| Vertical profiles of CO taken from the MOZAIC aircraft database
are used to present (1) a global analysis of
CO seasonal averages and interannual variability for the years
2002-2007 and (2) a global validation of CO estimates produced by the
MACC models for 2004, including an assessment of their ability to
transport pollutants originating from the Alaskan/Canadian wildfires.
Seasonal averages and interannual variability from several MOZAIC sites
representing different regions of the world show that CO
concentrations are highest and most variable during the winter season.
The inter-regional variability is significant with concentrations increasing
eastward from Europe to Japan. The impact of the intense boreal fires,
particularly in Russia, during the fall of 2002 on the Northern Hemisphere
CO concentrations throughout the troposphere is well represented by
the MOZAIC data.
A global validation of the GEMS/MACC GRG models which include three stand-alone
CTMs (MOZART, MOCAGE and TM5) and the coupled ECMWF Integrated Forecasting
System (IFS)/MOZART model with and without MOPITT CO data assimilation show that
the models have a tendency to underestimate CO. The models perform
best in Europe and the U.S. where biases range
from 0 to -25\% in the free troposphere and 0 to -50\% in the surface
and boundary layers (BL). The biases are largest in the winter and during
the daytime when emissions are highest, indicating that current
inventories only represent the minimum emissions. Data assimilation
is shown to reduce biases by up to 25\% in some regions. The models
are not able to reproduce well the CO plumes originating from the
Alaskan/Canadian wildfires at downwind locations in the
eastern U.S. and Europe, not even with
assimilation. Sensitivity tests reveal that this is mainly due to deficiencies in the fire emissions inventory and injection height. |