Tropical Synoptic‐Scale Waves Propagating Across the Maritime Continent and Northern Australia

Abstract

The structure and characteristics of tropical synoptic‐scale wave disturbances over the Maritime Continent (MC) and northern Australia during the Southern Hemisphere summer are analyzed. The tropical synoptic‐scale waves are identified by an extended empirical orthogonal function analysis on 2‐ to 8‐day‐filtered daily 850‐hPa meridional wind anomalies during December–February for the period 1979–2016. Extended empirical orthogonal function‐based composite analyses of various fields reveal a synoptic‐scale wave train, with a well‐organized structure, which is coupled with deep convection anomalies. The composite waves are considered to be tropical depression‐type waves that develop along a strong meridional gradient of the mean monsoon westerly flow. These waves propagate westward at approximately 8 m/s, with zonal wavelengths of about 3,000–4,000 km. Eastward amplification of wave troughs and ridges due to group propagation occurs within the synoptic‐scale wave train. Wave activity diagnostics confirm that downstream wave energy propagation facilitates the development of the synoptic‐scale wave train along the monsoon westerly flow. Rainfall is enhanced over the MC and the ocean in the vicinity of the north coast of Australia, which is associated with the passage of the wave trough. The development of this synoptic‐scale wave is found to play an important role in day‐to‐day weather variation over the MC. Extratropical forcing of the tropical synoptic‐scale waves is also explored. Southerly surges that originated in the midlatitude Indian Ocean could intensify the tropical synoptic‐scale wave trough. The southerly surges are induced by the development of midlatitude synoptic‐scale baroclinic disturbances over the eastern Indian Ocean.

Impact of Southerly Surge on Rainfall Pattern Over Java, Bali, West Nusa Tenggara and East Nusa Tenggara during Asian Winter Monsoon and Its Relationship to MJO Condition

“…The surge can be identified by the streamline over the midlatitude of the Indian Ocean (around 25°-30° S), which supports the high moisture (200-300 kg/m/s) over this area to be transported toward the Maritime Continent (Figure 16b, d, f). The development of baroclinic synoptic disturbances in this midlatitude area induced the development of the surge (Fukutomi, 2019). Furthermore, the moistening over the Maritime Continent due to MJO is explained by a previous study (Hu H. et al, 2023).…”

Moisture Origin and Transport for Extreme Precipitation over Indonesia's New Capital City, Nusantara in August 2021

“…BSISO is a large-scale weather system that strongly influences intra-seasonal rainfall variability during boreal summer as a result of interaction between Madden Julian Oscillation (MJO) and monsoonal system [7][8][9]. Furthermore, the tropical synoptic activities associated with tropical high and low in a period range of about 2-8 days also often play a key role in modulating summertime convection that causes day-to-day weather variations and heavy rainfall over East Kalimantan during boreal summer [10]. In addition, the rainfall variation in East Kalimantan is also affected by the interannual variability of the tropical sea surface temperature (SST) in the Pacific and Indian Oceans associated with El Niño-Southern Oscillation (ENSO) [11,12].…”

Analysis of Synoptic Disturbance in Maritim Continent Using Spherical Harmonics Transformation Method

“…On other hand, synoptic weather in tropics was influenced by various types of equatorial waves (e.g. Fukutomi et al, 2016;Fukutomi, 2019;Kim et al, 2019;Matsuno, 1966;Yang et al, 2018), which theoretically include Kelvin waves, equatorial Rossby (ER), westward inertia-gravity (WIG), eastward inertia-gravity (EIG) and mixed Rossby gravity (MRG) (Matsuno, 1966).…”