A Trial of Climate Classification Based on Dynamic Climatology Using Distribution of Frontal Zone in Mid- and High Latitudes

Abstract

Here, I create a dataset of fronts in mid- and high latitudes by applying an objective front detection method to the JRA-55 reanalysis and try climate classification based on dynamic climatology from temperate to polar regions. Additionally, I describe the interannual variations and long-term trends in the frontal zone. The unique feature of this study lies in the methods used for frontal data creation. This includes adding the geopotential height condition at 500-hPa to the conventional thermal-based objective method with equivalent potential temperature, including incorporating latitude-dependent parameters. The former increased the similarity between fronts created by the objective method and manually counted fronts on surface weather maps, while the latter enabled an examination of climate classification based on dynamic climatology by increasing the frontal frequency at high latitudes. The areas where climatic zones can be clearly defined are limited to the east of the great mountains in the mid-latitudes and the region where the Siberia-Canada Arctic frontal zone exists due to the obscuration or unclear seasonal movement of the frontal zones in other areas. The interannual variability in frontal zones is generally consistent with the characteristics of the regional climate variability associated with the El Niño Southern Oscillation, Pacific Decadal Oscillation, and Arctic Oscillation, as reported by previous studies. This study also reveals significant trends in some frontal zones since 1979, such as the northward shift in the eastern part of the North Pacific polar frontal zone during boreal autumn and winter and the decreasing frontal frequency on the northern coast of Norway in the European Arctic frontal zone from boreal winter to summer, including around the Beaufort Sea in the Siberia-Canada Arctic frontal zone in boreal summer.