16 December 200816 December 2008 CAVIAR Annual Meeting 2008CAVIAR Annual Meeting 2008 11

Claudine Chen and Claudine Chen and John E HarriesJohn E Harries

Space and Atmospheric Physics group,Space and Atmospheric Physics group,Blackett Laboratory, Blackett Laboratory,

Imperial College,Imperial College,London,London,

UKUK

Initial calculations of continuum effect on outgoing IR spectrum:

Preparations for CAVIAR WP 5

16 December 200816 December 2008 CAVIAR Annual Meeting 2008CAVIAR Annual Meeting 2008 22

Earth spectrum studies at Imperial and a view for the future

• At Imperial College for over a decade, we have studied the information

contained in the Earth’s outgoing infrared spectrum, with a view to exploiting

this information to study the changing climate.

• We have used model simulations and real observations, and more

recently re-analysis data.

• We have focussed attention on the far IR.

• Now we are looking at future missions, such as CLARREO*, which seek

to measure the spectrally resolved energy flux into and out of the planet,

and the setting up in space of a “measurement standard” satellite, capable of

inter-calibrating other missions.* (Climate and Absolute Radiance and Refractometry Observatory)

16 December 200816 December 2008 CAVIAR Annual Meeting 2008CAVIAR Annual Meeting 2008 33

The CAVIAR component of this project: • As part of this study of the Earth’s IR spectrum, we

have simulated the effect of the Continuum absorption on the OLR spectrum of the Earth.

• We have used MT CKD v1.3 of the continuum, in the LBLRTM code v10.3 to simulate the OLR spectrum, with and without the continuum.

• We have used the NCEP re-analysis to provide atmospheres as input to the RT code. ERA-40 atmospheres will also be used, and ERA-Interim is also being introduced. We report here only the initial results using NCEP.

16 December 200816 December 2008 CAVIAR Annual Meeting 2008CAVIAR Annual Meeting 2008 44

16 December 200816 December 2008 CAVIAR Annual Meeting 2008CAVIAR Annual Meeting 2008 55

16 December 200816 December 2008 CAVIAR Annual Meeting 2008CAVIAR Annual Meeting 2008 66

Pure rotation H2O

CO2CH4

O3 (highly variable)

2 H2O

16 December 200816 December 2008 CAVIAR Annual Meeting 2008CAVIAR Annual Meeting 2008 88

Summary • We have simulated the effect of the continuum

absorption on the OLR spectrum of the Earth using LBLRTM v10.3, which uses MT-CKD v1.3, using NCEP reanalysis data as input

• Water continuum contributes to almost 10% of the radiance for profiles over the tropical oceans in the window region and pure rotation band

• The water continuum is also potentially significant when looking at time evolution and future projections. In this case, water continuum contributed a radiative forcing of ~0.5 W/m2 to the difference signal