AIRS Profiles Capture Warm Boundary Layer

The Atmospheric Infrared Sounder (AIRS)–a component of the EOS Polar Orbiter Aqua–retrieves atmospheric temperature and moisture profiles. It’s hyperspectral nature enables the sounder to produce near-rawinsonde-quality observations within an accuracy of 1 K per 1-km layer and 15% per 2-km layer. AIRS is more coarsely resolved near the surface than rawinsondes or other land-based observation due to its space-based approach. Also, surface emissivity definition at times is problematic to the retrieval methodology. That being said, recent algorithm developments have improved the methodology for obtaining near-surface observations; thus eliminating some of the poorer-quality surface observations. The profiles from this updated algorithm are able to capture the planetary boundary layer (PBL) quite well. Here, the AIRS profile is compared to the Microwave Profiling Radiometer (MPR) that currently resides on the Mobile Integrated Profiling System (MIPS) run by the University of Alabama in Huntsville. The MIPS resides in the back parking lot of the NSSTC and samples the lower 10-km of the atmosphere with high resolution (approximately 0.1 km) near the surface. The observations occur approximately once every 10 minutes. The MPR is a great tool for comparison and/or validation of the AIRS profiles in the near-surface environment.

The Skew-T/Log-P plots below show a comparison between an AIRS profile (red) and a MPR profile (black) valid at 1929 UTC on May 27, 2009 where an AIRS profile was only 27 km from the MPR. The solid lines are for temperature and the dashed lines are for dew point temperature. The top figure shows the soundings for the troposphere, and the bottom figure shows a zoom of the soundings in the PBL. While the AIRS dew point profile in the near-surface environment is approximately 5-7 degrees drier than the MPR, the AIRS profile does a good job of capturing the pattern of the near surface profile–essentially mimicking the warm surface followed by the steep cooling at around 950 mb.

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