Simone Tilmes

Postdoctoral Fellow
TIIMES - ACD
UTLS

Contact Information:
PO Box 3000, Boulder, CO 80307-3000
Office: FL1 -
Telephone: 303-497-1445
Email: @ucar.edu
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Project Summary:

Spotlight Article by SERE's Advanced Study Program:

Simone Tilmes - Investigation of chemical and dynamical processes using observations and chemistry-climate models

Figure 1: Ozone distribution (in ppm) in the Polar vortex in Antarctica in April. The two black curves indicate the double transport barrier.

The chemical composition in the Earth's troposphere and stratosphere is controlled by the interaction of radiation, transport, chemistry and dynamics. The importance of individual processes depends on location and season. Various observations have been taken and models have been developed to understand processes and interactions and to estimate the impact of changing climate conditions. The current research of Simone Tilmes is to combine information from different observations (satellite, aircraft, in-situ) and chemistry-climate model results, to investigate atmospheric processes. Her topics are the polar region and the exchange region between stratosphere and troposphere at all latitudes, the UTLS (Upper Troposphere/Lower Stratosphere) region.

A very specific situation occurs each year in the winter polar stratosphere. Since the eighties, the Antarctic ozone hole develops as the result of enhanced halogens in the atmosphere. Activated halogen compounds under special polar conditions effectively destroy ozone. During the last decade, a lot of research was performed to understand the impact of chemical and dynamical processes on polar ozone, with increasing interest in the northern hemisphere as well. Simone enhanced and established a technique to quantify the chemical part of ozone depletion in the lower stratosphere. She derived chemical ozone loss for Arctic and Antarctica using different satellite observations and in-situ observations. The ILAS and ILAS-2 satellite observations were used to derive detailed information of the evolution of chemical ozone loss during the cause of the winter in both hemispheres. Further, she used these observations to derive chemical ozone loss in the early winter. Interesting dynamical behavior of a double transport barrier of the polar vortex was discussed (Figure 1) ... article continues

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 the extend of 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.

Here, we are using sparse aircraft observations of several campaigns that took place over North America (POLARIS, STRAT, ACCENT, SOLVE and AVE) to establish a climatology to serve as a reference for CTMs and CCMs. We separate regions base on dynamical and transport characteristics in the following:

• Tropics: Region is controlled by convection in the Troposphere, cold point temperatures around the tropopause and ascending air masses and isentropic exchange in the lower stratosphere.

• Sub-tropic: Region that is mainly controlled by isentropic mixing and intrusion processes between the tropical troposphere and the sub-tropical stratosphere.

• Extra-tropics/Polar: Region is mainly controlled by descending air masses in the stratosphere.

To separate data in these regions, we use the information of the height of the thermal tropopause.
Based on statistic analysis, the tropopause height of profiles, which are located equatorward of the sub-tropical jet stream, are above 370 K potential temperature (about 14 km).  The tropopause height at locations poleward of the subtropical jet is in general located between a 320 and 370 K. If the tropopause height is at and below 320 K potential temperatures, in general all profiles are located poleward of the sub-tropical and polar jet.

Click on picture to view the entire figure.

Figure 2.Tracer Scatter CO Mozart flights - a sample O3/CO tracer-tracer correlation of  aircraft observations and MOZART3 CTM model results in comparison. Averaged values from aircraft data are shown as black crosses in both observation and model results for each region, respectively, for summer only.

Using the described criterion we establish a tool to separate aircraft observations and model results in the same way and compare the impact of transport and mixing and the influence of different seasons in more detail. Figure 2 gives an example of the application of these criteria showing possibility functions of  O3/CO tracer-tracer correlation of  aircraft observations and MOZART3 CTM model results in comparison. Averaged values from aircraft data are shown as black crosses in both observation and model results for each region, respectively, for summer only.

The characteristic shapes of tracer-tracer correlations for the chosen regions can be identified in both model and observations. On the other hand, differences between model and observations for different regions indicate shortcomings, for example the too high CO mixing ratios in the lower stratosphere in the model for all regions considered, and a too extended mixing most significant in sub- and extra tropics. Using the model, shortcomings can be further identified by separating the results depending on different transport events.

START08

Simone is a co-investigator of the upcoming Stratosphere-Troposphere Analyses of Regional Transport Experiment (START08).

Publications:

Tilmes, S., R. Mueller, R. J. Salawitch, U. Schmidt, C. R. Webster, H. Oelhaf, J. M. Russell III, C. C. Camy-Peyret, 2007: Chemical ozone loss in the Arctic winter 1991-1992. Atmos. Chem. Phys. Discuss., 7, 10097-10129.

Huck, P. E., S. Tilmes, G. E. Bodeker, W. J. Randel, A. J. McDonald, H. Nakajima, 2007: An improved measure of ozone depletion in the Antarctic stratosphere. J. Geophys. Res., 112, D11104, doi: 10.1029/2006JD007860.

Tilmes, S., R. Mueller, J.-U. Grooss, H. Nakajima, Y. Sasano, 2006: Development of tracer relations and chemical ozone loss during the setup phase of the polar vortex. J. Geophys. Res., 111, D24S90, doi: 10.1029/2005JD006726.

Tilmes, S., R. Mueller, A. Engel, M. Rex, J. M. Russell III, 2006: Chemical ozone loss in the Arctic and Antarctic stratosphere between 1992 and 2005. Geophys. Res. Lett., 33, L20812, doi: 10.1029/2006GL026925.