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Articles by Isla Simpson
Attributing surface climate impacts to decadal variability of the Northern Hemisphere stratospheric polar vortex
Abstract The role of the stratosphere for decadal surface cooling in subpolar and midlatitude Eurasia over the last few decades despite Arctic amplification is isolated using two sets of simulations in four different coupled ocean-atmosphere climate models.
Gaps and ways forward in atmospheric blocking and extreme weather research
Abstract Atmospheric blocking often results in significant weather extremes and associated impacts such as heatwaves, droughts, wildfires, cold spells, and floods in mid-latitude regions. However, the physical processes behind blocking and associated extreme weather events are not well understood, hampering prediction and decision-making for mitigation and adaptation.
Externally-Forced Changes to Southern Hemisphere Stratosphere-Troposphere Coupling Variability
1 Introduction Observed and projected changes in the Southern Hemisphere (SH) mean circulation have been linked to increasing greenhouse gases, stratospheric ozone depletion, and ozone recovery (Eyring et al., 2013; Son et al., 2010, 2018).
On the Robustness of Modeled Non‐Local Temperature Effects of Historical Land Use Changes
1 Introduction Historically, industrial combustion of fossil fuels, as well as land use and land cover changes (LULCC), have fundamentally altered the climate we live in (IPCC, 2019).
Is the High ECS in CESM2 Degrading Transient Climate Change Projections Over the 21st Century?
1 Introduction The Coupled Model Intercomparison Project Phase 6 (CMIP6) presents the climate science community with a large number of “hot models” (Hausfather et al., 2022). Sixteen of 53 CMIP6 models have equilibrium climate sensitivities (ECS) greater than 4.5 K, the highest ECS of the CMIP5 models (Zelinka, 2022).
Seasonal and regional jet stream changes and drivers - Nature Reviews Earth & Environment
Abstract The eddy-driven jet streams, which are regions of strong westerly wind in the mid-latitudes of both hemispheres, exert a leading influence on regional climate. In this Review, we outline the seasonally and regionally varying drivers, characteristics and changes in the jet streams.
Publisher Correction: Recent southwestern US drought exacerbated by anthropogenic aerosols and tropical ocean warming - Nature Geoscience
The Impact of Soil Preconditioning on the Evolution of Heatwaves Under Constrained Circulation: A Case Study of the 2021 Pacific Northwest Heatwave
1 Introduction In late June 2021, the North American Pacific Northwest (PNW) experienced an unprecedented heatwave. Many locations in the states of Washington and Oregon in the United States and the provinces of British Columbia and Alberta in Canada, recorded temperatures 10–20 ° ${}^{\circ}$ C above the climatological mean, and more than 4 ° ${}^{\circ}$ C above the all time record (Conrick & Mass, 2023; Loikith & Kalashnikov, 2023; White et al., 2023, see also Figure 1).
The Path Toward Vertical Grid Options for the Community Atmosphere Model Version 7: The Impact of Vertical Resolution on the QBO and Tropical Waves
1 Introduction Earth System Models (ESMs) are numerical representations of the coupled Earth system that are used to study the fundamental processes involved in the Earth's climate and to provide predictions for how the climate will evolve on timescales ranging from weeks to centuries. Model developers continue to strive to improve the representation of the processes relevant to the climate system under the constraint of available computing resources.
Recent southwestern US drought exacerbated by anthropogenic aerosols and tropical ocean warming - Nature Geoscience
Abstract The southwestern United States is currently in a multi-decade drought that has developed since a precipitation maximum in the 1980s. While anthropogenic warming has made the drought more severe, it is the decline in winter–spring precipitation that has had a more profound effect on water resources and ecosystems.
Confronting Earth System Model trends with observations
Abstract Anthropogenically forced climate change signals are emerging from the noise of internal variability in observations, and the impacts on society are growing. For decades, Climate or Earth System Models have been predicting how these climate change signals will unfold.
