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GACP Projects

Arctic Haze Measurements and Exploitation of Geostationary Satellite Data

Rolf Stuhlmann, PI
Andreas Macke, Co-I
Johannes Mueller, Co-I
Frank Albers, Co-I

Abstract: This proposal describes a two-part study related to the aerosol-cloud-radiation interaction research. Part one covers a short-term component related to validation, the second part a long-term component related to the analysis of satellite data.

The objective of the first part, the short-term component, is to participate in the Arctic Radiation and Turbulence Interaction Study (ARTIST) to study the influence of clouds and Arctic haze on the radiative fluxes over sea ice from in situ data taken in March and April 1998. ARTIST is conducted as a three year research project supported by funds of the European Commission. It includes an extensive field programme within the Fram Strait region north-west of Svalbard. The aim of the project within this proposed study is to generate a data set applicable for investigating the effect of Arctic haze and clouds on the radiation field above sea ice.

The objective of the second part, the long-term component, is to use data from instruments aboard the geostationary satellite Meteosat Second Generation (MSG), scheduled for launch 2000, - the Geostationary Earth Radiation Budget (GERB) instrument for measurements of the Earth Radiation Budget and the Spinning Enhanced Visible and InfraRed Imager (SEVIRI) for detection of aerosol and cloud properties - to study changes in ERB in relation to aerosol and cloud properties. After launch of MSG, its instruments GERB and SEVIRI simultaneously will observe regions with large tropical aerosol loading due to both Saharan dust outbreaks and, more seasonally, biomass burning, as well as industrial pollution. In respect to the study proposed here, it is expected that possibly the signatures of these aerosols and their impact on the ERB my be detectable by examination of data form the MSG instruments.

Project Description

Introduction
Atmospheric aerosols could, by reflecting solar radiation directly and by changing cloud optical properties indirectly, play an important role in global climate change. This potential effect of aerosols on climate is recognized as being one of the largest sources of uncertainty in understanding of long term climate change (IPCC,1995). Related to this uncertainty, two key questions arising from a parochially radiative perspective are: What are the effects of springtime Arctic haze on the solar radiation in and outside of polar clouds? What is the relationship between aerosol and cloud optical properties in connection to the Earth Radiation Budget (ERB) at the top of the atmosphere (TOA).

The sensitivity of the Arctic radiation balance to changes in cloud optical properties that could be attributed to aerosols has been examined theoretically by Curry and Ebert (1990,1992). An increasing amount of cloud condensation nuclei (CCN) would act to reduce the effective particle size for liquid water clouds. For the short-wave radiation, cloud reflectivity increases for drop sizes becoming smaller, reducing the incoming short-wave radiation at the surface. As the emissivity of Arctic clouds is less than unity, the decrease in drop size will increase the downward long-wave radiation to the surface. For a decrease in drop size, it is also expected that due to the decreasing efficiency of the precipitation process, there will be an increase of total liquid water content of the cloud (Albrecht, 1989, Twomey, 1991), which will alter the lifetime of the cloud and thus the total cloud cover in the Arctic. A change in the surface radiation due to aerosol cloud interaction will change the sea ice characteristics (fraction of open water), which in return will modify the surface radiation as well as sensible and latent heat. This change in surface fluxes will modify the atmospheric thermodynamic and dynamic structure and thus feed back on the aerosol and cloud properties (Curry, 1993).

First investigations to study aerosol optical thickness together with broadband reflected short-wave radiation TOA over cloud free oceans for a thirteen years (1981-1993) period was done was done by L.L. Stowe (WCRP, 1998). He found an aerosol forcing ranged from about -40Wm-2, cooling in the tropics to about +20Wm-2, heating at mid-latitudes. A disadvantage related to this study is, that the broad band reflected flux was derived from the narrow band AVHRR measurements by applying a fixed, aerosol independent conversion algorithm. Since the narrow to broadband conversion strongly depends on the spectral properties of the reflected radiation, it is expected that the narrow to broad band conversion parameters will change for different aerosol loading, which could not be taken into account so far. MSG, for the first time, will supply co-located narrow band and broad band radiation measurements with the same repetition cycle and thus will be excellent for these type of studies.

