Performance of AIRS ozone retrieval over the central Himalayas: use of ozonesonde and other satellite datasets

Abstract

Data from 242 ozonesondes launched from ARIES, Nainital (29.40◦ N, 79.50◦ E; 1793 m elevation), are used to evaluate the Atmospheric Infrared Sounder (AIRS) version 6 ozone profiles and total column ozone during the period 2011–2017 over the central Himalayas. The AIRS ozone products are analysed in terms of retrieval sensitiv ity, retrieval biases/errors, and ability to retrieve the natu ral variability in columnar ozone, which has not been done so far from the Himalayan region, having complex topog raphy. For a direct comparison, averaging kernel informa tion is used to account for the sensitivity difference between the AIRS and ozonesonde data. We show that AIRS has more minor differences from ozonesondes in the lower and middle troposphere and stratosphere with nominal underes timations of less than 20 %. However, in the upper tropo sphere and lower stratosphere (UTLS), we observe a con siderable overestimation of the magnitude, as high as 102 %. The weighted statistical error analysis of AIRS ozone shows a higher positive bias and standard deviation in the upper troposphere of about 65 % and 25 %, respectively. Similarly to AIRS, the Infrared Atmospheric Sounding Interferometer (IASI) and the Cross-track Infrared Sounder (CrIS) are also able to produce ozone peak altitudes and gradients success fully. However, the statistical errors are again higher in the UTLS region, which are likely related to larger variability in ozone, lower ozone partial pressure, and inadequate re trieval information on the surface parameters. Furthermore, AIRS fails to capture the monthly variation in the total col umn ozone, with a strong bimodal variation, unlike unimodal variation seen in ozonesondes and the Ozone Monitoring In strument (OMI). In contrast, the UTLS and the tropospheric ozone columns are in reasonable agreement. Increases in the ozone values of 5 %–20 % after biomass burning and during events of downward transport are captured well by AIRS. Ozone radiative forcing (RF) derived from total col umn ozone using ozonesonde data (4.86 mW m−2 ) matches well with OMI (4.04 mW m−2 ), while significant RF under estimation is seen in AIRS (2.96 mW m−2 ). The fragile and complex landscapes of the Himalayas are more sensitive to global climate change, and establishing such biases and error analysis of space-borne sensors will help us study the long term trends and estimate accurate radiative budgets.