Improving Madden–Julian Oscillation Simulation in Atmospheric General Circulation Models by Coupling with Snow–Ice–Thermocline One-dimensional Ocean Model

A one-column turbulent kinetic energy–type ocean mixed-layer model Snow–Ice–Thermocline (SIT) when coupled with three atmospheric general circulation models (AGCMs) to yielded superior Madden–Julian Oscillation (MJO) simulation. SIT is designed to have fine layers similar to those observed near the ocean surface and therefore can realistically simulate the diurnal warm layer and cool skin. This refined discretization of the near ocean surface in SIT provides accurate sea surface temperature (SST) simulation, thus facilitating realistic air–sea interaction. Coupling SIT with European Centre Hamburg Model, Version 5 (ECHAM5); Community Atmosphere Model, Version 5 (CAM5); and High Resolution Atmospheric Model (HiRAM) significantly improved MJO simulation in three coupled AGCMs compared with the AGCM driven with prescribed SST. This study suggests two major improvements to the coupling process. First, during the preconditioning phase of MJO over Maritime Continent (MC), the over underestimated surface latent heat bias in AGCMs can be corrected. Second, during the phase of strongest convection over MC, the change of the intraseasonal circulation in the meridional circulation is the dominant factor in the coupled simulations relative to the uncoupled experiments. The study results indicate that a fine vertical resolution near the surface, which better captures temperature variations in the upper few meters of the ocean, considerably improves different models with different configurations and physical parameterization schemes; this could be an essential factor for accurate MJO simulation.

Testing Vertical Wind Shear and Nonlinear MJO/ENSO Interactions as Predictors for Subseasonal Atlantic Tropical Cyclone Forecasts

Hansen et al. (2020) found patterns of vertical wind shear, relative humidity (RH) and non-linear interactions between the Madden-Julian Oscillation and El Niño-Southern Oscillation that impact subseasonal Atlantic TC activity. We test whether these patterns can be used to improve subseasonal predictions. To do this we build a statistical-dynamical hybrid model using Navy-ESPC reforecasts as a part of the SUBX project. By adding and removing Navy-ESPC reforecasted values of predictors from a logistic regression model, we assess the contribution of skill from each predictor. We find that Atlantic SSTs and the MJO are the most important factors governing subseasonal Atlantic TC activity. RH contributes little to subseasonal TC predictions, however, shear predictors improve forecast skill at 5-10 day lead times, before forecast shear errors become too large. Non-linear MJO/ENSO interactions did not improve skill compared to separate linear considerations of these factors but did improve the reliability of predictions for high-probability active TC periods. Both non-linear MJO/ENSO interactions and the subseasonal shear signal appear linked to PV streamer activity. This study suggests that correcting model shear biases and improving representation of Rossby wave-breaking is the most efficient way to improve subseasonal Atlantic TC forecasts.

Modulation of East African boreal fall rainfall: combined effects of the Madden Julian Oscillation (MJO) and El Niño Southern Oscillation (ENSO)

Climate variabilities can have significant impacts on rainfall in East Africa, leading to disruption in natural and human systems and affecting the lives of tens of millions of people. Subseasonal and interannual variabilities are critical components of total rainfall variability in the region. The goal of this study is to examine the combined effects of the Madden Julian Oscillation (MJO), operating at subseasonal timescale, and the El Niño Southern Oscillation (ENSO), operating at an interannual scale, on the modulation of East African boreal fall (October-November-December; OND) rainfall, commonly called the short rains. Composite analysis shows that daily rainfall responses depend on MJO phase and its interaction with ENSO state. In particular, MJO modulation of rainfall is generally stronger under El Niño conditions relative to ENSO neutral and La Niña conditions, leading to increased potential for daily precipitation excesses during wet MJO phases under El Niño. There is evidence for both dynamic and thermodynamic mechanisms associated with these impacts, including an increase in westerly moisture transport and easterly advection of temperature and moist static energy. Seasonal analysis shows that the frequency and intensity of wet MJO phases during an El Niño contribute notably to the seasonal total precipitation anomaly. This suggests that MJO can mediate El Niño’s impact on OND rainfall in East Africa.

