Abstract
A new weakly coupled data assimilation (CDA) system based on the dimension-reduced projection four-dimensional variational data assimilation (DRP-4DVar) with a simplified off-line localization technique and a fully coupled model, i.e., the Grid-point Version 2 of Flexible Global Ocean-Atmosphere-Land System Model (FGOALS-g2), was developed for the initialization of decadal predictions. A 1-month assimilation window was adopted for the CDA system, in which monthly mean temperature and salinity analyses were assimilated along the trajectory of the coupled model during the initialization for the period of 1945–2006. The system is efficient because the 62-year initialization only takes about 2.375 times of the time cost of the uninitialized run for the same period. Compared with the uninitialized simulation and the initialization without localization, ocean temperature and salinity, sea surface elevation, surface air temperature, and precipitation are in better agreement with the verification data. Furthermore, climate variabilities in the Pacific and Atlantic regions such as El Niño-Southern Oscillation, Pacific Decadal Oscillation (PDO), and Atlantic Multidecadal Oscillation (AMO) are more realistically captured. Starting from the initial conditions (ICs) generated by the initialization, 10-member ensemble decadal prediction experiments were conducted each year from 1961 to 1996. The results demonstrate that higher decadal prediction skills of surface air temperature anomalies averaged over the globe, ocean, land, and the North Pacific subpolar gyre are achieved than those obtained from persistence, the uninitialized simulation, and the prediction initialized from the ICs without localization. Besides, PDO and AMO indices exhibit significant correlation skills in most lead times.
| Original language | English |
|---|---|
| Article number | e2019MS001768 |
| Journal | Journal of Advances in Modeling Earth Systems |
| Volume | 12 |
| Issue number | 4 |
| DOIs | |
| State | Published - Apr 1 2020 |
| Externally published | Yes |
Funding
This work was supported by the National Natural Science Foundation of Chin (grants 91737307 and 41875127). The initialization and decadal prediction experiments were performed on the “Explorer 100” cluster system of Tsinghua University (Zhang et al., 2017 ). The ds285.3 ocean temperature and salinity analyses were downloaded from https://rda.ucar.edu/datasets/ds285.3/ . The EN.4.2.1 analyses were downloaded from http://hadobs.metoffice.com/en4/download‐en4‐2‐1.html . The ORAS4 reanalysis was obtained from https://climatedataguide.ucar.edu/climate‐data/oras4‐ecmwf‐ocean‐reanalysis‐and‐derived‐ocean‐heat‐content . The SODA 2.2.4 reanalysis was obtained from http://apdrc.soest.hawaii.edu/datadoc/soda_2.2.4.php . The HadCRUT4 analysis was downloaded from https://www.metoffice.gov.uk/hadobs/hadcrut4/ . The GPCP version 2.3 analysis was downloaded from https://www.esrl.noaa.gov/psd/data/gridded/data.gpcp.html . The NCEP/NCAR Reanalysis 1 was obtained from https://www.esrl.noaa.gov/psd/data/gridded/data.ncep.reanalysis.surface.html . The results of the initialization and hindcast experiments are available from the corresponding author upon reasonable request. This work was supported by the National Natural Science Foundation of Chin (grants 91737307 and 41875127). The initialization and decadal prediction experiments were performed on the ?Explorer 100? cluster system of Tsinghua University (Zhang et al.,?2017). The ds285.3 ocean temperature and salinity analyses were downloaded from https://rda.ucar.edu/datasets/ds285.3/. The EN.4.2.1 analyses were downloaded from http://hadobs.metoffice.com/en4/download-en4-2-1.html. The ORAS4 reanalysis was obtained from https://climatedataguide.ucar.edu/climate-data/oras4-ecmwf-ocean-reanalysis-and-derived-ocean-heat-content. The SODA 2.2.4 reanalysis was obtained from http://apdrc.soest.hawaii.edu/datadoc/soda_2.2.4.php. The HadCRUT4 analysis was downloaded from https://www.metoffice.gov.uk/hadobs/hadcrut4/. The GPCP version 2.3 analysis was downloaded from https://www.esrl.noaa.gov/psd/data/gridded/data.gpcp.html. The NCEP/NCAR Reanalysis 1 was obtained from https://www.esrl.noaa.gov/psd/data/gridded/data.ncep.reanalysis.surface.html. The results of the initialization and hindcast experiments are available from the corresponding author upon reasonable request.