(2001) concluded that anemometer measurements of 10-m winds (which are the winds estimated by NWP models) are typically about 0.2 m s−1 lower than the equivalent neutral-stability winds at 10 m. This mean difference is verified in section 5 by the heavy solid and dashed lines in Fig. Scatterometers measure small-scale roughness, which depends on surface stress. Proc. of differences between scatterometer and buoy wind speeds (not shown). Scatterometers thus measure the wind relative to the moving sea surface.
The winds measured by a scatterometer are the winds that are relevant to air–sea fluxes of momentum, heat and gases. Root-mean-squared component differences, Local impact of stochastic shallow convection on clouds and precipitation in the tropical Atlantic, Diagnosing the influence of a receding snow boundary on simulated midlatitude cyclones using piecewise potential vorticity inversion, The Rapid Intensification of Hurricane Michael (2018): Storm Structure and the Relationship to Environmental and Air-Sea Interactions, Nowcasting Multicell Short-Term Intense Precipitation Using Graph Models and Random Forests, Assessing Predictive Potential Associated with the MJO during the Boreal Winter, © Copyright 2019 American Meteorological Society. Figure 6.29. A significant difference is apparent in the offset value, −0.4 for NDBC versus −1.1 for TAO. In the vicinity of the Pacific equatorial cold tongue, for example, Kelly et al. As a consequence of this localized bias in the NCEP wind speeds, the relative bias between NCEP and ECMWF is near zero over the ACC (bottom two panels in the right column of Fig.
The model function linking NRSC to local wind speed for probing at the angle ϕ0 to the wind direction is given by. In this region, the currents are not purely driven by local wind conditions (Boulanger and Menkes 1999). The reasons for the improvements of the ECMWF and NCEP 10-m wind analyses cannot be determined from the analysis presented here. Instantaneous backscatter measurements are obtained at fixed incidence angles of 46° and 54° (Fig. developed empirical models relating QuikSCAT measurements of brightness temperature at 13.4 GHz (a by-product of the scatterometer σ0 measurement approach) to rain rate. The statistical parameters of errors between OSCAT and the moored buoys are given in Table 1. 1991). This may be explained partly because there were several changes in the numerical model and assimilation scheme within the considered 6-yr time period. The highest residual correlations are obtained with a sea state parameter roughly proportional to the long-wave rms orbital velocity. As in the scatterometer–NWP wind comparisons in Fig. A check on sea state impacts near the equator can be derived using the collocated ERS scatterometer and TOGA–TAO buoy compilation. The eastward ERS wind component is lower in the area of eastward currents. These data are useful for the global ocean surface wind studies.
8 is that the NSCAT and QuikSCAT observations have nearly identical accuracies and that the scatterometer measurement accuracies are very similar to the accuracies of buoy measurements of near-surface winds. 9. For the υ differences, the modes of the distributions for both ECMWF and NCEP decreased significantly between each of the three successive time periods considered here. Cross-swath variations in comparisons between QuikSCAT measurements and spatially and temporally interpolated ECMWF (solid lines) and NCEP (dashed lines) 10-m wind analyses: (top) standard deviations of wind speed differences, and (bottom) standard deviations of wind direction differences. This appears to provide further evidence that surface condition changes can directly effect the scatterometer measurements and, thus, surface wind retrieval estimates and possibly their application. While the scatterometer views at oblique angles, the altimeter views at nadir (very small incident angles). This procedure could be extended to buoys in other regions in a straightforward fashion, provided altimetric SSH and an estimate of the mean current are available. 2002). While σ0 measurements are obtained at a constant incidence angle for each beam, the relative azimuth angles between collocated backscatter measurements vary systematically with cross-track location.
The objective criteria for selecting the open-ocean buoys and the data editing criteria are the same as those used by Freilich and Dunbar (1999). Climatological estimators are used for drifter and ADCP data, owing to relatively sparse spatial and temporal sampling.
These two latter mechanisms can then significantly contribute to airflow modification above the surface. A separate measurement of the noise-only power is made and subtracted from the signal+noise measurement to determine the backscatter signal power. Explicitly taking into account buoy errors helps to better estimate the low wind speed errors. First, the OSCAT wind data are collocated with moored buoy and ASCAT wind data to obtain quasisynchronous collocated data.
2019, Article ID 1651267, 9 pages, 2019. https://doi.org/10.1155/2019/1651267, 1The First Institute of Oceanography, Ministry of Natural Resources of China, Qingdao 266061, China.
A surface current is known to have direct influences on the short-wave growth to modify the amplitude of the short gravity wavelets. For the buoys, errors originate from spatial/temporal miscollocation, from spatial representativeness errors, or from corrections used to derive 10-m neutral wind vector. This can complicate the relationship between the radar cross section and the usual geophysical parameter, the 10-m neutral wind U10N. Comparisons with collocated, simultaneous buoy measurements of wind adjusted for stability effects to obtain the 10-m equivalent neutral-stability wind provide the most accurate quantitative assessment of satellite wind measurement accuracy (see, e.g., Freilich and Dunbar 1999 and references therein for NSCAT, and Ebuchi et al. OSCAT experienced an irrecoverable malfunction and stopped working on 20 February 2014. To understand the abundance of the collocated data for an entire possible range of ocean surface wind, probability distribution functions (PDFs) of the collocated data are plotted for wind speed and direction as shown in Figure 5.
Scatterometer-derived high winds are found to be underestimated due largely to deficiencies of the empirical scatterometer algorithms. For the NRT wind product, the overlapping σ0 measurements obtained from each of the four possible antenna geometrics (inner/outer beam and fore/aft viewing geometry) are averaged within each wind vector cell to obtain a single σ0 estimate.
The apparent bias of the ECMWF wind speeds was further investigated from comparisons with direct measurements by the 22 open-ocean NDBC buoys shown in Fig. The analyses of OSCAT wind vector errors in the different buoys’ wind speeds show that the accuracy of the OSCAT wind speed first increases and then decreases with the increasing wind speed. Int. The 10-m wind speeds in the ECMWF model, however, are shown to be biased low by about 0.4 m s−1.
A SAR looks perpendicular to the aircraft path at only one azimuth angle, and cannot resolve the UN direction like the scatterometer. In addition to assimilation of QuikSCAT data, the improved accuracy during the 2002 time period may be attributable to the increase in the model grid resolution from T319 to T511 (i.e., from 0.564° to 0.352°) on 21 November 2000.
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