Solar proton event: influence on stratospheric ozone

Large-scale reductions in the ozone content of the middle and upper stratosphere over the polar cap regions were associated with the major solar proton event of 4 August 1972. This reduction, which was determined from measurements with the backscattered ultraviolet experiment on the Nimbus 4 satellite, is interpreted as being due to the catalytic destruction of ozone by odd-nitrogen compounds (NO(x)) produced by the event.     

Solar Absorption in a Stratosphere Perturbed by NOx Injection

The changes in the solar absorption by nitrogen dioxide and ozone induced by the injection of NO(x) (oxides of nitrogen) in the stratosphere are complementary, even though the nitrogen dioxide absorption is only a small fraction of the ozone absorption for an unperturbed stratosphere. The factors causing this effect are described, and an analysis is made of the perturbed solar radiation budget.     

Eleven-year variation in polar ozone and stratospheric-ion chemistry

A mechanism for producing an 11-year oscillation in ozone over the polar caps is the modulation of galactic cosmic rays by the solar wind. This mechanism has been shown to give the observed phase in ozone oscillations and the correct qualitative dependence on latitude. However, the production of nitrogen atoms from cosmic-ray collisions seems inadequate to account for the ozone amplitude. Negative ions are also produced as a result of cosmic-ray ionization, and negative-ion chemistry may be of importance in the stratosphere. Specifically, NO(x)(-) may go through a catalytic cycle in much the same fashion as NO(x), but with the important distinction that it does not depend on oxygen atoms to complete the cycle. Estimates of the relevant rates of reaction suggest that negative ions may be especially important over the winter polar cap.     

Energetic radiation belt electron precipitation: a natural depletion mechanism for stratospheric ozone

During geomagnetically disturbed periods the precipitational loss of energetic electrons from the outer radiation belt of the earth can readily provide the major ionization source for the mesosphere and upper stratosphere. One particularly intense manifestation of this interaction between the radiation belts and the lower atmosphere is the relativistic electron precipitation (REP) event which occurs at subauroral latitudes during magnetospheric substorm activity. At relativistic energies the precipitating electrons produce copious fluxes of energetic bremsstrahlung x-rays, the major portion of which penetrate deep into the stratosphere before undergoing excitation and ionization collisions with the neutral atmosphere. If such REP events occur more than a few percent of the time, they can, on an annual basis, provide a local source of upper stratospheric nitric oxide molecules (via the dissociation of molecular nitrogen) comparable to that from either galactic cosmic rays or energetic solar proton events. Since nitric oxide plays a major role in the removal of stratospheric ozone, it appears that the influence of REP events must also be considered in future photochemical modeling of the terrestrial ozone layer.     

A Reevaluation of the Ozone Budget with HALOE UARS Data: No Evidence for the Ozone Deficit

Recently, additional ozone production mechanisms have been proposed to resolve the ozone deficit problem, which arises from greater ozone destruction than production in several photochemical models of the upper stratosphere and lower mesosphere. A detailed ozone model budget analysis was performed with simultaneous observations of O(3), HCl, H(2)O, CH(4), NO, and NO(2) from the Halogen Occultation Experiment (HALOE) on the Upper Atmosphere Research Satellite (UARS) under conditions with the strongest photochemical control of ozone. The results indicate that an ozone deficit may not exist. On the contrary, the use of currently recommended photochemical parameters leads to insufficient ozone destruction in the model.     

Solar cycle variability, ozone, and climate

Results from a global climate model including an interactive parameterization of stratospheric chemistry show how upper stratospheric ozone changes may amplify observed, 11-year solar cycle irradiance changes to affect climate. In the model, circulation changes initially induced in the stratosphere subsequently penetrate into the troposphere, demonstrating the importance of the dynamical coupling between the stratosphere and troposphere. The model reproduces many observed 11-year oscillations, including the relatively long record of geopotential height variations; hence, it implies that these oscillations are likely driven, at least in part, by solar variability.     

Stratospheric ozone with added water vapor: influence of high-altitude aircraft

Simple, steady-state models for ozone photochemistry, radiative heat balance, and eddy-diffusive mass transport can be combined to estimate water-induced changes in the stratospheric ozone concentrations and temperatures, the integrated ozone column, the solar power transmitted to the earth's surface, and the surface temperature. These changes have been computed parametrically for mixing fractions of water vapor between 3 x 10(-6) and 6.5 x 10(-6). With added water from the exhausts of projected fleets of stratospheric aircraft, the ozone column may diminish by 3.8 percent, the transmitted solar power increase by 0.07 percent, and the surface temperature rise by 0.04 degrees K in the Northern Hemisphere. Due to a cancellation of terms, temperatures in the lower stratosphere remain essentially unchanged. These results are sensitive to the form of the water profile and emphasize the potential role of convective transients near 30 kilometers.     

