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Reinhard Hagenbrock, Andreas Hense, Felix Ament

The atmospheric moisture budget in the Arctic – introducing and applying a consistent method to use radiosonde data. Reinhard Hagenbrock, Andreas Hense, Felix Ament Meteorological Institute, University of Bonn, Germany Martin Göber Met Office, Bracknell, UK.

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Reinhard Hagenbrock, Andreas Hense, Felix Ament

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  1. The atmospheric moisture budget in the Arctic – introducing and applying a consistent method to use radiosonde data Reinhard Hagenbrock, Andreas Hense, Felix Ament Meteorological Institute, University of Bonn, Germany Martin Göber Met Office, Bracknell, UK WATER VAPOR OBSERVATIONS AND PROCESSES Long Beach, 11. Feb. 2003

  2. Motivation: Why the Arctic? Why fresh water? Why radiosondes? Method Use of radiosonde data Calculation of moisture flux convergence (MFC) Results MFC north of 70° Horizontal distribution of MFC Summary and outlook Outline WATER VAPOR OBSERVATIONS AND PROCESSES Long Beach, 11. Feb. 2003

  3. The freshwater input into the Arctic Ocean... ...has strong effect on the thermohaline circulation ...is expected to alter under climate change conditions ...is difficult to determine: Direct measurements of evaporation E and precipitation P are sparse (or not available at all). Reanalyses are not designed to evaluate the Arctic moisture budget. Radiosondes... Why Arctic? Why fresh water? Why radiosondes? WATER VAPOR OBSERVATIONS AND PROCESSES Long Beach, 11. Feb. 2003

  4. Method: Use of radiosonde data Radiosonde stations used Source: Historical Arctic Rawinsonde Archive (HARA) WATER VAPOR OBSERVATIONS AND PROCESSES Long Beach, 11. Feb. 2003

  5. Method: Use of radiosonde data The atmospheric moisture budget: WATER VAPOR OBSERVATIONS AND PROCESSES Long Beach, 11. Feb. 2003

  6. Method: Use of radiosonde data There exists a discrepancy between existing estimates based on radiosondes and those calculated from reanalysis data! • Different horizontal scales • Large uncertainties in the analyses model • Reanalysis uses additional information WATER VAPOR OBSERVATIONS AND PROCESSES Long Beach, 11. Feb. 2003

  7. Conventional way to calculate moisture flux divergence/convergence: • Interpolate to a regular grid • Calculate Differentiations Calculation of Moisture Flux Convergence 2 Problems!!! WATER VAPOR OBSERVATIONS AND PROCESSES Long Beach, 11. Feb. 2003

  8. Problem No. 1: Mass consistency Problem turns up whenever (moisture) flux divergences are calculated Error in calculated flux divergence is dominated by a term proportional to the (erroneous) mass divergence Calculation of Moisture Flux Convergence Solution: remove divergent parts of the wind field! → variational approach, “mass consistent model“ WATER VAPOR OBSERVATIONS AND PROCESSES Long Beach, 11. Feb. 2003

  9. Variational approach: Set up of a cost function Calculation of Moisture Flux Convergence WATER VAPOR OBSERVATIONS AND PROCESSES Long Beach, 11. Feb. 2003

  10. Problem No. 2: Irregular grid What you should do: first to differentiate, then to interpolate Change of this order results in serious errors in data sparse regions Calculation of Moisture Flux Convergence • Solution: Do calculations on irregular grid! • Discretize with finite elements WATER VAPOR OBSERVATIONS AND PROCESSES Long Beach, 11. Feb. 2003

  11. Calculation of Moisture Flux Convergence Discretization: All scalar fields are expanded in linear basis functions hi. WATER VAPOR OBSERVATIONS AND PROCESSES Long Beach, 11. Feb. 2003

  12. … so the cost function reads (in 1D): Calculation of Moisture Flux Convergence With this expansion, the contributions to the volume integral read: WATER VAPOR OBSERVATIONS AND PROCESSES Long Beach, 11. Feb. 2003

  13. The minimization of the cost function leads to a linear equation system. This is solved with a preconditioned conjugate residual solver. boundary conditions (BCs) not necessary for solvability physically motivated BCs may be included by introducing an extra term in the cost function We prevent mass flux through the lower boundary. Calculation of Moisture Flux Convergence WATER VAPOR OBSERVATIONS AND PROCESSES Long Beach, 11. Feb. 2003

