Thomas Spengler

Bias Attribution Linking Moist Dynamics of Cyclones and Storm Tracks (BALMCAST)

2020-2025 (12 Mio NOK)

Summary

There is a dichotomy between theoretical understanding and modeling of weather and climate, where the former mainly assumes a dry atmosphere while the latter relies on parameterizations of physical processes, especially related to moisture and phase changes that can yield a significant feedback on the dynamics. With prevailing model biases in jet streams and storm tracks often being tied to these processes, we thus lack a theoretical underpinning that can aid a physical attribution and alleviation of these biases. For example, while the development of cyclones is traditionally thought to reduce the midlatitude temperature gradient that gives rise to storm development, latent heating within these storms enhances the temperature gradient, sometimes even yielding a net increase. These cycles are most likely associated with events of cyclone clustering with significant socio-economic impact. While the mechanisms by which cyclone lifecycles alter temperature gradients must be determined by frontal dynamics, we lack a detailed understanding of the interplay between processes along fronts and their relation to cyclone clustering as well as storm track intensity and variability. We therefore propose to develop a framework combining moist dynamics across fronts, cyclones, and the storm track.

Our framework will clarify the pertinent mechanisms and the role of frontal lifecycles and cyclone development in storm track variability and thereby aid our understanding of prevailing model biases. It will also contest our understanding of cyclone development, as our new paradigm allows for cyclones to increase temperature gradients. As our new moist storm track model will explain the positioning, intensity, and variability of storm tracks in terms of moist processes, it will allow us to physically attribute model biases and formulate alternative hypotheses about the cause for future shifts of storm tracks.

Atmosphere-Ocean Interactions over Key Regions of the Arctic and Their Linkages to Midlatitudes (ARCLINK)

2022-2026 (10 Mio NOK)

Summary

State-of-the-art weather and climate prediction models suffer from significant errors due to misrepresentations in both atmosphere-ocean interactions and atmospheric weather patterns. We aim to improve models by identifying processes and weather events leading to significant forecast errors. Our findings will guide model development in the polar regions with benefits for global weather and climate models. In particular, we will focus on atmosphere-ocean interactions during cold air outbreaks, which are large excursions of cold polar air masses over the relatively warmer ocean. These cold air outbreaks comprise the majority of the overall atmosphere-ocean heat exchange in the polar regions. Several recent and upcoming field campaigns provide valuable data to assess the fidelity of our models.

As the aforementioned weather events are connected to the larger-scale setting of the atmospheric circulation, we will investigate coupling mechanisms between the polar and lower latitudes. Particular focus will be on incursions of heat and moisture into the Arctic. It has recently been argued that these incursions are becoming more frequent with climate change, though a thorough assessment of the representation of these events in our weather and climate models is still lacking. We will characterize these teleconnection events to identify and attribute model errors.

Our results will explain errors in weather and climate models associated with atmosphere-ocean heat exchange and the representation of weather events. Given the importance of the atmosphere-ocean heat exchange in the subpolar regions, our findings will leave a profound impact on the weather and climate research community.