scholarly journals DUACS DT2014: the new multi-mission altimeter data set reprocessed over 20 years

Ocean Science ◽  
2016 ◽  
Vol 12 (5) ◽  
pp. 1067-1090 ◽  
Author(s):  
Marie-Isabelle Pujol ◽  
Yannice Faugère ◽  
Guillaume Taburet ◽  
Stéphanie Dupuy ◽  
Camille Pelloquin ◽  
...  
Keyword(s):  
Measurement Errors ◽  
Large Scale ◽  
Temporal Correlation ◽  
Error Reduction ◽  
Internal Tides ◽  
Global Ocean ◽  
Altimeter Data ◽  
Data Set ◽  
Error Budget ◽  
Spatial Coverage

Abstract. The new DUACS DT2014 reprocessed products have been available since April 2014. Numerous innovative changes have been introduced at each step of an extensively revised data processing protocol. The use of a new 20-year altimeter reference period in place of the previous 7-year reference significantly changes the sea level anomaly (SLA) patterns and thus has a strong user impact. The use of up-to-date altimeter standards and geophysical corrections, reduced smoothing of the along-track data, and refined mapping parameters, including spatial and temporal correlation-scale refinement and measurement errors, all contribute to an improved high-quality DT2014 SLA data set. Although all of the DUACS products have been upgraded, this paper focuses on the enhancements to the gridded SLA products over the global ocean. As part of this exercise, 21 years of data have been homogenized, allowing us to retrieve accurate large-scale climate signals such as global and regional MSL trends, interannual signals, and better refined mesoscale features.An extensive assessment exercise has been carried out on this data set, which allows us to establish a consolidated error budget. The errors at mesoscale are about 1.4 cm2 in low-variability areas, increase to an average of 8.9 cm2 in coastal regions, and reach nearly 32.5 cm2 in high mesoscale activity areas. The DT2014 products, compared to the previous DT2010 version, retain signals for wavelengths lower than  ∼  250 km, inducing SLA variance and mean EKE increases of, respectively, +5.1 and +15 %. Comparisons with independent measurements highlight the improved mesoscale representation within this new data set. The error reduction at the mesoscale reaches nearly 10 % of the error observed with DT2010. DT2014 also presents an improved coastal signal with a nearly 2 to 4 % mean error reduction. High-latitude areas are also more accurately represented in DT2014, with an improved consistency between spatial coverage and sea ice edge position. An error budget is used to highlight the limitations of the new gridded products, with notable errors in areas with strong internal tides.

scholarly journals DUACS DT2014 : the new multi-mission altimeter dataset reprocessed over 20 years

2016 ◽  
Author(s):  
M.-I. Pujol ◽  
Y. Faugère ◽  
G. Taburet ◽  
S. Dupuy ◽  
C. Pelloquin ◽  
...  
Keyword(s):  
Large Scale ◽  
Internal Tide ◽  
Error Reduction ◽  
Global Ocean ◽  
Additional Signal ◽  
Spatial Coverage ◽  
Climate Signals ◽  
Ice Edge ◽  
Sea Ice Edge ◽  
Activity Areas

Abstract. The new DUACS DT2014 reprocessed products are available since April 2014. Numerous and impacting evolutions have been implemented at each step of this new data processing. The main one is the use of a new 20-year altimeter reference period that changes the SLA and SLA gradient signature. Although all the DUACS products have been improved, this paper focuses on gridded products quality description over the global ocean. As part as this exercise, 21 years of data have been homogenized allowing us to retrieve accurate large scale climate signals such as global and regional MSL trend as well as interannual signals, but also refined mesoscale features. Extensive assessment has been performed on this dataset, which allowed us to establish a consolidated error budget. The errors at mesoscale are about 1.5cm2 in low variability areas and increase to 9cm2 in average in coastal regions, to reach more than 30cm2 in high mesoscale activity areas. The DT2014 products, compared to the previous version DT2010, presents additional signal for wavelengths lower than ~250km inducing SLA variance and mean EKE increase of respectively +5.1% and +15%. Comparison with independent measurements underlined the improved mesoscales restitution with this new dataset. The errors reduction at mesoscale reaches nearly 10% of the error observed with DT2010. The DT2014 also presents improved coastal signal with a 2 to 4% mean error reduction. High latitudes areas are also better represented in DT2014, with a better consistency between map spatial coverage and sea ice edge position. The budget error is finally discussed, in order to highlight the limitation of gridded products, notably in strong internal tide area.