This proposal describes a two-part study related to the two research topics addressed above. The short-term objective of the first part of the proposal is to participate in the Arctic Radiation and Turbulence Interaction Study (ARTIST) to study the influence of clouds and Arctic haze on the radiative fluxes over sea ice. The long-term objective of the second part of the proposal is to use data from instruments aboard the geostationary satellite Meteosat Second Generation (MSG) - the Geostationary Earth Radiation Budget (GERB) instrument for the radiation budget and the Spinning Enhanced Visible and InfraRed Imager (SEVIRI) for detection of aerosol and cloud properties - to study changes in the ERB in relation to aerosol and cloud properties.

Short-Term Component

In spring, high concentrations of aerosol, known as Arctic haze, have been recorded in the region of Svalbard. The vertical and horizontal distribution and its optical properties significantly influence the radiation balance during Arctic spring season. Some measurements could already be taken during the REFLEX III experiment in 1995.

It is expected to gather more detailed information on Arctic haze and clouds during ARTIST. ARTIST is conducted as a three year research project supported by funds of the European Commission. It includes an extensive field programme within the Fram Strait region north-west of Svalbard. Longyearbyen will be the base for two aircraft, POLAR-2 and POLAR-4, from the Alfred Wegener Institute. For flights north of Greenland station Nord will be used as 2nd base. The experiment is scheduled for a six weeks period starting March 7th 1998. During this time of the year the ice edge is expected to be at about 80o north. Aircraft measurement will be taken over the ice and the ocean during cold air outbreaks, where clouds will form off the ice edge. GKSS will equip the two aircraft of the Alfred Wegener Institute with its particle probes and liquid water sensors (Nevzorov). It is planned to make in situ measurements of Arctic haze and cloud particles within in the range 0.1 to 6400 ?m, together with liquid and total water content of clouds taken by the Nevzorov probes. Auxiliary data as atmospheric state and upward and downward shrort-wave and long-wave radiation is taken by the basic equipment of the aircraft. A full list of the instrumentation carried by the two aircraft during ARTIST is given below:

POLAR-2:

  • Basic meteorological equipment (wind, temperature, humidity,GPS-position
  • Upward and downward looking pyranometer and pyrgeometer
  • Liquid water sensor (Nevzorov)
  • Laseraltimeter
  • Meteopod turbulence equipment
  • Digital color line scanner

POLAR-4:

  • Basic meteorological equipment (wind, temperature, humidity,GPS-position
  • Upward and downward looking pyranometer und pyrgeometer
  • Liquid water sensor (Nevzorov)
  • Drop sonde equipment
  • Digital color line scanner
  • Infrared line scanner
  • Microwave radiometer
  • Sun photometer, optical window
  • GKSS partical probes

The aim of the project within this proposed study is to generate a data set applicable for investigating the effect of Arctic haze and clouds on the radiation field above sea ice.

Long Term Component

MSG is a spin-stabilised spacecraft inheriting a certain number of the Meteosat features, but with a strongly improved instrument SEVIRI in terms of resolution and number of spectral channels (12 channels between 0.6-13.4 ?m, spatial resolution of 3 km , and image repeat cycle 15 min). These new features of MSG will allow to derive aerosol and cloud optical properties with high resolution in space and time. In addition, MSG will carry GERB, an ESA Announcement of Opportunity instrument jointly funded by UK and Belgium, to measure the ERB with a spatial resolution of 50km and an image repeat cycle similar to SEVIRI of 15 min. GKSS three year research project "Exploitation of GERB for Climate and Meteorological Applications" (start February 1st, 1998), funded by the European Commission to provided value added GERB satellite data to the user community for climate studies. GKSS together with the University of Kiel plan to use data of the two MSG instruments to derive consistent aerosol, cloud and radiation budget information. Prior to the launch of MSG, scheduled for 2000, data of the current Meteosat satellite together with radiation budget measurements of the Scanner for Radiation Budget (ScaRaB) instrument are used to develop and test algorithms for a synergy of instruments with different sizes of field of views. After launch of MSG, the instruments GERB and SEVIRI simultaneously will observe regions with large tropical aerosol loading due to both Saharan dust outbreaks and, more seasonally, biomass burning, as well as industrial pollution. In respect to the study proposed here, it is expected that possibly the signatures of these aerosols and their impact on the ERB my be detectable by a combined examination of data form the two MSG instruments.

