Frequency Spectra of Wind Velocity Fluctuations between 1 hour and 1 month in the Atmospheric Boundary Layer over Equatorial Indonesia

Abstract

Frequency power spectra are analyzed from zonal and meridional wind velocities observed continuously in a height range below 2.5 km with the Kyoto University Boundary Layer Radar (BLR) in Serpong, Indonesia (6.4°S, 106.7°E). We find that (i) the spectral slope in a period range from a few hours to a few days is approximately -1; (ii) the power spectral densities in the rainy season are at least about two times larger than those in the dry season; (iii) the diurnal component is dominant both in dry and rainy seasons; (iv) components with periods of about 4 and 10 days are probably associated with mixed Rossbygravity wavelike cloud clusters and Kelvin wavelike super cloud clusters, respectively; and (v) the power spectral amplitudes increase at least one order of magnitude from the bottom to the top of the equatorial Planetary Boundary Layer (PBL), and the values at the top of the PBL are comparable to those in the upper troposphere over mid-latitudes. The last feature suggests that the equatorial PBL is probably a major source of kinetic energy of the earth's atmosphere.

Quasi 4 Day Mode Observed by a Boundary Layer Radar at Serpong (6°S, 107°E), Indonesia

“…Since November 1992, the RASC (Radio Atmospheric Science Center) of Kyoto University, Japan in collaboration with BPPT (Agency for Assessment and Application of Technology), and LAPAN (National Institute of Aeronautics and Space), Indonesia, has been continuously carrying out three-dimensional wind observations of high-resolution, in altitude and in time (100m and 1min) in the lower troposphere (0.3-3.2km altitude), at Serpong near Jakarta, Indonesia (6.4oS, 106.7oE), using a 1357.5MHz Boundary Layer Radar (BLR) (Hashiguchi et al, 1995a). Hashiguchi et al (1995b) have shown wind and rainfall disturbances with periods of a few days or longer, and Hashiguchi et al (1997) have done frequency spectral analysis.…”