A Long-Term Record of Photosynthetically Available Radiation (PAR) and Total Solar Energy at 38.6°N, 78.2°W

• Published in: Estuaries Vol. 26; no. 6; pp. 1450 - 1460
• Main Authors: Fisher, Thomas R., Gustafson, Anne B., Radcliffe, Gregory M., Sundberg, Karen L., Stevenson, J. Court
• Format: Journal Article
• Language: English
• Published: Lawrence, KS Estuarine Research Federation 01.12.2003; Springer Nature B.V
• Subjects: Animal and plant ecology; Animal, plant and microbial ecology; Aquatic environment; Biological and medical sciences; Brackish water ecosystems; Climatology; Cloud cover; Datasets; Energy value; Estuaries; Frequency distribution; Fundamental and applied biological sciences. Psychology; Optical thickness; Photosynthesis; Photosynthetically active radiation; Phytoplankton; Primary production; Pyranometers; Radiation; Sensors; Solar energy; Solar radiation; Synecology; Time series; Water column; Estuaries; Brackish water environment; Long term
• ISSN: 0160-8347; 1559-2723; 1559-2758; 1559-2731
• DOI: 10.1007/BF02803653

Photosynthetically available radiation (PAR; 400-700 nm, E m-2 d-1) is the fraction of the total solar energy (Mjoules m-2 d-1) that is used by organisms for photosynthesis and vision. We present a statistical summary of a 17-yr time series of PAR data (1982-1998) collected near Chesapeake Bay as well as a second set of data on PAR and total solar energy gathered over a shorter time span (1997-1998). The time series data (5,126 daily totals) varied between 1-67 E m-2 d-1 and were used to estimate the minimum and maximum values of PAR as a function of day of the year. In monthly frequency distributions of the PAR data, three modes were observed corresponding to sunny, partly cloudy, and overcast days. The second set of PAR and total solar energy data were used to examine the ratio of PAR to total solar energy, which was 2.04 E Mjoule-1 for PAR between 10 and 70 E m-2 d-1. On overcast days, the ratio increased to as high as 3 E Mjoule-1 as PAR increased in importance as a fraction of the total solar energy. These values were consistent with others in the literature, and the relationships reported here can be used to predict the climatology of PAR and total solar energy within the Chesapeake region. The PAR data were also combined with reported minimum values of PAR for net primary production in the surface mixed layer of the water column of aquatic systems to estimate the combinations of mixed layer depth and diffuse attenuation coefficient (number of optical depths) under which light limitation of phytoplankton primary production is expected to occur.