摘要:

A simple slab ocean of 50 m depth, which allows for seasonal ocean heat storage but no ocean heat transport, is coupled to a global spectral general circulation model with global domain, realistic geography, and computed clouds. Globally averaged, the annual mean surface air temperature increase computed over the last 3 years of an integration with a full annual cycle for 2×CO2compared to the control for ×CO2is 3.5°C. Zonal mean air temperature differences indicate stratospheric cooling and tropospheric warming as seen in Other CO2modeling studies. Greatest increases of surface air temperature in the 2×CO2case, compared to the control, occur near the sea ice margins. Retreat of sea ice in the 2×CO2case is associated with changes in the positions of the cloud maxima. Ice‐free areas of ocean in the 2×CO2case, which are ice covered in the 1×CO2case, store relatively more heat during the summer season. Warmer surface air temperatures then occur in areas that are much colder in the control case because of the lack of the insulating effect of the sea ice, especially in winter. Increases of zonal mean precipitation are evident at most latitudes as a result of increases of available moisture evaporated from the warmer oceans. In the tropics this is associated with a strengthening of the mean meridional circulation and with intensification of the upper level zonal‐component winds in the subtropics. Warming near the surface associated with the retreat of the ice line in the 2×CO2case slackens the meridional temperature gradient and results in weaker upper level zonal‐component winds in the mid‐latitudes. Three‐year seasonal means of soil moisture show decreases in tropical and subtropical continental areas and increases at high latitudes, but at mid‐latitudes the change depends on the season. An analysis of the statistical significance of the geographical distribution of 7‐year seasonal means of surface air temperature and soil moisture differences is given for the 2×CO2case compared to the control. Areas of significant differences correspond to similar regions of large differences seen in the 3‐year seasonal means. Certain regions experience summer drying seen in other studies, but zonal mean soil moisture differences show increases of soil moisture at mid and high latitudes of the northern hemisphere year‐round, with a relative minimum of increase in late summer. These differences are attributed to large increases of soil moisture in late spring that persist into summer and cause a positive feedback with precipitation and low clouds. This inhibits continental warming and limits summer drying seen in the zonal mean as a result of the doubling of CO2. A comparison of the present experiment with the previous swamp model experiments is consistent with other studies in that the extent of sea ice in the control case critically influences the climatic response to increased CO2such that more extensive sea ice is associated with a larger response. The seasonal cycle along with ocean heat storage in the mixed layer model are shown to be important in producing a more realistic simulation of the present climate than does the swamp experiment and, presumably, a more credible response to increased CO2. However, in the context of recent studies the overextensive sea ice in the present mixed layer model suggests that the inclusion of ocean heat transport from a fully computed ocean model and a resulting sea ice distribution closer to the observed would possibly produce less of a

ISSN:0148-0227    

DOI:10.1029/JD089iD06p09475

年代:1984

数据来源: WILEY

摘要:

A global circulation model has been used to explore observed relationships between cold sea surface temperature anomalies in the Australian region and drought over the Australian continent. The model employed a comprehensive physics package, was set up for fixed January conditions, and used climatological sea surface temperatures. Two experiments were performed: one involving a large cold sea surface temperature anomaly located north of Australia but extending well into the Pacific and Indian Oceans, together with a much smaller cold anomaly in the tropical Atlantic; the other added a warm anomaly in the tropical eastern Pacific to the previous anomalies. The overall results were very similar in the two experiments. Droughtlike conditions were produced over parts of Australia, southern Africa, South America, and North America. By relating variations in evaporation and precipitation rates to changes in the synoptic meridional velocity distribution, a reasonably coherent understanding of the model's responses to the anomalies was obtained. The dominant response was in the Australian region, with secondary responses being produced over southern Africa and South America. This might indicate some form of synchronous behavior over the continents of the southern hemisphere to such sea surface temperature anomalies. The tropical easterlies were enhanced by the SST anomalies, resulting in a single westerly duct remaining between the two hemispheres. Difference charts of the 200‐mbar height field for the anomaly and control experiments revealed a weak wave train that originated in the duct region and propagated to North America, where it apparently caused large changes in the synoptic conditions over North America. Overall the experiments help to establish a cause‐and‐effect relationship between cold sea surface temperature anomalies and drought in the adjacent Australian region together with a re‐inforcement of these effects when an El Nino type warm anomaly is located in the east Pacific. Nevertheless, the need is highlighted for much further research before the requirements for forecasting drought can be a

