PAR COMPARISON


Resources

We compare moored PAR measurements from MBARI mooring locations in Monterey Bay and the equatorial Pacific to PAR products available for model forcing. The PAR products for comparison to moored observations include:

Access to MBARI moored daily integrated PAR:


Methods

The PRR-600 instrument provided 10-minute PAR (400-700 nm) measurements at MBARI bio-optical mooring locations in the Monterey Bay region and equatorial Pacific regions. These were integrated relative to the solar day and averaged to the appropriate interval for NCEP (7-day) and SeaWiFS (8-day).

The SeaWiFS and M1 PAR were converted from Einsteins m-2 day -1 to W m-2 using the conversion:
(6.02e23 quanta/Ein) / (86,400 seconds/day * 2.77e18 quanta/s/W)
where the factor 2.77e18 quanta s-1 W-1 converts in the PAR range to an accuracy of a few percent (Morel and Smith, 1974).

NCEP short wave radiation was converted from langley s-1 to W / m2 according to:
1 langley s-1 = 1 cal cm-2 s-1 = 41,868 W m-2
PAR was computed as 0.45*Qsw.


Results

Bottom Line: None of the incident light products that can be used for forcing the model accurately represent incident light during spring and summer in the Monterey Bay region. All products overestimate incident light during this period, but not winter. The bias appears to be due to inaccurate representation of clouds and fog. We do not see the same problem in comparing equatorial Pacific moored light observations with these same products.

The first comparison is at the Monterey Bay mooring M1 (36.75°N, 122.03°W); note that M2 is close to M1 and shows very similar results.





The second comparison is at the MBARI equatorial Pacific mooring EP1 (155°W on the equator).