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A SAR Observation and Numerical Study on Ocean Surface Imprints of Atmospheric Vortex Streets

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ABSTRACT

The sea surface imprints of Atmospheric Vortex Street (AVS) off Aleutian Volcanic Islands, Alaska were observed in two RADARSAT-1 Synthetic Aperture Radar (SAR) images separated by about 11 hours. In both images, three pairs of distinctive vortices shedding in the lee side of two volcanic mountains can be clearly seen. The length and width of the vortex street are about 60-70 km and 20 km, respectively. Although the AVS's in the two SAR images have similar shapes, the structure of vortices within the AVS is highly asymmetrical. The sea surface wind speed is estimated from the SAR images with wind direction input from Navy NOGAPS model. In this paper we present a complete MM5 model simulation of the observed AVS. The surface wind simulated from the MM5 model is in good agreement with SAR-derived wind. The vortex shedding rate calculated from the model run is about 1 hour and 50 minutes. Other basic characteristics of the AVS including propagation speed of the vortex, Strouhal and Reynolds numbers favorable for AVS generation are also derived. The wind associated with AVS modifies the cloud structure in the marine atmospheric boundary layer. The AVS cloud pattern is also observed on a MODIS visible band image taken between the two RADARSAT SAR images. An ENVISAT advance SAR image taken 4 hours after the second RADARSAT SAR image shows that the AVS has almost vanished.

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MM5 model simulation of the AVS at 0500 UTC on January 14, 2004. (a) Wind fields (in m s-1) at the lowest model level (σ = 0.9986, i.e. about 10 m above the sea surface). Black arrows represent wind vectors and color-coding denotes wind speeds. Green lines denote topography over the islands with a contour interval of 300 m. The letters “M”, “V”, “R” and “T” represent Markushin Volcano, Mount Vsevidof, Mount Recheshnoi and Tulik Volcano, respectively. The rectangle domain is the lateral boundaries for figure b; (b) Detailed vortex structure within the rectangle domain in figure a. The line AB is the width of AVS.
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f3-sensors-08-03321: MM5 model simulation of the AVS at 0500 UTC on January 14, 2004. (a) Wind fields (in m s-1) at the lowest model level (σ = 0.9986, i.e. about 10 m above the sea surface). Black arrows represent wind vectors and color-coding denotes wind speeds. Green lines denote topography over the islands with a contour interval of 300 m. The letters “M”, “V”, “R” and “T” represent Markushin Volcano, Mount Vsevidof, Mount Recheshnoi and Tulik Volcano, respectively. The rectangle domain is the lateral boundaries for figure b; (b) Detailed vortex structure within the rectangle domain in figure a. The line AB is the width of AVS.

Mentions: The digital elevation of 30 seconds United States Geological Survey (USGS) topography data is used in the simulation. In the 1-km model finest resolution, Mount of Recheshnoi and Mount Vsevidof is visible with a model height of 1500 m, and Makushin Volcano in Unalaska Island is visible with a model height of 1800 m (Figure 3a).


A SAR Observation and Numerical Study on Ocean Surface Imprints of Atmospheric Vortex Streets
MM5 model simulation of the AVS at 0500 UTC on January 14, 2004. (a) Wind fields (in m s-1) at the lowest model level (σ = 0.9986, i.e. about 10 m above the sea surface). Black arrows represent wind vectors and color-coding denotes wind speeds. Green lines denote topography over the islands with a contour interval of 300 m. The letters “M”, “V”, “R” and “T” represent Markushin Volcano, Mount Vsevidof, Mount Recheshnoi and Tulik Volcano, respectively. The rectangle domain is the lateral boundaries for figure b; (b) Detailed vortex structure within the rectangle domain in figure a. The line AB is the width of AVS.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3675546&req=5

f3-sensors-08-03321: MM5 model simulation of the AVS at 0500 UTC on January 14, 2004. (a) Wind fields (in m s-1) at the lowest model level (σ = 0.9986, i.e. about 10 m above the sea surface). Black arrows represent wind vectors and color-coding denotes wind speeds. Green lines denote topography over the islands with a contour interval of 300 m. The letters “M”, “V”, “R” and “T” represent Markushin Volcano, Mount Vsevidof, Mount Recheshnoi and Tulik Volcano, respectively. The rectangle domain is the lateral boundaries for figure b; (b) Detailed vortex structure within the rectangle domain in figure a. The line AB is the width of AVS.
Mentions: The digital elevation of 30 seconds United States Geological Survey (USGS) topography data is used in the simulation. In the 1-km model finest resolution, Mount of Recheshnoi and Mount Vsevidof is visible with a model height of 1500 m, and Makushin Volcano in Unalaska Island is visible with a model height of 1800 m (Figure 3a).

View Article: PubMed Central

ABSTRACT

The sea surface imprints of Atmospheric Vortex Street (AVS) off Aleutian Volcanic Islands, Alaska were observed in two RADARSAT-1 Synthetic Aperture Radar (SAR) images separated by about 11 hours. In both images, three pairs of distinctive vortices shedding in the lee side of two volcanic mountains can be clearly seen. The length and width of the vortex street are about 60-70 km and 20 km, respectively. Although the AVS's in the two SAR images have similar shapes, the structure of vortices within the AVS is highly asymmetrical. The sea surface wind speed is estimated from the SAR images with wind direction input from Navy NOGAPS model. In this paper we present a complete MM5 model simulation of the observed AVS. The surface wind simulated from the MM5 model is in good agreement with SAR-derived wind. The vortex shedding rate calculated from the model run is about 1 hour and 50 minutes. Other basic characteristics of the AVS including propagation speed of the vortex, Strouhal and Reynolds numbers favorable for AVS generation are also derived. The wind associated with AVS modifies the cloud structure in the marine atmospheric boundary layer. The AVS cloud pattern is also observed on a MODIS visible band image taken between the two RADARSAT SAR images. An ENVISAT advance SAR image taken 4 hours after the second RADARSAT SAR image shows that the AVS has almost vanished.

No MeSH data available.


Related in: MedlinePlus