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Introducing VESPA-22: Ground-Based Microwave Spectrometer for Polar Water Vapor

Learn about measuring atmospheric water vapor at polar latitudes using VESPA-22, its setup, challenges, and future work. Explore the impact of water vapor on climate and ozone.

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Introducing VESPA-22: Ground-Based Microwave Spectrometer for Polar Water Vapor

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  1. Introducing VESPA-22: a ground-based microwave spectrometer formeasuring middle atmospheric water vapour at polar latitudes Pietro Paolo Bertagnolio, Giovanni Muscari, Irene Fiorucci and Massimo Mari 27 April 2012 EGU General Assembly 2012 IstitutoNazionale di Geofisica e Vulcanologia, Rome, Italy Department of Earth Sciences, University of Siena Distributed under Creative Commons Attribution 3.0

  2. Our goal To observe changes in the water vapour concentration profile in the stratosphere and mesosphere in the polar regions Long-term (decadal trends) Short-term (diurnal cycle) With a new ground-based microwave spectrometer to measure the 22.235 GHz transition of water vapour as part of the NDACC network

  3. Outline • Stratospheric H2O and its impact on PSCs • The observational challenges of the 22-GHz H2O line • How does the technique work? • Our instrumental setup • First measured and calibrated spectra • Conclusions and future work

  4. DecadalchangeinstratosphericH2Oas yet notwellunderstood • Steady rise since 1980 • 10% decrease in 2000 • Influence on surface warming 30% of GHG from “Contributions of stratospheric water vapor to decadal changes in the rate of global warming.” S. Solomon et al. – Science - 2010

  5. ImpactofH2OincreaseonArcticPSCformation + 1 ppmv H2O from “Quantifying Denitrification and Its Effect on Ozone Recovery”, Tabazadeh at al. – Science - 2000

  6. The observational challenge thermo meso strato tropo

  7. Balanced Beam-Switching Measurement Technique Stratosphere Reference beam Signal beam Troposphere Receiver Compensating Sheet

  8. VESPA-22 (water Vapor Emission Spectrometer for Polar Atmospheres at 22 GHz) Parabolic mirror Receiver Quarter-wavelength shift Chopper mirror

  9. Parabolic antenna Half-PowerBeamWidth (HPBW) = 3.5° Sidelobes < -40 dB below main lobe Cross-polarization < -24 dB below main polarization

  10. Noise diode calibration Hot body Cold body (LN2) Calibration sources

  11. Noise diode calibration Trec = 312 K

  12. Future work (now the fun starts…) Conclusions • Long-term monitoring of polar stratospheric water vapour is needed • We designed and built a new 22-GHz spectrometer for polar observations • We measured the first atmospheric spectra (“first light”) • Improve baseline flatness: • λ/4 wobbler instead of fixed shift • Delrin compensating sheet • Front-end optimization • Improve sensitivity and Trec • Test single-sideband mixer • Test with longer integration times from an high-altitude observatory (Gran Sasso) • Set up inversion algorithm

  13. References • Bertagnolio, P. P., Muscari, G., & Baskaradas, J. (2012). Development of a 22 GHz ground-based spectrometer for middle atmospheric water vapour monitoring. European Journal of Remote Sensing, 51-61. doi:10.5721/EuJRS20124506 • Solomon, S., Rosenlof, K. H., Portmann, R. W., Daniel, J. S., Davis, S. M., Sanford, T. J., & Plattner, G.-K. (2010). Contributions of stratospheric water vapor to decadal changes in the rate of global warming. Science (New York, N.Y.), 327(5970), 1219-23. doi:10.1126/science.1182488 • Tabazadeh, A., Santee, M. L., Danilin, M. Y., Pumphrey, H. C., Newman, P. A., Hamill, P. J., & Mergenthaler, J. L. (2000). Quantifying Denitrification and Its Effect on Ozone Recovery. Science, 288(5470), 1407-1411. doi:10.1126/science.288.5470.1407 Thank you for your attention!

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