Surface Energy Balance Measurements Above an Exurban Residential Neighbourhood of Kansas City,Missouri

Previous measurements of urban energy balances generally have been limited to densely built, central city sites and older suburban locations with mature tree canopies that are higher than the height of the buildings. In contrast, few data are available for the extensive, open vegetated types typical of low-density residential areas that have been newly converted from rural land use. We made direct measurements of surface energy fluxes using the eddy-covariance technique at Greenwood, a recently developed exurban neighbourhood near Kansas City, Missouri, USA, during an intensive field campaign in August 2004. Energy partitioning was dominated by the latent heat flux under both cloudy and near clear-sky conditions. The mean daytime Bowen ratio (β) values were 0.46, 0.48, and 0.47 respectively for the cloudy, near clear-sky and all-sky conditions. Net radiation (R _n ) increased rapidly from dawn (−34 and −58W m⁻²) during the night to reach a maximum (423 and 630W m⁻²) after midday for cloudy and near clear-sky conditions respectively. Mean daytime values were 253 and 370W m⁻², respectively for the cloudy and near clear-sky conditions, while mean daily values were 114 for cloudy and 171W m⁻² for near clear-sky conditions, respectively. Midday surface albedo values were 0.25 and 0.24 for the cloudy and near clear-sky conditions, respectively. The site exhibited an angular dependence on the solar elevation angle, in contrast to previous observations over urban and suburban areas, but similar to vegetated surfaces. The latent heat flux (Q _E ), sensible heat flux (Q _H ), and the residual heat storage ΔQ _s terms accounted for between 46–58%, 21–23%, and 18–31% of R _n , respectively, for all-sky conditions and time averages. The observed albedo, R _n , and Q _E values are higher than the values that have been reported for suburban areas with high summer evapotranspiration rates in North America. These results suggest that the rapidly growing residential areas at the exurban fringe of large metropolitan areas have a surface energy balance that is more similar to the rural areas from which they were developed than it is to the older suburbs and city centres that make up the urban fabric to which they are being joined.     

A Study of the Reaction of OH Radicals with N-Methyl Pyrrolidinone,N-Methyl Succinimide and N-Formyl Pyrrolidinone

A study of the oxidation mechanism of N-methyl pyrrolidinone (C₅H₉NO, NMP) initiated by hydroxyl radicals was made at EUPHORE at atmospheric pressure (1000 ± 10) mbar of air and ambient temperature (T = 300 ± 5 K). The main products were N-methyl succinimide (NMS) (52 ± 4)% and N-formyl pyrrolidinone (FP) (23 ± 9)%. The relative rate technique was used to determine the rate constants of OH with NMP, NMS and FP, the measured values were (in units of cm³ molecule ^{− 1} s^{− 1}): k_NMP = (2.2 ± 0.4) × 10^{− 11}, k_NMS = (1.4 ± 0.3) × 10^{− 12} and k_FP = (6 ± 1) × 10^{− 12}. The results are presented and discussed in terms of the atmospheric impact.     

On the Scaling Laws of the Velocity-Scalar Cospectra in the Canopy Sublayer Above Tall Forests

The scaling laws of the vertical (F _wc ) and longitudinal (F _uc ) velocity-scalar cospectra within the inertial subrange are explored using dimensional arguments and a simplified cospectral budget in the canopy sublayer above three distinct forested ecosystems. The cospectral budget was shown to be consistent with plausible scaling laws originating from dimensional considerations. Using the analytical solution to the novel cospectral budget, it was shown that F _wc (k) and F _uc (k) are governed by the linear superposition of two terms that scale as k ^−2/3−α and k ^−β , where k is the wavenumber, −α is the exponent of the velocity spectrum, and β( ≥ 7/3) depends on the ratio of the similarity constants for the pressure-scalar covariance and the flux transport terms. It was also demonstrated that, when the magnitude of the mean scalar concentration gradient is large, the k ^−2/3−α term dominates the velocity-scalar cospectral budget. For such a case, correcting for biases emerging from high frequency losses in eddy-covariance scalar flux measurements can be readily formulated by using the measured velocity spectral exponent in the inertial subrange.     

