Developed a climate modeling framework for India

A better representation of the poorly understood sub-grid scale processes in the Global Circulation Model is imperative for the skilful simulation of the Indian Summer Monsoon (ISM). We customized the parametrizations for deep convection, gravity wave, and surface layer; incorporated them into the NCAR Community Atmosphere Model 5.0 (NCAR CAM5, base model). The modified deep convective parametrization includes dynamic tau (dynamic convective adjustment timescale), which allows a spatiotemporally varying tau instead of constant tau and the stochastic entrainment rate in place of a fixed entrainment rate. Similarly, the modified gravity wave parametrization facilitates estimating the response of upper-level gravity wave drag induced from secondary sources. Likewise, the modified surface layer parametrization enables a better representation of near-surface variables as well as surface fluxes. The simulations of default and customized NCAR CAM5 have been carried out for eleven years (one year for spin-up and the rest ten years considered for analysis). The analysis has been performed for two major climate change indicators, i.e., temperature and precipitation for the ISM season (June to September). The model simulated near-surface temperature and precipitation during ISM were evaluated against observation (Indian Meteorological Department). A significant improvement has been noted in simulating the total precipitation pattern and magnitude over India, as well as for surface air temperature, particularly over northern India. In addition, based on performance, the customized model alleviates some of the long-standing biases evident in the default NCAR CAM5 simulation over India. Furthermore, compared to the base model, the customized model realistically simulates the annual cycle of precipitation, medium and extreme precipitation rates, meridional tropospheric temperature gradient, upper (200 hPa) and lower (850 hPa) tropospheric winds, Madden Julian Oscillation, and equatorial waves. The study’s findings illustrate the significance of model parametrizations towards improving the ISM simulation. Meanwhile, the modeling framework would be essential for credible future climate projections of India and would become a vital tool for policymakers and diverse stakeholders.

Keywords: Indian Summer Monsoon, NCAR CAM5, Deep convection, Gravity wave, Surface layer