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Aerosols in the Stratosphere and Mesosphere

#G-870


Stratified Altitudinal Distribution of Aerosol in the Stratosphere and Mesosphere

Tech Area / Field

  • ENV-MIN/Monitoring and Instrumentation/Environment
  • ENV-APC/Air Pollution and Control/Environment
  • ENV-OTH/Other/Environment
  • OBS-NAT/Natural Resources and Earth Sciences/Other Basic Sciences
  • PHY-OPL/Optics and Lasers/Physics
  • PHY-OTH/Other/Physics

Status
3 Approved without Funding

Registration date
03.04.2002

Leading Institute
Evgeni Kharadze Georgian National Astrophysical Observatory, Georgia, Tbilisi

Supporting institutes

  • Center for Coordination and Implementation of Scientific, Technological and Socio-Economic Projects, Georgia, Tbilisi

Collaborators

  • University of New Mexico / Department of Earth and Planetary Sciences, USA, NM, Albuquerque\nInstitut d'Aeronomie Spatiale de Belgique, Belgium, Brussels

Project summary

The past decade has seen increasing public concern about the Earth’s atmosphere and climate changes. It is important to realize the need to study not only the lower atmosphere (or troposphere), but also the other layers of the atmosphere, namely the stratosphere and the mesosphere.
Aerosol plays an important role in the physics and chemistry of the atmosphere and is to be taken into account in different fields of atmospheric science.
Stratospheric aerosols, which are mainly of volcanic origin, affect the atmospheric energy balance by scattering and absorbing solar and terrestrial radiation. They can catalyze heterogeneous reactions that affect global ozone abundance by converting stable chlorine species into photochemically active in ozone destruction ones. Ozone is one of the most important atmospheric species because it absorbs the dangerous for health solar ultraviolet radiation and serves as a source of heat in the stratosphere, so its reduction will impact on climate. This brings up a question about simultaneous measurements of aerosol and ozone for future investigation of aerosol role in ozone depletion.
Mesospheric aerosol consists mainly of dust particles resulting from meteor ablation and of much smaller ones which are recondensed from meteor vapors. Nowadays space-age debris are an important factor of mesospheric contamination. The knowledge about formation, total amount, and dynamics of settling of mesospheric aerosol to the stratosphere is very restricted.
A set of experimental methods exists for probing stratospheric and mesospheric aerosol. The global distribution of aerosols is monitored through satellite experiments, which record the extinction of solar radiation by aerosols. The aerosol extinction depends on their total number density and on their size distribution as well as on unknown a priori parameters, namely, their shape and refractive index. Because of this, satellite data are always supplemented with data obtained by other methods, both in situ sampling and scattering measurements. An example of ground-based remote sensing technique, which is used for validation procedures of satellite data, is lidar technique. It permits one to study local aerosol distribution with high temporal and space resolution, although it is restricted by altitude (up to 30 km) and operates with one or a few wavelengths. Another possibility of remote aerosol measurements gives twilight sounding method (TSM).
The following physical phenomenon lies in the basis of TSM. It is well known that red color of the twilight sky is usually observed when aerosol particles are abundant in the stratosphere, especially after strong volcanic eruptions. Spectral measurements of intensity of scattered light of the twilight sky in wide range of wavelengths (300-1100nm) at different depression angles of the Sun allow to obtain quantitative characteristics of the atmospheric aerosol, such as aerosol size distribution and change of aerosol concentration with altitude. Intensive meteor showers may bring a large amount of cosmic dust in the mesosphere, which also causes an increase of brightness of the twilight sky.
The main problem in application of the method was requirement of highly sensitive photoreceivers with response of high linearity. Nowadays the development of CCD light receivers allow to solve this problem easily. Moreover, recently developed theoretical approaches in radiative transfer and in solving techniques of the inverse problem in the atmosphere allow to improve significantly the method.
The proposed technique allows to carry out simultaneous measurements of atmospheric ozone and aerosol utilizing the fact that ozone absorption in Chappuis band is sufficiently strong in twilight conditions. Such measurements will make possible to investigate the role of aerosol in destruction of ozone layer.
The main goal of the project is the investigation of aerosol distributions in the stratosphere and mesosphere in the middle latitudes, over Caucasus region using the TSM. An influence of stratospheric aerosol on ozone depletion will also be investigated.
The proposed measurements by TSM will allow to investigate aerosol distribution in the atmosphere in the range of altitudes as wide as 15 to 120 km. This feature attaches a clear innovative character to the project, because such wide height range will allow to create a unique model of aerosol distribution comprising both stratospheric and mesospheric aerosol simultaneously and aerosol exchange between the stratosphere and mesosphere.
The project would permit advancements in:
