The frequency response of temperature and precipitation in a climate model

Abstract

[1] Dynamic aspects of the climate's response to forcing are typically explored through transient simulations in the time domain. However, because of the large range of time-scales involved, some features are more easily observed in the frequency domain. We compute the frequency-response of the HadCM3L general circulation model (GCM) to sinusoidal perturbations in solar radiative forcing, with periods between 2 −1/2 and 2 9 (512) years. The global mean temperature response decreases with increasing frequency, and the frequency scaling at time-scales longer than one year is consistent with the behavior of diffusion into a semi-infinite slab. The land-sea contrast and land-averaged precipitation, however, exhibit relatively little dependency on the frequency of the imposed perturbation, with significant response at both short and long periods. Understanding these relative characteristics of different climate variables in the frequency domain is important to understanding the transient response of the climate system to both anthropogenic and natural (e.g., volcanic) forcings; the frequency response is also relevant in understanding the spectrum of natural variability.Citation: MacMynowski, D. G., H.-J. Shin, and K. Caldeira (2011), The frequency response of temperature and precipitation in a climate model, Geophys. Res. Lett., 38, L16711,

Comment on "Scaling regimes and linear/nonlinear responses of last millennium climate to volcanic and solar forcing" by S. Lovejoy and C. Varotsos (2016)

“…5. On the long timescales this assumption is in direct contradiction to L&V's own claim that GCMs do not reproduce low-frequency (multicentennial) variability (see also MacMynowski et al, 2011;Geoffroy et al, 2013;Fredriksen and Rypdal, 2016).…”

“…Linear-response models with two characteristic response times or a long-memory power-law response have had considerable success in describing global temperature response in GCM data, instrumental data and in multiproxy reconstructions (Held et al, 2010;MacMynowski et al, 2011;Geoffroy et al, 2013;Caldeira and Myhrvold, 2013;Rypdal and Rypdal, 2014;Østvand et al, 2014;Rypdal et al, 2015;Lovejoy et al, 2015;Fredriksen and Rypdal, 2016). The credibility of these results depends crucially on the validity of the linear approximation in the global response.…”

Solar geoengineering to limit the rate of temperature change

“…The parameter λ describes the natural climate feedback (the change in radiation due to a change in surface temperature), C = cρH is the surface layer heat capacity per unit area, κ is the thermal diffusivity and β = cρκ for density ρ and specific heat capacity c. The time constants of this model can be obtained from a fit to the frequency-dependent response of HadCM3L as in MacMartin et al [4]; this frequency response was previously calculated by simulating the response to sinusoidal variations in the solar 'constant' at different frequencies [31]. These simulations give the HadCM3L response to solar forcing; to account for the difference in efficacy of solar forcing relative to CO 2 , the result is scaled to match the HadCM3L response to RCPs.…”

Temperature change vs. cumulative radiative forcing as metrics for evaluating climate consequences of energy system choices

“…When appropriately calibrated, these simple equations closely follow the global mean temperature results of more complex 3D coupled atmosphere-ocean simulations (4). A characteristic timescale τ for this system is…”