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Implementation of multiple regions in Edwards-Slingo

Explore the optimization of radiative transfer calculations using a multiregion approach to address anomalous horizontal transport in atmospheric science. The method involves solving a matrix problem for fluxes in multiple layers, enhancing the accuracy by eliminating unwanted elements and enabling easy implementation of triple or more regions with improved efficiency.

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Implementation of multiple regions in Edwards-Slingo

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  1. Implementation of multiple regions in Edwards-Slingo Robin Hogan and Jon Shonk

  2. Shadows! Natural logarithm of IWC (g m-3) • Need separate regions even in clear skies? Downward short-wave flux (W m-2) Upward short-wave flux (W m-2)

  3. Anomalous horizontal transport • Homogenization of clear-sky fluxes: • Reflected radiation has more chance to be absorbed -> TOA shortwave bias • Effect is very small in the longwave • This problem can be solved in a way that makes the code more efficient Single cloud

  4. Two-stream scheme TOA flux:STOA- F0.5+ F0.5- • Consider a two-layer atmosphere • Solve a tridiagonal matrix problem to obtain the fluxes Layer 1 reflection, transmission and emission:R1, T1, S1+, S1- F1.5+ F1.5- Layer 2 reflection, transmission and emission: R2, T2, S2+, S2- F2.5+ F2.5- Surface emission and albedo: Ss+, as

  5. It is conceptually convenient to solve the system by Working up from the surface calculating the albedo ai and upward emission Gi of the whole atmosphere below half-level i. Then working down from TOA, calculating the upwelling and downwelling fluxes from ai and Gi. Edwards-Slingo solution

  6. With 2 regions (a & b), matrix is denser Latest Edwards-Slingo only has approximate solvers SOLVER_MIX_DIRECT and SOLVER_TRIPLE for the 3-region version OK for upright convection but unacceptable errors introduced with realistic overlap Two-regions: cloud and clear-sky a b Layer 1 a b Layer 2 Note that the overlap coefficients have been omitted in this example

  7. But some elements represent unwanted anomalous horizontal photon transport Remove them and the problem can be solved exactly, and in closer agreement with ICA Enables triple (and quadruple, quintuple…) regions to be implemented quite easily! New version a b Layer 1 Rab a b Layer 2 Rab is the reflection from region a to region b at the same level

  8. Performance of new solver • In calculating upwelling flux at half-level 1.5, downwelling flux sees albedo of whole atmosphere below, a1.5, which it reflects back into the same region • Much closer to the independent column approximation! 0.5 1.5 a1.5

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