Publication Date:
2020-11-30
Description:
The Indian Ocean Dipole Mode (IODM) is examined by comparing the characteristics
of oceanic and atmospheric circulations, heat budgets, and possible mechanisms of IODM
between El Nino and non-El Nino years. ERA-40 reanalysis data, Reynold SST, and ocean
analysis from Modular Ocean Model with the assimilation of the temperature profile from
World Ocean Dataset 1998 are used to form three-year composites of IODM during El Nino (72,
82, 97) and non-El Nino (61, 67, 94) years. In El Nino years, two off-equatorial, anti-cyclonic
circulations develop as a Rossby-wave response to the increased pressure over the Indian Ocean.
The resultant winds from easterlies to northeasterlies (from southerlies to southeasterlies) in the
northwestern (southeastern) tropical Indian Ocean warms (cools) the mixed layer temperature
by inducing an anomalous zonal (meridional and vertical) component in the ocean current that
advects the basic-state mixed layer temperature. In non-El Nino years, a monsoon-like flow
induces winds from westerlies to southwesterlies (from southerlies to southeasterlies) in the
northwestern (southeastern) Indian Ocean. As a result, the cold advection by the anomalous
eastward current (northward current) in the northwestern (southeastern) tropical Indian Ocean
becomes dominant in non-El Nino years. In addition, the anomalous winds in these regions
are the same sign as the climatological monthly mean winds. Hence the anomalous latent and
sensible heat fluxes further contribute to the decrease of SST in the northwestern and the
southeastern Indian Ocean. Consequently, the cooling of the eastern tropical Indian Ocean
rather than the warming of western tropical Indian Ocean becomes the major feature of the
IODM during non-El Nino years.
Description:
Published
Description:
2961–2977
Description:
4A. Oceanografia e clima
Description:
JCR Journal
Description:
open
Keywords:
Indian Ocean Dipole
;
El Nino
;
03. Hydrosphere::03.03. Physical::03.03.01. Air/water/earth interactions
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
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