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

Abstract

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).

Climatic features of the Red Sea from a regional assimilative model

“…An assimilative regional model is expected to perform better than a global model, as it benefits from increased resolution and the incorporation of additional local observations. However, it may also degrade global predictions over certain areas in certain situations by amplifying biases in the global fields due to insufficient resolution and/or errors from inappropriate physics (Srinivas et al , ). To demonstrate the added values at the different stages of the adopted methodology, we computed various error statistics following Xu and Yang () and presented them in Table .…”

“…Using a similar setup for the Red Sea region, Jiang et al () reported that the 10‐km WRF configuration described well the regional features of mean seasonal wind patterns by downscaling the final (FNL) global analysis data from the National Centers for Environmental Prediction (NCEP). The efficiency of WRF has been also demonstrated by many studies (Mukhopadhyay et al , ; Srinivas et al , , ; Raju et al , , ) for downscaling and investigating the regional rainfall characteristics during Indian summer monsoon region.…”

“…The Weather Research and Forecasting (WRF) model has been proven to be a reliable tool for simulating regional climatic features via downscaling of global reanalysis fields (Lo et al, 2008;Caldwell et al, 2009;Jiang et al, 2009;Zhang et al, 2009;Dasari et al, 2014aDasari et al, , 2014bSrinivas et al, 2014Srinivas et al, , 2015Hari Prasad and Srinivas, 2015). For example, Heikkila et al (2011) demonstrated the efficiency of a two-way nested domains WRF configuration of 30-and 10-km for reducing bias in temperature and rainfall data over Norway.…”

Assessment of the weather research and forecasting model generalized parameterization schemes for advancement of precipitation forecasting in monsoon‐driven river basins

“…The subgrid-scale convective process and shallow clouds are managed by the cumulus parameterization. The Indian summer monsoon rainfall prediction using the WRF model has been found to be sensitive to the choice of convective parameterization scheme [Srinivas et al, 2015]. Many studies on the Indian summer monsoon rainfall reported that the Betts-Miller-Janjic CP scheme performs better in that region [e.g., Mukhopadhyay et al, 2010;Vaidya, 2006;Srinivas et al, 2013].…”

Sensitivity of initial‐condition and cloud microphysics to the forecasting of monsoon rainfall in South Asia

“…Numerous studies reported that the ISMR is sensitive to the choice of CP scheme (e.g. Srinivas et al, 2015;Sikder and Hossain, 2016). Many of these studies found that the Betts-Miller-Janjic (BMJ) CP scheme (Janjic, 1994) performs reasonably well in the case of ISMR (e.g.…”