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

Abstract

A spectral analysis of lower tropospheric winds, observed by the Boundary Layer Radar (BLR) at Serpong (60S, 1070E) in West Java, Indonesia during 1992/93, 1993/94, and 1994/95 rainy seasons reveals a pronounced spectral peak, at a period near 4 days. Filtered analysis of this quasi 4 day mode (Q4DM) shows almost an in-phase structure in the vertical. The CANAL (Global Objective Analysis by Japan Meteorological Agency) data for 1992/93 rainy seasons shows that in general the meridional wind component, at the altitude 700 hPa, has a westward phase propagation.

Relationship between Wind and Precipitation Observed with a UHF Radar, GPS Rawinsondes and Surface Meteorological Instruments at Kototabang, West Sumatera during September-October 1998.

“…For example, Takayabu et al (1996) found out a quasi-2 day mode from cloud activities by GMS, rainfall data by meteorological radars, rawinsondes, a UHF wind profiler and meteorological buoy data over the equatorial Pacific, and identified it with westward propagating inertio-gravity waves. Widiyatmi et al (1999) found out a quasi-4 day mode in the Serpong BLR data, and GMS data in rainy seasons of Java Island, and considered that it may be mixed Rossby-gravity waves propagating westward. However, these are shorter than the time scales of periodicities found in this case study.…”

“…A similar type of BLR has been operated at Serpong near Jakarta, West Java of Indonesia (6.4 S, 106.7 E) ( Fig. 1) since November 1992, and several studies related to cloud convection systems have been carried out (Hashiguchi et al 1995(Hashiguchi et al , 1996Widiyatmi et al 1999). At Kototabang, the first intensive observation had been conducted with BLR, GPS rawinsondes, ozonesondes and a tipping-buckettype rain gauge during 27 September-7 October 1998 in collaboration with Kobe University, Kyoto University and the University of Tokyo, Japan and BPPT (Agency for Assessment and Application of Technology) and BMG (Indonesian Meteorological and Geophysical Agency), Indonesia.…”

Seasonal Variations of Tropospheric Wind over Indonesia: Comparison between Collected Operational Rawinsonde Data and NCEP Reanalysis for 1992-99

“…Data on February 29 of a leap year have been omitted. By this pentad-mean procedure some equatorial wave-like components such as two-or four-day period modes (cf., Takayabu and Nitta 1993;Sato et al 1994;Widiyatmi et al 1999Widiyatmi et al , 2001) may be almost filtered out. Furthermore, the intraseasonal variations with 30-to 60-day periods have been removed from the pentad mean Table 2 and also indicated in Fig.…”

“…In global climate studies by zonal-mean description, Oort and Yienger (1996) have discussed seasonal intensity of Hadley circulation on the basis of operational rawinsonde data, except for data around the Indonesian maritime continent. For vertical distributions of wind variations over Indonesia, a wind profiler station has been constructed near Jakarta (see Subsection 2.3), and several case studies have been done: a convection center passage at the beginning of rainy season (Hashiguchi et al 1995b), a mixed Rossby-gravity wave activity in the rainy season (Widiyatmi et al 1999(Widiyatmi et al , 2001, and others. Much longer-period data analysis has also been done (H. Hashiguchi, private communication), and striking year-to-year variations have been found, although these results have not been published.…”

Equatorial Atmosphere Radar (EAR): System description and first results

“…These may be mixed Rossby-gravity waves [Yanai and Maruyama, 1966;Wheeler and Kiladis, 1999;Widiyatmi et al, 1999Widiyatmi et al, , 2001.…”