Report
on participation in VIII Congress of IAMAS (Innsbruck, Austria, 10-18 July, 2001)
The IAMAS Congress included more 30 Symposiums on different lines of recent investigations in the field of atmospheric science.
At Plenary Session, sir D. Hotton (England) gave the review of main results of the working group on Anthropogenic Climate Change. Dr. R. Anthes (Austria) presented scientific-futurologic report on forecasting the weather in 2025. Reliability of weather forecasts is expected to be essentially enhanced due to the increase of spatial resolution of atmospheric numerical models, accuracy of satellite sounding and the capacity of hardware. The last argument of the author is coming improvement of comprehension and description of atmospheric processes.
Much attention was centered on problem of the Earth climate (at six Symposiums).
Atmospheric Satellite Sounding
A number of reports were dedicated to planned satellite projects and first results of projects executed in last years.
ESA representatives informed on the ENVISAT scientists apparatus of the satellite designed for atmospheric sounding. Special attention was given to three devices. Limb interferometer MIPAS will be measure the radiation of Earth horizon in middle IR spectral range with high spectral resolution. The main task is to get data on vertical profiles of temperature, humidity, ozone and trace gas contents in global scale. These data will be used in different investigations of atmospheric physics and chemistry.
Other device – GOMOS – will use the star radiation for occultation observations of ozone, other atmospheric components and aerosol. It would be noted that the accuracy of ozone sounding given in the report (0.2-1.0% - the relative error, 1-2% - the absolute error) is too optimistic and doubtful. This fact became evident after the report of Yu.M. Timofeyev (Influence of star scintillations on accuracies of retrieving the ozone content – co-authors are A.V. Polyakov, A.S. Gurvich, V. Kan, V.N. Vorobyev, Jeng-Hwa Yee). This report will be discussed further.
Third device for atmospheric studies – SCIMACHI – will have different measurement schemes – nadir and limb above dayside and use Sun and Moon for twilight atmospheric sounding. This device is able to measure in some thousands of channels in UV, visible and near-IR spectral ranges. The aim is to receive the information on gas and aerosol atmospheric content, surface and cloud characteristics in global scale. It would be noted that a simple sample of the SCIAMACHI has been successfully functioned at the ERS-2 satellite during above five years.
At the Symposium "Satellite sounding of atmosphere", Yu.M. Timofeyev represented the above report on atmospheric sounding by measurements of star radiation. In the first methodical part, results of numerical estimations of potential accuracy of retrieving the ozone profile in the presence of star scintillations of different types caused by inhomogeneities of layered atmosphere. On the basis of the scintillation model developed in Obukhov Institute of Atmospheric Physics (OIAP) and based on numerical experiments at stations "Salut" and "Mir", it was shown that errors of retrieving the ozone content could increase by 2-5% (especially in lower stratosphere) under assumption on an uncertainty of scintillations (which change in space and time). In second part of the report, an example of retrieving the profiles of O3, NO3 and aerosol extinction from the UVISI (MSX satellite) data was given. Comparison of the satellite ozone retrieval with independent lidar measurements shown that differences were 10-20%. Main conclusion is the star scintillations prevents the ozone retrieval with the 1-2% error.
John Gille (USA) with co-authors considered first results of retrieving the global spatial maps of CO content in middle troposphere from the MOPITT (TERRA satellite) data received in about 400 days. But the measurement processing meets some difficulties connecting with equipment problems. In particular, up to now the near-IR channels (2.2-2.4µm) do not put on the processing. All the same, these results demonstrated the valuable of satellite information for determining the CO sources of anthropogenic nature.
It would be noted the poster of authors from many countries (including OIAP and SPbSU) dedicated to validation of above CO satellite measurements. Ground-based measurements forwarded the refinement of the MOPITT characteristics and interpretation method.
Dr. M. Halley et al. informed on successful launch of OSIRIS satellite on 20.02.2001. A number of atmospheric and astrophysical investigations are supposed to be performed during two years. This satellite is equipped by the spectrophotometer ODIN for limb sounding by diffused solar radiation. ODIN has many channels in the 280-800 nm spectral range (the spectral resolution is 1 nm) with the spatial resolution of 1x40 êì. Investigations of gas and aerosol atmospheric content are planned with this device.
Second device at the OSIRIS is sub-mm radiometer for measuring the Earth horizon radiation to determine vertical profiles of content of many atmospheric gases: ozone, water vapor, oxygen, etc.
