ENSO Amplitude Asymmetry in Met Office Hadley Centre Climate Models

Long climate simulations with the Met Office Hadley Centre General Circulation Model show weak El Niño-Southern Oscillation (ENSO) amplitude asymmetry between El Niño and La Niña phases compared with observations. This lack of asymmetry is explored through the framework of a perturbed parameter experiment. Two key hypotheses for the lack of asymmetry are tested. First, the possibility that westerly wind burst activity is biased is explored. It is found that the observed difference in wind burst activity during El Niño and La Niña tends to be underestimated by the model. Secondly, the warming due to subsurface non-linear advection is examined. While the model exhibits non-linear dynamic warming during both La Niña and El Niño, and thus a contribution to ENSO asymmetry, it is shown to be consistently underestimated in comparison with ocean reanalyses. The non-linear zonal advection term contributes most to the deficiency and the simulation of the anomalous zonal currents may be playing a key role in its underestimation. Compared with the ocean reanalyses, the anomalous zonal currents associated with ENSO are too weak in the vicinity of the equatorial undercurrent and the surface wind driven zonal currents extend too deep.

Forecasting northern Australian summer rainfall bursts using a seasonal prediction system

Rainfall bursts are relatively short-lived events that typically occur over consecutive days, up to a week. Northern Australian industries like sugar farming and beef are highly sensitive to burst activity, yet little is known about the multi-week prediction of bursts. This study evaluates summer (December to March) bursts over northern Australia in observations and multi-week hindcasts from the Bureau of Meteorology’s multi-week to seasonal system, ACCESS-S1 (Australian Community Climate and Earth-System Simulator, Seasonal version 1). The main objective is to test ACCESS-S1’s skill to confidently predict tropical burst activity, defined as rainfall accumulation exceeding a threshold amount over three days, for the purpose of producing a practical, user-friendly burst forecast product. The ensemble hindcasts, made up of 11 members for the period 1990–2012, display good predictive skill out to lead week 2 in the far northern regions, despite overestimating the total number of summer burst days and the proportion of total summer rainfall from bursts. Coinciding with a predicted strong Madden-Julian Oscillation (MJO), the skill in burst event prediction can be extended out to four weeks over the far northern coast in December, however this improvement is not apparent in other months or over the far northeast, which shows generally better forecast skill with a predicted weak MJO. The ability of ACCESS-S1 to skillfully forecast bursts out to 2-3 weeks suggests the Bureau's recent prototype development of a Burst Potential forecast product would be of great interest to northern Australia’s livestock and crop producers, who rely on accurate multi-week rainfall forecasts for managing business decisions.

Oxidative burst and phagocytic activity of phagocytes in canine parvoviral enteritis

Canine parvoviral enteritis (CPE) is a severe disease characterized by systemic inflammation and immunosuppression. The function of circulating phagocytes (neutrophils and monocytes) in affected dogs has not been fully investigated. We characterized the functional capacity of canine phagocytes in CPE by determining their oxidative burst and phagocytic activities using flow cytometry. Blood was collected from 28 dogs with CPE and 11 healthy, age-matched, control dogs. Oxidative burst activity was assessed by stimulating phagocytes with opsonized Escherichia coli or phorbol 12-myristate 13-acetate (PMA) and measuring the percentage of phagocytes producing reactive oxygen species and the magnitude of this production. Phagocytosis was measured by incubating phagocytes with opsonized E. coli and measuring the percentage of phagocytes containing E. coli and the number of bacteria per cell. Complete blood counts and serum C-reactive protein (CRP) concentrations were also determined. Serum CRP concentration was negatively and positively correlated with segmented and band neutrophil concentrations, respectively. Overall, no differences in phagocyte function were found between dogs with CPE and healthy control dogs. However, infected dogs with neutropenia or circulating band neutrophils had decreased PMA-stimulated oxidative burst activity compared to healthy controls. Additionally, CPE dogs with neutropenia or circulating band neutrophils had decreased PMA- and E. coli–stimulated oxidative burst activity and decreased phagocytosis of E. coli compared to CPE dogs without neutropenia or band neutrophils. We conclude that phagocytes have decreased oxidative burst and phagocytic activity in neutropenic CPE dogs and in CPE dogs with circulating band neutrophils.

A neutron star–white dwarf binary model for periodically active fast radio burst sources

ABSTRACT We propose a compact binary model with an eccentric orbit to explain periodically active fast radio burst (FRB) sources, where the system consists of a neutron star (NS) with strong dipolar magnetic fields and a magnetic white dwarf (WD). In our model, the WD fills its Roche lobe at periastron, and mass transfer occurs from the WD to the NS around this point. The accreted material may be fragmented into a number of parts, which arrive at the NS at different times. The fragmented magnetized material may trigger magnetic reconnection near the NS surface. The electrons can be accelerated to an ultrarelativistic speed, and therefore the curvature radiation of the electrons can account for the burst activity. In this scenario, the duty cycle of burst activity is related to the orbital period of the binary. We show that such a model may work for duty cycles roughly from 10 min to 2 d. For the recently reported 16.35-d periodicity of FRB 180916.J0158 + 65, our model does not naturally explain such a long duty cycle, since an extremely high eccentricity (e > 0.95) is required.