Influence of ENSO on tropical cyclone intensity in the Fiji region
- Authors: Chand, Savin , Walsh, Kevin
- Date: 2011
- Type: Text , Journal article
- Relation: Journal of Climate Vol. 24, no. 15 (2011), p. 4096-4108
- Full Text: false
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- Description: This study examines the variation in tropical cyclone (TC) intensity for different phases of the El Niño-Southern Oscillation (ENSO) phenomenon in the Fiji, Samoa, and Tonga (FST) region. The variation in TC intensity is inferred from the accumulated cyclone energy (ACE), which is constructed from the 6-hourly Joint Typhoon Warning Center best-track data for the period 1985-2006. Overall, results suggest that ACE in the FST region is considerably influenced by the ENSO signal. A substantial contribution to this ENSO signal in ACE comes from the region equatorward of 15°S where TC numbers, lifetime, and intensity all play a significant role. However, the ACE-ENSO relationship weakens substantially poleward of 15°S where large-scale environmental variables affecting TC intensity are found to be less favorable during El Niño years than during La Niña years; in the region equatorward of 15°S, the reverse is true. Therefore, TCs entering this region poleward of 15°S are able to sustain their intensity for a longer period of time during La Niña years as opposed to TCs entering the region during El Niñao years, when they decay more rapidly. © 2011 American Meteorological Society.
The influence of the Madden-Julian oscillation on tropical cyclone activity in the Fiji region
- Authors: Chand, Savin , Walsh, Kevin
- Date: 2010
- Type: Text , Journal article
- Relation: Journal of Climate Vol. 23, no. 4 (2010), p. 868-886
- Full Text: false
- Reviewed:
- Description: This study examines the modulation of tropical cyclone (TC) activity by the Madden-Julian oscillation (MJO) in the Fiji, Samoa, and Tonga regions (FST region), using Joint Typhoon Warning Center best-track cyclone data and the MJO index developed by Wheeler and Hendon. Results suggest strong MJO-TC relationships in the FST region. The TC genesis patterns are significantly altered over the FST region with approximately 5 times more cyclones forming in the active phase than in the inactive phase of the MJO. This modulation is further strengthened during El Niño periods. The large-scale environmental conditions (i.e., low-level relative vorticity, upper-level divergence, and vertical wind shear) associated with TC genesis show a distinct patterns of variability for the active and inactive MJO phases. The MJO also has a significant effect on hurricane category and combined gale and storm category cyclones in the FST region. The occurrences of both these cyclone categories are increased in the active phase of the MJO, which is associated with enhanced convective activity. The TCs in the other MJO phases where convective activity is relatively low, however, show a consistent pattern of increase in hurricane category cyclones and a concomitant decrease in gale and storm category cyclones. Finally, TC tracks in different MJO phases are also objectively described using a cluster analysis technique. Patterns seen in the clustered track regimes are well explained here in terms of 700-500-hPa mean steering flow. © 2010 American Meteorological Society.