Langley DAAC Version Number: LD_008_022_001_00_00_0_19990408 OVERVIEW This data set contains over 15 years of polar Arctic and Antarctic aerosol profiles obtained with the Stratospheric Aerosol Measurement II (SAM II) satellite experiment. The data coverage begins October 1978 and extends through December 1993. For each measurement event, vertical profiles of extinction km-1, extinction km-1 uncertainty, extinction ratio, extinction ratio uncertainty, NMC temperature, temperature uncertainty, and pressure are provided as a function of altitude. THE SAM II SATELLITE EXPERIMENT The SAM II instrument, aboard the Earth-orbiting Nimbus 7 spacecraft, was designed to measure solar irradiance attenuated by aerosol particles in the Arctic and Antarctic stratosphere. The scientific objective of the SAM II experiment was to develop a stratospheric aerosol data base for the polar regions by measuring and mapping vertical profiles of the atmospheric extinction due to aerosols. This data base allows for studies of aerosol changes due to seasonal and short-term meteorological variations, atmospheric chemistry, cloud microphysics, volcanic activity and other perturbations. The results obtained are useful in a number of applications, particularly the evaluation of any potential climatic effect caused by stratospheric aerosols. SAM II Instrument The SAM II instrument consists of a single-channel Sun photometer with a 0.04 micron passband centered at a wavelength of 1.0 micron. This is a region of the spectrum where absorption by atmospheric gases is negligible; consequently, any attenuation of sunlight is due to scattering by aerosol particles and air molecules. In operation, the instrument is activated shortly before each sunrise or sunset encountered by the satellite. A sensor with a wide field-of-view is used to indicate the Sun's presence. Two similar sensors then point the SAM II to within +-0.03 degrees in azimuth (left and right). A mirror begins a rapid vertical scan until the Sun's image is acquired by the SAM II telescope. The mirror then slowly scans vertically across the Sun at a rate of 0.25 degree per second reversing itself each time a Sun-limb crossing occurs. The entrance window to the SAM II telescope only passes sunlight of wavelengths greater than 0.9 micron. A circular aperture placed at the image plane serves to define the instantaneous field of view of the instrument to be 0.5 minute of arc. This corresponds to a vertical resolution in the atmosphere of approximately 0.5 km altitude. From the telescope, the light is directed through an interference filter, which rejects all but the 1.0 micron wavelength (+-0.02 micron) passband, to a photodiode detector. The solar intensity as a function of time is digitized, recorded, and periodically telemetered back to Earth. A description of the SAM II instrument, and of the experiment in general, is given by McCormick et al. (1979). The SAM II instrument, along with a number of other sensors, is mounted on the Nimbus 7 Earth-orbiting spacecraft. The orbital characteristics of this spacecraft determine the frequency and geographic locations of the SAM II measurements. The mode of operation of the SAM II instrument is such that it takes data during each sunrise and sunset encountered. The Nimbus 7 spacecraft has an orbital period of 104 minutes, which means that it circles the Earth nearly 14 times per day. There is a measurement opportunity for the SAM II each time that the spacecraft enters into or emerges from the Earth's shadow. Consequently, the instrument takes data during approximately 14 sunrises and 14 sunsets each Earth