NRG 0.1

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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