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Intisari Keberadaan pergeseran puncak curah hujan diurnal (DR) terhadap Madden-Julian Oscillation (MJO) aktif di Maritime Continent (MC) masih diperdebatkan sehingga studi ini bertujuan untuk menginvestigasi perubahan tersebut. Selain itu, intensitas rata-rata dan amplitudo DR juga dikaji dalam penelitian ini berbasis GSMaP Gauge-Calibrated V7. Komposit anomali intensitas rata-rata (Ra), amplitudo (Rax) DR MJO aktif dan perbandingan fase puncak DR MJO aktif terhadap klimatologinya (Pax-Pm) pada periode Desember-Januari-Februari (DJF), Maret-April-Mei (MAM), Juni-Juli-Agustus (JJA) dan September-Oktober-November (SON) digunakan dalam tulisan ini dengan uji-z 80%. MJO aktif berbasis rekonstruksi outgoing longwave radiation (OLR) dari kedua indeks realtime multivariate MJO (RMM). Hasil memperlihatkan bahwa MJO aktif memodulasi peningkatan intensitas rata-rata dan amplitudo DR di lautan dan mempengaruhi pergeseran puncak DR menjadi lebih cepat 1 jam dari klimatologi musimannya. Abstract The occurrence of peak phase shift of diurnal rainfall (DR) to active Madden-Jullian Oscillation (MJO) has been debatable, so this study is aimed to investigate the change. Moreover, the mean and amplitude intensity of DR were also analyzed in this study based on GSMaP Gauge-Calibrated V7. The composite of the mean (Ra) and amplitude (Rax) intensity anomaly of DR, and the comparison of DR peak phase during the active MJO to its climatology (Pax-Pm) in the period December-January-February (DJF), March-April-May (MAM), June-July-August (JJA), and September-October-November (SON) were used in the study with the z-test of 80%. The active MJO was based on reconstructed outgoing longwave radiation (OLR) of two real-time multivariate MJO (RMM) indexes. The results showed that active MJO modulated the increased mean and amplitude intensity of DR over the ocean and influenced the DR peak phase shift to be faster than its seasonal climatology by one hour.

Tulisan ini merupakan studi awal yang membuktikan pengaruh Mesoscale Convective System (MCS) terhadap curah hujan (CH) ekstrem di pesisir barat Sumatra dengan menggunakan citra rapidscan 10 menit Himawari-8 kanal IR1. Untuk mendapatkan data yang berkualitas, penulis melakukan koreksi data CH penakar Hellman terhadap data standar CH di Moelaboh (MLH), Sibolga (SBG), Teluk Bayur (TBR) dan Bengkulu (BKL) serta koreksi paralaks data citra Himawari-8. Dalam mengidentifikasi MCS, penulis menggunakan kriteria brightness temperature (BT) ≤ 221 derajat kelvin (K), luasan BT ≥ 10.000 km2 dan durasi ≥ 3 jam. Hasil penelitian mengindikasikan bahwa CH ekstrem bersamaan dengan keberadaaan MCS yang membuktikan bahwa CH ekstrem diakibatkan oleh MCS di MLB, SBG, TBR dan BKL. MCS tersebut sangat dipengaruhi oleh kemunculan Westerly Wind Burst (WWB) yang terhalangi oleh Bukit Barisan untuk kasus CH ekstrem di SBG dan TBR atau berinteraksi dengan angin pasat tenggara dari Samudra Hindia sebelah barat daya Sumatra untuk kasus CH ekstrem di BKL. Untuk kaus CH ekstrem di MLB, MCS terbentuk akibat interaksi angin pasat di Samudra Hindia sebelah barat Sumatra dan aliran siklonik sebelah barat MLB. This paper was a preliminary study that proved the impact of the mesoscale convective system (MCS) on extreme rainfall on the west coast of Sumatra using rapid scan imagery of 10 minutes Himawari-8 channel IR1. To get qualified data, we conducted the correction of rainfall data of Hellman gauge to the rainfall standard data in Moelaboh (MLH), Sibolga (SBG), Teluk Bayur (TBR), and Bengkulu (BKL) and the parallax correction to Himawari-8 imagery data. To identify MCS, we used brightness temperature (BT) ≤ 221 K, BT area ≥ 10.000 km2 and duration ≥ 3 hours as the criteria. The results indicated that extreme rainfall occured simultaneously with MCS proved that the extreme rainfall caused by MCS in MLB, SBG, TBR, and BKL. The MCS was greatly influenced by the appearance of westerly wind burst (WWB) which was blocked by Bukit Barisan for extreme rainfall cases in SBG and TBR or interacted with the southeast trade winds of the Indian Ocean in the southwest of Sumatra for extreme rainfall case in BKL. For extreme rainfall case in MLB, MCS was formed due to the interaction of trade winds of the Indian Ocean in the west of Sumatra and cyclonic flow in the west of MLB.

