CCMP Wind Vector Analysis Product

Version 2 CCMP Wind Product

The Cross-Calibrated Multi-Platform (CCMP) gridded surface vector winds are produced using satellite, moored buoy, and model wind data, and as such, are considered to be a Level-3 ocean vector wind analysis product. We have updated the CCMP product, using improved and additional input data.  This web site documents the new CCMP V2.0 data set now available from Remote Sensing Systems (RSS).  The V2 CCMP processing now combines Version-7 RSS radiometer wind speeds, QuikSCAT and ASCAT scatterometer wind vectors, moored buoy wind data, and ERA-Interim model wind fields using a Variational Analysis Method (VAM) to produce four maps daily of 0.25 degree gridded vector winds.  The original CCMP product (V1.1) was originally produced by Bob Atlas and his team with funding from the NASA REASoN and MEaSUREs programs.  The original MEaSUREs product is still available from the NASA Physical Oceanography DAAC (podaac.jpl.nasa.gov). RSS has transitioned the CCMP processing code to run using our most up-to-date satellite data observations. All methodology remains the same as that used in the original CCMP product and most of the CCMP processing code is unchanged, with only minor alterations to compensate for the different operating systems and compilers. 

Introduction

Gap-free ocean surface wind data of high quality and high temporal and spatial resolution are useful for a variety of purposes and are necessary for studying large scale air-sea interactions affecting the atmosphere and the ocean. Ocean vector winds are dynamic, continually evolving over short time scales.  This characteristic makes the production of global, gridded, gap-free wind fields a challenge, especially at temporal scales of less than one day and spatial scales smaller than typical wind features.  Accurate research requires ocean vector wind data for a long enough time period to resolve wind-induced patterns such as the El Niño-Southern Oscillation (ENSO) and the Madden-Julian Oscillation (MJO). Remote Sensing Systems has invested many years of research into validating and cross-calibrating passive and active microwave wind retrievals from satellites.

The Variational Analysis Method (VAM) of data assimilation was utilized by Atlas et al. [1996, 2011] to find the most dynamically suitable way to combine satellite observations and in situ wind measurements into gap-free wind fields.  The VAM generates a gridded surface wind analysis which minimizes an objective function measuring the misfit of the analysis to the background, the data and certain a priori constraints. The CCMP wind analyses are at temporal and spatial resolutions suitable for scientific study. The CCMP Version 2.0 (V2) data product described here is a continuation of the highly-used original CCMP product (V1.1 available from NASA JPL PO.DAAC) and builds on the decades of careful VAM development. Two peer-reviewed publications (Atlas et al. 1996, Atlas et al., 2011) describe the original CCMP product and (Hoffman et al, 2003) describes the VAM.  This documentation describes the new CCMP V2.0 product available from Remote Sensing Systems.

The original V1.1 CCMP product was processed incrementally, over a number of years, in small batches using the satellite data available at the time of processing, and therefore, assimilated inconsistently processed satellite winds.  That is, earlier V4 through V6 RSS winds were used for early production years with V7 winds for the later few years of production.  Funding for the original CCMP (V1.1) ended in 2012 with no CCMP winds produced since December 2011.  There has been considerable demand for the continuation of the CCMP product, so we have transitioned the code to RSS with the purpose of meeting several distinct goals: 

  • Extend the product to the present time and continue processing into the future.
  • Reprocess using a consistent version of satellite data.
  • Add newly available sensors.
  • Utilize a higher resolution and consistently produced background model wind field throughout the analysis product.

The new RSS V2.0 CCMP product is now available.  We provide the Level-3.0 (L3.0) and Level-3.5 (L3.5) products in netCDF4 format.  The L3.0 CCMP V2.0 product contains four daily maps (00, 06, 12, and 18Z) on a 0.25 degree mapped grid of U and V vector wind components, and the L3.5 CCMP V2.0 product contains one monthly map centered on the middle of the calendar month on a 0.25 degree mapped grid of U and V vector wind components.  A consistent, gap-free multi-decadal time-series of ocean surface vector wind fields from July 1987 through May 2016 is now available. Updates to the CCMP V2.0 product will be made twice a year, around January and July.

