Andrew Gettelman

Project Scientist
TIIMES - ACD - CGD
UTLS

Contact Information:
PO Box 3000, Boulder, CO 80307-3000
Office: ML - 300b & FL0-2162
Telephone: 303-497-1887
Email: andrew@ucar.edu
Home Page

Project Summary:

UTLS OZONE (validation)

Click on picture to view the entire figure.

Figure 1. Differences between AIRS and GPSO3 at altitude relative to the tropopause height. Gray crosses are individual differences between sonde data binned to AIRS levels. Dashed lines are layer average differences. Solid lines and boxes mark the median, upper and lower quartiles for each layer.

This year Gettelman and Pan contributed to a joint project with the Institute for Atmospheric Physics (IAP) in Beijing, China studying UTLS Ozone. This resulted in a paper in JGR.

Ozonesondes launched from Beijing, China, over a 3 year time period (September 2002 to July 2005) are used to evaluate the performance of ozone profile retrievals in the upper troposphere and lower stratosphere (UTLS) satellites. Results show that although the new GPSO3 sensor has a positive bias (about 20–30%) below 200 hPa and a negative bias (about 5–10%) above 60 hPa relative to known sensors, the measured ozone variability is consistent with Vaisala ECC ozonesondes, particularly in the UTLS region. The GPSO3 ozonesonde profiles over Beijing are then used to evaluate coincident ozone profiles from AIRS version 4 retrieval and MLS version 1.5 retrieval. Qualitatively, both satellite data sets can reproduce the gradients and variability of ozone in the UTLS region. Quantitatively, the agreement between the AIRS and ozonesonde ozone profiles is largely within 10% in the UTLS region (from 400 to 70 hPa). The statistical difference between the retrieval and ozonesonde data is minimum in the vicinity of the tropopause. The MLS ozone profiles also show good quality in the UTLS region with the best performance between 147 and 46 hPa.

Future work will include expanding the collaborations with IAP Beijing to study the Asian monsoon over the Tibetan plateau.

Bian, J., A. Gettelman, H. Chen, and L. Pan, 2006: Validation of Satellite Ozone Profile Retrievals Using Beijing Ozonesonde Data. Journal of Geophysical Research, 112, D06305, doi:10.1029/2006JD00750.

Click on picture to view the entire figure.

Figure 2. (a) March Arctic (60°N to 90°N) total column ozone anomalies from CCMs (colored lines) and the mean from four observational data sets (thick black line for smoothed curve and black dots for individual years). (b) As for Figure 2a, but October Antarctic (90°S to 60°S) total column ozone anomalies. Time series have been smoothed as in Figure 1(in the paper listed to the right) and anomalies have been calculated by subtracting the 1980-1984 mean from the smoothed time series. Light gray shading between 2060 and 2070 shows the period when stratospheric concentrations of halogens in the polar lower stratosphere are expected to return to their 1980 values.

SIMULATING OZONE

Gettelman contributed to the 2006 WMO Ozone assessment, as a co-author of the modeling chapter, a co-author on two papers published regarding simulations of ozone in the future, as well as co-coordinator of the SPARC Chemistry Climate Model Validation Project.

Simulations from eleven coupled chemistry-climate models (CCMs) employing nearly identical forcings have been used to project the evolution of stratospheric ozone throughout the 21st century. In general, the simulated ozone evolution is mainly determined by decreases in halogen concentrations and continued cooling of the global stratosphere due to increases in greenhouse gases (GHGs). Column ozone is projected to increase as stratospheric halogen concentrations return to 1980s levels. Because of ozone increases in the middle and upper stratosphere due to GHG-induced cooling, total ozone averaged over midlatitudes, outside the polar regions, and globally, is projected to increase to 1980 values between 2035 and 2050 and before lower-stratospheric halogen amounts decrease to 1980 values. None of the CCMs predict future large decreases in the Arctic column ozone. By 2100, total column ozone is projected to be substantially above 1980 values in all regions except in the tropics.

Future work includes expanding the model evaluations and preparing for the next WMO ozone assessment runs.

Eyring, V., N. Butchart, D. W. Waugh, H. Akiyoshi, J. Austin, S. Bekki, G. E. Bodeker, B. A. Boville, C. Brühl, M. P. Chipperfield, E. Cordero, M. Dameris, M. Deushi, V. E. Fioletov, S. M. Frith, R. R. Garcia, A. Gettelman, M. A. Giorgetta, V. Grewe, L. Jourdain, D. E. Kinnison, E. Mancini, E. Manzini, M. Marchand, D. R. Marsh, T. Nagashima, P. A. Newman, J. E. Nielsen, S. Pawson, G. Pitari, D. A. Plummer, E. Rozanov, M. Schraner, T. G. Shepherd, K. Shibata, R. S. Stolarski, H. Struthers, W. Tian, and M. Yoshiki, 2007: Multi-model projections of stratospheric ozone in the 21st century. Journal of Geophysical Research, 112, D16303, doi:10.1029/2006JD008332.