KETERKAITAN PERIODISITAS CURAH HUJAN DI DAERAH PESISIR DAN PEGUNUNGAN PROVINSI JAWA TIMUR DENGAN VARIABILITAS CUACA SKALA GLOBAL DAN REGIONAL

Intisari Jawa Timur merupakan wilayah yang memiliki variasi curah hujan yang dipengaruhi oleh fenomena cuaca global dan regional seperti Dipole Mode, El Nino Southern Oscillation (ENSO), Intertropical Convergence Zone, Madden Julian Oscillation, dan monsun. Topografi yang beragam juga menjadi faktor yang memengaruhi curah hujan di daerah Jawa Timur. Berbagai indeks digunakan untuk melihat aktivitas-aktivitas fenomena cuaca tersebut, seperti DMI untuk aktivitas Dipole Mode, NINO 3.4 untuk aktivitas ENSO, Indeks RMM untuk aktivitas MJO, WNPMI dan, AUSMI untuk aktivitas monsun. Pada penelitian ini digunakan analisis spektral dengan menggunakan metode Fast Fourier Transform untuk melihat periodisitas indeks masing-masing terhadap periodisitas curah hujan dari data 11 pos hujan yang terbagi menjadi 6 pos hujan daerah pesisir dan 5 pos hujan daerah pegunungan. Hasil dari penyeragaman periodisitas fenomena cuaca dengan curah hujan antara lain Dipole Mode (periodisitas 18 bulan), ENSO (periodisitas 18 dan 40 bulan), dan MJO (periodisitas 2 dan 3 bulan). Fenomena yang memengaruhi curah hujan di daerah pesisir maupun pegunungan secara dominan adalah fenomena monsun dengan diikuti ITCZ. Fenomena lain yang memengaruhi di daerah pesisir antara lain dominan MJO, serta fenomena ENSO dan Dipole Mode yang memengaruhi daerah Lamongan, Bunder, dan P3GI dengan kecenderungan lebih kuat pada fenomena Dipole Mode. Sementara itu, fenomena yang memengaruhi hujan di daerah pegunungan secara dominan adalah ENSO. Adapun fenomena lain yang memengaruhi hujan di daerah pegunungan antara lain fenomena MJO di daerah Tosari, serta daerah Kebon Teh Wonosari yang memiliki kecenderungan dipengaruhi oleh fenomena Dipole Mode meskipun pengaruhnya tidak signifikan. Abstract East Java is a region whose variations in rainfall are influenced by global and regional weather phenomena such as Dipole Mode, El Niño Southern Oscillation (ENSO), Intertropical Convergence Zone, Madden Julian Oscillation, and monsoons. Diverse topography is also a factor affecting rainfall in the area of East Java. Various indices are used to observe the activities of the weather phenomenon, such as DMI for Dipole Mode activities, NINO 3.4 for ENSO activities, RMM Index for MJO activities, as well as WNPMI and AUSMI for monsoon activities. In this study, spectral analysis was used by utilizing the Fast Fourier Transform method to see the periodicity of each index against the periodicity of rainfall from the 11 rainwater data points, which were divided into 6 coastal data points and 5 mountainous data points. Uniformity of weather phenomena with rainfall result among others Dipole Mode (18 months periodicity), ENSO (18 and 40-month periodicity), and MJO (2 and 3-month periodicity). Phenomena that affect rainfall in coastal and mountainous areas predominantly are monsoon, followed by ITCZ. Other phenomena affecting the coastal area include MJO dominant, and the ENSO and Dipole Mode phenomena that affect the Lamongan, Bunder, and P3GI regions with a stronger tendency to the Dipole Mode phenomenon. Another phenomenon that influences rain in the mountainous area is dominantly ENSO, while other phenomena include MJO phenomena in the Tosari area and Kebon Teh Wonosari region which has a tendency to be influenced by the Dipole Mode phenomenon despite the insignificant effect.

PENGARUH PROPAGASI MADDEN JULIAN OSCILLATION (MJO) DI BENUA MARITIM INDONESIA (BMI) TERHADAP SIKLUS DIURNAL DINAMIKA ATMOSFER DAN CURAH HUJAN DI PROVINSI LAMPUNG TAHUN 2018

