This study aims to modify the idea of WK99-analyzing the existence of signature in wave-number and frequency spectrum when the analyzed Outgoing Longwave Radiation (OLR) data is associated with a unique phenomenon in Maritime Continent (MC), Borneo vortex (BV). Although BV is often related to easterly equatorial wave disturbances, there was no specific study to examine its behavior in the spectral domain. The purpose of this study is to develop a method to diagnose certain signatures of BV through spectrum analysis of OLR data when BV occurs. In contrast to previous studies, to present the unique phenomenon in MC as a target for diagnostics, spectrum analysis is performed by Spherical Harmonics (SH). The results of the OLR data spectrum comparison when BV occurs with the OLR data spectrum when BV does not occur that in the anti-symmetrical component when BV occurs, the tropical depression-mixed Rossby gravity (TD-MRG) wave spectrum is stronger, especially in zonal wave-numbers 5 to 10 and frequencies 0.12 to 0.2. Similar to the anti-symmetrical component, the TD-MRG spectrum of the symmetrical component is also stronger at zonal wave-numbers 5 to 10 and frequencies 0.12 to 0.2. Moreover, the westward-propagating inertio-gravity (WIG) wave spectrum in the symmetrical component is also stronger at the time of BV than when there is no BV, especially at zonal wave-numbers 7 to 13 and frequencies 0.38 to 0.5. It can be concluded that when BV occurs, equatorial waves that propagate to the west, especially the types of TD-MRG and WIG waves are stronger than when BV did not occur. The results of durational grouped spectrum analysis of OLR data when BV occurs indicate that the longer the duration of BV occurs, the stronger the spectrum of TD-MRG and WIG wave types gets.
Kejadian angin puting beliung adalah sebuah fenomena cuaca ekstrem yang terjadi di wilayah tropis seperti wilayah Indonesia. Banyaknya kejadian angin puting beliung di Indonesia menjadikan kejadian ekstrem ini menarik untuk diteliti lebih lanjut. Pada hari Kamis tanggal 21 September 2021 sekitar pukul 15.00 WIB telah dianalisis kejadian ekstrem angin puting beliung di wilayah Kota Bogor. Dilakukan analisis data Reanalysis Sea Surface Temperature (SST), curah hujan, kelembapan relatif (RH), K-indeks dan TT indeks. Dilakukan juga analisis data observasi suhu udara permukaan dan tekanan udara permukaan. Sedangkan untuk analisis citra satelit Himawari-8 dilakukan menggunakan software SATAID. Melalui analisis tersebut didapatkan bahwa nilai suhu udara permukaan dan tekanan udara permukaan menurun secara signifikan dan telah terjadi shearline pada analisis streamline angin di wilayah Kota Bogor. Sedangkan untuk analisis sea surface temperature (SST) dan kelembapan relatif (RH) berpengaruh lemah terhadap kejadian angin puting beliung. Untuk analisis K indeks dan TT indeks juga dihasilkan nilai sedang untuk dijadikan parameter terjadinya kejadian angin puting beliung. Selanjutnya untuk analisis citra satelit Himawari-8 melalui kanal IR, timeseries IR, dan contour menggunakan SATAID dihasilkan terdapat penebalan awan konvektif dan kenaikan suhu puncak awan saat terjadi kejadian angin puting beliung.
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