SUPERSATURATION

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Figure 3. Frequency of supersaturation at 200 hPa for four seasons: (a) January-March, (b) April-June, (c) July-September, and (d) October-December. Red line is the seasonal mean tropopause from NCEP-NCAR reanalysis data.

Gettelman also has been doing significant work on supersaturation in the atmosphere, including a climatological study of the frequency of super saturation, as well as model simulations with supersaturation.

Satellite data from the Atmospheric Infrared Sounder (AIRS) is analyzed to examine regions of the upper troposphere that are supersaturated: where the relative humidity (RH) is greater than 100%. AIRS data compare well to other in situ and satellite observations of RH and provide daily global coverage up to 200 hPa, though satellite observations of supersaturation are highly uncertain. The climatology of supersaturation is analyzed statistically to understand where supersaturation occurs and how frequently. Supersaturation occurs in humid regions of the upper tropical tropopause near convection 10%–20% of the time at 200 hPa. Supersaturation is very frequent in the extratropical upper troposphere, occurring 20%–40% of the time, and over 50% of the time in storm track regions below the tropopause. The annual cycle of supersaturation is consistent for the ~2.5 yr of data analyzed. More supersaturation is seen in the Southern Hemisphere midlatitudes, which may be attributed to higher temperature variance.

Gettelman, A., E. J. Fetzer, A. Eldering, and F. W. Irion, 2006:  The Global Distribution of Supersaturation in the Upper Troposphere from the Atmospheric Infrared Sounder. Journal of Climate, 19, doi:10.1175/JCLI3955.

Ice supersaturation is important for understanding condensation in the upper troposphere. Many general circulation models however do not permit supersaturation. A coupled chemistry climate model, the Whole Atmosphere Community Climate Model (WACCM), is modified to include supersaturation for the ice phase. Rather than a study of a detailed parameterization of supersaturation, the study is intended as a sensitivity experiment, to understand the potential impact of supersaturation, and of expected changes to stratospheric water vapor, on climate and chemistry. High clouds decrease and water vapor in the stratosphere increases at a similar rate to the prescribed supersaturation (20% supersaturation increases water vapor by nearly 20%). The stratospheric Brewer-Dobson circulation slows at high southern latitudes, consistent with slight changes in temperature likely induced by changes to cloud radiative forcing. The cloud changes also cause an increase in the seasonal cycle of near tropopause temperatures, increasing them in boreal summer over boreal winter. There are also impacts on chemistry, with small increases in ozone in the tropical lower stratosphere driven by enhanced production. The radiative impact of changing water vapor is dominated by the reduction in cloud forcing associated with fewer clouds (~+0.6 Wm−2) with a small component likely from the radiative effect (greenhouse trapping) of the extra water vapor (~+0.2 Wm−2), consistent with previous work. Representing supersaturation is thus important, and changes to supersaturation resulting from changes in aerosol loading for example, might have a modest impact on global radiative forcing, mostly through changes to clouds. There is no evidence of a strong impact of water vapor on tropical tropopause temperatures.

Gettelman, A. and D. E. Kinnison, 2007: The global impact of supersaturation in a coupled chemistry-climate model. Atmospheric Chemistry & Physics, 7, 1629-1643.

Future work includes developing a more sophisticated paramterization of supersaturation to go along with improved microphysics in the NCAR Global models.

Community Service:

• communications secretary - Atmospheric Sciences Execuctive Committee, American Geophysical Union (AGU)
• member - Middle Atmosphere Committee, American Meteorological Society (AMS)
• member - Steering Committee: Atmospheric Chemistry and Climate Project, Stratospheric Processes And their Role in Climate (SPARC) - International Global Atmospheric Chemistry (IGAC)

Presentations:

• An Introduction to Climate Modeling, Durham USA, November 2006
• An Introduction to Climate Modeling, Grand Junction USA, September 2007
• Climate and Climate Change, Other, Boulder USA, May 2007
• Climate and Climate Change, Other, Grand Junction USA, September 2007
• Cloud-aerosol interactions in the Community Atmosphere Model, Chemistry-Climate Working Group, January 2007, Boulder USA, March 2007
• Ice Supersaturation and its effect on the Upper Troposphere and Lower Stratosphere, University of Reading Meteorology Department Seminar, November 2006, Reading GBR, November 2006
• Observed and Simulated Structure of the Tropical Tropopause Layer and processes that maintain the TTL, Portland USA, August 2007
• Tropical Tropopause Layer Structure in Coupled Chemistry Climate Models, Leeds GBR, June 2007
• Two-moment stratiform cloud microphysics and cloud-aerosol interactions in the Community Atmosphere Model, AGU Fall meeting, 2006, San Francisco USA, December 2006
• Two-moment stratiform cloud microphysics and cloud-aerosol interactions in the Community Atmosphere Model, Atmospheric Model Working Group, January 2007, Boulder USA, January 2007
• Validating Upper Tropospheric Climate Feedbacks, AGU Fall meeting, 2006, San Francisco USA, December 2006

