Monitoring the Atmospheric Boundary Layer (ABL) by Radio Occultation Signals Recorded by COSMIC Satellites

The Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) uses radio occultation (RO) observations of the Global Positioning System (GPS) satellites to retrieve vertical profiles of the bending angle and refractivity in the atmosphere. Unlike previous RO missions utilizing the phaselocked loop (PLL) signal tracking technique, COSMIC receivers record L1 GPS signals in open-loop (OL) mode in the lowest 10 km of the troposphere by allowing penetration of the retrieved profiles down to the ocean surface. This provides an opportunity for monitoring the atmospheric boundary layer (ABL) with high vertical resolution (50-100 m), not available from other satellite data and not generally possible with PLL RO data from previous RO missions due to insufficient penetration and tracking errors. The optimal way of utilizing information about the ABL from RO observations is direct assimilation of the inverted bending angle and refractivity profiles into atmospheric models with sufficiently high vertical resolution in the lower troposphere. Alternatively, estimates of the depth of the ABL, which is an important parameter for meteorology and climatology, can be extracted from the structure of RO signals and inverted profiles. FORMOSAT-3/COSMIC (Constellation Observing System for Meteorology, Ionosphere and Climate) 6 Satellites launched 01:40 UTC 15 April 2006 Three instruments: GPS receiver, TIP, Tri-band beacon Weather + Space Weather data Global observations of: Pressure, Temperature, Humidity Refractivity Ionospheric Electron Density Ionospheric Scintillation Demonstrate quasi-operational GPS limb sounding with global coverage in near-real time Climate Monitoring FORMOSAT-3/COSMIC Final Deployment •71 Degrees inclination •800 Km •2500 Soundings per day •6 Planes •Latency 50-140 minutes from observation to NOAA Global coverage 2500 Daily Soundings by early 2007 180 240 300 0 60 120 180 -60 0 60 •Red Daily average Radiosondes •Green Daily COSMIC Soundings With the open-loop tracking, by accurate modeling of the frequency and range in receiver, the RO signals are recorded deeper than with the closed-loop tracking. This results in: (i) better penetration of retrieved profiles (especially in tropics); over oceans, most of open-loop profiles penetrate close to z=0; closed-loop profiles, commonly do not penetrate in layers with sharp vertical N-gradients (ii) smaller negative N-bias in tropical lower troposphere (iii) larger standard deviation of retrieved N profiles in the troposphere from those reproduced by atmospheric models; this is explained by insufficient vertical resolution of the atmospheric models (in closed-loop, only RO signals corresponding to vertically smooth N-profiles are tracked deep enough; in open-loop all RO signals are tracked and all N-profiles are equally represented in statistics) Statistical comparison with ECMWF analyses CHAMP COSMIC