Studi ini berfokus pada analisis tailwind penyebab go-around pada 38 bandara di Indonesia dalam periode Januari-Februari 2020. Dalam studi ini dilakukan perbandingan tailwind laporan pilot, tailwind observasi permukaan (10 m), dan tailwind pada ketinggian 1000 ft untuk mengetahui akurasi tailwind yang dilaporkan oleh pilot. Literatur menyebutkan bahwa angin kecepatan tinggi di troposfer bawah berkaitan dengan wind gust yang berasal dari awan cumulonimbus (Cb). Dengan dasar tersebut maka dilakukan analisis perbandingan laporan pilot terhadap keberadaan awan Cb sampai sejauh 40 km dari runway in use dengan menggunakan kombinasi kriteria brightness temperature difference (BTD) kanal IR1-IR2 dan brightness temperature (BT) kanal IR1 citra satelit Himawari-8. Hasil penelitian menunjukkan bahwa tailwind laporan pilot lebih besar daripada tailwind angin permukaan dan 1000 ft, serta kebanyakan tailwind laporan pilot tersebut berkaitan dengan potensi wind gust yang muncul dari awan Cb baik di sekitar atau di luar runway.Kata kunci: Cumulonimbus, go-around, tailwind, wind gust. AbstractAn Analysis of Go-Around-Causing Tailwind at 38 Airports in Indonesia in the Period of January-February 2020: This study focused on analyzing the tailwind that causing go-around at 38 airports in Indonesia in the period of January to February 2020. We made a tailwind comparison of the pilot report, surface observation (10 m), and observation of 1000 ft to determine the accuracy of the tailwind reported by the pilot. The literature stated that high-speed winds in the lower troposphere were related to wind gust coming from cumulonimbus (Cb) clouds, so we compared pilot report to the presence of Cb clouds as far as 40 km from the runway in use by using a combination of brightness temperature difference (BTD) IR1-IR2 channels and brightness temperature (BT) IR1 channel of Himawari-8 satellite imagery. The results showed that the tailwind of the pilot report was larger than the tailwind of surface and 1000 ft observations and most of the tailwind was related to the potential wind gust that emerged from the Cb clouds either around or outside the runway.Keywords: Cumulonimbus, go-around, tailwind, wind gust.

This study was focused on cumulonimbus (Cb) cloud prediction based on Integrated Forecast System (IFS) European Medium-Range Weather Forecast (ECMWF) model in the Flight Information Region (FIRs) Jakarta and Ujung Pandang. The Cb cloud prediction was calculated using convective cloud cover (CC) of the precipitation product. The model predictability was examined through categorical verification. The Cb cloud observation was based on brightness temperature (BT) IR1 and brightness temperature difference (BTD) IR1-IR2. The results showed that CC 50%' predictor was the best predictor to estimate the Cb cloud. The study in the period other than 2019 is suggested for the next research because Indian Ocean Dipole (IOD) is extreme that may affect the Cb cloud growth in the study area.