References

  • Albrecht, B. A., 1989, Aerosols, cloud microphysics, and fractional cloudiness, Science, 245, 1227-1230.
  • Curry, J. A., 1993: Interactions among aerosols, clouds and climate of the Arctic Ocean, International Symposium on the Ecological Effects of Arctic Airborne Contaminants, Reykjavik, Iceland, October 4-8, 1993.
  • Curry, J. A., and E.E. Ebert, 1990: Sensitivity of the thickness of Arctic sea ice to the optical properties of clouds, Ann. Glaciol., 14, 43-46.
  • Curry, J. A., and E.E. Ebert, 1992: Annual cycle of radiation fluxes over the Arctic Ocean: Sensitivity to cloud optical properties, J. Climate, 5, 1267-1280. IPCC, 1995: Climate Change 1994 - Radiative Forcing of Climate Change, eds. J.T. Houghton, et al., University Press, 339 pp.
  • Twomey, S., 1991: Aerosols, clouds, and radiation, Atmos. Environ., 25, 2435. WCRP, 1998: Report of the ninth session of the WCRP/GEWEX Radiation Ppanel (GRP), 22-25 July, 1997, Honolulu, Hawaii, DRAFT January 1998, 48 pp.

Management Approach

The proposal involves two institutions located in north Germany, about 130 km apart. The GKSS research center, located in Geesthacht, a town about 30 km south east of Hamburg, will be the coordinating institution. Partners from GKSS and the University of Kiel will cooperate using modern telecommunication (e-mail, ftp, telephone). In addition, all partners will meet regularly in two month intervals. The meetings will serve to monitor the work done at both institutions and to prepare contributions for presentation at the Aerosol Radiative Forcing Science Team meetings.

The proposed research "Arctic Haze Measurements and Exploitation of Geostationary Satellite Data" is part of the 1998-1999 "Research and Development Programme" of GKSS. The relevant work of scientists at the Institute of Atmospheric Physics (Director Prof. Dr. Ehrhard Raschke) to contribute to the proposed research and to participate at the Aerosol Radiative Forcing Science Team meetings are presently funded within internal GKSS-projects and external projects of the European Commission. The contribution of the CO-I from the University of Kiel is funded by a GKSS Research Grant under the GKSS-University programme: GKSS-Research Center is one of the 16 non-profit governmentally supported research establishments in Germany. GKSS is engaged in material sciences, environmental technology and environmental research. In the area of environmental research, use is made of sounding techniques to observe clouds, aerosols, phytoplankton and ocean waves.

GKSS cooperates in studies with many universities, which in this case is the University of Kiel. Dr. Andreas Macke of the Institute for Oceanography at the University of Kiel, Dept. for Marine Meteorology (a non-profit educational establishment) is supported by a GKSS Reseach Grant to study radiative transfer through inhomogeneous cloud fields for remote sensing applications. The Institute of Atmospheric Physics at GKSS, involved in this project, is headed by Prof. Dr. Ehrhard Raschke. He and his group has gained special experience in research on cloud radiation interaction. Both participating institutes have excellent facilities for satellite data analysis and image processing available on various work-stations. AVHRR and TOVS data are directly archived by an NOAA-receiving station at GKSS. GKSS has also access to the ERBE, ScaRaB and POLDER data and keeps an archive of Meteosat ISCCP-B2 data. As member of the GERB International Science Team (GIST), MSG data will be available at GKSS in the future. For validation of satellite based retrieving methods, the instrumentation and experiences to take in situ aircraft measurements of aerosol and cloud properties and surface based Lidar and Cloud-Radar (95 GHz ) measurements of aerosol and cloud structure are available.

The principal investigator Dr. Rolf Stuhlmann will be responsible for the overall management of the proposed research program, where each of the CO-investigators will be responsible for a special task. Dr. Johannes Mueller, responsible for the ScaRaB calibration and work related to GERB at GKSS, will work together with Rolf Stuhlmann on the remote sensing of clouds, aerosols and radiation part. Frank Albers, the ARTIST project scientist at GKSS, will be responsible for the in situ measurements of aerosol and cloud properties. Dr. Andreas Macke, University of Kiel, will be responsible for the complex radiative transfer calculations to derive improved remote sensing algorithms.

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