The role of barrier layer in southeastern Arabian Sea during the development of positive Indian Ocean Dipole events

Using data from Argo and simple ocean data assimilation (SODA), the role of the barrier layer (BL) in the southeastern Arabian Sea (SEAS: 60°E–75°E, 0°–10°N) is investigated during the development of positive Indian Ocean Dipole (IOD) events from 1960 to 2008. It is found that warmer sea surface temperature (SST) in the northern Indian Ocean appears in June in the SEAS. This warm SST accompanying anomalous southeastern wind persists for six months and a thicker BL and a corresponding thinner mixed layer in the SEAS contribute to the SST warming during the IOD formation period. The excessive precipitation during this period helps to form a thicker BL and a thinner mixed layer, resulting in a higher SST in the SEAS. Warm SST in the SEAS and cold SST to the southeast of the SEAS intensify the southeasterly anomaly in the tropical Indian Ocean, which transports more moisture to the SEAS, and then induces more precipitation there. The ocean-atmosphere interaction process among wind, precipitation, BL and SST is very important for the anomalous warming in the SEAS during the development of positive IOD events.     

POSSIBLE INFLUENCES OF THE TROPICAL INDIAN OCEAN DIPOLE ON THE EASTWARD PROPAGATION OF MJO

Based on multiple datasets, correlation and composite analyses, and case studies, this paper investigated possible influences of the Indian Ocean dipole （IOD） mode on the eastward propagation of intraseasonal oscillation in the tropical atmosphere. The results showed that （1） the 30-60 day outgoing longwave radiation anomalies in the southeastern Indian Ocean and the 30-60 day 850-hPa zonal wind anomalies over the equatorial central Indian Ocean were significantly correlated with the IOD index; （2） during positive IOD years, the anomalously cold water in the southeastern Indian Ocean and the 850-hPa anomalous easterlies over the equatorial central Indian Ocean might act as barriers to the continuously eastward propagation of the intraseasonal convection, which interrupts the Madden-Julian oscillation （MJO） propagation in the eastern equatorial Indian Ocean and western Pacific; and （3） during negative IOD years, the anomalously warm water in the southeastern Indian Ocean and the low-level westerly anomalies over the equatorial central Indian Ocean favor the eastward movement of MJO.     

ENSO对印度洋偶极子非对称性的影响及机制研究北大核心

利用海表温度再分析资料、NCEP/NCAR大气环流再分析资料以及MPI-ESM1-2-LR气候模式PI-Control试验输出数据等,通过对不同强度的厄尔尼诺-南方涛动(El Nino-Southern Oscillation, ENSO)事件所对应的印度洋偶极子(Indian Ocean Dipole, IOD)事件的分析,探讨了ENSO对IOD偏度的调制作用。结果表明,伴随着赤道中东太平洋明显的正海温偏度,秋季印度洋海表温度存在西正东负的偏度。IOD与ENSO之间呈现出较强的非线性关系,且大部分强的正IOD事件对应着强El Nino事件。强El Nino位相下,IOD事件相关的海温与风场表现出很强的响应,强于La Nina事件产生的响应,表现为强的非对称性;相比较而言,弱El Nino事件与La Nina事件下引起的印度洋海温和风场的强度相当,并没有显著的非对称性。因此,ENSO可通过激发非对称的大气遥相关对IOD强度非对称性产生调制作用,印度洋海表温度偏度很大程度上是由强El Nino事件导致的强正IOD事件所贡献。