Secondary Ozone Maximum Research Articles

Solar Cycle Modulation of Nighttime Ozone Near the Mesopause as Observed by MLS

AbstractEleven‐year solar cycle variations of nighttime ozone near the secondary ozone maximum layer in the mesosphere are analyzed with Aura Microwave Limb Sounder (MLS) observations since 2004, fully covering solar cycle 24. Produced primarily from the recombination of molecular oxygen (O2) with atomic oxygen (O) transported from the lower thermosphere, the mesospheric nighttime ozone concentration is proportional to atomic oxygen density [O], which itself is modulated by ultraviolet (UV) solar cycle variations. MLS nighttime ozone data and UV data at 240 nm from Solar Radiation and Climate Experiment (SORCE) Solar‐Stellar Irradiance Comparison Experiment (SOLSTICE) show a positive correlation over the solar cycle. Nighttime O3 and nighttime carbon monoxide (CO) distributions are highly correlated with each other with similar seasonal and solar cycle variations, because both [O3] and [CO] depend strongly on UV photolysis and are modulated by Eddy diffusion in this region. Nighttime ozone correlates strongly with temperature, with a generally positive correlation, except at high latitudes during boreal winter.

Enhanced vertical mixing associated with a nocturnal cold front passage and its impact on near‐surface temperature and ozone concentration

AbstractA sudden rise in surface temperature is sometimes observed during the nighttime hours with the passage of cold fronts. The physics contributing to such nocturnal warming events and their potential impacts on atmospheric chemistry are not yet fully understood. In this study, a nocturnal warming event associated with a cold front passage in Oklahoma on 3 April 2006 is simulated with the Weather Research and Forecasting model with Chemistry (WRF/Chem). During the prefrontal period under clear‐sky and calm conditions, surface radiative cooling resulted in a decoupled shallow surface layer in which air temperature and wind speed decreased quickly and ozone was removed efficiently by chemical reactions. During the passage of the cold front, strong wind shear enhanced turbulent mixing, which weakened the temperature inversion near the surface. Warmer and ozone‐richer air from aloft was mixed downward to the surface. Thus, a sudden warming and nocturnal secondary ozone maxima were observed near the surface. Dry deposition of ozone at the surface was also enhanced in this warming event.

Vertical ozone characteristics in urban boundary layer in Beijing

Vertical ozone and meteorological parameters were measured by tethered balloon in the boundary layer in the summer of 2009 in Beijing, China. A total of 77 tethersonde soundings were taken during the 27-day campaign. The surface ozone concentrations measured by ozonesondes and TEI 49C showed good agreement, albeit with temporal difference between the two instruments. Two case studies of nocturnal secondary ozone maxima are discussed in detail. The development of the low-level jet played a critical role leading to the observed ozone peak concentrations in nocturnal boundary layer (NBL). The maximum of surface ozone was 161.7ppbv during the campaign, which could be attributed to abundant precursors storage near surface layer at nighttime. Vertical distribution of ozone was also measured utilizing conventional continuous analyzers on 325-m meteorological observation tower. The results showed the NBL height was between 47 and 280m, which were consistent with the balloon data. Southerly air flow could bring ozone-rich air to Beijing, and the ozone concentrations exceeded the China's hourly ozone standard (approximately 100ppb) above 600m for more than 12h.

Mesospheric intrusion and anomalous chemistry during and after a major stratospheric sudden warming

Several major stratospheric sudden warmings (SSWs) characterized by a rapid vertical displacement of the winter polar stratopause are simulated in the National Center for Atmospheric Research's Whole Atmosphere Community Climate Model. The stratopause descends into the mid-stratosphere at the onset of the SSW, and then abruptly reforms near 70km. The SSWs are accompanied by a strong equatorward and downward residual circulation between 40 and 60km. The descent occurs mainly through the core of the highly displaced vortex, and is accompanied by an intrusion of air rich in carbon monoxide (CO) from the mesosphere into the mid-stratosphere. Around the periods when the stratopause undergoes rapid vertical displacement, the simulation shows that the air of mesospheric origin is being cut off and remains distinct from surrounding stratospheric air masses for at least a month after SSW onset. Such mesospheric cut-off intrusion of CO-rich appears to be a defining signature of winters with major SSWs. Due to its strong temperature dependency, the secondary ozone maximum (between 90 and 110km) abruptly decreases in amplitude at the time of the high-altitude stratopause reformation that influences the thermal structure at these altitudes. The vertical location of the tertiary ozone maximum (between 70 and 75km) shows significant variations in response to the changing vertical motion during SSW.

