摘要:

Sea ice/snow and land snow models are developed using a vertically integrated formulation (VIF). The VIF model has the capability of simulating the nonlinear effects of heat storage and transfer through the layers of snow and ice, which are felt particularly in spring and fall, yet this is achieved without resorting to the addition of layers to the numerical scheme. For comparison, a stable multilayer model is developed and tested. It is demonstrated that the VIF shares the accuracy of the multilayer formulation, and at the same time benefits from computational flexibility typical of linear formulations. The validity of the VIF assumptions and their parameter dependence are analyzed using an analytically solvable example. It is suggested that the VIF model may be specifically suitable for the implementation in a variety of climate models and general circulation models. A simple parameterization is applied to include seasonal and latitudinal changes in the heat flux from the mixed layer to the ice layer. This flux, though small in magnitude on an annual and latitudinal average, has an important influence on the ice thickness and its seasonal cycle and was taken as a constant in previous sea ice modeling. Latitudinal dynamical sea ice transport is also included in a simple parameterized form.

ISSN:0148-0227    

DOI:10.1029/JD093iD04p03663

年代:1988

数据来源: WILEY

摘要:

The VIF sea ice/snow and land snow models developed in a companion paper are implemented in a seasonal dynamic zonally averaged climate model. The simulation of the seasonal cycle of the present climate is compared to climatological data and to results of other models. The addition of ice/snow is found to have interesting consequences for the relative dominance of the opposing winter and summer effects of variations in the Earth's orbital elements, as already implied by Held (1982). In response to a change between extreme high and low summer insolation orbits, it is found that for sea ice (but not for land snow) the winter orbital change dominates over the opposite summer change, causing sea ice shifts which are contrary to the direction predicted by the Milankovitch theory. This is explained by the orbitally induced changes in the length of the seasons, causing insolation anomalies that peak at high latitudes in October and March, coupled with the lag effect of sea ice accretion/Melting/heat storage, large thermal capacity of seawater, and sea ice area‐thermal inertia feedback. On the other hand, for snow over land the shorter but more pronounced summer orbital change dominates, causing shifts in the region of positive annual snow budgets that agree in direction with the Milankovitch theor

ISSN:0148-0227    

DOI:10.1029/JD093iD04p03677

年代:1988

数据来源: WILEY

摘要:

It is well known that there has been a close relation between sea surface temperature (SST) variations in the eastern equatorial Pacific (El Niño region) and tropospheric temperature variations in the tropics, with the amplitude of the SST variations averaging about twice that of the tropospheric temperature variations. In particular, it is shown in this paper that during 1960–1986 there was a correlation of 0.66 (significant at the 1% level) between SST in the region 0°–10°S, 180°–80°W and zonally averaged 850‐ to 300‐mbar temperature in the equatorial zone one season later. In the north and south subtropics the maximum correlations between this SST and 850‐ to 300‐mbar temperature were 0.48 and 0.52 (significant at the 5% level) at a lag of two seasons. In temperate and polar latitudes the correlations were a maximum (though nonsignificant except in the south polar zone) at lags of two to three seasons. There is the implication of a tropospheric thermal pulse originating at the equator and spreading poleward, decaying as it does so. On the basis of the magnitude of these lagged correlations in the tropics it appears that the reason tropospheric temperatures cooled following the Agung eruption in 1963 but warmed following the El Chichón eruption in 1982 is the occurrence of a very strong El Niño after El Chichón but only a relatively weak El Niño after Agung. When tropical tropospheric temperatures are adjusted by “subtracting out” the usual relation with equatorial SST (by displacing the tropospheric temperatures two seasons earlier with respect to SST and dividing the SST deviations from the mean by 2 before subtraction from the tropospheric temperature deviations), the magnitude of the tropical tropospheric cooling following El Chichón becomes similar to that following Agung (about 0.5°C) but is of shorter duration. When a similar adjustment procedure is applied to the five major volcanic episodes since 1880, the eruptions of the tropical volcanoes of El Chichón, Agung, Santa Maria‐Pelée‐Soufrière, and Krakatau are all indicated to have brought about a decrease in northern hemisphere continental surface temperatures of about 0.3°C, whereas the eruption of Katmai in Alaska is indicated to have decreased this temperature by only about 0.1°C. It is proposed that the reason the evidence for volcanically induced cooling of the Earth's surface has been so uncertain and controversial in the past is that such cooling may or may not be observed depending on the extent of sea surface warming in the eastern equatoria

