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The accuracy of broadband radiation codes for models is less studied for cloudy atmosphere than for cloud- free atmosphere. In this study, various test cases are proposed for atmosphere with clouds. The calculations of the heating rate (HR) profiles were made for 15 cloudy test cases with vertical resolution of 1 km by using the two broadband shortwave radiation codes (CLIRAD-SW-M and CLIRAD(FC05)-SW) characterized by different parameterizations of gaseous absorption and one line-by-line radiative transfer model (FLBLM). The calculation results show that the HR error of both broadband codes is about 20% in cloud layers, while it is less than 5-10% in cloud-free layers. The mean absolute HR value in cloud layers of 1 km thickness is about 10-15 K/day as compared with 1-3 K/day in cloud-free low atmosphere. These errors are not high and can be accepted by current atmospheric models. But further improvement of models’ performance will require improvement of accuracy of radiation calculations in cloud layers.

São utilizados dados de velocidade do vento obtidos por anemômetros dispostos verticalmente em uma torre de 60m na Rebio- Jarú, RO, projeto LBA. O objetivo foi de analisar as características da filtragem de momentum por escala pelo dossel da floresta amazônica. Aplicou-se a ondeleta de Morlet às séries de velocidade de vento amostradas a 0,1 Hz. Foram consideradas duas classes de eventos: ventos muito fortes (I) e fracos (II). Foram analisados os acoplamentos por escala entre as velocidades do vento medidas a diferentes alturas acima e dentro do dossel através do coeficiente de correlação linear. Para a classe I há bom acoplamento entre os campos de vento acima e dentro do dossel, inclusive nas escalas menores. Porém, para a classe II, o grau de acoplamento é menor e diminui para as escalas menores até que se chega a um limiar, além do qual não há mais acoplamento.

High-speed video recordings of two lightning flashes confirm that positive cloud-to-ground (CG) strokes can be produced by extensive horizontal intracloud (IC) discharges within and near the cloud base. These recordings constitute the first observations of CG leaders emanating from IC discharges of either polarity. In one case, the discharge began with a negative leader that propagated horizontally, went upward and produced an IC discharge. After the beginning of the IC discharge, a positive leader emanated from the lowest portion of the IC discharge, and initiated a positive return stroke. In the other case, the IC discharge began with a positive leader and then initiated a downward-propagating positive leader that contained recoil processes and produced a bright return stroke followed by a long continuing luminosity. These observations help to understand the complex genesis of positive CG flashes, why IC lightning commonly precedes them and why extensive horizontal channels are often involved.

Earthen mounds with archaeological artifacts have been well known in Marajó Island since the 19th century. Their documented dimensions are impressive, e.g., up to 20 m high, and with areas as large as 90 ha. The mounds, locally known as tesos, impose a significant relief on the very low-lying landscape of this region, which averages 4 to 6m above present sea level. These features have been traditionally interpreted as artificial constructions of the Marajoara culture, designed for defense, cemetery purposes, or escape from flooding. Here, we provide sedimentological and geomorphological data that suggest an alternative origin for these structures that is more consistent with their monumental sizes. Rather than artificial, the Marajoara tesos seem to consist of natural morphological features related to late Pleistocene and Holocene fluvial, and possibly tidal-influenced, paleochannels and paleobars that became abandoned as depositional conditions changed through time. Although utilized and modified by the Marajoara since at least 2000 years ago, these earthen mounds contain a significant non-anthropogenically modified sedimentary substratum. Therefore, the large Marajoara tesos are not entirely artificial. Ancient Marajoara cultures took advantage of these natural, preexisting elevated surfaces to base their communities and develop their activities, locally increasing the sizes of these fluvial landforms. This alternative interpretation suggests less cumulative labor investment in the construction of the mounds and might have significant implications for reconstructing the organization of the Marajoara culture.

We investigated the seasonal patterns of water vapor and sensible heat flux along a tropical biome gradient from forest to savanna. We analyzed data from a network of flux towers in Brazil that were operated within the Large-Scale Biosphere-Atmosphere Experiment in Amazonia (LBA). These tower sites included tropical humid and semideciduous forest, transitional forest, floodplain (with physiognomies of cerrado), and cerrado sensu stricto. The mean annual sensible heat flux at all sites ranged from 20 to 38 Wm2, and was generally reduced in the wet season and increased in the late dry season, coincident with seasonal variations of net radiation and soil moisture. The sites were easily divisible into two functional groups based on the seasonality of evaporation: tropical forest and savanna. At sites with an annual precipitation above 1900 mm and a dry season length less than 4 months (Manaus, Santarem and Rondonia), evaporation rates increased in the dry season, coincident with increased radiation. Evaporation rates were as high as 4.0 mm d1 in these evergreen or semidecidous forests. In contrast, ecosystems with precipitation less than 1700 mm and a longer dry season (Mato Grosso, Tocantins and São Paulo) showed clear evidence of reduced evaporation in the dry season. Evaporation rates were as low as 2.5 mm d1 in the transitional forests and 1 mm d1 in the cerrado. The controls on evapotranspiration seasonality changed along the biome gradient, with evaporative demand (especially net radiation) playing a more important role in the wetter forests, and soil moisture playing a more important role in the drier savannah sites.

