Oceanic maintenance of atmospheric blocking in wintertime in the North Atlantic

Abstract

The connection between atmospheric blocking over the North Atlantic and the diabatic influence of the Gulf Stream is investigated using potential vorticity and moist potential vorticity diagnostics in the ERA5 reanalysis data set during wintertime (1979 - 2020). In line with previous research, the reliance atmospheric blocking has on turbulent heat fluxes over the Gulf Stream and its extension, for induction and maintenance, is shown to be significant. The air-sea heat flux generates negative potential vorticity air masses in the atmospheric boundary layer. These air masses subsequently contribute to the block’s negative potential vorticity anomaly at upper levels through ascending motion in the warm conveyor belt. It is shown that the block’s size and frequency partially depends on oceanic preconditioning via anomalous oceanic heat transport and heat content, prior to the blocking event, both of which allow for stronger turbulent heat fluxes. It is further hypothesized that the block feeds back positively on itself through the advection of cold dry air over the Gulf Stream, sustaining this air-sea interaction. This in turn decreases ocean heat content, eventually halting this air-sea interaction and severing the atmospheric block from its maintenance pathway.

Gulf Stream Moisture Fluxes Impact Atmospheric Blocks Throughout the Northern Hemisphere

“…Their experiment, suppressing latent heating along the warm conveyor belt of a cyclone, resulted in the subsequent suppression of atmospheric blocks, with some blocks failing to form at all. The ocean's role as a primary moisture source for atmospheric blocks was highlighted by Yamamoto et al (2021), with theories by Mathews and Czaja (2024) suggesting that western boundary currents, like the Gulf Stream (GS), modulate atmospheric blocking. This link was evidenced by increased blocking following heightened GS heat transport, leading to warm water anomalies that boost surface latent heat flux (SLHF), and consequently moisture, aiding block formation by transporting anomalously low potential vorticity (PV) air from lower to upper levels (Wenta et al, 2024).…”

“…This experiment underscores the significant role that air-sea interactions, specifically the GS's SLHF, play in modulating atmospheric blocking and its impacts. The proposed theory byMathews and Czaja (2024) suggests that air-sea interactions diabatically influence boundary layer air, which is then transported to the block via warm conveyor belts, altering the quality and quantity of its negative PV anomalies. Further research is needed to fully comprehend this process, including its seasonality and robustness across different models.…”