A Model for Estimating Future Emissions of Sulfur Hexafluoride and Perfluorocarbons

Sulfur hexafluoride (SF₆), perfluoromethane (CF₄) and perfluoroethane (C₂F₆) are strong greenhouse gases with long (>1000 year) atmospheric residence times. We derive emission factors for the major anthropogenic sources and project future emissions for 5 regions and the world. Although firms in many industrialized countries are already limiting emissions, without further policy intervention global emissions will rise 150% (CF₄ and C₂F₆) and 210% (SF₆) between 1990 and 2050; radiative forcing will increase 0.026 W m^-2. Full application of available low-cost and costless policies in industrialized nations would cut that radiative forcing by one-quarter. Increased forcing due to these gases is small (<2%) relative to other gases but permanent on the timescale of human civilization. We also quantify plausible manipulations to governmental data that will be used to determine compliance with the 1997 Kyoto Protocol, which includes commitments for industrialized countries to regulate these and other greenhouse gases. More complete and transparent data are urgently needed. West European nations, for example, can cut their emissions of these gases by half by 2010 simply by manipulating emission factors within the current bounds of uncertainty.     

Global Warming Potentials: 1. Climatic Implications of Emissions Reductions

The use of Global Warming Potentials (GWPs) to calculate equivalent carbon dioxide emissions reductions in the climate change context is examined. We find that GWPs are accurate only for short time horizons. Over long time horizons their use implicitly leads to tradeoffs between near-term and long-term climate change. For one of the most policy-relevant cases, comparing reductions in methane and carbon dioxide, the long-term effect on climate of reducing methane emissions is relatively small, at variance with the common perception based on published GWP values.     

Measurements of solar radiation and estimation of optical depth in the high Andes of Peru

Summary During an expedition to the high Andes of Southern Peru in June–July 1977, measurements of direct solar radiation in four spectral bands (0.270–0.530–0.630–0.695–2.900 ) were conducted at six sites in elevations ranging from sea level to 5645 m. These measurements were evaluated in Langley plots to determine total optical depths () and irradiances at the top of the atmosphere. In addition, water vapor optical depths (_wv) were calculated from the mean radiosounding over Lima during the expedition, and Rayleigh (_ray) and ozone (_oz) optical depths were obtained from published tabulations. Subtracting _ray, _oz, and _wv from yielded estimates of aerosol optical depth _aer. The components _ray and _oz decrease from the shorter towards the longer wavelength bands and from the lower towards the higher elevation sites; _aer also decreases towards the higher elevations. Particularly pronounced is the decrease of _aer and from the lowlands of the Pacific coast to the highlands of the interior, reflecting the effect of a persistent lower-tropospheric inversion and the contrast from the marine boundary layer to the clear atmosphere of the high Andes.With 4 Figures     

Some characteristics of the PBL over the ocean during the Indian summer monsoon

Data collected during the Indo-Soviet Monsoon-77 expedition are used to determine quadratic expressions for the universal constants A and B, as functions of the stability parameter, . A quadratic expression has also been obtained for u _*, in terms of the surface wind u _s. It is shown, from the mean values of q and _E , that the entire area covered by the expedition could be divided into four regions around the point 13° N, 78° E. The mean thermal characteristic of each region differs. It is shown that the northeastern quadrant is most favourable for the sustenance of a tropical storm once it has formed.     

Tropical Glacier and Ice Core Evidence of Climate Change on Annual to Millennial Time Scales

