Abstract
A climatological study was performed to understand the characteristics of the diurnal variation and vertical structure of the “Karakkaze wind,” which is the local wind observed over the Kanto Plain in winter. The data for a 15-year period (1992–2006) were analyzed. The data used in this study not only include the conventional AMeDAS data, surface observation, and sonde station data but also tower and wind profiler data, which have not been used in previous studies.
The following characteristics of the Karakkaze wind were revealed. 1) The surface wind system of the averaged Karakkaze-wind days shows a clearer diurnal variation than that of the winter average. In the area with clear diurnal variation, the daytime wind speed of the average of Karakkaze-wind days is strong and nearly twice that of the winter average. However, the wind weakens at night. 2) In the upper level of the atmospheric boundary layer, the wind speed decreases in the late morning and increases in the evening. 3) The convective mixed layer height may be higher on the Karakkaze-wind days because of weak atmospheric stability. Therefore the downward momentum transfer is larger on the averaged Karakkaze-wind days than the winter average, which results in the formation and maintenance of a strong Karakkaze wind in the daytime. 4) Relative humidity and precipitation are relatively high in the Hokuriku area and low in the Kanto Plain. Solar radiation is greater in the Kanto Plain and less in the Hokuriku area. This difference is more marked on the averaged Karakkaze-wind days than the winter average. These results indicate that the Karakkaze wind is associated with the foehn phenomenon, which can form a higher convective mixed layer and a larger downward momentum transfer.
