DOI: 10.26050/wdcc/icon-nwp_mh_convection
title: ICON-NWP simulations of the mid-Holocene West African Monsoon using parameterized an explicit convection and present-day land surface

description: Project: Influence of the representation of convection on the mid-Holocene West African Monsoon - Global climate models have difficulties to simulate the northward extension of the monsoonal precipitation over north Africa during the mid-Holocene as revealed by proxy data. A common feature of these models is that they usually operate on too coarse grids to explicitly resolve convection, but convection is the most essential mechanism leading to precipitation in the West African monsoon region. Here, we investigate how the representation of tropical deep convection in the ICON climate model affects the meridional distribution of monsoonal precipitation during the mid-Holocene, by comparing regional simulations of the summer monsoon season (July to September, JAS) with parameterized (40km-P) and explicitly resolved convection (5km-E). In the 5km-E simulation, the more localized nature of precipitation and the absence of permanent light precipitation as compared to the 40km-P simulation is closer to expectations. However, in the JAS-mean the 40km-P simulation produces more precipitation and extends further north than the 5km-E simulation, especially between 12°N and 17°N. The higher precipitation rates in the 40km-P simulation are consistent with a stronger monsoonal circulation over land. Furthermore, the atmosphere in the 40km-P simulation is less stably stratified and notably moister. The differences in atmospheric water vapor are the result of substantial differences in the probability distribution function of precipitation and its resulting interactions with the land surface. The parametrization of convection produces light and large-scale precipitation, keeping the soils moist and supporting the development of convection. In contrast, less frequent but locally intense precipitation events lead to high amounts of runoff in the explicitly resolved convection simulations. The stronger runoff inhibits the moistening of the soil during the monsoon season and limits the amount of water available to evaporation in the 5km-E simulation. Summary: The experiment aims to investigate how the representation of convection influences the West African Monsoon during the mid-Holocene. Atmospheric and SST input data originate from the MPI-ESM Holocene simulations reflecting Holocene condition. External Parameters (surface condition) reflect present-day conditions similar to the experimental setup of PMIP1: The Sahara remains a desert. We use the ICON (ICOsahedral Nonhydrostatic) model framework version 2.5.0 (see Zängl et al. (2014) for more details). The provided data covers one simulation from June to October (JJASO) for the year 7023 before present (BP) with the year 2000 as the reference year. The time axes of the NetCDF files reflect the model year which is based on the time axes of the MPI-ESM slo0021a Holocene simulations. The artificial model year 1001 in slo0021a refers to the year 8000 BP. Therefore, the model year 1977 refers to the year 7023 BP. The experiment compares a 5km horizontal resolution, cloud-resolving simulation with a 40km-horizontal resolution, parameterized convection simulation. The 40km-domain (DOM01) covers a range from 70.5°W - 99.5°E; 49°S - 59°N The 5km-domain (DOM04) covers a range from 37°W - 53°E; 0°N - 40°N The dataset provides daily mean values on the triangular ICON grid. The datasets provide atmospheric (3D), surface (2D) and precipitation (2D) data an the following variables: rain_con_rate, rain_gsp_rate, clct, geopot, temp, rh, qv, u, v, w, w_so, runoff_g, runoff_s, lhfl_s, shfl_s, soiltyp