Modelagem Catt-Brams na Previsão de Curto Prazo

The difference between two simulations with different initial conditions in the CCATT-BRAMS modelling system in downward shortwave radiation at surface and cloudiness was studied for the zone corresponding to the state of Rondonia, on September 1 and 2, 2010, month in which was observed the greatest amount of fire outbreaks in the Amazon region. The difference in the initial configuration of the model was settled in activating aerosol background option in one of the simulations and turning it off in the other. No major differences in the fields of both analyzed variables and not much dependence with the amount of particulate matter in the atmosphere were observed. This was proved by calculating the correlation between aerosols and the changes of the variables in both simulations, showing low values (~0.2) within 48 hours studied.Estudou-se a diferença entre duas rodadas com diferente configuração inicial do modelo CCATT-BRAMS na radiação de onda curta descendente em superfície e nebulosidade para a zona correspondente ao estado de Rondônia, nos dias 1 e 2 de setembro de 2010, mês em que observaram-se a maior quantidade de focos de queimadas na região amazônica. A diferença na configuração inicial do modelo, radicou em ativar a opção de background de aerossóis em uma das rodadas e desligando essa opção na outra. Observaram-se diferenças pouco significativas nos campos das ambas variáveis analisadas e não muita relação em dependência da quantidade de material particulado presente na atmosfera. Isto foi comprovado com o cálculo da correlação entre os aerossóis e as mudanças das variáveis de uma rodada a outra, apresentando valores baixos (~0.2) nas 48 horas de rodada

Cloud droplet number closure for tropical convective clouds during the ACRIDICON CHUVA campaign

The main objective of the ACRIDICON-CHUVA campaign in September 2014 was the investigation of aerosol-cloud-interactions in the Amazon Basin. Cloud properties near cloud base of growing convective cumuli were characterized by cloud droplet size distribution measurements using a cloud combination probe and a cloud and aerosol spectrometer. In the current study, an adiabatic parcel model was used to perform cloud droplet number closure studies for several flights in differently polluted air masses

Análise da Sensibilidade de um Esquema de Microfísica Single-Moment a Variações na sua Configuração

Resumo Este trabalho tem como objetivo determinar a sensibilidade da chuva gerada pelo esquema de microfísica de Ferrier a mudanças na sua configuração e selecionar as modificações com maior potencial na redução da precipitação. Foi utilizado o modelo Kinematic Driver, uma plataforma para isolar o esquema de microfísica das complexas interações que têm lugar nos modelos de previsão do tempo e o clima, que permite simular situações hipotéticas na atmosfera de forma espacialmente unidimensional. Foi analisada a influência das taxas dos processos de microfísica representados, assim como o efeito produzido por diferentes métodos de cálculo da autoconversão e do intercepto da distribuição de tamanhos da chuva. Também foram testados diferentes valores da concentração de gotas de nuvem e da fração entre o conteúdo de gelo de nuvem e o conteúdo de neve. A coleta de água de nuvem por gotas de chuva foi o processo dominante na geração de precipitação, permitindo controlar a produção de chuva quente e de origem mista. Além disso, as modificações nos métodos de cálculo da autoconversão e do intercepto da distribuição de tamanhos das gotas de chuva, assim como na concentração de gotículas de nuvem, mostraram potencialidade na redução da chuva

Sensitivity Analysis of a Single-Moment Microphysics Scheme to Changes in its Configuration

<p></p><p>Abstract In order to determine the sensitivity of the rain generated by the microphysics scheme to changes in its configuration and select the changes with the greatest potential in reducing precipitation, this research was conducted. The Kinematic Driver model, a platform to isolate the microphysics of the complex interactions that take place in weather and climate models, was used to simulate hypothetical situations in the atmosphere. The influence of varying the rates of microphysics processes, as well as the effect produced by different methods to estimate the autoconversion and the intercept of rain size distribution, was analyzed. Variations in the cloud droplet concentration and in the cloud ice-snow ratio were also tested. The cloud water collection by raindrops was the most influential process in the generation of precipitation, it allowed to remarkably decrease the rain generated by both warm and mixed-phase clouds. In addition, some changes in methods to estimate the autoconversion rate and the intercept of the rain size distribution, as well as in the concentration of cloud droplets have shown potential in reducing the rain.</p><p></p

