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

Here we use the Community Earth System Model version 2 (CESM2) to develop a novel overriding technique 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). There are also two 1-D labels: ExpID lists 11 Exps. I, II, and 0 to 8, while CldTp identifies 4 cloud types of high, middle, low, and total in turn. 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 cmip6 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.

本研究采用社区地球系统模型第2版（Community Earth System Model version 2，CESM2）开发了一种新型覆盖（overriding）技术，并开展了一系列年CO₂浓度递增1%（1pctCO2）的150年模拟试验。这些试验逐步分离了表层海洋对大气的热力学、动力学与辐射响应，并探究云反馈对海-气相互作用的触发效应。在实时模拟中，我们将1pctCO2情景下的关键变量替换为当前气候态的对应变量，例如下行短波辐射、潜热与感热相关的风速，以及风应力。
该数据集提供全球分布的逐月输出结果，涵盖地表温度、风场与降水等要素；大气模块的空间分辨率为纬度1.9°×经度2.5°，共设32层；海洋模块采用gx1v7配置，空间分辨率约1°，共设60层。
本气候变化下海-气部分耦合的开放获取数据集，有助于理解全球变暖的区域分布特征，并量化各强迫机制的相对贡献。
数据集包含两个NetCDF（网络通用数据格式）文件，分别对应模型第61-80年与第131-150年的气候平均结果，文件名为"CESM2_1pctCO2_Ovrd_Clim_F20yr.nc"与"CESM2_1pctCO2_Ovrd_Clim_L20yr.nc"。其中，"Ovrd"代表覆盖（overriding），"Clim"代表气候平均，"F20yr"与"L20yr"分别对应前20年（61-80年）与后20年（131-150年）。
两个NetCDF文件均包含默认试验与覆盖试验的模拟结果，共包含25个逐月气候变量，变量维度分为2维或3维；同时附带两个1维标签：ExpID列出11个试验（编号I、II与0至8）；CldTp依次标识4种云型，即高云、中云、低云与总云。
二维变量的实际维度为12（月）×11（试验）×96（纬度）×144（经度）；三维变量的维度为12（月）×11（试验）×32（层次）×96（纬度）×144（经度），但云量（CldAmt）的层次维度需替换为4（云型）。
此外，归档文件"ScptPrgms.zip"压缩了包含修改后CESM2程序的SourceMods目录，以及名为"change_my_settings"和"query_my_settings"的自动化Shell脚本。这些脚本用于整合并校验模型运行前所需的所有复杂且针对特定案例的参数设置命令，以确保模型可正常输出数据集。
遵循耦合模型比较计划第6阶段（Coupled Model Intercomparison Project Phase 6，CMIP6）的惯例，本次数据集共包含8个三维变量，分别为：气温（ta，单位：K）、纬向风（ua，单位：m s⁻¹）与经向风（va，单位：m s⁻¹）、气压速度（wap，单位：Pa s⁻¹）、比湿（hus，单位：kg kg⁻¹）与相对湿度（hur，单位：%）、位势高度（zg，单位：m），以及按云型（高、中、低、总）分类的云量（CldAmt，单位：比例）。
二维变量共17个，均位于地表层面，包括：地表温度（ts，单位：K）、地表气温（tas，单位：K）、降水（pr，单位：m s⁻¹，包含对流性与大尺度降水、液态与固态降水）、海平面气压（psl，单位：Pa）、纬向风（uas，单位：m s⁻¹）与经向风（vas，单位：m s⁻¹）、近地面风速（sfcWind，单位：m s⁻¹）、比湿（huss，单位：kg kg⁻¹）与相对湿度（hurs，单位：%）、纬向风应力（tauu，单位：N m⁻²）与经向风应力（tauv，单位：N m⁻²）、潜热通量（hfls，单位：W m⁻²）与感热通量（hfss，单位：W m⁻²）、下行短波辐射（rsds，单位：W m⁻²）与净短波辐射（rsns，单位：W m⁻²）、下行长波辐射（rlds，单位：W m⁻²）与净长波辐射（rlns，单位：W m⁻²）。