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Mesospheric Chemistry and Dynamics

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Future stratospheric aircraft and spacecraft could emit water vapour and nitric oxide into the stratosphere and, as a result of the introduction of advanced supersonic and hypersonic aircraft, environmental issues may ensue. For example the emissions of additional H2O and NOx may strongly enhance PSC formation. Improved understanding of stratospheric chemical processes and distributions of trace constituents, including aerosol and PSCs, is essential for environmental assessments of future space and aviation activities.

SCIAMACHY’s studies of the stratospheric chemistry and dynamics will utilise the simultaneous retrieval of total columns from nadir measurements and vertical stratospheric profiles from limb and occultation measurements of O3, NO2, BrO, H2O, OClO (under ozone hole conditions), as well as aerosol and stratospheric cloud information. SCIAMACHY is intended to make measurements when halogen loading of the stratosphere maximizes at the beginning of the 21st century. In general, SCIAMACHY observations will yield detailed information about the development of stratospheric O3 above the Arctic and Antarctica, the global stratospheric active halogen species (BrO, OClO), and the global O3 budget as a function of the height in the atmosphere. Thus the SCIAMACHY data set may allow testing of the accuracy of current stratospheric models and their predictive capabilities.


Mesospheric Chemistry and Dynamics

The mesosphere extends from the temperature maximum at the stratopause around 50 km altitude to the atmospheric temperature minimum at the mesopause around 85 km. There has been much discussion of upper stratospheric and mesospheric chemistry in the context of the Ozone Deficit Problem (Crutzen at al. 1995, Summers et al. 1997). It has also been suggested that monitoring of H2O in the lower mesosphere may offer an opportunity for the early detection of climate change (Chandra et al. 1997). Satellites have provided some data about mesospheric temperatures and the temporal and spatial distributions of O3. In this context, little is known about the global dynamics and chemistry. It is expected that the growth in atmospheric CH4 will lead to an increase in mesospheric H2O concentrations which might also result in enhanced PMC formation around 85 km.

In the upper stratosphere and lower mesosphere, SCIAMACHY measurements yield profiles of temperature, O3, NO, and O2(1D) as well as data on PMCs. These measurements can be used to study the distribution of O3 and the global circulation. The O3 destruction by mesospheric and upper stratospheric NO will be investigated. In contrast to the retrieval of the majority of trace gases from SCIAMACHY data, NO and O2(1D) profiles are to be determined from their emission features rather than their absorptions. The combination of height resolved O3, O2(1D), and UV radiance products from SCIAMACHY provides detailed information about the photolysis of O3 in the upper stratosphere and mesosphere. This will serve as an excellent opportunity to test our current photochemical knowledge of the mesosphere.

Global Warming and Climate Change

Although already discussed over a century ago by Arrhenius in 1896 (Arrhenius 1896), the issue of global warming caused by the injection of the so-called greenhouse gases such as CO2 and CH4 into the atmosphere has become prominent in recent years. This is because of the rapid increase in atmospheric CO2 associated with the combustion of fossil fuels in the second half of the 20th century. The recognition that other species can behave in a similar manner, but often more effectively than CO2, has resulted in the definition of the global warming potential of trace gases. The list of greenhouse gases now comprises many species including H2O, CO2, CH4, nitrous oxide, CFCs and tropospheric ozone. Governments of many nations, concerned with the potential harmful consequences of global warming, have mandated to make evaluations aiming to provide national and international policymakers with an accurate assessment of our current understanding of climate change (IPCC 2007). The increasing evidence that current global warming is to a large extent man-made was documented in the 4th assessment report of the Intergovernmental Panel of Climate Change (IPCC) in 2007. Figure 1-6 summarises the global annual mean radiative forcing of relevant agents contributing to global warming. (see fig. 1-6)

 

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fig. 1-6:

image
Global, annual mean radiative forcings (Wm-2) due to a number of agents for the period from pre-industrial (1750) to present (late 1990s; about 2000). The height of each box denotes a central or best estimate value while its absence indicates that no best estimate is possible. The vertical bars visualise an estimate of the uncertainty range, for the most part guided by the spread in the published values of the forcing. The uncertainty range specified here has no statistical basis and therefore differs from the use of the term elsewhere in this document. A 'level of scientific understanding' index is associated to each forcing, with high, medium, low and very low levels, respectively. (IPCC 2001)
 


As the concentrations of atmospheric greenhouse gases and their radiative forcing have continued to increase as a result of human activities, global warming and its impact on the Earth-Atmosphere system will further increase. One of the future challenges is to quantify the complex feedback cycles (see figure 1-3) between climate, atmospheric composition, natural and human activity which are driven by global warming. For example global warming is expected to result in more frequent dry, hot summer periods in Europe – like the summer of 2003 – with degraded air quality in wide parts of Europe.

For use in climate research, SCIAMACHY measurements will provide the distributions of several important greenhouse gases (CH4, CO2, and tropospheric O3), aerosol and cloud data, surface spectral reflectance (280-2386 nm), the incoming solar spectral irradiance and the outgoing spectral radiance (214-2386 nm). The observation of the greenhouse gases CH4 and CO2 will help to better quantify natural emissions globally, thereby improving the scientific basis of the Kyoto Protocol, which was put into force in spring 2005.

As it is intended that SCIAMACHY observations are to be made for many years, this long-term data set will also deliver much unique information useful for the study of the solar-terrestrial interactions and variations of the solar output including its impact on climate change. To maintain continuity with other spectrometers measuring solar spectral irradiance such as SBUV or GOME, SCIAMACHY was calibrated using standard methods which had also been applied to the GOME or SBUV calibration.

 

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