Abstract
Abstract. Ozone (O3) plays a significant role in weather and climate on regional to global spatial scales. Most studies on the variability in the total column of O3 (TCO) are typically carried out using daytime data. Based on knowledge of the chemistry and transport of O3, significant deviations between daytime and night-time O3 are only expected either in the planetary boundary layer (PBL) or high in the stratosphere or mesosphere, with little effect on the TCO. Hence, we expect the daytime and night-time TCO to be very similar. However, a detailed evaluation of satellite measurements of daytime and night-time TCO is still lacking, despite the existence of long-term records of both. Thus, comparing daytime and night-time TCOs provides a novel approach to verifying the retrieval algorithms of instruments such as the Atmospheric Infrared Sounder (AIRS) and the Microwave Limb Sounder (MLS). In addition, such a comparison also helps to assess the value of night-time TCO for scientific research. Applying this verification on the AIRS and the MLS data, we identified inconsistencies in observations of O3 from both satellite instruments. For AIRS, daytime–night-time differences were found over oceans resembling cloud cover patterns and over land, mostly over dry land areas, which is likely related to infrared surface emissivity. These differences point to issues with the representation of both processes in the AIRS retrieval algorithm. For MLS, a major issue was identified with the “ascending–descending” orbit flag, used to discriminate night-time and daytime MLS measurements. Disregarding this issue, MLS day–night differences were significantly smaller than AIRS day–night differences, providing additional support for the retrieval method origin of AIRS in stratospheric column ozone (SCO) day–night differences. MLS day–night differences are dominated by the upper-stratospheric and mesospheric diurnal O3 cycle. These results provide useful information for improving infrared O3 products.
Highlights
Atmospheric ozone (O3) is a key factor in the structure and dynamics of the Earth’s atmosphere (London, 1980)
Over 90 % of the globe, Atmospheric Infrared Sounder (AIRS) total column of O3 (TCO) is smaller during night-time than during daytime
The seasonal averaged O3 day-to-night relative difference shown in Fig. 1a–d reveals that AIRS TCO day and night difference variations in Asia, Europe, and North America during winter in the Northern Hemisphere (DJF) are smaller than during summertime (JJA), which is in line with the efficiency of photochemical production between seasons in the Northern Hemisphere
Summary
Atmospheric ozone (O3) is a key factor in the structure and dynamics of the Earth’s atmosphere (London, 1980). In addition to the quadrennial O3 assessments, the Bulletin of the American Meteorological Society (BAMS, American Meteorological Society, 2011) annually publishes its “State of the Climate”; since 2015, this annual publication includes tropospheric O3 trends and effects from the El Niño–Southern Oscillation (ENSO), a description of the relevant stratospheric events of the past year, the state of the Antarctic O3 hole, and an annual update of global and zonal trends in stratospheric O3 These regularly recurring reports and publications illustrate the continued attention and monitoring of the O3 layer and its recovery, in which the long-term records of satellite observations play a crucial role. Establishing and maintaining the quality of the satellite observations of stratospheric O3 is highly relevant
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