|
Differential spectral imaging made possible by the new generation of hyperspectral sounders, such as AIRS, has applications for process studies and may also have applications for short-term weather forecasting. We use AIRS data to evaluate one such application: measurements of water vapor at 600 and 300 mb. The opacity of the 4.3 micron R-branch channels is almost entirely due to carbon dioxide, with weighting function peaks in the lower troposphere. Differences between these channels and selected pure water channels between 1300 and 1600 cm-1 cancel the local variability of the temperature to first order and measure the water column. Images of bt2388-bt1392, which measure the total water column above 600 mb from AIRS show large-scale patterns with sharp transitions between dry and wet upper tropospheric water vapor zones along frontal boundaries. The wealth of spatial features suggest applications to weather forecasting similar to the use of cloud images from satellite data, but unlike the visible light data, these images are available day and night. Data from tropical storm Arlene on 10 June 2005 are used to illustrate the potential of using high spectral resolution difference images. The motion of feature in these images correlate with the wind at 600 mb from upper airs measurements. The method does not require microwave channels or knowledge of the temperature profiles from a GCM and retains the full spatial resolution of the data. While the 15 km spatial resolution and 12 hour temporal repeat cycle of the EOS Aqua limits the practical application of AIRS data to mesoscale imaging and process studies, extension of the AIRS design concept can be used from hyper-spectral sounding with 1km spatial resolution from Low Earth Orbit (LEO) with AIRS-like spectral resolution, signal-to-noise ratio and calibration quality. Similar performance available with 4 km spatial resolution from geostationary satellites with one hour repeat coverage will allow future hyper-spectral sounders in geostationary orbits to measure the hourly advance of frontal zones in support of short term regional forecasting.
The Atmospheric Infrared Sounder, AIRS, was launched in May 2002 on the EOS Aqua satellite. The 4 million spectra gathered globally each day since September 2002 are being assimilated in the global forecast by the major NWP centers in near real time since May 2003. Details about AIRS and data availability can be found at http://jpl.nasa.gov/airs.
|
