Added Value of Atmosphere-Ocean Coupling in a Century-Long Regional Climate Simulation

Fanni Dóra Kelemen,Bodo Ahrens,Hendrik Feldmann,Cristina Primo

doi:10.3390/atmos10090537

Fanni Dóra Kelemen, Bodo Ahrens + Show 2 more

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https://doi.org/10.3390/atmos10090537

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Abstract

A twentieth century-long coupled atmosphere-ocean regional climate simulation with COSMO-CLM (Consortium for Small-Scale Modeling, Climate Limited-area Model) and NEMO (Nucleus for European Modelling of the Ocean) is studied here to evaluate the added value of coupled marginal seas over continental regions. The interactive coupling of the marginal seas, namely the Mediterranean, the North and the Baltic Seas, to the atmosphere in the European region gives a comprehensive modelling system. It is expected to be able to describe the climatological features of this geographically complex area even more precisely than an atmosphere-only climate model. The investigated variables are precipitation and 2 m temperature. Sensitivity studies are used to assess the impact of SST (sea surface temperature) changes over land areas. The different SST values affect the continental precipitation more than the 2 m temperature. The simulated variables are compared to the CRU (Climatic Research Unit) observational data, and also to the HOAPS/GPCC (Hamburg Ocean Atmosphere Parameters and Fluxes from Satellite Data, Global Precipitation Climatology Centre) data. In the coupled simulation, added skill is found primarily during winter over the eastern part of Europe. Our analysis shows that, over this region, the coupled system is dryer than the uncoupled system, both in terms of precipitation and soil moisture, which means a decrease in the bias of the system. Thus, the coupling improves the simulation of precipitation over the eastern part of Europe, due to cooler SST values and in consequence, drier soil.

Highlights

High-resolution climatological data is essential for studying the climate system’s features and its changes—both in the past and in the future
To analyze the changes in the sensitivity experiments, we investigate the time evolution of the field means for precipitation and 2 m temperature over the Mediterranean Sea, the North and Baltic Seas and over the continental areas (Figure 2)
The changes in the precipitation and 2 m temperature fields are directly proportional to the SST values, when the SST values rise, the precipitation and 2 m temperature rises

Summary

Introduction

High-resolution climatological data is essential for studying the climate system’s features and its changes—both in the past and in the future. One way of improvement in climate research is the development and usage of regional climate models (RCM), or limited area models [1]. These models enable us to increase the spatial resolution of simulations without being as expensive as global models on the same high resolution. One further step in the improvement is the use of regional climate system models (RCSM). This means that the atmosphere and land surface, and other parts of the climate system are modelled in detail by numerical models and coupled together in an interactive way. Since the changes undergoing in the ocean have great relevance on the climate timescale, the coupling of an atmosphere and an ocean model is one often-used combination

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