A13H-01 INVITED
Observations Show that the Increase of Carbon Dioxide is Fully Caused by Human Activities.
There are two independent lines of evidence showing that the observed increase in atmospheric carbon dioxide is 100% due to human activities. The first is mass balance. The observed increases in the atmosphere and oceans add up, within uncertainty, to the total amount emitted from the burning of fossil fuels. The second line of evidence rests on observed changes in isotopic ratios of carbon dioxide. Interannual variations of the global atmospheric growth rate can be shown to depend largely on variations in temperature and precipitation. Removal of the variance caused by the latter factors clearly brings out the acceleration of the growth rate in recent years, which is almost certainly caused by the acceleration of the global emissions. Trends of the observed atmospheric spatial pattern do not contradict the above assertions.
A13H-02
Recent Trends in Atmospheric 14CO2
The radiocarbon content of atmospheric CO2 (14CO2) varies due to a number of factors. After the near-doubling of the 14CO2 loading in the early 1960s (due to atmospheric nuclear weapons testing), many studies examined the fate of this 'bomb 14C' to understand exchange processes of CO2 with the surface reservoirs. Today, however, the atmosphere and surface reservoirs are close to equilibrium with respect to bomb 14C, and instead, changes in 14CO2 more strongly reflect the response to the addition of 14C-free fossil fuel CO2 to the atmosphere. We use an atmospheric transport model to simulate recent atmospheric 14CO2, and compare this to observations at several sites over the Northern Hemisphere continents. We show that, in the Northern Hemisphere, 14CO2 variability is dominated by the effect of fossil fuel CO2 emissions. The model simulates the time trends quite well, including both the overall secular trend and the seasonal cycle. A seasonal cycle in 14CO2 is observed at the high altitude sites of Niwot Ridge, Colorado, and Jungfraujoch, Switzerland, but the magnitude varies from year to year. Our modeling studies demonstrate that this inter-annual variability can be explained by differences in atmospheric transport. This is in contrast to CO2 concentration seasonal cycles, which are dominated by seasonal changes in CO2 source strengths.
A13H-03
Interannual Variability And Trends Of CO As Seen By SCIAMACHY
The SCIAMACHY near-infrared satellite instrument currently provides 4 years of global carbon monoxide (CO) data. The sensitivity of SCIAMACHY to surface CO allows the investigation of sources and sinks as well as long- term variability and global trends. SCIAMACHY CO shows significant interannual variability, which is mainly due to variability in biomass burning. For example, extensive burning in Alaska in July 2004 has been clearly observed with SCIAMACHY, as well as the Siberian forest fires in Spring 2003 and in Indonesia in 2006. Of particular interest is the interannual variation of CO in the Southern Hemisphere where biomass burning is the main source of CO. SCIAMACHY data clearly show enhanced CO columns during the biomass-burning season in good agreement with chemistry-transport model simulations using the new independent satellite-based GFEDv2 biomass-burning emission data base. It is shown that up to 35% of the observed CO total columns over Australian biomass-burning regions during the 2004 fire season is due to CO transported from South American biomass-burning regions. In fact, the interannual variation in excess CO in Australia during the biomass-burning season is caused by interannual variation in biomass-burning CO emissions in South America. Differences between SCIAMACHY CO and model simulations over Australia are thus not only due to uncertainties in local emissions but also in overseas emissions followed by efficient long-range transport. Synergy of SCIAMACHY CO with MOPITT which is mostly sensitive to middle and upper tropospheric CO, will allow a better quantification of the contribution of local and overseas emissions in order to improve current emission estimates.
A13H-04
Effects of Plume-Rise Parameterization On The Simulation Of Boreal Fire
Over the last 30 years, global boreal forests have experienced significantly warming and drying, leading to both increased frequency and intensity of the boreal fire regime. These intense boreal fires are very energetic and may inject a large amount of carbon monoxide (CO) and fire-associated aerosols into the upper troposphere and stratosphere through a pyro-convection process. Accurate simulation of lofting height of these fires is challenging. In this study, we evaluated a parameterization of plume lofting by dry and moist convection in the NCAR Community Atmospheric model (CAM) driven by NCEP meteorological data. This allows studies of individual fire- weather events. Our simulations are focused on the Alaska-Yukon boreal fires observed by MOPITT (Measurements of Pollution in The Troposphere) and AIRS (Atmospheric InfraRed Sounder) satellites during the summer of 2004. We will compare the simulated CO with AIRS and MOPITT measured CO. We will also present the effectiveness of a plume-rise parameterization, developed originally for subtropical application, in the simulation of plume height.
