Influence of the Boundary Forcing on the Internal Variability of a Regional Climate Model

Kevin Sieck,Daniela Jacob

doi:10.4236/ajcc.2016.53028

Abstract

The internal variability of a ten-member ensemble of the regional climate model REMO over Europe is investigated. It is shown that the annual cycle of internal variability behaves differently compared to earlier studies that focused on other regions. To gain better insight into the dependence of the internal variability on the boundary forcing variability, a circulation type classification is performed on the forcing data. It can be shown that especially in the winter season internal variability is dependent on the circulation type included in the boundary forcing, whereas in the summer season the level and pattern of internal variability is rather independent from the circulation type of the driving field. It is concluded that for Europe the internal variability of REMO in winter is governed by circulation patterns related to the North-Atlantic Oscillation, whereas in summer local processes play a bigger role.

Highlights

The sensitivity of regional climate models (RCMs) to the initial conditions of the simulation at constant external forcing has recently drawn increasing attention
The mean-sea-level pressure patterns for circulation type 5 and circulation type 6 can be related to a positive phase of the NAO that is characterized by enhanced storm activity and higher wind speeds in central Europe
The circulation type classification of the lateral boundary forcing has shown that the episodic behavior of internal variability can be related to the variability of the boundary forcing as already speculated by [8]

Summary

Introduction

The sensitivity of regional climate models (RCMs) to the initial conditions of the simulation at constant external forcing has recently drawn increasing attention. This sensitivity is often referred to as the internal variability (IV) of a RCM. Reference [2] finds that large differences between two ensembles often occur simultaneously with large IV. They conclude that the comparison between only two runs in, e.g., sensitiv-. (2016) Influence of the Boundary Forcing on the Internal Variability of a Regional Climate Model.

Methods

Results

Conclusion