The contrasting features of Asian summer monsoon during surplus and deficient rainfall over India

Raju, P. V. S.; Mohanty, U. C.; Rao, P. L. S.; Bhatla, R.

doi:10.1002/joc.855

Cited by 23 publications

(11 citation statements)

References 27 publications

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“…Saji and Yamagata (2003a) confirmed that the IOD affects the ISMR. Raju et al (2002) stressed the role of Western Indian warming during the positive IOD event in the modulation of the ISMR. In another recent study, Ashok et al (2004a) showed, by use of observed datasets and an AGCM, the importance of the western pole of the IOD in modulating the rainfall over the northwest regions of India and neighboring Pakistan, and in reducing the impact of ENSO on Indian summer rainfall.…”

Section: Introductionmentioning

confidence: 99%

On the impacts of ENSO and Indian Ocean dipole events on sub-regional Indian summer monsoon rainfall

2007

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The relative impacts of the ENSO and Indian Ocean dipole (IOD) events on Indian summer (June-September) monsoon rainfall at sub-regional scales have been examined in this study. GISST datasets from 1958 to 1998, along with Willmott and Matsuura gridded rainfall data, all India summer monsoon rainfall data, and homogeneous and sub-regional Indian rainfall datasets were used. The spatial distribution of partial correlations between the IOD and summer rainfall over India indicates a significant impact on rainfall along the monsoon trough regions, parts of the southwest coastal regions of India, and also over Pakistan, Afghanistan, and Iran. ENSO events have a wider impact, although opposite in nature over the monsoon trough region to that of IOD events. The ENSO (IOD) index is negatively (positively) correlated (significant at the 95% confidence level from a two-tailed Student t-test) with summer monsoon rainfall over seven (four) of the eight homogeneous rainfall zones of India. During summer, ENSO events also cause drought over northern Sri Lanka, whereas the IOD events cause surplus rainfall in its south. On monthly scales, the ENSO and IOD events have significant impacts on many parts of India. In general, the magnitude of ENSO-related correlations is greater than those related to the IOD. The monthly-stratified IOD variability during each of the months from July to September has a significant impact on Indian summer monsoon rainfall variability over different parts of India, confirming that strong IOD events indeed affect the Indian summer monsoon.

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Section: Introductionmentioning

confidence: 99%

On the impacts of ENSO and Indian Ocean dipole events on sub-regional Indian summer monsoon rainfall

2007

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“…It provided for the first time a unique database to examine climate variability of circulation features and energetics of the monsoon. Recent studies (ANNAMALAI et al, 1999;SPERBER et al, 2000;RAJU et al, 2002) conducted making use of the NCEP reanalysis, confirm the usefulness of these data sets. As a result, understanding the dynamical mechanisms of the monsoon variability in time-scales ranging from weeks to years is an issue of considerable importance.…”

Section: Introductionmentioning

confidence: 81%

“…162, 2005 Climatological Features of the Asian Summer Monsoon 1517 (1997). Further, RAJU et al (2002) stated that on a seasonal scale the NCEP precipitation appears to be reliable as regards the distribution of rainfall over India.…”

Section: Precipitation Olr and Net Tropospheric Moisturementioning

confidence: 99%

A Study on Climatological Features of the Asian Summer Monsoon: Dynamics, Energetics and Variability

Mohanty

Raju

Bhatla

2005

Pure appl. geophys.