Intisari Pada penelitian ini, penulis mengkaji uji performa kualitatif konvergensi angin permukaan model reanalisis ERA5 di BMI yang dibandingkan dengan hasil penelitian menggunakan limited area model ( LAM ) oleh Qian, Im dan Eltahir serta Alfahmi et al. Konvergensi angin permukaan dan anomali angin permukaan dihitung dengan menggunakan finite difference. Hasil penelitian menunjukkan bahwa model reanalisis ERA5 mampu mensimulasikan konvergensi anomali angin permukaan dengan baik terhadap model regional climate model (RegCM) maupun The MIT regional climate model (MRCM) resolusi 27 km di Pulau Jawa dan sekitarnya serta BMI bagian barat dengan nilai konvergensi yang lebih tinggi. Sedangkan terhadap model weather research forecast (WRF) 9 km di BMI bagian timur, model reanalisis ERA5 juga dapat mensimulasikan konvergensi angin permukaan, tetapi dengan nilai yang lebih rendah. Selain itu, model reanalisis ERA5 mensimulasikan konvergensi angin permukaan lebih cepat 2 jam di BMI bagian barat dan timur dibandingkan MR C M27 dan WRF. Abstract In this study, we discuss the qualitative performance testing of ERA5 surface wind convergence over the Indonesia maritime continent (BMI) compared with research based on limited area model (LAM) by Qian, Im, and Eltahir and also Alfahmi et al. Wind surface convergence and wind surface anomalies convergence is calculated using finite-difference. The results show that the ERA5 reanalysis model can simulate convergence of surface wind anomalies compared with both regional climate model (RegCM) and 27 km MIT regional climate model (MRCM) over Java and also western BMI with higher convergence values. While ERA5 reanalysis model can also simulate convergence of surface winds, but with lower values compared to 9 km weather research forecast (WRF) model over eastern BMI. Besides, the ERA5 reanalysis model simulates convergence of surface winds, which is 2 hours faster over western and eastern BMI compared to MRCM27 and WRF.

The diurnal cycle pattern of rainfall was indicated as an intense feature in East Java. The research of diurnal cycle generally was only based on satellite estimation which had limitations in accuracy and temporal resolution. The hourly rainfall data of Climate Prediction Center Morphing Technique (CMORPH) and gauge were blended using the best correction method between transformation distribution (DT) and quantile mapping (QM) to increase the accuracy. We used spatiotemporal composite to analyse the concentration patterns of maximum rainfall and principal component analysis (PCA) to identify the spatial and temporal dominant patterns of diurnal rainfall. QM was corrected CMORPH data since it was best method. The eastern region of East Java had a rainfall peak at 14 local time (LT) and the western region had a rainfall peak at 16 LT.

Dalam penelitian sebelumnya, pengaruh ElNino terhadap gelombang signifikan tidak mampu dianalisa dengan baik karena simulasi model yang digunakan tidak mencakup periode ElNino super. Oleh karena itu, kajian ulang perlu dilakukan dengan mempergunakan data yang mencakup periode ElNino super. Sebelum dilakukan analisa, penulis menilai akurasi gelombang signifikan model wavewatch III (WW3) dengan menghitung korelasi dan root mean square error (RMSE) terhadap data gelombang signifikan satelit altimeter. Pengaruh ElNino terhadap gelombang signifikan didapatkan dari nilai korelasi antara oceanic nino index (ONI) 3.4 dengan gelombang signifikan WW3. Penulis juga menghitung rasio antara komposit gelombang signifikan saat ElNino/LaNina serta ElNino super dengan gelombang signifikan saat normalnya. Hasil penelitian menunjukkan bahwa gelombang signifikan WW3 yang digunakan memiliki akurasi yang baik pada perairan Indonesia. ElNino dan LaNina memiliki pengaruh yang kuat terhadap gelombang signifikan di Laut Jawa dan Selat Sunda pada periode Desember-Januari-Februari (DJF). ElNino (LaNina) dapat mengurangi (menambah) tinggi gelombang signifikan sampai 30% dari normalnya di Laut Jawa dan Selat Sunda. Pada kasus ekstrim, ElNino super mampu mengurangi tinggi gelombang signifikan sampai 50% terhadap normalnya.