In the Symposium, there were a number of reports dedicated to the atmospheric sounding by refraction radio wave measurements using different satellites. Scientists of many countries are interesting this method which is perspective for sounding the atmospheric temperature and water vapor. In addition to methodical studies (estimates of sounding accuracy at different altitudes, application of tomography and etc.), some examples of processing the data of different satellites were given.
Great attention were given to satellite measurements of atmospheric aerosol. High level of aerosol studies by the AVHHR and POLDER was noted in a number of reports. POLDER is characterized by high spatial resolution (6x7 km) acceptable for this problem, 9 spectral intervals in visible and near-IR ranges, the possibility of sounding the same atmospheric areas at 14 angles and polarization measurements. It gives a possibility to measure not only aerosol and cloud optical characteristics but also their microphysical parameters.
Dr. Valero presented the new satellite (TRIANA) which would launched at "special" space point (Lagrangian point) for constant location relative to Earth. This Project (First Deep Space Climate Observatory) will give a possibility to study radiation fluxes radiated and reflected by Earth from very great distance. Instruments at this satellite will measure the radiation balance of Earth as a planet and map Earth with spatial resolution of 8 km in 10 spectral intervals in the 317.5–905 nm range.
Dr. John Gille described characteristics of new radiometer HIRDLS intended for determining the three-dimensional global fields of atmospheric temperature and gas content in wide altitude diapason (from upper atmosphere to 80 km) with high horizontal resolution. But the errors of future measurements of a number of atmospheric parameters (e.g. ozone) given by the author are evidently underestimated as the HIRDLS ozone retrievals are very difficult during daylight under non-LTE conditions because the device has relatively poor resolution and channel number. These circumstance lead to the solution of relevant inverse problem with great amount of additional a priori information (excitation models for the vibrational states of ozone molecule) which do not correspond to recent requirements.
Similar comment is applicable to the report of Dr.Mlynczek which described the radiometer SABER and estimated accuracies of measurements of atmospheric parameters.
It would be noted that if European scientists (K.Grossmann, H. Fisher) tend to develop the equipment of high spectral resolution for measuring the Earth horizon radiation (and hence to solve inverse problems without using additional a priori information), American scientists develop such devices with medium and poor spectral resolution. Although the second way gives a possibility to develop more simple and durable satellite devices, the first one is more perspective with physical point of view. It is lesser-depended on the quality of additional a priori information and more-informative as the main information on the atmospheric content is derived from just outgoing radiation measurements.
The report of Yu.M. Timofeyev et al. (SPbSU, Russia) with co-authors from OIAP dedicated to the validation of the ozone and NO2 measurements by GOME device belonged also to satellite theme. Comparison of GOME ozone measurements (different periods of 1996-2000) with data of Russian ground-based ozonometric network shown that satellite measurements underestimated the ozone content by 4-9 % on average . It would be noted that the improvement of GOME data processing during last two years gives a possibility to decrease these differences. Similar comparison NO2 data revealed very large differences between satellite and ground-based measurements (up to 100 % and more). Further studies are necessary to clear causes of such differences.
Ground-based Remote Sensing
In the framework of the Symposium "Ground-based Remote Sensing", many reports dedicated to methodical aspects of different passive and active atmospheric remote sensing and results of using different remote methods for solving the problems of atmospheric physics and chemistry were presented.
Dr.Ackerman and others (Van Lammern, Illinworth, Boitel et al, Englebart) gave reviews of scientific results and described characteristics of ground-based remote sounding systems in different Earth regions.
J. Ellingston described the experience of using the ground-based systems to determine the atmospheric optical depth during night. Report of Ya. Virolainen et al. (Russia) with German colleagues from Max Plank Institute of Meteorology and Potsdam Meteorological Observatory was dedicated to a review of new results of interferometric measurements of downward thermal atmospheric radiation with high resolution. The most original of these studies is the demonstration of possibilities of observing the daily variations of total contents of a number of atmospheric trace gases (e.g. CH4 and NO2). This new information may be useful for testing the recent photochemical tropospheric models and validation of satellite measurements.
Main conclusion after proposed reports – at present ground-based remote methods use radiation measurements in wide spectral range (from visible to radio waves), different devices for passive and active atmospheric sounding and give a possibility to derive a great amount of information on atmospheric state – temperature and humidity profiles, cloud microphysical characteristics, trace gas contents etc. Important recent problem is an inter-calibration of different systems of atmospheric sounding.
