摘要:

Carbon‐dioxide releases associated with a mid‐Cretaceous super plume and the emplacement of the Ontong‐Java Plateau have been suggested as a principal cause of the mid‐Cretaceous global warming. We developed a carbonate‐silicate cycle model to quantify the possible climatic effects of these CO2releases, utilizing four different formulations for the rate of silicate‐rock weathering as a function of atmospheric CO2. We find that CO2emissions resulting from super‐plume tectonics could have produced atmospheric CO2levels from 3.7 to 14.7 times the modern pre‐industrial value of 285 ppm. Based on the temperature sensitivity to CO2increases used in the weathering‐rate formulations, this would cause a global warming of from 2.8 to 7.7°C over today's global mean temperature. Altered continental positions and higher sea level may have been contributed about 4.8°C to mid‐Cretaceous warming. Thus, the combined effects of paleogeographic changes and super‐plume related CO2emissions could be in the range of 7.6 to 12.5°C, within the 6 to 14°C range previously estimated for mid‐Cretaceous warming. CO2releases from oceanic plateaus alone are unlikely to have been directly responsible for more than 20% of the mid‐Cretaceou

ISSN:0094-8276    

DOI:10.1029/91GL01237

年代:1991

数据来源: WILEY

摘要:

The role of convergence feedback on the stability of a coupled ocean‐atmosphere system is studied using model III of Hirst (1986). It is shown that the unstable coupled mode found by Hirst is greatly modified by the convergence feedback. If the convergence feedback strength exceeds a critical value, several new unstable intraseasonal modes are also introduced. These modes have very weak dependence on the wave number. These results may explain the behaviour of some coupled models and to some extent provide a mechanism for the observed aperiodicity of the El‐Nino and Southern Oscillation (ENSO) eve

ISSN:0094-8276    

DOI:10.1029/91GL00968

年代:1991

数据来源: WILEY

摘要:

Both recent and some older field measurements reveal condensation nucleus concentrations which attain local maxima within clouds. Model calculations are presented which suggest that, if the enhanced actinic radiation flux in clouds is taken into account, homogeneous, bimolecular nucleation within clouds is a viable mechanism for production of such particles.

ISSN:0094-8276    

DOI:10.1029/91GL01239

年代:1991

数据来源: WILEY

摘要:

Fifteen experiments were conducted in an open burning system to determine the amounts of N2O produced from burning savanna grass (VenezuelanTrachypogon, AustralianSorghum intrans), straw, hay, oak, pine needles and litter of pine forest. Samples in stainless steel canisters were analyzed within one day after sampling in order to avoid artifact N2O formation during storage. Emissions of N2O were observed to be nearly coincident with the emissions' of CO2during the burning period for all the experiments. The amount of N2O produced was dependent on the nitrogen content of the biomass. About 0.7% of the fuel nitrogen was oxidized to N2O and most of the N2O was formed during the flaming stage. Using our experimental data and the amounts of different types of vegetation burned globally per year, we estimate that about 2.7 × 1011g of N2O‐N are produced per year from burning biomass, contributing only 2% to the global source of N

ISSN:0094-8276    

DOI:10.1029/90GL02583

年代:1991

数据来源: WILEY

摘要:

We have made the first unequivocal measurement of hydrogen peroxide in the stratosphere, a concentration profile obtained from a balloon platform using Fourier transform thermal emission spectroscopy in the far infrared. Measurements were made using the 112 cm−1RQ5branch of the rotational‐torsional spectrum, with some confirmation from the 94 cm−1RQ4branch. The atmospheric spectra were obtained from a balloon flight on September 26–27, 1989, launched from Fort Sumner, NM.The volume mixing ratio of H2O2is 1.6 × l0−10at 38.4 km, decreasing to 0.6 × l0−10at 23.8km, with uncertainties of about 16% (1σ). Our measurements are compared to a recent stratospheric mod

ISSN:0094-8276    

DOI:10.1029/91GL01224

年代:1991

数据来源: WILEY

摘要:

