Sensitivity of the Monsoon Onset to Differential Heating

Krishnamurti, T. N.; Ramanathan, Y.

doi:10.1175/1520-0469(1982)039<1290:sotmot>2.0.co;2

Cited by 166 publications

(77 citation statements)

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“…Also, the kinetic energy increases at the lower levels over the Bay of Bengal and the Indian peninsular region during the onset phase. This is in good agreement with the findings of earlier results (Krishnamurti and Ramanathan, 1982;Pearce and Mohanty, 1984;Ramesh et al, 1996). Although, significant changes are noticed over these regions, the Arabian Sea region has a higher magnitude of kinetic energy following the onset of the monsoon.…”

Section: Evolution Of Summer Monsoonsupporting

confidence: 93%

“…However, the net moisture build up over the Arabian Sea is accompanied by a fall/no change in net moisture after a certain amount of increase in net moisture (43 mm). This characteristic decrease in net moisture is due to the transient convective activity that is organized and developed in association with local meso/synoptic-scale systems (Krishnamurti and Ramanathan, 1982;Pearce and Mohanty, 1984). The diabatic heating pattern shows an increase in convective activity during the onset phase over the Arabian Sea, Bay of Bengal and Indian landmass.…”

Section: Evolution Of Summer Monsoonmentioning

confidence: 97%

“…These include the northward displacement of upper tropospheric westerly flow to the north of the Himalayas, establishment of the upper tropical easterly jet (TEJ) stream (Koteswaram, 1958) and lower tropospheric westerly jet (Somali jet) over the Arabian Sea (Findlater, 1969). The intensification of the monsoon flow is mainly dictated by the release of convective instability and tropospheric diabatic heating (Krishnamurti and Ramanathan, 1982;Mohanty et al, 1983;Pearce and Mohanty, 1984;Rao and Aksakal, 1994). Studies by Soman (1988, 1989) and Soman and Krishnakumar (1993) documented the climatological structure of the meteorological fields associated with the onset phase of the summer monsoon.…”

Section: Introductionmentioning

confidence: 99%

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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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Section: Evolution Of Summer Monsoonsupporting

confidence: 93%

Section: Evolution Of Summer Monsoonmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

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Onset characteristics of the southwest monsoon over India

2005

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“…Many previous studies have described features of the vortex, including the distribution of precipitation and the vortex structure (e.g., Pisharoty and Asnani 1957;Rao and Rajamani 1970;Sharma and Srinivasan 1971). Subsequent studies suggested that barotropic instability associated with horizontal wind shear leads to the formation of the vortex, and that diabatic heat supplies the energy to the vortex required for its development (Krishnamurti 1981(Krishnamurti , 1985Krishnamurti and Ramanathan 1982;Krishnamurti et al 1981). Mak and Kao (1982) found that vertical wind-shear and baroclinic instability play an important role in the development of the vortex.…”

Section: Introductionmentioning

confidence: 99%

Air–sea interaction and formation of the Asian summer monsoon onset vortex over the Bay of Bengal

Guan

Liu

et al. 2011

Clim Dyn

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In spring over the southern Bay of Bengal (BOB), a vortex commonly develops, followed by the Asian summer monsoon onset. An analysis of relevant data and a case study reveals that the BOB monsoon onset vortex is formed as a consequence of air-sea interaction over BOB, which is modulated by Tibetan Plateau forcing and the land-sea thermal contrast over the South Asian area during the spring season. Tibetan Plateau forcing in spring generates a prevailing cold northwesterly over India in the lower troposphere. Strong surface sensible heating is then released, forming a prominent surface cyclone with a strong southwesterly along the coastal ocean in northwestern BOB. This southwesterly induces a local offshore current and upwelling, resulting in cold sea surface temperatures (SSTs). The southwesterly, together with the near-equatorial westerly, also results in a surface anticyclone with descending air over most of BOB and a cyclone with ascending air over the southern part of BOB. In the eastern part of central BOB, where sky is clear, surface wind is weak, and ocean mixed layer is shallow, intense solar radiation and low energy loss due to weak surface latent and sensible heat fluxes act onto a thin ocean layer, resulting in the development of a unique BOB warm pool in spring. Near the surface, water vapor is transferred from northern BOB and other regions to southeastern BOB, where surface sensible heating is relatively high. The atmospheric available potential energy is generated and converted to kinetic energy, thereby resulting in vortex formation. The vortex then intensifies and moves northward, where SST is higher and surface sensible heating is stronger. Meanwhile, the zonal-mean kinetic energy is converted to eddy kinetic energy in the area east of the vortex, and the vortex turns eastward. Eventually, southwesterly sweeps over eastern BOB and merges with the subtropical westerly, leading to the onset of the Asian summer monsoon.

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“…Formation of the monsoon onset vortex (Krishnamurti et al, 1981) in the southeast AS was investigated with summer MONEX-1979 data. Diagnostic models have also been used to understand the dynamics of monsoon onset (Krishnamurti and Ramanathan, 1982). Dynamical instability associated with monsoon onset was examined by Mishra et al (1985).…”

Section: Onset Of Monsoon Over Keralamentioning

confidence: 99%

Dynamical simulation of Indian summer monsoon circulation, rainfall and its interannual variability using a high resolution atmospheric general circulation model

Ratna

Sikka

Dalvi

et al. 2011

Intl Journal of Climatology

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This paper discusses the simulations of Indian summer monsoon (ISM) using a high-resolution National Center for Environmental Prediction (NCEP) T170/L42 model for a 20-year period (1985)(1986)(1987)(1988)(1989)(1990)(1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004) with observed Sea Surface Temperature (SSTs) as boundary conditions and using five initial conditions in the first week of May. Good agreement is found between the observed and simulated climatologies. Interannual variability (IAV) of the ISM rainfall as simulated in individual ensemble members and as provided by ensemble average shows that the two series are found to agree well; however, the simulation of the actual observed year-to-year variability is poor. The model simulations do not show much skill in the simulation of drought and excess monsoon seasons. One aspect which has emerged from the study is that where dynamical seasonal prediction has specific base for the large areal and temporal averages, the technique is not to be stretched for application on short areal scale such as that of a cluster of a few grid point. Monsoon onset over Kerala (MOK) coast of India and advance from Kerala coast to northwest India is discussed based on ensemble average and individual ensemble member basis. It is suggested that the model is capable of realistically simulating these processes, particularly if ensemble average is used, as the intermember spread in the ensemble members is large. In short, the high-resolution model appears to provide better climatology and its magnitude of IAV, which compares favourably with observations, although year-to-year matching of the observed and simulated seasonal/monthly rainfall totals for India as a whole is not good.

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Sensitivity of the Monsoon Onset to Differential Heating

Cited by 166 publications

References 0 publications

Onset characteristics of the southwest monsoon over India

Onset characteristics of the southwest monsoon over India

Air–sea interaction and formation of the Asian summer monsoon onset vortex over the Bay of Bengal

Dynamical simulation of Indian summer monsoon circulation, rainfall and its interannual variability using a high resolution atmospheric general circulation model

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