Are Midtwentieth Century Forced Changes in North Atlantic Hurricane Potential Intensity Detectable?

The impact of anthropogenic forcings on tropical North Atlantic hurricane potential intensity (PI) is evaluated in Climate Model Intercomparison Project 5 models for the period 1958–2005. Eleven models are examined, but only seven models have a forced response that is distinguishable from internal variability. The use of discriminant analysis to optimize detectability does not yield a clear, common climate change signal. Of the seven models with a significant response, one has a negative linear trend while two have a positive linear trend. The trend in PI is not even consistent among reanalyses, although this difference is not statistically significant because of large uncertainties. Furthermore, estimates of PI internal variability have significantly different variances among different reanalysis products. These disagreements between models, reanalysis products, and between models and reanalyses, in conjunction with relatively large uncertainties, highlight the difficulty of detecting and attributing observed changes in North Atlantic hurricane potential intensity

Kinetics of HCN Decomposition on the Pt(111) Surface by Time-Dependent Infrared Spectroscopy

Time-dependent reflection absorption infrared spectroscopy has been used to investigate the kinetics of HCN decomposition on the Pt(111) surface over the temperature range of 120 to 135 K. At these low temperatures, HCN bonds at an atop site with the HCN axis perpendicular to the surface, which gives rise to an intense C–H stretch at ∼3300 cm^–1. Further support for this HCN adsorption geometry is obtained through HCN/CO coadsorption experiments in which both molecules are seen to compete for the atop sites. The disappearance of the C–H stretch peak of HCN at low temperatures is indicative of dissociation to produce adsorbed H and CN. When the decrease in HCN coverage is followed for a sufficiently long time, the data deviate from the expected first-order rate law, and the temperature dependence of the rate constant deviates from the Arrhenius form. Over a more restricted coverage range, simpler behavior is observed, and an activation energy for HCN dissociation of 0.33 eV is obtained