Gulf Stream Moisture Fluxes Impact Atmospheric Blocks Throughout the Northern Hemisphere

• Published in: Geophysical research letters 2024-07, Vol.51 (13), p.n/a
• Main Authors: Mathews, J. P., Czaja, A., Vitart, F., Roberts, C.
• Format: Article
• Language: English
• Subjects: Air flow; air‐sea interactions; Anticyclones; Atmospheric blocking; Blocking anticyclones; Blocking events; Blocking patterns; Boundary currents; ECMWF IFS; Fluctuations; Frequency dependence; Gulf Stream; Heat flux; Heat transfer; Identification methods; jet stream; Latent heat; Latent heat flux; Life span; Moisture; Moisture flux; Moisture transfer; Northern Hemisphere; Ocean currents; Planetary waves; Rivers; Rossby waves; Sea currents; Statistical analysis; Wave propagation; Wavelengths; Western boundary currents
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2024GL108826

In this study, we explore the impact of oceanic moisture fluxes on atmospheric blocks using the ECMWF IFS. Artificially suppressing surface latent heat flux over the Gulf Stream (GS) region reduces atmospheric blocking frequency across the Northern Hemisphere by up to 30%. Affected blocks show a shorter lifespan (−6%), smaller spatial extent (−10%), and reduced intensity (−0.4%), with an increased number of individual blocking anticyclones (+17%). These findings are robust across various blocking detection thresholds. Analysis reveals a qualitatively consistent response across all resolutions, with Tco639 (∼18 km) showing the largest statistically significant change across all blocking characteristics, although differences between resolutions are not statistically significant. Exploring the broader Rossby wave pattern, we observe that diminished moisture fluxes favor eastward propagation and higher zonal wavenumbers, while air‐sea interactions promote stationary and westward‐propagating waves with zonal wavenumber 3. This study underscores the critical role of the GS in modulating atmospheric blocking. Plain Language Summary In our study, we investigated how changes in oceanic moisture, specifically from the Gulf Stream (GS), affect atmospheric blocking events using the ECMWF Integrated Forecast System. By artificially reducing the moisture flux from the GS area, we observed a notable decrease in the occurrence of atmospheric blocks across the Northern Hemisphere‐up to 30%. These blocks also showed changes in their characteristics: they had shorter durations by 6%, were 10% smaller in spatial size, and had a slight decrease in intensity, alongside a 17% increase in their detection rates. Our findings were consistent across different methods of identifying blocks. We also discovered that the model's resolution influences the observed changes, with coarser resolutions (larger than approximately 18 km) not showing significant alterations in some blocking traits despite the overall frequency reduction. Further analysis into Rossby wave patterns revealed that reduced moisture flux tends to favor faster eastward‐moving patterns with shorter wavelengths, whereas interactions between the air and sea support more stationary or westward‐moving waves, particularly those with a zonal wavenumber of 3. This highlights the crucial role that moisture from western boundary currents like the GS plays in the development and behavior of atmospheric blocking patterns. Key Poin