Influence of multi-mission chlorophyll-a data on the simulation of upper ocean thermal structure in the eastern Pacific Ocean

ABSTRACT

The importance of providing multi satellite-based chlorophyll-a in an ocean model for accurate representation of penetrative shortwave radiation is demonstrated in this study using Modular Ocean Model. It questions the traditional usage of chlorophyll-a climatology in models. The model sensitivity experiments Chl_IA (with interannually varying multi satellite-based chlorophyll-a) and Chl_Clim (with chlorophyll-a climatology) during 1998–2016 reveals the importance of using the interannual chlorophyll. The maximum difference between the two chlorophyll-a products is found during the peak phase of strong El Niño (January-March 1998 and 2016) in the Niño1 + 2 region, allowing 5–11 W m⁻² more shortwave radiation to penetrate below 25 m in Chl_IA, effectively warming the subsurface temperature and cooling the sea surface temperature (SST) by ~0.4°C in the Niño1 + 2 region. The reduction in SST bias (warm) by 0.5°C, deepening of mixed layer and isothermal layer, enhancement of upwelling, reduction of upper ocean stability with realistic distribution of upper ocean heat content are some of the major improvements in Chl_IA. The interannual chlorophyll-a variability in fact rectifies the warm (cold) bias in surface (subsurface) temperature commonly found in ocean models especially in the eastern Pacific region during the peak phase of strong El Niño. 

Acknowledgements

We acknowledge Director of IITM and Ministry of Earth Sciences, Government of India for support. Figures are prepared using PyFerret. We thank the Editor and anonymous reviewers for suggestions and comments which improved our manuscript.