Kane A. Stone

Stratospheric Injection of Brominated Very Short‐Lived Substances: Aircraft Observations in the Western Pacific and Representation in Global Models

We quantify the stratospheric injection of brominated very short‐lived substances (VSLS) based on aircraft observations acquired in winter 2014 above the Tropical Western Pacific during the CONvective TRansport of Active Species in the Tropics (CONTRAST) and the Airborne Tropical TRopopause EXperiment (ATTREX) campaigns. The overall contribution of VSLS to stratospheric bromine was determined to be 5.0 ± 2.1 ppt, in agreement with the 5 ± 3 ppt estimate provided in the 2014 World Meteorological Organization (WMO) Ozone Assessment report (WMO 2014), but with lower uncertainty. Measurements of organic bromine compounds, including VSLS, were analyzed using CFC‐11 as a reference stratospheric tracer. From this analysis, 2.9 ± 0.6 ppt of bromine enters the stratosphere via organic source gas injection of VSLS. This value is two times the mean bromine content of VSLS measured at the tropical tropopause, for regions outside of the Tropical Western Pacific, summarized in WMO 2014. A photochemical box model, constrained to CONTRAST observations, was used to estimate inorganic bromine from measurements of BrO collected by two instruments. The analysis indicates that 2.1 ± 2.1 ppt of bromine enters the stratosphere via inorganic product gas injection. We also examine the representation of brominated VSLS within 14 global models that participated in the Chemistry‐Climate Model Initiative. The representation of stratospheric bromine in these models generally lies within the range of our empirical estimate. Models that include explicit representations of VSLS compare better with bromine observations in the lower stratosphere than models that utilize longer‐lived chemicals as a surrogate for VSLS.

On the Identification of Ozone Recovery

As ozone depleting substances decline, stratospheric ozone is displaying signs of healing in the Antarctic lower stratosphere. Here we focus on higher altitudes and the global stratosphere. Two key processes that can influence ozone recovery are evaluated: dynamical variability and solar proton events (SPEs). A nine-member ensemble of free-running simulations indicates that dynamical variability dominates the relatively small ozone recovery signal over 1998–2016 in the subpolar lower stratosphere, particularly near the tropical tropopause. The absence of observed recovery there to date is therefore not unexpected. For the upper stratosphere, high latitudes (50–80°N/S) during autumn and winter show the largest recovery. Large halogen-induced odd oxygen loss there provides a fingerprint of seasonal sensitivity to chlorine trends. However, we show that SPEs also have a profound effect on ozone trends within this region since 2000. Thus, accounting for SPEs is important for detection of recovery in the upper stratosphere. Plain Language Summary With the continuing decline in ozone depleting substances, upper-atmospheric ozone is displaying signs of healing in the Antarctic region. Using a state-of-the-art model that simulates the Earth system, the nature of future ozone recovery outside of the Antarctic region is investigated to identify potential fingerprints for observing future ozone recovery. The model results show that ozone recovery near 40 km is expected to be largest near the poles in both hemispheres during winter and spring, while there is still large variability in the tropical region. However, energetic protons from solar events also have an effect on ozone in these regions through well-known chemical mechanisms. Therefore, taking these effects into account will be important for detecting this ozone recovery in observations.

On the Role of Heterogeneous Chemistry in Ozone Depletion and Recovery

We demonstrate that identification of stratospheric ozone changes attributable to ozone depleting substances and actions taken under the Montreal Protocol requires evaluation of confounding influences from volcanic eruptions. Using a state‐of‐the‐art chemistry‐climate model, we show that increased stratospheric aerosol loading from volcanic eruptions after 2004 impeded the rate of ozone recovery post‐2000. In contrast, eruptions increased ozone loss rates over the depletion era from 1980 to 1998. We also present calculations without any aerosol chemistry to isolate contributions from gas‐phase chemistry alone. This study reinforces the need for accurate information regarding stratospheric aerosol loading when modeling ozone changes, particularly for the challenging task of accurately identifying the early signs of ozone healing distinct from other sources of variability.

