The Cross-Equatorial Northerly Surge over the Maritime Continent and Its Relationship to Precipitation Patterns

Abstract

This study describes the characteristics of the cross-equatorial northerly surge (CENS), a northerly flow that appears intermittently over the equatorial region between October and April, and its relationship to the precipitation patterns over the Maritime Continent. The CENS in this study was defined as the area-averaged northerly wind exceeding 5 m s À1 over 105 E-115 E, 5 S-EQ based on the QuikSCAT sea surface wind data. During the 10 winters from December 2000 to March 2009, 62 CENS events were extracted and classified into the following patterns: 11 events were associated with cold surges and termed the CS pattern; 20 events were associated with tropical intra-seasonal variations and termed the MJO pattern; 16 events were associated with both cold surges and tropical intra-seasonal variations and termed the CS-MJO pattern; and other 15 events were not associated with these patterns. In the CS pattern, the development and dissipation processes of the cold surge appeared, and the increased precipitation to the north of the island of Java was significant. In the MJO pattern, a wide area of northerly winds in the vicinity of the depression around 10 S continued for a longer period than in the CS pattern, and the increased precipitation west of Sumatra and south of Java was significant. The CS-MJO pattern showed features of the northerly wind fields of both the CS and MJO patterns and was associated with the greatest increase in precipitation of the three patterns in the Maritime Continent, in particular, in northwestern Java and both north and south of Java. The generation of CENS was an important environmental factor for inducing the wide positive precipitation anomaly compared to the climatological mean over the Maritime Continent.

The Effects of an Active Phase of the Madden-Julian Oscillation on the Extreme Precipitation Event over Western Java Island in January 2013

“…3) showed that during 4−13 January, strong westerly winds > 10 m s −1 were observed from near the surface up to 400 hPa (~8 km), with maximum wind speed being at the 900600hPa layer, consistent with the passage of the strong active phase of the MJO over the Maritime Continent and the western Pacific regions. It is note worthy that the upper westerly winds continued over Java Island to a lower latitude and can even penetrate into the Southern Hemisphere (Wu et al 2007;Hattori et al 2011). A strong and persistent transequatorial monsoonal flow is a crucial factor in extremely heavy rain over western Java Island.…”

“…The effects of the active phase of the MJO on the extreme precipitation event Hattori et al (2011) investigated the occurrence of cross equatorial northerly surge and its relation to precipitation over the Maritime Continent during the regional wet season from December to March for the 11 years from 1998 to 2009. Their results showed that during crossequatorial northerly surge events, enhanced precipitation is evident over the northern coast of Java Island and the Java Sea in both active and inactive MJO phases.…”

“…This is because the comparatively strong winds prevented accu mulation of heated air on the mountain slope, inhibiting upslope winds and suppressing afternoon convection over the mountains. However, in the statistical analysis of Hattori et al (2011), sup pression of convection over the mountainous areas of Java Island is indistinct in the crossequatorial northerly surge events with an active phase of the MJO (their Fig. 16).…”

Impact of the Radiosonde Observations of Cold Surge over the Philippine Sea on the Tropical Region and the Southern Hemisphere in December 2012

“…Thus, the observation has conducted during the period of developed northerly cold surge in the Philippine Sea and the active phase of MJO convection over the Maritime Continent. In other words, it corresponds to the northerly surge/MJO combined pattern where the precipitation significantly increases over the Maritime Continent as shown in Hattori et al (2011).…”

“…Moreover, the analysis indicated that the northerly surge greatly affects not only convective activity but also rainfall distributions in the tropics near the equator and over the Indonesian Maritime Continent in the Southern Hemisphere (Hattori et al 2011;Wu et al 2013;Pullen et al 2015). Hattori et al (2011) showed that the northerly surge/MJO (Madden-Julian Oscillation) combined pattern (16 cases) produced much greater precipitation over the Maritime Continent than either MJO (20 cases) or northerly surge (11 cases) alone. Love (1985) showed that the zonal pressure gradients near the equator induced by cold surges in the winter hemisphere influence the development of tropical cyclones (TCs) in the summer hemisphere.…”