INCITE: Indian Summer Monsoon
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Tracking the Indian Summer Monsoon Onset back to the preinstrument period
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The
Indian summer monsoon onset is one of the most expected meteorological
events of the world, affecting the lives of hundreds of millions of
people. The India Meteorological Department has dated the monsoon onset
since 1901, but its original methodology was considered subjective and
it was updated in 2006. Unfortunately, the new method relies on OLR
measurements, which impedes the construction of an objective onset
series before the 1970s. An alternative approach is the use of the wind
field, but the development of such an index is limited to the period
covered by reanalysis products. In this paper historical wind records
taken on board ships are used to develop a new onset series using
only wind direction measurements, providing an objective record of the
onset since the late nineteenth century. The new series captures the
rapid precipitation increase associated with the onset, correlates well
with previous approaches, and is robust against anomalous (bogus)
onsets. A tendency for later-than-average onsets during the 1900–25 and
1970–90 periods and earlier-than-average onsets between 1940 and 1965
was found. A relatively stable relationship between ENSO and Indian
monsoon onset dates was found; however, this link tends to be weaker
during decades characterized by prevalent La Niña conditions.
Furthermore, it was found that the link between the Pacific decadal
oscillation (PDO) and the onset date is limited to the phases
characterized by a shift from negative to positive PDO phases.
Key Words: Indian Ocean; Monsoons; Precipitation; Climate variability; Reconstruction; Logbook
Reference: Ordoñez, P., D. Gallego, P. Ribera, C. Peña-Ortiz, and R. García-Herrera,
2016: Tracking the Indian Summer Monsoon Onset Back to the Preinstrument Period.
J. Climate, 29, 8115–8127, https://doi.org/10.1175/JCLI-D-15-0788.1
Figure 1: Monsoon onset over Kerala (MOK) series (gray line) and 15-yr running average (black line).
The MOK series can be downloaded HERE.
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