Source:

National Center for Atmospheric Research (NCAR)

Additional Notes:

The CESM2 Large Ensemble (LENS2) consists of 100 members at 1-degree spatial resolution covering the period 1850-2100 under CMIP6 historical and SSP370 future radiative forcing scenarios. We follow the ensemble numbering scheme noted on the CESM2-LE webpage (see above)

1. Members 1-10: These begin from years 1001, 1021, 1041, 1061, 1081, 1101, 1121, 1141, 1161, and 1181 of the 1400-year pre-industrial control simulation. This segment of the control simulation was chosen to minimize drift.
2. Members 11-90: These begin from 4 pre-selected years of the pre-industrial control simulation based on the phase of the Atlantic meridional overturning circulation (AMOC). For each of the 4 initial states, there are 20 ensemble members created by randomly perturbing the atmospheric potential temperature field by order 10^-14K. The chosen start dates (model years 1231, 1251, 1281, and 1301) sample AMOC and sea surface height (SSH) in the Labrador Sea at their maximum, minimum, and transition states.
3. Members 91-100: These begin from years 1011, 1031, 1051, 1071, 1091, 1111, 1131, 1151, 1171, and 1191 of the 1400-year pre-industrial control simulation. This group includes an extensive / comprehensive set of output fields -- referred to as the mother of all runs, "MOAR" outputs, which can be used to drive regional climate models, in addition to COSP output.

LENS2 is divided into two 50-member sub-ensembles: one which uses the original CMIP6 Biomass Burning protocol (BMB) and one which uses a smoothed version of the CMIP6 BMB protocol (11-year running means) that is more comparable to the treatment of CMIP6 BMB emissions used before 1997 and after 2014.

Recent publications document the sizeable effect that the different treatments have on the climate of the model, including the hydrological cycle, Arctic sea ice, climate variability, and global surface temperature. Because the greatest impact is on the recent climate, this difference affects both attribution of extreme events relative to past climates, and the projections of the future climate relative to the present. Therefore we treat these two as separate model ensembles. Data is available for download for those who wish to combine the two biomass burning ensembles into a single 100-member ensemble.