Observations of stable nocturnal boundary layers over the heterogeneous surface of northern Alabama

This paper documents observations of the moderately stable nocturnal boundary layer over heterogeneous terrain during an intensive observational study conducted near Huntsville during the period 23 October to 1 December 1999. This analysis focuses on two cases, 5 and 9 November. Observations include 3-hour serial soundings between 0 and 12Z, 915 MHz wind profiler, sodar wind and ceilometer observations, hourly RASS soundings, and surface mesonet observations (including 30m and 100 m instrumented towers). For both cases, the observational area was located to the west of surface based high pressure, under clear skies, and a 10K surface based inversion developed approximately 150 m deep. However, wind, moisture and thermal characteristics were quite different. This paper will characterize the boundary layer for these specific cases by describing the stability regime and details of the evolving airflow within the NBL . The surface mesonet was used to determine surface flows, such as subtle surface drainage, and to observe the occurrence and behavior of bursting associated with the intermittent breakdown of the stable nocturnal boundary layer. Particular attention will be placed on the sodar data. The sodar was operated at 20-m gate spacing, with the lowest gate at 40 m. Sodar backscattered power and vertical motion fields will be used to describe and characterize transient features occurring during the two nocturnal observational periods, and to determine the relation of elevated transients to surface observations.