Aeronautics and Space Report of the President FY 1995 Activities


Studies of the Planet Earth

Atmospheric Studies and Applications

A significant highlight of FY 1995 was conclusive results regarding the Antarctic "ozone hole." Several years of data from satellites and aircraft had provided proof that human-produced chemicals comprised at least 80 percent of the chlorine in the stratosphere causing Antarctic ozone depletion. Ozone, a molecule made up of three atoms of oxygen, forms a thin layer of the atmosphere that absorbs harmful ultraviolet radiation from the Sun. The term "ozone hole" is used to describe a large area of intense ozone depletion that occurs over Antarctica during late August through early October and typically fills in late November. Ground-based measurements by NASA and NOAA indicated that lower atmospheric growth rates of major ozone-depleting substances have declined significantly in response to international efforts to reduce emissions. NASA's Upper Atmosphere Research Satellite (UARS) has provided the only global monitoring of this process.

An early highlight for FY 1995 was the third flight of NASA's ATLAS payload on the Space Shuttle. ATLAS-3 was designed to measure the variations in the solar output and its effects on the Earth's atmosphere over the course of an 11-year cycle. It successfully calibrated instruments to measure both atmospheric and solar energy. In addition, the ATLAS-3 instruments were able to measure precise levels of more than 30 chemicals in the atmosphere.

Researchers used data from a small instrument, the Optical Transient Detector (OTD), launched in April 1995 on the Microlab I commercial satellite, to identify the formation of tornadoes and severe storms from space. The OTD gave researchers a much more comprehensive view of lightning generated by severe storms than is generally available from ground observations. The OTD is the testing model of the lightning imaging sensor instrument, part of the upcoming Tropical Rainfall Measuring Mission (TRMM), a joint U.S.-Japan spacecraft.

From August to September 1995, NASA, the Brazilian Space Agency (AEB), and Brazil's National Space Research Institute conducted the Smoke/Sulfate, Clouds and Radiation Experiment-Brazil. This experiment marked the first large-scale cooperation between NASA and AEB, which was established in 1994. The experiment successfully used aircraft and ground-based sensors to study atmospheric aerosols and their influence on clouds and climate.

The GOES spacecraft series provided continuous operational environmental monitoring coverage with images and soundings during FY 1995. GOES-8, the first satellite in a new series, was moved to its final, operational position in February 1995, and on June 9, 1995, NOAA declared it fully operational. Its three-axis stabilized design allows its sensors to continuously observe Earth and thus provide more frequent views of weather systems, compared with the earlier spin-stabilized satellites that view Earth only 5 percent of the time. NASA successfully launched GOES-9, the second advanced satellite in this series, on May 23, 1995, and NOAA personnel assumed control on July 21, 1995. Upon completion of on-orbit satellite and instrument checkout in October 1995, GOES-9 was scheduled to join GOES-8 in early 1996 in providing the United States with full coverage by the most advanced weather monitoring capability. NOAA is responsible for operating GOES, including command and control, data reception, product generation, and data and product distribution. NASA manages the design, development, testing, launch, and postlaunch checkout of GOES for NOAA.

In the Polar-orbiting Operational Environmental Satellite (POES) program, NASA successfully launched the NOAA-J satellite on December 30, 1994, from Vandenberg Air Force Base, CA. This satellite, renamed NOAA-14 once it achieved orbit, assumed the role as the primary afternoon spacecraft in the POES constellation. Following the initial spacecraft checkout, NOAA-14 assumed full operational capability in June 1995. The POES spacecraft continued to provide temperature and humidity profiles for weather forecasting, imagery for cloud/frontal/snow cover analysis, warnings of tropical cyclones and volcanic eruptions, data for sea-surface temperature and ice analyses, and vegetation indices for climate and global change.

Work to define the observational requirements and satellite configuration of the National Polar-orbiting Operational Environmental Satellite System (NPOESS) continued at the program's tri-agency (DoC, DoD, and NASA) integrated program office. The NPOESS program, which converges the military and civilian polar-orbiting operational environmental satellite programs of DoD and NOAA into a single system, proceeded successfully through its initial planning phases. The Secretaries of Commerce and Defense and the NASA Administrator signed a Memorandum of Agreement in May 1995 to implement the President's Directive of May 1994.

