Clouds, Precipitation and Marine Boundary Layer Structure during the MAGIC Field Campaign

English Abstract:

The recent ship-based MAGIC field campaign with the marine-capable Second ARM Mobile Facility (AMF2) deployed on the Horizon Lines cargo container M/V Spirit provided nearly 200 days of intra-seasonal high-resolution observations of clouds, precipitation and marine boundary layer (MBL) structure on multiple legs between Los Angeles, California, and Honolulu, Hawaii. During the deployment, MBL clouds exhibited a much higher frequency of occurrence than other cloud types and occurred more often in the warm season than in the cold season. MBL clouds demonstrated a propensity to produce precipitation, which often evaporated before reaching the ocean surface. The formation of stratocumuli is strongly correlated to a shallow MBL with a strong inversion and a weak transition, while cumuli formation is associated with a much weaker inversion and stronger transition. The estimated inversion strength (EIS) is shown to depend seasonally on the potential temperature at the 700 hPa. The location of the commencement of systematic MBL decoupling (DE) always occurred eastward of the locations of cloud breakup (CBs), and the systematic decoupling showed a strong moisture stratification. The entrainment of the dry warm air above the inversion appears to be the dominant factor triggering the systematic decoupling, while surface latent heat flux, precipitation and solar radiation did not play major roles. MBL clouds broke up over a short spatial region due to the changes in the synoptic conditions, implying that in real atmospheric conditions, the MBL clouds do not have enough time to evolve as is in the idealized models.