Riyan Arasyid Kurniawan

Jurusan Program Studi Fisika, Fakultas Matematika dan Ilmu Pengetahuan Alam, Universitas Jember

Erma Yulihastini

Pusat Riset Iklim dan Atmosfer, Badan Riset dan Inovasi Nasional, Bandung

Narizka Nanda Purwandari

Pusat Riset Iklim dan Atmosfer, Badan Riset dan Inovasi Nasional, Bandung

Supriyadi

Jurusan Program Studi Fisika, Fakultas Matematika dan Ilmu Pengetahuan Alam, Universitas Jember

DOI: https://doi.org/10.19184/jid.v27i2.60019

ABSTRACT 

The Cross-Equatorial Northerly Surge (CENS) phenomenon contributes to increased convective activity and rainfall in the Indonesian Maritime Continent (IMC). However, studies on the interaction of CENS and the Southerly Surge (SS) on atmospheric variability in the region remain limited. This study aims to analyze the effect of CENS and SS interaction on atmospheric humidity conditions, water vapor convergence, and convective activity in Java using European Reanalysis 5 (ERA5) reanalysis data for the December to February (DJF) period of 2000–2025. The parameters used include zonal and meridional winds at 925 hPa, Relative Humidity (RH), Moisture Flux Convergence (MFC), and Outgoing Longwave Radiation (OLR). Identification of CENS and SS events is carried out using the meridional wind index based on climatological values and standard deviations in the study area. Furthermore, surge events are classified into strong (k) and weak (l) conditions to determine the atmospheric characteristics of each event. The results of this study indicate that the CENS+SS event produces humid atmospheric conditions compared to the CENS event, where the RH value is around 0.5–2%, while the MFC value is around 0.125–0.5 × 10⁻⁶ kg m⁻² s⁻¹ in central to eastern Java. In addition, the 925 hPa layer wind pattern shows a strengthening of the west–north wind flow in the advection process and the accumulation of water vapor in the lower atmosphere. The OLR composite results show a negative anomaly of around -2.5 to -10 W/m² during the CENS+SS event, indicating an increase in convective activity in Java. Based on the surge intensity classification, the strong CENS condition (kCENS) shows a significant influence compared to the strong SS condition (kSS) on atmospheric variability.

Keywords: Cross-Equatorial Northerly Surge, Southerly Surge, Relative Humidity, Moisture Flux Convergence, Outgoing Longwave Radiations, Java.