Reaserch Scholar

Department Of Physical Oceanography, Cochin University Of Science And Technology  - Nisa Anil
Nisa Anil
Reg. No. 4748



Email  |

Phone |  9567358830


PhD Details

Joining Date |  23.07.2014

Supervising guide |  Dr. R. Sajeev

Field of study |  Oceanography

Title |  Air-Sea interaction processes over the Indo-Pacific region



Air-Sea interaction processes over the Indo-Pacific region

The atmosphere and ocean act as an interdependent system. The observations show that whatever happens in one of the system can change the other. The continuous exchange of heat and momentum between two systems results in a complex feedback loops. To get a proper understanding of the processes in the atmosphere and ocean, their mutual interaction must be examined. The major coupled ocean-atmosphere phenomenas are the El-Nino Southern Oscillation (ENSO) in the Pacific and the Indian Ocean Dipole (IOD) in the Indian Ocean. Both have a profound impact on the global climate.

The Indian Ocean sea surface temperature has a positive correlation with Indian Summer Monsoon Rainfall (ISMR) due to high surface evaporation. It is noticed that the anomalous convergence in the Bay of Bengal during positive IOD events that brings excess ISMR. There are studies proving that, when El Nino and Positive IOD co-occur, the negative impact of ENSO is reduced by the presence of IOD and leads to a normal ISMR. The present study looked into the effect of different flavors of IOD on ISMR. In this classification IOD is categorized into three types according to the peaking time and duration, as Unseasonable IOD , Normal IOD and Prolonged IOD (Yan, 2013). During Unseasonable IOD which peaks in summer monsoon months, the Arabian Sea experiences a positive sea surface temperature and an enhanced evaporation. The cross equatorial flow is found stronger and the low-level wind flow at 850 hPa was more into the peninsular India which resulted in the decrease in number of break events. The combined effect of all these processes increases the monsoon rainfall over the Indian subcontinent like a prolonged IOD during the unseasonable IOD, even if its intensity and life span are less. When compared to the prolonged and unseasonable IOD, the normal IOD had more break days and contributes less to trigger the ISMR.

The IOD and El-Nino also plays a key role in modulating the Australian climate. The El-Niño is associated with a reduced rainfall in the northern as well as the eastern part of the continent on the other hand a positive IOD is on the southern and central Australia. In the case of ISMR, the IOD can reduce the negative impact of El-Nino. But in this case a positive IOD can increase the impact of El-Nino when both co-occur. This may ended up in the forest bush fires, heat waves etc. A positive IOD coincides with the winter crop growing season of Australia hence the below average rainfall in the southern and eastern parts will have a negative influence on agriculture. A negative IOD on the other hand brings an above average winter-spring rainfall. The frequent occurrence of IOD and the co-occurrence of IOD with El-Nino will further worsen the situation. Within the years from 1994 to 1998 there occurred two positive IOD and two negative IOD events. And a frequent occurrence of positive IOD happened from 2006 till 2008. Hence this study is to observe the impact of frequently occurring events on Australian rainfall.

The IOD and El-Nino are two important modes of climate variability in the tropical oceans associated with the ocean temperature as well as air pressure anomalies. Of these anomalies one of the most recent is the warm pool of the Indian and Pacific oceans, which holds the warmest sea waters of the world. In recent years, a significant amount of heat is missing in the atmosphere is expected to store in the Pacific is transferred to the Indian Ocean by excess heat advection (Indonesian through flow). The studies also shows that the decrease in cooling from net air-sea fluxes equally contribute to this excess warming. The study about excess warming of Indian Ocean is inevitable because it can increase the tremendous occurrence of tropical cyclones, excess rainfall and leads the warming of nearby land and atmosphere. The main influence of Indian Ocean Dipole and El-Nino is on tropics. However the inter-annual variability of Equatorial Indian Ocean is not addressed. Hence this study includes an observation on how the equatorial heat content is varying with independent IOD and when it is co-occurred with El-Nino. An empirical orthogonal function analysis is also going to carry out to identify the major mode of oceanic heat content variability in the Indian Ocean.