Validation of water vapor results measured by the Limb Infrared Monitor of the Stratosphere Experiment on NIMBUS 7

Abstract

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...

Characterizing polar atmospheres and their effect on Rayleigh‐scattering optical depth

“…In Antarctica, the water vapor mixing ratio measurements were derived from (1) LIMSE [ Russell et al , 1984], (2) HALOE [ Harries et al , 1996; Randel et al , 2001], (3) the UARS experiment using the Microwave Limb Sounder [ Lahoz et al , 1996], (4) the SAGE II experiment [ Chiou et al , 1997; Rind et al , 1993], (5) the AMSWOS experiment [ Peter , 1998], and (6) the Microwave Limb Sounder campaign in winter months of 1992 [ Morrey and Harwood , 1998]. The South Pole measurements of water vapor mixing ratio were obtained from (1) frost point sounding observations [ Rosen et al , 1991] and (2) ground‐based lidar measurements [ Fiocco et al , 1996; Cacciani et al , 1997].…”

Validation of MIPAS-ENVISAT H<sub>2</sub>O operational data collected between July 2002 and March 2004

“…One of the first spaceborne instruments able to measure stratospheric H 2 O was the Limb Infrared Monitor of the Stratosphere (LIMS) (Fischer et al, 1981;Russell III et al, 1984), a limbemission filter radiometer which was deployed aboard the Nimbus-7 satellite launched in October 1978. In the 1980s and 1990s the Atmospheric Trace Molecule Spectroscopy instrument (ATMOS) as the first limb occultation Fourier transform infrared (FTIR) spectrometer provided H 2 O profiles from the upper troposphere to the lower mesosphere during four short missions of the Space Shuttle between 1985 and 1994 (Abbas et al, 1996a, b).…”

On the quality of the Nimbus 7 LIMS Version 6 water vapor profiles and distributions

“…A constant H 2 O value of 6.5 ppmv was used in the LIMS forward radiance model to estimate the effects of water vapor radiance above the first retrieved layer. That assumed value is based on observations of H 2 O for the lower mesosphere from HALOE and MLS and from ground-based microwave measurements of the 1990s, with a slight downward adjustment for the lower values of CH 4 and their oxidation to H 2 O for the 1978/79 period (Remsberg et al, 1984). Figure 2a is the zonally-averaged distribution of V6 H 2 O for 15 November 1978 from its descending (north-to-south or local nighttime) orbital segments.…”

“…Estimates of the systematic errors in Table 1 were adopted from the simulation studies in Russell et al (1984) for radiometric bias, H 2 O line parameter uncertainties (8%), the main IFOV lobe, and the approximations for the forward model. The H 2 O profiles also have a bias of order 10 to 15% due to estimates of the V6 temperature biases from Remsberg et al (2004, their Remsberg et al (1984b), followed by the zonal mean, V6 minus V5 differences for T(p) in Remsberg et al (2007, their Fig.…”

“…The precisions and accuracies for the LIMS V5 H 2 O profiles were reported in Russell et al (1984), Remsberg et al (1984a), and Remsberg and Russell (1987). Their combined errors are no greater than 17% in the middle stratosphere (3 to 30 hPa), due primarily to the effects of profile registration and temperature biases for their retrievals.…”