John Gilson - Academia.edu (original) (raw)

Papers by John Gilson

Journal of Physical Oceanography, Mar 1, 2001

... Valuable suggestions were made by B. Qiu, R. Davis, D. Stammer, and anonymous reviewers. REFE... more ... Valuable suggestions were made by B. Qiu, R. Davis, D. Stammer, and anonymous reviewers. REFERENCES. Bennett, A., and W. White, 1986: Eddy heat flux in the subtropical North Pacific. J. Phys. Oceanogr.,16, 728???740. ... Ph.D. thesis, Princeton University, 172 pp. ...

Journal of Physical Oceanography, 2016

Nature Climate Change, 2016

Journal of Atmospheric and Oceanic Technology, 2012

Progress in Oceanography, 2009

The Argo Program has achieved 5 years of global coverage, growing from a very sparse global array... more The Argo Program has achieved 5 years of global coverage, growing from a very sparse global array of 1000 profiling floats in early 2004 to more than 3000 instruments from late 2007 to the present. Using nearly 350,000 temperature and salinity profiles, we constructed an upper-ocean climatology and monthly anomaly fields for the 5-year era, 2004-2008. A basic description of the modern upper ocean based entirely on Argo data is presented here, to provide a baseline for comparison with past datasets and with ongoing Argo data, to test the adequacy of Argo sampling of large-scale variability, and to examine the consistency of the Argo dataset with related ocean observations from other programs. The Argo 5year mean is compared to the World Ocean Atlas, highlighting the middle and high latitudes of the southern hemisphere as a region of strong multi-decadal warming and freshening. Moreover the region is one where Argo data have contributed an enormous increment to historical sampling, and where more Argo floats are needed for documenting large-scale variability. Globally, the Argo-era ocean is warmer than the historical climatology at nearly all depths, by an increasing amount toward the sea surface; it is saltier in the surface layer and fresher at intermediate levels. Annual cycles in temperature and salinity are compared, again to WOA01, and to the National Oceanography Center air-sea flux climatology, the Reynolds SST product, and AVISO satellite altimetric height. These products are consistent with Argo data on hemispheric and global scales, but show regional differences that may either point to systematic errors in the datasets or their syntheses, to physical processes, or to temporal variability. The present work is viewed as an initial step toward integrating Argo and other climate-relevant global ocean datasets.

Nature Climate Change, 2012

ABSTRACT Changing temperature throughout the oceans is a key indicator of climate change. Since t... more ABSTRACT Changing temperature throughout the oceans is a key indicator of climate change. Since the 1960s about 90% of the excess heat added to the Earth's climate system has been stored in the oceans. The ocean's dominant role over the atmosphere, land, or cryosphere comes from its high heat capacity and ability to remove heat from the sea surface by currents and mixing. The longest interval over which instrumental records of subsurface global-scale temperature can be compared is the 135 years between the voyage of HMS Challenger (1872-1876) and the modern data set of the Argo Programme (2004-2010). Argo's unprecedented global coverage permits its comparison with any earlier measurements. This, the first global-scale comparison of Challenger and modern data, shows spatial mean warming at the surface of 0.59°C+/-0.12, consistent with previous estimates of globally averaged sea surface temperature increase. Below the surface the mean warming decreases to 0.39°C+/-0.18 at 366m (200fathoms) and 0.12°C+/-0.07 at 914m (500fathoms). The 0.33°C+/-0.14 average temperature difference from 0 to 700m is twice the value observed globally in that depth range over the past 50 years, implying a centennial timescale for the present rate of global warming. Warming in the Atlantic Ocean is stronger than in the Pacific. Systematic errors in the Challenger data mean that these temperature changes are a lower bound on the actual values. This study underlines the scientific significance of the Challenger expedition and the modern Argo Programme and indicates that globally the oceans have been warming at least since the late-nineteenth or early-twentieth century.

Church/Understanding Sea-Level Rise and Variability, 2010

The oceans are a central component of the climate system, storing and transporting vast quantitie... more The oceans are a central component of the climate system, storing and transporting vast quantities of heat. Indeed, more than 90% of the heat absorbed by the Earth over the last 50 years as a result of global warming is stored in the ocean ). Understanding how the ocean heat content varies in space and time is central to understanding and successfully predicting climate variability and change.