Ground-based radio observations to probe the ozone content in the meteor region

Radar studies of the plasma irregularities produced by meteoroid ablation provide a powerful diagnostic probe of the Earth's atmosphere. This role is especially important as an inexpensive route for studying several atmospheric processes in comparison with other remote sensing techniques or satellite measurements. Ozone concentration has been indirectly measured in the upper mesosphere/lower thermosphere region by the BLM (Bologna-Lecce-Modra) Forward Scatter (FS) meteor radar by the detection of meteoroids interacting with the Earth's atmosphere. Results of variations of mesospheric ozone concentration at different height levels and time scales were deduced in 1992-2000 from the cumulative duration distributions of overdense echoes. Data of the BLM radar obtained in the last millennium decade confi rm the existence of a secondary ozone layer at atmospheric heights of 85-90 km and show a gradual yearly depletion of the ozone content, similarly to the decrease measured in the eighties by the Solar Mesosphere Explorer (SME) satellite throughout consecutive years (Rusch et al., 1990). Radio observations show in addition large seasonal variations at middle latitudes where the abundance at a secondary ozone maximum at 85-90 km is found to be as much as a factor of two higher in spring months than that in summer months.

Determination of transport processes of nocturnal ozone in Istanbul atmosphere

Ozone, usually having a minimum value at night, often increase its concentration level which is known as nocturnal ozone. In this study, the magnitude, frequency and timing of nocturnal ozone maxima were determined between May and September for four years (2001-2004) for stations in the Asian and European sides of Istanbul, Turkey. The magnitude and frequency of late and early peaks for peak ozone nights were monitored. A total of 40 days, having secondary ozone maxima due to horizontal transport processes, have been selected, and HYSPLIT model with back trajectory analysis was conducted at different ground levels.

Satellite observations of high nighttime ozone at the equatorial mesopause

Measurements by the Sounding of the Atmosphere using Broadband Emission Radiometry instrument enable the characterization of the seasonal variation of ozone and temperature in the upper mesosphere. These are the first global measurements that resolve both the structure of the secondary ozone maximum at night and the temperature over all seasons of the year. The average nighttime mixing ratios at the altitude of the maximum vary with latitude and season. Analysis shows that the highest mixing ratios are clustered near the equator during equinoxes. The high ozone mixing ratios are observed in exactly the place and time at which the diurnal tide is largest. The diurnal tidal phase is such that coldest temperatures at 95 km occur near midnight. The high ozone is coincident with regions that have both low temperature and low amounts of atomic hydrogen. We focus particularly on ozone mixing ratios in the range of 18–50 ppmv; these occur intermittently in the equinoctial tropics on days when the night temperature is particularly cold. The occurrence of ozone maxima over 20 ppmv was unexpected but is shown in this paper to be consistent with theory and is a result of large‐amplitude diurnal tides. The same seasonal and latitudinal characteristics are seen in ozone density measured by Global Ozone Monitoring by Occultation of Stars.

Main results of LSO (Lightning and sprite observations) on board of the international space station

The experiment LSO (Lightning and Sprite Observations), on board of the International Space Station, was the first experiment dedicated to nadir observations of sprites from space. Such observations are innovative as sprites are generally observed at the horizon. At the nadir, sprites are superimposed with lightning flashes and the observation concept is based on a spectral differentiation of sprites and lightning by using an adapted filter. The experiment is composed of two micro-cameras, fixed on a station window. One camera is equipped with a filter and measures the sprites in the N2 1P most intense sprite emission line, which coincides also to the atmospheric absorption band of the molecular oxygen. The second microcamera provides observations of lightning flashes in the visible. Measurements were performed during four ESA missions: Andromede, Odissea, Cervantes and Delta. During 19h of effective observations, 180 flashes were analyzed and several possible sprites were identified, demonstrating the interest of this differentiation method. In addition during sunset and sunrise conditions when the lower atmosphere is in the dark, LSO observed the airglow of the secondary ozone maximum at about 90 km modulated by gravity wave activity.

Space-based observations of O 2 A (0,0) band emission near the solar terminator and their interpretation

The LSO (Lightning and Sprite Observations) experiment under sunset/sunrise conditions from International Space Station (ISS) has provided new information about the emission of the visible and near infrared portions of the optical spectrum. Two CCD cameras have been used in the LSO experiment. One of them had a filter for the Atmospheric O 2 (0–0) band registration (762 ± 5 nm). Observations have been performed at limb- and nadir-viewing geometry. Images obtained by both cameras under sunset/sunrise conditions demonstrate the sharp emission layer at an altitude about 90 km. The images have been obtained when tropospheric, stratospheric and lower mesospheric domains were in the Earth’s shadow, and the upper atmosphere regions were illuminated by the rising or setting Sun. The O 2 A (0,0) band emission layer at 90 km was simulated with known chemistry. The major production process of the airglow is O( 1D) production by ozone photolysis followed by energy transfer from O( 1D) to O 2, generating the metastable excited state, O 2 ( b 1 Σ g + ) . It has been shown that under sunset/sunrise conditions the “secondary ozone maximum” provides the main contribution to the observed O 2 A (0,0) band emission. The images taken with these cameras clearly show a vertical distribution of airglow and demonstrate its appreciable variations with horizontal distance across the cameras field of view. The latter feature may be used as a tool for global monitoring of gravity wave activity at the upper mesosphere/lower thermosphere region.