Tropical cyclones and polar lows: Velocity,size, and energy scales,and relation to the 26°C cyclone origin criteria

The goal of this paper is to quantitatively formulate some necessary conditions for the development of intense atmospheric vortices. Specifically, these criteria are discussed for tropical cyclones (TC) and polar lows (PL) by using bulk formulas for fluxes of momentum, sensible heating, and latent heating between the ocean and the atmosphere. The velocity scale is used in two forms: (1) as expressed through the buoyancy flux b and the Coriolis parameter l_c for rotating fluids convection, and (2) as expressed with the cube of velocity times the drag coefficient through the formula for total kinetic energy dissipation in the atmospheric boundary layer. In the quasistationary case the dissipation equals the generation of the energy. In both cases the velocity scale can be expressed through temperature and humidity differences between the ocean and the atmosphere in terms of the reduced gravity, and both forms produce quite comparable velocity scales. Using parameters b and l_c, we can form scales of the area and, by adding the mass of a unit air column, a scale of the total kinetic energy as well. These scales nicely explain the much smaller size of a PL, as compared to a TC, and the total kinetic energy of a TC is of the order 10¹⁸-10¹⁹ J. It will be shown that wind of 33 m s^-1 is produced when the total enthalpy fluxes between the ocean and the atmosphere are about 700 W m^-2 for a TC and 1700 W m^-2 for a PL, in association with the much larger role of the latent heat in the first case and the stricter geostrophic constraints and larger static stability in the second case. This replaces the mystical role of 26^oC as a criterion for TC origin. The buoyancy flux, a product of the reduced gravity and the wind speed, together with the atmospheric static stability, determines the rate of the penetrating convection. It is known from the observations that the formation time for a PL reaching an altitude of 5--6 km can be only a few hours, and a day, or even half a day, for a TC reaching 15--18 km. These two facts allow us to construct curves on the plane of T^s and ΔT=T_s-T_a to determine possibilities for forming an intense vortex. Here, T_a is the atmospheric temperature at the height z=10 m. A PL should have ΔT>20^oC in accordance with the observations and numerical simulations. The conditions for a TC are not so straightforward but our diagram shows that the temperature difference of a few degrees, or possibly even a fraction of a degree, might be sufficient for TC development for a range of static stabilities and development times.     

Variance Method to Determine Turbulent Fluxes of Momentum And Sensible Heat in The Stable Atmospheric Surface Layer

Evidence is presented that in the stable atmospheric surface layer turbulent fluxes of heat and momentum can be determined from the standard deviations of longitudinal wind velocity and temperature, σ _u and σ _T respectively, measured at a single level. An attractive aspect of this method is that it yields fluxes from measurements that can be obtained with two-dimensional sonic anemometers. These instruments are increasingly being used at official weather stations, where they replace the standard cup anemometer–wind vane system. With methods such as the one described in this note, a widespread, good quality, flux network can be established, which would greatly benefit the modelling community. It is shown that a ‘variance’ dimensionless height (ζ _σ) defined from σ _u and σ _T is highly related to the ‘conventional’ dimensionless stability parameter ζ=z/L, where z is height and L is the Obukhov length. Empirical functions for ζ _σ are proposed that allow direct calculation of heat and momentum fluxes from σ _u and σ _T. The method performs fairly well also during a night of intermittent turbulence.     

An analysis of the turbulent structure in the unstable surface layer nearby a shelter belt

An analysis was performed of the turbulent data obtained from Yucheng experimental station in the Shandong Province in 1984. [t is shown that at variant wind speed, the spectra of streamwise velocity remain similar and the intensity of wind fluctuations is proportional to wind speed in the downwind area of shelter belt. Therefore, we may decide the similarity of wind fluctuations by a speed scale and a length scale which is not correlated with stability, σu /V0 = F(X / H). The -5/3 power range of temperature spectra extends to lower frequency. The variation of ratio σ0 /T. with stability becomes σ0 / T . = C(X / H)( - Z / L)-1/3 . There is not such an extension of -5 / 3 power range in the humidity spectra.     

