Summary

To understand climate change and current weather extremes, it is important to have observations of the Earth system going back as far as possible in time. The Ocean is the major component of the Earth system. However, observations over the Ocean have always been unevenly distributed and come with errors. Even satellite observations alone cannot provide a complete and accurate picture of the 3D state of the Ocean at a given point in time. Reanalyses fill the gaps in the observational record, and they do so in a way that is consistent in time, thus minimizing any spurious signals of change by combining models and observations. Accurate ocean reanalyses are essential, as they provide the most realistic representations of past oceanic conditions, serving as benchmarks against which climate models are validated on different time scales. In recent times, the rise of artificial intelligence (AI) has revolutionized data analysis, allowing us to uncover complex patterns in large datasets. Reanalysis datasets have emerged as tools of excellence for these objectives due to their ability to offer a physically consistent global reconstruction of past weather conditions devoid of spatial or temporal gaps.

Ocean reanalyses have been routinely produced by most of the operational centers (ECCO: NASA,USA; BRAN: BoM, Australia; SODA: University of Maryland, USA; NCEP-GODAS:NOAA/NCEP,USA;ORAS5: ECMWF,EU; GLORYS: Mercator Ocean, France,C-GLORS: CMCC, Italy; GloSea5: Met Office,UK etc ) across the world (https://www.cen.uni-hamburg.de/icdc/data/ocean/easy-init-ocean.html).

The Indian National Centre for Ocean Information Services (INCOIS) provides near real-time global ocean analyses based on MOM4p0d using the Global Ocean Data Assimilation System (GODAS) initially adopted from NOAA/NCEP. The INCOIS GODAS analysis is routinely provided to the Indian Institute of Tropical Meteorology (IITM) for the initialization of the coupled model CFSv2, which is used for seasonal prediction of the Indian Summer Monsoon Rainfall. Although present operational INCOIS-GODAS generates daily ocean analysis, long-term ocean reanalysis has not yet been produced. We generated forty-five (45) years of Ocean reanalysis (1979-2023) with the upgraded GODAS in collaboration with NOAA/NCEP, USA. GODAS consists of a physical ocean general circulation model MOM5 developed by NOAA/GFDL and a 3Dvar assimilation scheme to assimilate observed temperatures and salinity profiles from all insitu-platforms over the global Ocean. We use CORE-II (1979-2009) and NCEP-R2(2010-2023) atmospheric forcing to produce this reanalysis product.

Figure-1: Monthly sea surface temperature (SST) comparison (2003-2007) over the global ocean for (a) IGORA v1 reanalysis and (b) OISST observation.

Figure-2: SST Comparison with respect to OISST at 110°W and 0°N (NiNO 3.4 region).

Citing the IGORA v1 data:

When using the data set in a paper or any other documents, please provide the data were downloaded from the INCOIS LAS Server (https://las.incois.gov.in/), and cite the following reference:

Hasibur Rahaman, Samir Pokhrel, Subodh Saha, Raheema Rahman, Stephen Penny, Eric Hackert, James Carton, Balakrishnan Nair T.M., T. Srinivasa Kumar & M. Ravichandran. Improved GODAS reanalysis with MOM5 and impact of altimeter assimilation. Model. Earth Syst. Environ. 11, 88 (2025). https://doi.org/10.1007/s40808-024-02269-9

Contact Details:

For any further information, please contact:
Dr.Hasibur Rahaman, Scientist-F, INCOIS,
E-mail: rahman@incois.gov.in