Product Development

The CCMP data set combines cross-calibrated satellite microwave winds and instrument observations using a Variational Analysis Method (VAM) to produce high-resolution (0.25 degree) gridded analyses. Satellite wind retrievals derived by Remote Sensing Systems from a number of satellite-borne passive and active microwave instruments are used. RSS intercalibrates radiometers at the brightness temperature level to within 0.2 degree Celsius, applying a refined sea-surface emissivity model and radiative transfer function to derive surface winds. The resulting wind retrievals are highly consistent between microwave radiometer instrument platforms, including SSM/I, SSMIS, AMSRTMI, WindSat, and GMI.  RSS has also developed a geophysical model function for deriving wind speeds and directions from microwave scatterometers, including QuikSCAT and ASCAT.  Both radiometer and scatterometer data are validated against ocean moored buoys, which confirm the measurements are in agreement (to within 0.8 m/s) despite the difference in wind measurement and retrieval methodologies. The VAM combines RSS instrument data with moored buoy measurements and a starting estimate (first-guess) of the wind field. The European Center for Medium-Range Weather Forecasts (ECMWF) ERA-Interim Reanalysis winds are used in the CCMP V2.0 processing as the first-guess wind field. This 0.25 deg model wind field is consistently processed, as opposed to that of the ECMWF operational model for which the model changes over time.  All wind observations (satellite and buoy) and model analysis fields are referenced to a height of 10 meters.

CCMP Version-2 Updates

RSS cooperated with Dr. Ross Hoffman and Mark Leidner to transition the maintenance, update, and continued processing of CCMP. Once the transition was confirmed to be accurately functioning, RSS conducted a full reprocessing of the CCMP data set bringing it out of first-look status and delivering a consistently-reprocessed V2.0 data product for public use in scientific research. The version changes associated with the RSS V2.0 CCMP release include:

  • Use of uniform inputs and satellite retrievals, with all satellite winds produced using RSS Version-7 (or higher) Ocean Radiative Transfer Model (ORTM) and a consistent processing methodology.
  • Extension of the CCMP data set to July 2015 with plans to provide bi-annual extensions and updates to the dataset.
  • Addition of winds from new instruments: ASCAT Metop-A, AMSR2, and GMI.
  • Upgrade of the first-guess background wind field.  Now using the 0.25-deg, 6-hourly ERA-Interim Reanalysis winds.
  • Use of improved moored buoy data with better quality control, including winds from NDBC, TAO, TRITON, RAMA, PIRATA, and Canadian buoys.
  • Upgrade of the data file format to netCDF4 with CF-1.6 metadata.  Each daily file contains four 6-hourly wind analyses and self-describing metadata.

A time series of all input data used in the VAM is shown below.   Passive radiometers are plotted in red and active scatterometers are plotted in green.  The version of data used for each instrument is provided. The moored buoy winds and ERA-Interim Reanalysis winds are available for the entire data range.  Quality controlled buoy data have been obtained from the Pacific Marine Environmental Lab (PMEL), from the National Data Buoy Center (NDBC), and from the Fisheries and Ocean Canada Oceanography and Scientific Data branch (OSD).  

Full reprocessing of the entire data set takes approximately 1-2 months. Twice per year, in January and July, we will update the data product to include the past 6 months.  For example, in January 2017, we will release June 2016 to December 2016. In transitioning the code to run at RSS, special care was taken to make no changes to the overall approach or the methodology of the original CCMP product.  The code was changed, only where necessary, to account for changes in system architecture and compilers. Source code that was needed for the addition of new satellite winds (AMSR2 or GMI) was adapted from already existing code.  This type of careful transition ensures that the same high-quality CCMP product is still produced, but with updated satellite, buoy and model wind data as input.

