October 26, 2007
Remote Sensing of CO2 in the Upper Troposphere
with the Atmospheric Infrared Sounder (AIRS)
Moustafa Chahine (JPL)
The Atmospheric Infrared Sounder (AIRS) has completed 5 years in Earth orbit
on the NASA Aqua satellite. AIRS is currently retrieving a wide range of
atmospheric parameters including several trace gases such as CO2. Daily
concentrations of CO2 are retrieved globally directly from observed infrared
spectra, with an accuracy of 1-2 PPMV without relying on a priori or background
information (Chahine et al in GRL, 2005). In this presentation we focus
our analysis on the CO2 distributions in the mid-troposphere between 4 and 14
km above the surface. We validate the retrieved results with available
in situ aircraft data (from Flask measurements by aircraft obtained by Matsueda,
NOAA’s Climate Monitoring & Diagnostics
Laboratory (CMDL) and the Intercontinental Chemical Transport Experiment
(INTEX-NA). The spatial patterns of retrieved CO2 are consistent
with the large-scale circulations. All 3-D Chemical Transport Models (CTMs)
underestimate the amplitude of the seasonal cycle and geospatial variability
of CO2 in the upper troposphere. Sensitivity studies reveal that modification
of the convection mass flux in the CTMs is required for the correct simulation
of upper tropospheric CO2. In conclusion, we show that the daily retrieval
of the global distribution of CO2 provides a tool to understand how CO2 is transported
from the surface sources and around the globe.
AIRS was launched into a sun-synchronous 705 km altitude polar
orbit on May 4, 2002 and it covers the 3.7mm to 15.4 mm region
of the thermal infrared spectrum with spectral resolution of l/dl=1200.
Since the start of routine data gathering in September 2002, AIRS
has demonstrated a stability of 8 milliKelvin per year and spectral
accuracy of 10-7 cm-1. AIRS returns 3.7
million spectra of the upwelling radiance each day. The operational
assimilation of AIRS data at Numerical Weather Prediction centers
including the National Centers for Environmental Prediction (NCEP)
and the European Center for Mid-Range Weather forecasts (ECMWF),
have already produced significant positive impact of more than
6 hours in 5 days of forecasts in both the northern and southern
hemispheres (Chahine et al in BAMS, July 2006).
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