Search

At the altitudes of the mesosphere – lower thermosphere, OH and HO2 play a significant role in many physicochemical processes. Thus, monitoring of their spatiotemporal evolution together with other chemically active trace gases is one of the most important problems for this atmosphere region, in which direct measurements are difficult. The paper studies the nighttime OH and HO2 chemical equilibria using the 3D chemical transport modeling within the general approach including the extraction of the main sources and sinks in the equilibrium space-time areas and derivation of analytical criteria for equilibrium validity. The presented analysis shows that there are extended areas, where nighttime HO2 and OH are close to their local equilibrium concentrations determined mainly by the reaction between HOx – Ox components themselves and with H2O2, N, NO, NO2, and CO. In the upper mesosphere – lower thermosphere, the equilibrium expressions can be shortened, including the HOx – Ox chemistry only. These conditions describes the HO2 and OH equilibrium from the top to the some lower borders, the altitude position of which vary in the interval between 72–73 and 85 km and depends essentially on season and latitude. The developed analytical criteria almost everywhere well reproduce the main features of these borders. The obtained results allow to extend the abilities of previously proposed methods for the retrieval of poorly measured components from measurement data and to develop new approaches. [ABSTRACT FROM AUTHOR]

Abstract. At the altitudes of the mesosphere -- lower thermosphere, OH and HO2 play a significant role in many physicochemical processes. Thus, monitoring of their spatiotemporal evolution together with other chemically active trace gases is one of the most important problems for this atmosphere region, in which direct measurements are difficult. The paper studies the nighttime OH and HO2 chemical equilibria using the 3D chemical transport modeling within the general approach including the extraction of the main sources and sinks in the equilibrium space-time areas and derivation of analytical criteria for equilibrium validity. The presented analysis shows that there are extended areas, where nighttime HO2 and OH are close to their local equilibrium concentrations determined mainly by the reaction between HOx -- Ox components themselves and with H2O2, N, NO, NO2, and CO. In the upper mesosphere -- lower thermosphere, the equilibrium expressions can be shortened, including the HOx -- Ox chemistry only. These conditions describes the HO2 and OH equilibrium from the top to the some lower borders, the altitude position of which vary in the interval between 72-73 and 85 km and depends essentially on season and latitude. The developed analytical criteria almost everywhere well reproduce the main features of these borders. The obtained results allow to extend the abilities of previously proposed methods for the retrieval of poorly measured components from measurement data and to develop new approaches. [ABSTRACT FROM AUTHOR]

The assumption of nighttime ozone chemical equilibrium (NOCE) is widely employed for retrieving the O x -HO x components in the mesopause from rocket and satellite measurements. In this work, the recently developed analytical criterion of determining the NOCE boundary is used (i) to study the connection of this boundary with O and H spatiotemporal variability based on 3D modeling of chemical transport and (ii) to retrieve and analyze the spatiotemporal evolution of the NOCE boundary in 2002–2021 from the SABER/TIMED dataset. It was revealed, first, that the NOCE boundary reproduces well the transition zone dividing deep and weak photochemical oscillations of O and H caused by the diurnal variations of solar radiation. Second, the NOCE boundary is sensitive to sporadic abrupt changes in the middle-atmosphere dynamics, in particular due to powerful sudden stratospheric warmings leading to the events of an elevated (up to ∼ 80 km) stratopause, which took place in January–March 2004, 2006, 2009, 2010, 2012, 2013, 2018, and 2019. Third, the space–time evolution of this characteristic expressed via pressure altitude contains a clear signal of an 11-year solar cycle in the 55 ∘ S–55 ∘ N range. In particular, the mean annual NOCE boundary averaged in this range of latitudes anticorrelates well with the F10.7 index with the coefficient of -0.95. Moreover, it shows a weak linear trend of 56.2±42.2 m per decade. [ABSTRACT FROM AUTHOR]

The assumption of nighttime ozone chemical equilibrium (NOCE) is widely used for retrieval of the Оx-НOx components in the mesopause from rocket and satellite measurements. In this work, recently developed analytical criterion of determining the NOCE boundary is applied (1) to study of connection of this boundary with O and H spatiotemporal variability basing on the 3D chemical transport modeling, and (2) to retrieve and analyze the spatiotemporal evolution of the NOCE boundary in 2002–2021 from SABER/TIMED data set. It was revealed, first, that the NOCE boundary well reproduces the transition zone dividing deep and weak diurnal oscillations of O and H at the low and middle latitudes. Second, the NOCE boundary is sensitive to sporadic abrupt changes in the middle atmosphere dynamics, in particular, due to powerful sudden stratospheric warmings leading to events of elevated (up to ~80 km) stratopause, which took place in January–February 2004, 2006, 2009, 2010, 2012, 2013, 2018 and 2019. Third, the space-time evolution of this characteristics expressed via pressure-height contains a clear signal of 11-year solar cycle in the range of 55º S–55º N. In particular, average annual the NOCE boundary averaged in this range of latitudes anticorrelates well with F10.7 index with the coefficient of -0.96. Moreover, it shows a weak linear trend of 49.2±36.2 m/decade. [ABSTRACT FROM AUTHOR]

The assumption of nighttime ozone chemical equilibrium (NOCE) is widely used for retrieval of the Ox-HOx components in the mesopause from rocket and satellite measurements. In this work, recently developed analytical criterion of determining the NOCE boundary is applied (1) to study of connection of this boundary with O and H spatiotemporal variability basing on the 3D chemical transport modeling, and (2) to retrieve and analyze the spatiotemporal evolution of the NOCE boundary in 2002-2021 from SABER/TIMED data set. It was revealed, first, that the NOCE boundary well reproduces the transition zone dividing deep and weak diurnal oscillations of O and H at the low and middle latitudes. Second, the NOCE boundary is sensitive to sporadic abrupt changes in the middle atmosphere dynamics, in particular, due to powerful sudden stratospheric warmings leading to events of elevated (up to ~80 km) stratopause, which took place in January-February 2004, 2006, 2009, 2010, 2012, 2013, 2018 and 2019. Third, the space-time evolution of this characteristics expressed via pressure-height contains a clear signal of 11-year solar cycle in the range of 55°S-55°N. In particular, average annual the NOCE boundary averaged in this range of latitudes anticorrelates well with F10.7 index with the coefficient of -0.96. Moreover, it shows a weak linear trend of 49.2±36.2 m/decade. [ABSTRACT FROM AUTHOR]