Nature Climate Change, 2015

ABSTRACT Increasing heat content of the global ocean dominates the energy imbalance in the climat... more ABSTRACT Increasing heat content of the global ocean dominates the energy imbalance in the climate system1. Here we show that ocean heat gain over the 0–2,000 m layer continued at a rate of 0.4–0.6 W m−2 during 2006–2013. The depth dependence and spatial structure of temperature changes are described on the basis of the Argo Program's2 accurate and spatially homogeneous data set, through comparison of three Argo-only analyses. Heat gain was divided equally between upper ocean, 0–500 m and 500–2,000 m components. Surface temperature and upper 100 m heat content tracked interannual El Niño/Southern Oscillation fluctuations3, but were offset by opposing variability from 100–500 m. The net 0–500 m global average temperature warmed by 0.005 °C yr−1. Between 500 and 2,000 m steadier warming averaged 0.002 °C yr−1 with a broad intermediate-depth maximum between 700 and 1,400 m. Most of the heat gain (67 to 98%) occurred in the Southern Hemisphere extratropical ocean. Although this hemispheric asymmetry is consistent with inhomogeneity of radiative forcing4 and the greater area of the Southern Hemisphere ocean, ocean dynamics also influence regional patterns of heat gain.

Progress in Oceanography, 2011

The California Current System is described in its regional setting using two modern datasets. Arg... more The California Current System is described in its regional setting using two modern datasets. Argo provides a broadscale view of the entire eastern North Pacific Ocean for the period 2004-2010, and the High Resolution XBT Network includes transects from Honolulu to San Francisco (1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010) and to Los Angeles (2008)(2009)(2010). Together these datasets describe a California Current of 500-800 km width extending along the coast from 43°N to 23°N. The mean southward transport of the California Current is about 5 Sv off Central and Southern California, with about 2.5 Sv of northward flow on its inshore side. Interannual variations are 50% or more of the mean transports. The salinity minimum in the core of the California Current is supplied by the North Pacific Current and by freshwater from the northern continental shelf and modified by alongshore geostrophic and across-shore Ekman advection as well as eddy fluxes and air-sea exchange. The heat and freshwater content of the California Current vary in response to the fluctuating strength of the alongshore geostrophic flow. On its offshore side, the California Current is influenced by North Pacific Intermediate Waters at its deepest levels and by Eastern Subtropical Mode Waters on shallower density surfaces. In total, the sources of the California Current, its alongshore advection, and its strong interactions with the inshore upwelling region and the offshore gyre interior combine to make this a rich and diverse ecosystem. The present work reviews previous contributions to the regional oceanography, and uses the new datasets to paint a spatially and temporally more comprehensive description than was possible previously.

Journal of Physical Oceanography, Feb 1, 2007

An increase in the circulation of the South Pacific Ocean subtropical gyre, extending from the se... more An increase in the circulation of the South Pacific Ocean subtropical gyre, extending from the sea surface to middepth, is observed over 12 years. Datasets used to quantify the decadal gyre spinup include satellite altimetric height, the World Ocean Circulation Experiment (WOCE) hydrographic and float survey of the South Pacific, a repeated hydrographic transect along 170°W, and profiling float data from the global Argo array. The signal in sea surface height is a 12-cm increase between 1993 and 2004, on large spatial scale centered at about 40°S, 170°W. The subsurface datasets show that this signal is predominantly due to density variations in the water column, that is, to deepening of isopycnal surfaces, extending to depths of at least 1800 m. The maximum increase in dynamic height is collocated with the deep center of the subtropical gyre, and the signal represents an increase in the total counterclockwise geostrophic circulation of the gyre, by at least 20% at 1000 m. A comparison of WOCE and Argo float trajectories at 1000 m confirms the gyre spinup during the 1990s. The signals in sea surface height, dynamic height, and velocity all peaked around 2003 and subsequently began to decline. The 1990s increase in wind-driven circulation resulted from decadal intensification of wind stress curl east of New Zealand-variability associated with an increase in the atmosphere's Southern Hemisphere annular mode. It is suggested (based on altimetric height) that midlatitude gyres in all of the oceans have been affected by variability in the atmospheric annular modes on decadal time scales.

Journal of Physical Oceanography, 2001

High-resolution XBT transects in the North Pacific Ocean, at an average latitude of 22°N, are ana... more High-resolution XBT transects in the North Pacific Ocean, at an average latitude of 22°N, are analyzed together with TOPEX/Poseidon altimetric data to determine the structure and transport characteristics of the mesoscale eddy field. Based on anomalies in dynamic height, 410 ...