This paper examines the potential of the stable isotopic ratios, ¹⁸O/¹⁶O ( ¹⁸O_ice)and ²H/¹H ( D_ice), preserved in mid to low latitude glaciers as a toolfor paleoclimate reconstruction. Ice cores are particularly valuable as they contain additional data, such as dust concentrations, aerosol chemistry, and accumulation rates, that can be combined with the isotopic information to assist with inferences about the regional climate conditions prevailing at the time of deposition. We use a collection of multi-proxy ice core histories to explore the ¹⁸O-climate relationship over the last 25,000 years that includes both Late Glacial Stage (LGS) and Holocene climate conditions. These results suggest that on centennial to millennial time scales atmospheric temperature is the principal control on the ¹⁸O_ice of the snowfall that sustains these high mountainice fields.Decadally averaged ¹⁸O_ice records from threeAndean and three Tibetan ice cores are composited to produce a low latitude ¹⁸O_ice history for the last millennium. Comparison ofthis ice core composite with the Northern Hemisphere proxy record (1000–2000A.D.) reconstructed by Mann et al. (1999) and measured temperatures(1856–2000) reported by Jones et al. (1999) suggests the ice cores have captured the decadal scale variability in the global temperature trends. These ice cores show a 20th century isotopic enrichment that suggests a large scale warming is underway at low latitudes. The rate of this isotopically inferred warming is amplified at higher elevations over the Tibetan Plateau while amplification in the Andes is latitude dependent with enrichment (warming) increasing equatorward. In concert with this apparent warming, in situobservations reveal that tropical glaciers are currently disappearing. A brief overview of the loss of these tropical data archives over the last 30 years is presented along with evaluation of recent changes in mean ¹⁸O_ice composition. The isotopic composition of precipitation should be viewed not only as a powerful proxy indicator of climate change, but also as an additional parameter to aid our understanding of the linkages between changes in the hydrologic cycle and global climate.     

Competitiveness of terrestrial greenhouse gas offsets: are they a bridge to the future?

Activities to reduce net greenhouse gas emissions by biological soil or forest carbon sequestration predominantly utilize currently known, readily implementable technologies. Many other greenhouse gas emission reduction options require future technological development or must wait for turnover of capital stock. Carbon sequestration options in soils and forests, while ready to go now, generally have a finite life, allowing use until other strategies are developed. This paper reports on an investigation of the competitiveness of biological carbon sequestration from a dynamic and multiple strategy viewpoint. Key factors affecting the competitiveness of terrestrial mitigation options are land availability and cost effectiveness relative to other options including CO₂ capture and storage, energy efficiency improvements, fuel switching, and non-CO₂ greenhouse gas emission reductions. The analysis results show that, at lower CO₂ prices and in the near term, soil carbon and other agricultural/forestry options can be important bridges to the future, initially providing a substantial portion of attainable reductions in net greenhouse gas emissions, but with a limited role in later years. At higher CO₂ prices, afforestation and biofuels are more dominant among terrestrial options to offset greenhouse gas emissions. But in the longer run, allowing for capital stock turnover, options to reduce greenhouse gas emissions from the energy system and biofuels provide an increasing share of potential reductions in total US greenhouse gas emissions.     

Examination of ‘global atmospheric temperature monitoring with satellite microwave measurements’: 2. Analysis of satellite data

Using Microwave Sounding Unit (MSU) channel 2 (Ch. 2, 53.74 GHz) data, Spencer and Christy (1992a) determined that the earth exhibits no temperature trend in the period 1979–90, while other authors find a temperature increase of roughly 0.1 K. Based on a theoretical analysis Prabhakara et al. (1995) showed that the information about the global atmospheric temperature deduced from MSU Ch. 2 observations has a small contamination, T ₂, as a result of the attenuation due to hydrometeors in the atmosphere. A method is developed in this study, that utilizes coincident measurements made by MSU in Ch. 1 (50.3 GHz), to estimate this T ₂ over the global oceans. The magnitude of T ₂ is found to be about 1 K over significant parts of the tropical oceanic rain belts and about 0.25 K over minor portions of the mid-latitude oceanic storm tracks. Due to events such as El Niôo, there is variability from year to year in the rain areas and rain intensity leading to significant change in the patterns of T ₂. The patterns of T ₂ derived for March 82 and March 83 reveal such a change. When averaged over the global oceans, from 50° N to 50° S, T ₂ has a value of 0.25 and 0.29 K for March 1982 and 1983, respectively. Due to these reasons the interannual temperature change derived by Spencer and Christy from MSU Ch. 2 will contain a residual hydrometeor effect. Thus in evaluating decadal trend of the global mean temperature of the order of 0.1 K from MSU Ch. 2 data one has to take into account completely the contamination due to hydrometeors.     

