Reactions of alkoxy radicals under atmospheric conditions: The relative importance of decomposition versus reaction with O2

The reactions of alkoxy radicals determine to a large extent the products formed during the atmospheric degradations of emitted organic compounds. Experimental data concerning the decompositions, 1,5-H shift isomerizations and reactions with O₂ of several classes of alkoxy radicals are inconsistent with literature estimations of their absolute or relative rate constants. An alternative, although empirical, method for assessing the relative importance under atmospheric conditions of the reactions of alkoxy radicals with O₂ versus decomposition was derived. This estimation method utilizes the differences in the heats of reaction, (H)=(H_{decomposition}–H_{O 2 reaction}), between these two reactions pathways. For (H)[22–0.5(H_{O 2 reaction})], alkoxy radical decomposition dominates over the reaction with O₂ at room temperature and atmospheric pressure of air, while for (H)[25-0.5(H_{O 2 reaction})], the O₂ reaction dominates over decomposition (where the units of H are in kcal mol^–1). The utility and shortcomings of this approach are discussed. It is concluded that further studies concerning the reactions of alkoxy radicals are needed.     

Diurnal variation of horizontal wind direction fluctuations in complex terrain at Geysers,Cal.

Horizontal diffusion in the surface layer is dependent on the standard deviation of wind direction fluctuations . Diurnal variation of this parameter in complex terrain was studied for the July 1979 Geysers, Cal., experiment using data from a network of 11 short meteorological towers in the 25 km² Anderson Creek watershed Valley side slopes are roughly 20 ° and maximum terrain difference is about 1 km.Values of for wind directions sampled for one hour at a height of 10 m are about 35 ° during the daytime. They slowly decrease to about 20 ° by 8 to 10 p.m. as stability increases but wind speeds are still relatively high. After 10 p.m. the drainage flow sets in at most stations, with speeds of 1 to 2 m s^-1, and average increases to about 30° during the period 11 p.m. to 6 a.m. In general, highest values of at night are associated with lowest values of wind speed and greatest static stability. This enhancement of by the terrain suggests that horizontal diffusion at night always conforms to that expected during nearly neutral stabilities. That is, Pasquill class D diffusion applies to the horizontal component all night in complex terrain.     

Averaging Intervals For Spectral Analysis Of Nonstationary Turbulence

We formulate a method for determining the smallest time interval Tover which a turbulence time series can be averaged to decompose it intoinstantaneous mean and random components. From the random part the method defines the optimal interval (or averaging window) AW over which this part should be averaged to obtain the instantaneous spectrum. Both T and AW vary randomly with time and depend on physical properties of the turbulence. T also depends on the accuracy of the measurements and is thus independent of AW. Interesting features of the method are its real-time capability and the non-equality between AW and T.     

Reconstruction of the ice winter severity since 1701 in the Western Baltic

This reconstruction of the ice winter severity in the Western Baltic is based for the period 1878-1993 on the accumulated areal ice volume along the German Baltic coast with observations from 13 coastal stations; for the period 1701-1877 it is based on the accumulated areal ice volume divided into 7 classes (ice winter severity types). The various types of data consulted in the latter case provided ice data of good spatial and temporal resolution.Speerschneider's compilation of data relating to ice conditions in Danish Baltic waters was found to be a valuable source of information. Using a classification table for the periods 1907-1943 and 1947-1992, five of the seven ice winter types have been derived with certainty as they are characterized by typical stages of maximum ice cover throughout the Western Baltic.The Gaussian lowpass-filtered time series of the ice winter index numerals with a 20 year cutoff period shows four periods of varying ice winter severity over a secular range: 1701-1720: slightly increased ice winter severity with regard to the mean of the 1701-1993 time series; this period can be assigned to the end of a cooling phase during Little Ice Age which in central Europe peaked in the second half of the 17th c. 1721-1760: ice winter severity is clearly reduced in this period. 1761-1860: ice winter severity is clearly increased (maximum occurs around 1800) towards the end of the Little Ice Age, associated with increased variability of ice production. 1861-1993: the present-day ice winter regime when three short intervals with increased ice winter severity (the 1890s, 1940s and 1980s) and a period of greatly reduced ice winter severity (between 1900 and the mid-1920s) stand out.     

