Nested eddy permitting (1/4 degree) North Indian Ocean Model

High resolution regional Indian Ocean model with open boundary condition have been setup in collaboration with National Oceanic and Atmospheric Administration (NOAA)/Geophysical Fluid Dynamics Laboratory (GFDL),Princeton,USA and Indian Institute of Science (IISc), Bangalore using recent version of Modular Ocean Model (MOM4p1). A multi-model approach is adopted using MOM4p1 at GFDL Climate model (CM2.1) global resolution, and a regional model with uniform 25 km horizontal resolution and less than 1 meter vertical resolution near the surface. This is the first regional Indian Ocean model setup using MOM4p1 which takes lateral boundary from a global model. Main objective of this model development is to understand the intraseasonal variability of the North Indian Ocean (NIO).

The mean values of SSS and FW flux are only within 10 % when compared with observation. The most exciting result is that model could simulate the spatial distribution patter of SSS along the east and west coast of India. The timing and magnitude of low SSS which is due to the transport of low salinity water from north BoB over south eastern Arabian Sea (SEAS) is also captured with excellent agreement of observed values. In its first kind, model could capture the strong haline stratification over north Bay of Bnengal during winter season. Figure 1 shows the upper ocean fresh water content and its standard deviations from model simulations and observations. The inter-annual upper ocean salinity analysis shows that the bias over north Bay of Bengal is less than 0.2 psu except during winter time when it reaches ~ 0.8 psu when compared with ARGO observation (Figure 2).

Figure 1. Mean upper ocean (0–30m) fresh water content (m) and its standard deviation (STD) from (a) & (b) ARGO observations and (c) & (d) model simulations.

Figure 2. Upper ocean salinity comparison plot.

Reference:

Development of a regional model for the north Indian Ocean
Hasibur Rahaman , M. Ravichandran , Debasis Sengupta, Matthew J. Harrison, Stephen M. Griffies, Ocean Modelling 75(2014) 1–19. http://dx.doi.org/10.1016/j.ocemod.2013.12.005.

Nested eddy resolving (1/12 degree) North Indian Ocean Model

High resolution triply nested eddy resolving regional Indian Ocean model has been developed using recent version of Modular Ocean Model (MOM4p1). A multi-model approach is adopted using MOM4p1 and INCOIS-GODAS. In this setup, regional model in the Indian Ocean region (IOM-1/4) (1/4° (~ 25 km) horizontal resolution (eddy permitting) and less than 1 meter vertical resolution in the near the surface) takes initial and lateral boundary condition from INCOIS-GODAS. IOM-1/4 solutions are then used to give lateral boundary condition to a eddy resolving (1/12° horizontal resolution) north Indian Ocean Model (IOM-1/12). The physics in eddy permitting and eddy resolving model is same. The forcing is same in all three model simulations. The analysis of model simulations during January 2010 to June 2013 shows significant improvement in upper ocean variability in IOM-12 as compared to INCOIS-GODAS and IOM-1/4. One typical example of surface current simulation over Bay of Bengal and eastern Arabian Sea is shown in figure 1The costal currents along the Indian coast are more realistic in eddy resolving MOM-1/12 as compared to MOM-1/4 and INCOIS-GODAS.

Figure 1: The model domains

Figure 2: The upper ocean current from the nested solutions from 1/4° (upper panel), 1/12° (middle panel) Indian Ocean Model, and INCOIS-GODAS (lower panel).