The Kyoto Protocol Emission Allocations: Windfall Surpluses for Russia and Ukraine

The emission targets adopted in the Kyoto Protocol¹ far exceed thelikely level of emissions from Russia and Ukraine. These countries could selltheir surplus if the Protocol is followedand industrialized countries establish an international emission tradingsystem. Critics have condemned the potentialsale and dubbed the surplus hot air because it does not represent anyreduction in emissions below the level thatwould have occurred anyway. Using the most recent, comprehensive regionalscenarios² for the emissions of carbon dioxide from the energysystem, we estimate that during the Protocol's2008–2012 budget period the surplus will range from 9 MtC (milliontons of carbon) to 900 MtC for Russia andfrom 3 MtC to 200 MtC for Ukraine. Even scenarios with high economic growthand carbon-intensive technologies donot exhaust the surplus before the budget period. In the central (middlecourse) scenario, the total carbon surplusexceeds 1000 MtC and is worth 22 to 170 billion U.S. dollars (4 to 34 billionU.S. dollars per year). This flow ofrevenues, which could exceed Russian earnings from natural gas exports($10 billion in 1997³), is comparable with the projectedtotal investmentsof the Russian energy system for 2008–2012. If directed towardslow-carbon infrastructure investments (e.g., gaspipelines), surplus transfers could reinforce and partially lock-indecarbonization of the world energy system.     

Biomass burning in the tropical savannas of Ivory Coast: An overview of the field experiment Fire of Savannas (FOS/DECAFE 91)

FOS/DECAFE 91 (Fire of Savannas/Dynamique et Chimie Atmosphérique en Forêt Equatoriale) was the first multidisciplinary experiment organized in Africa to determine gas and aerosol emissions by prescribed savanna fires. The humid savanna of Lamto in Ivory Coast was chosen for its ecological characteristics representative of savannas with a high biomass density (900 g m^–2 dry matter). Moreover the vegetation and the climate of Lamto have been studied for more than twenty years. The emission ratios (X/CO₂) of the carbon compounds (CO₂, CO, NMHC, CH₄, PAH, organic acids and aerosols), nitrogen compounds (NO_x, N₂O, NH₃ and soluble aerosols) and sulfur compounds (SO₂, COS and aerosols) were experimentally determined by ground and aircraft measurements. To perform this experiment, 4 small plots (100×100 m) and 2 large areas (10×10 km) were prepared and burnt in January 1991 during the period of maximum occurrence of fires in this type of savanna. The detailed ecological study shows that the carbon content of the vegetation is constant within 1% (42 g C for 100 g of vegetal dry matter), the nitrogen content (0.29 g N for 100 g of dry matter) may vary by 10% and the sulfur content (0.05 g S/100 d.m.) by 20%. These variations of the biomass chemical content do not constitute an important factor in the variation of the gas and particle emission levels. With the emission ratios characteristic of humid savanna and flaming conditions (CO/CO₂ of 6.1% at the ground and 8% for airborne measurements), we propose a set of new emission factors, taking into account the burning efficiency which is about 80%: 74.4% of the carbon content of the savanna biomass is released to the atmosphere in the form of CO₂, 4.6% as CO, 0.2% as CH₄, 0.5% as NMHC and 0.7% as aerosols. 17.2% of the nitrogen content of the biomass is released as NO_x, 3.5% as N₂O, 0.6% as NH₃ and 0.5% as soluble aerosols.     

