PRODUCT USER MANUAL For Global Ocean Observation-based Products GLOBAL_ANALYSIS_PHYS_001_020

Transcription

1 PRODUCT USER MANUAL For Global Ocean Observation-based Products Issue: 1.3 Contributors: S. Mulet, S. Guinehut, N. Verbrugge, V. Rosmorduc, F. Mertz CMEMS version scope : V2 Approval Date :

2 CHANGE RECORD Issue Date Description of Change Author Checked By /12/15 Creation S. Mulet /03/16 header Minor Modification N. Verbrugge 1.2 4/4/16 IV.5.1 SSALTO => CMEMS N. Verbrugge /01/17 III.1 Reference to the reprocessed product S.Mulet EU Copernicus Marine Service Public Page 2/ 14

3 TABLE OF CONTENTS I INTRODUCTION... 6 I.1 Summary... 6 I.2 History of changes... 6 II HOW TO DOWNLOAD A PRODUCT... 7 II.1 Download a product through the Web Portal Subsetter Service... 7 II.2 Download a product through the Web Portal Directgetfile Service... 7 II.3 Download a product through the Web Portal Ftp Service... 7 III DESCRIPTION OF THE PRODUCT SPECIFICATION... 8 III.1 General Information... 8 III.2 Details of datasets... 8 IV NOmenclature of files... 9 IV.1 Nomenclature of files when downloaded through the Web Portal Subsetter Service... 9 IV.2 Nomenclature of files when downloaded through the Web Portal Directgetfile and Ftp Service 9 IV.3 Domain coverage... 9 IV.4 Vertical Levels... 9 IV.5 Processing IV.5.1 Input data IV.5.2 Method V file format V.1 Netcdf V.2 Structure and semantic of netcdf maps files V.3 Reading software EU Copernicus Marine Service Public Page 3/ 14

4 GLOSSARY AND ABBREVIATIONS AMSR AVHRR CF CTD DT FTP Meridional Velocity MFC NetCDF NOAA NRT OpenDAP RD RMS S SLA SSH SSS SST T XBT Zonal Velocity Subsetter Directgetfile Advanced Microwave Scanning Radiometer Advanced Very High Resolution Radiometer Climate Forecast (convention for NetCDF) Conductivity-Temperature-Depth Delayed Time File Transfer Protocol West to East component of the horizontal velocity vector Monitoring and Forecasting Centre Network Common Data Form National Oceanic and Atmospheric Administration Near Real Time Open-Source Project for a Network Data Access Protocol. Protocol to download subset of data from a n-dimensional gridded dataset (ie: 4 dimensions: lon-lat,depth,time) Reference Document Root mean square Salinity Sea Level Anomaly Sea surface height Sea surface salinity. Sea Surface Temperature Temperature expendable Bathy-Thermograph South to North component of the horizontal velocity vector CMEMS service tool to download a NetCDF file of a selected geographical box using values of longitude an latitude, and time range CMEMS service tool (FTP like) to download a NetCDF file EU Copernicus Marine Service Public Page 4/ 14

5 REFERENCE DOCUMENTS RD 1 Guinehut S., P.-Y. Le Traon, G. Larnicol and S. Philipps, Combining Argo and remote-sensing data to estimate the ocean three-dimensional temperature fields a first approach based on simulated observations, 2004 / J. Mar. Sys., 46, RD 2 Guinehut S., P.-Y. Le Traon and G. Larnicol, What can we learn from Global Altimetry/Hydrography comparisons?, 2006 / Geophys. Res. Lett, 33, L10604, doi: /2005GL RD 3 Dhomps A.-L., S. Guinehut, P.Y. Le Traon and G. Larnicol, 2011: A global comparison of Argo and satellite altimetry observations, Ocean Science, Vol.7, pp , SRef-ID : /os/ RD 4 Bretherton, F. P., R. E. Davis and C. B. Fandry, A technique for objective analysis and design of oceanographic experiments applied to MODE-73, 1976 / Deep-Sea Res., 23, RD 5 Gaillard, F., R. Charraudeau, New climatology and statistics over the global Ocean, 2008 / MERSEA-WP05-CNRS-STR A RD 6 Mulet, S., M.-H. Rio, A. Mignot, S. Guinehut and R. Morrow, 2012: A new estimate of the global 3D geostrophic ocean circulation based on satellite data and in-situ measurements. Deep-Sea Res. II., 77-80, 70-81, doi: /j.dsr RD 7 Rio M.-H., S. Guinehut and G. Larnicol, 2011: The New CNES-CLS09 global Mean Dynamic Topography computed from the combination of GRACE data, altimetry and in-situ measurements. J. Geophys. Res., 116, C07018, doi: /2010jc RD 8 Guinehut S., A.-L. Dhomps, G. Larnicol and P.-Y. Le Traon, 2012: High resolution 3D temperature and salinity fields derived from in situ and satellite observations. Ocean Sci., 8, , doi: /os EU Copernicus Marine Service Public Page 5/ 14