TIIMES External Collaborators:

Paul Field, United Kingdom Meteologic Office
Ray Nassar, Harvard University
Darryn Waugh, Johns Hopkins University
Robert Wood, University of Washington
Seok-Woo Son, Columbia University

Publications:

Field, P. R., A. Gettelman, R. Neale, R. Wood, P. J. Rasch, H. Morrison, 2007: Midlatitude cyclone compositing to constrain climate model behavior using satellite observations. J. Climate. (Submitted)

Park, M., W. J. Randel, A. Gettelman, S. T. Massie, J. H. Jiang, 2007: Transport above the Asian summer monsoon anticyclone inferred from Aura Microwave Limb Sounder tracers. J. Geophys. Res., 112, D16309, doi: 10.1029/2006JD008294.

Eyring, V., D. W. Waugh, G. E. Bodeker, E. Cordero, H. Akiyoshi, J. Austin, S. R. Beagley, B. A. Boville, P. Braesicke, C. Bruehl, N. Butchart, M. P. Chipperfield, M. Dameris, R. Deckert, M. Deushi, S. M. Frith, R. R. Garcia, A. Gettelman, M. A. Giorgetta, D. E. Kinnison, E. Mancini, E. Manzini, D. R. Marsh, S. Matthes, T. Nagashima, P. A. Newman, J. E. Nielsen, S. Pawson, G. Pitari, D. A. Plummer, E. Rozanov, M. Schraner, J. F. Scinocca, K. Semeniuk, T. G. Shepherd, K. Shibata, B. Steil, R. S. Stolarski, W. Tian, M. Yoshiki, 2007: Multimodel projections of stratospheric ozone in the 21st century. J. Geophys. Res., 112, D16303, doi: 10.1029/2006JD008332.

Kinnison, D. E., G. P. Brasseur, S. Walters, R. R. Garcia, D. R. Marsh, F. Sassi, V. L. Harvey, C. E. Randall, L. Emmons, J. F. Lamarque, P. Hess, J. J. Orlando, X. X. Tie, W. Randel, L. L. Pan, A. Gettelman, C. Granier, T. Diehl, U. Niemeier, A. J. Simmons, 2007: Sensitivity of chemical tracers to meteorological parameters in the MOZART-3 Chemical Transport Model. J. Geophys. Res.. (In Press)

Bian, J. C., A. K. Gettelman, H. Chen, L. L. Pan, 2007: Validation of satellite ozone profile retrievals using Beijing ozonesonde data. J. Geophys. Res., 112, D06305, doi: 10.1029/2006JD007502.

Gettelman, A., D. E. Kinnison, 2007: The global impact of supersaturation in a coupled chemistry-climate model. Atmos. Chem. Phys., 7, 1629-1643.

Zhan, R., J. Li, A. Gettelman, 2006: Intraseasonal variations of upper tropospheric water vapor in Asian monsoon region. Atmos. Chem. Phys. Discuss., 6, 8069-8095.

Gettelman, A., E. J. Fetzer, A. Eldering, F. W. Irion, 2006: The global distribution of supersaturation in the upper troposphere from the atmospheric infrared sounder. J. Climate, 19, 6089-6103, doi: 10.1175/JCLI3955.1.

Gettelman, A., W. D. Collins, E. J. Fetzer, A. Eldering, F. W. Irion, P. B. Duffy, G. Gala, 2006: Climatology of upper tropospheric relative humidity from the atmospheric infrared sounder and implications for climate. J. Climate, 19, 6104-6121, doi: 10.1175/JCLI3956.1.

Eyring, V., N. Butchart, D. W. Waugh, H. Akiyoshi, J. Austin, S. Bekki, G. E. Bodeker, B. A. Boville, C. Bruehl, M. P. Chipperfield, E. Cordero, M. Dameris, M. Deushi, V. E. Fioletov, S. M. Frith, R. R. Garcia, A. Gettelman, M. A. Giorgetta, V. Grewe, L. Jourdain, D. E. Kinnison, E. Mancini, E. Manzini, M. Marchand, D. R. Marsh, T. Nagashima, P. A. Newman, J. E. Nielsen, S. Pawson, G. Pitari, D. A. Plummer, E. Rozanov, M. Schraner, T. G. Shepherd, K. Shibata, R. S. Stolarski, H. Struthers, W. Tian, M. Yoshiki, 2006: Assessment of temperature, trace species, and ozone in chemistry-climate model simulations of the recent past. J. Geophys. Res., 111, D22308, doi: 10.1029/2006JD007327.