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

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 1 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.