Data Product Format

The CCMP V2.0 Level-3.0 (L3.0) winds are available as netCDF-4 data files.  Each L3.0 daily data file contains 3 arrays of size 1440 (longitude) by 628 (latitude for range -78.375 to 78.375) by 4 (time of 0Z, 06Z, 12Z, 18Z).  Two of the arrays are the U and V wind components in meters/second (m/s).  Standard U and V coordinates apply, meaning the positive U is to the right and positive V is above the axis.  Winds in the CCMP product are of oceanographic convention, meaning a wind blowing toward the Northeast has a positive U component and a positive V component.  The third array in the file is the number of observations used to derive the wind components.  A number of obs value of 0.0 means that the wind vector for that grid cell was obtained from the background field only as no satellite or moored buoy wind data were available.

The CCMP V2.0 Level-3.5 (L3.5) winds are available as netCDF-4 data files.  Each L3.5 monthly data file contains 2 arrays of size 1440 (longitude) by 628 (latitude for range -78.375 to 78.375) by 1 (time centered on the middle of the calendar month).  The two arrays are the U and V wind components in meters/second (m/s).  Standard U and V coordinates apply, meaning the positive U is to the right and positive V is above the axis.  Winds in the CCMP product are of oceanographic convention, meaning a wind blowing toward the Northeast has a positive U component and a positive V component.

A fill value of -9999.0 is used for any grid cell without any data. This should rarely happen. Longitude is given in degrees East from 0.125 to 359.875 and latitude is given in degrees North with negative values representing southern locations. While this is referred to as a global wind product, the extent of the data is  -79 degrees to 79 degrees latitude.  The time in the file is given as hours since midnight on Jan 1, 1987.

The netCDF file contains CF 1.6-compliant self-describing metadata.  The JPL metadata compliance checker was used to assess compliance. The RSS CCMP V2.0 data set is distributed as L3.0 daily and L3.5 monthly files. The V1.1 CCMP data set available from PO.DAAC also contained L2.5 (vectors on satellite data) and L3.5 pentad data products. However, RSS has chosen to not distribute the L2.5 or L3.5 pentad data products at this time.

Missing Data

There are gaps within these data. There are 11 days scattered between May and December of 1988 and 14 days in January through July 1989 that do not appear on our FTP server

During this time period, F08 is the only operational satellite input into the dataset. Days that are missing are because there was either very little or no data collected by the satellite on that day.

In future reprocessing, we may include these files for completeness, but the CCMP wind field would essentially be just the ERA-Int background except for minor differences near buoys.

Read Routines / Data Access

The CCMP netCDF4 files can be explored using tools such as Panoply or ncBrowse.  Matlab, IDL, and Python have built-in routines for reading netCDF files.  We have provided a sample read routine in Python.  The routine will plot and display the data for an example file.  CCMP data files can be obtained from RSS by ftp and http.  

File names have the structure CCMP_Wind_Analysis_YYYYMMDD_V02.0_L3.0_RSS.nc where YYYY is the 4-digit year, MM the month and DD the day-of-month. The files are stored in v02.0/Yyyyy/Mmm/ directory structure.

Browse Images / Graphic Maps

The following movies loop through the full 28 years of data.

CCMP Wind Speed Animation

CCMP Wind Speed Anomaly Animation

Product Details

Product

Cross-Calibrated Multi-Platform Ocean Winds

Version

2.0

Spatial Coverage

Region: Global
Northernmost Latitude: 80 degrees
Southernmost Latitude: -80 degrees
Westernmost Longitude: 0 degrees
Easternmost Longitude: 360 degrees

Temporal Coverage 1987-Jul-10 to 2016-May-30
Spatial Resolution

0.25 degrees (Latitude) x 0.25 degrees (Longitude)

Temporal Resolution 6 Hour
Latency < 6 month lag (updated twice yearly)

Input Data

Platform / Sensor / Data Version

AQUA / AMSR-E  V7.0
GCOM-W1 / AMSR2  V7.2
TRMM / TMI  V7.1
GPM / GMI  V8.1
QUIKSCAT / SEAWINDS  V4.0 (Ku-2011)
METOP-A / ASCAT  V2.1
DMSP-F08 / SSM/I  V7.0
DMSP-F10 / SSM/I  V7.0
DMSP-F11 / SSM/I  V7.0
DMSP-F13 / SSM/I  V7.0
DMSP-F14 / SSM/I  V7.0
DMSP-F15 / SSM/I  V7.0
DMSP-F16 / SSMIS  V7.0
DMSP-F17 / SSMIS  V7.0
Coriolis / WindSat  V7.0.1

