Projected Changes in Semi Permanent Systems of Indian Summer Monsoon in CORDEX-SA Framework

The semi-permanent systems such as Seasonal Heat Low (HL), Monsoon Trough (MT), Tibetan Anticyclone (TA), Tropical Easterly Jet (TEJ) and Low Level Jet (LLJ) or Somali jet are observed over Indian region during Indian summer monsoon season (June through September). These systems play a vital role in defining the strength of the Indian summer monsoon rainfall as a whole. Here we evaluate the ability of Consortium for Small-Scale Modeling (COSMO) regional Climate Model (COSMO-CLM), a high resolution regional climate model within the Coordinated Regional Climate Downscaling Experiment for South Asia (CORDEX-SA) framework, to simulate these systems of Indian summer monsoon. The historical runs of the COSMO-CLM for the period 1951-2000 are analysed. Overall the COSMO-CLM is able to simulate these components reasonably well. Possible changes in the position and the strength of these systems and their role in changing rainfall pattern over India are examined to assess the impact of global warming, under the RCP 4.5 simulations towards the end of the century (2051-2100). The analysis shows that the semi permanent systems may not strengthen in the future as compared to the present climate. The summer monsoon rainfall does not show uniform changes over the region. It is likely to enhance over the southern parts of the country, south of 20?S while it is projected to decrease in the northern parts under the global warming scenario

Spatial variability of intra-seasonal oscillations during extreme indian monsoons

The intra-seasonal variability of the Indian monsoon rainfall plays a dominant role in deciding the seasonal strength of the monsoon. The Indian monsoon is known to exhibit two dominant periodicities of intra-seasonal oscillations (ISOs) 30–60 days and 10–20 days on the spatial scale of entire landmass. In this paper the nature and intensity of these dominant periodicities have been studied on smaller spatial domains during all-India deficient and excess monsoons. The high resolution data 1° × 1° latitude/longitude over Indian domain for the recent period of 1951–2003 provided by India Meteorological Department have been used in this analysis. The multi-taper spectrum analysis (MTMA) method has been applied to identify the periodicities over four representative regions. The 30–60 days periodicity is dominant over west coast and South-east India during deficient monsoons while the excess monsoons are characterized by high frequency oscillations. The time variation of these periodicities is studied by applying wavelet transforms (WTs).During deficient Indian monsoons coherent regions with dominant oscillations are observed. Empirical Orthogonal Function (EOF) analysis reveals that both the oscillations have weakened after mid 1970s. Implications of this on forecasting Indian monsoon are discusse

Association between extreme monsoons and the dipole mode over the Indian subcontinent

The relationship of summer monsoon over India with the Indian Ocean Dipole Mode has been investigated applying simple statistical techniques. While a long time series of 132 years based on 1871-2002 for both summer monsoon rainfall as well as dipole mode index has been used in this study, the NCEP-NCAR reanalysis data (1948-2002) are used to examine the circulation features associated with the extreme dipole and monsoon phases. These flow patterns bring out the dynamics of the dipole - monsoon relationship. Lead/lag correlations between the dipole mode index and the Indian monsoon rainfall are computed. Results reveal that numerically the relationship is stronger following the monsoon. The lower troposphere flow patterns at 850-hPa associated with the extreme phases of the dipole and monsoon are consistent with the correlation analysis. Further a strong (weak) summer monsoon favours the development of the negative (positive) dipole event in autumn. The sliding correlations between Indian monsoon rainfall and the dipole mode index suggest that the impact of monsoon over dipole is weakening after 1960s. This weakening relationship has been evidenced by the composites of sea-surface temperature anomalies and circulation patterns. All the above analysis suggests that the summer monsoon has more influence on the dipole mode than vice-a-versa

Western Himalayan snow cover and Indian monsoon rainfall: A re-examination with INSAT and NCEP/NCAR data

