Abstract:The few previous studies of precipitation isotopes (δ 18 O and δD) in Indonesia, based on low spatial resolution observation datasets, have found several types of patterns in their seasonal variabilities. This study conducted high spatial resolution rainfall sampling and investigated the temporal characteristics of precipitation isotope in Indonesia. Rainfall samples were collected weekly from 33 stations in Indonesia. Cluster analysis showed that Indonesia could be divided into four types based on the seasonal variability of the precipitation of δ 18
The Indonesian Maritime Continent (IMC) is located in the tropics and consists of a number of islands and seas. This particular arrangement of land masses and seas produces unique weather and climate characteristics. Various hydrometeorology studies have been conducted exploring the variability of stable isotopes in precipitation over the IMC. Stable isotopes (δ 18 O and δD) in precipitation can be used to obtain information about atmospheric processes (e.g., precipitation, temperature and hydrological cycle). The Global Network of Isotopes in Precipitation, operated by the International Atomic Energy Agency, has been conducting worldwide monthly surveys of isotope levels in precipitation since 1961. To better understand the isotopic variability in the IMC, the Japan Agency for Marine-Earth Science and Technology began operating in the IMC region in 2001. There are three types of seasonal variation of stable isotopes in precipitation, depending on the level of precipitation amount and also stable isotopic value, namely, semiannual, anti-monsoonal and monsoonal. Negative correlations between the precipitation amount and stable isotope value (amount effect) were identified when using the monthly averages. The interannual variability of stable isotopes in precipitation was mainly because of El Niño Southern Oscillation activity, whereas intraseasonal variability was closely related to the Madden-Julian Oscillation. Stable isotope variability in short periods was found to be due to precipitation cloud types and post-condensation processes.
Intraseasonal variability of precipitation over the Indonesian Maritime Continent (IMC) is related mainly to the Madden-Julian oscillation (MJO). The MJO enhances and suppresses precipitation around the IMC according to its phase. This study examined the relationship between the MJO and the stable isotope of the precipitation over the IMC. Observations and simulation data from an isotope circulation model and colored moisture analysis (ICM/CMA) were used. Temporal analyses of the observed and simulated data showed that an active MJO stage, associated with a positive precipitation anomaly over the IMC, was correlated with the depletion of δ 18
The Megacity Jakarta has encountered serious floods associated with high intensity but a short-duration rainfall or low intensity with a long-duration rainfall. During the rainy season, on 4 Feb 2021, Jakarta was inundated as rainfall intensity increased. However, little is known about the meteorological factors that might contribute to this heavy rainfall. In this study, we used the 6-min X-Band Doppler radar, one-hour satellite and reanalysis data to understand the spatial distribution of rainfall and explore the background conditions that might influence the enhanced rainfall over Jakarta and Bekasi River. Other than previous studies, we found that over Jakarta, the areas receiving high rainfall are more widespread and further to the northeast ocean with an intensity of above 4.5 mm h-1. High intensity of rainfall starts to develop in the afternoon over the inland areas at around 08-10Z (3.00-5.00 PM). Background condition shows a strong westerly wind speed crossing over Java Island, and this might initiate the development of rainfall over the region.
