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Photosynthetically Active Radiation (PAR) Average Annual Maximum Anomaly, 2002-2013 - Hawaii

Published by Pacific Islands Ocean Observing System (PacIOOS) | National Oceanic and Atmospheric Administration, Department of Commerce | Metadata Last Checked: January 27, 2026 | Last Modified: 2017-03-14T00:00:00.000+00:00
Solar irradiance is one of the most important factors influencing coral reefs. As the majority of their nutrients are obtained from symbiotic photosynthesizing organisms, reef-building corals need irradiance as a fundamental source of energy. Seasonally-low irradiance at high latitudes may be linked to reduced growth rates in corals and may limit reef calcification to shallower depths than that observed at lower latitudes. However, high levels of irradiance can lead to light-induced damage, production of free radicals, and in combination with increased temperatures, can exacerbate coral bleaching. This layer represents the annual average of the maximum anomaly of irradiance (mol/m2/day) from 2002 -2013. Irradiance is here represented by PAR (photosynthetically active radiation), which is the spectrum of light that is important for photosynthesis. Monthly and 8-day 4-km (0.0417-degree) spatial resolution data were obtained from the MODIS (Moderate-resolution Imaging Spectroradiometer) Aqua satellite instrument from the NASA OceanColor website (http://oceancolor.gsfc.nasa.gov). The PAR average annual maximum anomaly was calculated by taking the average of the annual maximum PAR values in exceedance of the maximum monthly climatological PAR from 2002-2013 for each pixel. A quality control mask was applied to remove spurious data associated with shallow water, following Gove et al., 2013. Monthly climatologies were calculated from monthly time series using only full years over the Ocean Tipping Points (OTP) project time frame of interest (2002-2013). Time series of anomalies were calculated by quantifying the number and magnitude of events from the 8-day time series that exceed the maximum climatological monthly mean. Nearshore map pixels with no data were filled with values from the nearest neighboring valid offshore pixel by using a grid of points and the Near Analysis tool in ArcGIS then converting points to raster.

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