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A continuing goal in the diagnostic studies of the atmospheric general circulation is to estimate various quantities that cannot be directly observed. Evaluation of all the dynamical terms in the budget equations for kinetic energy, vorticity, heat and moisture provide estimates of kinetic energy and vorticity generation, diabatic heating and source/sinks of moisture. All these are important forcing factors to the climate system. In this paper, diagnostic aspects of the dynamics and energetics of the Asian summer monsoon and its spatial variability in terms of contrasting features of surplus and deficient summer monsoon seasons over India are studied with reanalysis data sets. The daily reanalysis data sets from the National Centre for Environmental Prediction/National Centre for Atmospheric Research (NCEP/ NCAR) are used for a fifty-two year period to investigate the large-scale budget of kinetic energy, vorticity, heat and moisture. The primary objectives of the study are to comprehend the climate diagnostics of the Asian summer monsoon and the role of equatorial convection of the summer monsoon activity over India.It is observed that the entrance/exit regions of the Tropical Easterly Jet (TEJ) are characterized by the production/destruction of the kinetic energy, which is essential to maintain outflow/ inflow prevailing at the respective location of the TEJ. Both zonal and meridional components contribute to the production of kinetic energy over the monsoon domain, though the significant contribution to the adiabatic generation of kinetic energy originates from the meridional component over the Bay of Bengal in the upper level and over the Somali Coast in the low level. The results indicate that the entire Indian peninsula including the Bay of Bengal is quite unstable during the summer monsoon associated with the production of vorticity within the domain itself and maintain the circulation. The summer monsoon evinces strong convergence of heat and moisture over the monsoon domain. Also, considerable heat energy is generated through the action of the adiabatic process. The combined effect of these processes leads to the formation of a strong diabatic heat source in the region to maintain the monsoon circulation. The interesting aspect noted in this study is that the large-scale budgets of heat and moisture indicate excess magnitudes over the Arabian Sea and the western equatorial Indian Ocean during surplus monsoon. On the other hand, the east equatorial Indian Ocean and the Bay of Bengal region show stronger activity during deficient monsoon. This is reflected in various budget terms considered in this study.

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“…The budget equations are obtained from the prognostic and diagnostic equations of an atmospheric model based on simple mathematical transformations and represented in flux form with pressure as the vertical coordinate (Raju et al, 2002). In this study, the time-mean large-scale balance equations are bifurcated into stable mean and transient eddy parts.…”

Section: Methodsmentioning

confidence: 99%

Onset characteristics of the southwest monsoon over India

2005

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Dynamic and thermodynamic characteristics of the Asian summer monsoon during the onset phase over the Indian Peninsula (Kerala coast) and its variability are examined with reanalysis data sets. For this study, daily averaged (0000 and 1200 UTC) reanalysis data sets of National Centre for Environmental Prediction-National Centre for Atmospheric Research for the period 1948-99 are used.Based on 52 years of onset dates of the Indian summer monsoon, we categorized pre-onset, onset and post-onset periods (each averaged 5 days) to investigate the mean circulation characteristics and the large-scale energetics of the Asian summer monsoon. It is found that the strength of the low-level Somali jet and upper tropospheric tropical easterly jet increase rapidly during the time of evolution of the summer monsoon over India. Over the Bay of Bengal and the Arabian Sea, predominant changes are noticed in the large-scale balances of kinetic energy, heat and moisture from the pre-onset to the post-onset periods. Prior to the onset of the summer monsoon over India, a zone of flux convergence of heat and moisture is noticed over the eastern sector of the Bay of Bengal and this intensifies in the onset and postonset periods. During onset of the monsoon over India, the horizontal flux convergence of heat and moisture, as well as diabatic heating, are enhanced over the Arabian Sea. These subsequently increase with the evolution and advancement of the monsoon over India.Further, the dynamics of the evolution processes (15 days before and 30 days after the onset date of the monsoon over Kerala for each annual cycle) are studied over various sectors, such as the Arabian Sea, Bay of Bengal and Indian Peninsula region. The study reveals that the low-level kinetic energy, vertically integrated generation of kinetic energy and net tropospheric moisture over Arabian Sea can be used as potential predictors for the prediction of the possible onset date of the summer monsoon over the Indian Peninsula.

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The contrasting features of Asian summer monsoon during surplus and deficient rainfall over India

Cited by 23 publications

References 27 publications

On the impacts of ENSO and Indian Ocean dipole events on sub-regional Indian summer monsoon rainfall

On the impacts of ENSO and Indian Ocean dipole events on sub-regional Indian summer monsoon rainfall

A Study on Climatological Features of the Asian Summer Monsoon: Dynamics, Energetics and Variability

Onset characteristics of the southwest monsoon over India

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