Air–Sea fluxes from ICOADS: the construction of a new gridded dataset with uncertainty estimates

Abstract

ABSTRACT:The methods used to calculate a new in situ global dataset of air-sea exchanges, called the NOCS Flux Dataset v2.0, are described. The fluxes have been derived from in situ weather reports from Voluntary Observing Ships (VOS) covering the period 1973-2006. The reports have been adjusted for known biases and residual uncertainties estimated. The dataset is constructed using Optimal Interpolation (OI) using new estimates of random uncertainty in the observations. Daily fields have been calculated on a 1°latitude by 1°longitude grid, each grid box and time step have an associated uncertainty estimate. Monthly fields have been calculated from simple averages of the daily fields and monthly uncertainty estimates from the daily uncertainties, using estimates of the autocorrelation between the daily uncertainty estimates. The uncertainties due to the choice of flux parameterisation have not been accounted for. Bias adjustments applied to the data are shown to reduce trends in the data and to improve the consistency of estimates of air temperature, sea surface temperature (SST) and specific humidity. The bias adjustments also improve the agreement of NOCS v2.0 with independent data from research moorings. Cross-validation of the dataset suggests that the uncertainty estimates are realistic, but that the uncertainties are probably underestimated in high variability regions and overestimated in regions with lower variability. Copyright BackgroundReliable estimates of air-sea fluxes of heat, freshwater and momentum are needed to improve our understanding of the coupled ocean-atmosphere system. The main physical interactions at the sea surface are the turbulent heat, moisture and momentum fluxes between the ocean and the atmosphere, the radiative warming of the ocean surface by solar radiation and the net cooling of the ocean surface by thermal radiation. Direct measurements of the turbulent fluxes are typically only made on air-sea interaction research cruises and dedicated moored buoys and platforms. This limits the availability of direct flux measurements in space and time and their usefulness for global studies. As a result, global marine flux datasets are typically constructed using bulk estimates of the mean meteorological parameters and bulk parameterisations (or bulk formulae) developed using coincident measurements of the direct and radiative fluxes and mean meteorological variables from research cruises.The meteorological parameters required by the bulk formulae are: air temperature and humidity; sea surface temperature (SST); wind speed; sea level pressure; and cloud cover. These parameters are available from different sources including ship and buoy observations,

Occurrence and characteristics of mesoscale eddies in the tropical northeastern Atlantic Ocean

“…Out of the 21 eddies formed each year in the TANWA along the eastern boundary, five dissipate in a band of about 250 km width near the coast and about 16 propagate into the open ocean adding up to an annual eddy net heat (salt) transport of about 50 × 10 11 W (−150 × 10 3 kg s −1 ). Converting the divergence of the heat transport in the transition zone (area II) into an equivalent surface heat flux we found a cooling of the ocean of −1.6 W m −2 due to eddy heat transport, which as such balances about 10 % of the net surface heat flux of 17.4 W m −2 as obtained from the NOC Surface Flux Dataset (Berry and Kent, 2011). The TANWA is a crossroad for water masses, with NACW prevailing in the northwest within the ventilated subtropical gyre and SACW in the eastern boundary upwelling region.…”

“…By multiplying the heat transport of the composite eddies with the number of eddies dissolving during a year in a given area (corresponding to an flux divergence) a mean heat release (in W m −2 ) and a mean salt release (in kg m −2 ) were calculated. The mean heat release can be compared to the net atmospheric heat flux in the area here derived from the NOCS Surface Flux Dataset (Berry and Kent, 2011).…”

“…Based on the mean temperature and salinity anomalies derived above, it equates to a heat (salt) transport of −35.9 × 10 11 W (−180.6 × 10 3 kg s −1 ) by cyclones, 23.0 × 10 11 W (85.3 × 10 3 kg s −1 ) by anticyclones, and −8. computed and compared with the annual mean net surface heat flux for the respective regions as taken from the NOC Surface Flux Dataset (Berry and Kent, 2011) (Fig. 14b).…”

Drivers of uncertainty in simulated ocean circulation and heat uptake

“…We use the monthly mean fields during the period 1979-2014 to compute monthly climatologies for the buoyancy and wind forcing fields. We also use the Surface Flux Data Set of the UK's National Oceanography Centre (NOC) whose air-sea fluxes are derived from observed and bias-corrected surface meteorological parameters using bulk parameterizations [Berry and Kent, 2011]. Additionally, we use a standard surface flux product from the MITgcm repository based on a climatological annual cycle (Trenberth et al [1989] and Jiang et al [1999], referred to as BLEND).…”

Surface In situ Datasets for Marine Climatological Applications

“…, Etienne Charpentier (5) , Sergey K. Gulev (6) ,Heike Haar (7) , Elizabeth C. Kent (3) , Richard W. Reynolds (8) , Gudrun Rosenhagen (9) , Martin Rutherford (10) , Val Swail (11) , Steven J. Worley (12) , Huai-Min Zhang (8) , Reinhard Zöllner ( …”