Document Type : Research Article
Authors
1
PhD student, Institute of Geophysics, University of Tehran, Tehran, Iran
2
Associate Professor, Department of Space Physics, Institute of Geophysics, University of Tehran
3
Institute of Geophysics
Abstract
The aim of this research is to analyze the climatology of the Northern Hemisphere extratropical storm tracks in different seasons using the ERA5 data for the period 1979-2023. To do this, we applied the Lagrangian feature tracking method on the relative vorticity and the positive meridional wind at 850 hPa to identify storm tracks. A positive V wind extrema indicates the poleward advection of warm air in the east of a cyclone center, while a negative value points out an equatorward advection of cold air in the west of a cyclone center. Therefore, tracking the positive V wind extrema can be applied to identify the storm-driven intrusion of warm air into the Arctic, which can accelerate the Arctic sea-ice melting. It should be noted that in identification and analysis of storm tracks based on the feature tracking method, it is important to choose an appropriate meteorological field. For instance, if we apply mean sea level pressure (MSLP) to track storm tracks, the western parts of the Mediterranean storm track can be detected, while it is not possible to detect the eastern parts. Also, tracking the positive V wind extrema is more usefule, compared to tracking ξ850 and MSLP fields, to investigate the impact of extratropical storm tracks on the Arctic sea ice, because this field is associated with the poleward advection of warm air. In this study, in addition to the track density and mean intensity of storms, we investigated the genesis and lysis densities. Also, we discussed the main entering pathways of extratropical storms into the Arctic.
Our results show that storm tracks are the strongest in winter and the weakest in summer. The west of the North Atlantic and North Pacific oceans are active oceanic basins for the genesis of storms. The center of the North Pacific is a secondary genesis region for oceanic storms, particularly in winter. There is a maximum of the genesis density in the east of the Rocky Mountains and the Tibetan Plateau. In the former case, most storms reach a lysis maxima on the west coast of North America and west of Greenland. In the latter case, some storms reach a lysis maxima on the east coast of Asia and some of them enter the North Pacific and penetrate into the Bering Sea. In some regions, storm tracks are connected with each other. For example, the Atlantic storm track can feed the storm track in North Russia, while the storm track in North Russia can feed the Northeast Asian storm track. We identified noticeable stretching of the Atlantic storm track from the west of the North Atlantic to the Arctic, through the Greenland and Norwegian seas, which indicates the storm-driven intrusion of warm and moist air from the North Atlantic into the Arctic. The tracking of the positive V wind extrema also indicates that the lysis density in the Bering Sea significantly increases. Hence, storms that penetrate as far as the Bering Sea/Strait can bring heat and moisture from the North Pacific into the Arctic. This storm-driven intrusion of warm and moist air can cause a local melting of sea ice in the Arctic or slow down the sea-ice production, especially in winter.
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