Estudo numérico da interação entre convecção rasa e radiação com ênfase no ciclo diurno do balanço de energia à superfície na Amazônia

Abstract

RESUMOEstuda-se neste artigo o efeito da convecção rasa no ciclo diurno do balanço de energia à superfície na Amazônia. O enfoque foi dado ao papel do sombreamento, devido aos cúmulos rasos na configuração do forçamento convectivo à superfície. Um esquema para o cálculo da cobertura de cúmulos rasos foi implementado no modelo BRAMS. Foram executados dois experimentos: um com convecção rasa e sem interação com a radiação, e o segundo com convecção rasa e interação com a radiação. Os resultados mostraram que a consideração da interação entre convecção rasa e radiação produz simulações mais realistas. Isso foi mais pronunciado por volta do meio-dia local e início da tarde, quando os cúmulos rasos estão com sua atividade máxima. Os fluxos e a cobertura foram bastante sensíveis às variações no forçamento radiativo. Apesar da melhoria da qualidade dos fluxos, do ponto de vista qualitativo, ficou evidente a deficiência do modelo em representar esses fluxos nas primeiras e últimas horas do ciclo diurno. Palavras-chave: convecção rasa, radiação, BRAMS. ABSTRACT: A NUMERIC STUDY OF THE INTERACTION BETWEEN SHALLOW CONVECTION AND RADIATION WITH EMPHASIS IN THE DIURNAL CYCLE OF THE SURFACE ENERGY BUDGET IN AMAZONIAThe effect of shallow convection on the diurnal cycle of the surface energy budget is investigated. Focus is on the role of the cloud shading on the establishment of the surface convective forcing. A scheme for calculating the shallow cumulus cover was implemented in the BRAMS atmospheric model. Two sets of experiments were performed: in the first experiment, the model had no interaction between shallow convection and radiation, and in the second type of experiment shallow convection interacts with radiation. Results show that the consideration of the interaction between shallow cumulus and radiation leads to more realistic simulations. This is more pronounced around the local noon and early afternoon, when the shallow cumulus activity reaches a maximum. The surface fluxes and the cumulus cover were very sensitive to the variations in the radiative forcing. Even though, from a qualitative viewpoint, there is an improvement on the quality of the simulated fluxes, it became evident a model flaw in representing these fluxes during the first hours of the diurnal cycle.

Analyses of Shallow Convection over the Amazon Coastal Region Using Satellite Images, Data Observations and Modeling

“…At 14:00 and 16:00 h on June 10 th , negative peaks of LE are shown and June 15 th presents a peak value at 20:00h. Studies per- Souza et al (2009) in their studies about shallow convection and radiation in the diurnal cycle using the BRAMS (Brazilian developments on the Regional Atmospheric Modelling System) and validating with Rondonia site experiments in the month of February found values around 100 W m -2 (H) and about 340 W m -2 (LE) at noon for the west wind regime and around 180 W m -2 (H) and 320 W m -2 for the east wind regime in the case of the interaction between the radiation and the shallow convection. Figure10 shows the vertical turbulent fluxes obtained by the SCM for 6:00, 12:00 and 18:00 h of at June 7 th , 10 th , 11 th , 14 th and 15 th .…”

“…Despite shallow cumulus clouds receiving less attention in numerical models (Souza et al, 2009), they play an important role in maintaining the structure of the earthatmosphere system, resulting in various mechanisms of retro-feed as found in Stull (1985). Typically a deep convection over the continents is preceded by a shallow convection.…”

“…Shallow convection and boundary layer processes precondition the atmosphere for a deep convection. This transition is a key element for an accurate representation of the diurnal cycle of precipitation (Khairoutdinov and Randall, 2003;Grabowski et al, 2006 andSouza et al, 2009). The absence of interaction processes between shallow convection and radiation causes the surface energy balance of the surface to be overestimated in models (Adams et al, 2009).…”

“…The absence of interaction processes between shallow convection and radiation causes the surface energy balance of the surface to be overestimated in models (Adams et al, 2009). Souza et al (2009) studying the effect of shallow convection in the diurnal cycle of the surface energy balance of the Amazon, implemented the BRAMS (Brazilian developments on the Regional Atmospheric Modeling System) and showed a good agreement between the interaction of shallow convection and radiation at noon and early afternoon and a qualitative deficiency of the model to represent these flows during the morning portion of the diurnal cycle. Lopes et al (2012) used the BRAMS model to investigate the relationship between soil moisture and cloud cover in the shallow cumulus energy balance of the Amazon, finding interactions among shallow convection and radiation.…”