Neste trabalho foram discutidas as características da Camada Limite Noturna (CLN) e o regime turbulento predominante, durante a campanha DRY-to-WET, período de transição seco para chuvoso (setembro a novembro) do experimento RaCCI/LBA 2002. Foi utilizado um sítio de pastagem (Faz. Nossa Senhora Aparecida - 10°45'S, 62°21'W, 290 m) na região de Ouro Preto D'Oeste - RO, com medidas de radiossonda (RS), balão cativo (BC), estação meteorológica automática (EMA) e de equipamento de sensoriamento remoto (SODAR). A determinação do regime turbulento ocorreu através do parâmetro de Monin-Obukhov. As alturas da CLN obtidas por várias técnicas (RS, BC e SODAR), que variaram de 156,3 ± 57,9 m ao pôr-do-sol a 301,0 ± 124,5 m no início da manhã do dia seguinte, apresentaram semelhança com resultados já obtidos na estação seca da mesma região. Entretanto a característica da estabilidade atmosférica foi similar a situações obtidas na estação úmida. Ou seja, durante o período de transição entre as estações seca e chuvosa, a atmosfera não fica totalmente estabelecida apresentando características tanto da estação seca (por exemplo os valores da altura da CLN) como da úmida (características da estabilidade).
In this study, we used the Standard Precipitation Index (SPI) to identify and to characterize the dry extreme events in the Amazon region. The results showed that the drought of 1998 was the most intense (SPI average equal to −1.69) in the period from 1979 to 2014. However, some papers have characterized the years 2005 and 2010 as the two largest droughts of the century. Thus, it was also carried out a comparative study of these droughts. The results showed that the drought 1998 was more intensive and extreme than the droughts of 2005 and 2010, although droughts of 2005 and 2010 lasted longer than 1998 due to oceanic and atmospheric conditions with influencing to cause greater social and economic impacts. Furthermore, it is suggested that the impact of the 2005 and 2010 droughts is a response from the dry occurred
Amazonian deforestation causes systematic changes in regional dry season precipitation. Some of these changes at contemporary large scales (a few hundreds of kilometers) of deforestation have been associated with a “dynamical mesoscale circulation,” induced by the replacement of rough forest with smooth pasture. In terms of decadal averages, this dynamical mechanism yields increased precipitation in downwind regions and decreased precipitation in upwind regions of deforested areas. Daily, seasonal, and interannual variations in this phenomenon may exist but have not yet been identified or explained. This study uses observations and numerical simulations to develop relationships between the dynamical mechanism and the local‐ and continental‐scale atmospheric conditions across a range of time scales. It is found that the strength of the dynamical mechanism is primarily controlled by the regional‐scale thermal and dynamical conditions of the boundary layer and not by the continental‐ and global‐scale atmospheric state. Lifting condensation level and wind speed within the boundary layer have large and positive correlations with the strength of the dynamical mechanism. The strength of these relationships depends on time scale and is strongest over the seasonal cycle. Overall, the dynamical mechanism is found to be strongest during times when the atmosphere is relatively stable. Hence, for contemporary large scales of deforestation this phenomenon is found to be the prevalent convective triggering mechanism during the dry and parts of transition seasons (especially during the dry‐to‐wet transition), significantly affecting the hydroclimate during this period.
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