EVALUASI PERFORMA INDEKS MONSUN AUSMI DAN WNPMI DI WILAYAH INDONESIA

Intisari Iklim di wilayah Indonesia sangat dipengaruhi oleh aktivitas monsun Asia-Australia. Variabilitas kedua sistem monsun tersebut dapat direpresentasikan dengan baik masing-masing oleh indeks monsun Australian Summer Monsoon Index (AUSMI) dan Western North Pacific Monsoon Index (WNPMI). Saat ini, BMKG secara operasional menggunakan indeks AUSMI dan WNPMI untuk memonitor aktivitas monsun di wilayah Indonesia sebagai bahan prakiraan musim. Meskipun banyak literatur menyatakan bahwa wilayah Indonesia merupakan bagian dari sistem monsun Asia-Australia, namun kondisi topografi lokal yang kompleks berpotensi memodifikasi sirkulasi monsun sehingga perlu dikaji performa kedua indeks tersebut sebelum digunakan secara operasional. Penelitian ini dilakukan untuk menguji performa indeks monsun AUSMI dan WNPMI dalam menggambarkan variasi antartahunan (interannual), variasi dalam musim (intraseasonal), dan siklus tahunan (annual cycle) hujan monsun Indonesia. Hasil penelitian mengungkapkan bahwa kedua indeks memiliki performa yang sangat baik hanya di wilayah dimana indeks tersebut didefinisikan namun kurang baik untuk wilayah Indonesia seperti yang ditunjukan oleh nilai koefisien korelasi yang tidak signifikan dari hasil uji statistik antara kedua indeks dengan curah hujan dari Global Precipitation Climatology Project (GPCP) pada periode 1981-2010. Selain itu, kedua indeks juga memperlihatkan karakteristik siklus tahunan yang berbeda dengan karakteristik siklus tahunan hujan wilayah Jawa sebagai wilayah kunci monsun Indonesia. Hasil ini mengindikasikan perlunya pendefinisian indeks sendiri untuk memonitor aktivitas monsun di wilayah Indonesia. Abstract The climate of Indonesia is strongly affected by the Asian-Australian monsoon system. The variability of the two monsoon systems can be well represented by the Western North Pacific Monsoon Index (WNPMI) and the Australian Summer Monsoon Index (AUSMI) respectively. For producing seasonal forecast, BMKG uses the WNPMI and AUSMI monsoon index to monitor monsoon activity in Indonesia. Although most literature states that the Indonesian region is part of the Asian-Australian monsoon system, the complex local topography may modify the monsoon circulation. Hence, it is necessary to assess the performance of the two indices before they are operationally used. This study was conducted to evaluate the performance of the AUSMI and WNPMI monsoon indices in describing the annual cycle, intraseasonal and interannual variability of the Indonesian monsoon rainfall. The results revealed that the two indices only performed very well in the areas where the index was defined but lack of skill for the Indonesian region because of insignificant linear correlation based on a statistical significance test between the two indices and the Global Precipitation Climatology Project (GPCP) rainfall in the 1981-2010 period. In addition, both monsoon indices and Java rainfall showed different characteristics of the annual cycle. These results indicate that it is necessary to define a specific index for monitoring monsoon activity in Indonesia.

Long-term climate variability over monsoon Asia as revealed by some proxy sources

Studies on climate variability over the region of monsoon Asia mostly during the Quaternary, based on various sources of proxy data have been reviewed. Increasing interest to understand the processes of monsoon system over the Asian region as well as the availability of data from variety of reliable proxy sources such as, ocean sediments, ice cores and historical documents have encouraged the palaeoclimatic studies in this region. Inferences drawn from the multiproxy sources indicate good association of glacial and inter-glacial phases with over all monsoon flow. Warm and wet periods are generally characterized by strong summer monsoon, where as, weak monsoonal activities were observed during cold and dry periods. All India monsoon rainfall since early 17th century based on dendroclimatic reconstructions shows trend-less nature with large interannual variability as seen in the instrumental record of recent century. Historical evidences over this region are a potential source of information on contemporary climate change.

Untersuchung des Einflusses von Biomasseverbrennung auf die Atmosphäre mit Hilfe der Verhältnisse stabiler Kohlenstoffisotope in VOC