Humidity Effect and Its Influence on the Seasonal Distribution of Precipitation δ18O in Monsoon Regions

The humidity effect, namely the markedly positive correlation between the stable isotopic ratio in precipitation and the dew-point deficit △Td in the atmosphere, is put forward firstly and the relationships between the δ18O in precipitation and △Td are analyzed for the Urumqi and Kunming stations, which have completely different climatic characteristics. Although the seasonal variations in δ18O and △Td exhibit differences between the two stations, their humidity effect is notable. The correlation coefficient and its confidence level of the humidity effect are higher than those of the amount effect at Kunming, showing the marked influence of the humidity conditions in the atmosphere on stable isotopes in precipitation.Using a kinetic model for stable isotopic fractionation, and according to the seasonal distribution of meanmonthly temperature at 500 hPa at Kunming, the variations of the δ18O in condensate in cloud aresimulated. A very good agreement between the seasonal variations of the simulated mean δ18O and themean monthly temperature at 500 hPa is obtained, showing that the oxygen stable isotope in condensateof cloud experiences a temperature effect. Such a result is markedly different from the amount effect atthe ground. Based on the simulations of seasonal variations of δ18O in falling raindrops, it can be foundthat, in the dry season from November to April, the increasing trend with falling distance of δ18O in fallingraindrops corresponds remarkably to the great ATd, showing a strong evaporation enrichment function infalling raindrops; however, in the wet season from May to October, the δ18O in falling raindrops displaysan unapparent increase corresponding to the small ATd, except in May. By comparing the simulated meanδ18O at the ground with the actual monthly δ18O in precipitation, we see distinctly that the two monthlyδ18O variations agree very well. On average, the δ18O values are relatively lower because of the highlymoist air, heavy rainfall, small △Td and weak evaporation enrichment function of stable isotopes in thefalling raindrops, under the influence of vapor from the oceans; but they are relatively higher because of the dry air, light rainfall, great △Td and strong evaporation enrichment function in falling raindrops, under the control of the continental air mass. Therefore, the δ18O in precipitation at Kunming can be used to indicate the humidity situation in the atmosphere to a certain degree, and thus indicate the intensity of the precipitation and the strength of the monsoon indirectly. The humidity effect changes not only the magnitude of the stable isotopic ratio in precipitation but also its seasonal distribution due to its influence on the strength of the evaporation enrichment of stable isotopes in falling raindrops and the direction of the net mass transfer of stable isotopes between the atmosphere and the raindrops. Consequently, it is inferred that the humidity effect is probably one of the foremost causes generating the amount effect.     

Uptake of the NO <Subscript>3</Subscript> Radical on Aqueous Surfaces

Using a single drop experiment, the uptake of NO₃ radicals on aqueous solutions of the dye Alizarin Red S and NaCl was measured at 293 K. Uptake coefficients in the range (1.7–3.1) ⋅ 10^{− 3} were measured on Alizarin Red S solutions. The uptake coefficients measured on NaCl solutions were in the range of (1.1–2.0) ⋅ 10⁻³ depending on the salt concentration. Both experiments lead to a consistent result for the mass accommodation coefficient of α_NO3 = (4.2_{− 1.7}^+2.2)⋅ 10⁻³. The product H(D_l k_Cl−^II)^0.5 for the NO₃ radical was determined to be (1.9 ± 0.2) M atm^{− 1} cm s^−0.5 M^−0.5 s^−0.5 by fitting the uptake data for the NaCl solutions to the so-called resistance model. The yield of the chemical NO₃ radical source was characterized using UV-VIS and FT-IR spectroscopy. The amount of gas-phase NO₃ radicals measured at elevated humidities was less than expected. Instead, a rise of the gas-phase HNO₃ concentration was found indicating a conversion of gas-phase NO₃ radicals to gas-phase HNO₃ on the moist reactor walls.     