day. The Nimbus 7 spacecraft was placed in a high-noon, Sun-synchronous orbit; that is, the spacecraft crossed the Equator during each orbit at local noon. In general terms, this means that the orbital plane of the spacecraft was fixed with respect to the Sun, and thus all sunsets occur in the Arctic region and all sunrises occur in the Antarctic region. In the course of a single day, measurements of the stratospheric aerosol are obtained at 14 points spaced 26 degrees apart in longitude in the Arctic region and similarly for the Antarctic region. All the points obtained during 1 day in a given region are at very nearly the same latitude, but as time progresses, the latitudes of the measurements slowly change with the season by 1 to 2 degrees each week, gradually sweeping out the area from approximately 64.0 to 83.0 degrees. The lowest latitude coverage occurs at the solstices whereas the highest latitudes are measured at the equinoxes. In the course of 1 week, therefore, the instrument makes about 98 measurements in each region, all in a band of latitude of approximately 1.0 degree. These measurements give a fairly spatially dense set of data points. When the locations of all the measurements obtained in one week are plotted on a geographic set of axes, one finds that the separation between points is only about 4.0 degrees in longitude. In a 6-month period of time, the total number of observations is on the order of 5000. However, due to an orbit degradation associated with the Nimbus 7 spacecraft, there has been a change and disruption in the collection of SAM II data beginning in 1987. During the period of time from 1987 through 1993, orbital precession caused the Nimbus 7 spacecraft to cross the equator earlier than the planned high-noon crossing. This gradually moved the Antarctic coverage equatorward and the maximum latitudinal Arctic coverage slightly poleward. Initially the Antarctic latitudinal coverage extended from the lowest latitude, 64.5 degrees at the solstices, to the highest latitude, 81.0 degrees at the equinoxes. By 1992 the Antarctic coverage gradually shifted to extend from 53.1 degrees at the solstices, to 69.2 degrees at the equinoxes. In the Arctic region the initial latitudinal coverage extended from the lowest latitude, 64.1 degrees at the solstices, to the highest latitude, 83.0 degrees at the equinoxes. Gradually by 1991 the highest Arctic latitudinal coverage extended to 86.2 degrees at the equinoxes. The orbital precession also affected the spacecraft orientation and prevented the SAM II instrument from acquiring the Sun for certain periods of time. In the Arctic region many sunset events were lost because an S-band antenna blocked SAM II's view to the Sun. Sunset events were lost for the following periods of time: mid-June through mid-August 1988; mid-March through mid-September 1989; mid-January through September 1990; and from January 7, 1991, through the present. In the Antarctic region the SAM II instrument was not able to acquire the Sun for the period of time from mid-January through October 1993. The final 2 months of SAM II data for the Antarctic region were collected during November and December 1993, and no further data is expected beyond 1993. Data Products The SAM II satellite data are processed after being telemetered to the ground, with the data on solar intensity versus time being mathematically inverted to yield extinction coefficient versus altitude (extinction profile) for each sunrise or sunset event. The mathematical inversion used is described by Chu and McCormick (1979). The basic data product, therefore, is the