Gap Winds and Atmospheric Rivers: Studies of Mesoscale Dynamics Using MISR's High-Resolution Cloud-Track Motion Vectors

The Multiangle Imaging SpectroRadiometer (MISR) instrument on NASA's polar orbiting Terra satellite provides a unique perspective on atmospheric dynamics by retrieving cloud motion vectors using observations made from nine unique viewing directions along the satellite track. An image matching technique is employed that simultaneously yields geometric height and true motion reported on a 17.6 km x 17.6 km grid across the ~400 km swath of the instrument. Heights are assigned with a vertical resolution better than 500 m. Because the time interval between camera views is less than 1 minute, the wind speeds reported by MISR represent a more instantaneous view of the dynamics than the complementary winds reported by geostationary platforms such as GOES, which require a significantly longer time interval. Due to these characteristics, MISR observations are particularly valuable in a variety of environments that are challenging for more conventional remote sensing techniques.

We will describe studies of two mesoscale phenomena performed using MISR's cloud motion vectors. Gap winds in the eastern tropical Pacific have been studied previously using near-surface winds from the QuikSCAT scatterometer, which provides 25-km spatial resolution retrievals. Due to the presence of scattered low clouds, we show that MISR provides similar observations of these low level winds in good agreement with the scatterometer observations. In addition, we relate the wind observations to MISR aerosol optical depth retrievals in the region made at the same 17.6 km resolution as the wind retrievals. Landfalling atmospheric rivers play an important role in the hydrology of coastal regions of the western United States. An important control on the precipitation is the relationship between the altitude of the atmospheric river and the underlying orography. Although atmospheric rivers are typically tracked through their signature in the total column precipitable water, we demonstrate that they are also associated with distinct cloud features. MISR observations provide both the height and wind speeds associated with these events as the systems move toward the coast, potentially enabling improved forecasting.