Free convection scaling over the ocean derived from buoy measurements during gate

The structure of atmospheric turbulence in the surface layer over the open ocean is examined under conditions of local free convection. The raw data consist of profile and fluctuation measurements of wind and temperature as obtained from a meteorological buoy. For near neutral conditions and for waves running approximately along the wind direction, wave-induced wind fluctuations can be described by a simplified linear theory based on Miles (1957). In this case, the spectrum of wind velocity is given as the sum of two parts; for the turbulent part, the parameterization as obtained by Kaimal et al. (1972) applies, while the wave-induced part is parameterized using a simplification of Miles' linear theory. For cases of local free convection, the measurements of the vertical component of the wind velocity are well described by similarity theory; as expected, _w /(-uw)^1/2 is proportional to (- z/L)^1/3. In order to scale the longitudinal wind velocity component, it seems to be reasonable to extend the list of relevant parameters by the height of the mixed layer z _i. We obtain _u /(- uw)^1/2 (z/z _i)^1/3(- z/L)^1/3 with only a poor correlation coefficient of r = 0.6. Overall, the results of local free convection scaling obtained from direct measurements show good agreement with those obtained from profile measurements. A comparison between direct and indirect determination of turbulent fluxes of momentum shows an unexplained difference of about 20%. This discrepancy is mainly due to a gap in the uw-cospectrum at the swell frequency.     

Small-Scale Variability in the Coastal Atmospheric Boundary Layer

The influence of the main large-scale wind directions on thermally driven mesoscale circulations at the Baltic southwest coast, southeast of Sweden, is examined. The aim of the study is to highlight small-scale alterations in the coastal atmospheric boundary layer. A numerical three-dimensional mesoscale model is used in this study, which is focused on an overall behaviour of the coastal jets, drainage flows, sea breezes, and a low-level eddy-type flow in particular. It is shown that synoptic conditions, together with the moderate terrain of the southeast of Sweden (max. height h₀ 206 m), governs the coastal mesoscale dynamics triggered by the land-sea temperature difference T. The subtle nature of coastal low-level jets and sea breezes is revealed; their patterns are dictated by the interplay between synoptic airflow, coastline orientation, and T.The simulations show that coastal jets typically occur during nighttime and vary in height, intensity and position with respect to the coast; they interact with downslope flows and the background wind. For the assigned land surface temperature (varying ±8 K from the sea temperature) and the opposing constant geostrophic wind 8 m s^-1, the drainage flow is more robust to the opposing ambient flow than the sea breeze later on. Depending on the part of the coast under consideration, and the prevailing ambient wind, the sea breeze can be suppressed or enhanced, stationary at the coast or rapidly penetrating inland, locked up in phase with another dynamic system or almost independently self-evolving. A low-level eddy structure is analyzed. It is governed by tilting, divergence and horizontal advection terms. The horizontal extent of the coastal effects agrees roughly with the Rossby radius of deformation.     

On the inner-layer scale height of boundary-layer flow over low hills

Jackson and Hunt's (1975) equation for the depth of the inner layer of flows over low hills does not depend on any closure assumption as contrarily supposed in literature. This equation contains a constant which can arbitrarily be specified. It is suggested that this inner-layer constant should be determined from experimental data. A preliminary check with some data from the Askervein experiment suggests that Jackson and Hunt's equation fits these data almost as well as Jensen's equation provided that fitted inner-layer constants are used.     

Robust estimation of background noise and signal detection in climatic time series

We present a new technique for isolating climate signals in time series with a characteristic red noise background which arises from temporal persistence. This background is estimated by a robust procedure that, unlike conventional techniques, is largely unbiased by the presence of signals immersed in the noise. Making use of multiple-taper spectral analysis methods, the technique further provides for a distinction between purely harmonic (periodic) signals, and broader-band (quasiperiodic) signals. The effectiveness of our signal detection procedure is demonstrated with synthetic examples that simulate a variety of possible periodic and quasiperiodic signals immersed in red noise. We apply our methodology to historical climate and paleoclimate time series examples. Analysis of a 3 million year sediment core reveals significant periodic components at known astronomical forcing periodicities and a significant quasiperiodic 100 year peak. Analysis of a roughly 1500 year tree-ring reconstruction of Scandinavian summer temperatures suggests significant quasiperiodic signals on a near-century timescale, an interdecadal 16–18 year timescale, within the interannual El Niño/Southern Oscillation (ENSO) band, and on a quasibiennial timescale. Analysis of the 144 year record of Great Salt Lake monthly volume change reveals a significant broad band of significant interdecadal variability, ENSO-timescale peaks, an annual cycle and its harmonics. Focusing in detail on the historical estimated global-average surface temperature record, we find a highly significant secular trend relative to the estimated red noise background, and weakly significant quasiperiodic signals within the ENSO band. Decadal and quasibiennial signals are marginally significant in this series.     

