Sensitivity of the nocturnal and polar boundary layer to transient phenomena

Abstract

Abstract. Numerical weather prediction and climate models encounter challenges in accurately representing flow regimes in the stably stratified atmospheric boundary layer and the transitions between them, leading to an inadequate depiction of regime occupation statistics. As a consequence, existing models exhibit significant biases in near-surface temperatures at high latitudes. To explore inherent uncertainties in modeling regime transitions, the response of the near-surface temperature inversion to transient small-scale phenomena is analyzed based on a stochastic modeling approach. A sensitivity analysis is conducted by augmenting a conceptual model for near-surface temperature inversions with randomizations that account for different types of model uncertainty. The stochastic conceptual model serves as a tool to systematically investigate what types of unsteady flow features, and in what contexts, may trigger abrupt transitions in the mean boundary layer state. The findings show that the incorporation of enhanced mixing, a common practice in numerical weather prediction models, blurs the two regime characteristic of the stably stratified atmospheric boundary layer. Simulating intermittent turbulence is shown to provide a potential workaround for this issue. Including key uncertainty in models could lead to a better statistical representation of the regimes in long-term climate simulation. This would help to improve our understanding and the forecasting of climate change especially in high-latitude regions.

Surface fluxes and flow structure for stably stratified near-calm conditions

“…Vercauteren et al (2019a) found different regimes of influence by submeso motions associated with different anisotropies of the Reynolds stress tensor. Boyko and Vercauteren (2023), Kaiser et al (2024), and Boyko and Vercauteren (2024) used different approaches to include randomization in models to simulate intermittency of the turbulence and potential abrupt transitions. Van de Wiel et al (2012) determined the minimum wind speed required for maintaining fully developed turbulence.…”