Variability Of Indian Monsoon Rainfall Research Articles

Effect of ENSO on Seasonal Temperature Over Tamil Nadu

Increased concentration of greenhouse gases is expected to alter the radiative balance of atmosphere, causing increase in temperature and changes in precipitation patterns. Climate variability has been principal source of fluctuations in Indian food production. Even though there is no long-term trend, inter - annual variability of Indian monsoon rainfall leading to frequent droughts and floods has profound influence on agriculture and intern, national economy. It is well recognized that El Niño / Southern Oscillation (ENSO) is the dominant mode of climate variability on seasonal to inter-annual scales and its impacts are felt worldwide. ENSO often affects seasonal temperature, precipitation and thus crop yields in many regions, however, the overall impacts of ENSO on global yields are uncertain Maximum and minimum average temperature was calculated for different seasons such as Cold Weather Period (CWP), Hot Weather Period (HWP), South West Monsoon (SWM), North East Monsoon (NEM) for each El Niño, La Niña and neutral years at various districts of Tamil Nadu. Relation between ENSO and temperature was analyzed by computing the anomaly in temperature at different districts of Tamil Nadu. The temperature deviation between the ENSO and neutral phases was not significant as the deviation was within + 0.3oC in all the seasons.

Inter-annual variability of Indian monsoon rainfall in the JMA’s seasonal ensemble prediction system in relation to ENSO and IOD

Inter-annual variability of Indian monsoon rainfall in the JMA’s seasonal ensemble prediction system in relation to ENSO and IOD

Potential of Reef Building Corals to Study the Past Indian Monsoon Rainfall Variability

Potential of Reef Building Corals to Study the Past Indian Monsoon Rainfall Variability

Non-stationary and non-linear influence of ENSO and Indian Ocean Dipole on the variability of Indian monsoon rainfall and extreme rain events

The El Nino Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD) are widely recognized as major drivers of inter-annual variability of the Indian monsoon (IM) and extreme rainfall events (EREs). We assess the time-varying strength and non-linearity of these linkages using dynamic linear regression and Generalized Additive Models. Our results suggest that IOD has evolved independently of ENSO, with its influence on IM and EREs strengthening in recent decades when compared to ENSO, whose relationship with IM seems to be weakening and more uncertain. A unit change in IOD currently has a proportionately greater impact on IM. ENSO positively influences EREs only below a threshold of 100 mm day−1. Furthermore, there is a non-linear and positive relationship between IOD and IM totals and the frequency of EREs (>100 mm day−1). Improvements in modeling this complex system can enhance the forecasting accuracy of the IM and EREs.

Pacific coral oxygen isotope and the tropospheric temperature gradient over the Asian monsoon region: a tool to reconstruct past Indian summer monsoon rainfall

AbstractHaving recognized that it is the tropospheric temperature (TT) gradient rather than the land–ocean surface temperature gradient that drives the Indian monsoon, a new mechanism of El Niño/Southern Oscillation (ENSO) monsoon teleconnection has been unveiled in which the ENSO influences the Indian monsoon by modifying the TT gradient over the region. Here we show that equatorial Pacific coralline oxygen isotopes reflect TT gradient variability over the Indian monsoon region and are strongly correlated to monsoon precipitation as well as to the length of the rainy season. Using these relationships we have been able to reconstruct past Indian monsoon rainfall variability of the first half of the 20th century in agreement with the instrumental record. Additionally, an older coral oxygen isotope record has been used to reconstruct seasonally resolved summer monsoon rainfall variability of the latter half of the 17th century, indicating that the average annual rainfall during this period was similar to that during the 20th century. Copyright © 2011 John Wiley & Sons, Ltd.

The Role of the Western Arabian Sea Upwelling in Indian Monsoon Rainfall Variability

AbstractThe Indian summer monsoon rainfall has complex, regionally heterogeneous, interannual variations with huge socioeconomic impacts, but the underlying mechanisms remain uncertain. The upwelling along the Somalia and Oman coasts starts in late spring, peaks during the summer monsoon, and strongly cools the sea surface temperature (SST) in the western Arabian Sea. They restrict the westward extent of the Indian Ocean warm pool, which is the main moisture source for the monsoon rainfall. Thus, variations of the Somalia–Oman upwelling can have significant impacts on the moisture transport toward India. Here the authors use both observations and an advanced coupled atmosphere–ocean general circulation model to show that a decrease in upwelling strengthens monsoon rainfall along the west coast of India by increasing the SST along the Somalia–Oman coasts, and thus local evaporation and water vapor transport toward the Indian Western Ghats (mountains). Further observational analysis reveals that such decreases in upwelling are caused by anomalously weak southwesterly winds in late spring over the Arabian Sea that are due to warm SST/increased precipitation anomalies over the Seychelles–Chagos thermocline ridge of the southwestern Indian Ocean (and vice versa for years with strong upwelling/weak west Indian summer monsoon rainfall). The latter SST/precipitation anomalies are often related to El Niño conditions and the strength of the Indonesian–Australian monsoon during the previous winter. This sheds new light on the ability to forecast the poorly predicted Indian monsoon rainfall on a regional scale, helped by a proper ocean observing/forecasting system in the western tropical Indian Ocean.

