Recent Trend of Stratospheric Water Vapor and Its Impacts Steve Rieck, Ning Shen, Gill-Ran Jeong EAS 6410 Team Project Apr

Overview Motivation How we look at Stratospheric Water Vapor –Physical Aspect –Chemical Aspect –Impact of Stratospheric Water Vapor Trend Implication from the precursors Take-Home Message

Motivation Better understand the process of the entry of water vapor into Stratosphere Obtain a picture of the Stratospheric Water Vapor (SWV) trend Study the interactions between the increasing SWV and other atmospheric chemical species Investigate the impact of SWV over the atmospheric activities

Dehydration Mechanism SWV Sources –Surface Evaporation – Dominant –Chemical Reaction – Secondary Convective Process Gradual Ascend Process Quoted: How Water Enters the Stratosphere. Karen H. Rosenlof, Science Vol DEC 2003 Two-steps process involving these two assumptions Isotope (Deuterium)

General Image of SWV Trend Quoted: Changes in the distribution of stratospheric water vapor observed by an airborne microwave radiometer Feist, Dietrich G., et al.; 2003

Interannual variability of entry value of H 2 O mixing ratio – Volcanic Eruptions – Brewer-Dobson Circulation Interannual variability of stratospheric dynamics –Quasi - Biennial Oscillation –El Niño - Southern Oscillation Processes Controlling Interannual SWV Quoted: Simulation of Interannual Variance of Stratospheric Water Vapor, Marvin A. Geller, et, al Journal of the Atmospheric Science ENSO Typical Pattern

Long Term SWV Trend Difficulty for long term SWV trend assessment –Lack of global coherent trend perspectives –Large measurement uncertainty Sample of Decreasing Trend Sample of Increasing Trend

Chemical Sources of Stratospheric H 2 O Chemical source from Methane oxidation Methane Oxidation is the primary anthropogenic source

Methane Oxidation Methane produces water by the following reaction: CH 4 + OH  CH 3 + H 2 0 Accounts for 90% of atmospheric Methane loss

Objective – To assess the contribution of the simulated water vapor increase the analyzed ozone decrease in the transient model simulation (Dameris et alo., 2005) – To investigate whether these shorter-term ozone change arise from a short-term water vapor increase such as volcanic eruption. Motivation –Water vapor in the upper troposphere and lower stratosphere plays a key role in atmospheric chemistry –Oxidation of H 2 O and CH 4 : O( 1 D) + H 2 O  2OH O( 1 D) + CH 4  OH + CH 3 Simulation of Stratospheric Water Vapor Trends: Impact on Stratospheric Ozone Chemistry

H 2 O_Chemistry = H 2 O_Background + H 2 O_Perturbation Table 1. Overview of analyzed model experiments EXP H 2 O perturbation simulation period CNTL 0 ppmv, reference simulation 11 years VOLC 2 ppmv, July and August, 5 annual cycles July-June short-term increase (last 5 years of CNTL) H 2 O_1 1 ppmv, long-term increase 11 years H 2 O_5 5 ppmv, long-term increase 11 years Approach to SWV Impact on O 3 Destruction Chemistry Zonally averaged volume mixing ratio of the water vapor perturbation (ppmv).

Catalytic ozone destruction cycle: X + O 3  XO + O 2 XO + O  X + O 2 Net: O 3 + O  2O 2 Additional HOx-cycle: OH + O 3  HO 2 + O 2 HO 2 + O 3  OH + O 2 + O 2 Net: 2O 3  3O 2 Coupling of HOx and NOx cycle: OH + NO 2 + M  HNO 3 + M Coupling of HOx and ClOx cycle: OH + HCl  H 2 O + Cl HO 2 + ClO  HOCl + O 2 Ozone production in methane oxidation chain : CH 3 O 2 + NO  CH 3 O + NO 2 HO 2 + NO  OH + NO 2 NO 2 + hv  NO + O Net: O 2 + O  O 3 JAN JULY Zonally and Monthly averaged changes of OH (Left) and Ozone (Right) Heterogeneous reactions on PSCs and sulfate aerosols in CHEM: HCl + ClONO 2  Cl 2 + HNO 3 H 2 O + ClONO 2  HOCl + HNO 3 HOCl + HCl  Cl 2 + H 2 O N 2 O 5 + H 2 O  2HNO 3 80N 50mb80S 50mb Ozone Destruction Resulting from Perturbation of SWV 50% increase (20 ~ 25 x 10 5 molec/cm 3 ) 10% 7%

Water Vapor and the Greenhouse Effect By far the most effective greenhouse gas More H2O Higher Temperature More Evaporation Responsible for 50-60% of natural global warming Effect Lead to a positive feedback loop

The trend of SWV is not globally coherent Large scale atmospheric circulations and natural events impact the behavior of SWV The Increasing of SWV leads to enhancing O 3 reduction Increasing SWV leads to a stronger greenhouse effectSummary

Take Home Messages Increasing trend of SWV in some regions Increasing CH 4 leads to increasing SWV More water vapor leads to more O 3 destruction Positive greenhouse effect of SWV The increasing trend of SWV needs more investigation –Physical perspective –Chemical perspective –Ecological perspective

More Reference NOAA Global Monitoring Division – World Climate Research Program -- Stratospheric Processes And their Role in Climate – Stenke, A., V. Grewe. “Simulation of stratospheric water vapor trends: impact on stratospheric ozone chemistry.” Atmos. Chem. Phys., 5, , 2005

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