Climate dynamics

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An evaluation of tropical waves and wave forcing of the QBO in the QBOi models

Quarterly Journal of the Royal Meteorological Society Wiley (2020) qj.3827

Authors:

Laura A Holt, François Lott, Rolando R Garcia, George N Kiladis, Yuan‐Ming Cheng, James A Anstey, Peter Braesicke, Andrew C Bushell, Neal Butchart, Chiara Cagnazzo, Chih‐Chieh Chen, Hye‐Yeong Chun, Yoshio Kawatani, Tobias Kerzenmacher, Young‐Ha Kim, Charles McLandress, Hiroaki Naoe, Scott Osprey, Jadwiga H Richter, Adam A Scaife, John Scinocca, Federico Serva, Stefan Versick, Shingo Watanabe, Seiji Yukimoto
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Improvements in Circumpolar Southern Hemisphere Extratropical Atmospheric Circulation in CMIP6 Compared to CMIP

Earth and Space Science American Geophysical Union (AGU) (2020)

Authors:

Tj Bracegirdle, Cr Holmes, Js Hosking, Gj Marshall, M Osman, M Patterson, T Rackow
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Dynamical-Chemical Feedbacks in General Circulation Models and Their Influence on Sudden Stratospheric Warming Events

(2020)

Authors:

Oscar Dimdore-Miles, Lesley Gray, Scott Osprey

Abstract:

<p>Sudden Stratospheric Warming events (SSWs) are rapid disruptions of the Northern Hemisphere (NH) winter stratospheric polar vortex and represent the largest source of inter-annual variability in the NH winter stratosphere. They have been linked to winter surface climate anomalies such as cold snaps over North America and Eurasia. Representing these events accurately in large scale GCMs as well as developing a greater understanding of them is key to improving predictability of winter surface climate. A key component of a GCM is its representation of atmospheric chemistry. Chemical distributions are either prescribed or calculated interactively by coupling an atmospheric chemistry model to radiation and dynamical components, thus capturing any chemical dynamical feedback mechanisms but incurring significant running cost.</p><p>This work evaluates the impact of interactive chemistry when modelling SSW events and explores the feedback mechanisms between chemical distributions and stratospheric dynamical variability. Pre-industrial control runs from the MetOffice HadGEMGC3.1 model which prescribes chemical fields and UKESM1 which calculates trace gas concentration interactively are utilised. Over the whole season - The Earth System Model appears to suppress warmings while the model with prescribed physics overestimates their occurrence compared to reanalysis. The differing representation of the equatorial stratosphere appears to be partially responsible for this difference. Additionally we find that middle stratosphere equatorial ozone concentration in late NH summer is closely associated with SSW probability in the ensuing winter in UKESM1. Anomalously low ozone is generally associated with an elevated SSW rate. This implies a chemical-dynamical coupling between the equator and the vortex in this model which preliminary results suggest could be driven by chemical feedbacks influencing the state of the early winter Quasi Biennial Oscillation (QBO) and Semi-Annual Oscillation (SAO) in zonal winds which can alter the distribution of planetary wave propagation and breaking (the primary cause of SSWs). Further work will assess whether this phenomenon is observed in other GCMs and further explore the physical mechanisms responsible.</p>
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Multi-thousand member ensemble atmospheric simulations with global 60km resolution using climateprediction.net

EGU General Assembly 2020 Copernicus GmbH (2020)

Authors:

Peter Watson, Sarah Sparrow, William Ingram, Simon Wilson, Drouard Marie, Giuseppe Zappa, Richard Jones, Daniel Mitchell, Tim Woollings, Myles Allen

Abstract:

<p>Multi-thousand member climate model simulations are highly valuable for showing how extreme weather events will change as the climate changes, using a physically-based approach. However, until now, studies using such an approach have been limited to using models with a resolution much coarser than the most modern systems. We have developed a global atmospheric model with 5/6°x5/9° resolution (~60km in middle latitudes) that can be run in the climateprediction.net distributed computing system to produce such large datasets. This resolution is finer than that of many current global climate models and sufficient for good simulation of extratropical synoptic features such as storms. It will also allow many extratropical extreme weather events to be simulated without requiring regional downscaling. We will show that this model's simulation of extratropical weather is competitive with that in other current models. We will also present results from the first multi-thousand member ensembles produced at this resolution, showing the impact of 1.5°C and 2°C global warming on extreme winter rainfall and extratropical cyclones in Europe.</p>
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Effect of the North Pacific tropospheric waveguide on the fidelity of model El-Niño teleconnections Effect of the North Pacific tropospheric waveguide on the fidelity of model El-Niño teleconnections

Journal of Climate American Meteorological Society 33:12 (2020) 5223-5237

Authors:

Ronald KK Li, Tim Woollings, Christopher O’Reilly, Adam A Scaife
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