scholarly journals The H.E.S.S. Galactic plane survey

2018 ◽  
Vol 612 ◽  
pp. A1 ◽  
Author(s):  
◽  
H. Abdalla ◽  
A. Abramowski ◽  
F. Aharonian ◽  
F. Ait Benkhali ◽  
...  
Keyword(s):  
Supernova Remnants ◽  
Large Scale ◽  
Gamma Ray ◽  
Galactic Center ◽  
Galactic Plane ◽  
High Energy ◽  
High Angular Resolution ◽  
Data Set ◽  
Cherenkov Telescopes ◽  
Spatial Coverage

We present the results of the most comprehensive survey of the Galactic plane in very high-energy (VHE) γ-rays, including a public release of Galactic sky maps, a catalog of VHE sources, and the discovery of 16 new sources of VHE γ-rays. The High Energy Spectroscopic System (H.E.S.S.) Galactic plane survey (HGPS) was a decade-long observation program carried out by the H.E.S.S. I array of Cherenkov telescopes in Namibia from 2004 to 2013. The observations amount to nearly 2700 h of quality-selected data, covering the Galactic plane at longitudes from ℓ = 250° to 65° and latitudes |b|≤ 3°. In addition to the unprecedented spatial coverage, the HGPS also features a relatively high angular resolution (0.08° ≈ 5 arcmin mean point spread function 68% containment radius), sensitivity (≲1.5% Crab flux for point-like sources), and energy range (0.2–100 TeV). We constructed a catalog of VHE γ-ray sources from the HGPS data set with a systematic procedure for both source detection and characterization of morphology and spectrum. We present this likelihood-based method in detail, including the introduction of a model component to account for unresolved, large-scale emission along the Galactic plane. In total, the resulting HGPS catalog contains 78 VHE sources, of which 14 are not reanalyzed here, for example, due to their complex morphology, namely shell-like sources and the Galactic center region. Where possible, we provide a firm identification of the VHE source or plausible associations with sources in other astronomical catalogs. We also studied the characteristics of the VHE sources with source parameter distributions. 16 new sources were previously unknown or unpublished, and we individually discuss their identifications or possible associations. We firmly identified 31 sources as pulsar wind nebulae (PWNe), supernova remnants (SNRs), composite SNRs, or gamma-ray binaries. Among the 47 sources not yet identified, most of them (36) have possible associations with cataloged objects, notably PWNe and energetic pulsars that could power VHE PWNe.

scholarly journals Improved Analyses of Changes and Uncertainties in Sea Surface Temperature Measured In Situ since the Mid-Nineteenth Century: The HadSST2 Dataset

2006 ◽  
Vol 19 (3) ◽  
pp. 446-469 ◽  
Author(s):  
N. A. Rayner ◽  
P. Brohan ◽  
D. E. Parker ◽  
C. K. Folland ◽  
J. J. Kennedy ◽  
...  
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Bias Correction ◽  
Measurement Errors ◽  
Large Scale ◽  
Sea Surface ◽  
Data Set ◽  
Total Uncertainty ◽  
Hadley Centre ◽  
Measurement Practices

