Blended Sea Winds
The Blended Sea Winds dataset contains globally gridded, high-resolution ocean surface vector winds and wind stresses on a global 0.25° grid, and multiple time resolutions of six-hourly, daily, monthly, and 11-year (1995–2005) climatological monthlies. The period of record is July 9, 1987, to present. Blending observations from multiple satellites (up to six satellites since June 2002) allows for the creation of gridded wind speeds. The wind directions come from two sources depending on the products: for the research delayed mode product, the source is the National Centers for Environmental Prediction (NCEP) Reanalysis 2 (NRA-2) and for the near-real-time products, the source is the numerical weather prediction of the European Centre for Medium-Range Weather Forecasts.
Blending multiple-satellite observations fills in the data gaps (in both time and space) of the individual satellite samplings and reduces the subsampling aliases and random errors. These products were developed in response to the demand for increasingly higher resolution global datasets. For example, scientists want to improve the accuracy of their forecasts of ocean and weather conditions. Links to articles on the high-resolution feasibility study and the blending methodology are available in the Bibliography section below.
Please note that these are research products, and thus, are experimental in nature. Users are encouraged to register to receive update notices and to provide comments.
The global 0.25° gridded data are available in netCDF and IEEE format for the period of record, July 1987 to present, with six-hourly, daily, and monthly time resolutions. There is also an 11-year (1995–2005) monthly climatological dataset. Users can use the data with support reading programs in FORTRAN, MATLAB, and GrADS. The data servers below will also allow users to subset, visualize, and download data in many formats (e.g., text, graphics, etc.). Users can access the data files through the following methods. (There will be a Readme file along with subdirectories.)
- Anonymous FTP
Download ASCII versions of the Blended Sea Winds data from our FTP area. This type of access is for individuals who have experience with FTP and programming languages.
Use Unix access to download the Blended Sea Winds data using the following method.
- Open eclipse.ncdc.noaa.gov
- login as anonymous
- password is your email address
- cd /pub/seawinds
The OPeNDAP/THREDDS Data Server allows you to subset and aggregate data from multiple data files, or open/transfer the data on the fly to your applications (e.g., in MATLAB, GrADS, etc.)
Disclaimer for Near-Real-Time Products (NRT)
A version of NRT (about a 24-hour delay) Blended Sea Winds is produced quasi-daily to satisfy the needs of some users. Since the updates are done automatically under a non-operational environment (no 24/7 IT support), timely production is not guaranteed. File naming conventions are very similar, i.e., uv20080101rt.nc (NRT with 'rt'=real time) and uv20080101.nc (Research Quality – version 1.2).
Frequently Asked Questions
- How can I get your data?
ANSWER: Use one of the methods listed in the Data Access section above. For data sub-setting (for a specific region and/or time period), in addition to the LAS and OPeNDAP/TDS servers, users can also use wget with region/time constraints. See my_wget.sh as an example.
- How often are the blended products are updated?
ANSWER: A set update frequency for the products has not been determined yet, but we update them at least once per quarter. This lack of a set update schedule is due to the input satellite data being in two forms: one with more stringent quality control and a lag time of about three to four weeks and the other that is provided in near real time but with less strict quality control. To date, we have produced the Blended Sea Winds datasets using the more strictly quality controlled satellite data, resulting in a delay of a few weeks. However, we do feel there is a need to produce the dataset in near real time. This is an area that user feedback plays an important role. Thus, we encourage you to fill out the user registration form and let us know what your needs are and how you are using our products.
- While getting the large datasets, some times a few files will got lost. How can I prevent this?
ANSWER: Especially for getting large datasets, we encourage you to use lftp instead of ftp because it allows repeated gets (m-get) to retrieve missed data files. See my_lftp.sh for an example.
- For the early time period (e.g., early January 1988), I get a field with only the bad flag value (-9999.0000). Why?
ANSWER: In the early days of the dataset (July 9, 1987–December 7, 1990), only the SSMI F13 satellite was available to provide data and at times retrieving data from it failed. In particular, no observational data is available from December 3, 1987 to January 12, 1988, and thus all values for that period are “bad” = -9999 globally.
- Sometimes I see wind data over some coastal land grid. Why?
ANSWER: The global 0.25-degree gridded products were generated using a Gaussian-like interpolation with a spatial radius of 62.5 km. The interpolations were done over the global 0.25-degree grid. No cleaning has been done over land along the coast (+/- 0.25 degree) because some users want this information for coastal applications. A topographic dataset on the blended wind grid is provided in this directory (see topo15g*).
- Sometimes I see noisy (unreasonably large) stress data points. Why?
ANSWER: We are aware of the noisy stress, and a new version of the wind stress data is in progress. The data currently provided are calculated by scaling the NCEP Reanalysis 2 (NRA2) stress by the ratio of blended satellite wind speed of the NRA2 wind speed squared (for stress). Thus, in areas where NRA2 winds are near zero while the Blended Seawinds are not near zero, you will see “geophysically unrealistic wind stress.” The NRA2 also contains noisy stresses. In the future, the wind stress will be computed using the COARE3.0 bulk formula. This will avoid nearly all of the issues with unrealistic air-sea fluxes associated with NWP and climate models. Turbulent air-sea heat fluxes will also be available.
The Readme files provide detailed data structures and support reading programs.
Zhang, H.-M., J. J. Bates, and R. W. Reynolds, 2006: Assessment of composite global sampling: Sea surface wind speed, Geophysical Research Letters, 33, L17714, http://dx.doi.org/10.1029/2006GL027086.
Zhang, H.-M., R.W. Reynolds, and J.G. Bates, 2006: Blended and gridded high resolution global sea surface wind speed and climatology from multiple satellites: 1987–present. 14th Conference on Satellite Meteorology and Oceanography, Atlanta, GA, American Meteorological Society, Paper 100004. [Available online at https://ams.confex.com/ams/Annual2006/webprogram/Paper100004.html.]
Peng, G., H.-M. Zhang, H.P. Frank, J.-R. Bidlot, M. Higaki, S. Stevens, and W.R. Hankins, 2013: Evaluation of various surface wind products with OceanSITES buoy measurements. Weather and Forecasting, 28, 1281–1303, doi:10.1175/WAF-D-12-00086.1.
Huai-Min Zhang, PhD
NOAA/NESDIS/National Centers for Environmental Information
151 Patton Ave
Asheville, NC 28801