Interpretation of convection cell signatures in radar images of the Greenland Sea

We present a comprehensive analysis of a convection cell pattern in two SAR images of a site in the Greenland Sea from the satellites ERS-2 and RADARSAT. It is not obvious whether the observed radar signatures can be attributed to oceanic or atmospheric convection phenomena. We show by numerical simulations that they are, on the on hand, not consistent with the theory of oceanic convection features and their radar imaging mechanism, while, on the other hand, they could very well be caused by atmospheric convection cells. The conclusion that the observed features must be atmospheric convection cells is supported by in-situ data and an AVHRR image of the scenario. We discuss the significance of our findings in view of the general problem of discriminating between radar signatures of oceanic and atmospheric phenomena

Interpretation of convection cell signatures in radar images of the Greenland Sea

We present a comprehensive analysis of a convection cell pattern in two SAR images of a site in the Greenland Sea from the satellites ERS-2 and RADARSAT. It is not obvious whether the observed radar signatures can be attributed to oceanic or atmospheric convection phenomena. We show by numerical simulations that they are, on the one hand, not consistent with the theory of oceanic convection features and their radar imaging mechanism, while, on the other hand, they could very well be caused by atmospheric convection cells. The conclusion that the observed features must be atmospheric convection cells is supported by in-situ data and an AVHRR image of the scenario. We discuss the significance of our findings in view of the general problem of discriminating between radar signatures of oceanic and atmospheric phenomena

Glycolysis is important for optimal asexual growth and formation of mature tissue cysts by Toxoplasma gondii

Toxoplasma gondii can grow and replicate using either glucose or glutamine as the major carbon source. Here, we have studied the essentiality of glycolysis in the tachyzoite and bradyzoite stages of T. gondii, using transgenic parasites that lack a functional hexokinase gene (Δhk) in RH (Type-1) and Prugniaud (Type-II) strain parasites. Tachyzoite stage Δhk parasites exhibit a fitness defect similar to that reported previously for the major glucose transporter mutant, and remain virulent in mice. However, although Prugniaud strain Δhk tachyzoites were capable of transforming into bradyzoites in vitro, they were severely compromised in their ability to make mature bradyzoite cysts in the brain tissue of mice. Isotopic labelling studies reveal that glucose-deprived tacyzoites utilise glutamine to replenish glycolytic and pentose phosphate pathway intermediates via gluconeogenesis. Interestingly, while glutamine-deprived intracellular Δhk tachyzoites continued to replicate, extracellular parasites were unable to efficiently invade host cells. Further, studies on mutant tachyzoites lacking a functional phosphoenolpyruvate carboxykinase (Δpepck1) revealed that glutaminolysis is the sole source of gluconeogenic flux in glucose-deprived parasites. In addition, glutaminolysis is essential for sustaining oxidative phosphorylation in Δhk parasites, while wild type (wt) and Δpepck1 parasites can obtain ATP from either glycolysis or oxidative phosphorylation. This study provides insights into the role of nutrient metabolism during asexual propagation and development of T. gondii, and validates the versatile nature of central carbon and energy metabolism in this parasite