Comprehensive assessment of RegCM4 towards interannual variability of
Indian Summer Monsoon using multi-year simulations
Abstract
In this study, the Interannual variability (IAV) of Indian Summer
Monsoon (ISM) is investigated using multi-year (1982‒2016) seasonal
scale simulations (May‒September) of the regional climate model RegCM4
developed by International Center for Theoretical Physics, Italy. Model
simulated fields such as surface temperature, wind and rainfall are
validated initially to testify the climatological behaviour of ISM.
Subsequently, different aspects of IAV associated with ISM are discussed
primarily focusing on model simulated rainfall and are verified against
high resolution rainfall analysis from India Meteorological Department
(IMD). Empirical Orthogonal Function (EOF) analysis technique is also
applied to identify the leading modes of IAV. Analysis indicated that
RegCM4 shows reasonable accuracy in simulating major large scale
features, however, has cold bias over entire India and wet (dry) bias
over northwest and peninsular (central) India. Easterly (westerly) bias
is noticed in the model simulated low (upper) level wind that affects
regional Hadley circulation. The model bias is found to be associated
with the feedback cycle of land-atmosphere interaction. Surface
evaporative cooling likely affects the instability in the atmospheric
column, thereby limiting the convection and thus reducing rainfall.
While categorizing, it is noticed that the deficit, normal and excess
rainfall years in the model simulation agrees well with the IMD
observation for about half of the study period, however, the normal
years are relatively better reproduced by the model than the extreme
years (deficit and excess). EOF analysis revealed that first two leading
modes of IMD rainfall are linked with large scale variabilities viz.,
El-Nino southern oscillation and Indian ocean dipole respectively but
RegCM4 could not well reproduce these relationships. Eventhough, the
model showed spectral peaks for 2‒7 years periodicity, these peaks are
very close to the red noise spectrum due to their weak power which
indicated the model’s limitation in capturing large scale variability.
Overall, this study suggests that the RegCM4 could capture the
climatological features of ISM fairly well, but needs further
improvement in representing the IAV more accurately.
Note: This manuscript is published in Theoretical and Applied Climatology. https://doi.org/10.1007/s00704-022-03961-5