The evolution of the nocturnal boundary layer in Houston, TX was examined using high-temporal resolution tethersonde profiles taken during the TexAQS II field campaign. The measurements were made at the University of Houston campus, located approximately 4 km southeast of the downtown Houston central business district, and consisted of vertical profiles of potential temperature, water vapor mixing ratio, wind speed, wind direction, and ozone concentration up to a maximum height of 400 m AGL. Profiles were taken at approximately 30 min intervals throughout selected nights during Intensive Observational Periods (IOPs), including both the evening and morning transitional periods. Tethersonde experiments also were performed during a few additional morning break-up periods during the campaign.

Preliminary results from the night of Sept 7-8, 2006 showed that the stability during the evening transition period remained near neutral in the lowest 200 m AGL. Cooling occurred uniformly within this layer but stronger surface cooling appeared to be delayed; it ultimately began between 2130 – 2315 CDT and continued through 0430 CDT. In the early morning an elevated bluff-like structure developed in the virtual potential temperature profiles indicating neutral stability within the 50 - 100 m AGL level. Just before sunrise a neutral layer with constant potential temperature developed between the surface and 50 m AGL indicating mixing processes occurring near the surface. Further analyses will be presented for the additional morning transitional and overnight period profiles taken during the campaign.