Abstract
Abstract. Stratospheric and middle-mesospheric ozone profiles above Bern, Switzerland (46.95° N, 7.44° E; 577 m) have been continually measured by the GROMOS (GROund-based Millimeter-wave Ozone Spectrometer) microwave radiometer since 1994. GROMOS is part of the Network for the Detection of Atmospheric Composition Change (NDACC). A new version of the ozone profile retrievals has been developed with the aim of improving the altitude range of retrieval profiles. GROMOS profiles from this new retrieval version have been compared to coincident ozone profiles obtained by the satellite limb sounder Aura Microwave Limb Sounder (MLS). The study covers the stratosphere and middle mesosphere from 50 to 0.05 hPa (from 21 to 70 km) and extends over the period from July 2009 to November 2016, which results in more than 2800 coincident profiles available for the comparison. On average, GROMOS and MLS comparisons show agreement generally over 20 % in the lower stratosphere and within 2 % in the middle and upper stratosphere for both daytime and nighttime, whereas in the mesosphere the mean relative difference is below 40 % during the daytime and below 15 % during the nighttime. In addition, we have observed the annual variation in nighttime ozone in the middle mesosphere, at 0.05 hPa (70 km), characterized by the enhancement of ozone during wintertime for both ground-based and space-based measurements. This behaviour is related to the middle-mesospheric maximum in ozone (MMM).
Highlights
Passive millimetre wave radiometry is a well-established technique to monitor atmospheric constituents by detecting the radiation emitted by the rotational transitions of the molecules
This study is based on stratospheric and mesospheric ozone volume mixing ratio (VMR) profiles observed by GROMOS
The scatter plots of averaged daytime and nighttime O3 VMR measurements of GROMOS and Microwave Limb Sounder (MLS) are shown in Fig. 5 at the same pressure levels as Fig. 4
Summary
Passive millimetre wave radiometry is a well-established technique to monitor atmospheric constituents by detecting the radiation emitted by the rotational transitions of the molecules. Marsh et al (2001) interpreted the tertiary peak by considering that in the middle mesosphere during winter, with a solar zenith angle close to 90◦, the atmosphere becomes optically thick to UV radiation at wavelengths below 185 nm, and, since photolysis of water vapour (Reaction R1) is the primary source of odd hydrogen, reduced UV radiation results in less odd hydrogen. The lack of odd hydrogen needed for the catalytic depletion of odd oxygen (Reactions R2, R3, and R4), in conjunction with an unchanged rate of odd-oxygen production (Reaction R5), leads to an increase in odd oxygen This results in higher ozone concentration because atomic oxygen recombination (Reaction R6) remains as a significant source of ozone in the mesosphere.
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