A climate dataset from overriding experiments on cloud and air-sea feedbacks with CESM2 under 1pctCO2 warming

Here we develop a novel overriding technique for climate projections that substitutes specific variables in control runs to isolate such feedback mechanisms. We apply this to the Community Earth System Model version 2 (CESM2) and perform a series of 150-year simulations with 1% CO2 increase per year (1pctCO2). These experiments progressively decouple the thermodynamic, dynamical, and radiative responses of the surface ocean to the atmosphere, and investigate the triggering effects of cloud feedback on air-sea interactions. In real time, we replace the key variables under 1pctCO2 with those from the current climate, such as downwelling shortwave radiation, wind speed in latent and sensible heat, and wind stress. They provide monthly output of global distributions including surface temperatures, winds, and precipitation, with a spatial resolution of 1.9° × 2.5° in latitude and longitude and 32 levels for the atmosphere, and of ~1° and 60 layers designated as gx1v7 for the ocean. This open access dataset for partial air-sea coupling under climate change can help understand the regional patterns in global warming and quantify the relative contributions of forcing mechanisms.The datasets are constructed in two NetCDF files for means of model years 61-80 and 131-150: “CESM2_1pctCO2_Ovrd_Clim_F20yr.nc” and “CESM2_1pctCO2_Ovrd_Clim_L20yr.nc”, respectively. Here, “Ovrd” stands for overriding, “Clim” for the means, “F20yr” and “L20yr” for the first (61-80) and last (131-150) 20 years. Both the .NC flies consist of the default and overriding experiments and contain the same 25 monthly climate variables along 2 or 3 dimensions (D). The actual dimensions are 12 (month) × 11 (experiment) × 96 (latitude) × 144 (longitude) for 2-D variables, and 12 (month) × 11 (experiment) × 32 (level) × 96 (latitude) × 144 (longitude) for 3-D variables, except that level should be replaced by 4 (type) for CldAmt (cloud amount). In addition, the ARCHIVE file “ScptPrgms.zip” compresses the SourceMods directory containing modified CESM2 programs, together with automated shell scripts named change_my_settings and query_my_settings. These scripts are designed to integrate and check all the complicated and case-specific parameter setting commands required by the model before it can be run to output the datasets.Following the Coupled Model Intercomparison Project phase 6 convention, the 3-D variables (8 in subtotal) are listed as air temperature (ta; unit: K), zonal (ua; unit:m s-1) and meridional (va; unit: m s-1) winds, pressure velocity (wap; unit: Pa s-1), specific (hus; unit: kg kg-1) and relative (hur; unit: percent) humidity, geopotential height (zg; unit: m), and cloud amount (CldAmt; unit: fraction) by type (high, middle, low, and total). On the other hand, the 2-D variables (17 in subtotal) are at the surface, including surface temperature (ts; unit: K), surface air temperature (tas; unit: K), precipitation (pr; unit: m s-1; total: convective plus large-scale, liquid and ice), sea level pressure (psl; unit: Pa), zonal (uas; unit: m s-1) and meridional (vas; unit: m s-1) winds, wind speed (sfcWind; unit: m s-1), specific (huss; unit: kg kg-1) and relative (hurs; unit: percent) humidity, zonal (tauu; unit: N m-2) and meridional (tauv; unit: N m-2) wind stress, latent (hfls; unit: W m-2) and sensible (hfss; unit: W m-2) heat fluxes, downwelling (rsds; unit: W m-2) and net (rsns; unit:W m-2) solar radiation, downwelling (rlds; unit: W m-2) and net (rlns; unit: W m-2) longwave radiative fluxes. There are two 1-D labels: ExpID lists 11 Exps. I and II, as well as 0 to 8, while CldTp identifies the 4 cloud types in turn. CAM6 determines these types using fixed pressure levels (Medeiros et al., 2008): high (0~400 hPa), middle (400~700 hPa), low (700~1000 hPa), and total (0-1000 hPa).