Journal of Geophysical Research, 1998

TOPEX/Poseidon altimetric height is compared with 20 transpacific eddy-resolving realizations of ... more 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 difference between steric height and altimetric height is 5.2 cm RMS. On long wavelengths (•, <500 km), the 3.5 cm RMS difference is due mainly to altimetric measurement errors but also has a component from steric variability deeper than the 800 m limit of the XBT. The data sets are very coherent in the long-wavelength band, with coherence amplitude of 0.89. This band contains 65% of the total variance in steric height. On short wavelengths (•, >500 km), containing 17% of the steric height variance, the 3.0 cm RMS difference and lowered coherence are due to the sparse distribution of altimeter ground tracks along the XBT section. The 2.4 cm RMS difference in the basin-wide spatial mean appears to be due to fluctuations in bottom pressure. Differences between steric height and altimetric height increase near the western boundary, but data variance increases even more, and so the signal-to-noise ratio is highest in the western quarter of the transect. Basinwide integrals of surface geostrophic transport from steric height and altimetric height are in reasonable agreement. The 1.9 x 104 m 2 s 'i RMS difference is mainly because the interpolated altimetric height lacks spatial resolution across the narrow western boundary current. A linear regression is used to demonstrate the estimation of subsurface temperature from altimetric data. Errors diminish from 0.8øC at 200 m to 0.3øC at 400 m. Geostrophic volume transport, 0-800 m, shows agreement that is similar to surface transport, with 4.8 Sverdrup (Sv) (106m 3 s -1) RMS difference. The combination of altimetric height with subsurface temperature and salinity proffiing is a powerful tool for observing variability in circulation and wansport of the upper ocean. The continuing need for appropriate subsurface data for verification and for statistical estimation is emphasized. This includes salinity measurements, which significantly reduce errors in specific volrune and steric height. 1. Introduction Changes in the height of the sea surface may be caused either by changes in the mass of water at a given location or by changes in the density at constant mass. The latter, known as steric height change, is thought to dominate sea surface variability at low frequency [e.g. Patullo et al., 1955]. A column of warm water stands higher than a column of cold water of equal mass. In the present work, sea surface height measured by the TOPEX/Poseidon (T/P) satellite altimeter is compared with steric height from a data set consisting of repeating temperature (expendable bathythermograph (XBT)) and temperature/salinity (expendable conductivity and temperature profiler (XCTD)) profiles. The XBT/XCFD data set consists of 20 quarterly eddy-resolving XBT transects, together with sparse XCTDs, along a 12,650 km track during Copyright 1998 by the American Geophysical Union. Paper number 98JC01680. 0148-0227/98/98 JC-01680509.00 the T/P era. The comparison, carried out over spatial scales ranging from tens of kilometers to the basin width, will serve to determine (1) the degree to which sea level height i s, indeed, controlled by upper ocean steric change, (2) an upper bound on errors in the T/P measurements as a function of spatial scale, (3)the limits imposed by across-track spatial resolution in the T/P data (i.e., interpolation errors), and (4) the errors in steric height when salinity information is missing or withheld. In places where the difference between steric height and altimetric height exceeds measurement and interpolation errors, deep-ocean steric change or redistribution of mass must have signlficant effects on sea surface height. The high correlations linking altimetric height to steric height and steric height to subsurface temperature variability permit an inversion of altimetric height in order to estimate temperature as a function of position, depth, and time (T( ). A substantial fraction of subsurface temperature variability can be recovered in this way. The relationship between temperature (or density) variability and altimetric height can be exploited to reduce the sampling deficiencies of 27,947

