Obtaining a diurnal climatology of the boundary layer along the California coast using ACARS

The atmospheric boundary layer along the coast of California plays a key role in the day-to-day weather that can significantly affect coastal communities and airports. For instance, stability near the surface is related to pollution events in Los Angeles and air traffic can be halted due to fog or low stratus. Radiosondes are typically launched twice daily and are the traditional source of lower atmospheric measurements. A growing number of commercial aircraft carry meteorological instruments that collect data including temperature, wind, and sometimes humidity at previously unavailable temporal scales. A common way to refer to the whole dataset is the Aircraft Communications Addressing and Reporting System (ACARS), but other names include the Meteorological Data Collection and Reporting System (MDCRS), Aircraft Meteorological Data Relay (AMDAR), and Tropospheric AMDAR (TAMDAR).

Especially at busy airports, the high frequency of soundings from ACARS since 2001 provides an opportunity to produce a climatological record of the diurnal cycle of the lower atmosphere including wind patterns, boundary layer height, and inversion strength which has not been done at this resolution over such a long time period. This study explores both the difficulties associated with using ACARS to produce a robust climatology and also the benefits of using ACARS to characterize the lower atmosphere. One key example is at Los Angeles International Airport (LAX). Since large horizontal gradients exist at the coast, a clear and significant difference in the characteristics of the boundary layer was found between the flight paths occurring east of the airport (offshore) and those to the west of the airport (inland). Thus, flight path must be considered when constructing the climatology or even when ingesting the data into model analysis fields. When applying ACARS data to depict the diurnal cycle of events such as the Catalina eddy, these issues must be considered or the results will be distorted.