Comparing two methods to estimate the sensitivity of regional climate simulations to tropical SST anomalies

We perform ensemble simulations using NCAR CAM3.1 T42 forced by perturbed SST fields to estimate the sensitivity of regional climate change at seasonal scales to tropical SST anomalies. We compare the sensitivity and linear reconstruction of regional climate change to tropical SST anomalies from the patch method and the random perturbation method (RPM). The patch method adds one SST anomaly patch at a certain location of the tropical ocean to the prescribed SST field at one time. The RPM method randomly perturbs the climatological SST field with spatially coherent anomalies and estimates the anomalous response with respect to the climatological equilibrium state. The two methods provide generally consistent sensitivity information and similar reconstruction of the regional response over the global scale and tropical regions. If only the dominant sensitivity information is desired, the RPM method is about twelve times more computationally efficient than the patch method due mainly to the larger area-integrated amplitude of the SST forcing used.