Ghosh, S., A. J. Miller, A. C.
Subramaniam, R. Bhatla and S. Das, 2023:
Signals of northward propagating Monsoon Intraseasonal Oscillations (MISO) in the
RegCM4.7 CORDEX-CORE simulation over South Asia domain.
Climate Dynamics, 61, 3237-3251.
Abstract.
Northward propagating summer monsoon intraseasonal oscillations
(MISOs) in the Indian Ocean region remain poorly understood and
difficult to predict. Here we examine a free-running high-resolution
regional atmospheric model (RegCM4.7 with 25km resolution), forced
distantly at the boundaries by atmospheric observations (ERA-Interim,
0.75.) and forced locally by observed SST over the period 1979-
2016, to assess its ability to reproduce key aspects of these MISOs.
We find that the model MISO exhibits spatial structures and northward
propagation characteristics broadly similar to observed MISO
when confining the analysis to the 25-90 day period band. The MISO
precipitation anomalies are then shown to be consistent with previously
known observed relationships to broad-scale sea-level pressure
patterns, ITCZ positioning, and changes in the regional Hadley Cell
component. The total simulated seasonal (JJAS) rainfall anomalies over
India are not significantly correlated with observations, indicating that
intrinsic variations in the regional model atmosphere dominate most
of the precipitation variability. However, the bandpass-filtered MISO
anomalies surprisingly exhibit a significant correlation (0.61) with observations.
This suggests that instabilities in the regional broad-scale
atmospheric circulation, e.g., linked to the ITCZ position or strength,
may be partly controlled by the large-scale atmospheric flows specified
at the domain boundaries and/or that specified local SST anomalies
may help to guide some fraction of the developing model MISO to
follow observations. This result motivates further research on MISO
initiation and development using this type of regional atmospheric model.
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