Surface Energy Fluxes over the Eastern North Pacific Measured during the MAGIC Field Campaign

The MAGIC field campaign, funded and operated by the ARM (Atmospheric Radiation Measurement) Climate Research Facility of the US Department of Energy, occurred between September 2012 and October, 2013 aboard the Horizon Lines cargo container ship Spirit making regular trips between Los Angeles, CA and Honolulu, HI. Along this route, which lies very near the GPCI (GCSS Pacific Cross-section Intercomparison) transect, the predominant cloud regime changes from stratocumulus near the California coast to trade-wind cumulus near Hawaii. The transition between these two regimes is poorly understood and not accurately represented in models. The goal of MAGIC was to acquire statistic of this transition and thus improve its representation in models by making repeated transects through this region and measuring properties of clouds and precipitation, aerosols, radiation, and atmospheric structure. To achieve these goals, the Second ARM Mobile Facility (AMF2) was deployed on the Horizon Spirit as it ran its regular route between Los Angeles and Honolulu. AMF2 consists of three 20-foot SeaTainers and includes three radars, lidars, a ceilometer, microwave radiometers, a total sky imager, disdrometers, and other instruments to measure properties of clouds and precipitation; a condensation particle counter, a cloud condensation nuclei counter, an Ultra-High sensitivity Aerosol Spectrophotometer (UHSAS), a three-wavelength nephelometer that operates under ambient conditions and controlled relative humidity, and a Particle Soot Absorption Photometer operating at three wavelengths to measure properties of aerosols; a Precision Spectral Pyranometer, a Sunshine Pyranometer, a Precision Infrared Radiometer, a Fast-Rotating Shadowband Radiometer, a Solar Array Spectrophotometer, and other instruments to measure properties of radiation; and instruments to measure meteorological quantities and sea surface temperature. Two technicians accompanied the AMF2, and scientists rode the ship as observers. Radiosondes were routinely launched four times daily, and during one round trip in July, 2013, eight radiosondes were launched each day. In total, more than 550 soundings were made. MAGIC made nearly 20 round trips between Los Angeles and Honolulu (and thus nearly 40 excursions through the stratocumulus-to-cumulus transition) and spent 200 days at sea, collecting an unprecedented data set.

With the suite of instruments available during MAGIC, surface energy fluxes were measured and/or calculated, and a time series of total energy fluxes for the entire deployment was acquired. The bulk aerodynamic method was used to calculate fluxes of surface and latent heat based on measurements of wind speed, temperature, relative humidity, and sea surface temperature. Downwelling shortwave and longwave radiation fluxes were measured directly, and upwelling shortwave and longwave radiation fluxes were calculated based on tabulated values of the sea surface albedo and on the sea surface temperature and emissivity of seawater, respectively. The contribution to energy fluxes from precipitation was included, although this was negligible in most instances. These energy fluxes are discussed and compared with other meteorological and environmental parameters.