Previous work showed that climate models capture historical large‐scale meteorological patterns (LSMPs) associated with California Central Valley heat waves including both ways these heat waves form. This work examines what models predict under the Representative Concentration Pathway (RCP) 4.5 and RCP8.5 scenarios. Model performance varies, so a multimodel average weights each model based on its historical performance in four parameters. An LSMP index (LSMPi) defined using upper atmosphere variables captures dates of past extreme surface temperature maxima. LSMPi correlates well with all values of California Central Valley‐average surface maximum temperature. LSMPi distributions in future simulations shift ~0.6 standard deviations higher between 1961–2000 and 2061–2100 for RCP8.5 data. Based on the historical climatology, future scenarios show a large increase in the frequency and duration of heat waves in every model. Four times as many heat waves occur and their median duration doubles, using historical thresholds. Of the two ways heat waves form, Type 1 has similar frequency in the future. But, Type 2 becomes much more common because Type 2 has a preexisting hot anomaly in Southwestern Canada, much like the historical to future climatological change in that region (a “global warming” signal). The 20‐year return value anomaly increases by 30–40%. The average of the 50 hottest temperatures increases 3.5–6 K depending on the scenario. When extreme values are defined using the future climatology, the models and their average have no consistent increase or decrease of distribution properties such as shape, scale, and return values of the extremes compared to historical values.
[1] In an attempt to assess the benefit of resolving the subsynoptic to mesoscale processes, the spatial and temporal characteristics of the annular modes (AMs), in particular those related to the troposphere-stratosphere interaction, are evaluated for moderate and high horizontal resolution simulations with the European Centre for Medium-Range Weather Forecast Integrated Forecast System global atmospheric general circulation model in comparison with the reanalysis. Notably, the performance with the high horizontal resolution (T1279 truncation,~16 km) version of the model is relatively more skillful than the moderate resolution (T159 truncation,~125 km) on most metrics examined, including the variance of the AMs at different seasons of the year, the intrinsic e-folding time scales of the AMs, and the downward influence from the stratosphere to troposphere in the AMs. Moreover, the summer Southern Annular Mode is more persistent in the high resolution and projected to respond in a greater magnitude to climate change forcing than the moderate resolution. Citation: Palipane, E., J. Lu, G. Chen, and J. L. Kinter III (2013), Improved annular mode variability in a global atmospheric general circulation model with 16 km horizontal resolution, Geophys. Res. Lett., 40,[4893][4894][4895][4896][4897][4898][4899]
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