Past 2007 JCSDA Seminars

To Be Supplied

The Eumetsat Satellite Application Facility for Numerical Weather Prediction (the NWPSAF) forms part of the Eumetsat Distributed Ground Segment. The mission of the NWPSAF is to improve and support the interface between satellite data and products and European activities in global and regional NWP. The NWPSAF partnership involves the Met Office (coordinators), ECMWF, KNMI and Meteo France. An important focus of the NWPSAF is the development of software modules for use in NWP Data Assimilation (DA) systems. Deliverables to date, since the development phase of the project started in 1998, have included AAPP, RTTOV, a range of 1DVar schemes, the Quickscat Data Processor and the SSMIS preprocessor. The NWPSAF also has an active visiting scientist programme.

The QuikSCAT satellite was launched on June 19, 1999 into a sun-synchronous, circular, 803 km orbit with a local equator crossing time at the ascending node of 6:30am. QuikSCAT carries a conically-scanning, dual pencil beam Ku-band scatterometer that acquires global backscatter measurements at 47 degrees (H-pol) and 55 degrees (V-pol) incidence angles. These measurements yield high quality 25 km and 12.5 km spatial resolution surface wind vector retrievals over 90% of the world's oceans in a single day.

NOAA's National Environmental Satellite, Data, and Information Service (NESDIS) in cooperation with NASA/JPL has been providing near real-time QuikSCAT ocean surface wind vector products at 25 km and 12.5 km resolutions to the operational community since shortly after launch. Significant improvements in operational weather forecasting and warnings have been realized through utilization of these near real-time products. This real-world experience has also revealed some of the limitations of QuikSCAT, which is a research mission, with respect to the operational forecasting and warning environment.

To address some of these limitations the scatterometer project at JPL implemented several changes in the QuikSCAT processing algorithm, and since May 2006 these improvements have been implemented in a parallel test mode at NOAA / NESDIS / STAR. The NRT QuikSCAT processing improvements were validated by examining 6 months of vector wind data from 2003 processed with both the old and the new algorithms. Validation was conducted by the Ocean Surface Winds Team in STAR, with evaluation from the operational forecaster perspective being conducted by colleagues at the Ocean Prediction Center (OPC) and the Tropical Prediction Center (TPC). Results of these analyses are presented here, and show that the retrievals from the new processing performs better than those from the old processing, especially at the swath edges. Also, the rain impact flag, which results in less data being flagged as potentially contaminated by rain, does not result in a degradation of the overall wind vector retrieval. Project website and data links here.

The accuracy of analyses produced by modern data assimilation systems depends strongly on the precision of forecast error covariances specified as input. Typically, these errors are synoptically dependent, anisotropic, and and inhomogeneous. This talk will begin with a review of techniques used to date to represent flow-dependent errors in variational data assimilation systems. Current NCAR efforts in this direction are based on the WRF model, and are two-fold. Firstly, the application of 4D-Var implicitly introduces flow-dependent covariances via the use of a linearised forecast model (and its adjoint). Secondly, the use of ensemble-based forecast error covariances in 3/4D-Var via additional control variables in a hybrid approach is seen as a way to practically combine the best of both variational and ensemble approaches to data assimilation for operational NWP. Preliminary results from WRF applications for both 4D-Var and the hybrid will be presented.