6 I INTRODUCTION I.1 Summary This guide describes the data product files from the GLO-OBS PU, what data services are available to access them, and how to use the files and services. The product described here is. It contains one dataset (dataset-armor-3d-v4-cmems-v2): near-real time global 3-D temperature, salinity, geopotential height and geostrophic current fields defined on a 1/4 regular grid, from the surface down to 5500-m depth at a weekly period; This product is a combination between satellite and in-situ data, processed in three steps: (1) satellite data (SLA + SST) are projected onto the vertical via a multiple linear regression method and covariances deduced from historical observations. This step gives synthetical fields, (2) combination between these synthetic fields with T/S in-situ profiles via an optimal interpolation method. This leads to combined fields. (3) use of the thermal wind equation to combine absolute geostrophic current fields from satellite altimetry with the combined 3D T/S fields. This last step generates global 3D geostrophic current fields. I.2 History of changes On April 2016, supersedes GLOBAL_ANALYSIS _PHYS_001_016. The grid has changed; it is now defined from S to N and from to E. Also improvements have been done; they are described in the QUID CMEMS-GLO-QUID EU Copernicus Marine Service Public Page 6/ 14

7 II HOW TO DOWNLOAD A PRODUCT II.1 Download a product through the Web Portal Subsetter Service You first need to register. Please find below the registration form: Once registered, the FAQ will guide you on How to download a product through the Web Portal Subsetter Service. Using the subsetter you can extract the product on a specific area of your interest, select which variable(s) you need and over a selected time period. II.2 Download a product through the Web Portal Directgetfile Service You first need to register. Please find below the registration form: Once registered, the FAQ will guide you on How to download a product through the CMEMS Web Portal Directgetfile Service. Using the direct get file, you will get the entire file. II.3 Download a product through the Web Portal Ftp Service You first need to register. Please find below the registration form: Once registered, the FAQ will guide you on How to download a product through the CMEMS Web Portal Ftp Service. Using the ftp, you will get the entire file. EU Copernicus Marine Service Public Page 7/ 14

8 III DESCRIPTION OF THE PRODUCT SPECIFICATION III.1 General Information Product Specification Customer Name Geographical coverage Variables Available time series Temporal resolution Target delivery time Delivery mechanism Horizontal resolution Number of vertical levels Format Global ( S, N, E) Temperature, Salinity, Geopotential Height, Eastward and Northward geostrophic Velocities 01/01/2014- ongoing Note that a REPROCESSED product GLOBAL_REP_PHY_001_021 exits. It starts the with at least two years of overlapping with the NEAR REAL TIME product Each Wednesday mean fields Wednesday at 8 pm Information Service (Subsetter, Directgetfile and MFTP) 1/4 on a regular grid 33 levels from 0 to 5500-m depth Netcdf CF3.0 Table 1: product specification customer name III.2 Details of datasets DATASETS VARIABLES AND UNIT NAME OF VARIABLES IN THE NETCDF FILE dataset-armor-3d-v4-cmems-v2 Salinity [PSU] Temperature [degc] Geopotential Height [m] Eastward Geostrophic Velocities [m/s] Northward Geostrophic Velocities [m/s] salinity temperature height zvelocity mvelocity Table 2 :List of the datasets (column 1), of the variable for each dataset (column 2) and their names in the NetCDF files (column 3) for EU Copernicus Marine Service Public Page 8/ 14

9 IV NOMENCLATURE OF FILES The nomenclature of the downloaded files differs on the basis of the chosen download mechanism Subsetter, Directgetfile and FTP service. IV.1 Nomenclature of files when downloaded through the Web Portal Subsetter Service files nomenclature when downloaded through the Web Portal Subsetter is based on product dataset name and a numerical reference related to the request date on the CMEMS Information System (CIS). The scheme is: dataset-armor-3d-v4-cmems-v2_nnnnnnnnnnnnn.nc where : nnnnnnnnnnnnn: 13 digit integer corresponding to the current time (download time) in milliseconds since January 1, 1970 midnight UTC..nc: standard NetCDF filename extension. Example: dataset-armor-3d-v4-cmems-v nc IV.2 Nomenclature of files when downloaded through the Web Portal Directgetfile and Ftp Service files nomenclature when downloaded through the Web Portal Directgetfile and FTP is based as follows: The nomenclature used for the dataset dataset-armor-3d-v4-cmems-v2 is: ARMOR3D_TSHUV_DATE.nc DATE:YYYYMMDD IV.3 Domain coverage The coverage of the data is global ( S, N, W) and the data are projected on a 1/4 regular grid. IV.4 Vertical Levels products are computed on 33 levels from 0 to 5500-m depth. The levels are the following (in meters): 0, 10, 20, 30, 50, 75, 100, 125, 150, 200, 250, 300, 400, 500, 600, 700, 800, 900, 1000, 1100, 1200, 1300, 1400, 1500, 1750, 2000, 2500, 3000, 3500, 4000, 4500, 5000, 5500 EU Copernicus Marine Service Public Page 9/ 14

