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

Abstract

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.

Interannual variability of Indian summer monsoon rainfall onset date at local scale

“…The ENSO‐related predictability of local onset date is also limited by the weak‐to‐moderate correlations between the antecedent Niño 3.4 index and the regional indices themselves (Table ). More work is nevertheless needed regarding the relationship between intraseasonal oscillations and the spatial scales of onset (Moron et al ., ).…”

The Relation of Intraseasonal Variations With Local Onset and Demise of the Indian Summer Monsoon

“…The extraction of ISO modes in the rainfall data is done using multichannel singular spectral analysis (MSSA; Ghil et al, 2002;Plaut & Vautard, 1994). This data-adaptive filtering technique is quite successful in extracting oscillatory signals from a short and noisy time series and has been used in many studies recently to understand the behavior of Indian monsoon (Karmakar et al, 2017a(Karmakar et al, , 2017bKarmakar & Krishnamurti, 2018;Krishnamurthy & Shukla, 2007;Moron et al, 2012). We removed the daily climatology at each grid point from the 104-year daily data.…”

Influence of Madden-Julian Oscillation on water budget transported by the Somali low-level jet and the associated Indian summer monsoon rainfall

“…On the other hand, the Madden‐Julian Oscillation (MJO) [ Madden and Julian , ] has been identified as a dominant mode of the intraseasonal variability of the ISM rainfall [ Hoyos and Webster , ; Pai et al ., ]. The MJO can be characterized by large‐scale convective anomalies that develop over the tropical Indian Ocean in a time scale ranging between 30 and 60 days [e.g., Qi et al ., ; Joseph et al ., ; Moron et al ., ] and propagates eastward, equatorially trapped, during winter; but it is characterized by a prominent northward propagation over the south Asian monsoon region during the boreal summer [ Yasunari , ; Sikka and Gadgil , ; Lau and Chan , ; Wang and Rui , , among others]. This northward propagation is closely associated with the active and break phases of the ISM rainfall [ Lawrence and Webster , ], and although it has received intensive attention during past decades [ Jiang and Li , ], its cause is still an open question [ Abhik et al ., ].…”