Carbon dioxide emissions in a methane economy

Increasing reliance on natural gas (methane) to meet global energy demands holds implications for atmospheric CO₂ concentrations. Analysis of these implications is presented, based on a logistic substitution model viewing energy technologies like biological species invading an econiche and substituting in case of superiority for existing species. This model suggests gas will become the dominant energy source and remain so for 50 years, peaking near 70 percent of world supply. Two scenarios of energy demand are explored, one holding per capita consumption at current levels, the second raising the global average in the year 2100 to the current U.S. level. In the first (efficiency) scenario concentrations peak about 450 ppm, while in the second (long wave) they near 600 ppm. Although projected CO₂ concentrations in a methane economy are low in relation to other scenarios, the projections confirm that global climate warming is likely to be a major planetary concern throughout the twenty-first century. A second finding is that data on past growth of world per capita energy consumption group neatly into two pulses consistent with longwave theories in economics.     

Estimates of diabatic wind speed profiles from near-surface weather observations

In this paper we analyse diabatic wind profiles observed at the 213 m meteorological tower at Cabauw, the Netherlands. It is shown that the wind speed profiles agree with the well-known similarity functions of the atmospheric surface layer, when we substitute an effective roughness length. For very unstable conditions, the agreement is good up to at least 200 m or z/L–7(z is height, L is Obukhov length scale). For stable conditions, the agreement is good up to z/L1. For stronger stability, a semi-empirical extension is given of the log-linear profile, which gives acceptable estimates up to ~ 100 m. A scheme is used for the derivation of the Obukhov length scale from single wind speed, total cloud cover and air temperature. With the latter scheme and the similarity functions, wind speed profiles can be estimated from near-surface weather data only. The results for wind speed depend on height and stability. Up to 80 m, the rms difference with observations is on average 1.1 m s^–1. At 200 m, 0.8 m s^–1 for very unstable conditions increasing to 2.1 m s^–1 for very stable conditions. The proposed methods simulate the diurnal variation of the 80 m wind speed very well. Also the simulated frequency distribution of the 80 m wind speed agrees well with the observed one. It is concluded that the proposed methods are applicable up to at least 100 m in generally level terrain.     

Transport-Dissipation Analytical Solutions to the E-∈Turbulence Model and their Role in Predictions of the Neutral ABL

E- turbulence model predictions of the neutralatmospheric boundary layer (NABL) are reinvestigated to determine thecause for turbulence overpredictions found in previous applications. Analytical solutions to the coupled E and equations for the case of steady balance between transport and dissipation terms, the dominant balance just below the NABL top, are derived. It is found that analytical turbulence profiles laminarizeat a finite height only for values of closure parameter ratio c ₂ /_e equal toor slightly greater than one, with laminarization as z for greater . The point = 2 is additionally foundthat where analytical turbulent length scale (l) profilesmade a transition from ones ofdecreasing ( < 2) to increasing ( > 2)values with height. Numerically predicted profiles near the NABL topare consistent with analytical findings. The height-increasingvalues of l predicted throughout the NABL with standard values ofclosure parameters thus appear a consequence of 2.5(> 2), implied by these values (c ₂ = 1.92, _{= 1.3}, _{e = 1}). Comparison of numericalpredictions with DNS data shows that turbulence overpredictions obtained with standard-valued parameters are rectifiedby resetting and _e to 1.1 and 1.6, respectively, giving, with c ₂ = 1.92, 1.3, and laminarization of the NABL's cappingtransport-dissipation region at a finite height.     

