Designing and Documenting Experiments in CMIP6

Abstract

Earth system modelling relies on contributions from groups who develop models and from those involved in devising, executing, and exploiting numerical experiments. Often these people work in different institutions, and they may communicate primarily via published information (whether journal papers, technical notes, or websites). The complexity of the models, experiments, and methodologies, along with the diversity (and sometimes inexact nature) of information sources can easily lead to misinterpretation of what was actually intended or done. In this paper we introduce a taxonomy of terms for more 5 clearly defining numerical experiments, put it in the context of previous work on experimental ontologies, and describe how we have used it to document the CMIP6 experiments. We describe how this process involved iteration with a range of CMIP6 stakeholders to rationalise multiple sources of information and add clarity to experimental definitions. We demonstrate how this process has added value to CMIP6 itself by a) helping those devising experiments to be clear about their goals and expected methodology, b) making it easier for those executing experiments to know what was intended, c) exposing inter-relationships 10 between experiments, and d) making it clearer for third parties (data users) to understand the CMIP6 experiments. We conclude with some lessons learned, and how these may be applied for any modelling campaign as well as future CMIP phases. IntroductionClimate modelling involves the use of models to carry out simulations of the real world, usually as part of an experiment aimed at understanding processes, hypothesis testing, or projecting some future climate system behaviour. Such numerical experi-15 ments can be organized into "Model Intercomparison Projects" (MIPs) in which participants execute common experiments and share results. Perhaps the best known of these are the CMIP series of Climate Model Intercomparison Projects, of which the latest is CMIP6 .The design, documentation and accompanying protocols have all evolved over time, reflecting both an increasing scope and wider-spread interest, and two important new constituencies: (1) Those who have organised "Diagnostic MIPs", which do not 20 require new experiments, but rather request specific output from existing planned experiments to address specific interests; and(2) an even wider group of downstream users who use the CMIP data opportunistically, having little or no direct contact with the modelling groups.

Climate Models Accumulated Cyclone Energy Analysis

“…A set of standard experiments was designed for CMIP, allowing results to be comparable across different model simulations, to see where models agree and disagree on past and future scenarios [38].…”

“…CMIP6 historical experiment covers the period 1850-2014, forced by datasets that are largely based on observations, used as an important benchmark for assessing performance through evaluation against observations, and are well suited for quantifying and understanding important climate change response characteristics [38,27]. The characteristics and forcings included in historical were described in [27]: SSP585 results of a complementary effort by SSP narrative and the Representative Concentration Pathways (RCPs), representing the high end of the range of future pathways.…”

The CMIP6 Data Request (version 01.00.31)

“…In order to manage these specifications which are aggregated across the many participating endorsed MIPs, the specifcations 165 themselves are required to fit within an information model, which we call the Data Request Information Model (DRIM) to distinguish it from the data model of the NetCDF files described by Hassell et al (2017), on the one hand, and the Common Information Model documenting the experiments, simulations and models (Pascoe et al, 2019), on the other hand. The DRIM is expressed through an XSD schema (Juckes, 2018a) discussed further in section 4.2 below.…”

“…The Experiment section contains information imported from experiment descriptions formalised by ES-DOC (Pascoe et al, 2019) and from the CMIP6 Controlled Vocabularies (CVs) 11 . The CVs serve as the reference source for such things as 290 experiment names, model names, institution names.…”

Coordinating an operational data distribution network for CMIP6 data

“…Earth System Documentation (ES-DOC;Pascoe et al, 2019) is a service that documents in detail all the models and experiments and the CMIP6 endorsed MIPs. Modelling centres are responsible for providing the ES-DOC team with the detailed information of the model configurations such as the resolutions, physics and parameterizations.…”