ISSN:0148-0227    

DOI:10.1029/JD089iD06p09504

年代:1984

数据来源: WILEY

摘要:

To evaluate the possible influence of natural background tropospheric aerosols upon the earth's present climate, we have incorporated aerosol radiation models for continental and maritime aerosols into the Lawrence Livermore National Laboratory statistical‐dynamical climate model. The model results suggest that background tropospheric aerosols produce 3°–4°C global surface cooling, with maximum cooling occurring at high latitudes, results which are essentially consistent with an energy balance climate model study by Coakley et al. (1983). To specifically delineate effects caused directly by the aerosols, as opposed to indirect effects resulting from aerosol‐induced climate change, a second climate perturbation was considered that consisted of reducing the solar constant so as to give exactly the same initial reduction in surface‐atmosphere solar absorption as for the inclusion of tropospheric aerosols. These separate climate perturbations produced nearly identical climate feedback effects, together with similar changes in atmospheric stability and hydrological cycle, despite the fact that the two perturbations have quite different latitudinal and vertical distributions. This finding is consistent with a general circulation model study by Manabe and Wetherald (1980) concerning perturbations of both atmospheric CO2and the solar constant. A related conclusion is that the model's climate response to tropospheric aerosols is insensitive to the manner in which the aerosols are vertically di

ISSN:0148-0227    

DOI:10.1029/JD089iD06p09521

年代:1984

数据来源: WILEY

摘要:

Time series data of atmospheric CO2concentrations are presented for three Canadian background stations: Ocean Weather Station P in the northeast Pacific Ocean, Sable Island off Nova Scotia, and Alert, Northwest Territories. The mean annual concentrations of CO2in dried samples of 338.73 parts per million by volume (ppmv) (1980) at Sable Island, 337.26 ppmv (1980) at Station P, and 340.30 ppmv (1980) and 341.71 ppmv (1981) at Alert appear consistent with the global pattern. From 1975 to 1981, the increase in CO2concentration averaged for these stations is 1.4 ppmv/yr. In 1975–1976 and in 1978, the annual growth rates of atmospheric CO2measurements decreased at all stations. Another dip in the growth rate of CO2concentrations was also observed in 1974–1975 at Station P. In general, the long‐term trends all show lower growth in the beginning, and more rapid growth at the end, of a typical 2‐year El Niño/Southern Oscillation event. The seasonal amplitude between winter and summer concentrations is about 14 ppmv at Station P and about 15 ppmv at the other stations. There is a phase shift of about 1 month in the onset of the decline to summer minimum between Sable Island (March–April) and the other stations (

ISSN:0148-0227    

DOI:10.1029/JD089iD06p09527

年代:1984

数据来源: WILEY

摘要:

We calculate the seasonal changes that are largely associated with the half‐yearly wave, auto‐correlation functions, and the mean planetary waves in the monthly mean sea level pressure from two data sources. One covers the period from 1951 to 1958 (from the South African Weather Bureau) and the other the period from 1972 to 1980 (from the Australian Bureau of Meteorology). Thirty years of data from stations over the southern hemisphere are used to assess the reliability of the differences between the two periods that the grid‐point data show. These differences are especially large over the Atlantic Ocean and the Pacific Ocean. The station data confirm the changes between the two periods and thus the observed differences in the mean waves, which are especially large for wave num

ISSN:0148-0227    

DOI:10.1029/JD089iD06p09541

年代:1984

数据来源: WILEY

摘要:

The mid‐latitude upper stratospheric ozone profiles obtained by the solar backscatter ultraviolet instrument on the Nimbus 7 satellite show a clear annual cycle both in the absolute ozone amounts between 0.98 and 15.6 mbar and in the magnitude of disturbances that reveal themselves as longitudinal structure. At the lowest pressures analyzed a winter maximum in ozone exists, but as one progresses downward in altitude a shift in the temporal phase of the annual cycle occurs in the vicinity of 3 to 4 mbar. Comparison of the observed behavior with the predictions of a one‐dimensional photochemical model shows a systematic tendency for calculated ozone amounts to be 20–27% below the data for pressures less than 7.8 mbar. The chemical model successfully predicts the change in phase of the annual cycle, although at a pressure greater than observed. Diagnosis of model results shows the observed shift to be closely coupled to the magnitude of the ozone column density near 3–4 mbar. The wavelength‐dependent attenuation of the solar radiation field by ozone alters the relative magnitude of the molecular oxygen and ozone dissociation rates, leading to a change in the temporal phase of the ann