Calculation of velocity skewness in real and artificial plant canopies

Wind velocities within a plant canopy are much more strongly skewed than those of the air flow above. We have examined the governing Eulerian equations for the velocity products u _i, u _j u_k using data from a wind tunnel study with an artificial canopy consisting of an array of 5 cm lengths of monofilament fishing line, and from measurements in corn (Zea mays L).Simple parameterizations for pressure-velocity correlations, and for the quadruple velocity products allowed reasonably accurate calculations of the third moments using measured profiles of the mean velocity, variance and covariance fields. Comparisons of individual terms in the rate equations for ovu _i, u _j u _krevealed that diffusion (from above) and mean shear were most important in creating large skewness in the canopy. A drag term also contributed but was of lesser importance. These terms were balanced by return-to-isotropy and a turbulence interaction term. A quasi-Gaussian approximation considerably underestimated the magnitude of the fourth moments within the canopy.     

Sensitivity Analysis of Emissions Corridors for the 21st Century

We investigate the sensitivity of emissions corridors for the 21st century to various factors that are currently under debate in the climate change arena. Emissions corridors represent the range of admissible emissions futures that observe some predefined guardrails on the future development of the human-climate system. They are calculated on the conceptual and methodological basis of the tolerable windows approach. We assess the sensitivity of the corridors to the choice of time-resolved as well as intertemporally aggregated guardrails that exclude an intolerable amount of climate change on the one hand and unbearable mitigation burdens on the other. In addition, we investigate the influence of climate sensitivity on the corridors.Results show a large dependence of emissions corridors on the choice of guardrails and the value of climate sensitivity T _{2CO 2}. If the guardrail on climate change is specified in terms of a maximum admissible global mean temperature increase T _max to be observed at any time, the size of the corridors is predominantly determined by a climate impact resilience parameter =T _max/T _{2CO 2}. As is varied from values below 0.5 to values above 1.5, we move from cases where no emissions profile whatsoever can observe all guardrails, to cases where no significant emissions reduction seems necessary given the range of emissions scenarios for the 21st century. The limits on admissible mitigation efforts influence predominantly the timing and the economic viability of emissions reductions. A large mitigation flexibility allows for wait then run emissions paths, while low flexibility asks for a significantly more prudent approach.     

Carbonyl sulfide emissions from biomass burning in the tropics

Carbonyl sulfide emissions from biomass burning have been studied during field experiments conducted both in an African savanna area (Ivory Coast) and rice fields, central highland pine forest and savanna areas in Viet-Nam. During these experiments CO₂, CO and C₂H₂ or CH₄ have also been also monitored. COS values range from 0.6 ppbv outside the fires to 73 ppbv in the plumes. Significant correlations have been observed between concentrations of COS and CO (R ²=0.92,n=25) and COS and C₂H₂ (R ²=0.79,n=26) indicating a COS production during the smoldering combustion. COS/CO₂ emission factors (COS/CO₂) during field experiments ranged from 1.2 to 61×10^–6 (11.4×10^–6 mean value). COS emission by biomass burning was estimated to be up to 0.05 Tg S/yr in tropics and up to 0.07 Tg S/yr on a global basis, contributing thus about 10% to the global COS flux. Based on the S/C ratio measured in the dry plant biomass and the COS/CO₂ emission factor, COS can account for only about 7% of the sulfur emitted in the atmosphere by biomass burning.     

Numerical studies of heat island circulations

A two dimensional model has been set up to investigate the circulation induced by an urban heat island in the absence of synoptic winds. The boundary conditions need to be formulated carefully and due to difficulties arising here, we restrict our attention to cases of initially stable thermal stratification. Heat island circulations are allowed to develop from rest and prior to the appearance of the final symmetric double cell pattern, a transitional multi-cell pattern is observed in some cases. The influence on the steady state circulation of various parameters is studied, among which are eddy transfer coefficients, the heat island intensity, the initial temperature stratification and the heat island size. Some results are presented for a case in which differential surface cooling beneath an initially stable atmosphere produces a circulation and an unstable layer capped by an elevated inversion over the city. It is hoped that this case is vaguely representative of the night-time heat island with no geostrophic wind.Notation c_p Specific heat at constant pressure - g Acceleration due to gravity - H Top of integration region - K_z Vertical eddy transfer coefficient - K_x, K_xH, K_xm Horizontal eddy transfer coefficients for heat and momentum - l ixing length - p Pressure - p₀ Reference surface pressure (1000 mb) - P_H (x, t) Pressure at z = H - R Specific gas constant for dry air - t Time - u, w Horizontal and vertical velocities - x, z Horizontal and vertical coordinates - x₁, x₂ Positions of discontinuities in surface temperature field (see Figure 2) - x_a Heat island half-width - x_b Boundary of integration region - Parameter in formula for eddy coefficients (variable-K case) = 18.0 - _s Intensity of heat island - Potential temperature field - Reference absolute temperature (variable-K case) - _r Reference temperature (° C) - _s Surface temperature - Q Air density     