Measurement and investigation of chamber radical sources in the European Photoreactor (EUPHORE)

It is essential to quantify the background reactivity of smog-chambers, since this might be the major limitation of experiments carried out at low pollutant concentrations typical of the polluted atmosphere. Detailed investigation of three chamber experiments at zero-NO _x in the European Photoreactor (EUPHORE) were carried out by means of rate-of-production analysis and two uncertainty analysis tools: local uncertainty analysis and Monte Carlo simulations with Latin hypercube sampling. The chemical mechanism employed was that for methane plus the inorganic subset of the Master Chemical Mechanism (MCMv3.1). Newly installed instruments in EUPHORE allowed the measurement of nitrous acid and formaldehyde at sub-ppb concentrations with high sensitivity. The presence of HONO and HCHO during the experiments could be explained only by processes taking place on the FEP Teflon walls. The HONO production rate can be described by the empirical equation W(HONO)_EUPHORE ^dry = a × j _{NO 2}× exp (− T ₀/T) in the low relative humidity region (RH < 2%, a = 7.3×10²¹ cm⁻³, T ₀ = 8945K), and by the equation W(HONO)_EUPHORE ^humid = W(HONO)_EUPHORE ^dry+ j _{NO 2}× b × RH ^q in the higher relative humidity region (2% < RH < 15%, b = 5.8×10⁸ cm⁻³ and q = 0.36, and RH is the relative humidity in percentages). For HCHO the expression W(HCHO)_EUPHORE = c × j _{NO 2}exp (− T′₀/T) is applicable (c = 3.1×10¹⁷ cm⁻³ and T′₀ = 5686 K). In the 0–15% relative humidity range OH production from HONO generated at the wall is about a factor of two higher than that from the photolysis of 100 ppb ozone. Effect of added NO₂ was found to be consistent with the dark HONO formation rate coefficient of MCMv3.1.     

Intercomparison of Two Hydroxyl Radical Measurement Techniques at the Atmosphere Simulation Chamber SAPHIR

At the atmosphere simulation chamber SAPHIR in Jülich both Laser-Induced Fluorescence Spectroscopy (LIF) and Long-Path Differential Optical Laser Absorption Spectroscopy (DOAS) are operational for the detection of OH radicals at tropospheric levels. The two different spectroscopic techniques were compared within the controlled environment of SAPHIR based on all simultaneous measurements acquired in 2003 (13 days). Hydroxyl radicals were scavenged by added CO during four of these days in order to experimentally check the calculated precisions at the detection limit. LIF measurements have a higher precision (σ= 0.88×10⁶ cm^–3) and better time resolution (Δt = 60 s), but the DOAS method (σ= 1.24×10⁶ cm^–3, Δt = 135 s) is regarded as primary standard for comparisons because of its good accuracy. A high correlation coefficient of r = 0.95 was found for the whole data set highlighting the advantage of using a simulation chamber. The data set consists of two groups. The first one includes 3 days, where the LIF measurements yield (1 – 2) ×10⁶ cm^–3 higher OH concentrations than observed by the DOAS instrument. The experimental conditions during these days are characterized by increased NO_x concentration and a small dynamic range in OH. Excellent agreement is found within the other group of 6 days. The regression to the combined data of this large group yields unity slope without a significant offset.     

Laboratory measurements of the <Superscript>12</Superscript>C/<Superscript>13</Superscript>C kinetic isotope effects in the gas-phase reactions of unsaturated hydrocarbons with Cl atoms at 298 ± 3 K

The carbon kinetic isotope effects (KIEs) in the reactions of several unsaturated hydrocarbons with chlorine atoms were measured at room temperature and ambient pressure using gas chromatography combustion isotope ratio mass spectrometry (GCC-IRMS). All measured KIEs, defined as the ratio of the rate constants for the unlabeled and labeled hydrocarbon reaction k ₁₂/k ₁₃, are greater than unity or normal KIEs. The KIEs, reported in per mil according to ^Cl ɛ = (k ₁₂/k ₁₃−1) × 1000‰ with the number of experimental determinations in parenthesis, are as follows: ethene, 5.65 ± 0.34 (1); propene, 5.56 ± 0.18 (2); 1-butene, 5.93 ± 1.16 (1); 1-pentene, 4.86 ± 0.63 (1); cyclopentene, 3.75 ± 0.14 (1); toluene, 2.89 ± 0.31 (2); ethylbenzene, 2.17 ± 0.17 (2); o-xylene, 1.85 ± 0.54 (2). To our knowledge, these are the first reported KIE measurements for reactions of unsaturated NMHC with Cl atoms. Relative rate constants were determined concurrently to the KIE measurements. For the reactions of cyclopentene and ethylbenzene with Cl atoms, no rate constant has been reported in refereed literature. Our measured rate constants are: cyclopentene (7.32 ± 0.88) relative to propene (2.68 ± 0.32); ethylbenzene (1.15 ± 0.04) relative to o-xylene (1.35 ± 0.21), all × 10⁻¹⁰ cm³ molecule⁻¹ s⁻¹. The KIEs in reactions of aromatic hydrocarbons with Cl atoms are similar to previously reported KIEs in Cl-reactions of alkanes with the same numbers of carbon atoms. Unlike the KIEs for previously studied gas-phase hydrocarbon reactions, the KIEs for alkene–Cl reactions do not exhibit a simple inverse dependence on carbon number. This can be explained by competing contributions of normal and inverse isotope effects of individual steps in the reaction mechanism. Implications for the symmetries of the transition state structures in these reactions and the potential relevance of Cl-atom reactions on stable carbon isotope ratios of atmospheric NMHC are discussed.     