Numerical integration errors in calculated tropospheric photodissociation rate coefficients

Tropospheric photodissociation rate coefficients (J values) were calculated for NO₂, O₃, HNO₂, CH₂O, and CH₃CHO using high spectral resolution (0.1 mm wavelength increments), and compared to the J values obtained with numerically degraded resolution (=1, 2, 4, 6, 8, and 10 nm, and several commonly used nonuniform grids). Depending on the molecule, substantial errors can be introduced by the larger increments. Thus for =10 nm, errors are less than 1% for NO₂, less than 2% for HNO₂, +6.5% to -16% for CH₂O, -6.9% to +24% for CH₃CHO, and -24% to +110% for O₃. The errors for CH₂O arise from the fine structure of its absorption spectrum, and are prevalently negative (underestimate of J). The errors for O₃, and to a lesser extent for CH₃CHO, arise mainly from under-resolving the overlap of the molecular action spectrum and the tropospheric actinic flux in the wavelength region of stratospheric ozone attenuation. The sign of those errors depends on whether the actinic flux is averaged onto the grid before or after the radiative transfer calculation. In all cases studied, grids with 2 nm produced errors no larger than 5%.     

Eddy energy dissipation rate and puff diffusion during calms

The paper considers a puff diffusion in its inertial stage when particle separation obeys the laws of the inertial subrange and depends only on eddy energy dissipation rate . The can be determined in the surface layer by the turbulent kinetic energy equation. Similarity equations connect with diffusion measure .A simple analytical model has been deduced to estimate pollutants diffusion during calms.     

The wind regime in coastal areas with special reference to results obtained from the Swedish wind energy program

The paper describes various aspects of the wind regime in coastal areas as obtained from several experimental programs along the Baltic coast of Sweden. The studies include the change with distance inland of mean wind structure as well as the turbulence structure in various conditions. It is found that wind spectra are usually well described by local similarity in its high frequency part, even in complex terrain. The low frequency parts of the spectra show clear spectral lag effects. The effects of a small slope, ca 5 m height change over 300 m travel distance, is clearly seen in some spectra, and it is shown that current flow over a hill theory can be used to account for it. The change of mean wind speed throughout the entire boundary layer as the wind passes a low but wooded island (Gotland), ca 30 km wide, has been studied in a series of relatively strong wind, near neutral cases. Some unexpected features are found; in particular the wind speed decreases more rapidly with distance inland than predicted by current numerical models. Two cases with a low level jet are discussed in some detail. Arguments are presented for the phenomenon to be caused by frictional decoupling at the Latvian coast, about 200 km upwind — the jet being thus an analogy in space to the classical Blackadar nocturnal jet frequently observed in continental areas.     

A Comparative Analysis of Transpiration and Bare Soil Evaporation

Transpiration E^v and bare soil evaporation E^b processes are comparatively analysed assuming homogeneous and inhomogeneous areal distributions of volumetric soil moisture content . For a homogeneous areal distribution of we use a deterministic model, while for inhomogeneous distributions a statistical-deterministic diagnostic surface energy balance model is applied. The areal variations of are simulated by Monte-Carlo runs assuming normal distributions of .The numerical experiments are performed for loam. In the experiments we used different parameterizations for vegetation and bare soil surface resistances and strong atmospheric forcing. According to the results theE^v()-^Eb() differences are great, especially in dry conditions. In spite of this, the available energy flux curves of vegetation A^v() and bare soil A^b() surfaces differ much less than the E^v() and ^Eb() curves. The results suggest that E^v is much more non-linearly related to environmental conditions than ^Eb. Both E^v and ^Eb depend on the distribution of , the wetness regime and the parameterization used. With the parameterizations, ^Eb showed greater variations than E^v. These results are valid when there are no advective effects or mesoscale circulation patterns and the stratification is unstable.     

The carbon isotopic ratio of atmospheric carbon dioxide at Tsukuba,Japan

To find out the secular and seasonal trends of the ¹³C value and CO₂ concentration in the surface air and the determination of the ¹³C in the atmospheric CO₂ collected at Tsukuba Science City was carried out during the period from July 1981 to October 1983. The monthly average of the ¹³C value of CO₂ in the surface air collected at 1400 LMT ranged from -7.52 to \s-8.45 with an average of -7.96±0.25 and the CO₂ concentration in the air varied from 334.5 l 1^-1 to 359 l 1^-1 with an average of 347.2±6.3 l 1^-1. The ¹³C value is high in summer and low in winter and is negatively correlated with the CO₂ concentration. In general, the relationship between the ¹³C and the CO₂ concentration is explainable by a simple mixing model of two different constant carbon isotopic species but the relationship does not always follow the model. The correlation between the ¹³C value and the CO₂ concentration is low during the plant growth season and high at other times. The observed negative deviation of the ¹³C value from the simple mixing model in the plant growth season is partly due to the isotopic fractionation process which takes place in the land biota.     