A number of reports were dedicated to examples of successful using the ground-based radiation measurements for the improvement of atmospheric radiative models (S. Bakan and H.-D. Hollweg).
Chemistry, Dynamics and Radiation in Middle Atmosphere
This Symposium was hold during 6 days and included many reports in the following lines:
Let us introduce the most important reports with new results.
V. Fomichev et al. (Canada) represented results of calculating the energetic balance of middle atmosphere on the basis of new widen version of Canadian model of common circulation of the atmosphere. Dr. Mlynczek proposed original method of measurements of energetic balance in wide altitude range on the basis of satellite measurements of thermal radiation and atmospheric glows. He demonstrated how this method could be used in satellite experiments with the radiometer SABER. Yu. Timofeyev and V.S. Kostsov (Russia) gave results of interpreting the outgoing radiation measurements in the 15 µm CO2 band by CRISTA spectrometer. They demonstrated retrieved vertical profiles of kinetic temperature, vibrational temperature and CO2 mixing ratio at the altitudes from 40 to 120 km. Two main conclusions were obtained:
1. In mesosphere temperature inversions of different amplitudes (up to 50 degrees) are observed.
2. In mesosphere CO2 mixing ratio is smaller by 10-20% than values used in models .
V. Ogibalov (Russia) gave a review of the problem of calculating the non-LTE population of different levels of CO2 molecule and estimated the heat influx in the CO2 bands.
Dr. Kauman (Germany) with colleagues presented numerous data on global distribution of temperature and different gas constituents which were obtained during two space experiments with CRISTA device. Authors concluded that recent models essentially overestimated the mixing ratio.
There was interesting poster of A. Kutepov with co-authors dedicated to calculations of populations of different states of CO2 molecule by practically standard method free from most assumptions used in recent methods. It was shown that although recent approximation methods for calculating the radiation fluxes gave rather reliable data, in a number of cases those could give calculation errors up to 100%. In this connection, there is the necessity in constructing new, more adequate parametrizations of heat influxes to use those in numerical models of upper atmosphere.
Atmospheric aerosols
Many reports at different Symposiums were dedicated to this line of investigation in the field of atmospheric physics and chemistry. Principal recent lines of investigation in the field of atmospheric aerosol are:
In a number of reports, new results of field measurements of aerosol microphysical and optical characteristics were discussed. Complex measurements with different platforms (space, satellite, aircraft) and by different methods is principal characteristic of such investigation. P. Caboe reported results of complex multiyear aerosol studies in different Atlantic areas. Investigations were executed onboard specially equipped aircraft flights collocating with satellite and ground-based measurements. Impactors of different types, optical instruments for studying the aerosol extinction and scattering and for determining the aerosol chemical composition were used in the experiments. Great amount of information on total concentration of aerosol particles, their size distribution functions, complex refractive indexes and extinction and diffusion coefficients in different spectral ranges (chiefly in visible range) were obtained. In addition to experimental studies theoretical calculations (in particular, aerosol optical characteristics) have been performed. Comparison of experimental and theoretical data gives contradictory picture. In a number of cases, a good agreement is observed but in some cases differences exceed total experimental and calculation errors. The last is explained by shortcomings of calculation method ( as a rule that is Mie algorithm) and the lack of data on different characteristics of atmospheric aerosols.
In a number of reports, data of ground-based measurements of optical (optical depth) and microphysical (size distribution function) characteristics obtained with solar spectrophotometers of known network AERONET. At present this network involves more 100 automatic instruments functioning in many countries. This network supplies with valuable regular information on atmospheric aerosol and gives a possibility for studying the climatic aerosol characteristics and realizing the validation of numerical satellite instruments.
IRC Business Meeting
In the framework of the IAMAS Congress, two sessions of IRC Business Meeting have been hold. The points of discussion :
In the first session, Yu.M. Timofeyev reported studies in the framework of the workgroup “Remote Sounding of Middle Atmosphere”. Results of international comparison of different radiation codes for calculating the non-LTE IR radiation were presented.
Two new IRC members from Russia – A.B. Uspensky and N.E. Chubarova – were presented.
In the short run the information on the IRC Business Meeting will be placed on IRC site.
It can be concluded that the participation on IAMAS Congress gave a possibility to obtain new scientific information, to meet with many leading scientists and to target future studies and plans of international cooperation.