North Atlantic climate far more predictable than models imply

Quantifying signals and uncertainties in climate models is essential for the detection, attribution, prediction and projection of climate change^1-3. Although inter-model agreement is high for large-scale temperature signals, dynamical changes in atmospheric circulation are very uncertain⁴. This leads to low confidence in regional projections, especially for precipitation, over the coming decades^5,6. The chaotic nature of the climate system^7-9 may also mean that signal uncertainties are largely irreducible. However, climate projections are difficult to verify until further observations become available. Here we assess retrospective climate model predictions of the past six decades and show that decadal variations in North Atlantic winter climate are highly predictable, despite a lack of agreement between individual model simulations and the poor predictive ability of raw model outputs. Crucially, current models underestimate the predictable signal (the predictable fraction of the total variability) of the North Atlantic Oscillation (the leading mode of variability in North Atlantic atmospheric circulation) by an order of magnitude. Consequently, compared to perfect models, 100 times as many ensemble members are needed in current models to extract this signal, and its effects on the climate are underestimated relative to other factors. To address these limitations, we implement a two-stage post-processing technique. We first adjust the variance of the ensemble-mean North Atlantic Oscillation forecast to match the observed variance of the predictable signal. We then select and use only the ensemble members with a North Atlantic Oscillation sufficiently close to the variance-adjusted ensemble-mean forecast North Atlantic Oscillation. This approach greatly improves decadal predictions of winter climate for Europe and eastern North America. Predictions of Atlantic multidecadal variability are also improved, suggesting that the North Atlantic Oscillation is not driven solely by Atlantic multidecadal variability. Our results highlight the need to understand why the signal-to-noise ratio is too small in current climate models¹⁰, and the extent to which correcting this model error would reduce uncertainties in regional climate change projections on timescales beyond a decade.

Diffusional Kurtosis along the Corticospinal Tract in Adult Normal Pressure Hydrocephalus

BACKGROUND AND PURPOSE

Normal Pressure Hydrocephalus is a reversible form of dementia characterized by enlarged ventricles, which can deform and cause disruptions to adjacent white matter fibers. The purpose of this work was to examine how diffusion and kurtosis parameters vary along the corticospinal tract and determine where along this path microstructure is compromised in patients diagnosed with normal pressure hydrocephalus. We hypothesized that disruption of the corticospinal tract from ventricular enlargement can be measured using diffusion MR imaging and this will be quantified in periventricular regions.

MATERIALS AND METHODS

We developed a method to analyze diffusion parameters at discrete points along neural tracts. We then used diffusion MR imaging data from patients with Alzheimer disease and healthy controls to compare whether diffusion along the corticospinal tract differs from that of patients with normal pressure hydrocephalus.

RESULTS

We found that diffusion parameters can differentiate patients with normal pressure hydrocephalus from those with Alzheimer disease and healthy controls: Axial diffusion, axial kurtosis, and the axonal water fraction were found to differ significantly across groups (P < .05) in an area located close to the superior internal capsule and corona radiata but below the cortex.

CONCLUSIONS

A lower axonal water fraction indicates a lower axonal density in the corticospinal tract, which may indicate permanent damage. Lower axial kurtosis may imply that axons are being more aligned due to compression.

Epidemic Legionnaires' disease two decades later: old sources, new diagnostic methods

In July 1995 we investigated a pneumonia outbreak in a Pennsylvania town. We conducted epidemiological and molecular microbiological studies to determine the outbreak source and interrupt transmission of disease. Legionnaires' disease (LD) was quickly identified by urine antigen testing, and a newly developed immunohistochemical stain confirmed nosocomial transmission to a hospital inpatient. LD was confirmed in 22 patients. Case-patients were more likely than controls to have been within 1,000 feet of the hospital (matched odds ratio, 21.0; 95% confidence interval, 2.9-368) during the 2 weeks prior to illness. Legionella pneumophila serogroup 1 (Lp-1) was isolated from hospital cooling towers (CTs) and rooftop air samples but not from hospital potable water or community CTs. Hospital CT and air Lp-1 isolates matched all five patient isolates by monoclonal antibody, arbitrarily primed polymerase chain reaction, and pulsed-field gel electrophoresis subtyping. Strategies to prevent LD must include minimizing transmission from CTs.

Perinatal and postnatal chest sonography

Sonography is the primary method used to image the fetal chest. Many significant congenital anomalies such as pleural effusion, congenital diaphragmatic hernia, cystic adenomatoid malformation, pulmonary sequestration, and congenital heart disease can be detected during early prenatal sonography. Fetal sonography also permits accurate assessment of the severity of these processes, allowing for parental counseling and optimal planning of postnatal care. After birth, sonography is the primary method for evaluating cardiac anatomy and diagnosing congenital heart disease. Sonography also serves as a useful adjunct to plain film radiology and other modalities in evaluation of the mediastinum, diaphragm, pleura, and chest wall.

Measurement of systemic and pulmonary blood flow and QP/QS ratio using Doppler and two-dimensional echocardiography

A noninvasive method for measuring systemic and pulmonary blood flow using Doppler velocimetry combined with 2-dimensional (2-D) echocardiography has been developed. High correlations were found between Fick- and Doppler-derived indexed measurements of systemic and pulmonary flow as well as the pulmonary to systemic flow ratio in 33 patients undergoing cardiac catheterization (systemic flow [n = 28], r = 0.78; pulmonary flow [n = 21], r = 0.88; Qp/Qs ratio [n = 24], r = 0.85). The random errors of the 2 methods were not significantly different. Outflow tract obstruction, semilunar valve regurgitation, and patent ductus arteriosus were the only lesions in which limitations to the use of this method were encountered. We anticipate that this method will be of use in initial and serial evaluations of adult and pediatric patients with low cardiac output or intracardiac shunts.

Effect of application force on noninvasive measurements of intracranial pressure

Application of the Ladd fiberoptic sensor to the anterior fontanel of the human newborn has been used as a method for monitoring intracranial pressure noninvasively. This study measures the effect of varying the force with which the sensor is applied to the fontanel. The Ladd sensor readings of five preterm human infants were continuously monitored while sensor application force was increased in a stepwise manner. The Ladd sensor readings for each infant varied with the force applied. In one infant sensor application was gradually increased while direct measurements of lumbar CSF pressure were made. Ladd sensor readings in this infant increased with increasing application force, while lumbar CSF pressure remained unchanged. It is concluded that readings obtained with the Ladd sensor applied to the anterior fontanel of the human infant depend on the force with which the sensor is applied. The effect of application force must be taken into account if noninvasive measurements of intracranial pressure are to be made with the Ladd device.