AbstrakBencana banjir harus diatasi dari segala aspek. Awan konvektif jenis cumulonimbus dapat menyebabkan bencana banjir lokal. Sistem cuaca skala meso seperti zona konvergensi intertropis (ZKI) dan siklon tropis dapat menyebabkan bencana banjir skala luas. Pada bulan Desember, Januari dan Februari (DJF) zona konvergensi intertropis berada di atas wilayah Indonesia belahan bumi selatan. Siklon tropis yang bergerak dekat dengan perairan Indonesia mampu meningkatkan intensitas bencana banjir. Baik hujan konveksional, hujan konvergensi, maupun hujan siklon tropis, ketiganya diakibatkan oleh sel tekanan udara rendah pada pusat konveksi, zona konvergensi intertropis dan mata siklon tropis. Hujan konveksional terjadi setelah insolasi maksimum. Sebagai wilayah monsun, Indonesia mengalami hujan lebat terutama pada musim panas dan gugur belahan bumi. Efek orografik di daerah monsun juga dapat meningkatkan jumlah curah hujan pada lereng di atas angin.Kata kunci : Curah hujan, monsun, zona konvergensi, bencana banjir, sel tekanan rendah.
AbstractFlood disaster must be overcomed from the whole aspects. Convective clouds of cumulonimbus type cause local flood disaster, while mesoscale weather system, such as intertropical convergence zone (ICZ), and tropical cyclone result in large scale flood disaster. In the months of December, January, February, the intertropical convergence zone lies over the southern hemisphere Indonesian region. Track of tropical cyclone near the Indonesian waters is able to increase the intensity of flood disaster. Either convectional or convergence rainfall as well as tropical cyclone rainfall, the three of them in consequence of the low air pressure at the convection center, the intertropical convergence zone and the tropical cyclone eye. Convectional rainfall occures after the maximum insolation. As a monsoon region, Indonesia suffer heavy rainfall especially in hemisphere summer and autumn. Orographic effect in monsoonal region can also increase the amount of rainfall in the windward slope.
Sudut datang sinar matahari menentukan banyaknya sinar matahari yang sampai dipermukaan sehingga faktor ini menentukan karakter cuaca suatu lokasi. Padang dan Selaparang (Mataram) selalu memiliki sudut datang sinar matahari yang berbeda setiap bulannya. Penelitian ini bertujuan membuktikan adanya perbedaan karakter parameter atmosfer antara dua lokasi tersebut. Pengujian dilakukan dengan dua metode. Pertama dengan metode statistik sederhana yaitu penentuan nilai rata-rata, maksimum dan koefisien variasi dan kedua dengan metode penentuan variansi dalam ANOVA1. Data yang digunakan adalah data tekanan, kelembapan, temperatur, curah hujan dan kecepatan angin dari OGIMET periode Januari sampai dengan Desember 2015. Berdasarkan selisih nilai-nilai maksimum, minimum, ratarata dan koefisien variasi untuk tekanan, kelembapan, temperatur, kecepatan angin dan curah hujan antara Padang dan Selaparang menunjukkan kedua data berbeda. Hasil perbandingan dengan metode ANOVA1 menunjukkan bahwa curah hujan bulan Maret dan kelembapan serta temperatur bulan April mempunyai karakter yang sama dengan p-value 0,6 sampai 0,9. Selain variabel dan bulan tersebut, karakter parameter di dua lokasi tersebut berbeda dengan p-value 0,0 sampai 0,2. Kata kunci: sudut datang sinar matahari, parameter atmosfer, ANOVA1
The radio acoustic sounding system (RASS) with the equatorial atmosphere radar (EAR) at Koto Tabang, Indonesia was adapted to test the effects of the acoustic source location and acoustic frequency range on the continuous measurement of height profiles of temperature in the tropical troposphere. We installed the acoustic transmitting system by using six high-power horn speakers and four subwoofers. We developed a three-dimensional ray-tracing method of acoustic waves to predict the shape of acoustic wavefronts, accounting for the effects of the background winds on acoustic wave propagation. Then, we selected the appropriate antenna beam directions for EAR that satisfy the Bragg condition between the radar and acoustic wave propagation vectors. We carried out eight campaign observations in 2016, testing the performance of EAR-RASS. We found that the location and acoustic frequency range affected the RASS echoes. We also tested the compensation method of the background wind velocity with EAR to obtain the true sound speed. We intensively analyzed the RASS results from August 29 to September 3, 2016, when radiosondes were launched 12 times from the EAR site. We successfully retrieved the temperature profiles from RASS from 2 to 6-14 km with time and height resolutions of about 10 min and 150 m, respectively. Some temperature profiles were obtained up to about the tropopause at 17 km, although the observation period was short. During the RASS campaign, we detected a few interesting events regarding temperature variations as well as large perturbations in the three components of wind velocity.
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