Relationship between large amounts of Cryptomeria japonica D. Don pollen dispersion and cold front passage

Abstract

Recently, with the proliferation of automatic Cryptomeria japonica pollen monitors, it has become possible to obtain data measured simultaneously from multiple locations. The KH-3000 monitor used by the Pollen Observation System of the Japanese Ministry of the Environment, “Hanako-san”, and the “Pollen Robo” monitor created by Weathernews Inc. were installed in various places in the Tohoku region for collection of simultaneous pollen count data, and the results indicated that the period of the day when large amounts of C. japonica pollen were dispersed may be related to the passage of a cold front extending from a low pressure system. When the types of pollen dispersed on that day were examined under a microscope, most of them were C. japonica pollen. Therefore, we investigated the relationship between the periods of these two events, with transit time of the cold front determined from the point when the wind direction changed from eastward to westward. The area with a high concentration of C. japonica pollen moved from the Sea of Japan side to the Pacific Ocean side in conjunction with the movement of the front. In 40% of the cases, the highest dispersion of C. japonica pollen occurred at the same time as the front passed, and 90% of the cases were within two hours before or after the passage. The number of dispersions was high in the northern part of the Tohoku region close to the low pressure system at the end of the front and low in the southernmost part of the Tohoku region away from this system.