Diurnal Evolution and Annual Variability of Boundary-Layer Height and Its Correlation to Other Meteorological Variables in California’s Central Valley

Abstract

One year of observations from a network of five 915-MHz boundary-layer radar wind profilers equipped with radio acoustic sounding systems located in California's Central Valley are used to investigate the annual variability of convective boundary-layer depth and its correlation to meteorological parameters and conditions. Results from the analysis show that at four of the sites, the boundary-layer height reaches its maximum in the late-spring months then surprisingly decreases during the summer months, with mean July depths almost identical to those for December. The temporal decrease in boundary-layer depth, as well as its spatial variation, is found to be consistent with the nocturnal low-level lapse rate observed at each site. Multiple forcing mechanisms that could explain the unexpected seasonal behaviour of boundary-layer depth are investigated, including solar radiation, precipitation, boundary-layer mesoscale convergence, low-level cold-air advection, local surface characteristics and irrigation patterns and synoptic-scale subsidence. Variations in solar radiation, precipitation and synoptic-scale subsidence do not explain the shallow summertime convective boundary-layer depths observed. Topographically forced cold-air advection and local land-use characteristics can help explain the shallow CBL depths at the four sites, while topographically forced low-level convergence helps maintain larger CBL depths at the fifth site near the southern end of the valley.

Fine-Scale Variations of Near-Surface-Temperature Lapse Rates in the High Drakensberg Escarpment, South Africa: Environmental Implications

“…The typically reported nocturnal cold air drainage reducing lapse rates at night, along with steeper lapse rates during the day, in summer, or associated with STEFAN W. GRAB / 511 enhanced cyclonic activity (low pressure and high relative vorticity) (e.g. Pepin, 2001;Blandford et al, 2008;Gillies et al, 2010;Bianco et al, 2011), are all to a considerable extent masked along the Drakensberg escarpment. This is owing to regional-scale westerly winds (particularly during the austral winter and spring) bringing dry air over and down the Great Escarpment, eradicating clouds and thus steepening lapse rates towards the upper escarpment zone.…”

Estimation of atmospheric mixing layer height from radiosonde data

“…The mixing layer begins to develop after sunrise due to the increased turbulent fluxes associated with surface-absorbed solar radiation and heating (Medeiros et al, 2005;Liu and Liang, 2010). The value of h reaches its maximum during the late afternoon over land (Liu and Liang, 2010;Bianco et al, 2011;Svensson et al, 2011). Comparing Fig.…”

Eddy covariance emission and deposition flux measurements using proton transfer reaction – time of flight – mass spectrometry (PTR-TOF-MS): comparison with PTR-MS measured vertical gradients and fluxes

“…This was mainly due to the dilution of the emissions into a larger mixing layer and faster oxidation of BVOC during daytime. A detailed discussion of diurnal boundary layer dynamics in this area and season can be found in Bianco et al (2011).…”