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= The Urban Microscale Model Intercomparison Project (UMMIP) =
Welcome to the homepage of the first computational fluid dynamics model intercomparison for building-resolving simulation of the urban atmospheric boundary layer. UMMIP is hosted by the Institute of Meteorology and Climatology at Leibniz University Hannover, Germany. This initiative a joint effort from model developers and researchers worldwide and was triggered and is coordinated by the Urban Climate Under Change ([UC]²) program, funded by the German Ministry of Education and Research (BMBF).

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News and Announcements
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      2022/01/22: Start of study design phase
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== Motivation ==
Over the past decades, urban microscale models have been increasingly used to simulate the urban atmosphere. Today, a multitude of models exist that differ in complexity, employed parameterizations, and degree of parallelization. While simple model configurations (i.e. simple building configurations, steady-state conditions, and no thermodynamics) have been often validated against wind tunnel experiments, the evaluation of more complex configurations is difficult. Wind tunnels are not able to take into account complex processes like radiative transfer, non-stationary boundary conditions, and complex thermodynamic interactions with the urban surface. By the same token, real urban environments are far too complex to be aggregated in data sets generated in field experiments. A validation based on such data sets is thus impossible.

The UMMIP aims at providing a comprehensive data set based on multi-model simulations for well-defined set-ups in urban environments. The complexity of the set-ups is increased in several stages based on existing and newly-developed set-ups suitable to be simulated by most of the participating models. UMMIP aims at showing how much the simulations results differ between individual models and therefore will provide an educated estimation of the reliability of urban microscale models. Uncertainties that do not arise from insufficiently accurate input data (like building shape, wall and roof mounting, distribution of vegetation, etc.) or external forcings but from model numerics and physical parameterizations are to be investigated. Finally, we also strive at providing detailed information about model optimization in terms of degree of parallelization and performance.

The model intercomparison encompasses models based on Reynolds-Averaged Navier-Stokes (RANS) equations and turbulence-resolving Large-Eddy Simulation (LES) models.

== Study design ==

Therefore, we aim at a sophisticated model intercomparison project following a two-step design. The first phase of UMMIP (UMMIP-1) shall shed light on the performance of different numerical models to resolve micro-scale atmospheric processes in urban environments under controlled conditions with well-defined reference data sets. The second phase of UMMIP (UMMIP-2) will be a follow-on activity where model performance will be tested using reference data from quality-controlled field observations. Since UMMIP-2 is a highly complex activity that needs both realistic atmospheric initial and boundary conditions as well as reference data with known errors, we will start with UMMIP-1 before setting up the UMMIP-2.
UMMIP-1 aims at providing a comprehensive data set based on multi-model simulations for well-defined set-ups in urban environments. The complexity of the set-ups is increased in several stages based on existing and newly-developed set-ups suitable to be simulated by most of the participating models. UMMIP-1 aims at showing how much the simulation results differ between individual models and therefore will provide an educated estimation of the reliability of urban microscale models. Uncertainties that do not arise from insufficiently accurate input data (like building shape, wall and roof mounting, distribution of vegetation, etc.) or external forcings but from model numerics and physical parameterizations are to be investigated.
UMMIP-1 encompasses numerical models based on Reynolds-Averaged Navier-Stokes (RANS) equations and turbulence-resolving Large-Eddy Simulation (LES) models. The study area is the well-known Michel-Stadt area.


== Stages ==

=== Stage 0: Complex urban geometry, no thermodynamics ===
- Description: Michelstadt
- Submission deadline: 2022/05/31
- Status: tbd.
- [wiki:/ummip/stage0 Details]

=== Stage 1: Complex urban geometry, with thermodynamics, steady-state ===
- Description: Michelstadt with constant surface temperature distribution and steady-state conditions
- Submission deadline: 2022/06/30
- Status: tbd.
- [wiki:/ummip/stage1 Details]

=== Stage 2: Complex urban geometry, with thermodynamics, diurnal cycle ===
- Description: Michelstadt with prescribed surface temperature diurnal cycle
- Submission deadline: 2022/07/31
- Status: tbd.
- [wiki:/ummip/stage2 Details]

=== Stage 3: Complex urban geometry, with full surface interaction and radiation ===
- Description: Michelstadt with interactive surface and radiation models using the individual models' flavors
- Submission deadline: 2022/08/31
- Status: tbd.
- [wiki:/ummip/stage3 Details]

== UMMIP Data Requirements ==
All model data has to be provided according to the UMMIP data requirements in NetCDF-4 data format. Details are given in the description of the individual stages.

== How to participate ==
We welcome contributions from any kind of microscale CFD model that is able to resolve the flow around complex building structures. The intercomparison project is sub-divided into several stages with increasing complexity. All contributing models are expected to at least participate in stages 1 and 2. Contributions for stages 2 and 3 are optional, but highly welcome. For models that can operate both in RANS and LES mode, submissions for both options are eligible.

== Coordination and contact ==
- Scientific coordination:
  - Björn Maronga, Leibniz University Hannover
  - Dieter Scherer, Technical University Berlin
  - Bernd Leitl, Universität Hamburg

- Administration: Johannes Schwenkel
- Please Contact us via: ummip@meteo.uni-hannover.de

== Participating models (proposal) ==
- PALM, Leibniz University Hannover
- uDALES / Maarten van Reeuwijk, Imperial College London
- MITRAS / Heinke Schlünzen, Universität Hamburg
- FITNAH / Groß, Leibniz University Hannover
- ASMUS / Groß, Leibniz University Hannover
- ENVI-met / Stephan Weber / Benjamin Bechtel
- City-LES / Hiroyuki Kusaka / Manabu Kanda (?)
- OpenFOAM / Zhengtong Xie, University of Southampton
- MUKLIMO_3 / Astrid Eichorn-Müller
- EULAG / Smolarkiewicz
- MSSG / Takahashi (?)


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