Relationship between Net Radiation and Broadband Solar Radiation in the Tibetan Plateau

The characteristics of net radiation (R_n)(0.3--10 μm) in Lhasa and Haibei in the Tibetan Plateau were analyzed based on long-term in-situ measurements of surface radiation data. The monthly average of daily R_n reached a minimum during the winter period followed by an increase until May and then a decline until January. This variation is consistent with solar activity. The annual mean daily total R_n values were 0.92 MJ m^-2 d^-1 and 0.66 MJ m^-2d^-1 in Lhasa and Haibei, respectively. A relationship between R_n and broadband solar radiation (R_s) was demonstrated by a good linear correlation at the two sites. R_n can be an accurate estimate from R_s. The estimated R_n values were similar to the observed values, and the relative deviations between the estimates and measurements of R_n were 2.8% and 3.8% in Lhasa and Haibei, respectively. The application of the R_n estimating model to other locations showed that it could provide acceptable estimated R_n values from the R_s data. Furthermore, we analyzed the influence of clouds on R_n by different clear index (K_s), defined as the ratio of R_s to the extraterrestrial solar irradiance on a horizontal surface. The results indicate that more accurate results are associated with increased cloudy conditions. The influence of the albedo was also considered, but its inclusion in the model resulted in only a slight improvement. Because surface albedo is not usually measured, an expression based solely on global solar radiation could be of more extensive use.     

Water interaction with MgCl<Subscript>2</Subscript>×6H<Subscript>2</Subscript>O and NaCl surfaces: measurements of the uptake coefficient

The uptake of water vapor on MgCl₂×6H₂O and NaCl salt dry solid films was studied over the temperature range 240 to 340 K and at 1 Torr pressure of helium using a flow reactor coupled to a modulated molecular beam mass spectrometer. The H₂O to salt uptake data were obtained from the kinetics of H₂O loss on salt coated Pyrex rods. The following Arrhenius expression was obtained for the initial uptake coefficient of H₂O on MgCl₂×6H₂O films: γ ₀ (MgCl₂) = (6.5 ± 1.0) × 10⁻⁶ exp[(470 ± 40)/T] (calculated with specific BET surface area, quoted uncertainties are 1σ statistical). The rate of H₂O adsorption on NaCl was found to be much lower than on MgCl₂×6H₂O, and only an upper limit was determined for the corresponding uptake coefficient: γ (NaCl) ≤ 5.6 × 10⁻⁶ at T = 300 K. The results show that the rate of H₂O adsorption to salt surfaces is drastically dependent on the salt sample composition.     

Kinetics of the reactions of soot surface-bound polycyclic aromatic hydrocarbons with NO<Subscript>2</Subscript>