Trends of mesospheric water vapor due to the increase of methane – A model study particularly considering high latitudes

For the water vapor trend analyses by means of our global 3D-model COMMA-IAP we employed estimated methane, dinitrogen oxide and CO 2 trends since the pre-industrial era. We especially consider in context with the increasing occurrence rate of NLC observations the change of the aeronomic conditions in the high latitude mesosphere. A particular problem for the model calculations is connected with the water vapor mixing ratio at the hygropause. We suppose that the hygropause was dryer at the pre-industrial time than currently. The middle atmosphere became more humid corresponding to the increasing methane concentration but depending on height and with a certain time delay due to the long transport time through the middle atmosphere. In order to get useful data of the solar Lyman-α flux back to the pre-industrial time we derived a quadratic fit using the sunspot number available since 1749 as the only solar proxy for the Lyman-α flux before 1947. The fit is based on Lyman-α flux values derived by Woods et al. [Woods, T.N., Tobiska, W.K., Rottman, G.J., Worden, J.R. (2000). Improved solar Lyman-α irradiance modeling from 1947 through 1999 based on UARS observations, J. Geophys. Res., 105, 27, 195–227, 215], available since 1947. This Lyman-α flux values are used to determine the water vapor dissociation rate. The solar influence on the water vapor mixing ratio is insignificant at about 80 km within the NLC area but it becomes increasingly more important with growing altitudes. The rising water vapor concentration reduces the mesospheric ozone due to higher concentrations of the hydrogen radicals. This fact causes a positive feedback between both constituents above about 65 km. The dissociation of smaller amounts of ozone entails the production of less amounts of O( 1D) destroying a smaller quantity of water vapor. The effect is most pronounced in the vicinity of the daytime secondary ozone maximum around an altitude of 85–90 km where the relative increase of the water vapor mixing ratio is strongest.

Secondary maxima in ozone profiles

Abstract. Ozone profiles from balloon soundings as well as SAGEII ozone profiles were used to detect anomalous large ozone concentrations of ozone in the lower stratosphere. These secondary ozone maxima are found to be the result of differential advection of ozone-poor and ozone-rich air associated with Rossby wave breaking events. The frequency and intensity of secondary ozone maxima and their geographical distribution is presented. The occurrence and amplitude of ozone secondary maxima is connected to ozone variability and trend at Uccle and account for a large part of the total ozone and lower stratospheric ozone variability.

Summer nocturnal ozone maxima in Göteborg, Sweden

The magnitude and frequency of nocturnal ozone maxima in a high mid-latitude city (Göteborg, Sweden) has been analysed. Nocturnal ozone maxima have been reported from cities in Europe and North America and can be explained by vertical mixing of high ozone concentrations from higher levels or horizontal transportation from rural areas through local and mesoscale wind systems. Data from four summer months (May–August) in 1994 were used to analyse the relative importance of local- and mesoscale wind systems and vertical mixing in Göteborg during clear and calm weather conditions. Results show that nocturnal ozone maxima frequently occur during these conditions, with a magnitude up to 104 μg m −3. The nocturnal ozone maxima were positively correlated to both situations with a well-developed land breeze and situations with vertical mixing. During the period investigated, in total 17 nights with secondary ozone maximum occurred. The majority of the secondary ozone maxima (80%) appeared early in the night, i.e. an ozone increase within the first 3 h after sunset and sometimes even two peaks occurred. Seven of these occasions can be explained by horizontal advection, eight by vertical mixing and five cannot by certainty be explained to be due to horizontal or vertical transportation only. During the measurement period the Swedish guideline of 80 μg m −3 (for 1-h value) was exceeded 55% of the days (i.e. 68 days, 557 h) and 33% of the nights (i.e. 41 nights, 103 h) in the central parts of Göteborg. The results thus show that in Scandinavia nocturnal ozone concentrations must be considered.