This study presents the monthly climatology and variability of the INSAT (Indian National Satellite) derived snow cover estimates over the western Himalayan region. The winter/spring snow estimates over the region are related to the subsequent summer monsoon rainfall over India. The NCEP/NCAR data are used to understand the physical mechanism of the snow-monsoon links. 15 years (1986-2000) of recent data are utilized to investigate these features in the present global warming environment. Results reveal that the spring snow cover area has been declining and snow has been melting faster from winter to spring after 1993. Connections between snow cover estimates and Indian monsoon rainfall (IMR) show that spring snow cover area is negatively related with maximum during May, while snow melt during the February-May period is positively related with subsequent IMR, implying that smaller snow cover area during May and faster snow melt from winter to spring is conducive for good monsoon activity over India. NCEP/NCAR data further shows that the heat low over northwest India and the monsoon circulation over the Indian subcontinent, in particular the cross-equatorial flow, during May are intensified (weakened) when the snow cover area during May is smaller (extensive) and snow melts faster (slower) during the February-May period. The well-documented negative relationship between winter snow and summer rainfall seems to have altered recently and changed to a positive relationship. The changes observed in snow cover extent and snow depth due to global warming may be a possible cause for the weakening winter snow-IMR relationship

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-yearly intervals, assessed and 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 global warming 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 show year-to-year random fluctuations, the decadal 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 the Eurasian continent has been increasing, which could be a result of enhanced precipitation due to the global warming

Extreme monsoons over East Asia: Possible role of Indian Ocean Zonal Mode

The influence of the Indian Ocean Zonal Mode on the extreme summer monsoon rainfall over East Asia (China, Korea, Japan) has been investigated applying simple statistical techniques of correlation and composite analysis. While the observed rainfall data are used as a measure of rainfall activity, the NCEP-NCAR Reanalysis data are used to examine the circulation features associated with the extreme monsoon phases and the dynamics of the zonal mode- monsoon variability connections. The data used covers the period 1960 to 2000. The equatorial Indian Ocean is dominated by westerly winds blowing towards Indonesia. However, during the positive phase of the zonal mode, an anomalous, intensified easterly flow prevails, consistent with the positive (negative) sea surface temperature anomalies over the western (southeastern) equatorial Indian Ocean. This positive phase of the zonal mode enhances summer monsoon activity over China, but suppresses the monsoon activity over the Korea-Japan sector, 3 to 4 seasons later. The relationship is more consistent and stronger over the Korea-Japan region than over China. The Indian Ocean influences the monsoon variability over East Asia via the northern hemisphere mid-latitudes or via the eastern Indian Ocean/west Pacific route. The monsoon-desert mechanism induces strong subsidence northwest of India due to the anomalous convection over the Indian Ocean region associated with the positive phase of the zonal mode. This induces a zonal wave pattern over the mid-latitudes of Asia propagating eastwards and displacing the north Pacific subtropical high over East Asia. The warming over the eastern Indian Ocean/west Pacific inhibits the westward extension of the north Pacific sub-tropical high. The location and shape of this high plays a dominant role in the monsoon variability over East Asia. The memory for delayed impact, three to four seasons later, could be carried by the surface boundary conditions of Eurasian snow cover via the northern channel or the equatorial SSTs near the Indonesian Through Flow via the southern channel

Projected changes in mean and extreme precipitation indices over India using PRECIS

The impact of global warming on the characteristics of mean and extremes of rainfall over India is investigated using a high resolution regional climate model PRECIS developed by Hadley Centre, UK. Five simulations of PRECIS made using the lateral boundary conditions from a suite of Perturbed Physics Ensembles (PPE) generated using Hadley Center Coupled Model (HadCM3) for Quantifying Uncertainty in Model Predictions (QUMP) project corresponding to IPCC A1B emission scenario have been analyzed here for this purpose. The projected changes depict seasonally dependent fine scale structure in response to the topographic forcing and changes in circulation, especially along the west coast and North East (NE) region of India towards the end of the 21st century i.e. 2080s (2071-2098). Analysis of the extreme precipitation indices indicates an increase in the intensity of rainfall on wet days towards 2080s under A1B scenario. Changes in extreme precipitation events and dry spells suggest not only shifts, but also a substantial increase in the spread of the precipitation distribution, with an increased probability of the occurrence of events conducive to both floods and droughts. The projected changes in various precipitation extremes show a large regional variability. Total rainfall on very heavy rainy days (R95p) is projected to increase by around 40-50 over the central parts of the country. The number of rainy days >. 10. mm (R10) may increase by 10-20 over west coast, east central India and northeastern parts while over northwest and rain shadow region they may increase by 40-50. The consecutive dry days (CDDs) may decrease by 10-20 over Indo-Gangetic plain, however over west coast there may not be any significant change. The CDDs are projected to rise by 10-20 over west central and peninsular India. The precipitation per wet day (SDII) may be more intense by 10-40 over the entire land mass, however there may not be any significant change over south peninsular India