Variability of the Antarctic slope current system in the northwestern Weddell Sea

The dense water outflow from the Antarctic continental shelf is closely associated with the strength and position of the Antarctic Slope Front. We explore the short-term and spatial variability of the Antarctic Slope Front system and the mechanisms that regulate cross-slope exchange using highly temporallyand spatially-resolved measurements from three ocean gliders deployed in 2012. Twenty-two sections along the eastern Antarctic Peninsula and west of the South Orkney Islands are grouped regionally and composited by isobaths. There is consistency in the front position around the Powell Basin, varying mostly between the 500 and 800m isobaths. In most of the study area the flow is bottom-intensified. The along-slope transport of the Antarctic Slope Current (upper 1000 m) varies between 0.2 and 5.9 Sv and does not exhibit a regional pattern. The magnitude of the velocity field shows substantial variability, up to twice its mean value. Higher eddy kinetic energy (0.003m2 s−2) is observed on sections with dense water, possibly due to baroclinic instabilities in the bottom layer. Distributions of potential vorticity show an increase towards the shelf along isopycnals and also in the dense water layer. Glider sections located west of the South Orkney Islands indicate a northward direction of the flow associated with the Weddell Front, which differs from previous estimates of the mean circulation. This study provides some of the first observational confirmation of the high frequency variability associated with an active eddy field that has been suggested by recent numerical simulations in this region

Slope exchange processes in the Weddell and Amundsen Seas

This thesis aims to investigate the dynamical processes of the along-slope currents in the Weddell and Amundsen Seas (Antarctica), their variability and the mechanisms that regulate the cross-slope exchange of properties. Firstly, this thesis explores the short-term and spatial variability of the Antarctic Slope Front system at the northwestern Weddell Sea using data from three ocean gliders. Twenty-two sections along the eastern Antarctic Peninsula are grouped regionally and composited by isobaths. The along-slope transport of the Antarctic Slope Current (upper 1000 m) varies between 0.2 and 5.9 Sv. Higher eddy kinetic energy (0.003m2s¡2) is observed on sections where dense water is present, possibly due to baroclinic instabilities in the deep layer. These results provide some of the first observational confirmation of the high frequency variability associated with an active eddy field that has been suggested by recent numerical simulations in this region. Using a multidisciplinary dataset, the physical processes associated with phytoplankton biomass distribution and how these relate to frontal processes east of the Antarctic Peninsula are assessed. There is a distinction between upperslope and off-shelf areas, which are likely disassociated from each other. Over the shelf, the relatively low stratification and the likely enhanced mixing and nutrient input from sediments would contribute to the relatively high primary production. Offshore, the stronger pycnocline and passive sinking of phytoplankton creates a deeper subsurface chlorophyll maximum. Finally, observations from moorings and from ship-based hydrographic stations at eastern Amundsen Sea are analysed to investigate the variability of the slope undercurrent and the Circumpolar Deep Water layer within troughs at the continental shelf. The cumulative onshore temperature transport of CDW was 1.21 TW and 1.79 TW at the central and eastern trough, respectively. High-frequency variability of temperature transport estimates are different among shelf-breakmoorings; eddies and coastal-trapped waves are likely contributors

Subsurface oceanic structure associated with atmospheric convectively coupled equatorial Kelvin waves in the eastern Indian Ocean

Atmospheric convectively coupled equatorial Kelvin waves (CCKWs) are a major tropical weather feature strongly influenced by ocean–atmosphere interactions. However, prediction of the development and propagation of CCKWs remains a challenge for models. The physical processes involved in these interactions are assessed by investigating the oceanic response to the passage of CCKWs across the eastern Indian Ocean and Maritime Continent using the NEMO ocean model analysis with data assimilation. Three-dimensional life cycles are constructed for “solitary” CCKW events. As a CCKW propagates over the eastern Indian Ocean, the immediate thermodynamic ocean response includes cooling of the ocean surface and subsurface, deepening of the mixed layer depth, and an increase in the mixed layer heat content. Additionally, a dynamical downwelling signal is observed two days after the peak in the CCKW westerly wind burst, which propagates eastward along the Equator and then follows the Sumatra and Java coasts, consistent with a downwelling oceanic Kelvin wave with an average phase speed of 2.3 m s −1. Meridional and vertical structures of zonal velocity anomalies are consistent with this framework. This dynamical feature is consistent across distinct CCKW populations, indicating the importance of CCKWs as a source of oceanic Kelvin waves in the eastern Indian Ocean. The subsurface dynamical response to the CCKWs is identifiable up to 11 days after the forcing. These ocean feedbacks on time scales longer than the CCKW life cycle help elucidate how locally driven processes can rectify onto longer time-scale processes in the coupled ocean–atmosphere system

Ocorrência, evolução anual de incêndios e queimadas no Brasil entre 2003 e 2018 e relação com desmatamento

