摘要:

This study examines the potential climatic effects of the radiatively active trace gases that have been detected in the atmosphere including chlorofluorocarbons, chlorocarbons, hydrocarbons, fluorinated and brominated species, and other compounds of nitrogen and sulfur, in addition to CO2and O3. A one‐dimensional radiative‐convective model is used to estimate trace gas effects on atmospheric and surface temperatures for three cases: (1) modern day (1980) observed concentrations are adopted and their present trends are extrapolated 50 years into the future. These projections are based on analyses of observed trends and atmospheric residence times; (2) the preindustrial to present increase in CO2and other trace gases are inferred from available observations; (3) a hypothetical increase of 0–1 ppbv is considered to provide insights into the radiative processes. Trace gases other than CO2are shown to be potentially as important as CO2for long‐term climate trends. The relative importance of the 30 or so trace gases included in this study depends on the problem under consideration. The inferred CO2increase from preindustrial to the present causes an equilibrium warming of the model surface by 0.5 K, which is amplified by 50% by CH4, CFCl3(F11), CF2Cl2(F12), and tropospheric ozone. For the projected increase from year 1980 to 2030, the other trace gases amplify the estimated CO2warming of 0.7 K by about 110%: CFCl3, CF2Cl2, ozone, and CH4each contribute in the 0.1–0.2 K range followed by N2O, CHClF2(F22), CH3CCl3, and CCl4in the 0.03–0.1 K range. Finally, on a per ppb basis, about 12 trace gases are identified to be important: CBrF3, C2F6(F116), CHF3, and CF3Cl (F13) have greenhouse effects comparable to those of CFCl3(F11) and CF2Cl2(F12). The narrow‐band overlap treatment and the accurate spectral and angular integration techniques employed in the present radiation model enable quantitative interpretation of the differences between various published estimates for the greenhouse effects of CFCl3and CF2Cl2. For the projected trace gas increase, we compute the stratospheric O3change by employing a photochemical model coupled to the radiative‐convective model. The O3change cools the stratosphere and the magnitude of the cooling is as large as that due to the projected CO2increase. Because of the O3‐induced stratospheric cooling and the surface warming due to the greenhouse effect, the trace gas effects on climate are virtually indistinguishable

ISSN:0148-0227    

DOI:10.1029/JD090iD03p05547

年代:1985

数据来源: WILEY

摘要:

CO2data obtained from discrete sampling during 1968–1982 at 23 National Oceanic and Atmospheric Administration/Geophysical Monitoring for Climatic Change and foreign cooperative stations are presented, together with a description of the measurement program and data quality. Monthly, seasonal, and annual CO2concentrations are determined by the individual stations from select (background) data. Temporal and spatial global CO2distributions yield annual and seasonal latitudinal gradients, abundances, airborne fractions, annual cycle amplitudes and phases, annual cycle amplitude growth rates, and global growth rate variations of CO2. The time‐series data sets reveal variations related to several El Niño/Southern Oscillation events, particularly with respect to the strength of the CO2source in the equatorial Pacific Ocean and global CO2growth rates. CO2growth rate anomalies correlate highly with the Southern Oscillation Index, which is related to the strength of the easterly trade winds that blow along the equ

ISSN:0148-0227    

DOI:10.1029/JD090iD03p05567

年代:1985

数据来源: WILEY

摘要:

