More Like this

1. Sensitivity of Sudden Stratospheric Warmings to Previous Stratospheric Conditions

   https://doi.org/10.1175/JAS-D-17-0136.1  

   Cámara, Alvaro de; Albers, John R.; Birner, Thomas; Garcia, Rolando R.; Hitchcock, Peter; Kinnison, Douglas E.; Smith, Anne K. (September 2017, Journal of the Atmospheric Sciences)

   null (Ed.)

   Abstract The Whole Atmosphere Community Climate Model, version 4 (WACCM4), is used to investigate the influence of stratospheric conditions on the development of sudden stratospheric warmings (SSWs). To this end, targeted experiments are performed on selected modeled SSW events. Specifically, the model is reinitialized three weeks before a given SSW, relaxing the surface fluxes, winds, and temperature below 10 km to the corresponding fields from the free-running simulation. Hence, the tropospheric wave evolution is unaltered across the targeted experiments, but the stratosphere itself can evolve freely. The stratospheric zonal-mean state is then altered 21 days prior to the selected SSWs and rerun with an ensemble of different initial conditions. It is found that a given tropospheric evolution concomitant with the development of an SSW does not uniquely determine the occurrence of an event and that the stratospheric conditions are relevant to the subsequent evolution of the stratospheric flow toward an SSW, even for a fixed tropospheric evolution. It is also shown that interpreting the meridional heat flux at 100 hPa as a proxy of the tropospheric injection of wave activity into the stratosphere should be regarded with caution and that stratospheric dynamics critically influence the heat flux at that altitude. 

   more » « less
2. Sudden Stratospheric Warmings

   https://doi.org/10.1029/2020RG000708  

   Baldwin, Mark P.; Ayarzagüena, Blanca; Birner, Thomas; Butchart, Neal; Butler, Amy H.; Charlton‐Perez, Andrew J.; Domeisen, Daniela I. V.; Garfinkel, Chaim I.; Garny, Hella; Gerber, Edwin P.; et al (January 2021, Reviews of Geophysics)

   Abstract Sudden stratospheric warmings (SSWs) are impressive fluid dynamical events in which large and rapid temperature increases in the winter polar stratosphere (∼10–50 km) are associated with a complete reversal of the climatological wintertime westerly winds. SSWs are caused by the breaking of planetary‐scale waves that propagate upwards from the troposphere. During an SSW, the polar vortex breaks down, accompanied by rapid descent and warming of air in polar latitudes, mirrored by ascent and cooling above the warming. The rapid warming and descent of the polar air column affect tropospheric weather, shifting jet streams, storm tracks, and the Northern Annular Mode, making cold air outbreaks over North America and Eurasia more likely. SSWs affect the atmosphere above the stratosphere, producing widespread effects on atmospheric chemistry, temperatures, winds, neutral (nonionized) particles and electron densities, and electric fields. These effects span both hemispheres. Given their crucial role in the whole atmosphere, SSWs are also seen as a key process to analyze in climate change studies and subseasonal to seasonal prediction. This work reviews the current knowledge on the most important aspects of SSWs, from the historical background to dynamical processes, modeling, chemistry, and impact on other atmospheric layers. 

   more » « less
3. Reduced Poleward Transport Due to Stratospheric Heating Under Stratospheric Aerosols Geoengineering

   https://doi.org/10.1029/2020GL089470  

   Visioni, Daniele; MacMartin, Douglas G.; Kravitz, Ben; Lee, Walker; Simpson, Isla R.; Richter, Jadwiga H. (September 2020, Geophysical Research Letters)

   Abstract By injecting SO₂into the stratosphere at four latitudes (30°, 15°N/S), it might be possible not only to reduce global mean surface temperature but also to minimize changes in the equator‐to‐pole and inter‐hemispheric gradients of temperature, further reducing some of the impacts arising from climate change relative to equatorial injection. This can happen only if the aerosols are transported to higher latitudes by the stratospheric circulation, ensuring that a greater part of the solar radiation is reflected back to space at higher latitudes, compensating for the reduced sunlight. However, the stratospheric heating produced by these aerosols modifies the circulation and strengthens the stratospheric polar vortex which acts as a barrier to the transport of air toward the poles. We show how the heating results in a feedback where increasing injection rates lead to stronger high‐latitudinal transport barriers. This implies a potential limitation in the high‐latitude aerosol burden and subsequent cooling. 

   more » « less
4. Robust winter warming over Eurasia under stratospheric sulfate geoengineering – the role of stratospheric dynamics

   https://doi.org/10.5194/acp-21-6985-2021  

   Banerjee, Antara; Butler, Amy H.; Polvani, Lorenzo M.; Robock, Alan; Simpson, Isla R.; Sun, Lantao (January 2021, Atmospheric Chemistry and Physics)

   Abstract. It has been suggested that increased stratospheric sulfate aerosol loadings following large, low latitude volcanic eruptions can lead to wintertime warming over Eurasia through dynamical stratosphere–troposphere coupling. We here investigate the proposedconnection in the context of hypothetical future stratospheric sulfategeoengineering in the Geoengineering Large Ensemble simulations. In thosegeoengineering simulations, we find that stratospheric circulation anomalies that resemble the positive phase of the Northern Annular Mode in winter are a distinguishing climate response which is absent when increasing greenhouse gases alone are prescribed. This stratospheric dynamical response projects onto the positive phase of the North Atlantic Oscillation, leading to associated side effects of this climate intervention strategy, such as continental Eurasian warming and precipitation changes. Seasonality is a key signature of the dynamically driven surface response. We find an opposite response of the North Atlantic Oscillation in summer, when no dynamical role of the stratosphere is expected. The robustness of the wintertime forced response stands in contrast to previously proposed volcanic responses. 

   more » « less
5. Stratospheric Aerosols, Polar Stratospheric Clouds, and Polar Ozone Depletion After the Mount Calbuco Eruption in 2015

   https://doi.org/10.1029/2018JD028974  

   Zhu, Yunqian; Toon, Owen Brian; Kinnison, Douglas; Harvey, V. Lynn; Mills, Michael J.; Bardeen, Charles G.; Pitts, Michael; Bègue, Nelson; Renard, Jean‐Baptiste; Berthet, Gwenaël; et al (November 2018, Journal of Geophysical Research: Atmospheres)