The CLIVAR C20C project: skill of simulating Indian monsoon rainfall on interannual to decadal timescales. Does GHG forcing play a role?

The ability of atmospheric general circulation models (AGCMs), that are forced with observed sea surface temperatures (SSTs), to simulate the Indian monsoon rainfall (IMR) variability on interannual to decadal timescales is analyzed in a multimodel intercomparison. The multimodel ensemble has been performed within the CLIVAR International “Climate of the 20th Century” (C20C) Project. This paper is part of a C20C intercomparison of key climate time series. Whereas on the interannual timescale there is modest skill in reproducing the observed IMR variability, on decadal timescale the skill is much larger. It is shown that the decadal IMR variability is largely forced, most likely by tropical sea surface temperatures (SSTs), but as well by extratropical and especially Atlantic Multidecadal Oscillation (AMO) related SSTs. In particular there has been a decrease from the late 1950s to the 1990s that corresponds to a general warming of tropical SSTs. Using a selection of control integrations from the World Climate Research Programme’s (WCRP’s) Coupled Model Intercomparison Project phase 3 (CMIP3), it is shown that the increase of greenhouse gases (GHG) in the twentieth century has not significantly contributed to the observed decadal IMR variability.

SST forcing of decadal Indian Monsoon rainfall variability

Using ensemble integrations of an Atmospheric General Circulation Model (AGCM) forced globally with observed sea surface temperature (SST) anomalies it is shown that the observed decadal variability of Indian monsoon rainfall (IMR) can be reproduced, although amplitudes are somewhat overestimated. A second AGCM ensemble forced only in the Indian Ocean region suggests that the local Indian Ocean SST forcing is contributing significantly to the decadal IMR variability. Here, cold (warm) equatorial SSTs cause low‐level divergence (convergence) that in turn modifies the local Hadley circulation and strengthens (weakens) the Indian monsoon circulation. This result is complementary to previous findings that IMR variability is mainly determined by an atmospheric teleconnection with ENSO.

Indian Monsoon Variability in a Global Warming Scenario

The Intergovernmental Panel on Climate Change (IPCC) constituted by the World Meteorological Organisation provides expert guidance regarding scientific and technical aspects of the climate problem. Since 1990 IPCC has, at five-yearlyintervals, assessedand reported on the current state of knowledge and understanding of the climate issue. These reports have projected the behaviour of the Asian monsoon in the warming world. While the IPCC Second Assessment Report (IPCC, 1996) on climate model projections of Asian/Indian monsoon stated ``Most climate models produce more rainfall over South Asia in a warmer climate with increasing CO2'', the recent IPCC (2001) Third Assessment Report states ``It is likely that the warming associated with increasing greenhouse gas concentrations will cause an increase in Asian summer monsoon variability and changes in monsoon strength.'' Climate model projections(IPCC, 2001) also suggest more El Nino – like events in the tropical Pacific, increase in surface temperatures and decrease in the northern hemisphere snow cover. The Indian Monsoon is an important component of the Asian monsoon and its links with the El Nino Southern Oscillation (ENSO) phenomenon, northern hemisphere surface temperature and Eurasian snow are well documented. In the light of the IPCC globalwarming projections on the Asian monsoon, the interannual and decadal variability in summer monsoon rainfall over India and its teleconnections have been examined by using observed data for the 131-year (1871–2001) period. While the interannual variations showyear-to-year random fluctuations, thedecadal variations reveal distinct alternate epochs of above and below normal rainfall. The epochs tend to last for about three decades. There is no clear evidence to suggest that the strength and variability of the Indian Monsoon Rainfall (IMR) nor the epochal changes are affected by the global warming. Though the 1990s have been the warmest decade of the millennium(IPCC, 2001), the IMR variability has decreased drastically. Connections between the ENSO phenomenon, Northern Hemisphere surface temperature and the Eurasian snow with IMR reveal that the correlations are not only weak but have changed signs in the early 1990s suggesting that the IMR has delinked not only with the Pacific but with the Northern Hemisphere/Eurasian continent also. The fact that temperature/snow relationships with IMR are weak further suggests that global warming need not be a cause for the recent ENSO-Monsoon weakening. Observed snow depth over theEurasian continent has been increasing, which could be a result of enhanced precipitation due to the global warming.