Sensitivities of the optical properties and of the radiative perturbations induced by the microphysical characteristics of smoke and dust aerosols in the aftermath of a nuclear war are investigated. All optical calculations assume homogeneous spherical particles, prescribed by lognormal size distributions. A change in the mode radius of the aerosol size distribution between 0.1 and 1.0 μm, for a constant smoke loading, results in a tenfold decrease in the visible optical depth. Over the same size range the long‐wave optical depth increases from 1/30 of the visible optical depth for a mode radius of 0.1 μm to 1/2 for a mode radius of 1.0 μm. The direct radiative forcing is studied using a spectrally dependent, one‐dimensional radiative transfer model. The radiative heating is strongly influenced by the vertical distribution of smoke and dust aerosols. When compared with a constant density profile, the maximum in the heating rate, owing to a 3‐km scale height profile of smoke aerosols (visible optical depth ∼3), is reduced from 16° to 4°K/d and is more widely distributed in the troposphere. Solar absorption in the troposphere is reduced by increases in dust loadings in the stratosphere (a loading of 0.5 g/m2results in a 30% reduction), while the planetary albedo is enhanced over the smoke‐only case (up to 150% for 0.5 g/m2). Perturbations to the long‐wave fluxes due to aerosols are modulated by the column amount of water vapor. The increase in the long‐wave flux at the surface, however, even for an order of magnitude enhancement in water vapor, is less than the decrease in the solar flux. A time‐marching, one‐dimensional radiative convective model, which uses an eddy diffusion approach to represent convective processes, is employed to study the temporal development of the thermal structure. The relative altitude of the maximum solar absorption to long‐wave emission determines the strength and vertical extent of the tropospheric inversion and the surface temperature response. For a nominal long‐wave smoke optical depth (0.2) the higher the altitude of solar absorption, the greater the reduction in the surface temperature. Thus the assumption of a constant smoke density profile between 0 and 10 km results in a surface cooling of 32°K after 20 days, while the assumption of a constant scale height profile of 3 km causes a cooling of 22°K. For an arbitrarily large long‐wave smoke optical depth (2.0) arising owing to the presence of large (>2 μm) particles in high concentrations in relation to the submicron sizes (a rare event in the unperturbed atmosphere) or owing to large smoke loadings, the altitudes of maximum solar absorption and long‐wave emission become identical. If this altitude is located near the surface, the surface temperature response becomes weak. Thus for a 3‐km aerosol scale height profile, the surface cooling is 3°K, while an extreme assumption of a 1‐km scale height profile cause

ISSN:0148-0227    

DOI:10.1029/JD090iD03p05597

年代:1985

数据来源: WILEY

摘要:

We investigate the adiabatic and diabatic thermal balance of an atmospheric general circulation model (GCM) under two conditions: the control case, representing today's atmosphere, and a “nuclear winter” scenario in which virtually all sunlight in northern hemisphere mid‐latitudes is absorbed in the upper troposphere by prescribed dense smoke clouds hypothesized to result from the burning of many cities in a nuclear war. We also examine the changes in moisture and cloudiness simulated by the model. Our object is to examine the reliability of existing simulations of the climatic response to assumed dense, widespread, high‐altitude smoke and to identify improvements needed in model parameterizations. We find that in the smoke‐perturbed case our model simulation of land surface temperature is particularly influenced (i.e., warmed) by parameterized diffusion of heat downward from the lower troposphere. In turn the lower troposphere over land is supplied with heat transported from the relatively warm oceans. Thermal balance in the perturbed atmosphere as a whole is dominated by intense solar heating of the upper troposphere smoke layer in mid‐latitudes balanced by parameterized dry convection and large‐scale dynamical heat transport. Clouds largely disappear in the mid to upper troposphere in smoke‐affected regions as a consequence of a decrease in local relative humidity that results from temperature increases and, to a smaller extent, from a reduction of vertical moisture transport. The computation of substantial downward vertical heat diffusion into the lowest model layer is almost certainly an overestimate for the smoke‐perturbed conditions of high vertical stability. Consequently, the use of the present diffusive parameterization will, in the absence of other errors, result in an underestimate of the magnitude of land surface cooling in the “nuclear winter” scenario. Current three‐dimensional model simulations, however, contain numerous additional omissions and approximations that make it difficult to say whether “nuclear winter” simulations, to date, produce effects that are more or less severe than those that might really occur given the hypothesized smoke amounts and distribution. We believe that the most important areas for GCM enhancement to study climatic effects of nuclear war‐generated aerosols include improved surface and planetary boundary layer processes and incorporation of radiatively active aerosol

ISSN:0148-0227    

DOI:10.1029/JD090iD03p05615

年代:1985

数据来源: WILEY

摘要:

Radiosonde data obtained over the past 30 years from nine tropical stations have been analyzed to investigate the variability in height of the tropical tropopause on interannual time scales and on hemispheric spatial scales. A high degree of spatial coherence was found to exist among the stations, indicating that the tropical tropopause responds to large‐scale driving forces as well as to local influences. The tropopause height was found to have a significant dependence on the phase of the quasi‐biennial oscillation in the zonal winds of the tropical stratosphere and on the sea surface temperature anomalies of the tropical Pacific Ocean (the El Nino/Southern Oscillation phenomenon). A strong positive correlation between tropical tropopause heights and solar activity, reported earlier by several authors, is shown to have been transitory and possibly coincidental. The implications of these results are discussed. A comparison of tropopause height/temperature and height/saturation water vapor mixing ratio relationships at Yap and Curacao is consistent with suggestions that the western tropical Pacific is an important source region for stratospheric water va

