Solar measurement, instrument error

Figure 2. CIO volume mixing ratio profiles across the vortex edge as measured by the ASUR instrument (solid line) on March 6, 1996, compared to results of the SI.IMCAT 3-D model (dashed line, rectangles) for identical positions at 12 UT. Also indicated are average times, positions, solar zenith angles, and 475 K-PV s for the individual measurements. The thick error bars represent the relevant statistical errors due to measurement noise, the thin dotted error bars include also the error due to the limited altitude resolution (the so-called null-space error). Modelled and measured data are in relatively good agreement inside, at the edge, and outside the Arctic polar vortex.

One of the advantages of the solar occultation method is that the concentrations are derived from the measurement of a ratio of 2 fluxes, and therefore are not substantially affected by instrument calibration errors or solar spectral features. Because of the observing geometry involved, this technique provides good vertical resolution. The major limitation results from the limited number of observations due to the sunrise or sunset contraints. Better coverage can be obtained by considering, in addition, lunar and stellar occultations. 

Nonradiogenic noble gases. For Ne, both of the two °Ne/ Ne ratios derived from different data bases (11.8 0.6 and 12.15 0.40 see Wieler s (2002) Table 8) require some fractionation relative to the solar value, although not quite to the same extent as that of the terrestrial atmosphere. The constraint on the Ne/ Ne ratio of <0.067 cannot be used to further limit the source of Ne. The °Ar/ Ar value of 5.45 0.10 measured by Venera spacecraft instruments is nominally somewhat above the terrestrial ratio but is essentially indistinguishable from it within error. 

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