Abstract
On 19 June 2013, the surface photochemical oxidant (Ox) concentration increased more than 100 ppbv over the Hokuriku region, while a depression with a baiu-front caused heavy rain. We investigated the mechanism of the increased Ox under the less photochemically active condition using meteorology observations and the chemical components, meteorological analysis data, and a numerical simulation conducted using the regional chemical transport model, NHM-Chem. We found that this event was characterized by multi-scale phenomena that consisted of the meso-α (200–2000 km) phenomenon over the coast of the Sea of Japan and the meso-β (20–200 km) phenomenon observed near the Noto Peninsula 1–2 h prior to the meso-α phenomenon. We estimated that the eastward high Ox flow at the post-front area caused the meso-α phenomenon. The analysis of the relative humidity and potential vorticity and NHM-Chem simulation revealed that the dry intrusion of stratospheric ozone occurred in the post-front area, which is caused by a folding of the dynamic tropopause on the northern side of the baiu-front. On the other hand, the increase in Ox with the meso-β scale occurred with a southward movement of shear caused by the cold air mass and southwesterly wind around the Noto Peninsula.
