1. Convective Feedback: Its Role in Climate Formation and Climate Change Igor N. Esau

2. Contents: Convective Feedback Concept Sketch Physical Mechanisms Damping Effect Atmosphere-Ocean Control Factors Climate Sensitivity Amplification/Damping Conclusions

3. Color shading – potential T (density) stratification important for turbulent mixing Concept: Background Tropics atmosphere ocean Curves – absolute T stratification important for radiation processes. H H Extra-Tropics

4. Concept Demonstration: Convective Feedback in Greenhouse Greenhouse limits mixing (R. Wood, 1909), i.e. H, amplifying DTR and particularly maximum SAT On average greenhouse is warmer than outside air Strong irradiation during clear but windy nights can cause excessive cooling in the greenhouse OBS: Erroneously these SAT changes are associated with radiation balance!

5. Physical Mechanisms: Absorbing Surface Solar radiation is mostly absorbed in a thin layer of soil ( ~ 1 mm) or water ( ~ 10 m) Local absorption causes strong overheating and convective instability (atmosphere) or stability (ocean)

6. Physical Mechanisms: Feedback to Local Overheating Instability, d  /dz < 0, results in fierce convection, transporting heat (moisture, aerosols) above the bulk of the atmosphere (by mass or optical thickness)

7. Physical Mechanisms: Feedback to Local Overheating Stability, d  /dz > 0, impedes convection, preventing heat transport and storage in deep ocean

8. Physical Mechanisms: Summary Convective Feedback always cools the system (counter-act heating) Efficiency of cooling is controlled by density not temperature gradients Side-effects of Convective Feedback are also cooling (PBL clouds, aerosols, evaporation) Overall cooling is locally consistent with SAT warming

9. Earth Climate Needs Cooling Earth is located at the inner (hot) edge of the solar habitable zone Earth surface as black body ~ -18 C Earth surface plus motionless atmosphere ~ +54 C S. Manabe and co- authors papers 1960s

10. What Controls Convective Feedback? Damping effect depends reciprocally on H H is controlled by: (i) mean lapse rate; (ii) surface temperature difference; (iii) large scale convergence In their combination and side effects O(100 m) O(1000 m)

11. Control Factors: Physical Inconsistency of Models Problem identified in GABLS experiment (Beare, Esau, et al., 2006) However, the needed correction is not a constant

12. Entrainment and Climate Sensitivity Entrainment is a rate of involvement of fresh air into convective mixing Steinforth et al. (2005, Nature, 433) – 50% reduction in the entrainment rate increase climate sensitivity, i.e probability of higher temperatures, especially in Amazonia 2.5 K 10.5 K

13. Sensitivity from LES Without diurnal cycle of the heat flux, the LES sensitivity is further reduces Strong nocturnal cooling is compatible with amplified sensitivity in LES

14. Convective Layer Thickness: CHAMP Satellite versus ERA-40 Convective layer thickness (PBL depth) as the altitude of minimum relative humidity gradient: left – by the CHAMP (GPS) satellite for all (87598) occultations during 2002-03, data is averaged over a 5 by 5 grid; right – by ERA40 ECMWF data (same time). Courtesy Engeln and Teixeira (2004; 2005) Less sensitive – More sensitive

15. Convective Layer Thickness: GLAS Satellite versus ECMWF Convective layer thickness (nocturnal PBL depth) as altitude of the first maximum of aerosol concentration from GLAS observations, averaged for 3.10 – 15.11.03 (left); and the average of ECMWF forecasts, 12 GMT 1.10 – 31.10.03. Courtesy Palm and Miller (2004). A bit odd intercomparison valid mostly for oceans and Pacific rim.

16. Conclusions Earth’s climate needs cooling Cooling is regulated by convective feedback Convective feedback depends on limitations of the convective layer thickness Limitations are strong Stronger limitations makes climate more sensitive to shifts in radiation balance