10 IV.5 Processing IV.5.1 Input data Five sources of data are used: - In-situ T and S profiles are from the IN-SITU TAC including Argo profiling floats, XBT, CTD and moorings; - The WOA13 ¼ climatology computed at NOAA ( - Altimeter sea level anomalies (SLA) are from CMEMS (SL TAC SEALEVEL_GLO_SLA_MAP_L4_NRT_OBSERVATIONS_008_026) and are weekly combined maps of all processed altimeters - Mean Dynamic Topography CNES-CLS13. - SST data are from daily Reynolds analyses with a 1/4 horizontal resolution, combining AVHRR and in-situ observations (no more AMSR since October 2011) and distributed by the National Climatic Data Center at NOAA ( IV.5.2 Method For the temperature (T) and salinity (S) fields available in near real time and in delayed time, the method used has been first developed using simulated data sets [RD 1] and has two steps [RD 8]. The first step of the method consists in deriving synthetic temperature (T) profiles from the surface down to 1500-meter depth from altimeter and SST data through a multiple linear regression method and covariances calculated from historical data. For synthetic salinity (S) profiles, the method uses only altimeter data. Pre-processing of altimeter SLA includes the extraction of the steric part of the SLA using regression coefficients deduced from an altimeter/in-situ comparison study [RD 2, RD 3]. The second step of the method consists in combining the synthetic profiles with in-situ temperature and salinity profiles using an optimal interpolation method [RD 4]. To gain maximum benefit from the qualities of both data sets, namely the accurate information given by in-situ T/S profiles and the mesoscale variability given by the T/S synthetic profiles, a precise statistical description of the errors of these observations has been introduced in the optimal interpolation method. For the in-situ profiles, since these observations are considered almost perfect, a very low white noise is applied. For the synthetic profiles, simulating remote-sensing (altimeter and SST) observations, since these observations are not direct measurements but are derived from the regression method, correlated errors have to be applied to correct long-wavelength errors or biases present in the synthetic fields and introduced by the regression method. Analyses are performed in near real time and in delayed time at a weekly period on each Levitus vertical level from the surface down to 1500-meter depth. An example of the input and output fields is given on Figure 1 for the 4 th of July Thanks to the mesoscale structures available in the altimetry and SST fields, the synthetic estimate shows also mesoscale structures in most part of the ocean with T anomalies ranging from -2 to 2 C at 100-meter depth (Figure 1). The combination of the synthetic estimates with all available in-situ temperature allows correcting the field in some regions like in the North-East Indian Ocean where the in-situ temperature are much colder than the synthetic ones. Amplitudes of the combined fields are thus more similar to the in-situ observations but with still small scale structure. The T/S fields are completed from 1500 to 5500 meter depth using the T/S climatology. Geopotential height and geostrophic current fields are additionally available. They are calculated using the thermal wind equation with a reference level at the surface to combine absolute current fields at the surface from satellite altimetry with the combined T/S fields [RD 6]. The surface currents are calculated by geostrophy from SLA and MDT CNES-CLS13. As the CNES-CLS13 Mean Dynamic Topographies used to calculate the absolute current fields at the surface are not defined for the Black and Red Seas [RD 7], the 3D geostrophic current fields are also not defined for those areas. EU Copernicus Marine Service Public Page 10/ 14

11 Altimeter SLA 04/07/2007 SST 04/07/2007 Climatology for July Synthetic T anomalies at 100-m depth 04/07/2007 In-situ temperature anomalies at 100-m around the 04/07/2007 T anomalies at 100-m depth from the combined estimates 04/07/2007 Figure 1: Input and outputs from the system calculating T and S fields for the 4 th of July EU Copernicus Marine Service Public Page 11/ 14