On the similarity in atmospheric fluctuations of carbon dioxide,water vapor and temperature over vegetated fields

This paper describes the similarity between atmospheric fluctuations of carbon dioxide, water vapor and temperature using data which cover a wide range of instability (0.02 < < 10). The is the Monin-Obukhov stability parameter including the humidity effect.The spectral analysis shows that the coherency between fluctuations of carbon dioxide and water vapor or temperature is very close to unity, and the phase difference is basically out of phase for whole frequency ranges analyzed. The stability dependence of the normalized standard deviation of carbon dioxide is very similar to those of water vapor and temperature. The normalized standard deviation is about 2.5 under near neutral conditions, and it decreases with increasing instability following the -1/3; power law as (-)^-1/3. The skewness factors of carbon dioxide, water vapor and temperature show a systematic departure with increasing instabilities for 0.02 < s- < 1, and level off at high instabilities for 1 < -\s < 10. The stability dependence of the flatness factors is not so clear as that noted in the standrard deviation and skewness factors. Dissipation rates of carbon dioxide, water vapor and temperature variance are well related to the spectral peak wavelength. This seems to be real since the local production and local dissipation rates are the main terms, almost balancing one another in the variance budget equations for scalar entities.     

Turbulence characteristics in a near neutrally stratified urban atmosphere

Turbulence measurements from the city of Uppsala, Sweden, are analysed. Measurements were taken at two sites: one in the central area, ca. 6 m above roof level, the average building height being ca. 15 m; the other at ca. 8 and 50 m above the ground on a tower situated 100 m downwind of a sharp discontinuity between the densely built-up urban area and flat grass-covered land. The average stability was close to neutral, the range being -0.2 < z/L < 0.2. The main emphasis of the study is on the non-dimensional standard deviations of the velocity components _i /u _*t and on the corresponding non-dimensional energy spectra, u _*t being a local velocity scale defined as _i /( _l is the local momentum flux). Comparison with results obtained from surface-layer measurements at ideal sites (with u _*, being the ordinary friction velocity) shows good general agreement. The most complete agreement is found for the tower 50 m measurements, a result which is notable as this measurement point is found to be within a distinctly transitional zone between the urban and post-urban boundary layers. The results from the central city measurement point are also fairly close to the ideal results, the deviations found being small in view of the fact that the site is probably inside the layer in which the roughness elements (the buildings) have direct influence. The measurements at the tower 8 m level show certain distinct deviations from ideal results: all three _i /u _*l , are higher by ca. 10%, the excessive energy being found at the low frequency end of the spectrum. Arguments are presented for this feature to be due to a spectral lag effect.     