Journal of Geophysical Research, 2001

Ocean heat transport near the tropical/subtropical boundary of the North Pacific during 1993-1999... more Ocean heat transport near the tropical/subtropical boundary of the North Pacific during 1993-1999 is described, including its mean and time variability. Twenty-eight trans-Pacific high-resolution expendable bathythermograph (XBT)/expendable conductivitytemperature-depth (XCTD) transects are used together with directly measured and operational wind estimates to calculate the geostrophic and Ekman transports. The mean heat transport across the XBT transect was 0.83 + 0.12 pW during the 7 year period. The large number of transects enables a stable estimate of the mean field to be made, with error bars based on the known variability. The North Pacific heat engine is a shallow meridional overturning circulation that includes warm Ekman and western boundary current components flowing northward, balanced by a southward flow of cool thermocline waters (including Subtropical Mode Waters). A near-balance of geostrophic and Ekman transports holds in an interannual sense as well as for the time mean. Interannual variability in geostrophic transport is strikingly similar to the pattern of central North Pacific sea level pressure variability (the North Pacific Index). The interannual range in heat transport was more than 0.4 pW during 1993-1999, with maximum northward values about 1 pW in early 1994 and early 1997. The ocean heat transport time series is similar to that of European Centre for Medium-Range Weather Forecasts air-sea heat flux integrated over the Pacific north of the XBT line. The repeating nature of the XBT/XCTD transects, with direct wind measurements, allows a substantial improvement over previous heat transport estimates based on one-time transects. A global system is envisioned for observing the time-varying ocean heat transport and its role in the Earth's heat budget and climate system.

Journal of Climate, 2005

The role of oceanic advection in seasonal-to-interannual balances of mass and heat is studied usi... more The role of oceanic advection in seasonal-to-interannual balances of mass and heat is studied using a 12-yr time series of quarterly eddy-resolving expendable bathythermograph (XBT) surveys around the perimeter of a region the authors call the Tasman Box in the southwestern Pacific. The region contains the South Pacific's subtropical western boundary current system and associated strong mesoscale variability. Mean geostrophic transport in the warm upper ocean (temperature greater than 12°C) is about 3.8 Sv (1 Sv ϵ 10 6 m 3 s Ϫ1 ) southward into the box across the Brisbane, Australia-Fiji northern edge. Net outflows are 3.3 Sv eastward across the Auckland, New Zealand-Fiji edge, and 2.7 Sv southward across Sydney, Australia-Wellington, New Zealand. Mean Ekman convergence of 2.2 Sv closes the mass budget. Net water mass conversions in the upper ocean consist of inflow of waters averaging about 26°C and 35.4 psu balanced by outflow at about 18°C and 35.7 psu, and reflect the net evaporation and heat loss in the formation of South Pacific Subtropical Mode Water. The mean heat balance shows good agreement between ocean heat flux convergence (42.3 W m Ϫ2 ), heat loss to the atmosphere from the NCEP-NCAR reanalysis (39.2 W m Ϫ2 ), and heat storage calculated from data in the box interior (1.3 W m Ϫ2 ). On interannual time scales, volume transport through the box ranges from about 1 to 9 Sv, with heat flux convergence ranging from about 20 to 60 W m Ϫ2 . An interannual balance in the heat budget of the warm layer is achieved to within about 10 W m Ϫ2 (or 6 W m Ϫ2 for the upper 100 m alone). Maxima in the advective heat flux convergence occurred in 1993, 1997, and 1999-2000, and corresponded to maxima in air-sea heat loss. The evolution of surfacelayer temperature in the region is the residual of nearly equal and opposing effects of ocean heat flux convergence and air-sea exchange. Hence, ocean circulation is a key element in the interannual heat budget of the air-sea climate system in the western boundary current region.

Journal of Atmospheric and Oceanic Technology, 2009

Two significant instrument biases have been identified in the in situ profile data used to estima... more Two significant instrument biases have been identified in the in situ profile data used to estimate globally integrated upper-ocean heat content. A large cold bias was discovered in a small fraction of Argo floats along with a smaller but more prevalent warm bias in expendable bathythermograph (XBT) data. These biases appear to have caused the bulk of the upper-ocean cooling signal reported by Lyman et al. between 2003 and. These systematic data errors are significantly larger than sampling errors in recent years and are the dominant sources of error in recent estimates of globally integrated upper-ocean heat content variability. The bias in the XBT data is found to be consistent with errors in the fall-rate equations, suggesting a physical explanation for that bias. With biased profiles discarded, no significant warming or cooling is observed in upper-ocean heat content between

Geophysical Research Letters, 2007

Geophysical Research Letters, 2011

Journal of Oceanography, 2002

Journal of Oceanography, Vol. 58, pp. 183 to 195, 2002 Mean and Temporal Variability in Kuroshio ... more Journal of Oceanography, Vol. 58, pp. 183 to 195, 2002 Mean and Temporal Variability in Kuroshio Geostrophic Transport South of Taiwan (1993-2001) John Gílson* and Dean Roemmich Scripps Institution of Oceanography, University of California, San Diego, La Mia, CA 92093-0230, ...

African Journal of Marine Science, 2011