DoC, through NOAA, has lead agency responsibility for a tri-agency executive committee for NPOESS. NOAA also has lead agency responsibilities to support the integrated program office's satellite operations and to interface with national and international civil users. DoD has lead agency responsibility to support the office for NPOESS acquisitions, launch, and systems integration. NASA has lead agency responsibility to support the office in facilitating the development and incorporation of new, cost-effective technologies to enhance the capabilities of NPOESS.

Negotiations continued with key European partners—the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT), with involvement as appropriate of the European Space Agency (ESA) — on a joint polar system, taking into account, on the U.S. side, the converged U.S. system. This complements long-standing plans by NOAA and EUMETSAT to exchange instrumentation for flight on meteorological operational satellites.

NOAA satellite measurements of ozone during the winter of 1994-95 indicated that the total column ozone amount was unusually low over regions of the Northern Hemisphere. For middle and high latitudes, ozone values were 10 to 20 percent lower than typical values observed during these months in 1979 and the early 1980's. Over some high-latitude regions, such as Siberia, total ozone in 1994-95 had decreased by up to 35 percent from 1979 values. Total ozone has decreased since 1979 over Northern Hemisphere midlatitudes at the rate of about 4 percent per decade. Researchers observed little or no significant long-term trend for the equatorial region. Temperatures observed over the north polar region were sufficiently low for chemical ozone destruction polar stratospheric clouds within the polar vortex during the 1994-95 winter-spring period. A stratospheric warming during February 1995 interrupted the period of record-low minimum temperatures, but record-low minimum temperatures returned in the polar region during March 1995.

Hurricane Luis

This Geostationary Operational Environmental Satellite (GOES-8) visible-channel image shows Hurricane Luis on September 6, 1995, as it made landfall over Puerto Rico. GOES-8 is operated by NOAA and circles the Earth in a geosynchronous orbit 22,300 miles above the Equator.

Also in the area of ozone monitoring, the use of the Television and Infrared Operational Satellite (TIROS) Operational Vertical Sounder (TOVS) 9.7-micron ozone channel as a robust, real-time monitor of the ozone shield steadily gained acceptance in the ozone community. Its unique polar night capability and enhanced sensitivity to lower stratospheric ozone depletion allowed it to complement more traditional atmospheric backscattering measuring instruments.

The AVHRR Atmosphere Pathfinder project is a National Environmental Satellite, Data, and Information Service (NESDIS) (part of NOAA) activity in support of the NOAA/NASA Pathfinder program. Its objectives are to use community consensus algorithms and uniformly calibrated AVHRR data to reprocess all afternoon NOAA satellite data back to 1981 into a consistent record of atmospheric parameters for climate change studies. During FY 1995, researchers processed 1 month of data (September 1989) into cloudy and clear radiance statistics, total cloud amount, top of the atmosphere radiation budget, and aerosol optical thickness over the oceans. Scientists also began to generate data for a benchmark period spanning from March 1987 through October 1988. The output products were provided twice daily on an equal area grid with a resolution of 110 kilometers and averaged over 5-day and monthly periods. A future extension is to include multilayer cloud amount by cloud type, surface radiation budget parameters, and cloud optical properties. Also during FY 1995, NOAA scientists produced a data set of deep layer mean temperature for the period December 1986 through December 1994. Scientists used this data set, based on observations of the microwave sounding unit on NOAA's POES, to study temperature trends throughout the troposphere and lower stratosphere.

In addition, NOAA's NGDC worked with many Pathfinder groups in NASA and NOAA to bring together the "Pathfinder Climate Data Collection." This CD-ROM includes data from AVHRR and TOVS Pathfinders for the benchmark period (April 1987-December 1988). NGCD stored these data in simple formats, allowing access with many popular science software tools. This CD was expected to be available during the first half of FY 1996.

NOAA's Global Climate Perspectives System achieved a new update capability for monthly and seasonal global temperature and precipitation during FY 1995. Researchers implemented complex quality control procedures, produced gridded global products, and published numerous scientific papers.

During FY 1995, NOAA's Comprehensive Aerological Reference Data Set project completed the building of a kernel data base containing daily global upper air observations for the period 1973-1990. Scientists combined data from about 20 different sources to form this online data base. In addition, they developed and implemented a complex quality control system.

NOAA scientists continued their work on the Trace Gas Project during FY 1995. They collected global baseline trace gas data sets, such as for CO2, CH4, O3, and chlorofluorocarbons, and checked the data sets for quality control. Researchers then documented, placed online, and secured the data sets in the NOAA/NCDC (National Climatic Data Center) archive.