  14. We combined the variational approach with a FE method in order to calculate the volume integrated moisture flux divergence (or rather: -convergence) Method . . . to sum up:  (P - E) WATER VAPOR OBSERVATIONS AND PROCESSES Long Beach, 11. Feb. 2003

  15. Results Typical numbers: ~ 70 stations ~ 800 nodes ~ 1500 tetrahedra WATER VAPOR OBSERVATIONS AND PROCESSES Long Beach, 11. Feb. 2003

  16. 1. The effect of missing mass consistency of the MFC north of 70°N. Results WATER VAPOR OBSERVATIONS AND PROCESSES Long Beach, 11. Feb. 2003

  17. Results: MFC north of 70°N from mass consistent radiosonde data average: 0.461 mm d-1 WATER VAPOR OBSERVATIONS AND PROCESSES Long Beach, 11. Feb. 2003

  18. Results: MFC north of 70°N from unmodified radiosonde data average: 0.547 mm d-1 WATER VAPOR OBSERVATIONS AND PROCESSES Long Beach, 11. Feb. 2003

  19. 2. MFC north of 70°N: Compare radiosonde and reanalysis based results. Use data of (ERA-15) reanalysis precisely where radiosonde data is given. Use radiosonde data on 11 mandatory pressure levels. Results WATER VAPOR OBSERVATIONS AND PROCESSES Long Beach, 11. Feb. 2003

  20. Results: MFC north of 70°N from mass consistent radiosonde data (on mandatory pressure levels) average: 0.449 mm d-1 average: 0.461 mm d-1 WATER VAPOR OBSERVATIONS AND PROCESSES Long Beach, 11. Feb. 2003

  21. Results: MFC north of 70°N from mass consistent reanalysis data (on mandatory pressure levels) average: 0.480 mm d-1 WATER VAPOR OBSERVATIONS AND PROCESSES Long Beach, 11. Feb. 2003

  22. Results: MFC north of 70°N radiosonde data (average: 0.449 mm d-1) ERA-15 reanalysis data (average: 0.480 mm d-1) Cullather et al.: radiosonde data (average: 0.45 mm d-1) Cullather et al.:ERA-15 reanalysis data (average: 0.50 mm d-1) WATER VAPOR OBSERVATIONS AND PROCESSES Long Beach, 11. Feb. 2003

  23. 3. Horizontal distribution of vertically integrated MFC (ave. 1979-93) Results WATER VAPOR OBSERVATIONS AND PROCESSES Long Beach, 11. Feb. 2003

  24. Results: Horizontal distribution of vertically integrated MFC from mass consistent radiosonde data WATER VAPOR OBSERVATIONS AND PROCESSES Long Beach, 11. Feb. 2003

  25. Results: Horizontal distribution of vertically integrated MFC from mass consistent radiosonde data (smoothed to T42) WATER VAPOR OBSERVATIONS AND PROCESSES Long Beach, 11. Feb. 2003

  26. Results: Horizontal distribution of vertically integrated MFC from full resolution reanalysis data (smoothed to T42) WATER VAPOR OBSERVATIONS AND PROCESSES Long Beach, 11. Feb. 2003

  27. A method to analyze atmospheric moisture flux convergence (MFC) is introduced. In order to receive a mass consistent wind field on the irregular grid of the radiosonde data, a variational approach is combined with the Finite Element method. The effect of missing mass consistency is not negligible, neither or average, nor when looking at spatial or temporal variability. Summary (1) WATER VAPOR OBSERVATIONS AND PROCESSES Long Beach, 11. Feb. 2003

  28. The method allows to compare budgets based on reanalysis and radiosonde data without the problem of different resolutions. The differences observed so far are strongly reduced. There remains a difference of ~ 0.03 mm d-1 (~7 %). For the first time it is possible to make an estimate of the horizontal distribution of the MFC based solely on radiosonde data, thus validating the estimated from reanalyses. Major patterns coincide, yet noticeable differences remain. Summary (2) WATER VAPOR OBSERVATIONS AND PROCESSES Long Beach, 11. Feb. 2003

  29. As a ”spin-off product“ of the method, several other aspects of the moisture budget (e.g. storage of moisture, storage and transport of energy) are easily analyzed. Summary (3) WATER VAPOR OBSERVATIONS AND PROCESSES Long Beach, 11. Feb. 2003

  30. The data is used to examine the connection between the moisture budget and large scale circulation. Outlook WATER VAPOR OBSERVATIONS AND PROCESSES Long Beach, 11. Feb. 2003

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