On the enhanced smoothing over topography in some mesometeorological models

An equation is derived for the components of the horizontal (turbulent) frictional force in the -coordinate system with special attention to mesometeorological flow models. The starting point is the horizontal equation of motion in its flux-form in the -system in which we replace (following Reynolds' procedure) the velocity components u,v and % MathType!MTEF!2!1!+- % feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGafq4WdmNbai % aaaaa!37B8! \[ \dot \sigma \] aswell as other relevant quantities by terms of the form u = + u,..., = ± + % MathType!MTEF!2!1!+- % feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGafq4WdmNbai % Gbauaaaaa!37C3! \[ \dot \sigma ' \] , etc. ( = time average of u; u = fluctuating part of u.) Next, the equation is averaged with respect to time and terms which we believe are small in mesometeorological flows, are neglected. On expressing by an appropriate expression that involves w, the result shows the appearance of two new terms which, have not been considered previously in the published literature. While the expression earlier used in the literature involved the -derivative of % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWaa0aaaeaace% WG1bGbauaaceWG3bGbauaaaaaaaa!380B!\[\overline {u'w'} \] alone, the new terms add the -derivatives of % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWaa0aaaeaace% WG1bGbauaadaahaaWcbeqaaiaaikdaaaaaaaaa!37EC!\[\overline {u'^2 } \] and % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWaa0aaaeaace% WG1bGbauaaceWG2bGbauaaaaaaaa!380A!\[\overline {u'v'} \] for the x-component of the force, and the -derivatives of % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWaa0aaaeaace% WG2bGbauaadaahaaWcbeqaaiaaikdaaaaaaaaa!37ED!\[\overline {v'^2 } \]} and % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWaa0aaaeaace% WG1bGbauaaceWG2bGbauaaaaaaaa!380A!\[\overline {u'v'} \] for the y-component, where and are the slopes of the -surfaces in the x- and y-directions, respectively. Further, a few numerical simulations of the sea-breeze over topography are carried out with and without the correction terms. It is shown that when corrections terms are not included the effective smoothing is stronger above the sloping regions and may amount to as high as 50 percent of the convergence with slopes of ~.04. The ìnclusìon of the new terms does not lead to any special computational difficulties and for that reason there is no compelling reason to neglect them, all the more so because, as is shown, the addition of the new terms results in a consistent apportioning of the degree of horizontal diffusion.On leave from CIMMS, Norman, OK.Now visiting Dept. of Met., Helsinki, Finland.     

On the mean monthly equivalent potential temperature and rainfall in West Africa

Summary Rainfall in West Africa is examined in relation to monthly mean equivalent potential temperature ( _e )at the earth's surface. The study revealed that monthly mean equivalent potential temperature ( _e ) and monthly rainfall (R) generally decreased northwards from the equator.A good relationship existed betweenR and _e in the northern zone of West Africa (i.e., north of 7.5° N). No definite relationship existed in the southern zone. In the northern zone, the departure of _e from its annual mean ( ) first became positive about a month before the onset of the rains. Positive departures from ) generally resulted in more than normal (or average) rainfall in this zone. In general, little or no rainfall occurred in West Africa whenever _e was less than 320 K.

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Zusammenfassung Der Niederschlag (MonatssummeR) in Westafrika wird in Zusammenhang mit der mittleren monatlichen Äquivalent-temperatur ( _e ) an der Erdoberfläche untersucht. Es zeigte sich, daß die Monatswerte beider Elemente im allgemeinen vom Äquator nach Norden abnehmen.ZwischenR und _e ergab sich für das nördliche Westafrika (nördlich von 7.5° N) eine gute, für die südliche Zone jedoch keine beweisbare Übereinstimmung. In der nördlichen Zone übertraf _e das Jahresmittel erstmals etwa einen Monat vor Beginn der Regenzeit. Positive Abweichungen vom mittleren _e hatten immer übernormalen Niederschlag in dieser Zone zur Folge. Dagegen gab es wenig oder keinen Niederschlag in Westafrika, wenn _e unter 320 K lag.

