The UARS CLAES instrument made extensive measurements of the infrared emission of stratospheric aerosol resulting from the June 15, 1991 eruption of Mount Pinatubo from October, 1991 until May, 1993. The aerosol distribution is shown as a series of daily zonal‐mean latitude cross‐sections of absorption coefficient and stratospheric infrared optical depth with coverage from 80°N to 80°S. Sulfuric acid mass estimates are presented.
The Cryogenic Limb Array Etalon Spectrometer, CLAES, was launched on September 12, 1991 aboard the NASA Upper Atmosphere Research Satellite (UARS) and has been acquiring data on stratospheric composition since October 1, 1991. Overviews of the CLAES experiment and hardware are given by Roche et al (1) and Burriesci et al. (2). In the OSA Topical Meeting on Optical Remote Sensing of the Atmosphere in 1990 we presented three papers, (3,4,5) that described our progress up to that time in defining the system spectral transmission. In this paper, we describe refinements to CLAES characterization since then. These have come from further work with the pre-launch cold test data and from on-flight data. The spectral transmission characterization described here is currently being used in CLAES retrieval software. Figure (1) shows a schematic diagram of the spectrometer. In normal operation the CLAES instrument achieves a 0.2-0.65 cm -1 spectral resolution by passing the radiation through one of nine passband blocking filters (FWHM ~10 cm -1 ) mounted in a filter wheel, and one of four Fabry-Perot etalons which are mounted in a paddle wheel to provide for spectral scanning by tilting. The transmitted radiation then falls on a focal plane array consisting of a main array of 20 elements and an HCI array of 3 elements. The main detector array is used by eight spectral channels from 5.3 to 12.8 μ m and takes atmospheric data in 20-2.5 km vertical increments. The 3-element HCL array is used only by the 3.5 μ m channel where each detector spans approximately 16 km for S/N augmentation.
We present an analysis of the temporal evolution of stratospheric constituents above the station of Dumont d'Urville in Antarctica (67°S, 140°E) from August 14 to September 20, 1992. Data sets include temperature profiles and H 2 O, ClO, O 3 , NO 2 , ClONO 2 , HNO 3 , N 2 O, and CH 4 mixing ratios and aerosol extinction coefficients from 46 to 1 hPa measured by the Microwave Limb Sounder (MLS) and the Cryogenic Limb Array Etalon Spectrometer (CLAES) instruments aboard the Upper Atmosphere Research Satellite (UARS). At the station, aerosol extinction coefficients and O 3 profiles are obtained by a lidar together with O 3 profiles provided by sondes. Integrated O 3 and NO 2 column amounts are given by a Système d'Analyse par Observation Zénithale (SAOZ) spectrometer located at the station. Column O 3 is also provided by the Total Ozone Mapping Spectrometer (TOMS) instrument aboard the NIMBUS 7 satellite, complemented with potential vorticity derived from the U.K. Meteorological Office assimilated data set and temperature fields provided by the European Centre for Medium‐Range Weather Forecasts. Time evolution of these measurements is interpreted by comparison with results from the SLIMCAT three‐dimensional chemical transport model. We show that the site is near the vortex edge on average and is alternately inside the vortex or just outside in the region referred to as the “collar” region. There are no observations of polar stratospheric clouds (PSCs) over the station above 46 hPa (∼18 km). In fact, PSCs mainly appear over the Palmer Peninsula area at 46 hPa. The rates of change of chemical species are evaluated at 46 hPa when the station is conservatively inside the vortex collar region. The ozone loss rate is 0.04 ppmv d −1 (∼1.3% d −1 ), which is consistent with other analyses of southern vortex ozone loss rates; chlorine monoxide tends to decrease by 0.03 ppbv d −1 , while chlorine nitrate increases by 0.025 ppbv d −1 . These negative ClO and positive ClONO 2 trends are only observed in the collar region of the vortex where O 3 amounts are far from near zero, and little denitrification is observed. Loss and production rates as measured by UARS are more pronounced than the ones deduced from the SLIMCAT model, probably because of the moderate model horizontal resolution (3.75° × 3.75°), which is not high enough to resolve the vortex crossings above Dumont d'Urville and which leads to a larger extent of denitrified air than indicated by the UARS data. The analysis also shows activated ClO inside the vortex at 46 hPa, a dehydrated vortex at 46 hPa, and rehydrated above, with no trace of denitrification in the lower stratosphere. Good agreement between coincident measurements of O 3 profiles by UARS/MLS, lidar, and sondes is also observed. Finally, the agreement between UARS and SLIMCAT data sets is much better in the middle stratosphere (4.6 hPa) than in the lower stratosphere (46 hPa).
