While the CERES input aerosol optical depth and precipitable water data are continuously available, the same parameters derived from BSRN site measurements are available only intermittently. Cloudiness disrupts the aerosol optical depth (AOD) retrieval and precipitable water (w) observation sampling. Irregularly sampled records, such as these, can cause systematic biases if the averages of the continuous data are not sampled at the same times as the observed data, as shown by high biases in Fig. 10 in our original paper. This, however, does not suggest that the CERES input aerosol optical depth and precipitable water are systematically significantly higher than ground-based observations. In this addendum, we show that when the monthly means are computed from only those CERES hourly means that have a BSRN match, then the resulting monthly means differ from BSRN-derived parameters to a much lesser extent. To be precise, the biases in the original Fig. 10 decrease 82%, 69% and 52%, respectively; the magnitudes of slopes in the original Fig. 11 decrease by 69% and 65%, respectively. Imposing a cloud fraction less than or equal to 5% further reduces AOD and w mean values but not biases. Nevertheless, the flux bias reduces from -16.9 W m(-2) to -4.2 W m(-2) after imposing the cloud fraction restraint relative to the RADFlux clear-sky fluxes which appear to represent the driest and clearest conditions. Published by Elsevier Ltd.

Surface broadband shortwave and longwave irradiance are key components of the surface energy budget and give insight on atmospheric constituents like clouds and aerosols as well as provide useful information for model evaluation. Surface irradiance measurements are particularly difficult to make over the ocean where few measurement platforms exist, and where the motion of ships and buoys makes the accuracy of the measurements challenging. During the US DOE ARM Measurements of Aerosols, Radiation, and Clouds over the Southern Ocean (MARCUS) field campaign, new shipborne broadband radiation systems (SHIPRAD) were deployed for the first time to test correction. The systems include pyrgeometer measurements for measuring longwave irradiance, an unshaded pyranometer to measure shortwave irradiance, a navigation system measuring pitch/roll/heading, and an SPN1 shortwave radiometer that measures direct and diffuse components with no moving parts. A tilt correction methodology was used to correct 1 second temporal resolution shortwave irradiance data for ship motion, designed to correct tilts of 10 degrees or less to within 10 W/m2. Two SHIPRAD systems were deployed on the port and starboard sides of the ship, and the measurements were combined in order to be able to eliminate measurements shaded by ship structures. The new methodology allows for high-temporal resolution irradiance measurements with higher accuracy. Results will be presented on the accuracy of the tilt correction methodology and the irradiance measurement results throughout the campaign.