Leonard R. McMaster

Annual variations of water vapor in the stratosphere and upper troposphere observed by the Stratospheric Aerosol and Gas Experiment II

This paper presents a description of the annual variations of water vapor in the stratosphere and the upper troposphere derived from observations of the Stratospheric Aerosol and Gas Experiment II (SAGE II). The altitude-time cross sections exhibit annually repeatable patterns in both hemispheres. The appearance of a yearly minimum in water vapor in both hemispheres at approximately the same time supports the idea of a common source(s) for stratospheric dry air. Annual patterns observed at northern mid-latitudes, like the appearance of a hygropause in winter and the weakening and upward shifting of the hygropause from January to May, agree with in situ balloon observations previously obtained over Boulder and Washington, D.C. An increase in water vapor with altitude in the tropics is consistent with methane oxidation in the upper stratosphere to lower mesosphere as a source for water vapor. A poleward gradient is also shown as expected based on a Lagrangian mean circulation. A linear regression analysis using SAGE II data from January 1986 to December 1988 shows that little annual variation occurs in the middle and upper stratosphere with the region of large annual variability near the tropopause. The semi-annual variability is relatively marked at altitudes of 24 and 40 km in the tropics.

Stratospheric Aerosol and Gas Experiment II and ROCOZ-A ozone profiles at Natal, Brazil: A basis for comparison with other satellite instruments

We present the results of comparisons of satellite measurements of ozone from the Stratospheric Aerosol and Gas Experiment II (SAGE II) with in situ measurements from ROCOZ-A and electrochemical concentration cell (ECC) ozonesondes at Natal, Brazil (5.9°S, 35.2°W), during the southern hemisphere autumn of 1985. Since data were collected over a region of low ozone variability, comparisons were made of the mean values of 14 SAGE II profiles with the mean values of 7 ROCOZ-A and 7 ECC profiles, rather than of a more limited set of paired comparisons. The basic comparison presented here is ozone number density versus geometric altitude, the fundamental ozone measurement from SAGE II. Over the altitude region from 20 to 52 km SAGE II ozone densities averaged 0.4% lower than ROCOZ-A. The average of the absolute values of the ozone density differences for the two instruments was 2.4% over these altitudes. Owing in large part to the number of profiles in the data sets, the 95% confidence limits for the ozone density differences in these comparisons averaged 3.5% from 20 to 52 km, a significant improvement over previous results. In terms of ozone mixing ratio versus geometric altitude from 20 to 52 km, SAGE II values had a difference of 3.4% from ROCOZ-A (SAGE II higher), an average absolute difference of 3.8%, and an average of 4.7% for the 95% confidence limits. Differences between the ozone density and mixing ratio results are due to the auxiliary temperature and pressure values for the satellite and in situ instruments. The effects of pressure differences on the vertical positioning of the ozone profiles are not important for the altitude-based comparisons of SAGE II and ROCOZ-A. However, they become an important consideration in the comparisons of SAGE II with pressure-based ozone measurements from other satellite instruments. The composite sets of ozone, temperature, and pressure values presented here form an excellent basis for comparisons with other satellite ozone measurements.

The Stratospheric Aerosol and Gas Experiment II (SAGE II) Design and In-Orbit Performance

The design and in-orbit performance data are presented for the Stratospheric Aerosol and Gas Experiment II (SAGE II) instrument which was launched by Shuttle on the Earth Radiation Budget Satellite. SAGE II is a Sun photometer that measures the extinction of Solar radiation caused by the Earths atmosphere in seven spectral channels ranging in center wavelength from 0.385 to 1.02 micrometers. These measurements, which occur twice each orbit during satellite sunrise and sunset, are inverted to yield vertical distributions of stratospheric aerosols, ozone, water vapor, and nitrogen dioxide. The SAGE II instrument consists of a Cassegrain telescope with a two axis gimbal mounting, a grating spectrometer, and a 12 bit data system. The instrument tracks the Solar centroid in the aximuth plane and vertically scans the instruments instantaneous field of view across the Sun for tangent altitudes ranging from the Earths horizon to 150 km. SAGE II is a third generation instrument following the highly successful Stratospheric Aerosol Measurement II (SAM II) and SAGE I programs.

Stratospheric aerosol and gas experiment III: aerosol and trace gas measurements for the Earth Observing System

The SAGE III instrument, the latest in a series of satellite-based instruments employing the self-calibrating solar occultation technique to monitor aerosols and trace gases in the atmosphere, and potential contributions to monitoring global change and other EOS objectives are described. Uses of these data are illustrated with SAGE I and II long-term ozone, aerosol, and water vapor data. The SAGE III instrument will improve the SAM II and SAGE data products with greater overall accuracy, and will provide the ability to extend these measurements over a greater height range. SAGE III will provide long-term self-calibrating global data sets from the midtroposphere to mesosphere, which will contribute greatly to the quantification and understanding of global change.

Error analysis of DIAL measurements of ozone by a Shuttle excimer lidar

An error analysis of DIAL (differential absorption lidar) measurements of stratospheric ozone from the Space Shuttle is discussed. A transmitter system consisting of a KrF excimer laser pumping gas cells of H2 or D2 producing output wavelengths in the near UV is shown to be useful for the measurement of ozone in a 15-50-km altitude range.

Calibration for the SAGE III/EOS instruments

The calibration plan for the SAGE III instruments for maintaining instrument performance during the Earth Observing System (EOS) mission lifetime is described. The SAGE III calibration plan consists of detailed preflight and inflight calibration on the instrument performance together with the correlative measurement program to validate the data products from the inverted satellite measurements. Since the measurement technique is primarily solar/lunar occultation, the instrument will be self-calibrating by using the sun as the calibration source during the routine operation of the instrument in flight. The instrument is designed to perform radiometric calibration of throughput, spectral, and spatial response in flight during routine operation. Spectral calibration can be performed in-flight from observation of the solar Fraunhofer lines within the spectral region from 290 to 1030 nm wavelength.

The Stratospheric Aerosol And Gas Experiment III Instrument Proposed For Eos: A Conceptual Design

A conceptual design is presented for the Stratospheric Aerosol and Gas Experiment III (SAGE III) instrument which is currently being proposed for the Earth Observing System (Eos). SAGE III is designed to monitor globally the vertical distribution of stratospheric aerosols, ozone, water vapor, nitrogen dioxide and temperature by measuring the extinction and scattering of solar radiation in the 0.3 to 1.6 μm range through the earths atmosphere. Solar radiation is reflected from a flat scanning mirror into a Cassegrain telescope, which forms an image on the entrance aperture of a grating spectrometer. The aspheric grating forms a stigmatic, flat field image on a silicon CCD array which serves as the detector for eight of the SAGE III channels. An interference filter in front of the array sorts the dispersed energy so that the desired order (either first, second, or third) reaches the focal plane. Pixels are grouped electronically to form the desired spectral bandpass of each channel. The ninth channel is taken from the grating zero order and uses a InGaAs PIN photodiode detector. A two axis gimbal system is capable of tracking (in azimuth) and scanning (in elevation) the sun through the earths atmosphere when in the solar occultation mode, and then performing earth limb scans between occultation events. Data is sampled at 64 times per second and digitized to 14 bit resolution. Wavelength and radiance calibrations can be performed on-orbit. SAGE III has evolved from the highly successful Stratospheric Aerosol Measurement II (SAM II), SAGE, and SAGE II programs.