Tracking oceanic nonlinear internal waves in the Indonesian seas from geostationary orbit

Nonlinear Internal Waves (NLIWs) in the ocean are observable from passive satellite radiometers. The surface manifestations of these internally propagating waves are curvilinear bands demarcating relatively smooth and rough surface waters, providing a means for their detection via observations of sunglint. Typical horizontal scales of NLIWs are such that traditionally only high resolution (<1 km pixel) sensors aboard polar orbiting satellites could resolve them. The launch on 28 October 2014 of the Japanese Meteorological Agency's Himawari-8 geostationary satellite and its Advanced Himawari Imager (AHI) opens up possibilities to study the spatio-temporal change of these relatively small scale NLIW features from geostationary orbit. Himawari-8 provides 500-m resolution visible imagery every 10 min over a hemispheric field of regard centered at 140.7° E longitude. These spatial and temporal resolutions allow for not only the identification of NLIWs over the low-latitude regions such as the Indonesian Seas, but also the ability to track the evolution of these waves in real time. Here, we present examples of NLIWs as viewed from Himawari-8/AHI and calculate a few basic wave quantities, including wavelength and propagation speed. These quantities were found to be consistent with previous observations and model simulations of NLIWs, but observations from AHI provide the ability to calculate wave propagation speeds in the same locations over multiple times a day for multiple days, which is impossible with polar-orbiting satellite data. Geostationary observations will augment the existing database of observed NLIWs and help to better quantify their spatial and temporal attributes.