MIXED Validation

The MIXED heat flux dataset was computed using TMI-AMSRE SST and ECMWF Analysis atmospheric state estimates. Atmospheric variables were linearly interpolated on to the satellite SST grid, and surface turbulent and radiative fluxes were then computed. Possibly incompatible SST and atmospheric states can lead to unrealistic results. The SST used in the ECMWF Analysis system is the NCEP Real-Time Global (RTG) produced with a two-dimensional variational interpolation analysis of the most recent 24-hour buoy and ship data, satellite-retrieved NOAA-17 AVHRR SST data, and SST’s derived from satellite-observed sea-ice coverage. Fig.1-A shows the daily centered root-mean squared difference (RMSD) between the RTG-SST used by ECMWF and the TMI-AMSRE SST used here to produce MIXED. The two products differ most along the Gulf Stream with RMSD values of 1o C , peaking locally at 2o C . The RMSD between Qnet obtained from ECMWF and MIXED is shown in Fig.1-B. Differences are again largest along the Gulf Stream with values reaching 125W.m−2 . Reassuringly this is of the same order of magnitude and spatial scale as the RMSD between ECMWF and NCEP-R1 original heat fluxes (Note that the RMSD between OCCA and NCEP-R1 heat fluxes is also very similar to the patterns shown here.) (not shown). This suggests that the MIXED heat flux does not contain spurious values and is as different from ECMWF as is NCEP.

We also compared time mean values of Qnet from MIXED with other datasets. Results are summarized in Fig.1-C which plots the zonal mean and time mean of the monthly time series of Qnet from National Oceanographic Center version 1.1 (NOC1.1) and the 2004-2006 daily time series from ECMWF, MIXED, OCCA and NCEP-R1. Relative to NOC1.1, ECMWF and NCEP heat fluxes overestimate the oceanic heat loss in the latitude band of interest in mode water formation (30N to 45N). MIXED is closer to NOC 1.1 than, for example, ECMWF and so can be considered acceptable.

Last, we estimated the performance of the MIXED heat flux locally. The CLIMODE pro ject deployed a meteorological buoy in the core of the Gulf Stream path at 38.5N/65W (denoted by a black cross on Fig.1-A and B) from which we compared daily sea surface heat fluxes with estimates from MIXED, OCCA, ECMWF and NCEP for the overlapping period of November 2005 to November 2006. The results are shown in a Taylor diagram in Fig.1-D taylor-2001. Each point represents a local time series (labeled A, B, C and D for the 4 global heat flux products, see legend in Fig.1-C). The distance from the center of the disk is the standard deviation (STD) and the angle from the x-axis is the correlation with the time series at the buoy. Thus the distance between the buoy point on the x-axis and other estimates is the RMSD between the time series. We see that ECMWF and MIXED have a similar STD to the buoy time series while OCCA underestimates it and NCEP overestimates it.

Global and local variabilities also with time mean of the MIXED heat flux was shown to be realistic, compared to several state of the art heat flux products.


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