Abstract A new flexible gridded dataset of sea surface temperature (SST) since 1850 is presented and its uncertainties are quantified. This analysis [the Second Hadley Centre Sea Surface Temperature dataset (HadSST2)] is based on data contained within the recently created International Comprehensive Ocean–Atmosphere Data Set (ICOADS) database and so is superior in geographical coverage to previous datasets and has smaller uncertainties. Issues arising when analyzing a database of observations measured from very different platforms and drawn from many different countries with different measurement practices are introduced. Improved bias corrections are applied to the data to account for changes in measurement conditions through time. A detailed analysis of uncertainties in these corrections is included by exploring assumptions made in their construction and producing multiple versions using a Monte Carlo method. An assessment of total uncertainty in each gridded average is obtained by combining these bias-correction-related uncertainties with those arising from measurement errors and undersampling of intragrid box variability. These are calculated by partitioning the variance in grid box averages between real and spurious variability. From month to month in individual grid boxes, sampling uncertainties tend to be most important (except in certain regions), but on large-scale averages bias-correction uncertainties are more dominant owing to their correlation between grid boxes. Changes in large-scale SST through time are assessed by two methods. The linear warming between 1850 and 2004 was 0.52° ± 0.19°C (95% confidence interval) for the globe, 0.59° ± 0.20°C for the Northern Hemisphere, and 0.46° ± 0.29°C for the Southern Hemisphere. Decadally filtered differences for these regions over this period were 0.67° ± 0.04°C, 0.71° ± 0.06°C, and 0.64° ± 0.07°C.

The dissipation of the internal tide inferred from a global ocean model, altimetry, and in-situ observations

2020 ◽  
Author(s):  
Maarten Buijsman ◽  
Harpreet Kaur ◽  
Zhongxiang Zhao ◽  
Amy Waterhouse ◽  
Caitlin Whalen
Keyword(s):  
Correction Factor ◽  
Internal Tide ◽  
Horizontal Resolution ◽  
Ocean Model ◽  
Internal Tides ◽  
Global Ocean ◽  
Flux Divergence ◽  
Data Set ◽  
Tidal Dissipation ◽  
Dissipation Rates

<p>In this presentation we combine several model and observational data sets to better understand the dissipation of the diurnal and semidiurnal internal tide in the global ocean, which is relevant for maintaining the global overturning circulation. We compute depth-integrated internal tide dissipation rates from a realistically-forced global HYbrid Coordinate Ocean Model (HYCOM) simulation with a horizontal resolution of 4 km (1/25 degrees) and 41 layers. We also compute dissipation rates from altimetry in two ways: 1) from the low-mode flux divergence away from topography and 2) by fitting exponential decay curves along low-mode internal tide beams. The internal-tide sea-surface height amplitude is computed with a least-squares harmonic analysis over a 20+ year altimetry data set. Hence, the altimetry-inferred dissipation rates both reflect the tidal dissipation and the energy scattered from the stationary to the nonstationary internal tide. To account for the dissipation of the nonstationary tide, we apply a spatially-varying correction factor to the stationary dissipation inferred from altimetry.  This correction factor is computed from a global 8-km HYCOM simulation with a duration of 6 years, from which the stationary and nonstationary internal tides can be easily isolated. We compare the simulated and the corrected altimetry-inferred dissipation rates with dissipation rates from finescale and microstructure observations. Preliminary results show that the simulated dissipation is up to a factor of two larger than the depth-integrated dissipation rates inferred from finescale methods, but smaller than the dissipation rates from microstructure.</p>

scholarly journals Decomposition of Random Errors Inherent to HOAPS-3.2 Near-Surface Humidity Estimates Using Multiple Triple Collocation Analysis

2016 ◽  
Vol 33 (7) ◽  
pp. 1455-1471 ◽  
Author(s):  
Julian Kinzel ◽  
Karsten Fennig ◽  
Marc Schröder ◽  
Axel Andersson ◽  
Karl Bumke ◽  
...  
Keyword(s):  
Measurement Errors ◽  
Large Scale ◽  
Heat Fluxes ◽  
Specific Humidity ◽  
Random Errors ◽  
Bias Analysis ◽  
Data Set ◽  
Near Surface ◽  
Ocean Atmosphere

