A. B. Kara

Comparisons of monthly mean 10 m wind speeds from satellites and NWP products over the global ocean

Received 31 December 2008; revised 15 June 2009; accepted 19 June 2009; published 27 August 2009. [1] The accuracy of wind speed at 10 m above the sea surface from two satellite and three numerical weather prediction (NWP) products is investigated over the global ocean. Rain-free equivalent neutral winds from the Quick Scatterometer (QuikSCAT) are converted to stability-dependent winds to be consistent with those from NWP products and are taken as truth in comparisons to winds from other products. Quantitative statistical analyses presented at each grid point over the global ocean reveal that monthly winds from NWP products have almost perfect skill relative to those from QuikSCAT winds during the 3-year common period (September 1999 to August 2002). Exceptions occur in tropical regions and high southern latitudes. Wind speeds adjusted to 10 m at many moored buoys located in different regions of the global ocean further confirm the accuracy of monthly NWP winds, giving RMS difference of 1.0 m s � 1 based on 1281 monthlong time series. The satellite-based QuikSCAT winds agree with buoy winds relatively better than NWP products. While there is good agreement among wind products on monthly timescales, large differences (>3 m s � 1 and more) in NWP winds are found in comparison to QuikSCAT winds on shorter time intervals at high latitudes. Daily means of sensible and latent heat fluxes based on NWP winds can therefore differ as much as 100 W m � 2 in comparison to those based on QuikSCAT winds. In general, NWP wind-based sensible and latent heat fluxes are more similar to their QuikSCATwind-based counterparts in tropical regions and midlatitudes.

Accuracy of 10 m winds from satellites and NWP products near land‐sea boundaries

Microwave/Imager. Large biases (e.g., >3 m s 1 ) may exist in NWP products near the land-sea boundaries, because wind speeds from the uniformly gridded global fields are generally at a spatial scale too coarse to appropriately define the contrast between water and land grid points. This so-called land contamination of ocean-only winds varies, and typically depends on the extent of the land-sea mask. A creeping sea-fill methodology is introduced to reduce errors in winds. It is based on the elimination of land-corrupted NWP grid points and replacement by adjacent, purely over-ocean values. In comparison to winds from many moored buoys, the methodology diminishes RMS errors (from >4 m s 1 to <1 m s 1 ) for NOGAPS and ERA-40. The creeping sea-fill is not advised for NCEP winds which have low contrast between land and sea points, thereby resulting in little impact from the land contamination.

Comment on “Seasonal heat budgets of the Red and Black seas” by Matsoukas et al.

Abstract : Matsoukas et al. [2007] present a monthly analysis of heat fluxes in relation to heat budget in the Red and Black Seas to provide further insight for air-sea exchange processes in the small ocean basins. Components of net surface heat flux are illustrated during 1984-1995. In computing latent and sensible heat fluxes, Matsoukas et al. [2007] apply traditional bulk formulations. A heat balance method that is based on the available energy for evaporation flux is also presented to compare latent heat fluxes with those from the bulk formulations. All near-surface atmospheric variables, including wind speed at 10 m, used in the heat balance method are obtained from reanalysis of a numerical weather product (NWP). Initial input data for radiation flux calculations are at resolutions of 1.0-degrees and 2-degrees, depending on the availability. Monthly means of heat budget components are computed on the basis of monthly means of atmospheric variables during 1984-2000.