====== Precipitation and ERF experiment ======

=====Objective=====

The more precipitating warm clouds are simulated in a model, the more
opportunity aerosols have to influence the parameterized liquid-phase
precipitation microphysics.  Therefore, the strength of the cloud-lifetime
effect in models may be related to the warm-rain fraction.  The aim of this
intercomparison project is to test whether this link exists across AeroCom
models. 

If warm-rain fraction and cloud-lifetime effect are linked, it may be
possible to use satellite observations of warm-rain fraction in the present-day
climate to constrain the cloud-lifetime effect.  In a preliminary study using
ECHAM-HAM, we found that it is possible to tune the model warm-rain fraction to
agree with the satellite climatology
of [[http://doi.org/10.1002/2015GL064604|Mülmenstädt et al. (2015)]]; this retuning of the model reduces the ERF
from −1.1 W m<sup>−2</sup> to
−0.9 W m<sup>−2</sup>.  (More details on this study, and a
preliminary comparison between the satellite-derived warm-rain fraction and
other models', can be found in
the [[http://home.uni-leipzig.de/jmuelmen/projects/documents.php?file=ams-170123.pdf|AGU 2016 Fall Meeting/AMS 2017
Annual Meeting slides]].)

=====References=====

[[http://doi.org/10.1002/2015GL064604|Mülmenstädt et al. (2015) satellite warm-rain climatology]]

[[http://home.uni-leipzig.de/jmuelmen/files.html?name=ams-170123.pdf|AGU/AMS presentation on warm rain as an ERF constraint in ECHAM-HAM]]

=====Simulation setup and required model diagnostics=====

The intention of this section is to require as little extra work as possible on
top of the [[indirect|AeroCom indirect forcing experiment]].

====If using the same model configuration as for the AeroCom indirect experiment====

Please repeat the ''all_2000'' simulation and save one of the following sets of
diagnostics:

  - 3D snow and rain mixing ratios
  - 3D snow and rain fluxes
  - 2D snow and rain water paths

As in the indirect experiment 2D output, the required time frequency is 3-hourly
non-accumulated.  If this is not feasible for the requested 3D fields, it is
possible to implement the warm-rain fraction as an online diagnostic in the
model; please contact me for details.

====If using a different model configuration than for the AeroCom indirect experiment====

To minimize the amount of work you have to do, and to make the results of this
study easier to correlate with other AeroCom results, I would strongly prefer
that you use the same model configuration (including model version) as for the
AeroCom indirect experiment.  If this is not possible, please perform runs as
close as possible to the indirect experiment ''all_2000'' and ''all_1850'' setup.  

Please try to provide the 3 h instantaneous diagnostics listed in table (1) of
the [[indirect|"Diagnostics" section of the indirect experiment description]].
If it is not possible to provide all, please provide at least

  * Surface convective and large-scale rain and snow rates
  * LWP and IWP

In addition, please provide one of the following three sets of diagnostics:
  - 3D snow and rain mixing ratios
  - 3D snow and rain fluxes
  - 2D snow and rain water paths

=====Models participating so far=====

CAM5 (Contact: Shipeng Zhang, Minghuai Wang)

SPRINTARS (Contact: Takuro Michibata, Toshi Takemura)

IFS (Contact: Amund Søvde, Gunnar Myhre)

ECHAM-HAM (Contact: Johannes Mülmenstädt)

=====Contact=====

Johannes Mülmenstädt: <johannes.muelmenstaedt@uni-leipzig.de>

=====Data deadline=====

Please provide data by June 2017 so that preliminary results will be ready in
time for the AeroCom meeting (October 9, 2017).