Agricultural fertilization significantly enhances amplitude of land-atmosphere CO2 exchange - Nature Communications
Abstract Observations show an increase in the seasonal cycle amplitude of CO2 in northern latitudes over the past half century. Although multiple drivers contribute, observations and inversion models cannot quantitatively account for the factors contributing to the increased CO2 amplitude and older versions of Earth System Models (ESMs) do not simulate it.
Revisiting the reanalysis-model discrepancy in Southern Hemisphere winter storm track trends - npj Climate and Atmospheric Science
Abstract Southern Hemisphere (SH) storminess has increased in the satellite era and recent work suggests comprehensive climate models significantly underestimate the trend. Here, we revisit this reanalysis-model trend discrepancy to better understand the mechanisms underlie it. A comprehensive like-for-like analysis shows reanalysis trends exhibit large uncertainty, and coupled climate model simulations exhibit weaker trends than most but not all reanalyses.
Resolving Weather Fronts Increases the Large‐Scale Circulation Response to Gulf Stream SST Anomalies in Variable‐Resolution CESM2 Simulations
1 Introduction North Atlantic sea-surface temperatures (SSTs) exhibit variability on seasonal to decadal timescales (e.g., Deser & Blackmon, 1993; R. Zhang et al., 2019), providing a potential source of predictability for atmospheric circulation and regional climate on these timescales. Recent work has improved our understanding of the ocean-atmosphere mechanisms governing North Atlantic SST variability (Årthun et al., 2021; Delworth et al., 2017; Menary et al., 2015; R. C. J. Wills et al., 2019; S.
Recent and near‐term future changes in impacts‐relevant seasonal hydroclimate in the world's Mediterranean climate regions
1 INTRODUCTION The world's Mediterranean climate regions (MCRs) occupy transitional zones between the subtropics and mid-latitudes on the western edges of continents. The Mediterranean climate type is characterized by temperate, wet winters and hot or warm dry summers. The wet winters arise from MCRs being on the equatorward flank of the mid-latitude storm tracks and just poleward of the descending branch of the Hadley Cell.
Two perspectives on amplified warming over tropical land examined in CMIP6 models
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What Drives the Spread and Bias in the Surface Impact of Sudden Stratospheric Warmings in CMIP6 Models?
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An unexpected decline in spring atmospheric humidity in the interior Southwestern United States and implications for forest fires
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An even drier future for the arid lands | Proceedings of the National Academy of Sciences
Recent heat extremes, wildfires, and droughts have afflicted multiple regions including parts of South America, the Mediterranean, and Middle East as well as the southwestern United States. These events underscore the vulnerability of societies to ongoing climate change as well as the precarious dependence of societies and ecosystems upon fresh water, the terrestrial lifeblood.
Forest mosaics, not savanna corridors, dominated in Southeast Asia during the Last Glacial Maximum | Proceedings of the National Academy of Sciences
Forest mosaics, not savanna corridors, dominated in Southeast Asia during the Last Glacial Maximum Edited by Carlos Nobre, University of São Paulo, Sao José dos Campos, Brazil; received July 3, 2023; accepted November 7, 2023 Significance We present new qualitative and statistical analyses of 59 palaeoecological records across Southeast Asia to show that, instead of swings between open savanna and dense rainforest ecosystems, the climatic changes of the Last Glacial Period (119–11.7 ka) and...
The CESM2 Single Forcing Large Ensemble and Comparison to CESM1: Implications for Experimental Design
Abstract Single Forcing Large Ensembles are a relatively new tool for quantifying the contributions of different anthropogenic and natural forcings to the historical and future projected evolution of the climate system.
Dynamics and Impacts of the North Pacific Eddy-Driven Jet Response to Sudden Stratospheric Warmings
ProCite RefWorks Reference Manager BibTeX Zotero Ayarzagüena, B., F. M.Palmeiro, D.Barriopedro, N.Calvo, U.Langematz, and K.Shibata, 2019: On the representation of major stratospheric warmings in reanalyses. Atmos. Chem. Phys., 19, 9469–9484, https://doi.org/10.5194/acp-19-9469-2019. Ayarzagüena, B., F. M. Palmeiro, D. Barriopedro, N. Calvo, U. Langematz, and K. Shibata , 2019: On the representation of major stratospheric warmings in reanalyses . Atmos. Chem.
