ISSN:0148-0227    

DOI:10.1029/96JD00538

年代:1996

数据来源: WILEY

摘要:

Aerosol surface area distributions inferred from satelliteborne 1‐μm extinction measurements are used as input to a two‐dimensional model to study the effects of heterogeneous chemistry upon anthropogenic ozone depletion at northern midlatitudes. It is shown that short‐term (interannual) and longer‐term (decadal) changes in aerosols very likely played a substantial role along with trends in anthropogenic chlorine and bromine in both triggering the ozone losses observed at northern midlatitudes in the early 1980s and increasing the averaged long‐term ozone depletions of the past decade or so. The use of observed aerosol distributions enhances the calculated ozone depletion due to halogen chemistry below about 25 km over much of the past decade, including many periods not generally thought to be affected by volcanic activity. Direct observations (especially the relationships of NOx/NOyand ClO/Clyratios to aerosol content) confirm the key aspects of the model chemistry that is responsible for this behavior and demonstrate that aerosol changes alone are not a mechanism for ozone losses in the absence of anthropogenic halogen inputs to the stratosphere. It is also suggested that aerosol‐induced ozone changes could be confused with 11‐year solar cycle effects in some statistical analyses, resulting in an overestimate of the trends ascribed to solar activity. While the timing of the observed ozone changes over about the past 15 years is in remarkable agreement with the model predictions that explicitly include observed aerosol changes, their magnitude is about 50% larger than calculated. Possible chemical and dynamical causes of this discrepancy are explored. On the basis of this work, it is shown that the timing and magnitude of future ozone losses at midlatitudes in the northern hemisphere are likely to be strongly dependent upon volcanic aerosol variations as well as on future chlorine and b

ISSN:0148-0227    

DOI:10.1029/95JD03353

年代:1996

数据来源: WILEY

摘要:

The odd nitrogen source strengths associated with solar proton events (SPEs), galactic cosmic rays (GCRs), and the oxidation of nitrous oxide in the Earth's middle atmosphere from 1974 through 1993 have been compared globally, at middle and lower latitudes (50°) with a two‐dimensional photochemical transport model. As discovered previously, the oxidation of nitrous oxide dominates the global odd nitrogen source, while GCRs and SPEs are significant at polar latitudes. The horizontal transport of odd nitrogen, produced by the oxidation of nitrous oxide at latitudes<50°, was found to be the dominant source of odd nitrogen in the polar regions, with GCRs contributing substantially during the entire solar cycle. The source of odd nitrogen from SPEs was more sporadic; however, contributions during several years (mostly near solar maximum) were significant in the polar middle atmosp

ISSN:0148-0227    

DOI:10.1029/95JD03386

年代:1996

数据来源: WILEY

摘要:

The sunset/sunrise NOxratios measured in 1994 by the Halogen Occultation Experiment (HALOE) onboard the Upper Atmosphere Research Satellite (UARS) peak at up to 2.8 in the tropics around 30 km and decrease to 1 at the stratopause. These ratios are interpreted by using a fully diurnal one‐dimensional model, which considers gas phase reactive nitrogen chemistry, and a two‐dimensional model, which includes a more complete set of chemical reactions. The diurnal cycle of nighttime N2O5formation followed by daytime photolysis entirely accounts for the observed ratios above about 35 km. In the lower to middle stratosphere, additional reactions involving ClONO2and HNO3also appear to contribute to the observed diurnal variations in NOx. The limitations of a simple function of ozone, temperature, and length of night, which estimates diurnal variations in NOxbased on gas phase reactive nitrogen chemistry, are tested through comparison to one‐dimensional model results. The function approximates the one‐dimensional model sunset/sunrise NOxratios well in the lower stratosphere but overestimates them by up to 10% in the upper stratosphere above about 35 km, corresponding to a large overestimate of N2O5formation. The function is extended to estimate sunrise N2O5in the middle strat

ISSN:0148-0227    

DOI:10.1029/96JD00058

年代:1996

数据来源: WILEY

摘要:

