9 Validation of MIPAS and SMR : Intercomparisons with ASUR N 2 O, HNO 3 and ClO measurements

9 Validation of ^MIPAS and ^SMR : Intercomparisons

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stands for the mid-latitude and the bottom panel stands for the tropical analysis. The statis-tics derived from the 12 mid-latitude profiles are shown in the middle and right plots (upper panel), where the∆ ^VMR (ASUR-MIPAS) is up to 30 ppb or - 5 to 40%. The deviation in the tropics (lower panel) is within 30 ppb or - 20 to 10% as deduced from the 39 coincidence measurements.

9.1.2

Data analyses: TheSMRdata (CTSOV222) from September 2002, February and March 2003 are analyzed for the N₂O comparison. The data are averaged for the nearestASUR measure-ment over 7.5 latitude 7.5 longitude area within 6 hours. The number of profiles averaged vary from 4 to 11. The altitude range of the SMRprofiles considered is 17-40 km due to the sensitivity issues outside this altitude limits. One tropical, two mid-latitude and one high lati-tudeSMRprofile remained as coincident measurements after the averaging.

Results: The collocated N₂O measurements of SMR and ASUR are shown in Figure 9.2.

Examples of the individual profile comparison are shown on the left, the ∆ ^VMRs (ASUR

-SMR) are shown in the middle, and the deviations in percentage are marked on the right plot respectively. The difference in the tropics and in the Arctic is up to 30 ppb or 15%, whereas the difference in the mid-latitude is within 10 ppb or -5 to 10%, except at 40 km.

Figure 9.2: Same as Figure 9.1, but forSMR/Odin.

9.2 NITRIC ACID 69

Figure 9.3: Same as Figure 9.2, but forMIPASHNO3.

9.2 Nitric acid

9.2.1

Results: Figure 9.3 shows the results from ASUR-MIPAS HNO3 comparisons in the mid and high latitudes ( 30 N). There are 13 coincident measurements in the Arctic and 18 in the mid-latitudes. The procedure of data analysis is the same as done for theMIPASN₂O. A very good agreement is found between theASURandMIPASprofiles at all latitudes. The difference in the mid-latitude is -0.3 ppb to 2 ppb or within 5% and the deviation in the Arctic is up to 1 ppm or 5%.

Figure 9.4: The profile comparison betweenASURandMIPASClO at specific measurements locations.

9.3 Chlorine monoxide

9.3.1

Results: There were not enoughMIPASmeasurements to compare with theASURClO, at least for the campaign period. In addition, because of the lower sensitivity of the MIPAS profiles, only a few profiles were available to compare with theASUR data. Moreover, after convolving with AKM, some negative values were still found in the lower stratosphere. So a detailed comparison was not possible with the restricted dataset. However, the data will be used for the validation purpose with a larger MIPAS dataset in future. The comparison ofMIPAS and

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ASUR ClO profiles at specific latitudes are shown in Figure 9.4. The profiles are not smoothed with theASURClO kernels as it only demonstrates the capabilites of the sensors to observe the variations in the trace gas distribution and illustrates the possibilities of a future validation. The comparison looks very promising in the sense that the structures observed by both instruments are very similar.

9.4 Discussion

The deviationMIPAS-ASURN2O is systematic, which is clearly depicted in the shape of the∆ profiles (Figure 9.1). The values around 18 km are higher in theMIPASand the values around 22 km are higher in theASUR as well. Above 30 km the deviation is very small, around 5 ppb.

However, the deviation is about 15% in general, except in the mid-latitude upper stratosphere.

The initial validation by airborne, balloonborne and groundbased instruments shows that the

MIPASN₂O have a high bias in theUTLS(Upper Troposphere and Lower Stratosphere) region (Camy-Peyret et al., 2004). Hence, the deviation can be due to the problems in the MIPAS

retrieval as it is very sensitive to clouds and aerosols in the UTLS. Since ASUR N2O has a small high bias in the lower stratosphere (Greenblatt et al., 2002), that could also contribute to the differences. Nevertheless, the ASUR-MIPAS results are comparable with the results of Camy-Peyret et al. (2004).

Unlike theMIPAS data, the comparisons are performed in the tropics, mid-latitudes and in the Arctic between theSMR and the ASUR data. The deviations in the Arctic and the tropics are in the same direction, where theASUR N₂O shows slightly higher values. However, the mid-latitude comparison yields quite good results as the deviation is very small. The high bias in the lower stratosphericASUR N₂O, uncertainty in the atmospheric variations and the remaining noise in theSMR profiles can be the reasons for the offset between the profiles. It has also been noticed that the differenceASUR-SMRis in the accuracy range (30 ppb or 15%) ofASUR N₂O as well.

The deviation betweenASURandMIPASHNO3in the mid-latitude is in the order of 0.2 ppb, where as in the high latitudes the difference is unidirectional for which theASURHNO₃shows slightly higher values. The difference can probably be arised from the airmass variability.

However, the difference is within 5% at all latitude sections, which is a very good agreement.

Moreover, the deviation is well inside the accuracy (15%) ofASUR HNO₃.

9.5 Conclusions

TheASUR N₂O, HNO₃and ClO observations duringSCIAVALUE andEUPLEX are compared with theMIPASandSMRmeasurements. The selection criteria for the comparisons is that the

ASUR measurements that were performed in a 1000 km radius in 6 hours of the satel-lite measurements. TheASUR N2O measurements in comparison withMIPASand SMRshow a deviation within 30 ppb or 15%, which is also inside the accuracy limit of the ASUR

measurements. Hence, theASUR N₂O in comparison MIPASand the SMRproduce promising results. TheMIPAS andASUR HNO₃ are in very good agreement, where the differences are within 5%. The initial comparison betweenASUR andMIPAS ClO profiles show encouraging results for a future validation study.

10 The ^B remen ^CTM : ^A new simple 3D model for