On January 18, 1996 a Science Team meeting for the Stratospheric Aerosol and Gas Experiment (SAGE) III was conducted at the Langley Research Center (LaRC).

M. Patrick McCormick, SAGE III Principal Investigator, kicked off the Science Team meeting with highlights of the Earth Observing System (EOS) Program, showing that several of the SAGE III data products (namely, aerosols, ozone, and clouds) are considered highly critical data sets within the EOS program and the overall EOS flight schedule. Currently, four flights of SAGE III are shown on the flight schedule. Efforts are being made to participate in flights of the French SPOT mission and a Canadian mission (SciSAT).

Lemuel E. Mauldin, SAGE III Project Manager, presented an overview of the instrument and discussed the status of the charge coupled device (CCD) testing and the verification unit.

The Science Team members or their representatives gave an overview of their accomplishments and future work, as summarized below.

Albert A. Chernikov's activities were described by Yuri A. Borisov, Central Aerological Observatory (CAO) in Russia. CAO could provide data validation based on ground, balloons, and rocket measurements in Russia, as well as, develop the methodology for comparing these measurements with the SAGE III data.

William P. Chu, LaRC, is the lead scientist for the algorithms, software, simulation, calibration, and verification teams. His activities involve developing the algorithms and software requirements, and consulting on test setups for the CCD and other instrument hardware. In addition, he is writing the transmission algorithm theoretical basis document (ATBD).

Derek M. Cunnold, School of Earth and Atmospheric Science at Georgia Institute of Technology, has been responsible for the development of the ozone ATBD. He presented results of SAGE I and II trend studies and evidence for the residual coupling of aerosol and ozone in the 600 nm channel. It has been concluded that a multichannel approach would minimize the coupling between aerosol and ozone spectral signatures.

John De Luisi, NOAA/ERL in Boulder, presented improvements in the understanding of the Umkehr effect and the uncertainties of the retrieved ozone profiles, including the uncertainties of stratospheric aerosol corrections. The SAGE data fit prominently into this work because the expected results will lead to increased credibility of the long-term ozone profile trends determined from Umkehr observations dating back to 1958.

For the creation of a long-term climatology of stratospheric aerosol properties, De Luisi will use SAGE data, dustsonde data, ground-based lidar data, and sunphotometer data. The New Umkehr algorithm improved the agreement of ozone retrievals in layers 3, 2, and 1. De Luisi noted a particular concern with layer 3 and to some extent with layer 4, because it appears that the retrieved Umkehr concentrations do not agree well with expected values as determined by SAGE II and satellites.

Philip A. Durkee, Naval Postgraduate School (NPS), was not able to attend but provided a brief summary of his activities. These include AVHRR aerosol analysis and validation studies using measurements from various field experiments. New observations with a remotely piloted aircraft are being planned.

Nikolai A. Elansky, Russian Academy of Sciences, would like to set up, develop, and coordinate a ground-based network in Russia for the correlation/validation of the SAGE III ozone, nitrogen dioxide, and aerosol measurements over Russia. He named four planned sites.

Benjamin M. Herman, University of Arizona, Tucson, has been supporting the development of the SAGE III algorithms that are presented in each of the SAGE III ATBD documents (transmission, solar occultation, and lunar occultation). Future work will refine the aerosol and pressure/temperature inversions, and quantify the coupling between measurements and update the algorithm sections in each ATBD.

Peter V. Hobbs, University of Washington, did not attend but provided a brief summary of his activities relevant to SAGE. Among various activities cited were a collaboration with NASA scientists on direct aerosol closure experiments in the Arctic, which showed the contributions from tropospheric and stratospheric aerosols. Also as part of SCAR-B he obtained an extensive data set on aerosols from biomass burning in Brazil.

Hobbs' future work plans revolve primarily around the TARFOX field project, which will take place next summer. The goal of TARFOX is to carry out a direct aerosol closure experiment on the US East Coast in order to quantify direct aerosol radiative forcing in a strongly polluted environment. TARFOX will provide an excellent field trial for the types of campaigns that will be needed to validate and utilize SAGE III data.

Geoffrey Kent, Science and Technology Corporation, has primarily been developing the cloud presence algorithm theoretical basis. He presented several areas of improvement and development for future work. Just two of these are called out here: 1.) study use of wavelengths between 0.525 µm and 1.02 µm since these have a potential application at altitudes below 6 km; 2.) study use of lunar data (above 15 km) for potential application to the detection of polar stratospheric clouds (PSCs).

Jacqueline Lenoble, Université des Sciences et Technologies de Lille, described aerosol observations by balloon-borne instruments. The observations were made in France and in Sweden: 1.) RADIBAL (RADIomètre BALlon, in French) is a near-infrared polarimeter with two channels at 850 and 1650 nm, which observes the radiance and the polarization diagrams during the balloon ascent or descent. Comparison flights following the Mt. Pinatubo eruption in June 1991, June 1992, May 1993, and October 1994 show a strong increase of the particle effective radius after the eruption (from 0.20 to 0.48 mm at 20 km) followed by a slow decrease (respectively 0.34 mm in 1993 and 0.31 mm in 1994); this fully confirms the values derived from SAGE II aerosol spectral extinction. 2.) BALLAD (BALloon Limb Aerosol Detection) observes the Earth's limb from the float altitude at three wavelengths 850, 600, and 450 nm, before sunset, including its polarization at 850 nm. BOCCAD (Balloon OCCultation for Aerosol Detection) operates after BALLAD is turned off and follows the sun during its occultation through the Earth's atmosphere.