Global variability and budgets of stratospheric nitrous oxide (N2O) are studied using output from a stratospheric version of the NCAR Community Climate Model. The model extends over 0–80 km, incorporating an N2O-like tracer with tropospheric source and upper-stratospheric photochemical sink, the latter parameterized using linear damping rates obtained from detailed two-dimensional model calculations. Results from the model over several seasonal cycles are compared with observations of N2O from the Cryogenic Limb Array Etalon Spectrometer instrument on the Upper Atmosphere Research Satellite. The model produces N2O structure and variability that is in reasonable agreement with the observations. Global budgets of stratospheric N2O are furthermore analyzed using model output, based on the transformed Eulerian-mean, zonal-mean framework. These budgets are used to quantify the importance of planetary wave constituent transport in the stratosphere, for both slow seasonal variations and fast planetary wave events. These results demonstrate that such wave fluxes act to form and sharpen the strong subtropical N2O gradients observed in satellite measurements.
Upper Atmosphere Research Satellite observations indicate that extensive denitrification, without significant dehydration, currently occurs only in the Antarctic during mid to late June. The fact that denitrification occurs in a relatively warm month in the Antarctic raises concern about the likelihood of its occurrence, and associated effects on ozone recovery, in a future colder and possibly more humid Arctic lower stratosphere. Polar stratospheric cloud lifetimes required for Arctic denitrification to occur in the future are presented and contrasted against the current Antarctic cloud lifetimes. Model calculations show widespread severe denitrification could enhance future Arctic ozone loss by up to 30%.
Precise measurements of CH4 in a column of near surface air, and in partial columns above this, would be very valuable in identifying sources/sinks of atmospheric CH4, and its transport. For this purpose we have proposed a grating mapping spectrometer (GMS) for deployment as an Instrument of Opportunity (IOO) on the NPOESS that acquires data in the 2990 to 3050 cm-1 spectral region. It will provide measurements of CH4 absorption of sunlight in the weaker CH4 features in the region, and of thermal emission in the stronger CH4 features in the region. It is the combination of the two that provides the vertical information. The IOO will acquire spectra on a crosstrack swath centered on nadir, and with 1/2 width of 55 degrees on each side of nadir (about 2800 km full width swath on the ground for a nominal 828 km satellite altitude). This with footprints that are about 3.1 km on a side at nadir. The small footprint facilitates cloud screening, and identification of CH4 source hotspots. A capability to project the slit to nadir along the direction from satellite to sun will be utilized for over the ocean viewing in order to facilitate measurements in solar glitter. It will obtain spectra with resolution n < 0.58 cm-1 and sample spacing < 0.17 cm-1. Based on the spectral characteristics and currently achievable very low-noise we do a linear error analysis (Rodgers, [1]) for the simultaneous retrieval of multi-column CH4, humidity, and surface parameters and 13CH4 total column. We show that useful multi-column CH4 retrievals can be obtained, with good near surface sensitivity in sunlit conditions. We also show the 13CH4 column can be retrieved with precision better than 3%. Retrieval of 13CH4 column in the earth's atmosphere is analogous in difficulty to retrieval of the major CH4 isotope column in the Martian atmosphere by a similar GMS deployed on a Mars orbiter. We show that H2O vertical information can be retrieved from these measurements and discuss the potential for ethane column retrieval.