Processes that Determine the Quasi-Biennial and Lower-Frequency Variability of the South Asian Monsoon.

The spatial and temporal structures of atmospheric circulation and SST associated with the Indian monsoon rainfall variability on quasi-biennial (2-3 year) and lower-frequency (3-7 year) time scales were investigated, using the domain-averaged Indian rainfall, the NCAR/NCEP reanalysis and Reynolds SST data. We took both time-filtering and composite analysis approaches. The results indicate that physical processes that determine the monsoon rainfall variation on the 2-3 year and 3-7 year time scales are different. The quasi-biennial variability of the monsoon is primarily determined by local processes in the Indian Ocean. Both local SST and moisture flux convergence anomalies are highly correlated with the monsoon at a lagged time of 3-6 months. It is argued that a positive SST anomaly in the Indian Ocean increases local moisture due to enhanced surface evaporation. The accumulation of these moistures leads to a strong monsoon through anomalous moisture advection by summer mean flows. The lower-frequency variability of the monsoon is primarily attributed to remote forcing mechanisms. Three possible processes may contribute to the monsoon variability on the 3-7 year time scale. The first is through the change of large-scale, east-west circulation induced by the eastern Pacific SST anomaly. The second is attributed to the effect of the SST anomaly in the Northwestern Pacific through enhanced (or suppressed) convective activity along the monsoon trough. The third is attributed to the tropical-midlatitude teleconnection-a strong north-south, land-ocean thermal contrast occurs six months prior to a wet monsoon, and it persists from the preceding winter to summer and is responsible for the monsoon intensity change.

Monsoon variability in relation to equatorial trough activity over Indian and West Pacific Oceans

Variability of Indian monsoon rainfall has been examined in relation to the convective activity of the equatorial trough over the Indian Ocean a~d the Pacific Qcean west of the International Date Line. It is found that the cyclogenesis (tropical cyclones) near the West Pacific equatorial trough is closely related to this variability through a see-saw in. convection between this ocean basin and north Indian Ocean, with period in the range 30-50 days. SST anomalies over north Indian Ocean and West Pacific Ocean can cause variability of the date of onset of monsoon and also the quantum of monsoon rainfall over India through the 30-50 day mode.

Relationships between interannual variability in the Arabian Sea and Indian summer monsoon rainfall

The interannual variability of the monthly mean upper layer thickness for the central Arabian Sea (5°N-15° N and 60° E-70° E) from a numerical model of the Indian Ocean during the period 1954–1976 is investigated in relation to Indian monsoon rainfall variability. The variability in the surface structure of the Somali Current in the western Arabian Sea is also briefly discussed. It is found that these fields show a great deal of interannual variability that is correlated with variability in Indian monsoon rainfall. Model upper layer thickness (H) is taken as a surrogate variable for thermocline depth, which is assumed to be correlated with sea surface temperature. In general, during the period 1967 to 1974, which is a period of lower than normal monsoon rainfall, the upper ocean warm water sphere is thicker (deeper thermocline which implies warmer surface water); in contrast, during the period 1954–1966, which is a period of higher than normal monsoon rainfall, the upper warm water sphere is thinner (shallower thermocline which implies cooler surface water). The filtered time series of uppper layer thickness indieates the presence of a quasi-biennial oscillation (QBO) during the wet monsoon period, but this QBO signal is conspicuously absent during the dry monsoon period.

The Relationship between Tibet-Tropical Ocean Thermal Contrast and Interannual Variability of Indian Monsoon Rainfall

Abstract During the northern summer the Tibetan Plateau is a heat source for the atmosphere, and the Equatorial Pacific Ocean Cold Tongue is a heat sink, both contributing to the thermal forcing of large-scale quasi-zonal atmospheric circulation. For the period 1954–1979 interannual variability of Indian monsoon rainfall (IM) is found to correlate highly with the thermal contrast between the Tibetan Plateau (TP) and the Equatorial Cold Tongue (ECT). An index of this thermal contrast (SLO for sea-land oscillation) is defined as the departure from the mean of the difference between the ground surface temperature of the Tibetan Plateau (Ts,) and the surface temperature of the Equatorial Cold Tongue (Tw). The interannual variability of Ts and Tw are of comparable magnitude and statistically independent of each other. The index of contrast (SLO) that contains them both correlates more strongly with Indian monsoon rainfall (0.61) than does either Ts(0.30) or Tw(0.52). The Ts and Tw each contributes about equall...