extinction profile obtained during each measurement opportunity, which can be analyzed to determine the spatial and temporal variations in the upper tropospheric and stratospheric aerosol. These extinction data are archived at the Langley Distributed Active Archive Center (DAAC), NASA Langley Research Center, Hampton, VA, after being subjected to an extensive validation program including comparisons with correlative aerosol observations. A detailed description of the archived data products is given in the SAM II Data User's Guide (Chu et al.,1988). Quality Control Questionable profiles identified using the procedures described in the SAM II Data User's Guide have been removed from this data set. In addition, a small number of events displaying incorrect measurement locations were deleted. CONTACT Kathy Powell, SAIC MS 475 NASA Langley Research Center Hampton, VA 23681-2199 Telephone: (757)864-2688 FAX: (757)864-2671 E-mail: k.a.powell@larc.nasa.gov REFERENCES The following list of references is provided as a starting point for someone wishing to learn more about the SAM II instrument, inversion method, validation studies and recent scientific studies. Albritton, D. L., et al., Scientific Assessment of Stratospheric Ozone: 1989, WMO Global Ozone Research and Monitoring Project Report No. 20, 1990. Chu, W. P. and M. P. McCormick, Inversion of Stratospheric Aerosol and Gaseous Constituents From Spacecraft Solar Extinction Data in the 0.38-1.0 5 micron Wavelength Region, Appl. Opt., 18, no. 9, 1404-1413, May 1, 1979. Chu, W. P., M. T. Osborn, and L. R. McMaster, SAM II Data Users' Guide, NASA RP-1200, July 1988. Hamill, P. and L. R. McMaster, Polar Stratospheric Clouds - Their Role in Atmospheric Processes, NASA CP-2318, 1984. Hamill, P., O. B. Toon, and R. P. Turco, Characteristics of Polar Stratospheric Clouds During the Formation of the Antarctic Ozone Hole, Geophys. Res. Lett., 13, no. 12, Nov. Suppl., 1288-1291, 1986. Hamill, P., O. B. Toon, and R. P. Turco, Aerosol Nucleation in the Winter Arctic and Antarctic Stratospheres, Geophys. Res. Lett., 17, 417-420, 1990. Hamill, P. and O. B. Toon, Denitrification of the Polar Winter Stratosphere: Implications of SAM II Cloud Formation Temperatures, Geophys. Res. Lett., 17, 441-444, 1990. Hofmann, D. J. and J. M. Rosen, On the Temporal Variation of Stratospheric Aerosol Size and Mass During the First 18 Months Following the 1982 Eruptions of El Chichon, J. Geophys. Res., 89, no. D3, 4883-4890, June 20, 1984. Kent, G. S. and M. P. McCormick, SAGE and SAM II Measurements of Global Stratospheric Aerosol Optical Depth and Mass Loading, J. Geophys. Res., 89, no. D4, 5303-5314, June 30, 1984. Kent, G. S., C. R. Trepte, U. O. Farrukh, and M. P. McCormick, Variation in the Stratospheric Aerosol Associated With the North Cyclonic Polar Vortex as Measured by the SAM II Satellite Sensor, J. Atmos. Sci., 42, no. 14, 1536-1551, July 15, 1985. Kent, G. S., P.-H. Wang, U. O. Farrukh, and G. K. Yue, Validation of SAM II and SAGE Satellite, Final Report, NASA CR-178256, April 1987. Kent, G. S., U. O. Farrukh, P.-H. Wang, and A. Deepak, SAGE I and SAM II Measurements of 1.0 micron Aerosol Extinction in the Free Troposphere, J. Appl. Meteorol., 27, 269-279, March 1988. Madrid, C. R., The Nimbus 7 Users' Guide, NASA Goddard Space Flight Center, NASA TM-79969, August 1978. McCormick, M. P., P. Hamill, T. J. Pepin, W. P. Chu, T. J. Swissler, and L. R. McMaster, Satellite Studies of the Stratospheric Aerosol, Bull. American Meteorol. Soc., 60, no. 9, 1038-1046, September 1979. McCormick, M. P., W. P. Chu, L. R. McMaster, G. W. Grams, B. M. Herman, T. J. Pepin, P. B. Russell, T. J. Swissler, SAM