Observations for Model Intercomparison Project (Obs4MIPs): status for CMIP6
Authors: Waliser Duane , Gleckler Peter J. , Ferraro Robert , Taylor Karl E. , Ames Sasha , Biard James , Bosilovich Michael G. , Brown Otis , Chepfer Helene , Cinquini Luca , Durack Paul J. , Eyring Veronika , Mathieu Pierre-Philippe , Lee Tsengdar , Pinnock Simon , Potter Gerald L. , Rixen Michel , Saunders Roger , Schulz Jörg , Thépaut Jean-Noël , Tuma Matthias 
Published: July 2020

Abstract. The Observations for Model Intercomparison Project (Obs4MIPs) was initiated
in 2010 to facilitate the use of observations in climate model evaluation
and research, with a particular target being the Coupled Model
Intercomparison Project (CMIP), a major initiative of the World Climate
Research Programme (WCRP). To this end, Obs4MIPs (1) targets observed
variables that can be compared to CMIP model variables; (2) utilizes dataset
formatting specifications and metadata requirements closely aligned with
CMIP model output; (3) provides brief technical documentation for each
dataset, designed for nonexperts and tailored towards relevance for model
evaluation, including information on uncertainty, dataset merits, and
limitations; and (4) disseminates the data through the Earth System Grid
Federation (ESGF) platforms, making the observations searchable and
accessible via the same portals as the model output. Taken together, these
characteristics of the organization and structure of obs4MIPs should entice
a more diverse community of researchers to engage in the comparison of model
output with observations and to contribute to a more comprehensive
evaluation of the climate models. At present, the number of obs4MIPs datasets has grown to about 80; many
are undergoing updates, with another 20 or so in preparation, and more than 100
are proposed and under consideration. A partial list of current global
satellite-based datasets includes humidity and temperature profiles; a wide
range of cloud and aerosol observations; ocean surface wind, temperature,
height, and sea ice fraction; surface and top-of-atmosphere longwave and
shortwave radiation; and ozone (O3), methane (CH4), and carbon
dioxide (CO2) products. A partial list of proposed products expected to
be useful in analyzing CMIP6 results includes the following: alternative products for the
above quantities, additional products for ocean surface flux and
chlorophyll products, a number of vegetation products (e.g., FAPAR, LAI,
burned area fraction), ice sheet mass and height, carbon monoxide (CO), and
nitrogen dioxide (NO2). While most existing obs4MIPs datasets consist
of monthly-mean gridded data over the global domain, products with higher
time resolution (e.g., daily) and/or regional products are now receiving more
attention. Along with an increasing number of datasets, obs4MIPs has implemented a
number of capability upgrades including (1) an updated obs4MIPs data
specifications document that provides additional search facets and
generally improves congruence with CMIP6 specifications for model datasets,
(2) a set of six easily understood indicators that help guide users as to a
dataset's maturity and suitability for application, and (3) an option to
supply supplemental information about a dataset beyond what can be found in
the standard metadata. With the maturation of the obs4MIPs framework, the
dataset inclusion process, and the dataset formatting guidelines and
resources, the scope of the observations being considered is expected to
grow to include gridded in situ datasets as well as datasets with a regional
focus, and the ultimate intent is to judiciously expand this scope to any
observation dataset that has applicability for evaluation of the types of
Earth system models used in CMIP.