Secondary ozone maxima in a very stable nocturnal boundary layer: observations from the Lower Fraser Valley, BC

The relationship between near-surface ozone concentration and the structure of the nocturnal boundary layer was investigated during a field campaign conducted in 1998 in the Lower Fraser Valley (LFV), British Columbia Canada. Despite the spatial and temporal variation in frequency and morphology, secondary nocturnal ozone maxima were shown to be an important feature of the diurnal ozone cycle throughout the LFV, and localised increases in ozone occasionally exceeded more than half the previous day's maximum concentration. Turbulence in the nocturnal boundary layer was shown to be weak and intermittent. Vertical profiles of Richardson number and ozone concentration indicated that the temporary turbulent coupling of the residual layer to the surface layer facilitated the transport of ozone stored aloft to the surface. Despite the overall complexity of the system, results show that seven out of the 19 ozone spikes observed at the Aldergrove site coincided with turbulence associated with the development of the down-valley wind system. A further nine spikes occurred during periods when a low-level jet was identified aloft. Significantly, ozone concentrations were shown to be highly variable in the residual layer and played an important role in determining the morphology of secondary ozone maxima at the surface. Largest increases in surface ozone concentration occurred when turbulence coincided with periods when ozone concentrations in excess of 80 ppb were observed aloft.

Nocturnal secondary ozone concentration maxima analysed by sodar observations and surface measurements

The occurrence of nocturnal secondary ozone maxima was investigated by ground-level meteorological and air quality measurements in an urban park in Essen, Germany, during 29 individual summer measurement campaigns between May 1995 and September 1997. In addition, during an intensive measurement campaign in May 1997, SODAR measurements of wind and turbulence were made. The spatial and temporal distribution of nocturnal ozone maxima within the measurement network of the Environmental Protection Office of North Rhine–Westphalia was also analysed. Two case studies of nocturnal secondary ozone maxima are discussed in more detail. They represent two different types of this phenomenon, associated with a nocturnal low-level jet (LLJ) and the passage of a front, respectively. In both cases, the nocturnal increase in ozone concentration was accompanied by a significant increase in the standard deviation of the vertical wind speed σ w across the lower stable boundary layer, indicating enhanced vertical mixing. During the LLJ case, ozone maxima were observed at 33% of the stations of the Environmental Protection Office network at approximately the same time. In the case of the front, the time of the ozone concentration rise could be allocated to the time of the passage of the front, moving from northwest to southeast across the study area. For the first time, the measurements presented here document turbulent mixing induced by shear forces in the whole layer between the core of the LLJ and the ground surface during secondary nocturnal ozone maxima.

Observations of convective and dynamical instabilities in tropopause folds and their contribution to stratosphere‐troposphere exchange

With aircraft‐mounted in situ and remote sensing instruments for dynamical, thermal, and chemical measurements we studied two cases of tropopause folding. In both folds we found Kelvin‐Helmholtz billows with horizontal wavelength of ∼900 m and thickness of ∼120 m. In one case the instability was effectively mixing the bottomside of the fold, leading to the transfer of stratospheric air into the troposphere. Also, we discovered in both cases small‐scale secondary ozone maxima shortly after the aircraft ascended past the topside of the fold that corresponded to regions of convective instability. We interpreted this phenomenon as convectively breaking gravity waves. Therefore we posit that convectively breaking gravity waves acting on tropopause folds must be added to the list of important irreversible mixing mechanisms leading to stratosphere‐troposphere exchange.

High-Resolution Lidar Measurements of Stratosphere–Troposphere Exchange

The tropospheric ozone lidar at the Fraunhofer-Institut für Atmosphärische Umweltforschung has been upgraded for measurements in an extended range with high accuracy (mostly 5%), high vertical resolution (50–500 m within the troposphere), and under automatic control. The operating range is now from 0.15 to about 16 km, the upper limit varying by ±2 km depending on the average ozone density in the troposphere. Routine measurements were resumed in January 1996. The current research efforts are concentrated mainly on an optimum observational coverage of tropopause folds and on evaluating more details of stratosphere–troposphere exchange. Ozone tongues associated with tropopause folds may be as narrow as 300 m. Their detection and correct analysis greatly benefits from the improved instrumental performance of the lidar. From the data acquired during the first 23 months of this project it is concluded that roughly 98% of the stratospheric air intrusions reach the Zugspitze summit station (2962 m above sea level). Many of the examples of stratospheric intrusions show pronounced secondary ozone maxima in the upper troposphere starting a few hours to one day after the subsidence of a tropopause fold and have been tracked with the lidar under automatic control for up to four consecutive days. More work is needed to understand and to analyze the contribution of these ozone structures to the overall downward flux during such an episode.

A case study of abnormal increase of Ozone over Ahmedabad (23°N) during February 1962

Changes in the total ozone amount and in the vertical distribution of ozone over Ahmedabad, associated with passing western disturbances during February 1962 are considered in this study. Remarkably high values of ozone were recorded in this period. A significant secondary ozone maximum was seen in a layer centred at 150 mb on 17 February when a distinct break in the tropopause was located to the north of Ahmedabad.