摘要:

Daily samples of dryfall were collected during the June 1982 Dry Deposition Measurement Intercomparison Study at Champaign, Illinois, using six Aerochem Metrics wet/dry collectors. Upon completion of the field experiment, these samples were analyzed at the Environmental Measurements Laboratory forpH and for their concentrations of major inorganic constituents. Contamination by rain and bird droppings rendered a number of dryfall samples unusuable. When data for these samples were removed, the remaining data displayed acceptable precision for sulfate, calcium, and magnesium. The measured deposition rates varied between 7 and 73 ng/m2/s for sulfate, between 7 and 44 for calcium, and between 0.8 and 8.1 for magnesium. The precision of the data for ammonium, nitrate, and phosphate was poor, so we have not calculated deposition rates for these constituents. The measurements of the atmospheric concentrations of sulfate reported by the Illinois State Water Survey have been used to calculate deposition velocities for particulate sulfate for 18 daily samples, even though the aerosol sampler and the dry bucket of the wet/dry collector may not sample the same size population of particulates. These velocities ranged from 0.1 to 1.2 cm/s, with a median value of 0.4 cm/s and a mean of 0.45±0.31 cm/s

ISSN:0148-0227    

DOI:10.1029/JD090iD01p02161

年代:1985

数据来源: WILEY

摘要:

The climate influence of the land ice that existed 18,000 years before present (18K B.P.) is investigated by use of a general circulation model of the atmosphere coupled with a static mixed layer ocean. Simulated climates are obtained from two versions of the model: one with the land ice distribution of the present and the other with that of 18K B.P. In the northern hemisphere the tropospheric flow field is strongly influenced by the Laurentide ice sheet and features a split flow straddling the ice sheet, with a strong jet stream forming the southern branch. The northern branch of the flow brings very cold air over the North Atlantic Ocean, where thick sea ice is maintained. The distribution of sea surface temperature (SST) difference between the two experiments in the northern hemisphere resembles the difference between the SST at 18K B.P. and at present, as estimated by the CLIMAP Project (1981). The 18K B.P. ice sheets have very little influence upon atmospheric temperature and SST in the southern hemisphere. This is because the interhemispheric heat transport hardly changes as the loss of heat energy due to the reflection of solar radiation by continental ice sheets in the northern hemisphere is almost completely counterbalanced by the in situ reduction of upward terrestrial radiation. Hydrologic changes in the model climate are also found, with statistically significant decreases in soil moisture occurring in a zone located to the south of the ice sheets in North America and Eurasia. These findings are consistent with some geological evidence of regionally drier climates from the last glacial maximum.

ISSN:0148-0227    

DOI:10.1029/JD090iD01p02167

年代:1985

数据来源: WILEY

摘要:

We present the results of a study of the sensitivity of the transient surface temperature response to a step function solar constant increase using a globally averaged energy balance climate model which is coupled to two different globally averaged thermodynamic ocean models. The first ocean model is a box model, in which the ocean is divided into a small number of isothermal reservoirs. Experiments with this model demonstrate some circumstances in which it is important to treat the mixed layer and deep ocean separately rather than lumping them into a single reservoir, as has been the practice in a number of recent studies using coupled atmosphere‐ocean‐cryosphere models over 104year time scales. The second ocean model has an isothermal mixed layer which is coupled to an advective‐diffusive deep ocean having a continuous vertical temperature profile. We permit the thermal diffusivityKand the advection velocitywto vary vertically and introduce a variety of plausible feedbacks betweenKand the vertical temperature gradient, and betweenwand the perturbation mixed layer wanning. We also permit the bottom water source temperature to change by a prescribed fraction of the mixed layer response. The transient surface response is relatively insensitive to changes inKandwfor the nonfeedback cases, but is more sensitive to individual feedback mechanisms. When multiple feedback processes are permitted a complex transient surface temperature response is possible. When applied with a periodic solar constant forcing, these feedback processes can either significantly reduce or increase the amplitude of the surface temperature response compared to the no‐feedba

ISSN:0148-0227    

DOI:10.1029/JD090iD01p02191

年代:1985

数据来源: WILEY

摘要:

