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<article language="en">
	<journal>
		<journal_title>Atmospheric Chemistry and Physics Discussions</journal_title>
		<journal_url>www.atmos-chem-phys-discuss.net</journal_url>
		<issn>1680-7367</issn>
		<eissn>1680-7375</eissn>
		<volume_number>9</volume_number>
		<issue_number>2</issue_number>
		<publication_year>2009</publication_year>
	</journal>
	<doi>10.5194/acpd-9-8187-2009</doi>
	<article_url>http://www.atmos-chem-phys-discuss.net/9/8187/2009/</article_url>
	<abstract_html>http://www.atmos-chem-phys-discuss.net/9/8187/2009/acpd-9-8187-2009.html</abstract_html>
	<fulltext_pdf>http://www.atmos-chem-phys-discuss.net/9/8187/2009/acpd-9-8187-2009.pdf</fulltext_pdf>
	<start_page>8187</start_page>
	<end_page>8222</end_page>
	<publication_date>2009-03-27</publication_date>
	<article_title content_type="html">First year of upper tropospheric integrated content of CO&lt;sub&gt;2&lt;/sub&gt; from IASI hyperspectral infrared observations</article_title>
	<authors>
		<author numeration="1" affiliations="1">
			<name>C. Crevoisier</name>
			<email>cyril.crevoisier@lmd.polytechnique.fr</email>
		</author>
		<author numeration="2" affiliations="1">
			<name>A. Chédin</name>
		</author>
		<author numeration="3" affiliations="2">
			<name>H. Matsueda</name>
		</author>
		<author numeration="4" affiliations="3">
			<name>T. Machida</name>
		</author>
		<author numeration="5" affiliations="1">
			<name>R. Armante</name>
		</author>
		<author numeration="6" affiliations="1">
			<name>N. A. Scott</name>
		</author>
	</authors>
	<affiliations>
		<affiliation numeration="1" content_type="html">Lab. de Météorologie Dynamique/CNRS/IPSL, Ecole Polytechnique, Palaiseau, France</affiliation>
		<affiliation numeration="2" content_type="html">Geochemical Research Department, Meteorological Research Institute, Tsukuba, Japan</affiliation>
		<affiliation numeration="3" content_type="html">Center for Global Environmental Research, National Institute for Environmental Studies, Tsukuba, Japan</affiliation>
	</affiliations>
	<abstract content_type="html">Simultaneous observations from the Infrared Atmospheric Sounding Interferometer (IASI)
and from the Advanced Microwave Sounding Unit (AMSU), launched together onboard the European MetOp
platform in October 2006, are used to retrieve an upper tropospheric content of carbon dioxide (CO&lt;sub&gt;2&lt;/sub&gt;)
covering the range 11–15 km (100–300 hPa), in clear-sky conditions, in the tropics, over sea, for the first
year of operation of MetOp (January 2008–December 2008). With its very high spectral resolution, IASI provides
fourteen channels in the 15 μm band highly sensitive to CO&lt;sub&gt;2&lt;/sub&gt; with reduced sensitivities to other atmospheric
variables. IASI observations, sensitive to both CO&lt;sub&gt;2&lt;/sub&gt; and temperature, are used in conjunction with AMSU
observations, only sensitive to temperature, to decorrelate both signals through a non-linear inference
scheme based on neural networks. A key point of this approach is that no use is made of prior information
in terms of CO&lt;sub&gt;2&lt;/sub&gt; seasonality, trend, or geographical patterns. The accuracy of the retrieval is estimated
to be about 2.0 ppmv (~0.5%) for a 5&amp;deg;&amp;times;5&amp;deg; spatial resolution on a monthly
time scale. Features of the retrieved CO&lt;sub&gt;2&lt;/sub&gt; space-time distribution include: (1) a strong seasonal cycle of
4 ppmv in the northern tropics with a maximum in June–July and a minimum in September–October. This cycle
is characterized by a backward two-months lag as compared to the surface, by a backward one-month lag as
compared to measurements performed at 11 km, and by a forward one-month lag as compared to observations
performed at the tropopause (16 km). This is likely due to the time-lag of CO&lt;sub&gt;2&lt;/sub&gt; cycle while transported
from the surface to the upper troposphere; (2) a more complex seasonal cycle in the southern tropics,
in agreement with in-situ measurements; (3) a latitudinal variation of CO&lt;sub&gt;2&lt;/sub&gt; shifting from a South-to-North
increase of 3.5 ppmv in boreal spring to a South-to-North decrease of 1.5 ppmv in the fall, in excellent
agreement with tropospheric aircraft measurements; (4) signatures of CO&lt;sub&gt;2&lt;/sub&gt; emissions (such as biomass burning)
transported to the troposphere. In addition to bringing an improved view of CO&lt;sub&gt;2&lt;/sub&gt; distribution, these
results from IASI should provide an additional means to observe and understand atmospheric transport
pathways of CO&lt;sub&gt;2&lt;/sub&gt; from the surface to the upper troposphere.</abstract>
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