Francis, T; Jayakumar, A; Sethunadh, J; Mohandas, S; Kumar, S; Rajagopal, EN (2020). Dust induced radiative perturbations during an episode of long-range dust transport over Delhi, India: a high-resolution regional NWP model study. METEOROLOGY AND ATMOSPHERIC PHYSICS.

Dust-induced modifications to the radiative fluxes/heating during a light-blocking haze episode over Delhi, India, 7-9th Nov 2017-triggered by long range transport from a severe Saudi Arabian dust storm-have been investigated with a regional NWP model, NCUM-R with prognostic dust-radiation feedbacks. The study employs 'Double Radiation Calls', wherein parallel runs of the radiation scheme 'with' (prognostic) and 'without' (diagnostic) dust radiative effects-while prognostic fields drive the forecast-isolate the dust-induced perturbations. The forecasted dust optical depth agreed spatially with the AOD from MODIS with Angstrom Exponent > 0.5, indicating that the dust was well mixed with the fine mode anthropogenic aerosols upwind. The 'downward shortwave (SW) flux' was diminished (upto - 12.9 Wm(-2)) in layers sampling (i) near-surface (L1(Avg)), (ii) well-mixed layer within the planetary boundary layer (PBL, L2(Avg)) and (iii) free-troposphere (FT, L3(Avg)). Dust-induced 'Solar heating' dominated in FT (upto 9.5 x 10(-7) Ks(-1)) and the patches below (in L2(Avg)) exhibited a cooling, leading to thermal dipoles. The 'upward longwave (LW) flux' in FT was reduced and 'LW heating' prevailed in all levels-peak (2.5 x 10(-6)Ks(-1)) in L2(Avg)-along with well-defined cooling zones in L1(Avg). The dust-radiation interaction in turn influenced the boundary layer meteorology, manifested as (i) shallow PBLs that spatially correlate with dust-induced cooling of the boundary layer column, (ii) enhanced surface humidity and (iii) reduced visibility. The study is an instance of prognostic dust-radiation feedbacks improving the skill of NWP models in dust-laden regions.