Use of Spaceborne Synthetic Aperture Radar Imagery of the Sea Surface in Detecting the Presence and Structure of the Convective Marine Atmospheric Boundary Layer

The generalized stability of the secondary atmospheric circulation over strong SST fronts is studied using a hydrostatic, Boussinesq, two-dimensional f-plane model. It is shown that even in a parameter regime in which these circulations are stable to small perturbations, significant nonnormal growth of optimal initial perturbations occurs. The maximum growth factor in perturbation total energy is 250 and is dominated by the potential energy, which obtains a growth factor of 219 two to five hours after the beginning of the integration. This domination of potential energy growth is consistent with the observation that the available potential energy (APE) of the secondary circulation is larger by two orders of magnitude than the kinetic energy as well as with the transfer of kinetic to potential perturbation energy at the beginning of the growth of the perturbations.The norm kernel is found to significantly influence the structure of the optimal initial perturbation as well as the energy obtained by the mature perturbations, but the physical mechanism of growth and the structure of the mature perturbations are robust.

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“…5). This is also seen in spaceborne synthetic aperture radar images (Weissman et al 1980;Sikora et al 1995, their Fig. 1).…”

Section: Introductionsupporting

confidence: 54%

Nonnormal Frontal Dynamics

Feliks

Tziperman

Farrell

2010

Journal of the Atmospheric Sciences

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“…Weissman et al (1980) produced the first analysis of SAR imagery of the Gulf Stream and how it depended on the wind speed and SST. Sikora et al (1995) noted distinct surface roughness patterns either side of the Gulf Stream North Wall in one particular image (reproduced in Fig. 6b).…”

Section: Gulf Stream and North Atlanticmentioning

confidence: 78%

“…The increase in stress can be due to changes in surface stability and/or wind speed, and is observed globally by scatterometer (Chelton et al 2004) and by SAR (Sikora et al 1995). In all cases, wind stress curl (divergence) anomalies are linearly related to the component of the background wind across (along) the fine scale SST gradients (Chelton et al 2004).…”

Section: Surfacementioning

confidence: 89%

Acknowledging contributions

2011

Dental Abstracts

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Air-sea interaction at ocean fronts and eddies exhibits positive correlation between sea surface temperature (SST), wind speed, and heat fluxes out of the ocean, indicating that the ocean is forcing the atmosphere. This contrasts with larger scale climate modes where the negative correlations suggest that the atmosphere is driving the system. This paper reviews studies of the interaction of sharp SST gradients and the overlying marine atmospheric boundary layer and deeper atmosphere. The importance of different physical mechanisms of atmospheric response to SST gradients, such as the effect of surface stability variations on momentum transfer, pressure gradients, secondary circulations and cloud cover will be assessed. These processes will be compared and contrasted for different regions such as the Equatorial Front in the Eastern Pacific, and oceanic fronts in mid-latitudes such as the Gulf Stream, Kuroshio, and Agulhas Return Current.

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“…Therefore, we believe that SAR can provide a powerful complement to conventional wind measurement techniques, because of its high resolution. Furthermore, because the SAR wind retrieval technique is based on an imaging process, it provides a useful diagnostic tool for other techniques and detects small-scale wind structures that could allow quantitative estimations of atmospheric stability (Sikora et al, 1995;Young et al, 2005). Wind fi eld data retrieved from SAR images in coastal areas are very valuable for offshore wind resource assessment, as they can provide suffi cient and accurate spatial information in the early stages of wind farm planning.…”

Section: Resultsmentioning

confidence: 99%

Deriving Changjiang coastal zone wind from C-band SAR and its application to salinity simulation

Wang

Zhou

Zhu

et al. 2014

Chin. J. Ocean. Limnol.

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Wind plays an important role in hydrodynamic processes such as the expansion of Changjiang (Yangtze) River Diluted Water (CDW), and shelf circulation in the Changjiang estuary. Thus, it is essential to include wind in the numerical simulation of these phenomena. Synthetic aperture radar (SAR) with high resolution and wide spatial coverage is valuable for measuring spatially inhomogeneous ocean surface wind fi elds. We have collected 87 ERS-2 SAR images with wind-induced streaks that cover the Changjiang coastal area, to verify and improve the validity of wind direction retrieval using the 2D fast Fourier transform method. We then used these wind directions as inputs to derive SAR wind speeds using the C-band model. To demonstrate the applicability of the algorithms, we validated the SAR-retrieved wind fi elds using QuikSCAT measurements and the atmospheric Weather Research Forecasting model. In general, we found good agreement between the datasets, indicating the reliability and applicability of SARretrieved algorithms under different atmospheric conditions. We investigated the main error sources of this process, and conducted sensitivity analyses to estimate the wind speed errors caused by the effect of speckle, uncertainties in wind direction, and inaccuracies in the normalized radar cross section. Finally, we used the SAR-retrieved wind fi elds to simulate the salinity distribution off the Changjiang estuary. The fi ndings of this study will be valuable for wind resource assessment and the development of future numerical ocean models based on SAR images.

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Use of Spaceborne Synthetic Aperture Radar Imagery of the Sea Surface in Detecting the Presence and Structure of the Convective Marine Atmospheric Boundary Layer

Cited by 51 publications

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Nonnormal Frontal Dynamics

Nonnormal Frontal Dynamics

Acknowledging contributions

Deriving Changjiang coastal zone wind from C-band SAR and its application to salinity simulation

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