Figures from the paper, showing simulated Ural blocking event.
Taking a simulated Ural blocking event as the reference state, the optimally growing boundary errors (OGBE) in Arctic sea ice concentration (SIC) is obtained by solving the corresponding nonlinear optimization problem (a). The OGBE could have the largest uncertainty of the 4-pentad Ural blocking prediction with certain constraint. The OGBE mainly shows positive SIC perturbations in the Greenland, Barents and Okhotsk Seas. (b) shows the temperature response in low troposphere during the 1st pentad to the OGBE, which has a consistent pattern with the SIC perturbations. (c) shows the zonal wind response at 500 hPa during the 4th pentad, which is mainly modulated through the thermal wind balance. It shows a strengthened zonal wind in the upstream of Ural sector, which is detrimental to the Ural blocking formation and underestimates the Ural blocking intensity in the 4th pentad. (d) shows the blocking indices derived from the model integrations with (red line) and without (black line) the OGBE, respectively. There is no big difference between the blocking indices derived from the two integrations during the first three pentads. But blocking index derived from the integration with OGBE is obviously smaller than the reference state and 0.5 reference line (blue dashed line) in the 4th pentad, and continues to decrease until the end of the integration. Credit: Ma et al. [2022], Figures 4a, 6e, 6l and 5a
Editors’ Highlights are summaries of recent papers by AGU’s journal editors.
Source: Journal of Geophysical Research: Atmospheres

In a new study, Ma et al. [2022] find that the Arctic Sea ice concentration is crucial for the prediction of strong and long-lasting Ural blocking formation. The authors adopt a conditional nonlinear optimal perturbation method to explore the influence of Arctic Sea ice on Ural blocking prediction.

Numerical results show that sea ice concentration in the Greenland, Barents, and Okhotsk seas is crucial for 4-pentad prediction of these Ural blockings. Further diagnoses reveal that sea ice perturbations in these areas first influence the local temperature through the diabatic heating process and further affect the temperature in the Ural sector mainly by advection and convection processes. Moreover, zonal winds in the Ural sector are adjusted by the thermal wind balance, thus affecting Ural blocking formation.

The local characteristics of the Arctic Sea ice concentration indicate that the Greenland, Barents and Okhotsk seas may be sensitive areas in regard to 4-pentad prediction of strong and long-lasting Ural blocking formations. These results provide scientific supports for future target observations and ensemble subseasonal forecast. 

Citation: Ma, X., Mu, M., Dai, G., Han, Z., Li, C., & Jiang, Z. (2022). Influence of Arctic sea ice concentration on extended-range prediction of strong and long-lasting Ural blocking events in winter. Journal of Geophysical Research: Atmospheres, 127, e2021JD036282.

—Yimin Liu, Associate Editor, Journal of Geophysical Research: Atmospheres

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