Clouds & The Earths Radiant Energy System (CERES) Synoptic (SYN1deg) Data Product Validation Using Buoys & Ship Borne Radiometers

The Clouds and the Earth's Radiant Energy System Synoptic (SYN1deg) data product provides climate-quality, global, gridded top of atmosphere (TOA), in-atmosphere, and surface radiant fluxes. Column fluxes are computed hourly with radiative transfer (RT) code using inputs from Terra and Aqua Moderate Resolution Imaging Spectroradiometer (MODIS), hourly geostationary (GEO) data (when MODIS is unavailable), and meteorological assimilation data from the Goddard Earth Observing System. The GEO visible and infrared imager calibration is tied to MODIS to ensure uniform MODIS-like cloud properties across all satellite cloud datasets. When neither CERES nor GEO data are available, cloud properties and TOA radiation are interpolated through time. The radiation transfer model used is a highly modified version of the Fu & Liou radiative transfer code with calculations archived on the SYN1deg at five atmospheric levels for each grid cell. We present here the validation of the SYN1deg RT model calculations over oceans.

Validation of SYN1Deg at the Earth's surface relies on systematic comparison with broadband radiometric observations by quality surface stations around the globe. Land based sites provide well maintained and calibrated instruments for comparisons. We maintain a database of observations collected from a number of sites including data from the Baseline Surface Radiation Network (BSRN), NOAA's Global Monitoring Division, the Surface Radiation Network (SURFRAD), and the U.S. Department of Energy's Atmospheric System Research (ASR) program. These data (as hour averages) can be accessed along with the SYN1deg calculations at: https://ceres-tool.larc.nasa.gov/cave/jsp/CAVESelection.jsp. Though most long-term surface observation data sets exist on land, comparisons of SYN1deg calculations over ocean are critical given the importance of oceans on long-term climate trends. However ocean observations are more sporadic and less geographically diverse with most buoys located in the tropics. Ships provide some observations but require careful consideration as they trace a path simultaneously through space and time within the SYN1deg data set. Also, buoy and ship observations can be problematic due to a number of reasons. Buoy instruments lack regular cleaning, sway, and maintain simpler instrumentation. The difference between radiant fluxes from SYN1Deg and buoy observations, however, does not appear to strongly depend on meteorological conditions such as wind speed and precipitation rate. Ship based instruments are subject to roll and pitch and contamination of the signal by aerosols from ship exhaust. Nonetheless comparisons of land and ocean based observations to the SYN1deg product show similar bias and root mean square differences (RMS) over long time periods. For example 37 land based sites for 8 years of 3-hourly comparison showed bias (RMS) for SW of 1%(28%) for land-based sites and 2%(26%) for ocean buoys. In LW there are similar statistics with 1%(6%) for the land-based sites and 1%(3%) for the buoys. The smaller RMS for the buoys is attributed to the fact that most buoys are located in the tropics where downwelling longwave flux is driven by large water vapor loadings and near surface temperature that do not vary significantly over the year.

In this work we show comparisons of SYN1deg calculations to 49 buoys, 7 EPIC/PACS ship cruises, 9 WHOI Stratus Buoy Deployment Cruises and a number of DOE/ARM mobile facility “MAGIC” cruises between Los Angeles and Hawaii. On both the STRATUS and EPIC cruises part of their task was to deploy meteorological buoys observing both longwave and shortwave downwelling radiation allowing simultaneous comparisons of SYN1deg calculations to ship and buoy radiometers. We find that the RMS between the SYN1deg and ship and buoys are similar though ship and buoy observations are more highly correlated.