High-Resolution Modelling of Climate Variability : Using the CESM 1.0.4

• Main Author: Westen, Renatus Maria van
• Other Authors: Dijkstra, H.A.
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: Utrecht University 2021
• Subjects: Climate Physics; Physical Oceanography; High-resolution Modelling; Climate Variability; Natural Variability; Ocean Eddies; Sea-level projections; Southern Ocean
• Online Access: https://dspace.library.uu.nl/handle/1874/401045

Most climate models have a 1◦ (100 km) horizontal resolution. This resolution is too coarse to resolve mesoscale processes in the ocean: ocean eddies. An ocean eddy is characterised by a swirling and turbulent fluid. To resolve ocean eddies within a climate model, a horizontal resolution of 0.1◦ (10 km) is required. Climate models with a horizontal resolution of 1◦ and 0.1◦ are referred to as low-resolution models and high-resolution models, respectively. Ocean eddies are relevant to the ocean circulation as they stir the (upper) ocean and contribute to the transport of heat and salt. Model biases are reduced in climate simulations in which ocean eddies are explicitly resolved. In low-resolution climate models, eddy-related processes (transport and mixing) are parameterised at the cost of losing eddy characteristics within the model. As a result, the ocean circulation appears to be laminar in low-resolution climate models, sometimes referred to as the ‘honey ocean’. In this thesis, model output (300 years) of a high-resolution version of the Community Earth System Model (CESM) is analysed. We explore the following research questions in this thesis: 1) Is a high-resolution version of the CESM capable of capturing climate variability (sub-annual - multidecadal) as seen in observations? 2) Are sea-level projections different between the high-resolution CESM and low-resolution CESM? For the first research question, the analysis is restricted to the Caribbean Sea and the Southern Ocean. The simulated sub-annual ocean variability matches well with observations in the Caribbean Sea. This sub-annual variability is related to ocean eddies. Apart from sub-annual variability, multidecadal variability is found in the Caribbean Sea and surroundings in the high-resolution CESM. This multidecadal variability is induced by ocean eddies in the Southern Ocean and this variability propagates through the entire ocean circulation. From observations, it is known that multidecadal variability exists in the Southern Ocean. However, ...