Na Amazônia, as áreas conhecidas como "Arco do Desmatamento" concentram os incêndios florestais e queimadas no Brasil. O desmatamento e a degradação de florestas por incêndios e queimadas são os processos responsáveis pela maior parte das emissões brasileiras de gases estufa. Embora as estimativas de emissões por desmatamento estejam maduras, as resultantes da degradação são menos precisas, pois é necessário acompanhar a trajetória posterior das áreas atingidas por fogo. Entender esta dinâmica temporal e espacial é fundamental para as ações de políticas públicas e para estimar as emissões de gases estufa. O objetivo deste trabalho foi avaliar as áreas de concentração de incêndios/queimadas no Brasil entre 2003 e 2018, sua evolução e a relação com o desmatamento. Utilizamos focos de calor (sensor Modis, Satélite Aqua_M-T). Quantificamos a quantidade de ocorrências anuais em cada célula de meio grau para evidenciar áreas de concentração e avaliamos a tendência de aumento ou redução de focos em cada célula utilizando a Correlação Pearson. Utilizamos dados de uso e cobertura do solo produzidos pelo MapBiomas para contextualizar as ocorrências. A concentração de focos esteve associada a processos econômicos (expansão da fronteira agrícola), climáticos (novas áreas da Amazônia passaram a queimar), e de detecção do fogo ativo (sugerindo que a probabilidade de detecção dos focos de calor não se distribuem uniformemente entre os biomas). A dinâmica temporal parece estar associada a processos econômicos, sobretudo ao avanço da fronteira agrícola e a consolidação da produção de grãos nas áreas desmatadas há mais tempo. A Amazônia, sobretudo nas fronteiras agrícolas, concentra a maior parte dos focos de calor registrados e há uma tendência de "migração" dos focos de calor para o norte, acompanhando a fronteira agrícola. Encontramos uma correlação negativa entre focos e ano de registro nas áreas de desmatamento consolidadas e uma correlação positiva em áreas de cobertura florestal mais preservada. Quando avaliados em uma escala de detalhe, os focos tendem a se localizar em áreas florestadas, próximas às áreas desmatadas. Nossos resultados apontam para sinergia das políticas públicas visando o combate ao desmatamento e a queimadas e apontam para a dinâmica temporal evolução das queimadas

Characterisation of the observed diurnal cycle of precipitation over the Maritime Continent

This study investigates the temporal and spatial complexities of the mean diurnal cycle (DC) of precipitation over the Maritime Continent during the wet season using the IMERG data product, and highlights systematic inaccuracies of amplitude and phase representation using the first diurnal harmonic (FDH). The first-order nature of the DC of precipitation is already well documented, typically featuring heavy precipitation over near-coastal land areas in the late afternoon and evening followed by maximum precipitation overnight over the surrounding seas, with offshore propagation evident in places. The DC is often concisely described in terms of an amplitude and phase based on the FDH parameters, however the omission of higher-order components of variability results in the FDH parameters being poor indicators of the magnitude and peak time of diurnal variability in many locations. This study improves the accuracy of the amplitude and phase parameters by characterising the DC using two novel waveforms - a skew-permitting waveform and a spike-permitting waveform - which are constructed to more accurately characterise single-peak cycles with rapid transitions. Key characterisation improvements include correction of a phase lag (averaging about one hour) over near-coastal land areas and capture of the short-lasting but extreme peak in precipitation rate over Java which increases the amplitude by the order of 20%. The new skew parameter shows that locations close to coastlines experience rapid intensification and gradual weakening of diurnal precipitation while there is a tendency toward gradual intensification and rapid weakening far inland and offshore. The new spike parameter shows that near-coastal land experiences a brief and precisely timed peak in precipitation, whereas diurnal activity over inland locations is less precisely timed, and waters surrounding Java experience a precisely timed suppression of precipitation. Other potential applications of the novel waveforms used in this study are discussed

Subsurface oceanic structure associated with atmospheric convectively coupled equatorial Kelvin waves in the eastern Indian Ocean

&amp;lt;p&amp;gt;Atmospheric convectively coupled equatorial Kelvin waves (CCKWs) are a major tropical weather feature strongly influenced by ocean--atmosphere interactions. However, prediction of the development and propagation of CCKWs remains a challenge for models. The physical processes involved in these interactions are assessed by investigating the oceanic response to the passage of CCKWs across the eastern Indian Ocean and MC using the NEMO ocean model analysis with data assimilation. Three-dimensional life cycles are constructed for &amp;quot;solitary&amp;quot; CCKW events. As a CCKW propagates over the eastern Indian Ocean, the immediate thermodynamic ocean response includes cooling of the ocean surface and subsurface, deepening of the mixed layer depth, and an increase in the mixed layer heat content. Additionally, a dynamical downwelling signal is observed two days after the peak in the CCKW westerly wind burst, which propagates eastward along the Equator and then follows the Sumatra and Java coasts, consistent with a downwelling oceanic Kelvin wave with an average phase speed of 2.3 m s&amp;lt;sup&amp;gt;-1&amp;lt;/sup&amp;gt;. Meridional and vertical structures of zonal velocity anomalies are consistent with this framework. This dynamical feature is consistent across distinct CCKW populations, indicating the importance of CCKWs as a source of oceanic Kelvin waves in the eastern Indian Ocean. The subsurface dynamical response to the CCKWs is identifiable up to 11 days after the forcing. These ocean feedbacks on time scales longer than the CCKW life cycle help elucidate how locally driven processes can rectify onto longer time-scale processes in the coupled ocean--atmosphere system.&amp;lt;/p&amp;gt;</jats:p