II Aerosol Profile Measurements, Poker Flat, Alaska, July 16-19, 1979, Geophys. Res. Lett., 8, no. 1, 3-4, January 1981. McCormick, M. P., W. P. Chu, G. W. Grams, P. Hamill, B. M. Herman, L. R. McMaster, T. J. Pepin, P. B. Russell, H. M. Steele, and T. J. Swissler, High-Latitude Stratospheric Aerosols Measured by the SAM II Satellite System in 1978 and 1979, Science, 214, no. 4518, 328-331, October 16, 1981. McCormick, M. P., H. M. Steele, P. Hamill, W. P. Chu, and T. J. Swissler, Polar Stratospheric Cloud Sightings by SAM II, J. Atmos. Sci., 39, no. 6, 1387-1397, June 1982. McCormick, M. P., C. R. Trepte, and G. S. Kent, Spatial Changes in the Stratospheric Aerosol Associated With the North Polar Vortex, Geophys. Res. Lett., 10, no. 10, 941-944, October 1983. McCormick, M. P., P. Hamill, and U. O. Farrukh, Characteristics of Polar Stratospheric Clouds as Observed by SAM II, SAGE, and Lidar, J. Meteorol. Soc. Japan, 63, no. 2, 267-276, April 1985. McCormick, M. P. and J. C. Larsen, Antarctic Springtime Measurements of Ozone, Nitrogen Dioxide, and Aerosol Extinction by SAM II, SAGE, and SAGE II, Geophys. Res. Lett., 13, no. 12, Nov. Suppl., 1280-1283, 1986. McCormick, M. P. and C. R. Trepte, SAM II Measurements of Antarctic PSC's and Aerosols, Geophys. Res. Lett., 13, no. 12, Nov. Suppl., 1276-1279, 1986. McCormick, M. P. and C. R. Trepte, Polar Stratospheric Optical Depth Observed Between 1978 and 1985, J. Geophys. Res., 92, no. D4, 4297-4306, April 20, 1987. McCormick, M. P., C. R. Trepte, and M. C. Pitts, Persistence of Polar Stratospheric Clouds in the Southern Polar region, J. Geophys. Res., 94,no. D9, 11241-11251, August 30, 1989. McCormick, M. P., P.-H. Wang, and M. C. Pitts, Background Stratospheric Aerosol and Polar Stratospheric Cloud Reference Models, Advances in Space Research, 13, no. 1, 7-29, 1993. McCormick, M. P., P.-H. Wang, and L. R. Poole, Chapter 8: Stratospheric Aerosols and Clouds, pp. 205-222, Aerosol-Cloud-Climate Interactions. Edited by Peter V. Hobbs, Copyright by Academic Press, Inc., Harcourt Brace & Company, 1993. McMaster, L. R., Stratospheric Aerosol and Gas Experiment (SAGE II), Sixth Conference on Atmospheric Radiation, American Meteorological Soc., J46-J48, 1986. Osborn, M. T. and C. R. Trepte, SAM II and SAGE Data Management and Processing, NASA CR-178244, February 1987. Osborn, M. T., M. C. Pitts, K. A. Powell, and M. P. McCormick, SAM II Aerosol Measurements During the 1989 AASE, Geophys. Res. Lett., 17, 397-400, 1990. Osborn, M. T., L. R. Poole, and P.-H. Wang, SAM II and Lidar Aerosol Profile Comparisons During AASE, Geophys. Res. Lett., 17, 401-404, 1990. Pepin, T. J. and M. P. McCormick, Stratospheric Aerosol Measurement Experiment MA-007, Apollo-Soyuz Test Project - Preliminary Science Report, NASA TMX-58173,1976. Pitts, M. C., L. R. Poole, and M. P. McCormick, Climatology of Polar Stratospheric Clouds Determined From SAM II Observations, in Digest of Topical Meeting on Optical Remote Sensing of the Atmosphere, 1990, (Optical Society of America, Washington, D.C., 1990), 4, 206-209. Pitts, M. C. and L. W. Thomason, The Impact of the Eruptions of Mount Pinatubo and Cerro Hudson on Antarctic Aerosol Levels During the 1991 Austral Spring, Geophys. Res. Lett., 20, no. 22, 2451-2454, November 19, 1993. Poole, L. R. and M. P. McCormick, Polar Stratospheric Clouds and the Antarctic Ozone Hole, J. Geophys. Res., 93, no. D7, 8423-8430, July 20, 1988. Poole, L. R., S. Solomon, M. P. McCormick, and M. C. Pitts, The Interannual Variability of Polar Stratospheric Clouds and Related Parameters in Antarctica