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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 33, issue 9
Ann. Geophys., 33, 1097–1115, 2015
https://doi.org/10.5194/angeo-33-1097-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 33, 1097–1115, 2015
https://doi.org/10.5194/angeo-33-1097-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.

Regular paper 11 Sep 2015

Regular paper | 11 Sep 2015

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

C. V. Srinivas1, D. Hari Prasad2, D. V. Bhaskar Rao3, R. Baskaran1, and B. Venkatraman1 C. V. Srinivas et al.
  • 1Radiological Safety Division, Radiological Safety {&} Envrionment Group, Indira Gandhi Centre for Atomic Research, Kalpakkam 603102, India
  • 2Physical Sciences and Engineering Division, King Abdullah University of Science and Technology, Thuwal, Saudi Arabia
  • 3Centre for Atmospheric Science, KL University, Vaddeswaram 522502, AP, India

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 Indian summer monsoon rainfall climatology during the monsoon onset phase in different climate zones is simulated using the regional model ARW for the decade 2000-2009, using NNRP global reanalysis. Comparisons with IMD & NNRP rainfall 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, and improves the onset time by 1-3 days in zones 4 and 7 over NNRP.
The Indian summer monsoon rainfall climatology during the monsoon onset phase in different...
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