Satellite-based Ocean Vector Wind Climate Data Record

Abstract:

We will describe our progress in bringing consistency to satellite observations of ocean vector winds from several space-based sensors, with an accuracy required for climate analyses. Surface wind speed and direction are identified as one of the essential atmospheric Environmental Parameters, as they drive atmospheric and oceanic processes with impact on long term global climate variability.

Most of the space-based wind vector observations are from scatterometers, which started in 1991 with ERS, followed by QuikSCAT, ASCAT and recently by RapidScat, and by the polarimetric radiometer WindSat. Our main goal is to intercalibrate all these measurements, in order to develop a 25-yr Climate Data Record (CDR) of ocean vector winds. Our approach is to intercalibrate all the scatterometer wind speeds to those from microwave radiometers. We first reprocessed all the radiometer data starting from 1988 with a common Radiative Transfer Model, the RSS V7, and then used those winds speed as calibration target to develop the model function (GMF) for each scatterometer type, at three frequency bands and for a wide range of incidence angles. The following intercalibrated scatterometer dataset have been reprocessed at RSS and are available to the public: ASCAT, QuikSCAT, RapidScat, and Aquarius. Next, we plan to process the ERS data, in order to complete the timeseries starting from 1991.

We will discuss our methodology, present results on the consistency of all these wind datasets among themselves and versus buoy data, show examples on how they are already used for climate research, and discuss other issues that need to be addressed before merging all the data into a unique CDR, like diurnal variability aliases, and other spurious biases that might affect the data.

Finally, we will introduce a newly reprocessed satellite-based wind vector analysis dataset, the Cross-Calibrated Multi-Platform (CCMP) winds Version 2. They have been recently reprocessed at RSS using consistent winds as input from the V7 radiometers and the QuikSCAT and ASCAT scatterometers. The CCMP V2 dataset additionally uses buoy data as input, and ERA-Interim surface winds as a background field for the variational analysis that leads to the final product. The CCMP V2 consists of 6-hourly global wind vector maps gridded at 0.25 degrees, starting from 1988 until 2014.