Periodicity in intraseasonal variation of summer monsoon rainfall over Orissa, India in relation to synoptic disturbances

Mohapatra, M.; Mohanty, U. C.

doi:10.1007/s00703-007-0268-1

Cited by 3 publications

(1 citation statement)

References 26 publications

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“…Computation of anomalies and/or extraction of oscillation/annual cycle Krishnamurthy and Shukla (2007) M-SSA and wavenumberfrequency spectral analysis Daily rainfall over 1°grid-point (1901-1970) Subtraction of the long-term mean annual cycle and then smoothing with a 5-day running mean Klingaman et al (2008) Correlation and composites Daily OLR , pentad CMAP rainfall , daily winds from ERA and ECMWF (2002ECMWF ( -2005, daily TMI SST (1998SST ( -2005 and daily AIRI (1901AIRI ( -2005 NA Krishnamurthy and Shukla (2008) M-SSA and wavenumberfrequency spectral analysis Daily OLR (1975OLR ( -2002 and daily rainfall over 1°grid-point (Rajeevan et al 2005) Subtraction of the long-term mean annual cycle and then smoothing with 5-day running mean Mohapatra and Mohanty (2008) Auto-correlation and Blackman-Tukey spectra Daily rainfall (1980)(1981)(1982)(1983)(1984)(1985)(1986)(1987)(1988)(1989)(1990)(1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999) NA Bhanu Wavelet and extended EOF Daily NRA winds and daily OLR (1979OLR ( -2006 NA Fujinami et al (2011) FFT, composite and regression Daily rainfall in 25 stations in Bangladesh …”

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confidence: 99%

Impact of the modulated annual cycle and intraseasonal oscillation on daily-to-interannual rainfall variability across monsoonal India

Moron

Robertson²,

Ghil

2011

Clim Dyn

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Variability of the Indian summer monsoon is decomposed into an interannually modulated annual cycle (MAC) and a northward-propagating, intraseasonal (30-60-day) oscillation (ISO). To achieve this decomposition, we apply multi-channel singular spectrum analysis (M-SSA) simultaneously to unfiltered daily fields of observed outgoing long-wave radiation (OLR) and to reanalyzed 925-hPa winds over the Indian region, from 1975 to 2008. The MAC is essentially given by the year-toyear changes in the annual and semi-annual components; it displays a slow northward migration of OLR anomalies coupled with an alternation between the northeast winter and southwest summer monsoons. The impact of these oscillatory modes on rainfall is then analyzed using a 1-degree gridded daily data set, focusing on Monsoonal India (north of 17°N and west of 90°E) during the months of June to September. Daily rainfall variability is partitioned into three states using a Hidden Markov Model. Two of these states are shown to agree well with previous classifications of ''active'' and ''break'' phases of the monsoon, while the third state exhibits a dipolar east-west pattern with abundant rainfall east of about 77°E and low rainfall to the west. Occurrence of the three rainfall states is found to be an asymmetric function of both the MAC and ISO components. On average, monsoon active phases are favored by large positive anomalies of MAC, and breaks by negative ones. ISO impact is decisive when the MAC is near neutral values during the onset and withdrawal phases of the monsoon. Active monsoon spells are found to require a synergy between the MAC and ISO, while the east-west rainfall dipole is less sensitive to interactions between the two. The driest years, defined from spatially averaged June-September rainfall anomalies, are found to be mostly a result of breaks occurring during the onset and withdrawal stages of the monsoon, e.g., mid-June to midJuly, and during September. These breaks are in turn associated with anomalously late MAC onset or early MAC withdrawal, often together with a large-amplitude, negative ISO event. The occurrence of breaks during the core of the monsoon-from late July to late August-is restricted to a few years when MAC was exceptionally weak, such as 1987 or 2002. Wet years are shown to be mostly associated with more frequent active spells and a stronger MAC than usual, especially at the end of the monsoon season. Taken together, our results suggest that monthly and seasonal precipitation predictability is higher in the early and late stages of the summer monsoon season.

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