A13H-05
Understanding Elevated Tropical Tropospheric Ozone and CO During the 2006 El Niño using TES Observations and GEOS-Chem Simulations
The moderate El Niño in 2006 resulted in changes in tropical trace gas mixing ratios measured by the Tropospheric Emission Spectrometer (TES). We investigate the mechanisms for these changes through simulations using the chemical transport model GEOS-Chem, comparing 2006 TES data with 2005 (a neutral year with respect to Pacific sea surface temperatures in the region defining El Niño or La Niña). The most prominent tropospheric changes during 2006 in both TES and GEOS-Chem data were elevated levels of ozone and CO over Indonesia and the eastern Indian Ocean. During October to December 2006, ozone and CO exceeded the previous year's values by more than 30 ppb and 80 ppb, respectively. The elevated CO can be traced to increased biomass burning in Indonesia during the dry El Niño conditions. The elevated ozone can only be adequately modeled by satisfactorily accounting for multiple factors such as transport, convection, fire emissions and lightning NOx. Overall, GEOS-Chem does a reasonable job of simulating the major ozone and CO features and inter-annual anomalies in the TES measurements. To further understand the importance of the factors contributing to elevated ozone, we test the sensitivity of the ozone anomaly to changes in fire emissions and lightning NOx.
A13H-06
ENSO-Induced Enhancement of Tropospheric O3 During Summer over South Asia
Long-term satellite observations from NASA-TOMS and ERSII-GOME/SCIAMACHY over north India especially the Indo-Gangetic plain show an enhanced abundance of tropospheric O3 and NOx in summer with substantial interannual variability linked to ENSO-induced changes in the Walker circulation. MATCH-MPIC model results using tagged CO tracers demonstrate how changes in this circulation lead to increased influence of emissions from China and southeast Asia on upper tropopsheric O3 over India during ENSO conditions. The impact of ENSO is further demonstrated in the correlation between the anomaly in tropospheric ozone residual data derived from TOMS and the velocity potential anomaly over north India and the equatorial Indian Ocean associated with convective uplift and transport through Walker cells.
A13H-07
Ozone trends (1975-2000) in the northern hemisphere UTLS using measurements from ozone sondes and regular aircraft
Ozone is a particularly strong greenhouse gas in the tropopause region, and therefore trends in this altitude are important for changes in radiative forcing. The knowledge of ozone trends in the UTLS is mostly based on a confined number of stations operating regular ozone measurements from balloons with the longest measurement series starting in the late 1960s. In this study we use ozone measurements from regular aircraft of the GASP project (Global Atmospheric Sampling Program) providing ozone data from four B-747 aircraft operated from USA from 1975 to 1979 in comparison with measurements of the ongoing MOZAIC project. For building climatologies of the two ozone data sets and hence their comparison, the data were binned relative to the dynamical tropopause, and coordinates in equivalent latitudes are used for analysis of stratospheric data. Additionally, in the upper troposphere, averages were computed for specific regions of the world such as, for example, North America, Europe, or Japan. The analysis shows that lower stratospheric ozone decreased significantly over northern mid- and high latitudes from the late 1970s to the second half of the 1990s in autumn and winter, and to a lesser extent also in spring. In the upper troposphere, pronounced increases are found over South Asia including India in the spring and summer seasons. On contrast, no clear changes are seen over the United States and Europe. In addition, a comparison of long-term changes deduced from the regular aircraft measurements and from ozonesondes is presented. Differences between the climatologies of the late 1970s and 1990s for the aircraft data over Europe and ozonesonde measurements at European stations show differing long-term changes, which will be discussed.