A nitric acid dataset from IASI for polar stratospheric denitrification studies
Résumé
In this paper, we exploit the first 10-year data-record (2008-2017) of nitric acid (HNO 3) total columns measured by the IASI-A/Metop infrared sounder, characterized by an exceptional daily sampling and a good vertical sensitivity in the mid-stratosphere (around 50 hPa), to monitor the causal relationship between the temperature decrease and the observed HNO 3 loss that occurs each year in the Antarctic stratosphere during the polar night. Since the HNO 3 depletion results from the formation of polar stratospheric clouds (PSCs) which trigger the development of the ozone (O 3) hole, its continuous monitoring is of high 5 importance. We verify here, from the 10-year time evolution of the pair HNO 3-temperature (taken from reanalysis at 50 hPa), the recurrence of specific regimes in the cycle of IASI HNO 3 and identify, for each year, the day and the 50 hPa-temperature ("drop temperature") corresponding to the onset of denitrification in Antarctic winter. Although the measured HNO 3 total column does not allow differentiating the uptake of HNO 3 by different types of PSC particles along the vertical profile, an average drop temperature of ∼191 ± 3 K, consistent with the nitric acid trihydrate (NAT) formation temperature (close to 10 195 K at 50 hPa), is found. The spatial distribution and inter-annual variability of the drop temperature are briefly investigated and discussed in the context of previous PSCs studies. This paper highlights the capability of the IASI sounder to monitor the long-term evolution of the polar stratospheric composition and processes involved in the depletion of stratospheric O 3 .
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