SPEAR: The Next Generation GFDL Modeling System for Seasonal to Multidecadal Prediction and Projection

Abstract

We document the development and simulation characteristics of the next generation modeling system for seasonal to decadal prediction and projection at the Geophysical Fluid Dynamics Laboratory (GFDL). SPEAR (Seamless System for Prediction and EArth System Research) is built from component models recently developed at GFDL—the AM4 atmosphere model, MOM6 ocean code, LM4 land model, and SIS2 sea ice model. The SPEAR models are specifically designed with attributes needed for a prediction model for seasonal to decadal time scales, including the ability to run large ensembles of simulations with available computational resources. For computational speed SPEAR uses a coarse ocean resolution of approximately 1.0° (with tropical refinement). SPEAR can use differing atmospheric horizontal resolutions ranging from 1° to 0.25°. The higher atmospheric resolution facilitates improved simulation of regional climate and extremes. SPEAR is built from the same components as the GFDL CM4 and ESM4 models but with design choices geared toward seasonal to multidecadal physical climate prediction and projection. We document simulation characteristics for the time mean climate, aspects of internal variability, and the response to both idealized and realistic radiative forcing change. We describe in greater detail one focus of the model development process that was motivated by the importance of the Southern Ocean to the global climate system. We present sensitivity tests that document the influence of the Antarctic surface heat budget on Southern Ocean ventilation and deep global ocean circulation. These findings were also useful in the development processes for the GFDL CM4 and ESM4 models.

Application of the Cyclone Phase Space to Extratropical Transition in a Global Climate Model

“…We do not know the generality with which the p95 modification introduced in this study will be useful, or how many other models/data sets contain grid‐scale structures similar to those in FLOR‐FA. However, similar noisy structures have been confirmed in a simulation with the Seamless System for Prediction and EArth System Research (SPEAR, Delworth et al, ), the latest modeling system developed at GFDL, in which a new double‐plume convection scheme (Zhao et al, ) is introduced. It can also be speculated that the Atmosphere Model 2.5 (AM2.5 Delworth et al, ) and the High Resolution Atmospheric Model (HiRAM Zhao et al, ), which use the same finite volume dynamical core on a cubed‐sphere grid (Putman & Lin, ) with the same divergence damping coefficient (Zhao & Held, ) as FLOR‐FA, may be susceptible to localized strong convection akin to that in FLOR‐FA.…”

The GFDL Earth System Model Version 4.1 (GFDL‐ESM 4.1): Overall Coupled Model Description and Simulation Characteristics

“…This calibrated age was then used in a series of 40 year test simulations to reproduce ventilation patterns in both the mode and intermediate waters of the Southern Ocean as well as the AABW circulation. Similar to the experience developing the equivalent 1° MOM6 ocean in the Seamless Prediction for EARth system (SPEAR) effort [Delworth et al, 2020], extremely high levels of viscosity (up to 2000 m 2 s -1 ) in ESM4.1 were necessary along the Antarctic coast to maintain the propagation of ventilated waters away from Antarctica, with the viscosity implemented as a strong function of latitude to avoid high values in mid latitudes which would have otherwise interfered with the propagation of North Atlantic Deep Water as described in Adcroft et al, [2019]. Note that after development was complete, it was discovered that the tidal component of vertical mixing had not been recalibrated from the parameterization in CM4.0 and constituted 1.5 TW of mixing rather than the intended 1.0 TW.…”

“…Extensive efforts to improve boreal climate were made with respect to the role of snow on land albedo through representation of high latitude larches and to assess the sensitivity of the spring transition to snow masking depth. Snow-on-glacier near infra-red albedo: As described in Delworth et al [2020], Southern Ocean heat fluxes in the MOM6 OM4 class of models is highly sensitive to the parameterization of the albedo of snow on glacier in the near infra-red region. As shown by Flanner et al [2007], the albedo of snow on glaciers in the near infrared is a strong function of wavelength, with values near 1.0 in the visible falling to values of 0.9 at 800 nm, 0.75-0.8 at 1.1 μm, and 0.55 at 1.3 μm.…”

Detected climatic change in global distribution of tropical cyclones

“…The last is that using a very new model developed at GFDL (SPEAR; ref. 29). We utilized SPEAR in addition to FLOR considering the potential model dependence of results.…”

“…We utilized SPEAR in addition to FLOR considering the potential model dependence of results. SPEAR can be considered as an independent model from FLOR and FLOR-FA with substantial upgrades in the physical and dynamical packages in SPEAR (29). Each configuration runs 30-to 35-member ensemble simulations.…”