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A new method for extracting the ENSO-independent Indian Ocean Dipole: application to Australian region tropical cyclone counts

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Werner, A and Maharaj, AM and Holbrook, NJ (2011) A new method for extracting the ENSO-independent Indian Ocean Dipole: application to Australian region tropical cyclone counts. Climate Dynamics, x (xx). x-x. (In Press)

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Abstract

We introduce a simple but effective means of
removing ENSO-related variations from the Indian Ocean
Dipole (IOD) in order to better evaluate the ENSO-independent
IOD contribution to Australian climate—specifically
here interannual variations in Australian region
tropical cyclogensis (TCG) counts. The ENSO time contribution
is removed from the Indian Ocean Dipole Mode
index (DMI) by first calculating the lagged regression of
the DMI on the sea surface temperature anomaly (SSTA)
index NINO3.4 to maximum lags of 8 months, and then
removing this ENSO portion. The new ENSO-independent
time series, DMINOENSO, correlates strongly with the original
DMI at r = 0.87 (significant at[99% level). Despite
the strength of the correlation between these series, the
IOD events classified based on DMINOENSO provide
important differences from previously identified IOD
events, which are more closely aligned with ENSO phases.
IOD event composite maps of SSTAs regressed on
DMINOENSO reveal a much greater ENSO-independence
than the original DMI-related SSTA pattern. This approach
is used to explore relationships between Australian region
TCG and IOD from 1968 to 2007. While we show that both
the DMI and DMINOENSO have significant hindcast skill
(on the 95% level) when used as predictors in a multiple
linear regression model for Australian region annual TCG
counts, the IOD does not add any significant hindcast skill
over an ENSO-only predictor model, based on NINO4.
Correlations between the time series of annual TCG count
observations and ENSO ? IOD model cross-validated
hindcasts achieve r = 0.68 (significant at the 99% level).

Item Type: Article
Keywords: Climate variability IOD ENSO Tropical cyclones Australia
Journal or Publication Title: Climate Dynamics
Page Range: x-x
Identification Number - DOI: 10.1007/s00382-011-1133-y
Additional Information:

Copyright © 2011 Springer-Verlag

Date Deposited: 12 Oct 2011 00:31
Last Modified: 18 Nov 2014 04:22
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