12 V FILE FORMAT V.1 Netcdf The products are stored using the NetCDF format. NetCDF (network Common Data Form) is an interface for array-oriented data access and a library that provides an implementation of the interface. The netcdf library also defines a machine-independent format for representing scientific data. Together, the interface, library, and format support the creation, access, and sharing of scientific data. The netcdf software was developed at the Unidata Program Center in Boulder, Colorado. Please see Unidata netcdf pages for more information, and to retrieve netcdf software package. NetCDF data is: * Self-Describing. A netcdf file includes information about the data it contains. * Architecture-independent. A netcdf file is represented in a form that can be accessed by computers with different ways of storing integers, characters, and floating-point numbers. * Direct-access. A small subset of a large dataset may be accessed efficiently, without first reading through all the preceding data. * Appendable. Data can be appended to a netcdf dataset along one dimension without copying the dataset or redefining its structure. The structure of a netcdf dataset can be changed, though this sometimes causes the dataset to be copied. * Sharable. One writer and multiple readers may simultaneously access the same netcdf file. V.2 Structure and semantic of netcdf maps files For ARMOR3D_TSHUV_YYYYMMDD.nc netcdf ARMOR3D_TSHUV_ { dimensions: time = UNLIMITED ; // (1 currently) depth = 33 ; latitude = 689 ; longitude = 1440 ; variables: int time(time) ; time:units = "hours since " ; time:_coordinateaxistype = "Time" ; time:axis = "T" ; time:long_name = "time" ; time:standard_name = "time" ; short depth(depth) ; depth:axis = "Z" ; depth:long_name = "depth" ; depth:positive = "down" ; depth:standard_name = "depth" ; depth:unit_long = "meter" ; depth:units = "m" ; float latitude(latitude) ; latitude:axis = "Y" ; latitude:long_name = "latitude" ; latitude:standard_name = "latitude" ; latitude:step = 0.25f ; EU Copernicus Marine Service Public Page 12/ 14

13 latitude:unit_long = "degrees north" ; latitude:units = "degrees_north" ; float longitude(longitude) ; longitude:axis = "X" ; longitude:long_name = "longitude" ; longitude:standard_name = "longitude" ; longitude:step = 0.25f ; longitude:unit_long = "degrees east" ; longitude:units = "degrees_east" ; short height(time, depth, latitude, longitude) ; height:_fillvalue = 32767s ; height:long_name = "absolute height from SURCOUF3D" ; height:scale_factor = ; height:standard_name = "geopotential_height" ; height:unit_long = "meter" ; height:units = "m" ; height:valid_range = s, 20000s ; short mvelocity(time, depth, latitude, longitude) ; mvelocity:_fillvalue = 32767s ; mvelocity:long_name = "meridional velocity from SURCOUF3D" ; mvelocity:scale_factor = ; mvelocity:standard_name = "northward_sea_water_velocity" ; mvelocity:unit_long = "meter per second" ; mvelocity:units = "m s-1" ; mvelocity:valid_range = -4000s, 4000s ; short salinity(time, depth, latitude, longitude) ; salinity:_fillvalue = 32767s ; salinity:add_offset = 20. ; salinity:long_name = "salinity from ARMOR3D" ; salinity:scale_factor = ; salinity:standard_name = "sea_water_salinity" ; salinity:unit_long = "practical salinity unit" ; salinity:units = "1e-3" ; short temperature(time, depth, latitude, longitude) ; temperature:_fillvalue = 32767s ; temperature:add_offset = 20. ; temperature:long_name = "temperature from ARMOR3D" ; temperature:scale_factor = ; temperature:standard_name = "sea_water_temperature" ; temperature:unit_long = "degree Celsius" ; temperature:units = "degc" ; short zvelocity(time, depth, latitude, longitude) ; zvelocity:_fillvalue = 32767s ; zvelocity:long_name = "zonal velocity from SURCOUF3D" ; zvelocity:scale_factor = ; zvelocity:standard_name = "eastward_sea_water_velocity" ; zvelocity:unit_long = "meter per second" ; zvelocity:units = "m s-1" ; zvelocity:valid_range = -4000s, 4000s ; // global attributes: :description = "ARMOR3D NRT V4 CMEMS V2" ; :title = "ARMOR3D NRT - TSHUV Global Ocean Obervation-based Product" ; :Conventions = "CF-1.0" ; :institution = "CLS" ; :domain_name = "GLO" ; :history = " :39:35 ARMOR3D NRT - TSHUV Global Ocean Obervationbased Product netcdf creation" ; } EU Copernicus Marine Service Public Page 13/ 14

14 V.3 Reading software NetCDF data can be browsed and used through a number of software, like: ncbrowse: NetCDF Operator (NCO): IDL, Matlab, GMT EU Copernicus Marine Service Public Page 14/ 14