Revisiting the Local Scaling Hypothesis in Stably Stratified Atmospheric Boundary Layer Turbulence: an Integration of Field and Laboratory Measurements with Large-eddy Simulations

The `local scaling' hypothesis, first introduced by Nieuwstadt two decades ago, describes the turbulence structure of stable boundary layers in a very succinct way and is an integral part of numerous local closure-based numerical weather prediction models. However, the validity of this hypothesis under very stable conditions is a subject of on-going debate. In this work, we attempt to address this controversial issue by performing extensive analyses of turbulence data from several field campaigns, wind-tunnel experiments and large-eddy simulations. Wide range of stabilities, diverse field conditions and a comprehensive set of turbulence statistics make this study distinct

Screen level temperature increase due to higher atmospheric carbon dioxide in calm and windy nights revisited

Long-term surface observations over land have shown temperature increases during the last century, especially during nighttime. Observations analyzed by Parker [2004] show similar long-term trends for calm and windy conditions at night, and on basis of this it was suggested that the possible effect of urban heat effects on long-term temperature trends are small. On the other hand, a simplified analytic model study by Pielke and Matsui [2005, henceforth PM05] suggests that at night the resultant long-term temperature trends over land should depend on height and strongly on wind speed (mostly due to alterations in the rate of nocturnal cooling in the stable boundary layer (SBL)). In this paper we expand the PM05 study by using a validated atmospheric boundary-layer model with elaborated atmospheric physics compared to PM05, in order to explore the response of the SBL over land to a change in radiative forcing. We find that the screen level temperature response is surprisingly constant for a rather broad range of both geostrophic wind speed (5-15 ms-1) and 10 meter wind (2-4.0 ms-1). This is mostly due to land surface-vegetation-atmosphere feedbacks taken into account in the present study which were not considered by PM05

Response and sensitivity of the nocturnal boundary layer over land to added longwave radiative forcing

One of the most significant signals in the thermometer-observed temperature record since 1900 is the decrease in the diurnal temperature range over land, largely due to rising of the minimum temperatures. Generally, climate models have not well replicated this change in diurnal temperature range. Thus, the cause for night-time warming in the observed temperatures has been attributed to a variety of external causes. We take an alternative approach to examine the role that the internal dynamics of the stable nocturnal boundary layer (SNBL) may play in affecting the response and sensitivity of minimum temperatures to added downward longwave forcing. As indicated by previous nonlinear analyses of a truncated two-layer equation system, the SNBL can be very sensitive to changes in greenhouse gas forcing, surface roughness, heat capacity, and wind speed. A new single-column model growing out of these nonlinear studies is used to examine the SNBL. Specifically, budget analyses of the model are provided that evaluate the response of the boundary layer to forcing and sensitivity to mixing formulations. Based on these model analyses, it is likely that part of the observed long-term increase in minimum temperature is reflecting a redistribution of heat by changes in turbulence and not by an accumulation of heat in the boundary layer. Because of the sensitivity of the shelter level temperature to parameters and forcing, especially to uncertain turbulence parameterization in the SNBL, there should be caution about the use of minimum temperatures as a diagnostic global warming metric in either observations or models