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With 7 Figures     

Australian public perception of the greenhouse issue

During 1987 and 1988 in Australia there have been two national meetings on the greenhouse effect and a campaign designed to increase public awareness. A study of the backgrounds, level of comprehension and attitudes of attendees at two state Greenhouse-88 meetings has been undertaken by means of a questionnaire survey and a set of personal interviews. Two crucial caveats pertain: (1) some of the questions reflect the prejudices of the author who is an atmospheric scientist and much of the interpretation is similarly tainted and (2) the respondents comprise a small, self-selected and probably highly motivated group. All the ensuing results should be viewed in the context of these caveats.Over 97% of the respondents believe that action should be taken now to alleviate or mitigate the effects of increased greenhouse gases. Despite the fact that the majority of the 321 respondents are professional people (73%) and that over 53% have tertiary level educational qualifications, there was a failure to grasp some fundamental issues. For example, only 120 (37%) correctly recognized that N₂ is not a greenhouse agent whilst also agreeing that CO₂, CH₄ and CFCs are greenhouse agents. On the other hand, the respondents generally demanded a relatively low level of confidence (50% to 70% certainty) about the greenhouse issue from scientists before action is taken. Sixty-four percent believe that life will be worse for them and/or their children in Australia in Greenhouse 2025 with the youngest age range being the second most pessimistic group about the future.Relatively little interest was shown in the possibility of obtaining more information on topics that interest climatic scientists such as the validity of measured temperature trends and inadequacies/errors in climate models but more information was desired on the social and economic implication and, interestingly, on the scientific background to the issues. Overall, teachers are perceived as trying to increase understanding; whereas politicians, multinational corporations, the media and some extreme environmentalists are perceived as often attempting to deceive intentionally. Scientists are seen as neither especially malevolent nor benign. A possible conclusion which might be drawn is that by attempting to simplify issues for public debate, scientists may significantly reduce, or even remove entirely, any chance of re-association of connected issues by members of the public. Perhaps more importantly, scientists need to recognize and learn to use the knowledge that the public may have the right views for the wrong reasons.     

Stability functions correct at the free convection limit and consistent for for both the surface and Ekman layers

For the thermal stability function _h used to calculate heat and moisture fluxes in the surface layer, we choose a formulation which has the theoretically correct free convection limit % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaaeikaiabgk% HiTGqaciaa-PhacaqGVaGaamitaiaabMcadaahaaWcbeqaaiabgkHi% TiaaigdacaGGVaGaaG4maaaaaaa!3DFE!\[{\rm{(}} - z{\rm{/}}L{\rm{)}}^{ - 1/3} \]. We then use the experimental result that z/L Ri to deduce a formulation with an exponent -1/6 for the momentum stability function _m. This formulation also resolves the matching problem at the interface between the surface and Ekman layers. The proposed functions are found to remain reasonably close to another formulation that is well supported by observations and has exponents -1/2 for _h and -1/4 for _m. The intent of the proposals is mainly to clarify and simplify the parameterization of the convective boundary layer in present day atmospheric models, without significantly altering the results.     

The spectral velocity tensor for homogeneous boundary-layer turbulence

We have postulated a simple model for the spectral tensor _ij (k) of an anisotropic, but homogeneous turbulent velocity field. It is a simple generalization of the spectral tensor _inf ^{ij piso}(k) for isotropic turbulence and we show how in the limit of isotropy, _ij (k) becomes equal to _inf ^{ij piso}(k). Whereas _inf ^{ij piso}(k) is determined entirely by one scalar function of k = ¦k¦, namely the energy spectrum, we need three independent scalar functions of k to specify _ij (k). We show how it is possible by means of the three stream-wise velocity component spectra to determine the three scalar functions in _ij (k) by solving two uncoupled, ordinary linear differential equations of first and second order. The analytic form of the component spectra each has a set of three parameters: the variance and the integral length scale of the velocity component and a dimensionless parameter, which governs the curvature of the spectrum in the transition domain from the inertial subrange towards lower wave numbers. When the three sets of parameters are the same, the three spectra correspond to isotropic turbulence and they are all interrelated and related to the energy spectrum. We show how it is possible to obtain these spectral forms in the neutral surface layer and in the convective boundary layer from data reported in the literature. The spectral tensor is used to predict the lateral coherences for all three velocity components and these predictions are compared with coherences obtained in two experiments, one using three masts at a horizontally homogeneous site in Denmark and one employing two aircraft flying in formation over eastern Colorado. Comparison shows reasonable agreement although with considerable experimental scatter.The National Center for Atmospheric Research is sponsored by the National Science Foundation.