We present a hemispherically averaged, seasonal model with land‐sea and surface‐air resolution that we use to compare the transient temperature response of different model components to changes in the radiative forcing. Horizontal heat transport coefficients were obtained by tuning the model to reproduce the present seasonal climate as closely as possible. Cross‐sensitivity experiments with a step function solar constant increase and a variety of ocean parameter feedback processes essentially duplicate the results obtained in part 1 (Harvey and Schneider, 1985) with a globally averaged model. We intercompare the global and hemispheric model surface and deep‐ocean transient response and show how both the global mean surface and mixed‐layer only transient response of the hemispheric model can be reproduced by using the globally averaged model. For a time‐dependent CO2increase scenario we find that the mixed‐layer warming lags moderately behind the atmosphere wanning but that the atmosphere over land and atmosphere over sea warmings are rather tightly coupled. Implementation of a number of ocean parameter feedbacks to a time‐dependent CO2increase has a similar qualitative effect on the transient temperature response as when implemented for a step function solar constant increase but causes less variation in the transient response than uncertainties about the equilibrium climate sensitivity. During the first year following a small negative perturbation to the solar constant, in order to mimic a volcanic dust veil, we find that the air temperature response over land is about twice that of the ocean mixed‐layer temperature. This suggests that one should distinguish between temperature responses over land and over ocean in any studies attempting to compare model‐generated volcanic signals with empirical surface temperature data. For complex short‐ and long‐term mixed forcing changes, such as volcanic and CO2, the lag between atmosphere and mixed‐layer temperature changes does not become large until the long‐term forcing change becomes dominant, although the land‐sea lags associated with short‐term perturbations may still be significant for regional climatic anomalies asso

ISSN:0148-0227    

DOI:10.1029/JD090iD01p02207

年代:1985

数据来源: WILEY

摘要:

The influence of cumulus convection on the equilibrium temperature perturbations due to the doubling of CO2is investigated by using a one‐dimensional radiative‐turbulent model. The model includes parameterizations of solar and infrared radiative flux transfer in clear and cloudy conditions, vertical eddy sensible and latent heat fluxes, surface albedo feedback, and an interactive cumulus convection. The cumulus parameterization employed is basically a Kuo‐type scheme described and modified by Anthes. In addition the criteria for cumulus convection to take place is derived from values associated with the surface relative humidity and the vertical profile of moist static energy. In the numerical experiments it is found that the extent of condensational heating due to cumulus convection is determined by the depth of the conditionally unstable layer and the total amount of buoyancy force generated by the excess cloud temperature over the surrounding temperature. With the incorporation of cumulus convection, an atmosphere with a high relative humidity will generate a higher temperature near the surface. Also, a higher surface relative humidity will generate a larger upward shift in equilibrium condensational heating rates. Perturbation experiments reveal that the sensitivity of cumulus convection to the surface temperature increase due to doubling of CO2is not apparent under mean annual global conditions with a realistic surface relative humidity of 85%. However, with the incorporation of cumulus convection and fixing the horizontal transport of sensible and latent heat fluxes, it is shown that the surface temperature increase in a tropical atmosphere due to doubling of CO2significantly reduces from 4.3 to 2.5°K with the upward shift of temperature increases especially evident in upper tropospheric levels. Finally, it is also noted that the tropospheric temperature profile in the tropics generated by the present one‐dimensional model with cumulus convection agrees closely with that provided by Oort and Rasmusson for mean annual climatological co

ISSN:0148-0227    

DOI:10.1029/JD090iD01p02223

年代:1985

数据来源: WILEY

摘要:

The zonal average momentum budget in the middle atmosphere (up to 0.1 mbar) is computed for 7 months of satellite observations in order to determine the forcing needed to obtain a balance. This momentum residual includes forcing by waves with small zonal scales, such as gravity waves. The results indicate that the forcing needed in the lower mesosphere reaches peak values of about 20 m s−1d−1, which is large compared to the Rayleigh friction used in that part of the atmosphere in numerical models, such as that of Holton and Wehrbein (1980a). The seasonal change follows that of Rayleigh friction; the northern hemisphere momentum deficit is large easterly in winter, decreases in the spring, and becomes small westerly in late spring. However, the largest momentum deficits are in middle and high latitudes (50°–80°N) in winter, whereas the largest Rayleigh frictional damping is in the vicinity of the jet (30°–50°N). The observations were also compared with the parameterized acceleration of the mean flow by gravity waves (Lindzen, 1981; Holton, 1983). The observations of the wintertime momentum residual are similar to the values used in the circulation model of Holton (1983). Derivation of the parameterization constant from the satellite observations results in an equivalent zonal wave number for gravity waves that is substantially smaller than that used by Holton (1983) in his model. Possible reasons for this difference are that many of the gravity waves break at levels above the region where data are available and that gravity waves with nonzero phase speeds may

ISSN:0148-0227    

DOI:10.1029/JD090iD01p02233

年代:1985

数据来源: WILEY

摘要:

The sensitivity of a thermodynamic sea ice model to changes in surface energy fluxes in the Arctic is investigated. The main emphasis of the paper is on the testing of the model sensitivity to changes in surface albedo parameterization. Climatologies of turbulent and long‐wave fluxes in the Arctic are scarce, and those that exist are shown to generate significant differences in the predicted ice thickness. There is considerable disagreement in the literature on albedo values, and in particular, proposed albedos of bare, puddled ice range from 0.4 to 0.66. The differences among published model simulations are shown to be potentially explicable in terms of this range in bare ice albedo. A new ice albedo parameterization is proposed, and its sensitivity is tested. It is shown that the increase in surface albedo with cloud cover can cause a doubling of the ice thickness, and the need to include melting snow as an albedo class distinct from dry snow is demonstrated. The value of bare‐ice albedo is shown to be important in determining whether the ice is in a multiyear or a seasonal ice zone, and the need for more observational data on the extent and role of melt puddles is emphasi

ISSN:0148-0227    

DOI:10.1029/JD090iD01p02243

年代:1985

数据来源: WILEY

摘要:

A thermodynamic sea ice model numerically structured to take time steps on the order of a week is found to be sensitive to time step size when new ice formed on open ocean is assumed to cover the ice‐free area. This sensitivity is caused by the extrapolation of initial ice growth rates on open ocean, which can be very high, over the length of the time step. The sensitivity to time step size is tremendously reduced when the parameterization for the formation of new ice is altered so that the new ice thickness is specified. However, the sensitivity continues during the winter, when the area of open ocean is small because the volume of ice formed over the time step is more than enough to fill the open area at the specified thickness. Therefore ice thickness during the winter is again determined by time step size. Suggestions are made on how the sea ice model's sensitivity to time step size can be further reduced without sacrificing computational efficienc

ISSN:0148-0227    

DOI:10.1029/JD090iD01p02251

年代:1985

数据来源: WILEY

摘要:

Based on climatological information over a long period, two case studies of typical flow situations near the Georg von Neumayer station (70°37′S, 8°22′W) are presented. A shallow katabatic layer develops under a small pressure gradient and considerable cooling of the surface layer. In situations with large horizontal pressure gradients, which are more frequent in winter than in summer, the flow is affected by the sloping terrain that leads to the Antarctic plateau. In this case, a marked difference between the temperatures of the air just above the ice shelf and the warmer air from the ocean can be observed within the lowest

ISSN:0148-0227    

DOI:10.1029/JD090iD01p02261

年代:1985

数据来源: WILEY

摘要:

Three rocket measurements of the solar spectral irradiance have been obtained for the wavelength region 150–200 nm. These flights occurred on November 16, 1978; May 22, 1980; and October 16, 1981. Evidence was found for a variation in the solar irradiance with the solar cycle but smaller than that reported by Mount and Rottman (1981). There is good agreement between the October 16, 1981, flight and the last two flights of Mount and Rottman (1983a,b, 1985

ISSN:0148-0227    

DOI:10.1029/JD090iD01p02265

年代:1985

数据来源: WILEY