In early November 2006, polar-orbiting Special Sensor Microwave/Imager (SSM/I) satellites documented the development of an intense atmospheric river (AR) over the eastern North Pacific Ocean and its subsequent downstream propagation toward western North America. The AR tapped into the tropical moisture reservoir and advected copious amounts of water vapor northeastward to Washington and Oregon. Record rainfall and anomalously high snow levels resulted in devastating flooding throughout the region.

Within this AR environment, new satellite-based GPS radio occultation soundings from the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) mission provided unique thermodynamic and moisture profiles over the data-sparse open ocean. The COSMIC soundings must be initialized with a first-guess profile such as from numerical weather prediction models. For this study, the first-guess source was obtained from the National Centers for Environmental Prediction (NCEP) Global Forecast System (GFS) model. Relevant offshore COSMIC soundings on 6-8 November 2006 were grouped into three clusters for compositing: those north of the AR (30 soundings), those within the AR (20 soundings), and those to its south (16 soundings). These groupings were made possible by referring to the twice-daily SSM/I integrated water vapor (IWV) images for guidance. The composite soundings for these three regions exhibited vertical-structure characteristics that are meteorologically consistent with earlier case-study results of other landfalling ARs. In addition, a curtain of 12 offshore COSMIC soundings through the AR of November 2006 yielded cross-sectional thermodynamic and moisture structures that were similarly consistent, including a description comparable in detail to previous aircraft-based dropsonde surveys.

Launched in April 2006, COSMIC is currently providing approximately 2500-3000 soundings per day distributed uniformly around the globe. It represents an exciting, new dataset possessing crucial, high-resolution vertical-profile information of temperature and moisture that can capture high-impact mesoscale phenomena – such as ARs – in otherwise data-sparse or data-void regions. Consequently, COSMIC can ultimately prove indispensable in a wide array of applications ranging from data assimilation and numerical weather prediction to climate studies.