Pulau panas adalah suatu fenomena dimana suhu udara di suatu daerah lebih tinggi daripada suhu udara terbuka di sekitarnya. Daerah urban (perkotaan) sering mempunyai suhu lebih tinggi 1-6 derajat Celsius dibandingkan daerah sekitarnya (daerah pinggiran/ rural). Fenomena inilah yang dikenal sebagai ”Pulau Panas perkotaan” atau ”Urban Heat Island” (UHI). Penelitian ini bertujuan untuk mengetahui pengaruh fenomena pulau panas perkotaan terhadap parameter iklim terutama suhu dan curah hujan di daerahJakarta dan sekitarnya. Data yang digunakan pada tugas akhir ini adalah data curah hujan dan temperatur udara harian pada 5 stasiun pengamatan iklim, periode Januari 1991 – Desember 2001 sebagai data permukaan. Citra satelit Landsat 7 ETM+ path / row 122/064 akuisisi tanggal 15/07/2001 band 5,4,2 digunakan untuk menganalisis tutupan lahan dan band 6 digunakan untuk distribusi temperatur permukaan. Hasil menunjukkan nilai temperatur permukaan Kota Jakarta dan sekitarnya berada antara 15.07˚C hingga 33.28˚C. Lokasi pulau panas perkotaan terdapat di daerah Jakarta pusat dan Jakarta utara, dengan perbedaan temperatur sebesar 3˚C dibandingkan dengan daerah sekitarnya.Tutupan lahan yang terdapat di lokasi tersebut merupakan lahan terbangun yang terdiri dari bangunan perumahan, perkantoran, dan jalan raya. Perhitungan nilai korelasi Spearman antara data temperatur udara dari lima stasiun pengamatan dengan nilai piksel temperatur permukaan memperlihatkan adanya korelasi positif antara dua variabel tersebut yang ditunjukkan oleh indeks korelasi sebesar 0.6.Dengan persamaan regresi diperoleh citra temperatur permukaan di seluruh daerah pengamatan yang hasilnya menggambarkan bahwa lokasi pulau panas perkotaan sangat berpengaruh terhadap distribusi temperatur udara di atasnya.Heat island was a phenomenon where the temperature of air in one region higher than the temperature of the open air around it. Urban areas often had the temperature higher 1-6 Celsius when compared the area of surrounding area (the area of outskirts/rural). This phenomenon that was known as ”Pulau Panas Perkotaan” or ”Urban Heat Island” (UHI). This Research aimed to knowing influence of the heat islands of urban areas to climate parameter especially the temperature and the rainfall in the Jakarta and surrounding area. Data used in this research was rainfall data and daily air temperaturefrom 5 climate observation stations, within time period from January 1991 to December 2001 as the surface data. The Landsat satellite image 7 ETM+ path/row 122/064 acquisition date 15/07/2001, band 5, 4, 2 was used to analyze the cover of land and the band 6 was used for the distribution of surface temperature was based on the pixels value.Results showed the value of surface temperature in Jakarta and surrounding area was between 15.07˚C through to 33.28˚C. Location of heat island were in the centre Jakarta and north Jakarta, with the difference of the temperature as big as 3˚C with thesurrounding area. The land cover in this location were the housing building, the office complex, and the highway. Calculation of Spearman correlation value between the air temperature and surface temperature showed the existence of the positive correlation between two variables that it was demonstrated by the correlation index 0.6. From the regression equation we get the interpolated air temperature in Jakarta area.
Diurnal variability of stable isotopes in precipitation and its controlling factors are poorly understood, especially in the tropics. This study investigated the diurnal variability of stable isotopes in rainfall observed at Bengkulu in southern Sumatra, Indonesia. Rainfall samples were collected at 6-h intervals from 1 December 2017 to 15 January 2018 for the Year of the Maritime Continent (YMC-Sumatra 2017). The oxygen and hydrogen isotopic compositions δ18O and δH) of the rainwater varied from –15.1%o to –1.8%o and from –108.9%o to –1.3%o, respectively, and the d-excess varied from 1.9%o to 17.1%o. The observations at Bengkulu revealed that diurnal variation in rainfall amount was not significant for the entire period; however, the δ18O was lighter in both the early morning and the afternoon and heavier before noon and overnight. The δ18O became gradually depleted in the periods of continuous rain that occurred during 1–4 and 21–24 December. The amount of morning rain was much greater than evening rain in these periods, whereas the amount of evening rain was greater than morning rain in other periods. Based on satellite-derived CMORPH data, it is assumed that morning rain and evening rain corresponded to weak rainfall over surrounding sea region and strong rainfall over inland regions of Sumatra, respectively. The differences in moisture source and ratio of stratiform/convective rain rate between morning and evening might affect the isotopic composition of rainfall in the tropics.
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