Recent  

Droughts and heatwaves have become some of the clearest manifestations of a changing climate. Near-term adaptation strategies can benefit from seasonal predictions, but these predictions still have limitations. We found that an intrinsic property of multi-system forecasts can serve to better anticipate extreme high-temperature and low-precipitation events during boreal summer in several regions of the Northern Hemisphere with different levels of predictability.

The differences between climate models can be exploited to infer how specific aspects of the climate influence the Earth system. This work analyses the effects of a negative temperature anomaly over the Tibetan Plateau on the winter atmospheric circulation. We show that models with a colder-than-average Tibetan Plateau present a reinforcement of the eastern Asian winter monsoon and discuss the atmospheric response to the enhanced transport of cold air from the continent toward the Pacific Ocean.

We investigate the role of the solar cycle in atmospheric domains with the Max Plank Institute Earth System Model in high resolution (MPI-ESM-HR). We focus on the tropical upper stratosphere, Northern Hemisphere (NH) winter dynamics and potential surface imprints. We found robust solar signals at the tropical stratopause and a weak dynamical response in the NH during winter. However, we cannot confirm the importance of the 11-year solar cycle for decadal variability in the troposphere.

It is not yet clear which variations in broader atmospheric conditions of the West African monsoon may lead to mesoscale convective system (MCS) occurrences in southern West Africa (SWA). In this study, we identified nine different weather patterns and categorized them as dry-, transition-, or monsoon-season types using a method called self-organizing maps (SOMs). It was revealed that a warmer Sahel region can create favourable conditions for MCS formation in SWA.

This study highlights how the sea ice variability in the Greenland Sea affects the terrestrial climate and the surface mass changes of peripheral glaciers of the Zackenberg region (ZR), Northeast Greenland, combining model output and observations. Our results show that the temporal evolution of sea ice influences the climate anomaly magnitude in the ZR. We also found that the changing temperature and precipitation patterns due to sea ice variability can affect the surface mass of the ice cap.

On summer days over mountains, upslope winds transport moist air towards mountain tops and beyond, making local rain showers more likely. We use idealized simulations to investigate how mountain steepness affects this mechanism. We find that steeper mountains lead to a delayed onset and lower intensity of the storms, because less moisture accumulates over the ridges and the thermal updraft zone at the top is narrower and thus more prone to the intrusion of dry air from the environment.

Heavy rainfall in tropical regions interacts with mid-latitude circulation patterns, and this interaction can explain weather patterns in the Northern Hemisphere during summer. In this analysis we detect these tropical–extratropical interaction pattern both in observational datasets and data obtained by atmospheric models and assess how well atmospheric models can reproduce the observed patterns. We find a good agreement although these relationships are weaker in model data.

Atmospheric blocking describes large and persistent high surface pressure. In this study, the relationship between block persistence and smaller-scale systems is examined. Persistent blocks result from more interactions with small systems, but a block's persistence does not depend as strongly on the strength of these smaller features. This work is important because it provides more knowledge as to how blocks can be allowed to persist, which is something we still do not fully understand.

Arctic sea ice loss might impact the atmospheric circulation outside the Arctic and therefore extremes over mid-latitudes. Here, we analyze model experiments to initially assess the influence of sea ice loss on occurrence frequencies of large-scale circulation patterns. Some of these detected circulation changes can be linked to changes in occurrences of European temperature extremes. Compared to future global temperature increases, the sea-ice-related impacts are however of secondary relevance.

Cyclone detection and tracking methods (CDTMs) have different approaches in defining and tracking cyclone centers. This leads to disagreements on extratropical cyclone climatologies. We present a new approach that combines tracks from individual CDTMs to produce new composite tracks. These new tracks are shown to correspond to physically meaningful systems with distinctive life stages.

The interaction between Arctic cyclones and the sea ice surface in summer is investigated by analysing the friction and sensible heat flux processes acting in two cyclones with contrasting evolution. The major finding is that the effects of friction on cyclone strength are dependent on a particular feature of cyclone structure: whether they have a warm or cold core during growth. Friction leads to cooling within both cyclone types in the lower atmosphere, which may contribute to their longevity.

Midlatitude storms and their downstream impacts have a major impact on society, yet their prediction is especially prone to uncertainty. While this can never be fully eliminated, we find that the initial rate of growth of uncertainty varies for a range of forecast models. Examination of the model of the European Centre for Medium-Range Weather Forecasts (ECMWF) suggests ways in which uncertainty growth could be reduced, leading to sharper and more reliable forecasts over the first few days.

We studied the relationship between the strength of mid-latitude cyclones and their precipitation, how this may change in the future, and whether it depends of the type of cyclone. The relationship between cyclone strength and precipitation increases in warmer climates and depends strongly on the type of cyclone. For some cyclone types there is no relation between cyclone strength and precipitation. For all cyclone types, precipitation increases with uniform warming and polar amplification.