Atmospheric blockings

WIND AND ENERGY OVER EUROPE

Introduction

Instead of the usual westerly flow, with the passing of low and high pressure systems with their associated cold and warm fronts, atmospheric blockings appear at mid-latitudes as large, quasi-stationary high pressure systems (anticyclones).

What is an atmospheric blocking?

Atmospheric blockings are stable configurations of the mid-latitude atmospheric circulation that yield persistent and anomalous weather in large regions for a time period from weeks to months.

Atmospheric blocking. deepfryedmind

On the left side of the high pressure, warm air is advected from lower latitudes, and anomalously high persistent temperatures are registered. On the right side, the opposite situation occurs, and anomalously cold conditions happen. These situations can lead to heat waves or cold spells waves depending on the season of the year.

Consequences of Atmospheric blockings

  • Persistent dry conditions do happen below the high pressure area, and also anomalously weak winds.
  • Depending on the topography and the position of the blocking, heavy rain and flooding can take place too, if the unstable persistent throughs at the sides of the blocking high pressure area have enough moisture sources (e.g., a warm water mass as the Mediterranean sea).

Atmospheric blocking patterns classification

The most typical atmospheric blocking patterns in the Euro-Atlantic sector are classified in two types: ‘omega’ block and ‘diffluent’ or ‘dipole’ block.

1. Omega block. Met Office
2. Diffluent block. Met Office
  • 1 An example of an ‘omega’ block, named after the uppercase greek letter Ω. This map would yield warm weather to ireland and cold to the Benelux. UK could suffer lack of rainfall.
  • 2 An example of a ‘diffluent’ or ‘dipole’ block. This map would yield rainy weather to France and drought to UK. This kind of blockings can be more persistent than the ‘omega’ blocks.
Explanation of Atmospheric blocking types. Met Office.

Atmospheric blockings have a huge impact on the energy sector

  • Less precipitation than average in central and northern Europe, leading to decreased hydropower generation.
  • Significant winter cold spells that affect vast areas over Europe, which increase energy demand for heating.
  • Summer heatwaves over Northern Europe, which lead to increased energy demand for cooling Summer.
  • Disruption of typical wind patterns and ‘wind drought’ events which decrease wind power generation.
  • Persistent clear skies in regions affected by high pressures, which increased solar PV generation.

Example: May 2005 Atmospheric blocking

Many of the most relevant heat waves and cold spells registered during the last decades in Europe are related to atmospheric blockings. Here we show an example of a strong blocking over Europe and its consequences.

Added value of high resolution

Atmospheric blocking. deepfryedmind

Several studies have showed that higher resolution improves the representation of the blocking in climate models. For example, Anstey et al., (2013) showed how the models with higher vertical and horizontal resolution represented more accurately the observed blocking statistics than coarser resolution models.

Contribution from PRIMAVERA

  • The PRIMAVERA project is developing a new generation of advanced high-resolution global climate models, capable of simulating and predicting regional climate with unprecedented fidelity.
  • The increase in model resolutions of the PRIMAVERA models (typically around 25km) will allow to study physical processes involved in atmospheric blockings and their future evolution with an unprecedented level of detail and accuracy.

Anstey, J. A., P. Davini, L. J. Gray, T. J. Woollings, N. Butchart, C. Cagnazzo, B. Christiansen, S. C. Hardiman, S. M. Osprey, and S. Yang (2013), Multi-model analysis of Northern Hemisphere winter blocking: Model biases and the role of resolution, J. Geophys. Res. Atmos., 118, 3956–3971, doi:10.1002/jgrd.50231