The Ocean Color Radiometry data portal of the NASA Giovanni system recently added mission-long climatology files from the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) mission, which were generated by the Ocean Biology Processing Group (OBPG)
at NASA Goddard Space Flight Center. Addition of these files to Giovanni restores the capability to create monthly, seasonal, and annual anomaly visualizations with SeaWiFS standard data products. Previously, Giovanni had used 10-year long SeaWiFS climatology files, but these files were removed due to data reprocessings and changes to the data file format. For the months of September-December, the climatology files are thirteen years long; for all other months, the climatology files are twelve years long.
The new climatology files now include data products which had not been previously available in Giovanni. All of the ocean remote-sensing radiance (Rrs) data products for SeaWiFS bands at 412, 443, 490, 510, 555, and 670 nanometers are now available; the previous data products had consisted of normalized water-leaving radiances (nLw). Other ocean data products available are the diffuse attenuation coefficient at 490 nanometers (K490), particulate organic carbon (POC), particulate inorganic carbon (PIC), and photosynthetically available radiation (PAR). In addition to these data products, two atmospheric data products are provided in the system, the aerosol optical thickness at 865 nanometers (τ865) and the Angström coefficient. These data products were generated in the atmospheric correction calculations for SeaWiFS ocean data. [The SeaWiFS aerosol data are now being compared to other atmospheric aerosol data to improve quantification of atmospheric aerosol concentrations, which was the subject of a poster presentation at the recent American Geophysical Union 2011 Fall Meeting in San Francisco, California.]
To demonstrate the new anomaly visualization capabilities with these data products, the effects of the record-breaking 1997-1998 El Niño event in the eastern equatorial Pacific Ocean were examined. Each of the Giovanni map plots shown here was created with a customized color palette, to enhance the visibility of the anomalies. Figure 1 shows the anomaly of chlorophyll a (chl a) concentration. The Peru Upwelling Region on the coast of Peru is one of ocean’s strong permanent coastal upwelling zones, an area of high phytoplankton productivity, where nutrient-laden deep ocean waters are pushed to the surface by wind-driven ocean currents. Warm waters from El Niño suppressed the strength of the upwelling, causing a marked negative anomaly in chl a concentrations along the coast. The newly available POC climatology allows a correlated quantification of how much the phytoplankton biomass was reduced by this event (Figure 2); in the central upwelling zone, the anomaly was greater than 200 milligrams of organic carbon per cubic meter of seawater.
Figure 1. SeaWiFS chlorophyll a concentration anomaly for the period January-February 1998 in the eastern equatorial Pacific Ocean. The marked decrease in phytoplankton productivity due to the El Niño event is seen as a deep negative anomaly along the coast of Peru and extending to the Galapagos Islands.
Figure 2. SeaWiFS particulate organic carbon (POC) anomaly for the period January-February 1998 in the eastern equatorial Pacific Ocean. The POC anomaly is due to the reduction of phytoplankton populations in the Peru Upwelling Zone, caused by the reduction in surface nutrient concentrations induced by the suppression of coastal upwelling during the El Niño event. El Niño events were initially noticed by Peruvian fishermen due to the impact on anchovies and sardines that feed on phytoplankton in the Peru Upwelling Zone.
Figure 3 demonstrates an associated effect of El Niño due to altered weather patterns over the ocean. Because warm water that is normally in the western Pacific Ocean moves eastward during the event, cloud cover from convection over the warm water mass is increased. The increased cloud cover reduces the amount of sunlight reaching the ocean surface, which is expressed in the value of PAR, the solar radiation that can be used by plants for photosynthesis. Figure 3 displays the widespread PAR anomaly that occurred during the height of the 1997-1998 Niño.
Figure 3. Anomaly of Photosynthetically Available Radiation (PAR) in the eastern Equatorial Pacific for January-February 1998 during the El Niño event. Warmer surface water in the eastern Pacific creates increased cloud cover, which reduces the amount of sunlight reaching the ocean surface. Thus, the blue negative anomaly region shows the extent of increased cloud cover overlying the warm surface waters during the event.
Restoration of SeaWiFS climatology files to Giovanni now allows further research analyses with this important data set. Work is in progress to add climatology files from the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument on the Aqua platform, including sea surface temperature (SST) data. This addition will be the first time that SST data is available for anomaly analysis in Giovanni.
Funding for support of ocean color radiometry data in Giovanni is provided through the "Water Quality for Coastal and Inland Waters Project", NNX09AV57G, from the National Aeronautics and Space Administration (NASA), and the National Oceanographic Partnership Program (NOPP) project, "Development, Assessment and Commercialization of a Biochemical Profiling Float for Calibration and Validation of Ocean Color and Ocean Carbon Studies" (Emmanuel Boss, University of Maine, PI).
The GES DISC and the Ocean Biology Processing Group are NASA earth science data centers, part of the NASA Earth Science Data and Information System (ESDIS) Project.