A FIRST look at the Far Infrared Dan Feldman Yuk Yung IR Meeting May 9, 2007

Introduction μm unmeasured >50% contribution to OLR, tropospheric cooling rates Upper-tropospheric water, cirrus clouds modulate OLR, cooling rates Cooling rates inferred from a suite of indirect measurements Cirrus causes radiative heating in mid-IR, cooling in far-IR Figures from Mlynczak et al, 2001

Remote sensing of far-infrared: a frontier in spectroscopy FIRST = Far Infrared Spectroscopy of the Troposphere FTS w/ 0.6 cm-1 unapodized resolution, ±0.8 cm scan length Multilayer beamsplitter –Germanium –Polypropylene –Optically inactive over broad spectral ranges μm spectral range NeDT ~ 0.2 K 10 km IFOV, 10 multiplexed detectors LN 2 cooled Scan time: sec

Prototype Configuration and Test Flight Pictures from

Mid- and Far Infrared Spectra Comparison: LBLRTM

AIRS vs. FIRST T, H 2 O, O 3 AKs T, O3 averaging kernels similar FIRST has superior H2O averaging kernels due to spectral coverage AIRSFIRST

Test Flight 1 Ft. Sumner, NM Clear-sky conditions Aqua overpass AQUA MODIS L2 Cloud Fraction Ft Sumner, NM Clear-sky conditions Aqua overpass

Measurements and RTM comparison: Test Flight 1

Ft. Sumner, NM; Clear-sky conditions; Aqua, Cloudsat overpass Test Flight 2 AQUA MODIS L2 Cloud Fraction

CALIOP Images 2-channel lidar on Calipso platform Linear-polarized signal Complementary to Cloudsat Minimum sensitivity: τ=0.005 Few clouds over test flight 2

Measurements and RTM comparison: Test Flight 2

Spectral Sensitivity to Clouds AIRS and FIRST instruments can detect clouds from window band Interaction between UT H2O and clouds notably observed in FIR spectra

Conclusions Far infrared spectroscopy provides new view of upper- tropospheric H 2 O and cirrus clouds –FIRST instrument is capable of such measurements FIRST vs AIRS –Agreement in CO 2 15 μm, window band –Disagreement in O μm band, H 2 O 6.3 μm band FIRST vs LBLRTM –Reasonable agreement in H 2 O rotational bands, CO 2 v 2 and window band –Disagreement in O μm band, H 2 O 6.3 μm band New test flight coincident with Cloudsat and Calipso in presence of cirrus would be very interesting