Large-scale transport into the Arctic: the roles of the midlatitude jetand the Hadley Cell

and the Hadley Cell Huang Yang1, Darryn W. Waugh1,2, Clara Orbe3, Guang Zeng4, Olaf Morgenstern4, Douglas E. Kinnison5, Jean-Francois Lamarque5, Simone Tilmes5, David A. Plummer6, Patrick Jöckel7, Susan E. Strahan8,9, Kane A. Stone10,11,a, and Robyn Schofield10,11 1Department of Earth and Planetary Sciences, Johns Hopkins University, Baltimore, Maryland, USA 2School of Mathematics, University of New South Wales, Sydney, Australia 3NASA Goddard Institute for Space Studies, New York, New York, USA 4National Institute of Water and Atmospheric Research, Wellington, New Zealand 5National Center for Atmospheric Research (NCAR), Atmospheric Chemistry Observations and Modeling (ACOM) Laboratory, Boulder, Colorado, USA 6Climate Research Branch, Environment and Climate Change Canada, Montreal, QC, Canada 7Deutsches Zentrum für Luftund Raumfahrt (DLR), Institut für Physik der Atmosphäre, Oberpfaffenhofen, Germany 8Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center, Greenbelt, Maryland, USA 9Universities Space Research Association, Columbia, Maryland, USA 10School of Earth Sciences, University of Melbourne, Melbourne, Victoria 3010, Australia 11ARC Centre of Excellence for Climate System Science, University of New South Wales, Sydney, New South Wales 2052, Australia anow at: Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139-4307, USA Correspondence: Huang Yang (hyang61@jhu.edu)

Tropospheric ozone in CCMI models and Gaussian emulation to understand biases in the SOCOLv3 chemistry-climate model

Previous multi-model intercomparisons have shown that chemistry-climate models exhibit significant biases in tropospheric ozone compared with observations. We investigate annual-mean tropospheric column ozone in 15 models participating in the SPARC/IGAC (Stratosphere-troposphere Processes and their Role in Climate/International Global Atmospheric Chemistry) Chemistry-Climate Model Initiative (CCMI). These models exhibit a positive bias, on average, of up to 40–50% in the Northern Hemisphere compared with observations derived from the Ozone Monitoring Instrument and Microwave Limb 5 Sounder (OMI/MLS), and a negative bias of up to ∼30% in the Southern Hemisphere. SOCOLv3.0 (version 3 of the SolarClimate Ozone Links CCM), which participated in CCMI, simulates global-mean tropospheric ozone columns of 40.2 DU – approximately 33% larger than the CCMI multi-model mean. Here we introduce an updated version of SOCOLv3.0, “SO1 Atmos. Chem. Phys. Discuss., https://doi.org/10.5194/acp-2018-615 Manuscript under review for journal Atmos. Chem. Phys. Discussion started: 26 June 2018 c

Observing the Impact of Calbuco Volcanic Aerosols on South Polar Ozone Depletion in 2015

The Southern Hemisphere Antarctic stratosphere experienced two noteworthy events in 2015: a significant injection of sulfur from the Calbuco volcanic eruption in Chile in April, and a record-large Antarctic ozone hole in October and November. Here, we quantify Calbucos influence on stratospheric ozone depletion in austral spring 2015 using observations and an earth system model. We analyze ozonesondes, as well as data from the Microwave Limb Sounder. We employ the Community Earth System Model, version 1, with the Whole Atmosphere Community Climate Model (CESM1(WACCM)) in a specified dynamics setup, which includes calculations of volcanic effects. The Cloud Aerosol Lidar with Orthogonal Polarization data indicate enhanced volcanic liquid sulfate 532 nm backscatter values as far poleward as 68°S during October and November (in broad agreement with WACCM). Comparison of the location of the enhanced aerosols to ozone data supports the view that aerosols played a major role in increasing the ozone hole size, especially at pressure levels between 150 and 100 hPa. Ozonesonde vertical ozone profiles from the sites of Syowa, South Pole, and Neumayer, display the lowest individual October or November measurements at 150 hPa since the 1991 Mt. Pinatubo eruption period, with Davis showing similarly low values, but no available 1990s data. The analysis suggests that under the cold conditions ideal for ozone depletion, stratospheric volcanic aerosol particles from the moderate-magnitude eruption of Calbuco in 2015 greatly enhanced austral ozone depletion, particularly at 55–68°S, where liquid binary sulfate aerosols have a large influence on ozone concentrations.