Intisari Madden Julian Oscillation (MJO) merupakan osilasi gelombang submusiman di wilayah tropis yang berpropagasi ke arah timur dari Samudera Hindia melewati Benua Maritim Indonesia (BMI) hingga Samudera Pasifik. Propagasi MJO dapat meningkatkan konvektivitas dan curah hujan pada wilayah yang dilewatinya. Lampung merupakan salah satu wilayah di BMI bagian barat yang berbatasan dengan Samudera Hindia sebagai tempat awal kemunculan MJO. Posisi Lampung tersebut menyebabkan perbedaan insolasi antara daratan dan lautan secara diurnal sehingga siklus diurnal ikut berperan dalam pembentukan cuaca. Oleh karena itu penelitian ini bertujuan untuk mengetahui pengaruh propagasi MJO dari Fase 3-5 pada tahun 2018 terhadap siklus diurnal dinamika atmosfer dan curah hujan di Lampung. Siklus diurnal dianalisis dengan membagi empat periode waktu yaitu dini hari (00.00-06.00 LT), pagi hari (06.00-12.00 LT), siang hari (12.00-18.00 LT) dan malam hari (18.00-00.00 LT). Berdasarkan rata-rata komposit data Reanalysis ECMWF, GSMaP, dan curah hujan observasi didapatkan bahwa selama penjalarannya MJO menguat ketika Fase 3-4 dan melemah ketika Fase 5. Secara diurnal konvektivitas yang kuat dan curah hujan tinggi terjadi di perairan pada dini hari hingga pagi hari, di daerah pesisir pada siang hari, dan di daratan pada malam hari yang meningkat dari Fase 3-4 dan melemah pada Fase 5. Hujan menjalar dari Lampung bagian barat menuju Lampung bagian tengah dengan jeda waktu selama 2-5 jam ketika Fase 3, 4-7 jam ketika Fase 4, dan 1-2 jam ketika Fase 5. Pada Fase 3-5 hujan terjadi di Lampung bagian timur dengan perbedaan waktu 1-3 jam dari Lampung bagian tengah. Abstract Madden Julian oscillation (MJO) is a sub-seasonal wave oscillation in the tropics that propagates eastward from the Indian Ocean through the Indonesian Maritime Continent (IMC) until the Pacific Ocean. MJO propagation can increase convective and rainfall in the regions it passes. Lampung is one of the regions in the western IMC which near the Indian Ocean for the MJO first appeared. The Lampung position causes different insolation between land and sea diurnally, so the diurnal cycles play an important role in weather formation. Therefore, this study aims to determine the effect of MJO propagation phases 3-5 in 2018 on the diurnal cycle of atmospheric dynamics and rainfall in Lampung. The diurnal cycle was analyzed by dividing four periods of time, in the early morning (00-06 LT), morning (06-12 LT), afternoon (12-18 LT), and night (18-00 LT). Based on the average composite of ECMWF, GSMaP, and precipitation observations data were obtained that propagation MJO strengthens during phase 3-4 and weakens during phase 5. Diurnal strong convective and high rainfall occur in the oceans from early morning to morning, in coastal during the day, and on land at night which increases from phase 3-4 and weakens in phase 5. Rain propagates from western Lampung to central Lampung with a time lag of 2-5 hours during phase 3, 4-7 hours when phases 4, and 1 -2 hours during phase 5. In the 3-5 phase, rain occurs in eastern Lampung with a time difference of 1-3 hours from central Lampung.

Comparison of forecasting accuracy for Madden Julian Oscillation (MJO) and Convectively Coupled Equatorial Waves (CCEW) using Tropical Rainfall Measuring Mission (TRMM) and ERA-Interim precipitation forecast data for Indonesia

Tropical Rainfall Measuring Mission (TRMM) and ERA-Interim forecast data analyzed using second-order autoregressive AR(2) and space-time-spectra analysis methods (respectively) revealed contrasting results for predicting Madden Julian Oscillation (MJO) and Convectively Coupled Equatorial Waves (CCEW) phenomena over Indonesia. This research used the same 13-year series of daily TRMM 3B42 V7 derived datasets and ERA-Interim reanalysis model datasets from the European Center for Medium-Range Weather Forecasts (ECMWF) for precipitation forecasts. Three years (2016 to 2018) of the filtered 3B42 and ERA-Interim forecast data was then used to evaluate forecast accuracy by looking at correlation coefficients for forecast leads from day +1 through day +7. The results revealed that rainfall estimation data from 3B42 provides better results for the shorter forecast leads, particularly for MJO, equatorial Rossby (ER), mixed Rossby-gravity (MRG), and inertia-gravity phenomena in zonal wavenumber 1 (IG1), but gives poor correlation for Kelvin waves for all forecast leads. A consistent correlation for all waves was achieved from the filtered ERA-Interim precipitation forecast model, and although this was quite weak for the first forecast leads it did not reach a negative correlation in the later forecast leads except for IG1. Furthermore, Root Mean Square Error (RMSE) was also calculated to complement forecasting skills for both data sources, with the result that residual RMSE for the filtered ERA-Interim precipitation forecast was quite small during all forecast leads and for all wave types. These findings prove that the ERA-Interim precipitation forecast model remains an adequate precipitation model in the tropics for MJO and CCEW forecasting, specifically for Indonesia.