The impact of revised simplified Arakawa‐Schubert scheme on the simulation of mean and diurnal variability associated with active and break phases of Indian summer monsoon using CFSv2

Abstract

The impact of revised simplified Arakawa‐Schubert (RSAS) convective parameterization scheme in Climate Forecast System (CFS) version 2 (CFSv2) on the simulation of active and break phases of Indian summer monsoon (ISM) has been investigated. The results revealed that RSAS showed better fidelity in simulating monsoon features from diurnal to daily scales during active and break periods as compared to SAS simulation. Prominent improvement can be noted in simulating diurnal phase of precipitation in RSAS over central India (CI) and equatorial Indian Ocean (EIO) region during active periods. The spatial distribution of precipitation largely improved in RSAS simulation during active and break episodes. CFSv2 with SAS simulation has noticeable dry bias over CI and wet bias over EIO region which appeared to be largely reduced in RSAS simulation during both phases of the intraseasonal oscillation (ISO). During active periods, RSAS simulates more realistic probability distribution function (PDF) in good agreement with the observation. The relative improvement has been identified in outgoing longwave radiation, monsoon circulations, and vertical velocities in RSAS over SAS simulation. The improvement of rainfall distribution appears to be contributed by proper simulation of convective rainfall in RSAS. CFSv2 with RSAS simulation is able to simulate observed diurnal cycle of rainfall over CI. It correctly reproduces the time of maximum rainfall over CI. It is found that the improved feedback between moisture and convective processes in RSAS may be attributed to its improved simulation. Besides improvement, RSAS could not reproduce proper tropospheric temperature, cloud hydrometeors over ISM domain which shows the scope for future development.

Performance of a very high-resolution global forecast system model (GFS T1534) at 12.5 km over the Indian region during the 2016–2017 monsoon seasons

“…In order to gain further insight into the precipitation and moisture processes over the core CI region (18 • −27 • N and 74 • −85 • E), we have analysed the vertical profile of RH as a function of the rain rate during JJAS of 2016-2017 (figure 10). This metric has been proved to be useful to look into the model moist dynamic processes (Thayer-Calder and Randall 2009;Ganai et al 2016;Abhik et al 2017). It is evident that for all lead times, the model is able to capture the vertical pattern of rainfall and RH pattern broadly.…”

“…Another important aspect of the model is the diurnal rainfall variation, namely, the diurnal phase and the diurnal absolute amplitude (figure 11a and b). The definition of the diurnal phase is that the local solar time when the maximum precipitation occurs in a day (Ganai et al 2016). Diurnal absolute amplitude is defined as the difference between maximum rainfall and minimum rainfall in a day (Ganai et al 2016).…”

“…The definition of the diurnal phase is that the local solar time when the maximum precipitation occurs in a day (Ganai et al 2016). Diurnal absolute amplitude is defined as the difference between maximum rainfall and minimum rainfall in a day (Ganai et al 2016). GFS T1534 captures the diurnal phase reasonably except over the region of NWI in all lead times.…”

Simulation of summer precipitation diurnal cycles over the Tibetan Plateau at the gray-zone grid spacing for cumulus parameterization

“…Among them, Grell and NSAS are non-scale-aware but have shown good performance in simulating summer precipitation over Asia (e.g. Ganai et al 2016;Yang et al 2019).…”

Revised cloud processes to improve the mean and intraseasonal variability of Indian summer monsoon in climate forecast system: Part 1

“…Ganai et al . [] employed the revised SAS scheme for long simulations in CFS and showed that the performance of the model improves in simulating diurnal variability and mean climate during the boreal summer. However, the ratio between convective and large‐scale rainfall over global tropics did not show any improvement.…”