Why the South Pacific Convergence Zone is diagonal

During austral summer, the majority of precipitation over the Pacific Ocean is concentrated in the South Pacific Convergence Zone (SPCZ). The surface boundary conditions required to support the diagonally (northwest-southeast) oriented SPCZ are determined through a series of experiments with an atmospheric general circulation model. Continental configuration and orography do not have a significant influence on SPCZ orientation and strength. The key necessary boundary condition is the zonally asymmetric component of the sea surface temperature (SST) distribution. This leads to a strong subtropical anticyclone over the southeast Pacific that, on its western flank, transports warm moist air from the equator into the SPCZ region. This moisture then intensifies (diagonal) bands of convection that are initiated by regions of ascent and reduced static stability ahead of the cyclonic vorticity in Rossby waves that are refracted toward the westerly duct over the equatorial Pacific. The climatological SPCZ is comprised of the superposition of these diagonal bands of convection. When the zonally asymmetric SST component is reduced or removed, the subtropical anticyclone and its associated moisture source is weakened. Despite the presence of Rossby waves, significant moist convection is no longer triggered; the SPCZ disappears. The diagonal SPCZ is robust to large changes (up to +/-6 degC) in absolute SST (i.e. where the SST asymmetry is preserved). Extreme cooling (change less than -6 degC) results in a weaker and more zonal SPCZ, due to decreasing atmospheric temperature, moisture content and convective available potential energy

Short taxonomic guide to the genus \u2018Candidatus Phytoplasma\u2019

The category of Candidatus was introduced to allow unambiguous reference to organisms that could not be cultivated in vitro. In plant pathology, a major impact of this novel taxonomic concept was to enable the classification of the diverse group of organisms, morphologically similar to the mycoplasmas, known by the trivial name of phytoplasmas. These plant pathogens were originally named according to the disease they caused. Later, extensive sequence analysis of the ribosomal RNA genes allowed the development of an evolution-based classification and the grouping of the phytoplasmas into phylogenetically distinct clades. Unfortunately, the phytopathological and the phylogenetic classification did not match and had striking contradictions. With the adoption of the category Candidatus, the description of the genus 'Ca. Phytoplasma' and several 'Ca. Phytoplasma' species, the scientific community is now attempting to provide a classification that takes into account both the phylogenetic and the biological/ecological characteristics of the organisms. Here we provide an outline of the characteristics and composition of the genus 'Ca. Phytoplasma'

Candidatus Phytoplasma australiense is associated with pumpkin yellow leaf curl disease in Queensland, Western Australia and the Northern Territory

Pumpkin plants (Cucurbita maxima and C. moschata) with pumpkin yellow leaf curl (PYLC) disease were observed at production fields in Queensland, Western Australia and the Northern Territory. Diseased samples were positive for a phytoplasma indistinguishable from Candidatus Phytoplasma australiense, the phytoplasma associated with papaya dieback and strawberry lethal yellows. This is the first time Candidatus Phytoplasma australiense has been detected in pumpkin