The onset of the southwest monsoon over Kerala: 1901–1980

Ananthakrishnan, R.; Soman, M. K.

doi:10.1002/joc.3370080305

Cited by 210 publications

(130 citation statements)

References 2 publications

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“…Observation indicates that the daily precipitation rate changes occur abruptly for the onset and demise, which agrees with similar findings for different regions across the Indian region and South East Asia (e.g. Ananthakrishnan and Soman, 1988;Soman and Kumar, 1993;Cook and Buckley, 2009). By applying Eqs.…”

Section: Moisture Contribution To Precipitation ((E − P ) < 0)supporting

confidence: 87%

The atmospheric branch of the hydrological cycle over the Indus, Ganges, and Brahmaputra river basins

Sorí

Nieto

Drumond

et al. 2017

Hydrol. Earth Syst. Sci.

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Abstract. The atmospheric branch of the hydrological cycle over the Indus, Ganges, and Brahmaputra river basins (IRB, GRB, and BRB respectively) in the South Asian region was investigated. The 3-dimensional model FLEXPART v9.0 was utilized. An important advantage of this model is that it permits the computation of the freshwater budget on air parcel trajectories both backward and forward in time from 0.1 to 1000 hPa in the atmospheric vertical column. The analysis was conducted for the westerly precipitation regime (WPR) (November-April) and the monsoonal precipitation regime (MPR) (May-October) in the period from 1981 to 2015. The main terrestrial and oceanic climatological moisture sources for the IRB, GRB, and BRB and their contribution to precipitation over the basins were identified. For the three basins, the most important moisture sources for precipitation are (i) in the continental regions, the land masses to the west of the basins (in this case called western Asia), the Indian region (IR), and the basin itself, and (ii) from the ocean, the utmost sources being the Indian Ocean (IO) and the Bay of Bengal (BB), and it is remarkable that despite the amount of moisture reaching the Indus and Ganges basins from land sources, the moisture supply from the IO seems to be first associated with the rapid increase or decrease in precipitation over the sources in the MPR. The technique of the composites was used to analyse how the moisture uptake values spatially vary from the sources (the budget of evaporation minus precipitation (E − P ) was computed in a backward experiment from the basins) but during the pre-onset and pre-demise dates of the monsoonal rainfall over each basin; this confirmed that over the last days of the monsoon at the basins, the moisture uptake areas decrease in the IO. The Indian region, the Indian Ocean, the Bay of Bengal, and the basins themselves are the main sources of moisture responsible for negative (positive) anomalies of moisture contribution to the basins during composites of driest (wettest) WPR and MPR.

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Section: Moisture Contribution To Precipitation ((E − P ) < 0)supporting

confidence: 87%

The atmospheric branch of the hydrological cycle over the Indus, Ganges, and Brahmaputra river basins

Sorí

Nieto

Drumond

et al. 2017

Hydrol. Earth Syst. Sci.

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“…As for rainfall, the onset phase is marked with a sharp and sustained increase in rainfall at a cluster of stations along the coast of Kerala in southern India (Ananthakrishnan and Soman, 1989;Ananthakrishnan et al, 1967;Bhaskar Rao et al, 2008;Chakraborty et al, 2006;Goswami, 2012;Rao 1976;Soman and Kumar, 1993). Remarkable changes in regional atmospheric circulation features occur around the onset time (Ananthakrishnan and Soman, 1988;Joseph et al, 1994;Krishnamurti, 1985;Pearce and Mohanty, 1984). An important phenomenon during the onset phase is a sudden increase of kinetic energy (KE) over the low-level jet (LLJ) region (55-65 • E, 5-15 • N) which is associated with a subsequent enhancement in precipitation over the monsoon region (70-110 • E, 10-30 • N) (Goswami, 2012).…”

Section: Introductionmentioning

confidence: 99%

Simulation of the Indian summer monsoon onset-phase rainfall using a regional model

et al. 2015

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Abstract. This study examines the ability of the Advanced Research WRF (ARW) regional model to simulate Indian summer monsoon (ISM) rainfall climatology in different climate zones during the monsoon onset phase in the decade 2000-2009. The initial and boundary conditions for ARW are provided from the NCEP/NCAR Reanalysis Project (NNRP) global reanalysis. Seasonal onset-phase rainfall is compared with corresponding values from 0.25 • IMD (India Meteorological Department) rainfall and NNRP precipitation data over seven climate zones (perhumid, humid, dry/moist, subhumid, dry/moist, semiarid and arid) of India to see whether dynamical downscaling using a regional model yields advantages over just using large-scale model predictions. Results show that the model could simulate the onset phase in terms of progression and distribution of rainfall in most zones (except over the northeast) with good correlations and low error metrics. The observed mean onset dates and their variability over different zones are well reproduced by the regional model over most climate zones. It has been found that the ARW performed similarly to the reanalysis in most zones and improves the onset time by 1 to 3 days in zones 4 and 7, in which the NNRP shows a delayed onset compared to the actual IMD onset times. The variations in the onset-phase rainfall during the below-normal onset (June negative) and above-normal onset (June positive) phases are well simulated. The slight underestimation of onset-phase rainfall in the northeast zone could be due to failure in resolving the wide extent of topographic variations and the associated multiscale interactions in that zone. Spatial comparisons showed improvement of pentad rainfall in both space and quantity in ARW simulations over NNRP data, as evident from a wider eastward distribution of pentad rainfall over the Western Ghats, central and eastern India, as in IMD observations. While NNRP under-represented the high pentad rainfall over northeast, east and west coast areas, the ARW captured these regional features showing improvement upon NNRP reanalysis, which may be due to the high resolution (30 km) employed. The onset-phase rainfall characteristics during the contrasting ISM of 2003 and 2009 are well simulated in terms of the variations in the strength of low-level jet (LLJ) and outgoing long-wave radiation (OLR).

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“…The twice-daily (00 and 12 UTC) reanalysis data sets produced at the NCEP with a horizontal resolution of 2.5°on a regular latitude-longitude grid are processed for the Asian summer monsoon domain (30-120°E, 15°S-45°N). Based on onset dates of the Indian summer monsoon over the southwest Kerala coast (Ananthakrishnan and Soman, 1988), we have categorized the onset phase into three subphases, viz. pre-onset, onset and post-onset periods in each annual cycle.…”

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 onset of the southwest monsoon over Kerala: 1901–1980

Cited by 210 publications

References 2 publications

The atmospheric branch of the hydrological cycle over the Indus, Ganges, and Brahmaputra river basins

The atmospheric branch of the hydrological cycle over the Indus, Ganges, and Brahmaputra river basins

Simulation of the Indian summer monsoon onset-phase rainfall using a regional model

Onset characteristics of the southwest monsoon over India

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