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.     

Modeling the earth's climate

Mathematical models of the earth's climate provide intriguing opportunities to study a wide range of interdisciplinary problems involving processes within the climate system in a controlled and systematic manner. This paper is intended as a nontechnical review of climate modeling to enable researchers who are unfamiliar with the topic to better evaluate and judge the credibility of the model results. The types of climate models available for climate research are reviewed here, and four broad categories of climate models are identified. These range from the more simple energy balance models (EBMs) and radiative-convective models (RCMs), to the more complex statistical-dynamical models (SDMs), to the most powerful tools yet available for studying climate, the general circulation models (GCMs). This last category includes gridpoint and spectral GCMs. Four representations of the oceans which can be coupled to GCMs are described and include prescribed sea surface temperatures, an energy balance or swamp ocean, a mixed layer or slab ocean, or a fully computed ocean general circulation model. Selected examples considered representative of the types of studies possible with the various classes of models are given. Taken together, the spectrum of climate models provides a hierarchy of learning and research tools with which to effectively study the extremes of past climates, the vagaries of present-day climate, and possible climatic fluctuations well into the future.The National Center for Atmospheric Research is sponsored by the National Science Foundation.     

Three-dimensional modeling of synthetic cold fronts interacting with northern Alpine foehn

Summary The effect of the Alpine orography on prototype cold fronts approaching from the west is investigated by three-dimensional numerical model simulations. The numerical experiments cover a range of parameter constellations which govern the prefrontal environment of the front. Especially, the appearance and intensity of prefrontal northern Alpine foehn varies from case to case.The behaviour of a cold front north of the Alps depends much on the prefrontal condition it encounters. It is found that prefrontal foehn can either accelerate or retard the approaching front.An important feature is the pressure depression along the northern Alpine rim that results from the southerly foehn flow. In cases where this depression compensates the eastward directed pressure gradient associated with the largescale flow, the front tends to accelerate and the foehn breaks down as soon as the front passes. In contrast, the foehn prevents the front from a rapid eastward propagation if it is connected with a strong southerly wind component.No-foehn experiments are performed for comparison, where either the mountains are removed, or the static stability is set to neutral. Also shown are effects of different crossfrontal temperature contrasts.List of Symbols c _F propagation speed of a front - x, y horizontal grid spacing (cartesian system) - , horizontal grid spacing (geographic system) - t time step - z vertical grid spacing (cartesian system) - cross-frontal potential temperature difference - _i potential temperature step at an inversion - E turbulent kinetic energy - f Coriolis parameter - FGP frontogenesis parameter (see section 2.2) - g gravity acceleration (g=9.81 m s^–2) - vertical gradient of potential temperature - h terrain elevation (above MSL) - h _i height of an inversion (h _i =1000 m MSL) - H height of model lid (H=9000 m MSL) - K _M exchange coefficient of momentum - K _H exchange coefficient of heat and moisture - longitude - N Brunt-Väisäla-frequency - p pressure - Exner function (=T/) - latitude - q _v specific humidity - R _d gas constant of dry air (R _d =287.06 J kg^–1 K^–1) - density of dry air - t time - T temperature - potential temperature - TFP thermal front parameter (see section 2.2) - u, v, w cartesian wind components - u _g ,v _g geostrophic wind components - horizontal wind vector - x, y, z cartesian coordinates Abbreviations GND (above) ground level - MSL (above) mean sea level - UTC universal time coordinated With 20 Figures     

The effect of synoptic-scale advection on the performance of the Priestley-Taylor evaporation formula

Measurements of the appropriate parameters for the calculation of the latent heat flux over a black spruce forest in northern Quebec were carried out in August, 1980. Values of the Priestley-Taylor parameter, , were derived by exploiting the Bowen-ratio-energy-balance (BREB) technique. Derived values of are then related to synoptic-scale warm air advection, derived from surface synoptic charts and tephigrams of the planetary boundary layer. It is found that when warm air advection is present, > 1.26, especially when the surface is wet. When advection enhancement is removed, however, values of approach unity. A new approach to calculating the latent heat flux, when warm air advection is present, is therefore proposed.