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Louis W. Uccellini and John E. Ten Hoeve

Abstract

As the cost and societal impacts of extreme weather, water, and climate events continue to rise across the United States, the National Weather Service (NWS) has adopted a strategic vision of a Weather-Ready Nation that aims to help all citizens be ready, responsive, and resilient to extreme weather, water, and climate events. To achieve this vision and to meet the NWS mission of saving lives and property and enhancing the national economy, the NWS must improve the accuracy and timeliness of forecasts and warnings, and must directly connect these forecasts and warnings to critical life- and property-saving decisions through the provision of impact-based decision support services (IDSS). While the NWS has been moving in this direction for years, the shift to delivering IDSS holistically requires an agency-wide transformation. This article discusses the elements driving the need for change at the NWS to build a Weather-Ready Nation; the foundational basis for IDSS; ongoing challenges to provide IDSS across federal, state, local, tribal, and territorial levels of government; the path toward evolving the NWS to deliver more effective IDSS; the importance of partnerships within the weather, water, and climate enterprise and with those responsible for public safety to achieve the Weather-Ready Nation vision; and initial supporting evidence and lessons learned from early efforts.

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Mark Z. Jacobson and John E. Ten Hoeve

Abstract

Land use, vegetation, albedo, and soil-type data are combined in a global model that accounts for roofs and roads at near their actual resolution to quantify the effects of urban surface and white roofs on climate. In 2005, ~0.128% of the earthrsquo;s surface contained urban land cover, half of which was vegetated. Urban land cover was modeled over 20 years to increase gross global warming (warming before cooling due to aerosols and albedo change are accounted for) by 0.06–0.11 K and population-weighted warming by 0.16–0.31 K, based on two simulations under different conditions. As such, the urban heat island (UHI) effect may contribute to 2%–4% of gross global warming, although the uncertainty range is likely larger than the model range presented, and more verification is needed. This may be the first estimate of the UHI effect derived from a global model while considering both UHI local heating and large-scale feedbacks. Previous data estimates of the global UHI, which considered the effect of urban areas but did not treat feedbacks or isolate temperature change due to urban surfaces from other causes of urban temperature change, imply a smaller UHI effect but of similar order. White roofs change surface albedo and affect energy demand. A worldwide conversion to white roofs, accounting for their albedo effect only, was calculated to cool population-weighted temperatures by ~0.02 K but to warm the earth overall by ~0.07 K. White roof local cooling may also affect energy use, thus emissions, a factor not accounted for here. As such, conclusions here regarding white roofs apply only to the assumptions made.

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Sergey Kravtsov, John E. Ten Hoeve, Steven B. Feldstein, Sukyoung Lee, and Seok-Woo Son

Abstract

Simulations using an idealized, atmospheric general circulation model (GCM) subjected to various thermal forcings are analyzed via a combination of probability density function (PDF) estimation and spectral analysis techniques. Seven different GCM runs are examined, each model run being characterized by different values in the strength of the tropical heating and high-latitude cooling. For each model run, it is shown that a linear stochastic model constructed in the phase space of the ten leading empirical orthogonal functions (EOFs) of the zonal-mean zonal flow provides an excellent statistical approximation to the simulated zonal flow variability, which includes zonal index fluctuations, and quasi-oscillatory, poleward, zonal-mean flow anomaly propagation. Statistically significant deviations from the above linear stochastic null hypothesis arise in the form of a few anomalously persistent, or statistically nonlinear, flow patterns, which occupy particular regions of the model’s phase space. Some of these nonlinear regimes occur during certain phases of the poleward propagation; however, such an association is, in general, weak. This indicates that the regimes and oscillations in the model may be governed by distinct dynamical mechanisms.

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Seok-Woo Son, Sukyoung Lee, Steven B. Feldstein, and John E. Ten Hoeve

Abstract

The physical processes that determine the time scale of zonal-mean-flow variability are examined with an idealized numerical model that has a zonally symmetric lower boundary. In the part of the parameter space where the time-mean zonal flow is characterized by a single (double) jet, the dominant form of zonal-mean-flow variability is the zonal index (poleward propagation), and the time-mean potential vorticity gradient is found to be strong and sharp (weak and broad). The e-folding time scale of the zonal index is found to be close to 55 days, much longer than the observed 10-day time scale. The e-folding time scale of the poleward propagation is about 40 days. The long e-folding time scales for the zonal index are found to be consistent with an unrealistically strong and persistent eddy–zonal-mean-flow feedback. A calculation of the refractive index indicates that the background flow supports eddies that are trapped within midlatitudes, undergoing relatively little meridional propagation.

Additional model runs are performed with an idealized mountain to investigate whether zonal asymmetry can disrupt the eddy feedback. For single-jet states, the time scale is reduced to about 30 days if the mountain height is 4 km or less. The reduction in the time scale occurs because the stationary eddies excited by the mountain alter the background flow in a manner that leads to the replacement of zonal-index events by shorter-time-scale poleward propagation. With a 5-km mountain, the time scale reverts and increases to 105 days. This threshold behavior is again attributed to a sharpening of the background zonal jet, which arises from an extremely strong stationary wave momentum flux convergence. In contrast, for double-jet states, the time scale changes only slightly and the poleward propagation is maintained in all mountain runs.

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Sid-Ahmed Boukabara, Vladimir Krasnopolsky, Stephen G. Penny, Jebb Q. Stewart, Amy McGovern, David Hall, John E. Ten Hoeve, Jason Hickey, Hung-Lung Allen Huang, John K. Williams, Kayo Ide, Philippe Tissot, Sue Ellen Haupt, Kenneth S. Casey, Nikunj Oza, Alan J. Geer, Eric S. Maddy, and Ross N. Hoffman

Capsule Summary

Current research applying artificial intelligence to the Earth and environmental sciences is progressing quickly, with emerging developments in terms of efficiency, accuracy, and discovery.

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