Papers in Meteorology and Geophysics

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A strong tropopause folding with a maximum ozone concentration of 103 ppbv was observed at the summit of Mt. Fuji (35.4°E, 138.7°E, 3776m asl) on November 15, 1995. Since the folding displayed a wavy ozone variation at the summit, vertical mixing lengths of ozone wave in the folding are estimated at the summit level as a case study by applying Prandtl's mixing length theory to the observed ozone variation. In the dominant ozone waves in the folding, the amplitude of the maximum ozone wave is estimated to be 10.1 ppbv and corresponds to a vertical mixing length of 245.1 m, while the wave's duration at the summit was only about 18 minutes. Other dominant ozone waves were observed for about four hours through the folding passage, and their vertical mixing lengths are estimated to be 45.1, 72.0, 70.8, and 102.5 m. The folding had an unusual wavy structure among tropopause foldings observed at the summit, so the vertical mixing lengths from this folding cannot be adopted as typical values of tropopause foldings in East Asia. Furthermore, it should be noted that the estimation is a case study and includes several assumptions. However, since the observation of tropopause folding in East Asia is very limited, this result is considered to be a significant basis of more specific analysis of tropopause foldings. If vertical turbulence velocities of dominant waves in the folding can be observed in addition to this analysis, it may be possible to estimate ozone fluxes in the folding observed at the summit of Mt. Fuji.

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   Wind-blown mineral particles were observed in the daytime on 5 February 1991 in Tsukuba, Japan. The time change in the number-size distribution of aerosol particles with radii between 0.15 and 5 μm were measured with an optical counter. Aerosol particles were collected on electron microscope grids with impactors to obtain the composition of individual particles by electron microscopy.
   A meteorological investigation indicated that the local dust episode was generated in the daytime during a strong vertical mixing of air. The number-size distribution measured during the dust episode revealed concentrations of many coarse particles with radii of more than 1 μm. However, an electron microscopic examination indicated the presence of another mode of mineral particles in the radius range of less than 0.5 μm, together with the dominant mode of coarse mineral particles.
   The lifting of mineral particles by a dust whirl is an important process in the generation of atmospheric mineral particles under strong horizontal wind velocities, as are saltation sandblasting and bombardment processes.

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