Synthetic aperture radar observation of the sea surface imprints of upstream atmospheric solitons generated by flow impeded by an island

Abstract

Two cases of upstream propagation of atmospheric solitons generated by atmospheric flow over topography were identified on two RADARSAT‐1 synthetic aperture radar (SAR) images acquired near St. Lawrence Island in the Bering Sea on 7 September 1997 and 6 June 2001, respectively. In both cases, a group of solitons was shown as three dark‐bright linear features on the SAR images. The soliton width and peak‐to‐peak distance measured from the two SAR images are about 3 km and 4.5 km, respectively. Simultaneous radiosonde measurements, a surface weather map and operational weather model results confirm that these waves did not propagate on the lee side of the island as is commonly observed with island lee waves, but indeed propagated against the flow in the upstream direction. In the second case, the same group of solitons was also identified as a wave‐like cloud pattern on a MODIS image taken about 4.5 hours later. In this MODIS image, the soliton train propagated further upstream with the leading crest reaching about 30 km north of the island, and the number of crest‐trough features increased from three to seven. In this study, we describe the generation and evolution of upstream atmospheric solitons using the Force KdV (fKdV) model with radiosonde and island topography data. The numerical solution of the fKdV exhibits a sequence of solitons propagating upstream of the island. Both temporal and spatial scales of the solitons are in good agreement with that estimated from the successive SAR and MODIS satellite images.