Intraseasonal Variability in Diurnal Rainfall over New Guinea and the Surrounding Oceans during Austral Summer

Abstract

High-resolution Tropical Rainfall Measuring Mission (TRMM) rainfall data for six wet seasons (December-March) were used to investigate the time and space structure of the diurnal cycle of rainfall over and around New Guinea, a major island of the Maritime Continent. The diurnal cycle shows a systematic modulation associated with intraseasonal variability in the large-scale circulation pattern, with regimes associated with low-level easterlies or westerlies over the island. Lower-tropospheric easterly (westerly) wind components correspond to periods of inactive (active) convection over the islands that are associated with the passage of intraseasonal atmospheric disturbances such as the Madden-Julian oscillation (MJO). A striking feature is the diurnal rainfall that develops over the central mountain ranges in the evening and propagates toward the southwest (northeast) of the island with an inferred phase speed of about 2-3 m s Ϫ1 under low-level easterly (westerly) flow. In the case of the easterly regime, diurnal rainfall is strongly concentrated over the southwestern part of the island, inhibited from spreading offshore southwest of New Guinea. Under the westerly regime, in contrast, the rainfall area spread far and wide along the low-level westerlies from the island toward the Pacific Ocean. Significant offshore rainfall propagation extending from the island appears during the night over the north-northeastern coast and moves with a phase speed of about 7-8 m s Ϫ1 , reaching the open ocean the following day. Possible processes for controlling the variability in diurnal rainfall through the interaction between large-scale circulation and previously denoted complex local circulation over the island are discussed.

Intraseasonal Variability and Seasonal March of the Moist Static Energy Budget over the Eastern Maritime Continent during CINDY2011/DYNAMO

“…The structure of circulation anomalies associated with MJO is also modulated by topography (Hsu and Lee 2005). The diurnal cycle in convective activity over and around islands (Mori et al 2004) interacts with MJO (Ichikawa and Yasunari 2008;Rauniyar and Walsh 2011;Peatman et al 2014), which may contribute to its eastward propagation (Ichikawa and Yasunari 2007). On the other hand, the view of MJO as driven by surface fluxes and radiation implies that the low heat capacity of the land surface should cause MJO-related intraseasonal variability in convection to weaken over land, consistent with what is observed (Sobel and Gildor 2003;Sobel et al 2010).…”

Mechanism of Orographic Precipitation around the Meghalaya Plateau Associated with Intraseasonal Oscillation and the Diurnal Cycle

“…Rauniyar and Walsh (2011) found that the amplitude of the diurnal precipitation cycle becomes one and a half times larger than normal during the active MJO phase, although this depends on the region. The propagation of diurnal cycle signals is also influenced by the MJO; this was revealed by TRMM observations (Ichikawa and Yasunari 2008;Oh et al 2012) and by GPS (Fujita et al 2011) around the Maritime Continent. Oouchi et al (2009) performed a global cloud-resolving model experiment that demonstrated that the direction of diurnal cycle propagation varies corresponding to dry/wet periods of the ISO.…”

Relationship between the direction of diurnal rainfall migration and the ambient wind over the Southern Sumatra Island

“…Many features of these variations have been well documented to date, e.g., the initiation of convection in a mountainous area in the afternoon, the peak of rainfall early in the night, and the movement of rain areas from the mountains to coast or offshore areas around midnight [Nitta and Sekine, 1994;Nesbitt and Zipser, 2003;Mori et al, 2004;Sakurai et al, 2005;Ichikawa and Yasunari, 2006;Love et al, 2011]. However, several fundamental issues still remain unexplained, such as the offshore shift mechanism, interactions with large-scale (longer-period) variations, and local orography effects, although they have been discussed by some previous studies [Ohsawa et al, 2001;Mapes et al, 2003;Ichikawa and Yasunari, 2008;Wu et al, 2009]. Owing to our poor understanding of diurnal rainfall variation, current state-of-the-art general circulation models, which are used for weather forecasting and climate projection, still have difficulty reproducing the diurnal precipitation cycle (e.g., amplitude and phase of rainfall).…”