ISSN:0148-0227    

DOI:10.1029/JD090iD03p05629

年代:1985

数据来源: WILEY

摘要:

In this paper we examine in detail the “spinup” of a general circulation model of the atmosphere, initialized with isothermal, dry, calm conditions with a constant surface pressure. The speed at which the spinup occurs depends on the atmospheric parameter and geographical location being examined. What is made clear here are the different thermodynamic and dynamic time scales associated with the problem, these ranging from a few to hundreds of days. A simple analysis suggests the spinup of the atmosphere may not be too different from the atmospheric response to a small perturbation, particularly in tropical regions. The times required for a simple model to readjust to “small” changes can be of the order of 6 months or more, in agreement with observational studies. Such long atmospheric time scales may be of considerable importance in explaining interannual vari

ISSN:0148-0227    

DOI:10.1029/JD090iD03p05637

年代:1985

数据来源: WILEY

摘要:

A one‐dimensional nonlinear ice age model developed by J. Imbrie and J. Z. Imbrie was used to investigate the 100,000 year cycle in climate records. It was already known that the model could mimic the 100,000 year cycle in the climate response, but it was not clear how this strong response was created. It is shown in this paper that the interference between the spectral components in the solar heating of 19,000 years and 23,000 years gives rise to an amplitude modulation, and how this modulation is converted by the nonlinearity to a 100,000 year cycle in the climate respons

ISSN:0148-0227    

DOI:10.1029/JD090iD03p05661

年代:1985

数据来源: WILEY

摘要:

Stationary and cyclostationary statistical models are developed to predict Arctic and Antarctic sea ice anomalies, using as predictors previous sea ice, atmospheric, and oceanic anomalies. A prediction model hierarchy is developed by using first internal (i.e., sea ice) predictors, including persistence, lateral advection, and diffusion, and a cyclostationary model that allows the prediction coefficients to vary seasonally. An external cyclostationary model hierarchy is developed next to investigate the ability of atmospheric winds, heat flux proxies air temperatures, and sea surface temperatures (SST's) to predict sea ice extent. In the Arctic the highest skill was generally achieved by the cyclostationary internal model. Attempts to forecast the ice data at 1–2 month intervals after removal of its autoregressive component, using external predictors, gave nonsignificant models. At longer lead times (e.g., 3 months) the SST in the North Pacific was superior to persistence for sea ice prediction in the western Bering Sea. In the Southern Ocean, especially off East Antarctica, the model that included lateral advection and diffusion outperformed both persistence and the cyclostationary internal model. In the Weddel Sea and the Ross Sea, persistence proved to be the best sea ice predictor. No external models were tested for Antarctic sea ice because of insufficient dat

ISSN:0148-0227    

DOI:10.1029/JD090iD03p05665

年代:1985

数据来源: WILEY

摘要:

An interesting feature of previous sea ice modeling studies [Semtner, 1976; Washington et al., 1976] was the multiyear cycles in sea ice thickness despite repeating year to year forcing. It is shown here that a number of factors combine to produce these cycles. The most important of these is the insulating properties of the snow layer; however, the timing of the refreezing of new ice at the end of an ice free summer season, and the vertical ocean flux play a role in determining the length and character of these cycles. It is also shown that the inclusion of the formation of white ice in the model greatly reduces its ability to produce multiyear cycles.

ISSN:0148-0227    

DOI:10.1029/JD090iD03p05676

年代:1985

数据来源: WILEY

摘要:

An analysis of available ozone data in the eastern two‐thirds of the United States indicates that a substantial reservoir of ozone is present in the summertime. Five‐year mean concentrations range from 40 to 65 ppbv. The reservoir covered an area of several million square kilometers and extends vertically from the surface to 1 to 2 km. The vertical distribution of ozone in the reservoir during midday supports a transport of additional ozone from the boundary layer to the free troposphere. Data are presented demonstrating the potential effect of transport by convective clouds and by the sea breeze circulation—mechanisms by which ozone may be transported out of the boundary layer into the free troposphere. The potential impact of this reservoir on the tropospheric ozone budget is discussed. It is shown that if less than half of the ozone mass in this reservoir is transported to the free troposphere, then the amount of ozone transported out of the boundary layer approximates the amount of ozone transported down‐ward during a tropopause fol

ISSN:0148-0227    

DOI:10.1029/JD090iD03p05687

年代:1985

数据来源: WILEY