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1. The role of the stratosphere in future mid-latitude climate projections

   Simpson, Isla R; Hitchcock, Peter; Seager, Richard; Wu, Yutian (April 2019, US CLIVAR VARIATINS)

   One of the greatest uncertainties when it comes to future projections of regional climate is how the large-scale atmospheric circulation will change (Shepherd 2014). While there is a general consensus among models on a zonal mean poleward shifting of the mid-latitude westerlies and associated storm tracks (Yin 2005; Kidston and Gerber 2010; Chang et al. 2012; Swart and Fyfe 2012; Wilcox et al. 2012; Barnes and Polvani 2013), there is a large spread in the magnitude of this response. In addition to this zonal mean, poleward shifting view, there are more localized changes in the circulation associated with altered stationary wave patterns (Stephenson and Held 1993; Joseph et al. 2004; Simpson et al. 2014). For many of these predicted changes, we do not have a good physical understanding of the mechanisms that produce them, or the factors that govern their uncertainty. The stratosphere and how it is expected to change in the future is one source of uncertainty, among many, in future tropospheric mid-latitude circulation change. There are a variety of ways in which the stratosphere’s mean state, variability and composition may impact on tropospheric climate change. Instead of providing an exhaustive review of this topic, we focus on the role of changes in the extra-tropical mean state of the stratosphere in future projections of tropospheric mid-latitude climate by considering two particular aspects. For the Northern Hemisphere we discuss the impact of uncertainty in future changes in the stratospheric polar vortex on tropospheric climate change. For the Southern Hemisphere we discuss the relative roles of stratospheric ozone depletion and changing greenhouse gas concentrations on the future evolution of the Southern Hemisphere mid-latitude jet stream. 

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2. Stratospheric Aerosol Injection Can Reduce Risks to Antarctic Ice Loss Depending on Injection Location and Amount

   https://doi.org/10.1029/2023JD039434  

   Goddard, P. B.; Kravitz, B.; MacMartin, D. G.; Visioni, D.; Bednarz, E. M.; Lee, W. R. (November 2023, Journal of Geophysical Research: Atmospheres)

   Abstract Owing to increasing greenhouse gas emissions, the Antarctic Ice Sheet is vulnerable to rapid ice loss in the upcoming decades and centuries. This study examines the effectiveness of using stratospheric aerosol injection (SAI) that minimizes global mean temperature (GMT) change to slow projected 21st century Antarctic ice loss. We simulate 11 different SAI cases which vary by the latitudinal location(s) and the amount(s) of the injection(s) to examine the climatic response near Antarctica in each case as compared to the reference climate at the turn of the last century. We demonstrate that injecting at a single latitude in the northern hemisphere or at the Equator increases Antarctic shelf ocean temperatures pertinent to ice shelf basal melt, while injecting only in the southern hemisphere minimizes this temperature change. We use these results to analyze the results of more complex multi‐latitude injection strategies that maintain GMT at or below 1.5°C above the pre‐industrial. All these multi‐latitude cases will slow Antarctic ice loss relative to the mid‐to‐late 21st century SSP2‐4.5 emissions pathway. Yet, to avoid a GMT threshold estimated by previous studies pertaining to rapid West Antarctic ice loss (1.5°C above the pre‐industrial GMT, though large uncertainty), our study suggests SAI would need to cool about 1.0°C below this threshold and predominately inject at low southern hemisphere latitudes (∼15°S ‐ 30°S). These results highlight the complexity of factors impacting the Antarctic response to SAI and the critical role of the injection strategy in preventing future ice loss. 

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3. Teleconnection of the Quasi-biennial oscillation with boreal winter surface climate in Eurasia and North America

   Kumar, Vinay; Hitchman, Matthew H.; Du, Wenyuan; Dhaka, S. K. (April 2024, Nature Communications Earth & Environment)

   The present study investigates dynamical coupling between the equatorial stratospheric Quasi31 biennial oscillation (QBO) and the boreal winter surface climate of the Northern Hemisphere mid and high latitudes using 42 years data (1979–2020). For neutral El Niño Southern Oscillation (ENSO) periods, QBO westerlies (W) at 70 hPa favor high sea level pressure in the polar region, colder conditions and deeper snow over Eurasia and North America, and the opposite effects for QBO easterlies (E). When QBO anomalies arrive in the upper troposphere and lower stratosphere (UTLS), it is observed that planetary wave activity is enhanced in the extratropical UTLS during QBO W and diminished during QBO E. This QBO teleconnection pathway along the UTLS to the high latitude surface is independent of the “stratospheric pathway” (Holton-Tan mechanism). Diagnosis of this pathway can help to improve understanding of internal sub-seasonal to seasonal variations, and long-range forecasting over Eurasia and North America. 

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4. From the Surface to the Stratosphere: Large‐Scale Atmospheric Response to Antarctic Meltwater

   https://doi.org/10.1029/2024GL110157  

   Beadling, Rebecca_L; Lin, Pu; Krasting, John; Ellinger, William; Coomans, Anna; Milward, James; Turner, Katherine; Xu, Xiaoqi; Martin, Torge; Molina, Maria_J (November 2024, Geophysical Research Letters)

   Abstract The ocean response to Antarctic Ice Sheet (AIS) mass loss has been extensively studied using numerical models, but less attention has been given to the atmosphere. We examine the global atmospheric response to AIS meltwater in an ensemble of experiments performed using two fully coupled climate models under a pre‐industrial climate. In response to AIS meltwater, the experiments yield cooling from the surface to the tropopause over the subpolar Southern Ocean, warming in the Southern Hemisphere polar stratosphere, and cooling in the upper tropical troposphere. Positive feedbacks, initiated by disrupted ocean‐atmosphere heat exchange, result in a change in the top‐of‐atmosphere radiative balance caused primarily through surface and near‐surface albedo changes. Changes in the atmospheric thermal structure alter the jet streams aloft. The results highlight the global influence of AIS melting on the climate system and the potential for impacts on mid‐latitude climate patterns and delayed regional warming signals. 

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5. Cold-air outbreaks in the continental US: Connections with stratospheric variations

   https://doi.org/10.1126/sciadv.adq9557  

   Agel, Laurie; Cohen, Judah; Barlow, Mathew; Pfeiffer, Karl; Francis, Jennifer; Garfinkel, Chaim I; Kretschmer, Marlene (July 2025, Science Advances)

   Mid-latitude Northern Hemisphere extreme cold events continue to occur despite overall winter warming trends. These events have been linked to weakened stratospheric polar vortex (SPV) states. In this study, we analyze both the upper and lower polar stratosphere for links to extreme winter cold and snow in the continental US, finding two SPV variations of interest. The first features an upper-level vortex displaced toward western Canada and linked to northwestern US severe winter weather. The second features a weakened upper-level vortex displaced toward the North Atlantic and linked to central-eastern US severe winter weather. Both variations feature lower-level stretched vortices and stratospheric wave reflection. Since 2015, a northwestward shift in severe winter weather across the US is concurrent with an increase in the frequency of the westward-focused variation relative to the eastward-focused variation and a shift to more negative phases of the El Niño–Southern Oscillation. 

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