Also during FY 1995, scientists from the U.S. Historical Climatology Network, a joint project between DoE and NOAA, prepared and quality-checked data sets of numerous climatological variables. On the global level, DoE and NOAA cooperated in the Global Historical Climatology Network for data collection and quality assurance of monthly temperature, precipitation, and pressure data.

The U.S. Precipitation Metadata Project produced data sets of monthly rainfall and snowfall during FY 1995. Researchers removed wind-induced turbulence biases by using data on such factors as gauge sitings, gauge shields, and average monthly wind speeds, as well as by developing algorithms for bias removal.

NOAA's Surface Reference Data Center supported precipitation validation within the Global Precipitation Climatology Project. The center provided support by collecting and validating precipitation station data from a number of globally distributed test-site areas. Work during FY 1995 concentrated on the production of area-averaged validation data for all test sites, with the inclusion of precipitation/elevation adjustment algorithms.

As part of the U.S. Global Change Research Program, scientists conducted numerous coordinated campaigns using lidar, radar, and all-sky optical imagery from the ground to obtain signatures of "breaking" gravity waves at mesopause altitudes. These scientists simulated wave structures by using a numerical model of breaking gravity waves. In addition, they used the characterization of the global semidiurnal tides to extend the Thermosphere-Ionosphere Mesosphere-Electrodynamics General Circulation Model to altitudes down to 30 kilometers.

The NSF has established a unique position in supporting studies of the way variations in the energy output from the Sun contribute to global change, as well as the way these results may affect conclusions related to the importance of anthropogenic effects. The Radiative Inputs from Sun to Earth program, for example, has supported photometric observation of sunspots, faculae, and other features that are sources of solar brightness variations.

In efforts to forecast space weather, scientists at Rice University developed the Magnetospheric Specification and Forecast Model, which provides short-term forecasts of particle fluxes in space. Rice scientists developed a magneto-hydrodynamic model of the magnetosphere in an attempt to simulate the dynamics of a substorm. Recently, researchers have begun to identify some of the physical processes that cause substorm initiation, while other triggering mechanisms remain unexplained.

One space weather effect that does not follow the trail of energy from the Sun is equatorial scintillations, which cause serious problems in space-based communications and navigation systems, such as GPS. NSF scientists mounted a campaign in September to October 1994, near the magnetic Equator in South America, to understand the physical processes that control the triggering of equatorial irregularities, which give rise to the intense scintillations, but further study was needed before a predictive capability could be developed.

On April 3, 1995, Orbital Sciences Corporation placed a MicroLab-1 satellite in low-Earth orbit. The NSF, along with the FAA, NOAA, and NASA's Jet Propulsion Laboratory (JPL), joined with Orbital Sciences Corporation and Allen Osborne Associates to sponsor a proof-of-concept experiment using MicroLab-1 to test whether GPS radio signals can provide accurate and high-resolution three-dimensional distributions of atmospheric temperature and water vapor. The initial results for temperature profiles between 5 and 40 kilometers were excellent when compared with standard radiosondes. Beyond this range, preliminary temperatures showed difficulties. In the upper atmosphere, the errors resulted from initial temperature and pressure assumptions in this region and initial ionospheric refraction assumptions. In the lower troposphere, the errors seemed to be associated with multipath effects caused by large gradients in refractivity caused by water vapor distribution.

An instrument designed to monitor ozone levels in the Earth's atmosphere was launched from French Guiana on April 20 aboard ESA's second European Remote Sensing Satellite (ERS-2). Scientists and engineers at the Smithsonian Astrophysical Institute (SAO) developed the Global Ozone Monitoring Experiment in cooperation with European scientists to generate a complete world ozone map every 3 days.

The Polar Ozone and Aerosol Measurement (POAM-II) experiment on the Sun-synchronous SPOT-3 satellite continued to provide vertical profiles of important middle atmosphere constituents, such as aerosols, nitrogen dioxide, oxygen, ozone, and water vapor, over the polar stratosphere. Sponsored by the Naval Research Laboratory and the Ballistic Missile Defense Organization (BMDO), this experiment was launched in September 1993. POAM-II data have contributed significantly to scientific understanding of infrared laser and electromagnetic wave propagation through the polar stratosphere, as well as to understanding of the polar ozone depletion process. POAM-II also confirmed the role of the polar vortices in ozone depletion and detected the presence of polar stratospheric clouds.


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Curator: Lillian Gipson
Last Updated: September 5, 1996
For more information contact Steve Garber, NASA History Office,
sgarber@hq.nasa.gov