Role of deep cloud convection in the ozone budget of the troposphere

Convective updrafts in thunderstorms prolong the lifetime of ozone (O(3)) and its anthropogenic precursor NOx [nitric oxide (NO) + nitrogen dioxide (NO(2))] by carrying these gases rapidly upward from the boundary layer into a regime where the O(3) production efficiency is higher, chemical destruction is slower, and surface deposition is absent. On the other hand, the upper troposphere is relatively rich in O(3) and NOx from natural sources such as downward transport from the stratosphere and lightning; convective overturning conveys the O(3) and NOx toward the Earth's surface where these components are more efficiently removed from the atmosphere. Simulations with a three-dimensional global model suggest that the net result of these counteractive processes is a 20 percent overall reduction in total tropospheric O(3). However, the net atmospheric oxidation efficiency is enhanced by 10 to 20 percent.     

Mount pinatubo aerosols, chlorofluorocarbons, and ozone depletion

The injection into the stratosphere of large quantities of sulfur during the June 1991 eruption of Mount Pinatubo (Philippines) and the subsequent formation of sulfate aerosol particles have generated a number of perturbations in the atmosphere with potential effects on the Earth's climate. Changes in the solar and infrared radiation budget caused by the eruption should produce a cooling of the troposphere and a warming of the lower stratosphere. These changes could affect atmospheric circulation. In addition, heterogeneous chemical reactions on the surface of sulfate aerosol particles render the ozone molecules more vulnerable to atmospheric chlorine and hence to man-made chlorofluorocarbons.     

The Impact of Solar Variability on Climate

A general circulation model that simulated changes in solar irradiance and stratospheric ozone was used to investigate the response of the atmosphere to the 11-year solar activity cycle. At solar maximum, a warming of the summer stratosphere was found to strengthen easterly winds, which penetrated into the equatorial upper troposphere, causing poleward shifts in the positions of the subtropical westerly jets, broadening of the tropical Hadley circulations, and poleward shifts of the storm tracks. These effects are similar to, although generally smaller in magnitude than, those observed in nature. A simulation in which only solar irradiance was changed showed a much weaker response.     

Tunguska meteor fall of 1908: effects on stratospheric ozone

In 1908, when the giant Tunguska meteor disintegrated in the earth's atmosphere over Siberia, it may have generated as much as 30 million metric tons of nitric oxide (NO) in the stratosphere and mesosphere. The photochemical aftereffects of the event have been simulated using a comprehensive model of atmospheric trace composition. Calculations indicate that up to 45 percent of the ozone in the Northern Hemisphere may have been depleted by Tunguska's nitric oxide cloud early in 1909 and large ozone reductions may have persisted until 1912. Measurements of atmospheric transparentiy by the Smithsonian Astrophysical Observatory for the years 1909 to 1911 show evidence of a steady ozone recovery from unusually low levels in early 1909, implying a total ozone deficit of 30 +/- 15 percent. The coincidence in time between the observed ozone recovery and the Tunguska meteor fall indicates that the event may provide a test of current ozone depletion theories.     

近几年拉萨上空大气臭氧变化特征

利用Brewer分光光谱仪观测资料分析青藏高原拉萨站近几年大气臭氧的变化特征,结果表明,拉萨上空臭氧主要分布在15～35km,反演结果的峰值出现在21～25 km。对比拉萨四季臭氧垂直分布发现,它们在平流层中上层的差异不大,且在36 km以上的分布大致相同,差异主要表现在从地面到21 km,冬春季的臭氧数密度大于夏秋季,近4年来拉萨的年平均臭氧总量的变化不大,臭氧总量的极值出现在冬春季节,臭氧总量的月平均值在8和9月较低,2008年6～9月臭氧低值的持续时间是近几年中最长的,达23 d。     

近几年拉萨上空大气臭氧变化特征（英文）

利用Brewer分光光谱仪观测资料分析青藏高原拉萨站近几年大气臭氧的变化特征,结果表明,拉萨上空臭氧主要分布在15~35 km,反演结果的峰值出现在21~25 km。对比拉萨四季臭氧垂直分布发现,它们在平流层中上层的差异不大,且在36 km以上的分布大致相同,差异主要表现在从地面到21 km,冬春季的臭氧数密度大于夏秋季,近4年来拉萨的年平均臭氧总量的变化不大,臭氧总量的极值出现在冬春季节,臭氧总量的月平均值在8和9月较低,2008年6~9月臭氧低值的持续时间是近几年中最长的,达23 d。     

The potential for ozone depletion in the arctic polar stratosphere

The nature of the Arctic polar stratosphere is observed to be similar in many respects to that of the Antarctic polar stratosphere, where an ozone hole has been identified. Most of the available chlorine (HCl and ClONO(2)) was converted by reactions on polar stratospheric clouds to reactive ClO and Cl(2)O(2) throughout the Arctic polar vortex before midwinter. Reactive nitrogen was converted to HNO(3), and some, with spatial inhomogeneity, fell out of the stratosphere. These chemical changes ensured characteristic ozone losses of 10 to 15% at altitudes inside the polar vortex where polar stratospheric clouds had occurred. These local losses can translate into 5 to 8% losses in the vertical column abundance of ozone. As the amount of stratospheric chlorine inevitably increases by 50% over the next two decades, ozone losses recognizable as an ozone hole may well appear.     

