Japan Geoscience Union Meeting 2018

Presentation information

[EJ] Evening Poster

A (Atmospheric and Hydrospheric Sciences) » A-CG Complex & General

[A-CG39] Multi-scale ocean-atmosphere interaction in the tropical Indo-Pacific region

Mon. May 21, 2018 5:15 PM - 6:30 PM Poster Hall (International Exhibition Hall7, Makuhari Messe)

convener:Yukiko Imada(Meteorological Research Institute, Japan Meteorological Agency), Tomoki Tozuka(Department of Earth and Planetary Science, Graduate School of Science, The University of Tokyo), Hiroki Tokinaga(京都大学防災研究所, 共同), Yu Kosaka(Research Center for Advanced Science and Technology, University of Tokyo)

[ACG39-P03] Effects of the Australian monsoon on the duration of La Niña longer than that of El Niño

*Taiga Shirai1, Tomohiko Tomita2 (1.Graduate School of Science and Technology, Kuamoto University, 2.Faculty of Advanced Science and Technology, Kumamoto University)

Keywords:duration of La Niña, the Australian monsoon

In general, La Niña has longer duration than El Niño. That is, La Niña tends to remain for one year or longer, while El Niño decays within a year. The Australian monsoon plays an essential role for this long duration of La Niña. In spring after the mature phase of La Niña, the precipitation anomaly around the Indonesian maritime continent (IMC) is positive with the upward branch of Walker circulation. The positive precipitation anomalies further remain due to the temperature difference between IMC and northern Australia (NA). When La Niña occurs, the sea surface temperature (SST) is barely high around IMC, while land cooling is strong over NA due to the positive precipitation anomalies there, both of which make the large temperature difference between IMC and NA (IMC > NA). From boreal spring to summer, i.e., from austral fall to winter, the temperature of NA seasonally decreases. Such seasonal and anomalous temperature decreases over NA give rise to the substantial large-scale land breeze from NA to IMC, i.e., the stronger-than-normal Australian “winter” monsoon forcing positively large precipitation anomalies over IMC and to the south through the activation of vertical instability near the surface. The positive precipitation anomalies retain the upward branch of Walker circulation around IMC and overcome the effects of Kelvin wave from the tropical Indian Ocean and others inducing the transition from La Niña to El Niño. Thus, La Niña continues until boreal fall or winter, while El Niño decays by boreal spring or summer without such self-maintenance mechanism.