Extreme weather events have attracted increasing attention, due to their damaging impacts on natural systems and human communities. “Weather whiplash” describes abrupt transitions from one persistent weather regime to another substantially different one, which is even more disruptive. When we turn our attention to the Arctic sea ice, we observe that the marginal sea ice also undergoes such abrupt declines, which we term as “sea ice decline whiplash”. In this work, we focus on these sea ice decline whiplash events occurring on the synoptic time scale over Barents-Kara Seas (BKS), which are identified based on a daily sea ice tendency index, when the index falls below the 5^th percentile of its probability density function distribution during winters of 1979-2020 for at least three consecutive days. A composite analysis of these sea ice decline whiplash events reveals that there is a significantly positive bottom-amplified temperature anomaly preceding the abrupt sea ice loss. This anomaly is closely associated with a wave train composed of a Ural blocking and an upstream positive phase of the North Atlantic Oscillation. Such a structure is favorable for the transport of warm and moist air into the BKS. As a result, the tropospheric temperature, including the surface air temperature, increases through horizontal warm-temperature advection, specifically through warm advection of the climatological temperature by the anomalous wind. The cooling over the BKS due to the adiabatic effect and vertical mixing opposes the horizontal warm-temperature advection above and below about 900 hPa, respectively. However, an increase in skin temperature prominently results from enhanced downward long-wave radiation, which is also the main contributor to the rapid sea ice loss. Furthermore, we examine how the abrupt sea ice decline events and their associated atmospheric conditions change in the context of global warming. This research sheds further light on the complex processes of Arctic weather and climate change.

How to cite: Jiang, Z. and Hu, X.: Arctic Sea Ice Decline Whiplash Events on the Synoptic Time Scale in the Context of Global Warming, EMS Annual Meeting 2025, Ljubljana, Slovenia, 7–12 Sep 2025, EMS2025-80, https://doi.org/10.5194/ems2025-80, 2025.

As a key driver of basal melting of ice shelves, ocean heat transport plays a central role in controlling ice shelf stability through ice-ocean interaction. A recent observational study confirmed the existence of an approximately 10 km-wide subsurface eddy (referred to as a cyclonic “thinny”) in Terra Nova Bay (TNB) and speculated that the shoreward advection of this observed eddy might enhance summertime melting of the Nansen Ice Shelf (NIS). Here, we for the first time report on the simulation of a cyclonic thinny transporting warm Antarctic Surface Water (AASW) into the cavity beneath the NIS performed using a regional coupled sea-ice/ocean model that includes the ocean-ice shelf dynamics/thermodynamics. By including eddy-wind interaction, our model successfully reproduced the occurrence of submesoscale cyclonic eddies in TNB, with warm AASW downward due to convergence at the eddy center, and demonstrated that the submesoscale eddy-meditated heat transport enhances the NIS basal melting. We examine how the cyclonic thinny influences the ice shelf melt through by analyzing the behavior of cyclonic eddies and its heat transport into the NIS cavity. Ocean heat supplied to the NIS cavity is most active when the cyclonic eddy elevating vertical heat transfer from the warm surface collides with the ice shelf front, which strengthens local basal melting at the ice shelf shallower than 200 m near the NIS front compared to the case without eddy collision with the ice shelf. This study highlights the significant role of subsurface eddies in localized ice shelf melting, which has the potential to impact the frequency of massive calving events.

How to cite: Kim, T., Choo, S.-H., and Moon, J.-H.: Occurrence of submesoscale eddy in Terra Nova Bay and its impact on basal melting of Nasen Ice Shelf, East Antarctica , EMS Annual Meeting 2025, Ljubljana, Slovenia, 7–12 Sep 2025, EMS2025-358, https://doi.org/10.5194/ems2025-358, 2025.

Seasonally frozen ground (SFG), a critical component of the cryosphere, covers approximately 50% of the Northern Hemisphere’s land area and significantly influences land surface and overlying atmospheric processes. The coexistence of ice and liquid water in soil alters its hydraulic and thermal properties, thereby influencing the distribution of water and energy fluxes. Accurately modeling parameters such as soil moisture, soil temperature, snow depth, etc., is particularly challenging due to processes like soil freezing and subsequent thawing. Variability in model performance remains a key challenge, highlighting the need for improved representation of SFG in cold regions.

The study compares standalone global simulations from two land surface models (LSMs) - JSBACH (Jena Scheme for Biosphere-Atmosphere Coupling in Hamburg) and CLM (Community Land Model) driven by 3-hourly ERA5 reanalysis data from 1941 to 2022, with a focus on the representation of SFG across the mid- to high latitudes of the Northern Hemisphere. CLM produces a more realistic distribution of frozen ground, whereas JSBACH significantly underestimates the extent of SFG, and ERA5-Land underrepresents permafrost extent. All models tend to underestimate SFG compared to the IPA (International Permafrost Association) map, with JSBACH showing the largest deviation. Global gridded outputs from JSBACH and CLM, along with ERA5-Land data, were intercompared to quantify differences between models. Results indicate that JSBACH performs poorly in cold regions, possibly due to issues in its multilayer snow scheme and the representation of snow thermal properties, which may contribute to underestimated snow depth and lower soil temperatures at 20 cm depth. In contrast, JSBACH performs better than CLM in mid-latitude snow-free regions, particularly over the Tibetan Plateau. Additionally, site-level analyses focusing on the onset and duration of SFG and snow cover revealed notable biases in simulating SFG onset and duration across all models due to snow insulation effects. The modal value of the soil-air temperature difference PDF (Probability Density Function) increases by ~5°C from shallow to thick snow, reflecting the stronger insulating effect of thicker snow. CLM tends to overestimate the insulating effect of snow, while JSBACH underestimates it. The study highlights the challenges of simulating SFG processes in cold regions, emphasizing the need to improve the representation of freeze-thaw dynamics through the thermal and hydraulic properties of soil and snow in land surface models (LSMs) to enhance model performance.

How to cite: Parmar, M., Ahrens, B., Froehlich, K., Luo, Z., Risto, D., Sanna, A., and Peano, D.: Evaluation of Frozen soil characteristics in JSBACH and CLM standalone simulations, EMS Annual Meeting 2025, Ljubljana, Slovenia, 7–12 Sep 2025, EMS2025-457, https://doi.org/10.5194/ems2025-457, 2025.