Characteristics of Local Wind “Aso Oroshi”

Abstract

The cold air formed in the Aso Basin flows out from the valley of the Aso somma under conditions of nocturnal radiative cooling. It is thought that this local wind influences agricultural production in this region. So, meteorological observations and mobile observations were carried out at Aso region, and then the characteristics of this local wind were clarified as follows. The local wind was named “Aso Oroshi”.
1) The wind speed of the “Aso Oroshi” was closely related to the temperature inversion in the Aso Basin. The wind speed of the “Aso Oroshi” was strong when temperature inversion developed.
2) The maximum wind speed of the “Aso Oroshi” was 6m/s and the maximum instantaneous wind speed was 9m/s. It is therefore thought that no wind damage occur due to “Aso Oroshi” because no damage occur by wind with a speed less than 10m/s.
3) Air temperature along the valley of Aso somma changed more than the dry adiabatic lapse rate as the “Aso Oroshi” wind speed exceed 3.8m/s. This result strongly suggests “Aso Oroshi” received heat from air above with higher potential temperature.
4) The air temperature decreased by “Aso Oroshi” at the higher altitudes above 230m. On the other hand, the decrease in air temperature was small due to “Aso Oroshi” at the lower altitudes below 230m. It is thought that the “Aso Oroshi” becomes a meteorological resource which prevents frost damage in the lower altitude below 230m.
5) The potential temperature was constant from lon. 130°54′E towards windward, but decreased towards leeward from lon. 130°54′E. Lon. 130°54′E point is located at the exit of the Aso somma valley.