ISSN:0148-0227    

DOI:10.1029/JD089iD06p09547

年代:1984

数据来源: WILEY

摘要:

Ozone mixing ratios at pressure levels near 2 mbar, derived from Nimbus 4 backscattered ultraviolet (BUV) profile data and averaged within 13 latitude zones between 65°N and 65°S, are studied for the period November 1970 to April 1972. In agreement with previous analyses the largest temporal variations are negatively correlated with changes in zonally averaged equivalent temperature measured simultaneously with the Nimbus 4 selective chopper radiometer. After approximately removing this component using a first‐order photochemical model, residual mixing ratios for latitudes ≲30° contain short‐term variations (periods ≲35 days; rms amplitude ∼1%) that are positively correlated with variations in the solar 10.7‐cm flux and in the 185–190 nm solar ultraviolet flux model of Lean et al. (1982). The correlation coefficients (R= 0.2–0.5;p>0.95) are larger for each latitude zone when computed versus the ultraviolet flux model than when computed versus the 10.7‐cm flux, suggesting that photochemical responses of upper stratospheric ozone to solar ultraviolet variability at wavelengths near 200 nm are primarily responsible. At latitudes ≳40°, larger‐amplitude wintertime ozone fluctuations associated with planetary‐scale pressure waves become dominant and reduce the computed correlation coefficients to statistically insignificant levels. Linear regression analyses are performed to obtain estimates for the average percent change of ozone at low latitudes and on the considered time scale for given changes in 10.7‐cm

ISSN:0148-0227    

DOI:10.1029/JD089iD06p09557

年代:1984

数据来源: WILEY

摘要:

Ozone in the mesosphere is determined from observations made by the near‐infrared spectrometer experiment on the Solar Mesosphere Explorer satellite (SME) between 50 and 90 km over most latitudes at 3:00 P.M. local time. The spectrometer measures emission from O2(1Δg) at 1.27 μm that is primarily due to the photodissociation of ozone. The instrument consists of a parabolic telescope that limits the field of view to less than 0.1°, an Ebert‐Fastie spectrometer, and a passively cooled lead sulfide detector system. The limb radiances, measured as the spacecraft spins, are inverted, producing volume emission rate profiles from which ozone densities are inferred. The vertical resolution is better than 3.5 km. The calculation of ozone accounts for quenching and atmospheric transmission of both solar radiation and 1.27‐μm radiation. We have established the existence of a secondary maximum of ozone density near 80km. An error analysis shows that the effects of random errors in the data and in the analysis on the final ozone profile are less than 10% between 50

ISSN:0148-0227    

DOI:10.1029/JD089iD06p09569

年代:1984

数据来源: WILEY

摘要:

A discharge flow system with laser magnetic resonance (LMR), resonance fluorescence (RF), and resonance absorption (RA) detection axes is used to study the kinetics of the title reaction. Pseudo‐first‐order decays of O in excess ClO and of ClO in excess O agree very well and yield a rate constant of (3.5±0.5)×10−11cm3molecule−1s−1near 300 K, with no discernable temperature dependence over the range 252–347 K. Both reactants, and for some experiments the Cl atom product, are detected directly with high sensitivity. Experiments are done both in helium and in argon, and the cited uncertainties include an estimate of systematic errors at the 2σ or 95% confidence level. Results are compared with other recent work, and implications of the somewhat slower rate constant on the chlorine‐induced destruction of O3in the stratospher

ISSN:0148-0227    

DOI:10.1029/JD089iD06p09581

年代:1984

数据来源: WILEY

摘要:

A two‐dimensional photochemical model based on diabatic circulation has been used to simulate the behavior of N2O, CFCl3(F‐11), and CF2Cl2(F‐12). The circulation is based on estimates of net heating from the ground to 60 km. Eddy diffusion has been reduced with respect to other model studies withKzz= 2 × 103cm2s−1everywhere above 100 mbar. Resulting tracer profiles show reasonable agreement with measured profiles in the tropics and fall off much more sharply with altitude than those produced by models using larger values ofKzz. The agreement obtained is at least as good as that obtained with adjustable, eddy diffusion parameters. The diabatic circulation treatment is more closely related to real physical processes and thus more easily interpreted. Diffusive mixing appears to be more important in determining the details of the tracer distributions than the basic mo

ISSN:0148-0227    

DOI:10.1029/JD089iD06p09589

年代:1984

数据来源: WILEY