Abstract.
The sensitivity of an idealized climate system model consisting of an atmospheric GCM coupled to an oceanic upper mixed layer on an aquaplanet is analyzed. There is no seasonal cycle and the solar radiation is taken to be symmetric about the equator. The system is integrated with the observed CO2 (330 ppm) until it reaches a quasi-equilibrium climate. To study the sensitivity we double the CO2 and again integrate until the system reaches a new equilibrium climate. To simplify the linear analysis we assume that the atmosphere is always in quasi-equilibrium (typical atmospheric adjustment times being much shorter than that of the oceanic upper mixed layer). We introduce a linear surface energy budget sensitivity (or response) operator consisting of a Jacobian matrix of the surface budget with respect to the surface temperature. The operator is used to construct a linear estimate of the surface temperature change that results from the CO2 doubling. It is found that the temperature response obtained from the linear extimate compares well with the results of the full 3D run. The shape of the response looks very similar to that of the least stable mode of the linear surface budget sensitivity operator. The importance of different components of the initial forcing at the surface is discussed. The role of the individual components in determining the final equilibrium climate is also studied.
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Acknowledgements.
The author would like to thank J.R. Bates for many stimulating and useful discussions and G.R. North for pointing out similarities between our results and those of his earlier papers. This work was supported by the Danish National Research Foundation, when the author was employed at the Danish Center for Earth System Science.
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Appendix
Appendix
- AM::
-
angular momentum
- B Srf ::
-
F S – F I – F L – F H
- B TOA ::
-
budget at the top-of-the-atmosphere
- c W ::
-
heat capacity of a unit mass of water, 4187 J/kg
- F S ::
-
net downward solar radiative flux at the surface
- F I ::
-
net upward longwave flux at the surface
- F L ::
-
latent heat flux
- F H ::
-
sensible heat flux
- (F L ) w ::
-
wind component of the latent heat flux response to changes in SST
- (F L ) h ::
-
humidity component of the latent heat flux response to changes in SST
- (F H ) T ::
-
temperature component of the sensible heat flux response to changes in SST
- GCM::
-
general circulation model
- H::
-
depth of the oceanic upper mixed layer, 50 m
- EquationSource% MathType!MTEF!2!1!+- % feaaeaart1ev0aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWefv3ySLgznf % gDOfdaryqr1ngBPrginfgDObYtUvgaiuaacqWFBeIuaaa!4086! \( {\cal R}\) ::
-
matrix of the surface budget response operator
- EquationSource% MathType!MTEF!2!1!+- % feaaeaart1ev0aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWefv3ySLgznf % gDOfdaryqr1ngBPrginfgDObYtUvgaiuaacqWFBeIudaWgaaWcbaGa % aiikaiaadofacaGGSaGaamysaiaacYcacaWGmbGaaiilaiaadIeaca % GGPaaabeaaaaa!475F! \( {\cal R}_{(S,I,L,H)} \) ::
-
components of SBSO matrix, corresponding to F S , F I , F L and F H sensitivity to changes in SST
- EquationSource% MathType!MTEF!2!1!+- % feaaeaart1ev0aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWefv3ySLgznf % gDOfdaryqr1ngBPrginfgDObYtUvgaiuaacqWFBeIudaWgaaWcbaGa % aiikaiaadYeacaGGSaGaamisaiaacMcacaWG3baabeaaaaa!4555! \( {\cal R}_{(L,H)w} \) ::
-
wind components of EquationSource% MathType!MTEF!2!1!+- % feaaeaart1ev0aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWefv3ySLgznf % gDOfdaryqr1ngBPrginfgDObYtUvgaiuaacqWFBeIudaWgaaWcbaGa % aiikaiaadYeacaGGSaGaamisaiaacMcaaeqaaaaa!4459! \( {\cal R}_{(L,H)} \)
- EquationSource% MathType!MTEF!2!1!+- % feaaeaart1ev0aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWefv3ySLgznf % gDOfdaryqr1ngBPrginfgDObYtUvgaiuaacqWFBeIudaWgaaWcbaGa % amitaiaadIgaaeqaaaaa!4270! \( {\cal R}_{Lh} \) ::
-
humidity components of EquationSource% MathType!MTEF!2!1!+- % feaaeaart1ev0aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWefv3ySLgznf % gDOfdaryqr1ngBPrginfgDObYtUvgaiuaacqWFBeIudaWgaaWcbaGa % amitaaqabaaaaa!4183! \( {\cal R}_L \)
- EquationSource% MathType!MTEF!2!1!+- % feaaeaart1ev0aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWefv3ySLgznf % gDOfdaryqr1ngBPrginfgDObYtUvgaiuaacqWFBeIudaWgaaWcbaGa % amisaiaadsfaaeqaaaaa!4258! \( {\cal R}_{HT} \) ::
-
temperature components of EquationSource% MathType!MTEF!2!1!+- % feaaeaart1ev0aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWefv3ySLgznf % gDOfdaryqr1ngBPrginfgDObYtUvgaiuaacqWFBeIudaWgaaWcbaGa % amisaaqabaaaaa!417F! \( {\cal R}_H \)
- SBRO::
-
surface budget response operator
- SST::
-
sea surface temperature
- S TOA ::
-
downward solar radiative flux at the TOA
- T S ::
-
surface temperature
- TOA::
-
top of the atmosphere
- ρ W ::
-
density of water, 1000 kg/m3
- Λ::
-
a set of external parameters of the system (or just one parameter)
- δΛ::
-
perturbation to Λ
- λ i ::
-
i-th eigenvalue of the surface budget response operator
- φ i ::
-
i-th eigenmode of the surface budget response operator
- τ i = 1/λ i ::
-
e-folding time of the i-th eigenmode of the SBRO
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Alexeev, V.A. Sensitivity to CO2 doubling of an atmospheric GCM coupled to an oceanic mixed layer: a linear analysis. Climate Dynamics 20, 775–787 (2003). https://doi.org/10.1007/s00382-003-0312-x
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DOI: https://doi.org/10.1007/s00382-003-0312-x