Mesoscale and synoptic scale dynamic phenomena in the Oyashio current region observed in SAR imagery

Abstract

ABSTRACT Satellite SAR images are an essential source of information on mesoscale and sub-mesoscale dynamic phenomena in the ocean with a resolution of 4–1000 m. They can be obtained irrespective of cloudiness and sun illumination. In this paper, the dynamic features in the large region in the Northwest Pacific associated with the cold Oyashio Current are considered. The combination of the Oyashio and Kuroshio currents, strong tides, and sharp changes in the topography of the Pacific Ocean shelf along the Kuril and Japan Islands together with storm winds accompanying the deep extratropical cyclones leads to a complicated water circulation. In the investigation, the attention is focused on dominant dynamic features including mesoscale and sub-mesoscale eddies, streamers and internal waves. They play a key role in physical and biological fluxes between waters of different origin. Under a clear sky, the mesoscale and sub-mesoscale features visualize themselves through prominent thermal and biological contrasts; however, under cloudy conditions, they can be detected in the sea surface roughness fields. The sea surface roughness contrasts caused by oceanic and atmospheric phenomena are observed on the Synthetic Aperture Radar (SAR) images acquired by Envisat ASAR and Sentinel-1A/-1B C-SAR at C-band and mainly by ALOS-1/-2 PALSAR at L-band at various polarizations. Spatial characteristics and seasonal features of the sub-mesoscale oceanic and atmospheric phenomena have been revealed on SAR images. The satellite visible and infrared images (NOAA AVHRR, Terra and Aqua MODIS, Landsat-8 OLI and TIRS, SNPP VIIRS) and various products (SST, chlorophyll-a concentration, surface analysis map, etc.) substantially complemented the SAR data.