Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session H21: Extreme Events in a Changing ClimateInvited Undergraduate
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Sponsoring Units: GPC DFD GSNP Chair: Brad Marston, Brown University Room: 281-282 |
Tuesday, March 14, 2017 2:30PM - 3:06PM |
H21.00001: Extreme events, tail statistics, and large deviation theory in geophysical flows Invited Speaker: Eric Vanden-Eijnden The talk will give an overview of analytical and numerical methods that have been recently introduced to characterize the pathway, rate, and likelihood of rare but important events observed in the context of geophysical flows. These methods build on large deviation theory, which indicates that the way such events occur is often predictable and offers way to compute them via solution of an optimization problem for their most likely path. These concepts and ideas will be illustrated via examples ranging from transitions between metastable patterns in atmospheric flows to rogue waves. [Preview Abstract] |
Tuesday, March 14, 2017 3:06PM - 3:42PM |
H21.00002: The signal and the noise: forced and unforced changes in temperature distributions and the probability of extremes Invited Speaker: Karen McKinnon Recent observed trends in climate variables are a combination of a forced climate change signal and unforced internal variability, or noise. In order to gain insight into important climate parameters such as climate sensitivity and make reasonable projections into the future, it is necessary to separate the forced signal from the random sampling of variability. Here, I focus on this goal in the context of the changing shape of daily temperature distributions. Because daily temperature distributions tend to be non-Gaussian, I will first introduce a non-parametric method based on quantile regression which summarizes changes in the shape of seasonal temperature distributions with a small set of basis functions. Next, I will explore the relative roles of circulation and the land surface in controlling the trends in daily temperature distributions in both the observations and the NCAR CESM1 Large Ensemble. In the context of the Large Ensemble, it is then possible to determine which trends -- and which physical mechanisms associated with the trends -- are the signal, and can reasonably be expected to continue into the future. [Preview Abstract] |
Tuesday, March 14, 2017 3:42PM - 4:18PM |
H21.00003: Influence of Anthropogenic Climate Change on Planetary Wave Resonance and Extreme Weather Events Invited Speaker: Michael Mann Persistent episodes of extreme weather in the Northern Hemisphere summer have been shown to be associated with the presence of high-amplitude quasi-stationary atmospheric Rossby waves within a particular wavelength range (zonal wavenumber 6-8) 1. The underlying mechanistic relationship involves the phenomenon of quasi-resonant amplification (QRA) of synoptic-scale waves with that wavenumber range becoming trapped within an effective mid-latitude atmospheric waveguide1-3. Recent work suggests an increase in recent decades in the occurrence of QRA-favorable conditions and associated extreme weather, possibly linked to amplified Arctic warming4 and thus a climate change influence5. Here, we isolate a specific fingerprint in the zonal mean surface temperature profile that is associated with QRA-favorable conditions. State-of-the-art (``CMIP5'') historical climate model simulations subject to anthropogenic forcing display an increase in the projection of this fingerprint that is mirrored in multiple observational surface temperature datasets. Both the models and observations suggest this signal has only recently emerged from the background noise of natural variability. [Preview Abstract] |
Tuesday, March 14, 2017 4:18PM - 4:54PM |
H21.00004: Human influence on tropical cyclone intensity Invited Speaker: Adam Sobel Recent assessments agree that tropical cyclone intensity should increase as the climate warms. Less agreement exists on the detection of recent historical trends in tropical cyclone intensity. We interpret future and recent historical trends by using the theory of potential intensity, which predicts the maximum intensity achievable by a tropical cyclone in a given local environment. Although greenhouse gas--driven warming increases potential intensity, climate model simulations suggest that aerosol cooling has largely canceled that effect over the historical record. Large natural variability complicates analysis of trends, as do poleward shifts in the latitude of maximum intensity. In the absence of strong reductions in greenhouse gas emissions, future greenhouse gas forcing of potential intensity will increasingly dominate over aerosol forcing, leading to substantially larger increases in tropical cyclone intensities. [Preview Abstract] |
Tuesday, March 14, 2017 4:54PM - 5:30PM |
H21.00005: Crazy Weather and the Arctic Meltdown: Emerging Connections Invited Speaker: Jennifer Francis \textbf{The issue:} In recent decades, the pace of Arctic warming was at least double that of the globe. A growing body of research suggests this differential warming will increase the frequency of extreme weather events in the northern hemisphere. \textbf{Why it matters:} Extreme weather events cause billions of dollars in damage, scores of deaths and injuries, and thousands of disrupted lives each year. The frequency of these events is increasing, and certain types have clear links to climate change. Rapid Arctic warming is expected to cause more persistent weather regimes that can lead to devastating drought, prolonged heat waves, extreme fire seasons, stormy winters, and heavy flooding, many of which have been prominent weather headlines across the U.S. in recent years. \textbf{State of the Science:} The dramatic Arctic warming during recent decades is reducing the temperature difference between the Arctic and mid-latitudes, which is weakening the jet stream's west-to-east winds. $^{\mathrm{\thinspace }}$Instead of a coherent river of strong winds, a weaker jet tends to waver, split, and wander north and south on its path around the northern hemisphere. These wavier jet streams are responsible for a variety of extreme weather events, which have become more frequent in the U.S., Canada, Europe, and Asia. [Preview Abstract] |
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