- a further development of the TSM, a ground-based technique of stratospheric and mesospheric aerosol measurements,
- a knowledge about the stratospheric and mesospheric aerosol distribution and an influence of different events, such as strong volcanic eruptions and cosmic dust intrusions, on this distribution,
- investigations of exchange of aerosol between stratosphere and mesosphere,
- investigations of the role of stratospheric aerosol in ozone layer destruction, taking into account a factor of solar activity.
The project team has a proved experience in the studies of atmospheric aerosol, both experimentally and theoretically, as documented in the current scientific literature. A wide database of twilight measurements carried out in Abastumani Observatory by project participants is collected. It will be used together with current measurements. This database contains ground-based measurements of spectral brightnesses of the twilight sky and data obtained during a few observational campaigns of photography of sunlit limb of the Earth from spacecrafts, in which Abastumani Observatory participated.
The following activities are proposed in this project:
- to improve the retrieval technique of aerosol distributions from spectral measurements of twilight sky brightness, basing on a modern approach developed for satellite-based remote sensing observations of atmospheric characteristics,
- to monitor the aerosol loading in the stratosphere using the proposed method of twilight measurements,
- to measure variations of the ozone concentration and to compare them with aerosol loading in order to study their correlation,
- to monitor the mesospheric aerosol by twilight measurements and to investigate its dynamics in relation with meteor showers,
- to investigate an influence of solar activity on the formation of ozone and aerosol.
The following arguments support realization of the project in Abastumani Observatory. The project team has an experience in the proposed activity, they possess a large database of twilight measurements that will allow to investigate long-term trends in aerosol loading. A high atmospheric transparency and remote location of Abastumani from large cities will provide perfect observational conditions. A lack of ground-based aerosol observational sites between Europe and Japan makes the aerosol data obtained in Abastumani representative not only for Caucasus region but also for a large sector of the northern midlatitude belt.
The following results will be obtained:
- the proposed method (TSM) of ground-based measurements of aerosol distributions in the stratosphere and mesosphere will be significantly improved,
- aerosol distributions and their variations in the stratosphere will be obtained for volcanically quiet and disturbed periods. An analysis of influence of aerosol loading on ozone depletion will be presented. The results will be analyzed together with the database of stratospheric aerosol and ozone monitoring carried out in frames of GOMOS experiment (onboard ENVISAT),
- the influx of the space dust particles into the mesosphere and its variations related with meteor showers will be estimated. The results will be compared with NASA stratospheric collections of cosmic dust for analysis of observed variations,
- a one-dimensional model of altitude-dependent aerosol distributions for middle-latitude atmosphere will be developed. The unique character of this model will consist in its wide (15-120 km) altitudinal coverage. The model will help to analyze processes of vertical dust transport,
- the obtained data will be used for making an estimate of possible ecological consequences of an extreme dust loading of the atmosphere.
The following methods and methodologies will be used in the project:
- In the theoretical part of the project the retrieval techniques of aerosol concentration from twilight measurements will be improved basing on the inverse methods developed for satellite measurements of atmospheric constituents. When interpreting the data, the Mie theory, which describes the scattering and absorption of radiation by homogeneous spheres, will be used in order to relate measured twilight scattering profiles to the particle fundamental properties (i.e. size parameter and refractive index). The Differential Optical Absorption Spectroscopy (DOAS) algorithm will be used to retrieve the effective slant column amounts of ozone.
- The experimental equipment will be assembled using spectrometric complex including two miniature fiber optics CCD spectrometers which will be purchased and supplied by optical unit and solar azimuth guide, which will be constructed. Such approach will give a possibility of precise measurements in wide spectral range, which will bring a novelty in the experimental methodology.
The results obtained under this project will be incorporated in the other databases of aerosol distributions in the atmosphere for further usage in climate modeling programs. In particular, they will serve for more precise modeling of climate changes over Caucasus region.
The collaborators agree to take part in the investigations specified in the project, to share information in course of realization of the project, to review reports, to discuss results in conferences, to visit participants of the project and to receive them.
The proposed project will provide an opportunity to scientists formerly engaged in defense to be involved in peaceful investigations. It will help them to be integrated in international scientific society and to participate in future international scientific projects.


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