The Life Cycle of Annual Waves in the Indian Ocean as Identified by Seamless Diagnosis of the Energy Flux

Abstract The authors examined the maintenance mechanisms of perturbation kinetic energy (PKE) in the tropical regions for multiple time scales by computing and analyzing its budget equation. The emphasis has been placed on the mean features of synoptic and subseasonal variabilities using a 33-yr dataset. From analysis of the contributions from u-wind and υ-wind components, the PKE maximum in the Indian Ocean is attributed less to synoptic variability and more to intraseasonal variability in which the Madden–Julian oscillation (MJO) dominates; however, there is strong evidence of seasonal variability affiliated with the Asian monsoon systems. The ones in the eastern Pacific and Atlantic Oceans are closely related to both intraseasonal and synoptic variability that result from the strong MJO and the relatively large amplitude of equatorial waves. The maintenance of the PKE budget mainly depends on the structure of time mean horizontal flows, the location of convection, and the transport of PKE from the extratropics. In the regions with strong convective activities, such as the eastern Indian Ocean to the western Pacific, the production of PKE occurs between 700 and 200 hPa at the expense of perturbation available potential energy (PAPE), which is generated by convective heating. This gain in PKE is largely offset by divergence of the geopotential component of vertical energy flux; that is, it is redistributed to the upper- and lower-atmospheric layers by the pressure field. Strong PKE generation through the horizontal convergence of the extratropical energy flux takes place in the upper troposphere over the eastern Pacific and Atlantic Ocean, and is largely balanced by a PKE loss due to barotropic conversion, which is determined solely by the sign of longitudinal stretching deformation. However, over the Indian Ocean, there is a net PKE loss due to divergence of energy flux, which is compensated by PKE gain through the shear generation.

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Indo-Pacific warm pool expansion modulates MJO lifecycle

10.5194/egusphere-egu2020-1039 ◽

2020 ◽

Author(s):

Panini Dasgupta ◽

Roxy Mathew Koll ◽

Michael J. McPhaden ◽

Tamaki Suematsu ◽

Chidong Zhang ◽

...

Keyword(s):

Life Cycle ◽

Indian Ocean ◽

Southern Oscillation ◽

Average Rate ◽

Warm Pool ◽

Dominant Mode ◽

Maritime Continent ◽

Pacific Warm Pool ◽

The Indian Ocean ◽

The Impact

The Madden&#8211;Julian Oscillation (MJO) is the most dominant mode of intraseasonal variability in the tropics, characterized by an eastward propagating zonal circulation pattern and rain bands. MJO is very crucial phenomenon due to its interactions with other timescales of ocean-atmosphere like El Ni&#241;o Southern Oscillation, tropical cyclones, monsoons, and the extreme rainfall events all across the globe. MJO events travel almost half of the globe along the tropical oceans, majorly over the Indo-Pacific Warm Pool (IPWP) region. This IPWP region has been warming during the twentieth and early twenty- first centuries in response to increased anthropogenic emissions of greenhouse gases and is projected to warm further. However, the impact of the warming of the IPWP region on the MJO life cycle is largely unknown. Here we show that rapid warming over the IPWP region during 1981&#8211;2018 has significantly changed the MJO life cycle, with its residence time decreasing over the Indian Ocean by 3&#8211;4 days, and increasing over the Indo-Pacific Maritime Continent by 5&#8211;6 days. We find that these changes in the MJO life cycle are associated with a twofold expansion of the Indo-Pacific warm pool. The warm pool has been expanding on average by 2.3 &#215; 105 km2 per year during 1900&#8211;2018 and at an accelerated average rate of 4 &#215; 105 km2 per year during 1981&#8211;2018. The accelerated warm pool expansion has increased moisture in the lower and middle troposphere over IPWP and thereby increased the gradient of lower-middle tropospheric moisture between the Indian Ocean and western Pacific. This zonal gradient of moisture between the Indian Ocean and west Pacific and the increased subsidence over the Indian ocean due to increased convective duration of MJO over maritime continent are likely the reasons behind the changing lifecycle of MJO.

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Physical Mechanisms for the Maintenance of GCM-Simulated Madden–Julian Oscillation over the Indian Ocean and Pacific

Journal of Climate ◽

10.1175/2010jcli3759.1 ◽

2011 ◽

Vol 24 (10) ◽

pp. 2469-2482 ◽

Cited By ~ 9

Author(s):

Liping Deng ◽

Xiaoqing Wu

Keyword(s):

Indian Ocean ◽

Energy Flux ◽

Wave Energy ◽

Western Pacific ◽

Eastern Pacific ◽

Convective Heating ◽

Trigger Condition ◽

Wave Energy Flux ◽

The Indian Ocean ◽

Central Eastern

Abstract The kinetic energy budget is conducted to analyze the physical processes responsible for the improved Madden–Julian oscillation (MJO) simulated by the Iowa State University general circulation models (ISUGCMs). The modified deep convection scheme that includes the revised convection closure, convection trigger condition, and convective momentum transport (CMT) enhances the equatorial (10°S–10°N) MJO-related perturbation kinetic energy (PKE) in the upper troposphere and leads to a more robust and coherent eastward-propagating MJO signal. In the MJO source region, the Indian Ocean (45°–120°E), the upper-tropospheric MJO PKE is maintained by the vertical convergence of wave energy flux and the barotropic conversion through the horizontal shear of mean flow. In the convectively active region, the western Pacific (120°E–180°), the upper-tropospheric MJO PKE is supported by the convergence of horizontal and vertical wave energy fluxes. Over the central-eastern Pacific (180°–120°W), where convection is suppressed, the upper-tropospheric MJO PKE is mainly due to the horizontal convergence of wave energy flux. The deep convection trigger condition produces stronger convective heating that enhances the perturbation available potential energy (PAPE) production and the upward wave energy fluxes and leads to the increased MJO PKE over the Indian Ocean and western Pacific. The trigger condition also enhances the MJO PKE over the central-eastern Pacific through the increased convergence of meridional wave energy flux from the subtropical latitudes of both hemispheres. The revised convection closure affects the response of mean zonal wind shear to the convective heating over the Indian Ocean and leads to the enhanced upper-tropospheric MJO PKE through the barotropic conversion. The stronger eastward wave energy flux due to the increase of convective heating over the Indian Ocean and western Pacific by the revised closure is favorable to the eastward propagation of MJO and the convergence of horizontal wave energy flux over the central-eastern Pacific. The convection-induced momentum tendency tends to decelerate the upper-tropospheric wind, which results in a negative work to the PKE budget in the upper troposphere. However, the convection momentum tendency accelerates the westerly wind below 800 hPa over the western Pacific, which is partially responsible for the improved MJO simulation.

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