ISSN:0148-0227    

DOI:10.1029/JD093iD04p03697

年代:1988

数据来源: WILEY

摘要:

Using a data set including large‐scale fields and collocated satellite observations (the NEPHOS file), we test the validity of the approach proposed for validating general circulation model type cloud schemes with the future International Satellite Cloud Climatology Project (ISCCP) and First ISCCP Regional Experiment (FIRE) data sets. An ensemble of 2866 atmospheric situations extracted from the NEPHOS file is used to test the European Center for Medium Range Weather Forecasts operational cloud cover scheme and to study the sensitivity to cloud cover of the regional radiation budget over the eastern Atlantic Ocean and the North Sea. This scheme, based on a simple function of the relative humidity, is shown to underestimate the cloud cover (by 26%), especially when stratocumulus clouds are present. This underestimation is related to too small values of the analyzed relative humidity in the model's planetary boundary layer. The vertical gradient of potential temperature is shown to be a better predictor for this low‐level cloudiness. Differences between the observed and generated radiation budget at the top of the atmosphere are induced by the differences in cloud cover. However, differences in the cloud radiative properties introduce some compensating effects, and the mean bias error is only +7 Wm−2. Particularly, the mean value of the shortwave albedo is too high in the model, and its variation as a function of the cloud cover is much too smooth, as the model does not account for the observed increase in the vertical optical depth of clouds when the cloud cover incr

ISSN:0148-0227    

DOI:10.1029/JD093iD04p03705

年代:1988

数据来源: WILEY

摘要:

Microwave radiances that may be measured from satellite‐borne radiometers operating at 37 GHz have been computed as a function of rainfall rates from horizontally finite precipitating clouds that contain both ice and liquid hydrometeors. It is found that precipitating ice at the top of the cloud depresses brightness temperatures significantly. Detailed comparison between finite clouds and the equivalent sections of plane‐parallel clouds are made. Footprint averaged brightness temperatures from finite clouds are found to deviate considerably from the sectioned plane‐parallel approximation, especially for large rain rates. Better agreement is achieved if a plane‐parallel source function is used in the finite cloud model. The effect of shape and orientation of the precipitating cells with respect to the satellite has also been considered. It is found that the largest errors introduced by plane‐parallel theory besides the footprint‐filling errors are encountered when precipitating cells have large fractions of their surface below the freezing level or contain large amo

ISSN:0148-0227    

DOI:10.1029/JD093iD04p03720

年代:1988

数据来源: WILEY

摘要:

We consider the weakly nonlinear three‐wave interactions in an isothermal atmosphere. The mutual interactions among the three linear branches of dynamical‐thermodynamical atmospheric motions (gravity waves, acoustic waves, and vortical motions) are investigated. In addition to the resonant case, nonresonant interactions are also considered. On the basis of the analytical solution of the linearized wave‐amplitude equation with possible existence of a frequency mismatch, the resonance surface, the interaction domain, and growth time in three‐dimensional geometry in k‐space in various cases have been calculated and some numerical results are given. It is found that the nonresonant interaction can be very important, especially when a gravity wave and two vortical modes of motions interact as a nonresonant trio. The energy transfer from the gravity wave to vortical motions might limit the growth of the gravity wave amplitude and hence might provide a reasonable mechanism for gravity waves to saturate in the middle a

ISSN:0148-0227    

DOI:10.1029/JD093iD04p03729

年代:1988

数据来源: WILEY

摘要:

We have measured gaseous methyl bromide (CH3Br) and bromoform (CHBr3) in air samples that were gathered approximately weekly from five ground‐level sites: Point Barrow, Alaska; Mauna Loa Observatory and Cape Kumukahi, Hawaii; Matatula, Samoa; and Kaitorete Spit, New Zealand. Approximately 750 samples have been analyzed for CH3Br between January 1985 and October 1987 and 990 samples have been analyzed for CHBr3between early 1984 and September 1987, all by gas chromatography/mass spectrometry. Methyl bromide concentrations are typically 10–11 parts per trillion (ppt) by volume; there are no clear indications of temporal increases. Bromoform concentrations are typically 2–3 ppt, but large seasonal variations are seen at Point B

ISSN:0148-0227    

DOI:10.1029/JD093iD04p03745

年代:1988

数据来源: WILEY

摘要:

Diurnal variations of isoprene and monoterpenes in the atmosphere were precisely measured at an interval of 1–2 hours in the rainy season and in fine midsummer in an agricultural area in Japan. It was observed that the mixing ratio of isoprene was much larger in fine daytime than in nighttime or in cloudy daytime; in contrast, a higher mixing ratio of monoterpenes was usually observed in nighttime. In fine midsummer the concentration of atmospheric isoprene increased gradually after midnight, reaching its maximum late in the afternoon, and decreased rapidly after sunset. The significant difference between atmospheric isoprene and monoterpenes was explained by suggesting that isoprene emission is more strongly affected by temperature and/or solar radiatio

ISSN:0148-0227    

DOI:10.1029/JD093iD04p03751

年代:1988

数据来源: WILEY

摘要:

Time histories of surface air composition and cloud water composition in winter in Central Ontario are compared in order to establish a winter data set for this region, and to identify dominant processes responsible for the incorporation of sulfate, nitrate, and acidity into cloud water. Cloud water comparisons are restricted to low‐level collections (median altitude 625 m above ground) within the boundary layer. Surface level measurements during the 6‐week period show a variety of conditions, including several episodes of elevated concentrations of SO2, NO3−, HNO3, aerosol SO4=, and occasionally aerosol NO3−. Nitric acid comprised the majority of soluble acidity at ground level more than half the time, and was relatively more important during the periods of elevated SO4=and NO3−concentrations. Examination of cloud water composition indicated that HNO3was also the dominant contributor to cloud water acidity on the majority of days sampled. Comparisons of air and cloud water absolute concentrations and concentration ratios suggest that aqueous SO2oxidation was of minor importance in determining cloud composition. The conclusion is supported by measurements of hydrogen peroxide in cloud water samples. Cloud water NO3−/SO4=ratios were found to exceed (HNO3+ aerosol NO3−)/SO4=ratios in air at the surface in most cases, and in a few instances cloud water NO3−concentrations were higher than expected based on the surface air composition data; several possible causes for this observation are discussed. It is concluded that in this region in winter, the composition of low‐level clouds can be estimated to within a factor of 2 by measurements of air composition at the surface, and that dissolution of soluble aerosol and gaseous species is primarily responsible for cloud composition. In‐cloud SO2oxidation is found to be of minor significance, but the data may indicate in‐cloud production

ISSN:0148-0227    

DOI:10.1029/JD093iD04p03760

年代:1988

数据来源: WILEY

摘要:

During autumn 1984, at a location in central Ontario, a study of the elemental composition of aerosols and precipitation was undertaken to determine the feasibility of making daily multielemental measurements on a routine basin, to probe the potential for gaining insight into pollutant origin from multielemental composition, and to estimate trace element deposition to an acid‐sensitive watershed. The concentrations of Ti, Br, Mn, In, Na, V, Al, Ca, Se, As, Sb, Pb, Fe, Mg, Cu, Zn, and Cd in aerosol and of Pb, Mg, Ca, As, Br, I, Mn, and V in precipitation were measurable routinely, using neutron activation, X ray fluorescence, and plasma emission spectroscopy. Standard high volume samplers for total aerosols below 15 μm diameter as well as dichotomous samplers and Andersen impactors for size fractionation were operated simultaneously with two wet‐only precipitation collectors. Aerosol data revealed four components: one soil (Mg‐Ti‐Al‐Ca‐Fe) and three anthropogenic (Se‐Sb‐Pb‐Cd‐Br; Mass‐Cu‐SO4=; In‐As). Ranked in order of increasing mass fraction in 2.1‐ to 10‐μm diameter particles are the elements Pb, S, Se, Br, As, Cl, Na, V, In, Cu, Mn, Al, Ba, Ti, and Ca. A comparison of air parcel origin on high‐ and low‐concentration days, using 3‐day back trajectories, revealed major source regions of SO4=, Pb, In, As, and Al. The element In is an excellent tracer of smelter emissions to the north. Although the estimated mean ratio of In/Se in smelter emissions from central Ontario is close to that used in the regional aerosol apportionment model of Rahn and Lowenthal, its variability is greater than they propose. In 21 precipitation events, strong correlations were found between H+‐SO4=, Ca++‐Mg++, NO3−‐NH4+‐Cl−‐V, and Pb‐Br. The mass ratio of Br/Pb was higher in precipitation (0.47) than in aerosols (0.27), possibly because of precipitation scavenging of HBr gas in addition to Br in aerosols. In ascending order, the estimated dry‐deposited fraction of total deposition of

ISSN:0148-0227    

DOI:10.1029/JD093iD04p03773

年代:1988

数据来源: WILEY