (PP); the other is adapted from the newly developed K-Profile Parameterization (K...
Sea surface temperature, sea level, and pseudo wind stress anomaly data from late 1996 to early 1998 are assimilated into an intermediate coupled model of the Tropical Pacific. Model data consistency is examined. Impact of the assimilation on forecast is evaluated. The ocean component of the coupled model consists of a shallow water model with two...
This paper provides a detailed illustration that it is beneficial for ENSO forecasting to improve in priority the model parameterizations, instead of increasing only the consistency of the initial conditions with the coupled model. Moreover it is shown that the latter can lead to misleading results. Using sea level data in addition to wind to initi...
The feasibility of assimilating satellite altimetry data into a global ocean general circulation model is studied. Three years of TOPEX/Poseidon data are analyzed using a global, three-dimensional, nonlinear primitive equation model. The assimilation's success is examined by analyzing its consistency and reliability measured by formal error estimat...
Sea surface elevation in the South China Sea is examined in the Topex/Poseidon altimeter data from 1992 to 1995. Sea level anomalies are smoothed along satellite tracks and in time with tidal errors reduced by harmonic analysis. The smoothed data are sampled every ten days with an along-track separation of about 40 km. The data reveal significant a...
TOPEX/Poseidon altimetric height is compared with 20 transpacific eddy-resolving realizations of steric height. The latter are calculated from temperature (expendable bathythermograph (XBT)) and salinity (expendable conductivity and temperature profiler (XCTD)) profiles along a precisely repeating ship track over a period of 5 years. The overall di...
The relation between large-scale sea level variability and ocean circulation is studied using a numerical model. A global primitive equation model of the ocean is forced by daily winds and climatological heat fluxes corresponding to the period from January 1992 to January 1994. The physical nature of sea level's temporal variability from periods of...
Investigated in this study is the response of a global ocean general circulation model to forcing provided by two wind products: operational analysis at 1000 mb from the National Center for Environmental Prediction (NCEP); observations made by the ERS-1 radar scatterometer. The sea level simulated by the model using the two wind fields is compared...
Satellite altimetry provides synoptic observation of sea surface elevation that manifests the ocean circulation through the entire water column. Assimilation of altimetry data thus provides a powerful tool for using an ocean model to estimate the three-dimensional state of the ocean and its temporal variation. The uncertainty of the estimate result...