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Contribution to Post-EPS discussion Darmstadt 1-2 Dec 2005

Contribution to Post-EPS discussion Darmstadt 1-2 Dec 2005. R. Boers, KNMI, Netherlands. Important issues to be addressed are. The accuracy /precision of the derived parameters The length of the data series (discontinuities)

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Contribution to Post-EPS discussion Darmstadt 1-2 Dec 2005

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  1. Contribution to Post-EPS discussionDarmstadt 1-2 Dec 2005 R. Boers, KNMI, Netherlands

  2. Important issues to be addressed are The accuracy /precision of the derived parameters The length of the data series (discontinuities) The relevance of the parameters for climate research / monitoring : the GCOS list

  3. Precision of fundamental data records,i.e. radiances, counts etc. Repeatibility, calibration, continuity, signal-to-noise issues data time

  4. If the only quantity that we want to record for posteriority is ‘radiance’, and we are not interested in geophysical parameters, then ‘precision and repeatability’ is sufficient

  5. The geophysical parameters that are derived should be ‘close’ to the original radiances: Should have as their basis physical models with as few assumptions as possible G. Stephens: ‘Calibrated radiances are an important climate product. These data have greater intrinsic accuracy and precision than any parameter derived from them. For monitoring purposes it is critical that the extent of reliance on a priory assumptions be firmly established, since any properties that are too constrained to such information will not provide proper measure of evolving climate change’

  6. Accuracy Is the quantity that you measure or derive without bias or offset from the parameter that you are after?

  7. Accuracy requirement is paramount because we want to derive a set of coherent geophysical parameters, study processes and ‘understand change’

  8. Hierarchy of products, priority setting,possible ordering principle: a reliance on a priori assumptions Error1 2. Radiance + Geophysical Model = Geophysical Parameter Error1+Error2 1. Radiance 3. Geophysical Parameter + Model= Another Geophysical Parameter Error1+Error2 +Error3

  9. Example : Optical thickness and liquid water path Radiance (visible) Radiance (near IR) Atmosphere without aerosols Tables for radiance to optical depth / effective radius conversion Formula to derive LWP: [ = (3/2) LWP / reff]

  10. Error Hierarchy: Atmospheric model (no aerosol) Error2a Atmospheric model (no aerosol) Error2b Tabel conversion optical depth Error3a Tabel conversion effective radius Error3b Radiance (visible) Error1a Radiance (near IR) Error1b Formula to obtain LWP Error 4 Conclusion: If the ordering principle is ‘ Error’ then Radiance is the highest order product, LWP is a ‘lower order’ product than optical depth and effective radius

  11. Example 2: Upward longwave flux at the surface TOA Irradiance (IR) Error1 Water Vapor profile Error2a Temperature profile Error2b Emissivity of the surface Error3 Cloud base height Error4 Emissivity of cloud (thin cloud prob.) Error5 RT to derive LW upward flux Error6

  12. The importance of the product needs to be weighted against the achievable accuracy. This determines whether such a product will be used by the climate community. The products need to be physically consistent! This needs to be checked by dedicated research investment in climate-products

  13. The role of aerosols in the climate research: a) In correcting the cloud optical depth estimates b) As a climate product in its own right

  14. Effect of aerosol on TOA SW fluxes aerosol=0.2 increases TOA SW flux by 14 Wm-2

  15. Aerosol optical depth of 0.2 is standard at mid-latitude continental conditions, therefore present operational cloud optical depth product might be 5 – 10 % too highbecause  observed =  aerosol +  cloud

  16. 1) include calibrated radiances in climate data stream Summary: 2) assess the potential error of each output parameter given the radiance input and the model used to derive the parameter 3) Save intermediate products as well as final products 4) Include aerosol optical depth as a standard climate output product 5) Include effective radius as standard climate output product

  17. TOA radiances: 1++ Some priority setting (1) (not complete) : TOA radiation budget: 1 Principal attribution of TOA radiation 1 such as: a) cloud cover b) cloud optical thickness c) cloud droplet effective radius d) surface albedo Aerosol optical depth 1

  18. Cloud Type 2 Some priority setting (2) : Cloud Phase 2 Cloud Liquid Water Path 2 Cloud Liquid Water Profile 2 Aerosol SSA 2 Irradiance budget at surface 2

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