A Comparison of Algorithms for Determination of Marine Boundary Layer Height

English Abstract:

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. During MAGIC, radiosondes were routinely launched four times daily, and during one round trip in July, 2013, radiosondes were launched eight times daily. In total, more than 550 soundings were made. Boundary layer heights were calculated from the radiosonde data using several different algorithms. Some of these algorithms gave values that correspond to the abrupt decrease in the relative humidity with height that occurs above a well-mixed boundary layer, but others routinely underestimated the boundary layer heights and appeared to occur at heights at which no obvious transitions are occurring. Heights determined by the various algorithms are compared and reasons for the differences are examined.