Observation and Validation of Methane from Ft-Ir over Addis Ababa
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Date
2011-06
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Addis Ababa University
Abstract
The concentration of methane, the most abundant organic trace gas in the atmosphere
has increased dramatically, over the past few centuries, to more than double its value. The
increase in its concentration is of special concern because of its e ects on climate and atmospheric
chemistry. High resolution Mid infra-red (MIR) solar absorption FTIR spectra
have been routinely recorded between May 2009 and Nov 2010 at Addis Ababa Observatory
(9.01oN, 38.76oE). By analyzing the shape of the pressure dependent absorption lines
and their di erent temperature sensitivities, the vertical distribution and column amount
of methane is retrieved. Unique time series of the column abundances and volume mixing
ratio (vmr) of methane are presented. The e ects of both dynamical and chemical seasonally
varying trace gas cycles can be seen in the retrieved pro les. These include little
variabilities in summer and winter seasons, which is typical of tropical atmosphere. Particular
events are selected and origin of air mass
ow is identi ed with the help of Air
Resource Laboratory's (ARL) Hybrid Single Particle Lagrangian Integrated Trajectory
(HYSPLIT) model. A detailed error analysis has been performed for each pro le. The
output from Atmospheric Infra-Red Sounder (AIRS) is compared to the total column
amount. Results agree well with a correlation coe cient of 0.8
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Keywords
Methane from Ft-Ir over Addis Ababa