Analysis of Equatorial Atmospheric PlanetaryWaves (EPW) in the Tropopause and Lower Stratosphere of Indonesia by Using NCEP/NCAR Reanalysis I Data

Abstract

Equatorial Atmospheric Planetary Waves (EPW) in the Tropopause and Lower Stratosphere of Indonesia are discussed. This research is motivated by complete unsolved problems relating to evidence of existence, behavior, propagation (horizontal and vertical structure), and periodicity of EPW as well as interconnected to other equatorial atmospheric oscillations in Indonesia. Based on linearized equations of EPW in β-plane, EPW n=0 mode has greatest meridional wind amplitude in Equator and decays exponentially when away from the Equator (Gaussian Decay). EPW n=1 mode has greatest amplitude of meridional wind pertubation (v’) at latitude y= ± 1 (dimensionless) and v’ equal to zero in Equator. For EPW n=2 mode, amplitude of v’ equal to zero at latitude y = ±1/2√2 and greatest amplitudes outside the Tropics. Simulation of mixed Rossby Gravity wave results that either zonal wind or geopotential field has greatest pertubation amplitudes at latitudinal domain y= ±1 (u’=0 in Equator). Pertubation of zonal wind (u’) and geopotential field (Ф’) be in geostrophic balance at latitude y>1 and y<-1 (dimensionless) or -(β-1√gH)1/2 < y < (β-1√gH)1/2 (length dimension unit). Simulation of Kelvin wave results that either zonal wind or geopotential field has symmetric amplitude and symmetric pertubation relative to Earth latitude. Based on spectral and kinetic energy (KE) analysis, Kelvin waves in the tropopause of Western Indonesia are found in the 15 days in wet season and 18 days in dry season. Energy of Kelvin wave in this region is stronger than others. In the Middle of Indonesia, these waves are found in a period of about 12.9-18 days in wet season and do not appear in dry season. While in Eastern Indonesia, this wave appears in period of 10-12.9 days (wet season) and 11.3-18 days (dry season). Their presence in transition season is not clearly found. KE response for Kelvin waves oscillations in 10- 18 days will exhibit when monsoon strengthened in the tropopause of Southeast Asia. In the Stratosphere of Indonesia Kelvin wave appears only in wet season. Presumably, existence of Kelvin wave in the lower stratosphere is produced by vertically propagation of Kelvin wave in the tropopause.