AbstractLatent heat fluxes (LHF) play an essential role in the global energy budget and are thus important for understanding the climate system. Satellite-based remote sensing permits a large-scale determination of LHF, which, among others, are based on near-surface specific humidity . However, the random retrieval error () remains unknown. Here, a novel approach is presented to quantify the error contributions to pixel-level of the Hamburg Ocean Atmosphere Parameters and Fluxes from Satellite Data, version 3.2 (HOAPS, version 3.2), dataset. The methodology makes use of multiple triple collocation (MTC) analysis between 1995 and 2008 over the global ice-free oceans. Apart from satellite records, these datasets include selected ship records extracted from the Seewetteramt Hamburg (SWA) archive and the International Comprehensive Ocean–Atmosphere Data Set (ICOADS), serving as the in situ ground reference. The MTC approach permits the derivation of as the sum of model uncertainty and sensor noise , while random uncertainties due to in situ measurement errors () and collocation () are isolated concurrently. Results show an average of 1.1 ± 0.3 g kg−1, whereas the mean () is in the order of 0.5 ± 0.1 g kg−1 (0.5 ± 0.3 g kg−1). Regional analyses indicate a maximum of exceeding 1.5 g kg−1 within humidity regimes of 12–17 g kg−1, associated with the single-parameter, multilinear retrieval applied in HOAPS. Multidimensional bias analysis reveals that global maxima are located off the Arabian Peninsula.

scholarly journals Impact of model resolution on sea-level variability characteristics at various space and time scales: insights from four DRAKKAR global simulations and the AVISO altimeter data

2009 ◽  
Vol 6 (2) ◽  
pp. 1513-1545 ◽  
Author(s):  
T. Penduff ◽  
M. Juza ◽  
L. Brodeau ◽  
G. C. Smith ◽  
B. Barnier ◽  
...  
Keyword(s):  
Sea Level ◽  
Large Scale ◽  
Coupled Processes ◽  
Global Ocean ◽  
Altimeter Data ◽  
Spatial Correlations ◽  
Temporal Correlations ◽  
Sea Level Anomalies ◽  
Day Range ◽  
Standard Deviations

Abstract. Four global ocean/sea-ice simulations driven by the same realistic 46-year daily atmospheric forcing were performed within the DRAKKAR project at 2°, 1°, ½° and ¼° resolutions. Model sea-level anomalies are collocated over the period 1993–2004 onto the AVISO SLA dataset. These five collocated SLA datasets are then filtered and quantitatively compared over various time and space scales regarding three characteristics: SLA standard deviations, spatial correlations between SLA variability maps, and temporal correlations between observed and simulated band-passed filtered local SLA timeseries. Beyond the 2°–1° transition whose benefits are quite moderate, further increases in resolution and associated changes in subgrid scale parameterizations simultaneously induce (i) strong increases in SLA standard deviations, (ii) strong improvements in the spatial distribution of SLA variability, and (iii) slight decreases in temporal correlations between observed and simulation SLA timeseries. These 3 effects are not only clear on mesoscale (14–180 days) and quasi-annual (5–18 months) fluctuations, but also on the slower (interannual), large-scale variability ultimately involved in ocean-atmosphere coupled processes. Most SLA characteristics are monotonically affected by successive resolution increases, but irregularly and with a strong dependance on frequency and latitude. Benefits of enhanced resolution are maximum in the ½°–¼° transition, in the 14–180 day range, and within eddy-active mid- and high-latitude regions. They are particularly clear in the Southern Ocean where mesoscale eddies probably sustain a substantial intrinsic interannual variability.

Seasonal and interannual variability of global internal tides

2021 ◽  
Author(s):  
Harpreet Kaur ◽  
Maarten Buijsman
Keyword(s):  
Time Series ◽  
Interannual Variability ◽  
Large Scale ◽  
Internal Tide ◽  
Empirical Orthogonal Functions ◽  
Internal Tides ◽  
Global Ocean ◽  
Spatial And Temporal Variability ◽  
Altimetry Data ◽  
Seasonal And Interannual Variability

