Observed differences in boundary layer structures between pristine pine forests and fire-burned landscapes

We deployed, in August 2010, the NCAR Mobile GPS Advanced Upper-Air Sounding System (MGAUS) at two mountain sites with similar elevations: the NCAR Manitou Forest Observatory (MFO) characterized by pristine ponderosa pines in Woodland Park, CO, and a nearby Hayman wildfire burned site. Two 2-day intensive campaigns with hourly sounding launched simultaneously at two sites during stable-convective transition periods were conducted for wet (13-14 August) and dry (21-22 August) soil conditions. Surface wind are mostly southerly flow and range from 1-4 m s-1 so the development of boundary layer over these two sites are largely determined by local surface heterogeneities. Compared to the MFO site, surface air temperature (humidity) at Hayman is generally higher (lower); its transition from morning stable to convective boundary layer is about an hour earlier; and the convective boundary layer collapses is delayed by about an hour. The profile of virtual potential temperature and wind speed are used to determine the boundary layer depths. Results show deep convective boundary layer (depths > 3000 m) over both sites. Daytime mixing layers over the Hayman site are deeper than that over MFO; such difference is enhanced when soils at both sites are dry and the peak boundary-layer depth over Hayman is about 400 m higher than that over MFO. Differences in these daytime and nighttime boundary-layer characteristics can impact forest air pollution and regional weather.