A51C-01
West Africa Mesoscale Convective Systems and Tropical Atlantic Cyclogenesis
This study focus on Mesoscale Convective Systems (MCSs) initiated in West Africa and their influence on tropical cyclogenesis. MCSs are obtained by a convective cloud cluster tracking algorithm performed at INPE/CPTEC (SP, Brazil) and using Meteosat data. We show that few MCSs associate to easterly waves moving from the continent throughout the tropical Atlantic. We present an example of Mesoscale Convective Vortices (MCV) of the stratiform clouds associated to an MCS. Although temporal lags and distances between MCSs dissipations and tropical cyclone initiations are ranged from 1 to 11 days and from 100 to 5000 km respectively, MCSs contribute to the humidification of the atmosphere that favours the development of cloud clusters necessary to the cyclogenesis. For both years 2004 and 2005, these MCSs were initiated in West Africa between 7°N-11°N and 10°W-6°E.
A51C-02
Assessment of RegCM3 over South America: Summer climatology and precipitation diurnal cycle
The RegCM3 (Regional Climate Model version 3) results over South America were evaluated during 14 summers, from 1989 to 2002 where the National Centers for Environmental Prediction (NCEP) reanalysis was used as initial and boundary conditions The model horizontal resolution is 50 km with 18 sigma-pressure levels. Due to availability of the observational data set the model climatology was constructed for the period 1989-2000 (12 summers) and the precipitation diurnal cycle from 1998 to 2002 (5 summers). The 12 summers climatology shows that the main climate systems associated to the precipitation (such as the South Atlantic Convergence Zone- ZCAS) and air temperature over South America were well reproduced by the model. Over the entire simulation domain, the seasonal errors were -5 percent for precipitation and a systematic cold bias of -0.9oC was obtained. The interannual variability of the precipitation relative bias was low and the relative bias at each summer was lower than 21 percent, which is within the expected error interval (5-30 percent) for the seasonal precipitation simulated by regional climate models. The temperature seasonal bias also presented low interannual variability and in each summer it does not overcome -1.3 K. The precipitation diurnal cycle observed by TRMM/satellite shows pronounced differences between tropical and extra-tropical parts of South America Some interesting features of the precipitation diurnal cycle were well-simulated by the RegCM3. The best agreement between the simulations and observations, especially the phase, were found over the continental area in the tropics and sub-tropics, which presented afternoon maximum (15:00 to 18:00 UTC) and morning minimum (08:00 to 12:00 UTC) precipitation. The large differences were obtained near the Atlantic and Pacific Oceans and in the northern Argentine. In this last region, the observations indicate a night maximum (03:00 UTC) and a morning (09:00 UTC) precipitation peak, which are probably associated to the presence of mesoscale convective systems in this area. The RegCM3 was not able to simulate neither event.
A51C-03
West afican monsoon in the gulf of Guinea
In the gulf of Guinea the rainfall regimes depend largely on the phenomenon of the monsoon. Thus, the arrival of this air mass, strongly wet, on the west African airspace due to its oceanic origin coincides with the starting of major rainfall activities. Considering the rainfall distribution along the gulf coast we can note that only the coming of the monsoon is not enough to account for the spreading of the rainfall regimes. Other parameters will be taken into account in the development of the process resulting in the formation of rainfall. The identification of all these parameters is significant to understand the functionning of the monsoon which gives rise to the regional rainfall distribution. In west Africa the harmattan is another favorable factor which could help undersand the nature of the future weather over the great rainy season. No other parameter today will yield the force of the harmattan. It will not be useless to identify a sery of parameters better describing this phenomenon characterised by a weather exceptionelly hazy in the day during which the content of different solid aerosols of the atmospheric air reaches unusual heigth. It would be interesting to establish the relation of cause and effect between the force of harmattan at the end of the great dry season and the nature of the great rainy season which comes later together with the coming of the monsoon. Could the proportion of the solid aerosol in the air during the harmattan influence one way or the other the coming rainy season~?
A51C-04
Influence Deforestation on Hydrological Cycle at Amazon Basin
The last three decades, the Amazon Basin has been affected for the occupation with consequence large deforestation. The principal area deforested is located from Maranhao state to Rondonia state. This area is common called "Arc Deforestation", and representing the transition between two important Brazilian ecosystems, Amazon Forest and Savanna Region. Theses ecosystems have precious biodiversity, and it has population about 10.331.000. The objective of this work was to evaluate the impact of arc deforestation on the hydrological cycle at Amazon basin, using BRAMS (Brazilian developments on the Regional Atmospheric Modeling System) including a model of dynamic vegetation, called GEMTM (General Energy and Mass Transport Model). In this study, numerical simulations were performed with a high spatial resolution regional model that allows capture some mesoscale aspects associated to the land used, topography, coastlines and large rivers. In order to predict the impact of the arc deforestation over the hydrological cycle, it was run two model simulations, conducted over a one-year period. In the first simulation, designated "control", it was used the scenarios derived from Soares Filho (2002), for the year 2002, in governance situation. In the second simulation called "deforestation", it was used the scenarios for the 2050, derived from results of Soares-Filho with governance, too. The higher-resolution regional modeling revealed important features of the deforestation process, displaying some associated mesoscale effects that are not typically represented in similar Global Circulation Model simulations. Near coastal zones and along large rivers, deforestation resulted in reduced precipitation. However, it was predicted increased precipitation over mountainous areas, especially on mountain slopes facing river valleys. Then, these higher-resolution simulations showed that, in general, orography, coastline profile and large river distribution play important roles in determining anomaly patterns of precipitation in Amazon Basin. It had seen an increase in the rain in the deforested regions, and it did not have substantial effect in the undisturbed regions. It was still observed, increase of temperature in the deforested region.
A51C-05
The Role of Land Surface Processes and Orography in the Hydroclimate of West Africa
A number of mechanistic experiments with the NASA Global Modeling and Assimilation Office (GMAO) global atmospheric general circulation model are used to assess the impact of soil moisture feedbacks, vegetation, and orography on the seasonal mean climatology and water cycle (including transient disturbances) of West Africa and the surrounding regions. Reanalyses (including ERA40 and NCEP Reanalysis II) and other independent observational data are used to characterize the major features of the West African water cycle and evaluate the model results.