Estimation of orographically induced wave drag in the stable boundary layer during the CASES-99 experimental campaign

This paper addresses the quantification of gravity wave drag due to small hills in the stable boundary layer. A single column atmospheric model is used to forecast wind and temperature profiles in the boundary layer. Next, these profiles are used to calculate vertical profiles of gravity wave drag. Climatology of wave drag magnitude and ¿wave drag events¿ is presented for the CASES-99 experimental campaign. It is found that gravity wave drag events occur for several relatively calm nights, and that the wave drag is then of equivalent magnitude as the turbulent drag. We also illustrate that wave drag events modify the wind speed sufficiently to substantially change the surface sensible heat flu

Een eerste inschatting van het Urban Heat Island effect voor Rotterdam en omgeving – een modelstudie

Tot nu toe is weinig bekend over het warmte-eiland effect in Nederland. Het doel van deze studie is om door middel van een modelstudie een eerste inschatting te maken van het warmte-eiland effect van de stad Rotterdam en naastgelegen omgeving, voor twee episodes in een hittegolf (in 2003, en 2006). Hiervoor wordt gebruik gemaakt van het mesoschaal meteorologisch model WRF, dat is uitgerust met een aparte module voor het stedelijk klimaa

The International Urban Energy Balance Comparison Project: Initial Results from Phase 2.

Many urban land surface schemes have been developed, incorporating different assumptions about the features of, and processes occurring at, the surface. Here, the first results from Phase 2 of an international comparison are presented. Evaluation is based on analysis of the last 12 months of a 15 month dataset. In general, the schemes have best overall capability to model net all-wave radiation. The models that perform well for one flux do not necessarily perform well for other fluxes. Generally there is better performance for net all wave radiation than sensible heat flux. The degree of complexity included in the models is outlined, and impacts on model performance are discussed in terms of the data made available to modellers at four successive stages

Stable Boundary Layer Issues

Understanding and prediction of the stable atmospheric boundary layer is a challenging task. Many physical processes are relevant in the stable boundary layer, i.e. turbulence, radiation, land surface coupling, orographic turbulent and gravity wave drag, and land surface heterogeneity. The development of robust stable boundary layer parameterizations for use in NWP and climate models is hampered by the multiplicity of processes and their unknown interactions. As a result, these models suffer from typical biases in key variables, such as 2m temperature, boundary layer depth, boundary layer wind speed. This paper summarizes the physical processes active in the stable boundary layer, their particular role, their interconnections and relevance for different stable boundary layer regimes (if understood). Also, the major model deficiencies are reported

Exploring the possible role of small scale terrain drag on stable boundary layers over land

This paper addresses the possible role of unresolved terrain drag, relative to the turbulent drag on the development of the stable atmospheric boundary layer over land. Adding a first-order estimate for terrain drag to the turbulent drag appears to provide drag that is similar to the enhanced turbulent drag obtained with the so-called long-tail mixing functions. These functions are currently used in many operational models for weather and climate, although they lack a clear physical basis. Consequently, a simple and practical quasi-empirical parameterization of terrain drag divergence for use in large-scale models is proposed and is tested in a column mode. As an outcome, the cross-isobaric mass flow (a measure for cyclone filling) with the new scheme, using realistic turbulent drag, appears to be equal to what is found with the unphysical long-tail scheme. At the same time, the new scheme produces a much more realistic less-deep boundary layer than is obtained by using the long-tail mixing function

Modelsimulaties van het stadsklimaat van Rotterdam

Modelsimulaties zijn uitgevoerd ter inschatting van het Urban Heat Island effect van Rotterdam. Hiervoor is de meest recente versie van het Weather Research & Forecasting (WRF) model gebruikt dat is uitgerust met een Urban Canopy Model. Bovendien is gebruik gemaakt van specifieke stadeigenschappen die zeer recent beschikbaar zijn gekome