Open AccessGlobal ERS 1 and 2 and NSCAT observations: Upwind/crosswind and upwind/downwind measurements
Author(s) -
Quilfen Y.,
Chapron B.,
Bentamy A.,
Gourrion J.,
El Fouhaily T.,
Vandemark D.
Publication year - 1999
Publication title -
journal of geophysical research: oceans
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/1998jc900113
Subject(s) - crosswind , scatterometer , wind speed , gravity wave , gravitational wave , physics , wind direction , wind wave , geology , meteorology , geophysics , atmospheric sciences , wave propagation , optics , astrophysics , thermodynamics
This paper presents an analysis of the wind speed dependence of upwind/downwind asymmetry (UDA) and upwind‐crosswind anisotropy (UCA) as derived from global C band VV‐polarized ERS 1 and 2 and Ku band VV‐ and HH‐polarized NASA scatterometer (NSCAT) data. Interpretation of the results relies on identifying relationships between the differing frequencies and incidence angles that are consistent with Bragg scattering theory from gravity‐capillary waves. It is shown that globally derived parameters characterizing UDA and UCA hold information on the wind dependence of short gravity and gravity‐capillary wave growth and dissipation. In particular, the UCA behavior is found quadratic for both the C and Ku band, peaking at moderate wind speeds. In addition, the dual‐frequency results appear to map out the expected, more rapid adjustment of centimeter‐scale (Ku band) waves to the wind direction at light winds. However, as wind increases, the directionality associated with these shorter waves saturates at a lower speed than for the slightly longer waves inferred at C band. It is suggested that this observed phenomenon may be related to increasing wave‐drift interactions that can potentially inhibit short‐scale surface wave growth along the wind direction. Concerning UDA properties, our present analysis reveals that the NSCAT and ERS 1 and 2 scatterometers give quite different results. Our preliminary interpretation is that C band measurements may be easier to interpret using composite Bragg scattering theory and that upwind/downwind contrasts are mainly supported by short gravity waves.