Simone Tilmes

General Information

ACD - TIIMES
Project Scientist I
UTLS

Contact Information:
PO Box 3000, Boulder, CO 80307-3000
Office: FL0
Telephone: 303-497-1445
Email: tilmes@ucar.edu
Middle-Upper Atmosphere & WACCM Group (ACD)
Vita

Research Focus FY08:

Top panels: The temporal development of PACl taking into account the changing halogen burden in the stratosphere for two geo-engineering cases between 2010 and 2050, to counteract global warming in case of CO2 doubling (expected to occur around 2050), using observed temperatures for a very cold Arctic winter (panel a) and a moderately cold Arctic winter (panel b). The temporal evolution of PACl for background surface area densities (SAD) (solid line), is also shown. Finally, values of PACl based on observed SAD, temperature, and halogen burden, are shown (dotted lines). Bottom panel: Chemical ozone loss versus time, derived from PACl (top panels) for the various SAD cases, is shown for meteorological conditions corresponding to a very cold Arctic winter (panel c) and a moderately cold Arctic winter (panel d). The ozone loss estimates are based on the linear relationship between chemical loss and PACl for the Arctic (Tilmes et al., Science, June 2, 2008).

Impact of Geo-engineered Aerosols on the Troposphere and Stratosphere

Geo-engineering schemes have been proposed to alleviate the consequences of global warming by continuous injection of sulfur into the stratosphere. Volcanic eruptions in the past have shown that strongly enhanced sulfate aerosols in the stratosphere result in a higher planetary albedo, leading to surface cooling. However, the increase of sulfate aerosol surface area enhances heterogeneous reactions in the stratosphere that lead to ozone loss. The potential for exceedingly high Arctic ozone depletion in the context of geo-engineering is known. On the other hand, decreasing halogen compounds in the atmosphere result in a recovery of the ozone layer and lessen the potential impact of aerosols.

Simone Tilmes investigated the sensitivity of polar ozone depletion to a proposed geo-engineering scheme for present and future halogen conditions. She used an empirical projection of past observations to future conditions. The deployment of a geo-engineering scheme to counteract global warming would result in a significant increase of polar stratospheric ozone depletion in the Northern Hemisphere up to the end of this century (Figure 1). Further, the recovery of the Antarctic ozone hole will be delayed by several decades in case geo-engineered aerosols would be applied to cool the climate (Tilmes et al, Science 2. June, 2008)

Further, Simone Tilmes used the NCAR, Whole Atmosphere Community Climate Model (WACCM), studying impact of Geo-engineering on the troposphere as well as on stratospheric chemistry and dynamics. Besides the cooling of the troposphere, local temperature changes and a decrease in precipitation in the Tropics is a possible result of geo-engineering. Further, changes in stratospheric chemistry and dynamics slow down the recovery of ozone for mid- and high latitudes in the Southern Hemisphere. A 200-300% increase of polar ozone depletion in the Northern Hemisphere in winter spring was also simulated.

Evaluation of Chemistry Transport Models (CTMs) and Chemistry Climate Models (CCMs) using Aircraft observations

A good representation of the Upper Troposphere Lower Stratosphere (UTLS) processes in CCMs is an important component for the model’s ability to predict climate changes. Currently, the international research community, led by SPARC, is working together on a process oriented validation project (CCMVal). As part of this project, diagnostics were proposed to quantify irreversible mixing processes in the UTLS region and the effect of Stratospheric Tropospheric Exchange (STE) on trace gas distribution using tracer-tracer correlations.

Depending on large-scale circulation and varying tropospheric weather systems, the signature of STE and mixing in the UTLS region varies with latitudes and season. Therefore, understanding the impact of transport and mixing for carefully separated regions based on dynamical and transport characteristics is important to localize shortcomings in the models.

