Intercomparison and Evaluation of MM5 and Meso-NH mesoscale models in the stable boundary layer

Abstract

Atmospheric numerical models depend critically on realistic treatment of the lower boundary conditions. In strongly thermally-stratified conditions, turbulence may be very weak and the models may find it difficult to produce a good forecast near the surface. Under clear skies and for weak synoptic winds the determining factors are the turbulent kinetic energy and surface-layer parameterizations, which can be very different between models. Here, two state-of-the-art mesoscale models (MM5 and Meso-NH) are operated under exactly the same conditions for two different nights over the Duero basin in the Iberian Peninsula: one night with a well-defined synoptic wind and a second with practically no horizontal pressure gradient. The models are inter-compared and checked against available information, and their performances are evaluated.

Vertical structure of the stable boundary layer detected by RASS-SODAR and in-situ measurements in SABLES 2006 field campaign

“…ish, 41°49′N, 4°56′W, 840 m asl) which is located around 30 km NW from Valladolid city in the center of the Duero basin, over a relatively flat, homogeneous high plain of nearly 800 km 2 elevated around 40-60 m above the plateau. As it has been shown from mesoscale models (Bravo et al 2008, Cuxart 2008, Martínez et al 2010, the nocturnal fair-weather flow at this high plain is the result of a complex set of drainage flows and mesoscale circulations of different scales which develop, interact and become organized within the Duero basin, as a result of the sheltering effect provided to this basin by the surrounding mountain ranges (see Fig. 1 in Cuxart et al 2000).…”

“…The evolution of the SBL at the CIBA site is quite similar some of the nights (nights of 21-22, 22-23, and those from 26-27 to 29-30), where the weak wind present at sunset allowed the developing of strong surface thermal inversions which were soon partially eroded by the turbulence generated by a katabatic wind reaching the site. These drainage flows, which have also been studied in the whole Duero basin from model simulations for similar synoptic conditions (Bravo et al 2008, Martinez et al 2010, are described in greater detail in Yagüe et al (2007) and Viana et al (2010). In the remaining nights of the IOP, drainage currents are weaker over the site and a moderate level of stratification prevails during the night (except the night of 24-25, where a well mixed boundary layer with nearly-neutral conditions is established due to a strong thunderstorm produced in the early evening).…”

Aramis un modelo regional para la gestión de la calidad del aire. Evaluación y validación

“…This diurnal underestimation could be caused by: (1) sea-breeze and land-breeze circulations that are difficult to reproduce, associated with the important role of circulation patterns in photochemical simulations , (2) a tendency to underestimate ozone precursors (nitrogen oxides, carbon monoxide and volatile organic compounds) in air quality modelling systems (Russell and Dennis, 2000) and (3) uncertainty in the emissions coming from the HIREM model and in their temporal distribution. Three main sources of nocturnal overestimation might be: (1) the model does not represent nocturnal physic-chemical processes accurately enough (Jiménez et al, 2006b), (2) the HIREM emission model may not calculate night-time emissions properly, and (3) meteorological parameters, such as wind speed, wind direction and vertical mixing, are not well reproduced by the model when the synoptic forcing is weak and the ambient winds are light and variable (Bravo et al, 2008;Schürmann et al, 2009).…”

“…In addition, this stable stratification in a non-uniform terrain induces local circulations, such as drainage flows (Soler et al, 2003), and leads to several phenomena such as gravity waves, density currents (Terradellas et al, 2005;Udina et al, 2013;Ferreres et al, 2013;Soler et al, 2014), intrusions and meandering, with the frequent presence of low-level jets (Conangla and Cuxart, 2006). The misrepresentation of these effects and the local physiographical features can lead to incorrect estimations of several degrees in the temperature, in the moisture levels and errors in the wind speed and wind direction (Bravo et al, 2008).…”

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

“…Atmospheric models for weather, climate and air quality encounter substantial problems in forecasting the nocturnal boundary layer , Bechtold et al 2008, Bravo et al 2008, Bosveld et al 2008. Typical errors are the overestimation of the surface and screen level minimum temperature, the underestimation and the dislocation of the so-called nocturnal wind maximum (Steeneveld et al 2008a, Storm et al 2009, and the overestimation of magnitude of the turbulence intensity.…”