Response of the Bay of Bengal to the Atmospheric Intraseasonal Oscillations
Abstract
The Indian monsoon is a complex, nonlinear phenomenon involving atmospheric, oceanic, and landbasedprocesses. The Indian Ocean (IO)" is unique due to many physical traits and characteristics thataffect oceanic processes and overall climatology of this region. In" the IO, the seasonal cycle is thedominant mode of variability with the characteristic seasonal reversal of southwest monsoon (June""-September) and northeast monsoon (December-March) and monsoon transitions in between, and seasonalchange of meridional gradients"" in Sea Surface Temperature (SST).Besides seasonal cycle, the IO is influenced and provides feedbacks to numerous scales of climate""variability, which have been investigated recently. Fluctuating on one of the longest timescales is El Ni~oSouthern Oscillation (E"NSO) that occurs predominantly in the Pacific Ocean but has an extensiveinfluence globally through an ~atmospheric bridge~ that adj"usts atmospheric waves. During El Ni~o,atmospheric convection is reduced over the IO as a result of subsidence in this region. Incr"eased solarradiation reaching the ocean surface leads to a basin-wide increase of SSTs. The La Ni~a phase isgenerally associated with a basin-wide cooling of SSTs reflecting atmospheric conditions during thistime. The Indian Ocean Dipole (IOD) is another form o"f inter-seasonal variability affecting the tropicalIO, which is seasonally linked to boreal summer and peaks in autumn. Strong air-"sea coupling isassociated with each phase of the IOD with positive SST anomalies generally triggering convection andnegative SST anomalies favoring reduced cloud-cover.The IO intraseasonal oscillations (ISOs) range in the scales from 3 to 7 day oscillations of" monsoontrough, from 10 to 20 day quasi~biweekly oscillations associated with westward moving synoptic-scaledisturbances, and from" 30 to 90 day Madden-Julian Oscillation (MJO). The MJO is an equatoriallytrapped eastward propagation of convection into the Pacifi"c Ocean, and exhibits a strong air-sea couplingthat also responds to the strong seasonal forcing which changes the magnitude and di""rection ofpropagation of the atmospheric component. During southwest monsoon season, atmospheric convectionof cloud bands associat""ed with MJO propagate eastward along the equator and also poleward towardsnorthern BoB, thus affecting the Indian monsoon rainfall" through its active- and break- phases. Thedynamics of MJO and its connection to Indian monsoon rainfall variability are poorly und"erstood. Itappears that positive SST anomalies in the BoB lead the convective phase of MJO over the BoB. Here, inthis project we f"ocus on the following research objectives:~ To study the upper ocean variability in the southern and northern BoB regions during the period ofsouthwest monsoon (June-September) and document the variability in the oceanic processes in theseregions associated with the intraseasonal atmospheric oscillations- that include the Madden JulianOscillations (MJOs).~ To quantify the extent of the MJO influence on the Indian summer monsoon rainfall.~ To assess the role of freshwater flux variability in the basin-scale air-sea coupling processes inrelation to the active- and break- phases of the monsoon rainfall.~ Why are air-sea gradients in the BoB so different from other warm oceans?~ To understand the intraseasonal subsurface temperature variability and its role on SST changes andair-sea interaction through air-sea coupled ocean atmosphere model and forced ocean model.~ To study the processes that determine t"he intraseasonal SST variability, and the relative importanceof MJO and sub-monthly intraseasonal oscillations during boreal summer"" and winter monsoon.e Indian monsoon is a complex, nonlinear phenomenon involving atmospheric, oceanic, and landbasedprocesses. Th"e Indian Ocean (IO) is unique due to many physical traits and characteristics thataffect oceanic processes and overall climatology" of this region. In the IO, the seasonal cycle is thedomina
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- May 05, 2017
- Source ID
- N000141712468
Entities
People
- Bulusu Subrahmanyam
Organizations
- Office of Naval Research
- United States Navy
- University of South Carolina