During September and October, Geophys. Res. Lett., 16, 1157-1160, 1989. Poole, L. R. and M. C. Pitts, Polar Stratospheric Cloud Climatology Based on SAM II Observations from 1978-1989, in press, J. Geophys. Res., 1994. Pueschel, R. F., K. G. Snetsinger, P. Hamill, J. K. Goodman, and M. P. McCormick, Nitric Acid in Polar Stratospheric Clouds: Similar Temperature of Nitric Acid Condensation and Cloud Formation, Geophys. Res. Lett., 17, 429-432, 1990. Russell, P. B., M. P. McCormick, L. R. McMaster, T. J. Pepin, W. P. Chu, and T. J. Swissler, SAM II Ground-Truth Plan Correlative Measurements for the Stratospheric Aerosol Measurement II (SAM II) Sensor on the NIMBUS G Satellite, NASA TM-78747, 1978. Russell, P. B., M. P. McCormick, T. J. Swissler, W. P. Chu, J. M. Livingston, W. H. Fuller, Jr., J. M. Rosen, D. J. Hofmann, L. R. McMaster, D. C. Woods, and T. J. Pepin, Satellite and Correlative Measurements of the Stratospheric Aerosol II: Comparison of Measurements Made by SAM II, Dustsondes and an Airborne Lidar, J. Atmos. Sci., 38, no. 6, 1295-1312, June 1981. Russell, P. B., T. J. Swissler, M. P. McCormick, W. P. Chu, J. M. Livingston, and T. J. Pepin, Satellite and Correlative Measurements of the Stratospheric Aerosol I: An Optical Model for Data Conversions, J. Atmos. Sci., 38, no. 6, 1279-1294, June 1981. Russell, P. B., M. P. McCormick, T. J. Swissler, J. M. Rosen, D. J. Hofmann, and L. R. McMaster, Satellite Correlative Measurements of the Stratospheric Aerosol III: Comparison of Measurements by SAM II, SAGE, Dustsondes, Filters, Impactors and Lidar, J. Atmos. Sci., 41, no. 11, 1791-1800, June 1, 1984. Russell, James M., III, Middle Atmosphere Program - Handbook for MAP, Volume 22, Univ. of Illinois, NASA CR-180128, September 1986. Steele, H. M., P. Hamill, M. P. McCormick, and T. J. Swissler, The Formation of Polar Stratospheric Clouds, J. Atmos. Sci., 40, no. 8, 2055-2067, August 1983. Turco, R. P., O. B. Toon, and P. Hamill, Heterogeneous Physiochemistry of the Polar Ozone Hole, J. Geophys. Res., 94, no. D14, 16493-16510, November 30, 1989. Twomey, S., Introduction to the Mathematics of Inversion in Remote Sensing and Indirect Measurements, Elsevier Scientific Publ. Co., 1977. Wang, P.-H. and M. P. McCormick, Behavior of Zonal Mean Aerosol Extinction Ratio and Its Relationship With Zonal Mean Temperature During the Winter 1978-1979 Stratospheric Warming, J. Geophys. Res., 90, no. D1, 2360-2364, February 20, 1985. Wang, P.-H. and M. P. McCormick, Variations in Stratospheric Aerosol Optical Depth During Northern Warmings, J. Geophys. Res., 90, no. D6, 10597-10606, October 20, 1985. Watterson, I. G. and A. F. Tuck, A Comparison of the Longitudinal Distributions of Polar Stratospheric Clouds and Temperatures for the 1987 Antarctic Spring, J. Geophys. Res., 94, no. D14, 16511-16525, November 30, 1989. Yue, G. K., M. P. McCormick, and W. P. Chu, A Comparative Study of Aerosol Extinction Measurements Made by the SAM II and SAGE Satellite Experiments, J. Geophys. Res., 89, no. D4, 5321-5327, June 30, 1984. SAM II NASA RP'S SAM II Measurements of the Polar Stratospheric Aerosol, Vol. I - October 1978 to April 1979, NASA RP-1081 Vol. II - April 1979 to October 1979, NASA RP-1088 Vol. III - October 1979 to April 1980, NASA RP-1106 Vol. IV - April 1980 to October 1980, NASA RP-1107 Vol. V - October 1980 to April 1981, NASA RP-1140 Vol. VI - April 1981 to October 1981, NASA RP-1141 Vol. VII - October 1981 to April 1982, NASA RP-1164 Vol. VIII - April 1982 to October 1982, NASA RP-1165 Vol. IX - October 1982 to April 1983, NASA RP-1244 Updated: LD_008_022_001_00_00_0_19990408