System for Analysis of Wind Collocations (SAWC): A Novel Archive and Collocation Software Application for the Intercomparison of Winds from Multiple Observing Platforms

The 2017-2027 decadal survey listed accurate atmospheric 3D winds as a high priority in the science community. Numerous studies, most involving atmospheric motion vectors (AMVs), have been conducted over the years to address this requirement; however, the results from these studies are not easily comparable, as they tend to use widely varying collocation criteria. As there are few collocation standard accepted in the literature and broader wind community, researchers are often forced to invent their own criteria and algorithms. Further, researchers often need to acquire and reformat disparate data from numerous sources, and develop their own analysis tools, all of which can be time-consuming and delay progress.

In support of researchers’ needs to acquire and analyze wind data from multiple sources, and to further address the 3D wind requirement, the System for Analysis of Wind Collocations (SAWC) was jointly developed by the NOAA/NESDIS/Center for Satellite Applications and Research (STAR), the University of Maryland/Cooperative Institute for Satellite Earth System Studies (CISESS), and the University of Wisconsin-Madison/Cooperative Institute for Meteorological Satellite Studies (CIMSS). SAWC provides the data and tools one needs for wind observation research in one place: a multi-year archive of global wind observations uniformly formatted in NetCDF—a universally accepted format—as well as select identified pairings of winds collocated in space and time, and a collocation software application developed for their intercomparison. At present, the archived datasets include Aeolus Level-2B (L2B) lidar winds from the European Space Agency (ESA), AMVs derived from satellite imagery and processed by the NOAA/National Centers for Environmental Prediction (NCEP), and in situ winds observed by aircraft, sondes, and stratospheric superpressure balloons from Loon, a former subsidiary of Google’s parent company Alphabet. The archived data span the entire lifetime of Aeolus (September 2018 – April 2023), except for the acquisition of AMVs and aircraft and sonde winds that continues beyond Aeolus’ lifetime to Present Day, and the Loon record that runs from 2011 to 2021 when the Loon project ended. SAWC is publicly available at https://www.star.nesdis.noaa.gov/data/sawc.

In this presentation, the utility of SAWC is demonstrated through a one-year (September 1, 2019-August 31, 2020) evaluation of Aeolus Rayleigh-clear and Mie-cloudy horizontal line-of-sight (HLOS) winds. Unique collocation techniques developed to match winds based on specified criteria are employed between Aeolus winds and the other four archived wind datasets, which are projected onto the Aeolus HLOS direction prior to analysis. Recommended quality controls are applied. Wind comparisons are assessed using the SAWC collocation application. Comparison statistics are stratified by season, geographic region, and Aeolus observing mode. The results emphasize the potential value of SAWC, from product validation and observation error characterization to advancements in the global Earth observing architecture. Further, SAWC’s capabilities could be employed to test and establish new wind collocation standards, as has been recommended in order to keep up with advancements in wind retrieval technologies and numerical weather prediction systems (e.g., AMV algorithm improvements, higher resolutions, and advanced global data assimilation (DA) systems), as well as to support observation error parameterizations in DA systems.