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The LIMS is a six channel limb scanning IR radiometer flying on the NIMBUS 7 spacecraft. It measured radiances from October 24, 1978, to May 28, 1979, from which vertical profiles of temperature, ozone, water vapor, nitrogen dioxide, and nitric acid were determined. Nitric acid (HNO3) plays an important role in stratospheric chemistryd both as reservoir and as sink for the nitrogen compounds and because of its relationship to the hydroxyl radical. This paper describes the validation of the HNO 3 results, beginning with an outline of the measurements and data reduction leading to the retrievals. The error sources due to instrumental effects and data reduction are described, and their effects on the results are calculated. The predicted random errors are shown to be somewhat larger than the observed values of •0.10 ppbv. The LIMS results are within 20% of a set of 15 correlative balloon-borne measurements, obtained with several techniques over a range of season, latitude, and pressure between 100 and 20 mbar, the region of largest HNO 3 mixing ratio. This is about the accuracy of the correlative measurements. The percent differences are larger at altitudes above 10 mbar. LIMS results agree with earlier measurements at all but the highest levels. Total overburdens above 200 mbar calculated from LIMS agree with those measured spectroscopically from aircraft. LIMS and other HNO 3 measurements show similar agreement with model predictions. The consistency suggests that the major LIMS error sources are reasonably well understood. The HNO3/NO 2 ratio also leads to reasonable OH concentrations. The global distribution of HNO 3 in November shows strong latitudinal variation at the altitude of the maximum, with a large build up over the northern hemisphere pole at • 40 mbar, but lower values over the southern pole. This reverses by early northern spring. Some characteristics and limits on the data are noted, but the LIMS HNO 3 determinations are usually of comparable accuracy to other determinations. These results provide a valuable addition to our knowledge of the distributions of trace gases in the stratosphere. By themselves, but especially in conjunction with the LIMS measurements of temperature, ozone, water vapor, and nitrogen dioxide, they form the basis for a wide range of atmospheric studies.

The LIMS experiment on NIMBUS 7 used the technique of thermal infrared limb scanning to sound the composition and structure of the upper atmosphere. One of the LIMS channels was spectrally centered at 6.9/•m to measure the vertical profile and global distribution of stratospheric water vapor. This paper describes the characteristics of and data from the water vapor channel and the steps taken to validate results. The mean difference between LIMS measurements and data from 13 balloon underflights is about 0.6 ppmv with LIMS mixing ratios biased high with respect to in situ data. This difference is of about the same order as the estimated LIMS accuracy and is less than the sum of the errors for LIMS and the balloon techniques. The precision measured in orbit is 0.2-0.3 ppmv, and the accuracy, based on computer simulations, is estimated to be 20-30% over the range from 50 mbar to about the stratopause. The vertical distribution in the tropics shows the presence of a hygropause where the mixing ratio decreases to a minimum above the tropopause and then increases with altitude. In extratropical regions, the profile is nearly constant with height and has a value of about 5 ppmv. An unexplained diurnal variation exists in the data which is largest at the 1-mbar level (1-2 ppmv) and virtually nonexistant at 10 mbar. Day values are higher than night. Until this phenomenon is better understood, caution must be used in drawing conclusions about the H,.O altitude behavior in the upper stratosphere. An anti-correlation exists in the fine structure of the vertical water and temperature profiles. This is brought about primarily by small temperature errors and should not be taken as real. For this and other reasons, more confidence is placed in zonal mean distributions averaged over several days rather than in single profiles. A zonal mean pressure-latitude cross section is described for January. NIMBUS 7 satellite measuring vertical radiance profiles across the atmospheric limb of the earth [see Russell and Gille, 1978; Gille et al., 1980; Gille and Russell, this issue]. These profiles were later ground processed to infer middle atmosphere temperature profiles and the concentrations of some of the key chemical compounds believed to be important in the stratospheric ozone photochemistry. In addition to temperature, LIMS measured vertical concentration profiles of ozone (03), nitric acid (HNO3) , nitrogen dioxide (NO2), and water vapor (H20). The LIMS instrument functioned virtually without flaw from the time it was turned on, October 24, 1978, until it was turned off, May 28, 1979, when the solid cryogen used for detector cooling had depleted as planned. A detailed description of the experiment including an overview of results, and discussion of potential data applications is presented in another paper in this issue by Gille and Russell [this issue]. The emphasis of this paper is on the water vapor measurements with the intended goal being to inform potential users about the data quality and limitations.Knowledge of stratospheri...

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HCl has been observed in the stratosphere from balloon borne spectroscopic measurements of a portion of the fundamental band in the 3 microns wavelength region. The observation of absorption lines using the sun as a source at solar zenith angles larger than 90° indicates an HCl volume mixing ratio equal to (3.8 ± 1.5) × 10−10 at 20 km increasing with altitude at least up to 30 km where the value is (1.4 ± 0.6) × 10−9. The total zenith amount above 21 km is found to be (10± 3.5) × 10−14 cm−2 in agreement with previous observations performed up to this altitude. A maximum number density equal to (7.2 ± 3) × 108 cm−3 is observed at 24 ± 2 km altitude.

The LIMS experiment launched on NIMBUS 7 measured vertical profiles of temperature and the concentrations of 0 3, H20, HNO 3, and NO 2 during the period from late October 1978 until late May 1979. This paper discusses the validation of results from the NO, channel and th.e quality of the data.The discussion includes channel characteristics, experiment errors due to instrument and spacecraft effects, predicted and measured precision, predicted accuracy, and comparisons with correlative measurements made in a series of balloon underflights. All balloon measurements used for comparisons were made using the solar occultation technique, and since NO 2 varies significantly over the diurnal cycle, a photochemical model was used to time translate the data to the LIMS time. Because of this the comparisons were primarily qualitative. Features such as profile shape and slope of the mixing ratio altitude distribution are in good agreement. The mean difference between LIMS results and the balloon data is well within the range of the sum of the error bars for the two data sets. Comparisons are also made with past balloon measurements taken in the 40øN to 50øN latitude band and with photochemical model predictions of the vertical profile. The LIMS data fall within the range of previous mixing ratio measurements, and they are consistent with model estimates. The calculated on-orbit precision is •0.3 ppbv and the estimated accuracy from simulations is •2 ppbv over the 3-mbar to 10-mbar range. Accuracy degrades at higher and lower pressure levels. These results provide the first day-night set of NO 2 measurements from space. INTRODUCTIONThe limb infrared monitor of the stratosphere (LIMS) instrument launched on NIMBUS 7 is a six-channel thermal infrared limb-scanning radiometer. Two channels are centered spectrally in the 15-#m CO: band for sounding the vertical temperature profile, and the others are located at 11.3 #m for nitric acid (HNO3), 9.6 #m for ozone (03), 6.9 #m for water vapor (H20), and 6.2 #m for nitrogen dioxide (NO:) [see Russell and Gille, 1978; Gille et al., 1980]. The LIMS experiment operated virtually without flaw from the time of launch on October 24, 1978 until it was turned off May 28, 1979. At this time, the ammonia-methane solid cryogen used for detector cooling had depleted as planned. The horizon was scanned almost continuously during the LIMS operation, and data were collected night and day over the latitude range from 64øS to 84øN. An experiment overview by J. C. Gille and J. M. Russell (unpublished manuscript, 1983) describes the instrumentation in more detail and discusses fundamental experiment objectives, orbital performance, duty cycle, types of data products, and typical results for each of the five parameters measured.The chemistry objectives of the LIMS experiment are focused on the effects of nitrogen compounds on the stratospheric ozone layer. These compounds arise in the strato-