PENGGUNAAN TRANSFORMASI WAVELET UNTUK MENGANALISIS OSILASI INTRAMUSIMAN CURAH HUJAN DI KOTOTABANG
DOI:
https://doi.org/10.25077/jfu.4.3.%25p.2015Abstract
ABSTRAK
Transformasi wavelet telah digunakan untuk menganalisis osilasi intramusiman (Madden-Julian Oscillation-MJO) curah hujan harian selama 11 tahun (2002-2012) yang terekam oleh Optical Rain Gauge di Kototabang, Sumatera Barat, Indonesia dengan tiga mother wavelet, yaitu Mexican Hat, Morlet, dan Paul. Berdasarkan global spektrum, ketiga mother memperlihatkan periode osilasi intramusiman yang tidak konstan setiap tahunnya. Mexican Hat memperlihatkan time series spektrum rata-rata yang lebih mendekati pola indeks MJO, tetapi periode MJO dari global spektrumnya melebihi periode dominan MJO pada literatur (40-60 hari). Untuk periode osilasi, Morlet memberikan hasil yang lebih mendekati literatur. Dengan demikian, tidak ada mother yang paling optimum dalam memodelkan MJO. Hasil penelitian ini memperlihatkan kelemahan transformasi wavelet untuk memodelkan osilasi yang relatif singkat. Untuk osilasi ini, spektrum global dari data pengamatan yang panjang tidak mampu memperlihatkan periode osilasi karena keberadaan osilasi musiman dan tahunan akan mendominasi sehingga menekan osilasi intramusiman. Osilasi intramusiman lebih jelas terlihat ketika data dipersingkat misalnya per tahun.Â
Kata kunci : transformasi wavelet, Kototabang, curah hujan, MJO
Abstract
Wavelet transform had been used to analyze the intraseasonal oscillation (Madden Julian Oscillation, MJO) of rainfall data that collected by an Optical Rain Gauge aloong 11 years (2002-2012) at Kototabang, West Sumatera, Indonesia with three mother wavelet (Mexican Hat, Paul, dan Morlet). The global spectrum of the three mothers showed that the oscillation period was not constant every year. The time series of Mexican Hat was more similar to that of MJO index than two other mothers, but its MJO periode of global spectrum was longer than the dominant periode of MJO in the literature (40-60 days). For the oscillation periode, the Morlet provided the result that was closer to literature. Thus, we can not conclude the most optimum mother to model the MJO. This study found a limitation of wavlet transform to analyze high frequency oscillation such as MJO in which global spectrum of long data record can not visualize the periode of such oscillation. This phenomenon was due to the lower frequency oscillation such as seasonal and annual oscillations dominating the global spcetrum and supressing the high frequency oscillation. The high frequency oscillation was more robust when the data period was shorther for example one year.
Keywords: wavelet transform, Kotabang, rainfall, MJO
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