Interactions of the land-surface with the atmospheric boundary layer

We study daytime land-atmosphere interaction using a one-dimensional (column) coupled land-surface - atmospheric boundary-Iayer (ABL) model and data sets gathered at Cabauw (1978, central Netherlands) and during the Hydrological and Atmospheric Pilot Experiment - Modélisation du Bilan Hydrique (HAPEX-MOBILHY, 1986, southwest France). The sensitivity of this interaction to the parameterization of soil hydraulic processes shows that the effects on surface fluxes and boundary layer development are largest for dry to moderate values of soil moisture, particularly for bare soil conditions. Boundary-Iayer clouds are controlled by the evolution of relative humidity (RH) at the boundary-Iayer top, which involves the interaction of soil moisture, surface heating, initial ABL conditions, and the moisture content and temperature stratification above the ABL with a number of competing feedback mechanisms. A fractional cloud cover formulation is developed based on a Gaussian distribution of total-water RH at the ABL top, where the distribution includes both turbulent vari ations (as a function of ABL-top dry air entrainment) and mesoscale variations (as a function of horizontal domain size); the modeled cloud cover is found to be more sensitive to the specified mean vertical motion than to the adjustable coefficients in the cloud cover formulation. Various improvements are made to the land-surface model and tested against data in off-line model runs without parameter tuning; using this improved land-surface model, coupled ABL - land-surface model runs yield realistic daytime surface fluxes and atmospheric profiles. Finally, it is shown in coupled landatmosphere modeling, analytically, and with data that the effect of soil moisture is to increase ABL-top RH tendency and thus cloud cover only if the stability above the ABL is not too weak (and there is sufficient initial ABL RH, and air above the ABL not too dry), while for weak stability above the ABL, drier soils yield a greater ABL-top RH tendency and thus cloud cover (again, with sufficient initial ABL RH, and air above the ABL not too dry)

Evaluation of a land-surface scheme at Cabauw

We study the response of the land-surface to prescribed atmospheric forcing for 31 May 1978 at Cabauw, Netherlands, using the land-surface scheme from the Coupled Atmospheric boundary layer-Plant-Soil (CAPS) model. Results from model runs show realistic daytime surface fluxes are produced using a canopy conductance formulation derived from Cabauw data (for 1987, a different year), and un-tuned parameterizations of root density (near-uniform with depth) and soil heat flux (reduced thermal conductivity through vegetation). Sensitivity of model-calculated surface heat fluxes to initial values of soil moisture is also examined. Results of this study provide the land-surface base state for a coupled land-atmosphere modeling stud

Modeling the actinides with disordered local moments

A first-principles disordered local moment (DLM) picture within the local-spin-density and coherent potential approximations (LSDA+CPA) of the actinides is presented. The parameter free theory gives an accurate description of bond lengths and bulk modulus. The case of $\delta$-Pu is studied in particular and the calculated density of states is compared to data from photo-electron spectroscopy. The relation between the DLM description, the dynamical mean field approach and spin-polarized magnetically ordered modeling is discussed.Comment: 6 pages, 4 figure

Tendências temporais de índices de vegetação nos campos do Pampa do Brasil e do Uruguai

O objetivo deste trabalho foi avaliar a redução do vigor vegetativo da cobertura vegetal do Pampa do Brasil e do Uruguai, por meio da identificação de tendências negativas em séries temporais de imagens. Utilizaram-se séries temporais de imagens de NDVI/EVI do sensor Modis, de 2000 a 2011; imagens de índices de umidade do solo do "climate forecast system reanalysis"; e dados de precipitação pluvial de estações meteorológicas. O estudo quantificou tendências lineares e não lineares nas séries de NDVI e EVI, em áreas de campos. Na tendência monotônica de Mann-Kendall, a 5% de probabilidade, 81,9% da área total estudada foi significativa com o NDVI, e 74,8%, com o EVI; no entanto, o EVI apresentou contraste superior na estimativa dos parâmetros. Os resultados mostraram maior sinal negativo a oeste, com valores médios de R²>0,15, r<-0,3 e τ <-0,15 na tendência dos índices de vegetação, e tendência decrescente para NDVI, EVI e precipitação pluvial, com menores valores médios de umidade do solo. A tendência negativa dos índices de vegetação, relacionada à combinação da ocorrência de deficit hídrico em solos rasos com o sobrepastoreio, indica alterações no padrão de cobertura vegetal do Pampa, com redução do vigor vegetativo

Interactions of the land-surface with the atmospheric boundary layer

We study daytime land-atmosphere interaction using a one-dimensional (column) coupled land-surface - atmospheric boundary-Iayer (ABL) model and data sets gathered at Cabauw (1978, central Netherlands) and during the Hydrological and Atmospheric Pilot Experiment - Modélisation du Bilan Hydrique (HAPEX-MOBILHY, 1986, southwest France). The sensitivity of this interaction to the parameterization of soil hydraulic processes shows that the effects on surface fluxes and boundary layer development are largest for dry to moderate values of soil moisture, particularly for bare soil conditions. Boundary-Iayer clouds are controlled by the evolution of relative humidity (RH) at the boundary-Iayer top, which involves the interaction of soil moisture, surface heating, initial ABL conditions, and the moisture content and temperature stratification above the ABL with a number of competing feedback mechanisms. A fractional cloud cover formulation is developed based on a Gaussian distribution of total-water RH at the ABL top, where the distribution includes both turbulent vari ations (as a function of ABL-top dry air entrainment) and mesoscale variations (as a function of horizontal domain size); the modeled cloud cover is found to be more sensitive to the specified mean vertical motion than to the adjustable coefficients in the cloud cover formulation. Various improvements are made to the land-surface model and tested against data in off-line model runs without parameter tuning; using this improved land-surface model, coupled ABL - land-surface model runs yield realistic daytime surface fluxes and atmospheric profiles. Finally, it is shown in coupled landatmosphere modeling, analytically, and with data that the effect of soil moisture is to increase ABL-top RH tendency and thus cloud cover only if the stability above the ABL is not too weak (and there is sufficient initial ABL RH, and air above the ABL not too dry), while for weak stability above the ABL, drier soils yield a greater ABL-top RH tendency and thus cloud cover (again, with sufficient initial ABL RH, and air above the ABL not too dry)

Single-Column Model Intercomparison for a Stably Stratified Atmospheric Boundary Layer

The parameterization of the stably stratified atmospheric boundary layer is a difficult issue, having a significant impact on medium-range weather forecasts and climate integrations. To pursue this further, a moderately stratified Arctic case is simulated by nineteen single-column turbulence schemes. Statistics from a large-eddy simulation intercomparison made for the same case by eleven different models are used as a guiding reference. The single-column parameterizations include research and operational schemes from major forecast and climate research centres. Results from first-order schemes, a large number of turbulence kinetic energy closures, and other models were used. There is a large spread in the results; in general, the operational schemes mix over a deeper layer than the research schemes, and the turbulence kinetic energy and other higher-order closures give results closer to the statistics obtained from the large-eddy simulations. The sensitivities of the schemes to the parameters of their turbulence closures are partially explore