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

Abstract

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.

Performance of cumulus parameterization schemes in the simulation of Indian Summer Monsoon using RegCM4

“…KUO and GRELL produce significantly weaker (5-8 m s -1 ) winds over the entire model domain. Raju et al (2010) and Mohanty et al (2005). This indicates that the model with the above mentioned schemes could be able to simulate the differences in wind magnitudes during contrasting monsoon years.…”

“…Due to its large impact on Indian economy, the ISM has been an important topic of research for more than a century now. Numerous studies have been conducted to understand the mechanism and physical processes (i.e., large scale circulation processes) of the ISM (Shukla and Paolino, 1983;Shukla and Fennessy, 1994;Bhaskaran et al, 1996;Goswami et al, 1998;Webster et al, 1998;Lal et al, 2000;Zhou and Li, 2002;Mohanty et al, 2002Mohanty et al, , 2005Kang et al, 2002;Rao et al, 2004;Singh et al, 2007;Raju et al, 2010;Zhou, 2013, 2014;Zhu, 2015;Almazroui et al, 2016). However, convection plays an important role in the development and maintenance of the ISM through the release of latent heat and vertical transport of heat, moisture and momentum (Ghosh et al, 1978;Kain, 1993;Zhu, 2015).…”

Influence of North Atlantic Oscillation on Indian Summer Monsoon Rainfall in Relation to Quasi-Binneal Oscillation

“…Indian summer Monsoon (ISM) is an active and most efficient branch of the Asian monsoon system. It is always of utmost concern of climate scientists to understand the relation of a particular climatic feature with different parameters (MOHANTY et al 2005;BHATLA et al 2016), located far away from the location of interest, which is also known as teleconnection. The Indian Summer Monson Rainfall (ISMR) has always been affected by some remotely located parameters at different spatial and temporal scales.…”

Reversal nature in rainfall pattern over the Indian heavy and low rainfall zones in the recent era

“…Previously, many attempts have been made to understand the year-to-year variability of ISMR (Krishnamurti et al, 1998;Goswami and Mohan, 2001;Mohanty et al, 2005;Mishra et al, 2012;Sinha et al, 2013;Walker et al, 2015). The major concern in the variation of the ISMR is that its spatiotemporal distribution is non-uniform, hence it's variability is independent of latitude or longitude.…”