Data Format NetCDF-4, CF-1.6 compliant
File Size ~25 Mb per file
Parameter ocean surface vector winds at 10 meters height
Parameter Range 0 to 50 m/s
Unit of Measurement meters/second
Contact  support@remss.com
Data Provider Remote Sensing Systems

Known Issues / Data Caveats

The following information should be taken into consideration when using this data product:

  • Users should not consider these winds suitable for studying global trends.  While the winds are derived from consistently processed satellite data suitable for climate study, the act of assimilating the model data into an analysis product potentially introduces spurious trends that may exist in the background wind field. These CCMP V2.0 winds may, however, be suitable for studying regional trends and patterns.
  • Caution should be used when studying high wind regions. We have noted differences between satellite data and the CCMP winds at high wind speeds (>25 m/s), where the background model wind is known to underestimate wind events. Since the VAM method attempts to find a consistent wind field solution somewhere between the satellite-observed high wind events and the lower model winds for those same events, CCMP, as a wind analysis product, will inevitably be lower than the satellite data indicates. Note, wind events of this magnitude tend to be infrequent and geographically limited. 
  • The V2.0 winds are different from the V1.1 winds.  Users should not compare or mix the two products. Differences between the versions do exist and are related to the changes in the satellite data and background wind field.  For example, the new Ku-2011 GMF QuikSCAT winds are much improved at high wind speeds resulting in lower CCMP V2.0 winds at speeds greater than 25 m/s when compared to the CCMP V1.1 winds.

Related Data

The original CCMP V1.1 FLK data are available at the NASA Physical Oceanography DAAC (podaac.jpl.nasa.gov)

References

Atlas, R., R. N. Hoffman, J. Ardizzone, S. M. Leidner, J. C. Jusem, D. K. Smith, D. Gombos, 2011: A cross-calibrated, multiplatform ocean surface wind velocity product for meteorological and oceanographic applications. Bull. Amer. Meteor. Soc., 92, 157-174. doi: 10.1175/2010BAMS2946.1

Atlas, R., R.N. Hoffman, S.C. Bloom, J.C. Jusem, and J. Ardizzone, 1996: A multiyear global surface wind velocity dataset using SSM/I wind observations. Bull. Amer. Meteor. Soc., 77, 5, 869-882.

Hoffman, R. N., M. Leidner, J. M. Henderson, R. Atlas, J. V. Ardizzone, and S. C. Bloom, 2003: A two-dimensional variational analysis method for NSCAT ambiguity removal: methodology, sensitivity, and tuning. Journal of Atmospheric & Oceanic Technology, 20, 585-605.

The original V1.1 Cross-Calibrated Multi-Platform Ocean Surface Wind Vector Analyses User Guide (.pdf) available from JPL PO.DAAC.

 

How to Cite These Data

Continued production of this data set requires support from NASA.  We need you to be sure to cite these data when used in your publications so that we can demonstrate the value of this data set to the scientific community.  Please include the following statement in the acknowledgement section of your paper:

"CCMP Version-2.0 vector wind analyses are produced by Remote Sensing Systems. Data are available at www.remss.com."

Data Set Citation

Wentz, F.J., J. Scott, R. Hoffman, M. Leidner, R. Atlas, J. Ardizzone, 2015:  Remote Sensing Systems Cross-Calibrated Multi-Platform (CCMP) 6-hourly ocean vector wind analysis product on 0.25 deg grid, Version 2.0, [indicate date subset, if used]. Remote Sensing Systems, Santa Rosa, CA. Available online at www.remss.com/measurements/ccmp. [Accessed dd mmm yyyy].   *Insert the appropriate information in the brackets.

Journal Reference

Atlas, R., R. N. Hoffman, J. Ardizzone, S. M. Leidner, J. C. Jusem, D. K. Smith, D. Gombos, 2011: A cross-calibrated, multiplatform ocean surface wind velocity product for meteorological and oceanographic applications. Bull. Amer. Meteor. Soc., 92, 157-174. doi: 10.1175/2010BAMS2946.1