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Diurnal Cycle in HiGEM

Diurnal Cycle in HiGEM. Atmosphere only model Vn 5.5 experiment 20 minute timestep N144 L38 resolution Radiation calls every timestep Top of atmosphere outgoing longwave radiation (OLR). GERB. G eostationary E arth R adiation B udget instrument on-board Meteosat-8

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Diurnal Cycle in HiGEM

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  1. Diurnal Cycle in HiGEM • Atmosphere only model • Vn 5.5 experiment • 20 minute timestep • N144 L38 resolution • Radiation calls every timestep • Top of atmosphere outgoing longwave radiation (OLR)

  2. GERB • Geostationary Earth Radiation Budget instrument on-board Meteosat-8 • First to measure broadband OLR from geostationary orbit – high temporal resolution • Location above Africa makes GERB ideal for diurnal cycle study • OLR fluxes calculated from total and shortwave • Processed onto regular 0.556lat × 0.833lon grid

  3. Method • One month (July) from both HiGEM and GERB • Averaged each onto single day & converted to LST • EOF analysis - disk over Africa (GERB comparison) • Fourier analysis - Tropics (CLAUS comparison)

  4. First EOF & PC PC1 describes 77.6% of the total variance • Strong signal over deserts suggests surface heating response • Note some small negative signals around African coast

  5. GERB HiGEM

  6. HiGEM GERB Sahara Comparison Contribution from PC1 Mean curve

  7. Convective cloud Stratocumulus Second EOF & PC PC2 describes 12.8% of total variance Hence first 2 PCs describe 90.4% Provides modification to PC1 for cloud

  8. GERB HiGEM

  9. HiGEM Mean curve Contribution from PC1 Combined contributions from PCs 1&2 What’s going on in the ITCZ? GERB PC2 dominates ~40Wm-2 amplitude Too Much convection too early?

  10. Fourier analysis – diurnal harmonic CLAUS HiGEM

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