Simone Tilmes uses aircraft observations of several campaigns that took place in the Northern Hemisphere to establish a climatology. Various trace gases are separated into seasons and regimes base on dynamical and transport characteristics (Figure 2). This aircraft serves as a reference for CTMs and CCMs, and can be used for satellite data validation. START08 data will be included into the climatology.

 

START08

Simone Tilmes is Co-investigator of the Stratosphere-Troposphere Analyses of Regional Transport Experiment UTLS (START08) campaign, which took part between 21 April 2008 and 28 June 2008. Together with Bill Hall, she works on the data merging products for the campaign. Initial data comparisons show a very promising upcoming data product. START08 data will be used for a detailed model comparison using the NCAR WACCM model.

In the News:
- Stratospheric Injections to Counter Global Warming Could Damage Ozone Layer (NCAR)
- Staff Notes: A close look at one - geoengineering scheme
- NSF: Windows to the Universe: Injecting Sulfate Particles into Stratosphere Could Have Drastic Impact on Earth's Ozone Layer

Scientific Talks FY08:

• Impact of geo-engineered aerosols on stratospheric composition and dynamics (AGU, San Francisco, CA, December 2007)
• Impact of geo-engineered aerosols on stratospheric composition and dynamics (MPI, Mainz, Germany, January 2008)
• Impact of geo-engineered aerosols on stratospheric composition and dynamics (MPI, Hamburg, Germany, January 2008)
• Transport Characteristics of the UTLS region based on tracers with different lifetimes using the MOZART3 model (START08 Workshop, Boulder, CO January 2008)
• HIRDLS use with WACCM3 and MOZART (HIRDLS Science Team Meeting, Boulder, CO, January 2008)
• Impact of Geo-engineered Aerosols on Stratosphere composition and dynamics (EGU, Vienna, Austria, April 2008) - poster
• Method of model evaluation for the extra-tropical tropopause region and its application to NCAR WACCM models (EGU, Vienna, Austria, April 2008)
• Impact of Geo-engineered Aerosol Particles on Troposphere and Stratosphere (ACD-NCAR Seminar, Boulder, CO, September 2008)

Publications FY08:

Tilmes, S., R. Müller, R. Salawitch, 2008: The sensitivity of polar ozone depletion to proposed geoengineering schemes. Science, 320, 1201-1204, doi: 10.1126/science.1153966.

Tilmes, S., R. Müller, R. J. Salawitch, U. Schmidt, C. R. Webster, H. Oelhaf, C. C. Camy-Peyret, J. M. Russell III, 2008: Chemical ozone loss in the Arctic winter 1991-1992. Atmos. Chem. Phys., 8, 1897-1910.

Tilmes, S., D. E. Kinnison, R. R. Garcia, R. Müller, F. Sassi, D. R. Marsh, B. A. Boville, 2007: Evaluation of heterogeneous processes in the polar lower stratosphere in the Whole Atmosphere Community Climate Model. J. Geophys. Res., 112, D24301, doi: 10.1029/2006JD008334.

Müller, R., S. Tilmes, J.-U. Grooss, A. Engel, H. Oelhaf, G. Wetzel, N. Huret, M. Pirre, V. Catoire, G. Toon, H. Nakajima, 2007: Impact of mesospheric intrusions on ozone-tracer relations in the stratospheric polar vortex. J. Geophys. Res., 112, D23307, doi: 10.1029/2006JD008315.

Rasch, P.J., S. Tilmes, R.P. Turco, A. Robock, L. Oman, C.-C. Chen, G. L. Stenchikov, R. R. Garcia, 2008: An overview of geoengineering of climate using stratospheric sulphate aerosols. Philos Transact of the Royal Society, 366, 1882.

Müller, Rolf, Simone Tilmes, 2008: Comment on "Middle atmospheric O3, CO, N2O, HNO3, and temperature profiles during the warm Arctic winter 2001-2002" by Giovanni Muscari et al. J. Geophys. Res., 113, D18303, doi:10.1029/2007JD009709.