Argus Instrument Team Research Activities
Research Staff: Max Loewenstein, Hansjürg Jost, James Podolske, Jeff Greenblatt, Jeff Grose, Margaret Swisher
The Argus instrument is a lightweight, infrared (3 to 5 micrometer wavelength) diode-laser spectrometer (see figure 1). It was designed for measuring the atmospheric nitrous oxide (N2O) and methane (CH4) tracer fields in situ from balloons and aircraft. These long-lived tracer molecules are very important in providing quantitative information on atmospheric dynamics. The instrument can return atmospheric measurements over the altitude range of 5 to 30 km.
The Argus team participated in ER-2 flights originating in Kiruna, Sweden from January through March of 2000, as part of the NASA SOLVE field campaign. The overall purpose of the campaign was to achieve a detailed understanding of the spatial extent and intensity of ozone loss inside the Arctic winter polar vortex. The Argus instrument specifically contributed to SOLVE by measuring the long-lived chemicals N2O and CH4 which act as dynamical tracers of the vortex motion. Two aspects of vortex dynamics are of importance: Subsidence of the vortex due to strong radiation cooling during the polar night and the formation of a vortex edge marking the boundary between the subsiding polar region and the mid-latitude atmosphere.
A post-mission workshop was held in Palermo, Italy in September 2000, where several Argus team members presented papers and posters. At this workshop several groups which had acquired N2O data in SOLVE agreed to produce a suitably averaged data set of N2O for use by the SOLVE community of scientists. This data set, dubbed unified-N2O, was created, and was placed in the SOLVE data archive. The methodology for creating unified-N2O was described by NOAA personnel. See figures 2 and 3 for examples of SOLVE data.
Figure 1. A photo of the Argus instrument with the flight cover removed. The 36 m folded-path absorption cell (astigmatic Herriott type) is in the foreground. The laser and detector liquid nitrogen dewar are visible in the background. Also visible are the black mounts for the optics which steer the beam from the laser through the absorption cell and into the detectors.
Figure 2. A time series of N2O acquired on March 11, 2000 during an ER-2 flight in the SOLVE campaign in Arctic winter 2000. The observed large variations of N2O over time are due to different vertical shifts of air masses within and outside the subsiding winter polar vortex. The aircraft crossed into the polar vortex at 4.5x104 UT with a corresponding rapid decrease of N2O of 174 ppb over a horizontal distance of 200 km.
Figure 3. The data of figure 2 plotted as theta (potential temperature) vs. N2O (theta, the potential temperature, is related to atmospheric temperature and acts as a "better" vertical coordinate replacing geometric altitude). The lower branch of the curve, labeled vortex in the figure, represents data sampled inside the polar vortex, the upper branch is data obtained outside the vortex. Data scattered between these branches arise from a broad, diffuse zone which is in the boundary between these two regions, the vortex edge region.