A Continuity Microwave Limb Sounder (MLS) instrument to augment the record from Aura MLS.

Abstract:

Sounding the atmosphere in a limb geometry (viewing the atmosphere edge-on) offers important advantages over other approaches (nadir, conical, etc.), particularly for observations of atmospheric composition. Firstly, the limb viewing geometry offers better vertical resolution than is typically achievable in nadir/conical viewing. Secondly, the long atmospheric path provides a strong signal-to-noise for measurements of tenuous trace gases. Limb observations in the microwave and submillimeter regions are unaffected by aerosols and all but the thickest clouds, a distinct advantage over shorter wavelength limb observations given how few cloud-free limb views are possible, particularly in the tropics. Limitations of limb sounding include inability to sound the atmosphere below ~5-10 km altitude, and poorer horizontal resolution than can, in principle, be achieved by nadir sounders. We briefly review the contributions of the Microwave Limb Sounder on NASA's Aura mission (launched in 2004) to research into the stratospheric ozone layer stability, climate variability and change, and the impact of stratospheric ozone on air quality. We then describe a new "Continuity-MLS" instrument under development. Capitalizing on the advances made in microwave and submillimeter technology over the last decade, Continuity-MLS observes 340 GHz and 640 GHz limb spectra and measures abundances of nearly all of the molecules targeted by Aura MLS, but in a far more compact form factor (20kg, 40W vs. 500kg, 500W). Specific new technology utilized includes custom Complementary Metal Oxide Semiconductor (CMOS) System-on-Chip devices for (1) generating 107-116 GHz tones that are the basis for the local oscillators, and (2) 4000+ channel, 3 GHz bandwidth digital spectrometers. Continuity MLS is ideally suited to measuring the targeted observables for the NASA Earth Explorer "Ozone and Trace Gas" opportunity, and would also be a strong candidate for a suitably scoped "Earth Venture-Continuity" call.