Efforts to control climate change require the stabilization of atmospheric CO(2) concentrations. This can only be achieved through a drastic reduction of global CO(2) emissions. Yet fossil fuel emissions increased by 29% between 2000 and 2008, in conjunction with increased contributions from emerging economies, from the production and international trade of goods and services, and from the use of coal as a fuel source. In contrast, emissions from land-use changes were nearly constant. Between 1959 and 2008, 43% of each year’s CO(2) emissions remained in the atmosphere on average; the rest was absorbed by carbon sinks on land and in the oceans. In the past 50 years, the fraction of CO(2) emissions that remains in the atmosphere each year has likely increased, from about 40% to 45%, and models suggest that this trend was caused by a decrease in the uptake of CO(2) by the carbon sinks in response to climate change and variability. Changes in the CO(2) sinks are highly uncertain, but they could have a significant influence on future atmospheric CO(2) levels. It is therefore crucial to reduce the uncertainties.

The stability of the Amazon forestclimate equilibrium is being perturbed by a number of human drivers of change (e.g. deforestation, global warming, forest fires, higher CO2 concentrations, and increased frequency of droughts and floods). Quantitative assessments for the maintenance of the tropical forest indicate that tipping points may exist for total deforested area (>40%) and for global warming (ÄT > 34°C). The likelihood of exceeding a tipping point can be greatly exacerbated by increases in forest fires and droughts, but quantification of those effects is still lacking. Forest resilience can be significantly increased if CO2 fertilization effect is proven to be taking place for tropical forests, but it can be offset by continued increases in temperature, rainfall seasonality, and forest fires.

No single model or scale can fully capture the causes of land change. For a given region, land changes may have different impacts at different places. Limits and opportunities imposed by biophysical and socio-economic conditions, such as local policies and accessibility, may induce distinct land change trajectories. These local land change trajectories may, in turn, indirectly affect other places, as local actions interact with higher-level driving forces. Such intraregional interdependencies cannot be captured by studies at a single scale, calling for multiscale and multilocality studies. This paper proposes a software organization for building computational models that support dynamical linking of multiple scales. This structure couples different types of models, such as cell-space models with agent-based models. We show how results in multiscale models can flow both in bottom-up and top-down directions, thus allowing feedback from local actors to regional scales. The proposal is general and independent of specific software, and it is effective to model intraregional, bottom-up and top-down interactions in land change models. To show the models potential, we develop a case study that shows how a multiscale model for the Brazilian Amazonia can include feedbacks between local to regional scales.

The mathematical models used to simulate the present climate and project future climate when forced by greenhouse gases and aerosols are generally referred to as General Circulation Models (GCMs). While they have demonstrated significant skill in the continental and hemispherical scales and incorporate a large proportion of the complexity of the global system, they are inherently unable to present local subgrid scale features and dynamics [Wigley el al., 1991].

Using the PRECIS regional climate modeling system this study analyses the distribution of extremes of temperature and precipitation in South America in the recent past (19611990) and in a future (20712100) climate under the IPCC SRES A2 and B2 emissions scenarios. The results show that for the present climate the model simulates well the spatial distribution of extreme temperature and rainfall events when compared with observations, with temperature the more realistic. The observations over the region are far from comprehensive which compromises the assessment of model quality. In all the future climate scenarios considered all parts of the region would experience significant and often different changes in rainfall and temperature extremes. In the future, the occurrence of warm nights is projected to be more frequent in the entire tropical South America while the occurrence of cold night events is likely to decrease. Significant changes in rainfall extremes and dry spells are also projected. These include increased intensity of extreme precipitation events over most of Southeastern South America and western Amazonia consistent with projected increasing trends in total rainfall in these regions. In Northeast Brazil and eastern Amazonia smaller or no changes are seen in projected rainfall intensity though significant changes are seen in the frequency of consecutive dry days.

Most of tropical South America east of the Andes and south of 23°S experienced a warm 2008, with annual mean temperatures 2° to 3°C warmer than normal. Likewise, warm conditions (1° to 2°C above normal) were observed in northern Venezuela, interior Brazil between Amazonia and Northeast Brazil, and in eastern Peru (Fig. 7.11a). Cooler-than-normal conditions (anomalies of −0.5 to −1°C) were observed in southeast Brazil. From January to April, warm temperature anomalies were detected in eastern Amazonia, Northeast Brazil, southern Paraguay, and northern Argentina. In the interior of Northeast Brazil, mean temperatures reached 32° to 34°C, exceeding the mean by more than 4°C. Negative daily maximum temperature anomalies of 2° to 3°C were reported in Uruguay, southern Brazil, and the Brazilian highlands, associated with the penetration of a cold air mass.

Rainfall and river indices for both the northern and southern Amazon were used to identify and explore long-term climate variability on the region. From a statistical analysis of the hydrometeorological series, it is concluded that no systematic unidirectional long-term trends towards drier or wetter conditions have been identified since the 1920s. The rainfall and river series showing variability at inter-annual scales linked to El Niño Southern Oscillation was detected in rainfall in the northern Amazon. It has a low-frequency variability with a peak at – 30 years identified in both rainfall and river series in the Amazon. The presence of cycles rather than a trend is characteristic of rainfall in the Amazon. These cycles are real indicators of decadal and multi-decadal variations in hydrology for both sides of the basin. Sea-level pressure (SLP) gradients between tropics and sub topics were explored in order to explain variability in the hydrometeorology of the basin. Sea surface temperature (SST) gradients inside the tropical Atlantic and between the tropical Atlantic and the sub-tropical Atlantic have been assessed in the context of changes in rainfall in the Amazon, as compared to northern Argentina. Trends in SSTs in the subtropical Atlantic are linked to changes in rainfall and circulation in northern Argentina, and they seem to be related to multi-decadal variations of rainfall in the Amazon.