AbstractsGeography &GIS

An ACARS climatology of the boundary layer near the coast of southern California

by Christopher John Mitchell

Institution: University of Kansas
Year: 2015
Keywords: Atmospheric sciences; Meteorology; ACARS; boundary layer; climatology; lower atmosphere; marine boundary layer; soundings
Posted: 02/05/2017
Record ID: 2091053
Full text PDF: http://hdl.handle.net/1808/21596


Typical late spring and early summertime conditions over California’s southern bight consist of a well-mixed coastal boundary layer (CBL) capped by warm and dry air associated with the subsiding branch of the subtropical Hadley circulation. The CBL in this region is often conceptualized as two overlapping layers that are laterally constrained on one side. The CBL significantly dominates daily weather throughout the southern California coastal region and is often responsible for frequent air traffic delays and impacts pollution events. An increasing number of commercial aircraft carry meteorological instruments that collect temperature and wind data at resolution scales. Fortunately since 2001 an abundance of sounding data has been achieved providing an opportunity to produce a climatological record of the diurnal cycle of the lower atmosphere. Meteorological variables such as wind patterns, boundary layer height, and inversion strength can be closely examined with high resolution over a record length of more than a decade. This study explores both the difficulties associated with using ACARS to produce a robust climatology and the benefits of using ACARS to characterize the lower atmosphere. Emphasis for this climatology is placed at Los Angeles International Airport (LAX). Considering distinct differences exist between the CBL just offshore and inland, data from nearshore flight paths must be analyzed when constructing CBL climatologies. Results from this study suggest the depth of the CBL depends greatly on downward mixing of radiatively cooled air from a cloud-topped CBL, and that the CBL does not deepen significantly on clear nights. The wind climatologies suggest downsloping northerly winds from the coastal mountain ranges directly to the north is unlikely the main control over the mean depth of the boundary layer because the CBL deepens at the peak time for northerly flow. In addition, southerly flow dominates the tops of the CBLs for both LAX and SAN throughout the morning and early afternoon, which is especially prominent for the CBL over LAX and suggestive of a low level coastal jet. Furthermore, persistent height difference exists between San Diego and Los Angeles with higher heights toward the south, forcing an acceleration of alongshore southerly flow overnight with a minimum in height difference and thus a minimum in the alongshore acceleration in the afternoon. Advisors/Committee Members: Rahn, David (advisor), Mechem, David (cmtemember), Braaten, David (cmtemember).