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Abstract Errors due to imperfect boundary conditions in numerical relativity simulations of binary black holes (BBHs) can produce unphysical reflections of gravitational waves which compromise the accuracy of waveform predictions, especially for subdominant modes. A system of higher order absorbing boundary conditions which greatly reduces this problem was introduced in earlier work (Buchman and Sarbach 2006Class. Quantum Grav.236709). In this paper, we devise two new implementations of this boundary condition system in the Spectral Einstein Code (SpEC), and test them in both linear multipolar gravitational wave and inspiralling mass ratio 7:1 BBH simulations. One of our implementations in particular is shown to be extremely robust and to produce accuracy superior to the standard freezing-Ψ₀boundary condition usually used bySpEC. 

Abstract This paper examines the trends in hot summer days for the Pacific Northwest in observations and a regional climate model ensemble. Hot days are identified by the temperature threshold for several percentile values computed over 10-year intervals (85, 90, 95, and absolute maximum) to differentiate heat events of different intensities and are compared to the median temperature (50 th percentile). For the stations analyzed, the observed rate of warming during hot days is not statistically different from the warming rate of median days since the 1950s. However, for projections to 2100, hot days show a statistically significant increase in the warming rate of the hottest days compared to the warming rate for median days. Depending on location, the 95 th percentile daily maximum temperature shows a warming rate of up to 0.2°C per decade above the median warming rate. The divergence in the trends of median and extreme temperature shows substantial regional variation depending on local terrain and coastlines. The warming trend during hot days is related to the unique circulation patterns during heat events, which respond to different feedbacks and amplifying effects in the land-atmosphere system from those that prevail during typical days. The regional climate model simulations are taken from an ensemble of Weather Research and Forecasting (WRF) model simulations forced by 12 global climate model simulations from the 5 th Climate Model Intercomparison Project (CMIP5) using the RCP8.5 emissions scenario and 12-km grid spacing.