Reconstructions of climate during last two millennium based on data assimilation using multiple types of proxy records

We use the Hybrid Gain Analog Offline EnKF (HGAOEnKF) with multiple types of proxy records, to reconstruct the temperature, precipitation, and large-scale climate variability during the last two millennia. First, a new reanalysis product (NNU-2ka Reanalysis) is generated through the HGAOEnKF with the expanded proxy database. A comparison with observed SST variability shows that our assimilated tropical SST variability performs reasonably well for the seasonal cycle and monthly ENSO characteristics, notably the phase-locking and onset timing, and more realistic spatial fields relative to the model simulations. Sensitivity experiments show that the proxy records from the ocean contribute more to the temperature reconstruction skill with both assimilation methods. We then further reconstruct the Pacific decadal variability (PDV) and Atlantic meridional overturning circulation (AMOC) using the marine oxygen isotope records.