16 December 2008 CAVIAR Annual Meeting 2008 1 Claudine Chen and John E Harries Claudine Chen and John E Harries Space and Atmospheric Physics group, Blackett.

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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

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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)

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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.

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Pure rotation H2O

CO2CH4

O3 (highly variable)

2 H2O

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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