How Unexpected Was the 2021 Pacific Northwest Heatwave?
3 The Relationship Between Skewness and the Magnitude of Extreme Heat The PNW, like most locations on the westward edge of continents but unlike the majority of land areas in the Northern Hemisphere extratropics (McKinnon et al., 2016), experiences summertime temperature values that are, on average, positively skewed.
Drought: Mechanisms and Impacts in the Past, Present, and Future I Oral
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Perspective | Fueled by climate change, costly Southwest drought isn’t going away
With absent rainy seasons, depleted snowpack, widespread heat waves, unprecedented wildfires and low reservoirs, the American West has experienced an extraordinary drought since early 2020. To inform and prepare Americans for droughts like this one, three questions are critical to answer: How bad is this drought? What caused it? And, when will it end?
Hot extremes have become drier in the United States Southwest
References 1. Seager, R. et al. Whither the 100th meridian? The once and future physical and human geography of America’s arid–humid divide. Part I: The story so far. Earth Interact. 22, 1–22 (2018). Google Scholar 2. Bradshaw, L. S., Deeming, J. E., Burgan, R. E. & Cohen, J. D. The 1978 National Fire-Danger Rating System: Technical Documentation (USDA Forest Service, 1983). 3. Evett, R. R., Mohrle, C. R., Hall, B. L., Brown, T. J. & Stephens, S. L.
Stratospheric Sulfate Aerosol Geoengineering Could Alter the High‐Latitude Seasonal Cycle
Research Letter Long Cao Corresponding Author E-mail address: longcao@zju.edu.cn Department of Atmospheric Sciences, School of Earth Sciences, Zhejiang University, Hangzhou, China Correspondence to: L.
Predictability of Northern Hemisphere Final Stratospheric Warmings and Their Surface Impacts
Research Letter Amy H. Butler Corresponding Author E-mail address: amy.butler@noaa.gov https://orcid.org/0000-0002-3632-0925 Cooperative Institute for Research in Environmental Sciences, University of Colorado Boulder, Boulder, CO, USA National Oceanic and Atmospheric Administration, Chemical Sciences Division, Boulder, CO, USA Correspondence to: A. H. Butler, E-mail address: amy.butler@noaa.gov Search for more papers by this author PDF PDF ShareShare Get access to the full version of this article.
Decadal predictability of late winter precipitation in western Europe through an ocean-jet stream connection
Abstract The characteristics of the North Atlantic jet stream play a key role in the weather and climate of western Europe.
Attributing the U.S. Southwest's Recent Shift Into Drier Conditions
Research Letter Attributing the U.S. Southwest's Recent Shift Into Drier Conditions Flavio Lehner Corresponding Author E-mail address: flehner@ucar.edu http://orcid.org/0000-0003-4632-9701 National Center for Atmospheric Research, Climate and Global Dynamics Laboratory, Boulder, CO, USA Search for more papers by this author Abstract The U.S. Southwest experienced a strong hydroclimate trend from the 1980s to the 2010s, from cool and wet to warm and dry conditions.
Climate Variability and Change of Mediterranean-Type Climates
Mediterranean-type climates are defined by temperate, wet winters, and hot or warm dry summers and exist at the western edges of five continents in locations determined by the geography of winter storm tracks and summer subtropical anticyclones. The climatology, variability, and long-term changes in winter precipitation in Mediterranean-type climates, and the mechanisms for model-projected near-term future change, are analyzed.
A stratospheric pathway linking a colder Siberia to Barents-Kara Sea sea ice loss
Previous studies have extensively investigated the impact of Arctic sea ice anomalies on the midlatitude circulation and associated surface climate in winter. However, there is an ongoing scientific debate regarding whether and how sea ice retreat results in the observed cold anomaly over the adjacent continents.
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