The two instruments are complementary and should provide the ozone profile and aerosol extinction profiles at 450 and 850 nm, as well as information about the aerosol particles from their phase function and their polarization.

Volker A. Mohnen's activities were described by Jianjun Lu, SUNY in Albany, NY. Working with SAGE II extinction measurements from 1985 to 1990, they have separated extinction due to aerosols from that due to clouds and separated the time frame into volcano-perturbed (1985) and volcano-free (1988-1990) periods. Among their findings were these: 1.) aerosols in volcano-free years showed seasonal variation with spring maximum and latitudinal asymmetry with larger extinction in the northern hemisphere than in the corresponding southern hemisphere. Volcanic influence increased the seasonal variation and latitudinal asymmetry. 2.) tropopause folding events showed seasonal difference with late winter-early spring maximum and latitudinal asymmetry with more foldings in the northern mid-latitudes.

V. Ramaswamy, NOAA/GFDL, presented a general circulation model (GCM) study which has been carried out to investigate the role of the 1979-1990 observed ozone depletion on the thermal structure of the lower stratosphere. The simulated temperature response in the global lower stratosphere is generally one of cooling. The ozone-induced cooling of the lower stratosphere over the past decade is substantially larger than the effects due to the increases in the well-mixed greenhouse gases. Thus there appears to be a strong influence of the ozone depletion on the lower stratospheric climate -- one that has occurred over a relatively short time period (~decade).

David Rind, NASA/GISS, in New York, discussed several different projects underway for 1996. Among his major activities and findings have been: (1) a review of the SAGE III relative humidity product. The major question which needs to be addressed is whether relative humidity should be calculated with respect to water or to ice at temperatures between 0 degree and -40 degree C. (2) A comparison of SAGE II data with ISCCP deep convective clouds indicates that with greater convection, i.e., during sunset, there is reduced water vapor in the stratosphere. There is a question as to whether this is a physical effect, extending well above the tropopause, or a retrieval problem due to light scattered from below.

Philip B. Russell, NASA Ames Research Center, has been responsible for the development of the aerosol ATBD. He presented recent work on the AMES radiometer with specific attention to the correspondence between SAGE III and radiometer channels and the upcoming TARFOX experiment.

Vinod Saxena, North Carolina State University, has been responsible for deriving the aerosol microphysical characteristics between 13-30 km and averaged columnar characteristics in a unit column between 15-25 km poleward of 50 degrees South (near Antarctica) during the austral springs of 1990 (background profile), 1991, 1992, and 1993, and summers of 1991 (background profile), 1992, 1993, and 1994.

Eric P. Shettle, Naval Research Laboratory, in Washington, D. C., has been responsible for the spectroscopic assessments for gaseous constituent retrievals in the visible and ultraviolet spectral regions. He concluded that a list of priority spectroscopic research (O2, OClO, and NO3) should be forwarded to the EOS Investigators Working Group (IWG) for concurrence and funding.

Gabor Vali, University of Wyoming, Laramie, presented data from the new 94 GHz airborne radar (on the University of Wyoming KingAir aircraft) that was used to correlate reflectivity from ice crystal clouds with optical extinction coefficient. The method promises to provide another possibility for validation of the SAGE data. On its own, the 94 GHz airborne radar has proven to be a powerful tool for cirrus studies; with the radar and with the coincident in-situ observations of crystal sizes and shapes, cloud structure and microphysical composition can be simultaneously examined on scales from a few meters up.

Steven C. Wofsy, Harvard University, has been responsible for the development of the OClO ATBD. He was not present for the Science Team meeting but provided a summary of his on-going studies. His group has noted that a significant abundance of OClO has only been observed during the polar winter and at night in the polar spring. The studies suggest that OClO concentrations will only become large enough to play a significant role in ozone destruction if temperatures become low enough to initiate heterogeneous catalytic cycles on polar stratospheric clouds (PSCs) and cold sulfate aerosols. In contrast, the NO3 abundance is expected to decrease substantially after such heterogeneous processing.

The contribution of bromine to polar ozone depletion is also to be studied.

Joseph M. Zawodny, LaRC, has been responsible for the development of lunar occultation measurement algorithms for the SAGE III experiment. The proposed method uses a multiple linear regression technique to assess vertical profiles of O3, NO2, NO3, and OClO from broadband lunar occultation measurements (380-680 nm at 1-2 nm resolution). SAGE II took part in a blind O3 intercomparison at Mauna Loa in mid-1995. The results were extremely favorable for SAGE II.

The next Science Team meeting is scheduled be held at LaRC on May 8 -10, 1996. The ATBDs should be ready for concurrence by the Science Team at that time.

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