Modeling the change in spectrally resolved outgoing longwave radiation Wing-Yee (Marie) Lau Aug 18, 2010
Modeled AIRS (clear) – modeled IRIS (a little cloud), ozone unchanged, offset applied
Questions about convolution code • The convolution code takes weighted average over a distance of “hw” from the center. for i=0,lines-1,1 do begin aindex=where(abs(wn-wn[i]) le hw) wn_temp=wn(aindex) rad_temp=rad(aindex) weight_temp=1.-abs(wn_temp-wn[i])/hw rad_temp=rad_temp*weight_temp smooth_rad[i]=total(rad_temp)/total(weight_temp) endfor • For a resolution of 2.8 cm-1, “hw” should be 1.4 cm-1. Was “hw” = 2.8 or 1.4 when convolving the measurement data? • I was told to set “hw” = 2.8. • The convolution code does not change the number of data points, but the AIRS spectra have a uniform wavenumber step of 1.39052 cm-1. What was done besides convolution?
Too large IRIS gas profiles • All gases are order of magnitude smaller, if in unit of number density per cubic meter • If scaled up by a factor of 10, look too large. • Check CO2 and methane, of which well accepted values are known for 1970.
IRIS gas profiles converted to volume mixing ratio • Accepted concentration of CO2 in 1970: 325 ppm; Our input: 335 ppm • Accepted concentration of methane in 1970: 1.4-1.5 ppm. Our input: 1.68 ppm at ground • US standard model atmosphere provides rough estimate at a few altitude levels only, and not for tropics. What was done besides interpolating to 101 levels?
More puzzles of the simulation • My IRIS and AIRS inputs, in ppmv: http://web.gps.caltech.edu/~mlau/IRIS_AIRS_inputs/ • Original IRIS profiles from Yibo: http://web.gps.caltech.edu/~mlau/TRP_1_MOD.100 • Ozone was increased by 8% to make AIRS profile, not physical • Methane was increased by 40% to make a -6.5 K brightness temperature difference. The true increase should be ~25%. • Does frequency shift contribute to the -8K difference at 1304 cm-1?
Simulation using profiles from Grigg’s paper • 16 altitude levels only • Source: page 17-19 of http://web.gps.caltech.edu/~mlau/Griggs-07-IRIS-IMG-AIRS.pdf
Comments on simulation with profiles from Griggs’s • Grigg’s 1970 profiles are closer than ours to other available sources. But her 2003 profiles are incorrect. • Positive difference in water vapor continuum and shape inverted: they used a much smaller water profile for 2003.
Continued • Fail to simulate the ozone signal: no significant difference in stratospheric temperature and ozone concentration in their 1970 and 2003 profiles. • Too few levels at the stratosphere, where ozone signal is sensitive to.
Decision? • Set “hw” to 1.4 or 2.8 for convolution? • Recalculate all profiles from US standard model of atmosphere, or use Griggs’s 1970 profiles and interpolate to more levels? • Keep ozone+8% and methane +40%?
Update on searching for inversion • Redoing the search for spectra with ozone band inversion, with the same search method for both AIRS and IRIS • Finished searching among IRIS and uploaded to http://web.gps.caltech.edu/~mlau/iris_spec_updated/. • Sample plots and statistics:
Continued • Checked every 1 in 10 among AIRS (Apr-Dec 2007, Apr-Dec 2008) for ozone band inversion. • Uploaded to http://web.gps.caltech.edu/~mlau/airs_spec/. • Sample plots and statistics:
Continued • When searching for CO2 inversion, require the whole CO2 band centered at 670 cm-1 to be inverted, or just the Q branch at 720 cm-1?
Thank you! I really want to, and I will, finish the exciting jobs at hand, though I’m leaving tomorrow.