<p>Im August/September 2018 fand die Messkampagne CAFE-Africa (Chemistry of the Atmosphere – Field Experiment in Africa) mit dem Forschungsflugzeug HALO statt. Stützpunkt des Flugzeugs war die kapverdische Insel Sal. Basierend auf CAMS-Vorhersagen wurden von dort aus Messflüge in ausgewählte Gebiete über dem Atlantik und über den Westen Afrikas durchgeführt. Ziel der Kampagne war die Untersuchung des Einflusses der Emissionen von Biomasseverbrennung auf die regionale und globale Atmosphäre mit einem Fokus auf die Biomasseverbrennung in Afrika. Mit dem Luftprobensammler MIRAH (Measurements of Isotope Ratios in the Atmosphere on HALO) wurden Gesamtluftproben gesammelt, die anschließend im Labor auf die Verhältnisse stabiler Kohlenstoffisotope in ausgewählten flüchtigen organischen Verbindungen (VOC) sowie auf deren Mischungsverhältnisse untersucht wurden. Die Isotopenverhältnisse bieten zusammen mit CAMS Re-Analysen, Rückwärtstrajektorien, Satellitendaten und weiteren Stützmessungen die Möglichkeit, die Herkunft, Transportzeiten und die Umsetzung von VOC zu bestimmen. Wir zeigen als Fallstudie die Ergebnisse des 10. Messfluges, bei dem über dem Atlantik nordwestlich der Kapverden zwei deutlich unterscheidbare Luftmassen aufeinandertrafen. Während eine Luftmasse von Emissionen aus dem nördlichen Afrika geprägt war und mit dem westafrikanischen Monsoon-System auf den Atlantik transportiert wurde, konnte die andere Luftmasse eindeutig Biomasseverbrennung im Norden des amerikanischen Kontinents zugeordnet werden. Der Vergleich der genannten Datensätze gibt einen guten Überblick über den globalen Transport von Spurenstoffen, auch wenn nicht alle Details konsistent zu sein scheinen.</p>

Floods and droughts in association with cold and warm ENSO events and related circulation features

For the Indian subcontinent. the occurrence of floods and droughts is closely linked with the summer monsoon activity. The phenomenon of El Nino-Southern Oscillation (ENSO) has been established to be one of the major teleconnections of Indian Summer Monsoon. Also the relationship between the circulation features and summer monsoon activity is well documented in the literature. The interaction of F.NSO with monsoon system was known to the seasonal forecasters in India from the days of G. Walker. Northland (1953) summarising these results has remarked that ‘Monsoon has a prolonged influence on the global weather rather than global weather parameters influencing the monsoon’. 1990-94 was a prolonged period of warm ENSO producing weather anomalies in different regions of the globe. Yet during the same period all India rainfall was very close to normal and in fact. 1994 was a year of abundant rainfall for India. The aim of the study is to examine some of these features more critically. It is observed that ENSO has a modifying effect on the regional scale circulation pattern and possible interactions and/or phase-Locking with the planetary scale circulation pattern. which results into the occurrence or non-occurrence of an extreme event. Also, a qualitative analysis is carried for a period 1960-90 to assess how far the mid-season rainfall deficiency is made up at the end of the season. It is observed that even during drought years, the mid-season rainfall deficiency is made up at the end of the season for a considerable percentage of the total number of cases.

Global horizontal irradiation: spatio-temporal variability on a regional scale in the south of the Pampeana region (Argentina)

The objective of this work is to analyze the spatio-temporal distribution of Global Horizontal Irradiation (GHI) on a regional scale and its relationship with frequent synoptic situations in the south of the Pampeana region (Argentina). It was verified that the latitudinal pattern of distribution of the GHI is modified in the region by cloud cover, which is in turn determined by the seasonal dynamics of action centers and the passage of fronts in summer and winter. The South America Monsoon System (SAMS) defines differential situations of cloudiness and rainfall in the region, which affect GHI. GHI increased successively between the decades 1981–2010, a factor associated with the variability of rainfall that characterizes the region.

Penultimate deglaciation Asian monsoon response to North Atlantic circulation collapse

During glacial terminations, massive iceberg discharges and meltwater pulses in the North Atlantic triggered a shutdown of the Atlantic Meridional Overturning Circulation (AMOC). Speleothem calcium carbonate oxygen isotope records (δ18OCc) indicate that the collapse of the AMOC caused dramatic changes in the distribution and variability of the East Asian and Indian monsoon rainfall. However, the mechanisms linking changes in the intensity of the AMOC and Asian monsoon δ18OCc are not fully understood. Part of the challenge arises from the fact that speleothem δ18OCc depends on not only the δ18O of precipitation but also temperature and kinetic isotope effects. Here we quantitatively deconvolve these parameters affecting δ18OCc by applying three geochemical techniques in speleothems covering the penultimate glacial termination. Our data suggest that the weakening of the AMOC during meltwater pulse 2A caused substantial cooling in East Asia and a shortening of the summer monsoon season, whereas the collapse of the AMOC during meltwater pulse 2B (133,000 years ago) also caused a dramatic decrease in the intensity of the Indian summer monsoon. These results reveal that the different modes of the AMOC produced distinct impacts on the monsoon system.

Sea surface temperature variability in Indonesia and its relation to regional climate indices

Sea surface temperature (SST) is an essential indicator of ocean condition. It can reveal many physical processes interacting with it. The present study aims to investigate the spatial-temporal pattern of significant SST variability in Indonesia seas. The Empirical Orthogonal Function (EOF) and Power Spectral Density (PSD) are used to analyze monthly SST data from 1979 to 2021. These two methods are combined with correlation analysis to verify the underlying phenomena and their spatiotemporal distribution pattern using regional climate indices as the reference signal. The result shows that the most prominent feature is the annual and semi-annual oscillation due to the Asia-Australia monsoon system. The annual oscillation signature is found almost in the entire Indonesian seas, with an exception in the low-latitude area and the western Pacific region. The signature of semi-annual oscillation is also protrusive, extending across Indonesia from the Timor Sea to the South China Sea. There is also a variation of SST in correlation with Dipole Mode Index (DMI), localized on the western coast of Sumatra.