Changes in stratospheric ozone

The ozone layer in the upper atmosphere is a natural feature of the earth's environment. It performs several important functions, including shielding the earth from damaging solar ultraviolet radiation. Far from being static, ozone concentrations rise and fall under the forces of photochemical production, catalytic chemical destruction, and fluid dynamical transport. Human activities are projected to deplete substantially stratospheric ozone through anthropogenic increases in the global concentrations of key atmospheric chemicals. Human-induced perturbations may be occurring already.     

Removal of Stratospheric O3 by Radicals: In Situ Measurements of OH, HO2, NO, NO2, ClO, and BrO

Simultaneous in situ measurements of the concentrations of OH, HO(2), ClO, BrO, NO, and NO(2) demonstrate the predominance of odd-hydrogen and halogen free-radical catalysis in determining the rate of removal of ozone in the lower stratosphere during May 1993. A single catalytic cycle, in which the rate-limiting step is the reaction of HO(2) with ozone, accounted for nearly one-half of the total O(3) removal in this region of the atmosphere. Halogen-radical chemistry was responsible for approximately one-third of the photochemical removal of O(3); reactions involving BrO account for one-half of this loss. Catalytic destruction by NO(2), which for two decades was considered to be the predominant loss process, accounted for less than 20 percent of the O(3) removal. The measurements demonstrate quantitatively the coupling that exists between the radical families. The concentrations of HO(2) and ClO are inversely correlated with those of NO and NO(2). The direct determination of the relative importance of the catalytic loss processes, combined with a demonstration of the reactions linking the hydrogen, halogen, and nitrogen radical concentrations, shows that in the air sampled the rate of O(3) removal was inversely correlated with total NOx, loading.     

Observations of ozone formation in power plant plumes and implications for ozone control strategies

Data taken in aircraft transects of emissions plumes from rural U.S. coal-fired power plants were used to confirm and quantify the nonlinear dependence of tropospheric ozone formation on plume NO(x) (NO plus NO(2)) concentration, which is determined by plant NO(x) emission rate and atmospheric dispersion. The ambient availability of reactive volatile organic compounds, principally biogenic isoprene, was also found to modulate ozone production rate and yield in these rural plumes. Differences of a factor of 2 or greater in plume ozone formation rates and yields as a function of NO(x) and volatile organic compound concentrations were consistently observed. These large differences suggest that consideration of power plant NO(x) emission rates and geographic locations in current and future U.S. ozone control strategies could substantially enhance the efficacy of NO(x) reductions from these sources.     

Anthropogenic and natural influences in the evolution of lower stratospheric cooling

Observations reveal that the substantial cooling of the global lower stratosphere over 1979-2003 occurred in two pronounced steplike transitions. These arose in the aftermath of two major volcanic eruptions, with each cooling transition being followed by a period of relatively steady temperatures. Climate model simulations indicate that the space-time structure of the observed cooling is largely attributable to the combined effect of changes in both anthropogenic factors (ozone depletion and increases in well-mixed greenhouse gases) and natural factors (solar irradiance variation and volcanic aerosols). The anthropogenic factors drove the overall cooling during the period, and the natural ones modulated the evolution of the cooling.     

The sensitivity of polar ozone depletion to proposed geoengineering schemes

The large burden of sulfate aerosols injected into the stratosphere by the eruption of Mount Pinatubo in 1991 cooled Earth and enhanced the destruction of polar ozone in the subsequent few years. The continuous injection of sulfur into the stratosphere has been suggested as a "geoengineering" scheme to counteract global warming. We use an empirical relationship between ozone depletion and chlorine activation to estimate how this approach might influence polar ozone. An injection of sulfur large enough to compensate for surface warming caused by the doubling of atmospheric CO2 would strongly increase the extent of Arctic ozone depletion during the present century for cold winters and would cause a considerable delay, between 30 and 70 years, in the expected recovery of the Antarctic ozone hole.     

UV dosage levels in summer: increased risk of ozone loss from convectively injected water vapor

The observed presence of water vapor convectively injected deep into the stratosphere over the United States can fundamentally change the catalytic chlorine/bromine free-radical chemistry of the lower stratosphere by shifting total available inorganic chlorine into the catalytically active free-radical form, ClO. This chemical shift markedly affects total ozone loss rates and makes the catalytic system extraordinarily sensitive to convective injection into the mid-latitude lower stratosphere in summer. Were the intensity and frequency of convective injection to increase as a result of climate forcing by the continued addition of CO(2) and CH(4) to the atmosphere, increased risk of ozone loss and associated increases in ultraviolet dosage would follow.