Search results for "Boundary layer"

Observations of boundary layer, mixed-phase and multi-layer Arctic clouds with different lidar systems during ASTAR 2007

2009

Abstract. During the Arctic Study of Tropospheric Aerosol, Clouds and Radiation (ASTAR), which was conducted in Svalbard in March and April 2007, tropospheric Arctic clouds were observed with two ground-based backscatter lidar systems (micro pulse lidar and Raman lidar) and with an airborne elastic lidar. An increase in low-level (cloud tops below 2.5 km) cloud cover from 51% to 65% was observed above Ny-Ålesund during the time of the ASTAR campaign. Four different case studies of lidar cloud observations are analyzed: With the ground-based Raman lidar, a pre-condensation layer was observed at an altitude of 2 km. The layer consisted of small droplets with a high number concentration (aroun…

Explicit Microphysical Simulations of Boundary Layer Clouds over the Sea and over Vegetated Land Surfaces

2007

Surface temperature in the context of FLuorescence EXplorer (FLEX) mission

2007

It has been demonstrated that the spectrum of fluorescence emission is dependent on leaf temperature, thus there is a need for thermal information in order to interpret fluorescence signals. Temperature is also related to transpiration and stomata closure, which affects CO2 uptake and fluorescence. Therefore temperature measurements help to confirm the trends observed in fluorescence measurements. While fluorescence is immediately and uniquely related to photosynthesis, temperature provides additional information about plant status and instantaneous energy/water fluxes between plants and the atmosphere. The objective of this paper is to demonstrate the role of surface temperature in the con…

SMOS REFLEX 2003: L-band emissivity characterization of vineyards

2005

The goal of the Soil Moisture and Ocean Salinity mission over land is to infer surface soil moisture from multiangular L-band radiometric measurements. As the canopy affects the microwave emission of land, it is necessary to characterize different vegetation layers. This paper presents the Reference Pixel L-Band Experiment (REFLEX), carried out in June-July 2003 at the Vale/spl grave/ncia Anchor Station, Spain, to study the effects of grapevines on the soil emission and on the soil moisture retrieval. A wide range of soil moisture (SM), from saturated to completely dry soil, was measured with the Universitat Polite/spl grave/cnica de Catalunya's L-band Automatic Radiometer (LAURA). Concurre…

Surface to boundary layer coupling in the urban area of Lisbon comparing different urban canopy models in WRF

2019

Abstract This work presents a sensitivity study to evaluate different Urban Canopy Models (UCM) existing within the Weather Research and Forecasting Model (WRF) in the urban area of Lisbon, Portugal. Several hind-cast simulations were carried out for a selected period in July 2010, in which synoptic conditions favoured urban heat island formation. We aim to gain knowledge on the feedback of modified urban canopy representation in WRF on local scale meteorology and the boundary-layer dynamics over the urban area, by comparing a single layer urban canopy model (SLUCM) and a more sophisticated multi-layer building effect parametrisation (BEP). We find significant differences in the characteris…

A numerical model of the cloud-topped planetary boundary-layer: Impact of aerosol particles on the radiative forcing of stratiform clouds

1997

In a numerical sensitivity study, the microphysical model of stratus MISTRA, is used to investigate the impact of aerosol particles on the evolution of stratiform clouds. Four model runs are presented, each for a different type of background aerosol. Two include aerosol particle size-distributions which are typical of marine and rural continental air masses; a third represents a mixture of marine and rural continental aerosol particles, and the fourth rural continental aerosol particles with a reduced solubility in water. The results show that the microphysical structure of layer clouds was strongly affected by the physico-chemical properties of the aerosol particles from which the cloud dr…

A numerical model of the cloud-topped planetary boundary-layer: radiative forcing of aerosols in stratiform clouds

1998

In a numerical sensitivity study with the microphysical stratus model MISTRA the impact of aerosol particles on the time evolution of stratiform clouds is investigated. Four model runs with different aerosol size distributions are presented. Two size distributions are typical for maritime and continental air masses. The third model run consists of a mixture of maritime and rural aerosol particles, while in the fourth case study rural aerosol particles with a reduced water solubility are utilized. The numerical results show that the microphysical structure of the clouds is strongly affected by the physico-chemical properties of the aerosol particles. In the maritime case, with a relatively l…

Viscous-Inviscid Interactions in a Boundary-Layer Flow Induced by a Vortex Array

2014

In this paper we investigate the asymptotic validity of boundary layer theory. For a flow induced by a periodic row of point-vortices, we compare Prandtl's solution to Navier-Stokes solutions at different $Re$ numbers. We show how Prandtl's solution develops a finite time separation singularity. On the other hand Navier-Stokes solution is characterized by the presence of two kinds of viscous-inviscid interactions between the boundary layer and the outer flow. These interactions can be detected by the analysis of the enstrophy and of the pressure gradient on the wall. Moreover we apply the complex singularity tracking method to Prandtl and Navier-Stokes solutions and analyze the previous int…

Initiation of deep convection at marginal instability in an ensemble of mesoscale models: a case-study from COPS

2011

The present study investigates the initiation of precipitating deep convection in an ensemble of convection-resolving mesoscale models. Results of eight different model runs from five non-hydrostatic models are compared for a case of the Convective and Orographically-induced Precipitation Study (COPS). An isolated convective cell initiated east of the Black Forest crest in southwest Germany, although convective available potential energy was only moderate and convective inhibition was high. Measurements revealed that, due to the absence of synoptic forcing, convection was initiated by local processes related to the orography. In particular, the lifting by low-level convergence in the planet…

2017

Abstract. Deep convection is an efficient mechanism for vertical trace gas transport from Earth's surface to the upper troposphere (UT). The convective redistribution of short-lived trace gases emitted at the surface typically results in a C-shaped profile. This redistribution mechanism can impact photochemical processes, e.g. ozone and radical production in the UT on a large scale due to the generally longer lifetimes of species like formaldehyde (HCHO) and hydrogen peroxide (H2O2), which are important HOx precursors (HOx =  OH + HO2 radicals). Due to the solubility of HCHO and H2O2 their transport may be suppressed as they are efficiently removed by wet deposition. Here we present a case …