The water vapor budget of the stratosphere is diagnosed from correlation studies of the UARS Halogen Occultation Experiment sunset measurements of CH4and H2O in the middle and upper stratosphere, where the correlations are most significant and highly negative. Analyses were conducted for the years 1992–1994 using the methods of (1) linear regression and (2) deterministic differences (or variances of the data). It is assumed that there is conservation of total hydrogen according to a methane oxidation chemical mechanism. Results consist of the zonal mean seasonal distributions of the chemical yield of H2O molecules from each molecule of CH4(or the β profile) and an estimate of the annual average value of H2O that enters the stratosphere from below (or [H2O]e), presumably at the tropical tropopause. Average seasonal β values range from 1.6 to 2.4, and their zonal mean patterns are in good agreement with the theoretical model distribution of LeTexier et al., especially for the upper stratosphere. The range for annual average [H2O]eis 2.9 to 3.4 parts per million by volume (ppmv). When adjusted upward by 10% due to known negative biases of about 5% in both the midstratospheric CH4and the H2O data, [H2O]ebecomes 3.2 to 3.7 ppmv and is more consistent with averages of in situ measurements of water vapor at low latitudes of the lower stratosphere. We also find coherent patterns in the seasonal estimates of zonal average water vapor yield that are related to (1) the downward descent of air at winter polar latitudes, (2) the presence of dehydrated air at high latitudes of the southern hemisphere lower stratosphere, and (3) the ascent and relative isolation of the annual (January) minimum in tropical water va

ISSN:0148-0227    

DOI:10.1029/95JD03858

年代:1996

数据来源: WILEY

摘要:

The basic stratospheric chemical and radiative processes which could be modified by volcanic injections to the stratosphere are reviewed. Observed effects after two major volcanic eruptions (El Chichón and Mount Pinatubo) are reported. Measurements of SO2, NO, NO2, HNO3, HCl, and O3clearly show the impact of volcanic injections to the stratosphere. Large amounts of SO2(up to 20 Mt) are observed to be injected by energetic volcanoes. Gaseous SO2is converted into sulfate aerosols within about 30 days. Reactive nitrogen (NO and NO2) are reduced by up to 50% of their column amounts in midlatitudes. Some observations have shown HNO3amounts to be increased where NO2is decreased; other observations have not shown an HNO3increase. Heterogeneous reactions on the surfaces of sulfate aerosol particles are implicated in the conversion of NO and NO2into HNO3. The direct injection of HCl by volcanic eruptions may increase the local column by up to 40%. Satellite observations have revealed local ozone decreases in the range of 5 to 10% of the column following El Chichón and Mount Pinatubo eruption

ISSN:0148-0227    

DOI:10.1029/95JD03763

年代:1996

数据来源: WILEY

摘要:

A quasi‐continuous record of ozone profiles throughout the stratosphere over the South Pole has been obtained over an 11‐month cycle, from February 1993 to January 1994. This record includes the first winter measurements of ozone profiles in the altitude region above ∼30 km. Observations were made approximately every 3 days, using a high‐sensitivity millimeter wave spectrometer to quantitatively measure the pressure‐broadened ozone rotational emission line at 276.923 GHz. Vertical mixing ratio profiles have been derived from pressure‐broadened lineshapes by a deconvolution technique. A number of interesting features are present. We find a persistent double‐peaked structure in the mixing ratio profiles, lasting through most of the winter period until the remains of the lower peak are destroyed by spring “ozone hole” chemistry. A new low‐altitude peak is reformed in December as the vortex breaks up. With the aid of circumpolar UARS/MLS ozone maps, we interpret the lower peak as due to transport from ozone‐rich regions near the edge of the continent, while the profile from ∼30 km upward, composing the “trough” region and upper peak, appears to be the result of normal polar summer photochemistry. This double‐peaked structure then becomes “fossilized” within the strong, isolated, fall‐winter vortex. The mixing ratio of the upper peak increases after polar sunset, which we interpret as due to poleward mixing causing an erasure of the negative poleward gradient maintained by photochemistry before sunset. Mixing ratio isopleths show a relatively steady downward trend for a 3‐month period after the winter vortex pattern is established, preceded by rapid variations in ozone mixing ratios over the 20‐ to 40‐km range. Downward transport rates derived from isopleth slopes in the upper stratosphere are significantly smaller than vertical transport derived from theoretical studies, and we propose an explanation for this discrepancy based on ozone flow from the mesosphere. Descent rates determined from ozone isopleths in the midstratosphere (25 to 35 km) are shown to be in good agreement with recent model estimates of downward transport in the winter vortex, and with the mid to lower stratospheric descent rate inferred from our own South Pole measurements of N2O. Total column measurements are in generally good agreement with those derived from a Dobson photospectrometer at the pole and from local ozonesonde measurements. All three indicate there was no significant increase in total ozone over the pole during the winter of 1993. The onset of the spring ozone hole over the pole was evident by mid‐ to late‐August, well before local stratospheric sunrise on September 11, indicating relatively rapid poleward transport of ozone‐depleted air from

ISSN:0148-0227    

DOI:10.1029/95JD03652

年代:1996

数据来源: WILEY

摘要:

The uptake of peroxynitric acid (PNA), HO2NO2or HNO4, on solid H2O ice at 193 K (−80°C) was studied using a fast flow‐mass spectrometric technique. An uptake coefficient of 0.15 ± 0.10 was measured, where the quoted uncertainty denotes 2 standard deviations. The uptake process did not result in the production of gas phase products. The composition of the condensed phase was investigated using programmed heating (3 K min−1) of the substrate coupled with mass spectrometric detection of desorbed species. Significant quantities of HNO4and HNO3desorbed from the substrates at temperatures above 225 K and 246 K, respectively. The desorbed HNO3, which was less than 9% of the desorbed HNO4and remained unchanged upon incubation of the substrate, was likely due to impurities in the HNO4samples rather than reaction of HNO4on the substrate. The onset temperatures for HNO4desorption increased with increasing H2O to HNO4ratios, indicating that HNO4, like HNO3, tends to be hydrated in the presence of water. These observations suggest possible mechanisms for removal of HNO4or repartitioning of total odd nitrogen species in the Earth's upper troposphere and strat

ISSN:0148-0227    

DOI:10.1029/96JD00065

年代:1996

数据来源: WILEY

摘要:

The absorption coefficients of the Q branch of the ν4band of ClONO2at 780 cm−1have been measured over a sample pressure range of 0.1 to 0.4 torr using a tuneable diode laser spectrometer. The peak absorption coefficients derived from these measurements are 1.98(42) × 10−18cm2mol−1at 296K, and 2.98(47)× 10−18cm2mol−1at 210K. These are in good agreement with those determined previously by Fourier transform spectroscopy once corrections for the resolution of the instruments are made. Band contour analysis of the ν4+ ν6− ν6and ν4+ 2ν9− 2ν9bands of35ClONO2has been carried out and the results incorporated in the fitting of the observed spectrum. At 213K the integrated intensity of the theoretical spectrum calculated for the range of identified bands is 6.4 × 10−18cm−1mol−1. The derived integrated intensity of this whole band system is 8.6 × 10−18cm−1mol−1, assuming all transition moments of the contributing bands are identical. For the 296K spectrum of the ν4system a value of 3.9 × 10−18cm−1mol−1is obtained, with a value of 8.4 × 10−18cm−1mol−1if all populated states are included. The differences between the integrated intensities of the theoretical spectrum and of the band system are associated with the “continuum” contributed by the large number of weak bands associated with thermally populated states. The values obtained for the band systems may be compared with those derived byBallard et al.[1988] over the range 750 to 830 cm−1for the entire ν3/ν4system, and byDavidson et al.[1987] over the range 750 to 791 cm−1. These were 2.09 × 10−17cm−1mol−1at 213K and 3.04 × 10−17cm−1mol−1at 296K for the entire ν

ISSN:0148-0227    

DOI:10.1029/95JD02927

年代:1996

数据来源: WILEY

摘要:

Tracer transport in the lower stratosphere is investigated using an off‐line semi‐Lagrangian transport model and winds from a mechanistic three dimensional middle atmosphere model, interpolated to the 650 K isentropic surface, over a winter season. By comparing two simulations, the effect of the quasi‐biennial oscillation's (QBO's) easterly or westerly wind phases on low‐latitude transport is examined, especially regarding the formation of an apparent subtropical transport barrier at the equatorward edge of the surf zone. The tracer field is diffused less than potential vorticity (PV) and shows sharper gradients and finer structures developing over the winter. In both QBO phases the winter extratropical surf zone is bounded by large tracer gradients equatorward of about 15° latitude. The inability of quasi‐stationary Rossby waves to propagate into QBO easterlies leads to a much sharper edge forming between the rapidly stirred extratropical surf zone and the relatively unstirred tropics during the easterly QBO phase than occurs during the westerly QBO phase. In the westerly phase some Rossby wave activity can propagate across the equatorial westerlies and break on reaching the summer hemisphere easterly winds, causing mixing there. Simulations using a tracer initially confined to the tropics show that more tropical air is mixed out to the winter extratropics by Rossby wave stirring when the QBO phase is easterly, despite the sharper band of stronger tracer (or PV) gradient which separates the tropics and the winter extratropics in this phase. While air was mixed out of the tropics in both QBO phase simulations, neither QBO phase simulation showed extratropical air being irreversibly mixed into the tropics. These results are related to observations of the tropical reservoir of stratospheric aerosols, especially the dynamics and transport of its winter hemispher

ISSN:0148-0227    

DOI:10.1029/96JD00001

年代:1996

数据来源: WILEY