Heterogeneous chemistry producing active chlorine has been identified as crucial to Antarctic ozone depletion. Most attention has focussed on reactions on solid polar stratospheric cloud (PSC) particles, although there is still no satisfactory understanding of the microchemical incorporation of HCl in PSCs. The alternative mechanism involving sulphuric acid aerosol as the reaction surface has been considered at lower latitudes, but its role in the special conditions of the polar stratosphere has been largely ignored. Recent data from the Antarctic stratosphere have suggested that HCl is present in sulphuric acid aerosol that remains liquid even at the lowest stratospheric temperatures. The available laboratory data show that cold, relatively dilute, sulphuric acid is particularly able to take up HCl that is available for reaction provided the aerosol remains liquid. Fast heterogeneous reaction rates compared to those at mid‐latitudes will produce active chlorine rapidly. Since the aerosol is present with significant surface area throughout the lower stratosphere, it should be very effective for heterogeneous reaction once temperatures drop. These surfaces, rather than PSCs, could host the initial conversion of Cl to its active form over the Antarcti

ISSN:0094-8276    

DOI:10.1029/91GL01158

年代:1991

数据来源: WILEY

摘要:

Vertical profiles of stratospheric water vapor and ozone were measured together at McMurdo and South Pole Stations in Antarctica, and at Kiruna, Sweden, on several occasions during the austral spring of 1990 and the boreal winter of 1991. The Antarctic data indicated that major dehydration had occurred on a continental scale over the winter stratospheric cloud formation period leaving only 2 to 3ppmv water vapor between 11 and 19km. Measurements before and after movement of the boundary of the polar vortex across McMurdo detected increases in both water vapor and ozone in the 17 to 20km region. This injected layer was still observed at South Pole Station a month later suggesting continental proportions. In early November, with the vortex still intact, South Pole measurements indicated a substantial degree of inhomogeneity in both water vapor and ozone in the lower stratosphere. In comparison, stratospheric water vapor measurements in the Arctic gave values of 4 to 5 ppmv indicating the absence of the gross stratospheric dehydration effects obvious in the Antarctic, and they did not reveal significant structure except on one occasion with very cold temperatures (−90°C) at 25km and nacreous cloud displa

ISSN:0094-8276    

DOI:10.1029/91GL01301

年代:1991

数据来源: WILEY

摘要:

The Total Ozone Mapping Spectrometer (TOMS) on the Nimbus 7 satellite has been measuring the total column amount of ozone over the globe for more than 11 years. Recent improvements in the data analysis have led to a technique for determining and removing drift in the calibration such that the data at the end of the record are precise to ±1.3% (2σ) relative to the data at the beginning of the record. A statistical model, including terms for seasonal variation, linear trend, quasi‐biennial oscillation, solar cycle and second‐order autoregressive noise has been fit to the TOMS time series of total ozone data. The linear trend obtained when this statistical model is fit to the TOMS data averaged between 65N and 65S latitudes is −0.26±0.14%/year or −3% over the 11.6 year time period from November, 1978 through May, 1990. The trend is near zero (0.0002±0.2 %/year) at the equator and increases towards both poles. At 50N the annually averaged trend is −0.5±.21%/year. The 50N trend over the 11.6 year time period shows a strong seasonal variation from more than −0.8%/year in winter and early spring (February and March) to about −0.2%/year in summer

ISSN:0094-8276    

DOI:10.1029/91GL01302

年代:1991

数据来源: WILEY

摘要:

Intense solar activity during the period August–December 1989 gave rise to several major energetic‐particle events, which were accompanied by greatly enhanced ionization rates and NOyproduction in the polar regions of both hemispheres. A two‐dimensional model of the chemistry and dynamics of the middle atmosphere has been used to calculate the production and subsequent fate of the NOyand its effect on ozone concentrations and temperatures. In the sunlit southern polar cap, NO increases as large as a factor of 20 are estimated near 60 km altitude, with column density enhancements of 55%. Corresponding peak ozone depletions of about 20% are calculated near 40km in late October 1989, with predicted temperature decreases of about 3–3.5K. Effects in the northern polar regions are considerably smaller, due to the lack of sunlight during the peak phase of the

ISSN:0094-8276    

DOI:10.1029/91GL01049

年代:1991

数据来源: WILEY

摘要:

A case study was conducted to investigate the mechanism of how the solar cycle and the equatorial quasi‐biennial oscillation (QBO) influence the stratospheric circulation during the Northern‐Hemisphere winter.It was found that the solar and QBO influences on the stratospheric jet exist rather independently in the upper stratosphere during December. The mean‐zonal wind anomalies produced in early winter persist by deformation until late winter through wave‐mean flow interactions with planetary waves. The modulation effect of the solar influence by the QBO [Labitzke, 1987] takes place during this

ISSN:0094-8276    

DOI:10.1029/90GL02298

年代:1991

数据来源: WILEY