Observed and Simulated Variability of Droplet Spectral Dispersion in Convective Clouds Over the Amazon

In this study, the variability of the spectral dispersion of droplet size distributions (DSDs) in convective clouds is investigated. Analyses are based on aircraft measurements of growing cumuli near the Amazon basin, and on numerical simulations of an idealized ice‐free cumulus. In cleaner clouds, the relative dispersion ϵ, defined as the ratio of the standard deviation to the mean value of the droplet diameter, is negatively correlated with the ratio of the cloud water content (qc) to the adiabatic liquid water content (qa), while no strong correlation between ϵ and qc/qa is seen in polluted clouds. Bin microphysics numerical simulations suggest that these contrasting behaviors are associated with the effect of collision‐coalescence in cleaner clouds, and secondary droplet activation in polluted clouds, in addition to the turbulent mixing of parcels that experienced different paths within the cloud. Collision‐coalescence simultaneously broadens the DSDs and decreases qc, explaining the inverse relationship between ϵ and qc/qa in cleaner clouds. Secondary droplet activation broadens the DSDs but has little direct impact on qc. The combination of a rather modest DSD broadening due to weak collision‐coalescence with enhanced droplet activation in both diluted and highly undiluted cloud regions may contribute to maintain a relatively uniform ϵ within polluted clouds. These findings can be useful for parameterizing the shape parameter (μ) of gamma DSDs in bulk microphysics cloud‐resolving models. It is shown that emulating the observed μ−qc/qa relationship improves the estimation of the collision‐coalescence rate in bulk microphysics simulations compared to the bin simulations.Key Points: Droplet size distribution patterns observed in warm cumuli reflect the roles of collision‐coalescence, secondary activation, and mixing. The intra‐cloud distribution of droplet spectral dispersion varies with aerosol loading. Emulating the observed shape‐parameter improves bulk estimations of collision‐coalescence in models.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) http://dx.doi.org/10.13039/501100001807Max Planck Society (MPG)U.S. Department of Energy (DOE) http://dx.doi.org/10.13039/100000015Deutsche Forschungsgemeinschaft (DFG) http://dx.doi.org/10.13039/501100001659HAL

Cloud droplet formation at the base of tropical convective clouds: closure between modeling and measurement results of ACRIDICON–CHUVA

International audienceAbstract. Aerosol–cloud interactions contribute to the large uncertainties in current estimates of climate forcing. We investigated the effect of aerosol particles on cloud droplet formation by model calculations and aircraft measurements over the Amazon and over the western tropical Atlantic during the ACRIDICON–CHUVA campaign in September 2014. On the HALO (High Altitude Long Range Research) research aircraft, cloud droplet number concentrations (Nd) were measured near the base of clean and polluted growing convective cumuli using a cloud combination probe (CCP) and a cloud and aerosol spectrometer (CAS-DPOL). An adiabatic parcel model was used to perform cloud droplet number closure studies for flights in differently polluted air masses. Model input parameters included aerosol size distributions measured with an ultra-high sensitive aerosol spectrometer (UHSAS), in combination with a condensation particle counter (CPC). Updraft velocities (w) were measured with a boom-mounted Rosemount probe. Over the continent, the aerosol size distributions were dominated by accumulation mode particles, and good agreement between measured and modeled Nd values was obtained (deviations ≲ 10 %) assuming an average hygroscopicity of κ∼0.1, which is consistent with Amazonian biomass burning and secondary organic aerosol. Above the ocean, fair agreement was obtained assuming an average hygroscopicity of κ∼0.2 (deviations ≲ 16 %) and further improvement was achieved assuming different hygroscopicities for Aitken and accumulation mode particles (κAit=0.8, κacc=0.2; deviations ≲ 10 %), which may reflect secondary marine sulfate particles. Our results indicate that Aitken mode particles and their hygroscopicity can be important for droplet formation at low pollution levels and high updraft velocities in tropical convective clouds