<p>In this study, we investigate the seasonal and interannual variability of internal tides in the global ocean using a Hybrid Coordinate Ocean Model (HYCOM) and altimetry data. The variability of internal tides is caused by the time varying stratification, mesoscale activity, large-scale shifts in amphidromic points, and changes in ice cover. The variation in the background fields generates the non-phase locked internal tides which are non-stationary. Non-stationary internal tides are less predictable than stationary tides, complicating regional model forcing with remote internal tide signals and the separation of internal tides from mesoscales. We will use 6 years of steric SSH extracted from a global HYCOM simulation with a horizontal resolution of 8 km and 32 layers to study the variability of internal tides. Our objective is to analyze the spatial and temporal variability of the amplitude and phase of the diurnal and semidiurnal internal tides. The SSH time series will be divided into time segments with different durations. The least-squares harmonic analysis will be used to extract SSH amplitude and phase for M2, K1, O1, and S2 constituents for these time segments. It has been found that the stationary amplitude decreases with an increase in the duration of the time series. We will also use empirical orthogonal functions (EOF) analysis to determine the seasonal and interannual variability in the monthly-mean internal tide amplitude and phase. The global maps of the non-stationarity fraction for the internal tidal constituents will be shown for each season. These results will be compared with 25 years of satellite altimetry data to find out whether similar variance decay trends are observed in the altimetry data.</p>

scholarly journals On the permeability of barrier layers

2009 ◽  
Vol 6 (1) ◽  
pp. 799-818 ◽  
Author(s):  
J. Mignot ◽  
C. de Boyer Montégut ◽  
M. Tomczak
Keyword(s):  
Large Scale ◽  
Sea Surface Salinity ◽  
Global Ocean ◽  
Computation Method ◽  
Western Boundary ◽  
Climatic Impact ◽  
Surface Salinity ◽  
Data Set ◽  
Barrier Layer Thickness ◽  
Barrier Layers

Abstract. We present a revisited 2-degree resolution global ocean climatology of monthly mean Barrier Layer Thickness (BLT) first proposed by de Boyer Montégut et al. (2007a). In addition to using an extended data set, we present a modified computation method in order to take into account the observed permeability of Barrier Layers (BL). We name permeability the fact that barrier layers can, in some areas, be very patchy regarding the space and time scales that are considered. This patchiness may have important consequences for the climatic impact of BLs. Differences between the two computation methods are weak for robust BLs that are formed by large-scale processes. The former approach can however largely underestimate the thickness of short and/or localized barrier layers. This is especially the case for the ones formed by mesoscale mechanisms (under the ITCZ for example and along western boundary currents) and patchy barrier layers detected equatorward of the sea surface salinity subtropical maxima. Complete characterisation of regional BL dynamics therefore requires the description of BL robustness through the determination of both BLT and BL permeability.

scholarly journals Mapping of the Topography of Continental Ice by Inversion of Satellite-altimeter Data

1989 ◽  
Vol 35 (119) ◽  
pp. 98-107 ◽  
Author(s):  
F. Remy ◽  
P. Mazzega ◽  
S. Houry ◽  
C. Brossier ◽  
J.F. Minster
Keyword(s):  
Measurement Errors ◽  
Large Scale ◽  
A Priori ◽  
Ice Sheet ◽  
Altimeter Data ◽  
Topographic Map ◽  
Satellite Altimeter ◽  
Climatic Variations ◽  
Orbit Errors ◽  
Satellite Altimeter Data

AbstractSatellite-altimeter data over ice sheets provide the best tool for mapping their topography and its possible climatic variations. However, these data are affected by measurement errors, orbit errors, and slope errors. We develop here a three-step inversion technique which accommodates the a priori information on the expected topography and correctly handles and propagates the data errors: it estimates first a large-scale reference surface, then maps the residuals related to undulations, and finally iteratively corrects the slope error. The method is tested on overlapping small fragments of the Antarctic ice sheet, using a sub-set of Seasat data. Finally, a topographic map of Terre Adélie is produced. Over areas of small slopes, the a posteriori error should be of the order of 0.4 m. Using ERS-I data, it is therefore expected that climatic variations in the ice-sheet topography since the introduction of Seasat will be observable.

ProGen:Provenance database generator for large-scale data set

2009 ◽  
Vol 28 (11) ◽  
pp. 2737-2740
Author(s):  
Xiao ZHANG ◽  
Shan WANG ◽  
Na LIAN
Keyword(s):  
Large Scale ◽  
Data Set ◽  
Large Scale Data ◽  
Scale Data
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