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An upgrade of the moist physics processing package (the so-called "New Moist Physics") was introduced within Cycle 47R3 (implemented 12 October 2021).  This improves the complicated aims to improve the representation of complicated interactions between turbulence in the lowest part of the atmosphere, convective motions and the cloud physics.  It is important that these processes interact with each other in a physically consistent way to represent real-world processes effectively.  The upgrade improvesadjusts the following:

• the physical representation of the convective boundary layer and modelling of Cu-topped, Sc-topped, and clear boundary layers and their transitions,
• deep convection, cloud and precipitation in the forecast,
• cloud amounts and humidity,
• general precipitation through better parameterisation of hydrometeor interactions and processes,
• the activity of the model.  The ensemble spread is increased more strongly in regions where convection dominates perturbation growth (i.e. in the northern hemisphere (in summer) and in the tropics) and here, the increase in spread persists out to day 15.

In most cases, but not all, the changes listed above manifest themselves as improvements in model output fields - for more forecaster-oriented detail on product impacts see here.

Aspects of the moist physics package are given below:

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The turbulent and convective mixing in the convective boundary layer is formulated in a simple and consistent way but there are several important differences which have been introduced:

• the mixed layer is layer top is typically near the inversion top in the clear boundary layer, near the cloud base for Cu-topped boundary layers, and near the cloud top for Sc‑topped boundary layers. 
• the computed strength of the temperature inversion is used to distinguish between Sc and Cu topped boundary layers.
• entrainment at the top of the mixed layer is proportional to the surface buoyancy flux (20%) for all types of boundary layers.  Additionally for Sc, there is an increased contribution to turbulent mixing from radiatively driven entrainment.
• all cloud processes are handled by the cloud scheme.

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• introducing additional processes for:
  • the depositional growth of precipitating snow,
  • the evaporation of cloud ice,
  • the collision-collection of rain and snow particles.
• the warm-rain collision–coalescence process at supercooled temperatures can form supercooled rain drops.  This will enables the IFS to predict freezing drizzle (but at present this is not an ECMWF product). Freezing rain is produced through a different process.

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• Read more on the changes and improvements and the impacts introduced by the Moist Physics package.
• Read more on the impact on model output fields (forecaster oriented document).
• Watch a comprehensive lecture on model physics (30sec delay before video begins).
• View ECMWF eLearning module on parameterisation of sub-grid processes.

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