The kinetics of heterogeneous reactions of NO₂ with 17 polycyclic aromatic hydrocarbons (PAHs) adsorbed on laboratory generated kerosene soot surface was studied over the temperature range (255–330) K in a low pressure flow reactor combined with an electron-impact mass spectrometer. The kinetics of soot-bound PAH consumption due to their desorption and reaction with NO₂ were monitored using off-line HPLC measurements of their concentrations in soot samples as a function of reaction time, NO₂ concentrations in the gas phase being analyzed by mass spectrometer. No measurable decay of PAHs due to the reaction with NO₂ was observed under experimental conditions of the study (maximum NO₂ concentration of 5.5 × 10¹⁴ molecule cm⁻³ and reaction time of 45 min), which allowed to determine the upper limits of the first-order rate constants for the heterogeneous reactions of 17 soot-bound PAHs with NO₂: k < 5.0 × 10⁻⁵ s⁻¹ (for most PAHs studied). Comparison of these results to previous studies carried on different carbonaceous substrates, showed that heterogeneous reactivity of PAHs towards NO₂ is, probably, dependent on the substrate nature even for resembling, although different carbonaceous materials. Results show that particulate PAHs degradation by NO₂ alone is of minor importance in the atmosphere     

An analogue model to derive additional climate change scenarios from existing GCM simulations

 Changes in land surface driving variables, predicted by GCM transient climate change experiments, are confirmed to exhibit linearity in the global mean land temperature anomaly, ΔT _l . The associated constants of proportionality retain spatial and seasonal characteristics of the GCM output, whilst ΔT _l is related to radiative forcing anomalies. The resultant analogue model is shown to be robust between GCM runs and as such provides a computationally efficient technique of extending existing GCM experiments to a large range of climate change scenarios. As an example impacts study, the analogue model is used to drive a terrestrial ecosystem model, and predicted changes in terrestrial carbon are found to be similar to those when using GCM anomalies directly. Received: 4 January 1999 / Accepted: 11 December 1999     

Characteristics of the atmospheric heat source and moisture sink over the Qinghai-Tibetan Plateau during the second TIPEX of summer 1998 and their impact on surrounding monsoon

Summary ?Using the data of 6 automatic heat balance observation (AWS) stations and a data set of 52 surface observation stations over the Qinghai-Tibetan Plateau (“the Plateau”) and surroundings, the horizontal distribution is studied of “apparent atmospheric heat sources” 〈Q ₁〉 and of “apparent atmospheric moisture sinks” 〈Q ₂〉. The AWS stations were established during the period May to August 1998 of the Tibetan Plateau Meteorological Experiment (second TIPEX) by a cooperation of China and Japan. For this period the Plateau mean of 〈Q ₁〉 is positive. Its value of 74 W/m² is a little greater than a climate value and than values from MONEX and the first TIPEX in 1979, respectively. Also the corresponding 〈Q ₂〉 is positive. Hence during that time the Plateau is a heat source and a moisture sink. A day-to-day change of 〈Q ₁〉 and 〈Q ₂〉 is more pronounced over the middle and east part of the Plateau than over the west part. Diagnostics accompanied by numerical simulations are used to study the daily relationship between 〈Q ₁〉 over the Plateau and the weather over China and Asia for this summer. The results suggest that 〈Q ₁〉 may affect precipitation over northern China and position of the west Pacific subtropical high. Abnormal southward retreat of this Pacific high seems to have caused the second flood over the middle and lower Yangtse river basin in July. Received May 20, 2001; revised February 2, 2002     

Quantitative reconstruction of the last interglacial vegetation and climate based on the pollen record from Lake Baikal, Russia

Changes in mean temperature of the coldest (T _c) and warmest month (T _w), annual precipitation (P _ann) and moisture index (α) were reconstructed from a continuous pollen record from Lake Baikal, Russia. The pollen sequence CON01-603-2 (53°57′N, 108°54′E) was recovered from a 386 m water depth in the Continent Ridge and dated to ca. 130–114.8 ky BP. This time interval covers the complete last interglacial (LI), corresponding to MIS 5e. Results of pollen analysis and pollen-based quantitative biome reconstruction show pronounced changes in the regional vegetation throughout the record. Shrubby tundra covered the area at the beginning of MIS 5e (ca. 130–128 ky), consistent with the end of the Middle Pleistocene glaciation. The late glacial climate was characterised by low winter and summer temperatures (T _c ~ −38 to −35°C and T _w~11–13°C) and low annual precipitation (P _ann~300 mm). However, the wide spread of tundra vegetation suggests rather moist environments associated with low temperatures and evaporation (reconstructed α~1). Tundra was replaced by boreal conifer forest (taiga) by ca. 128 ky BP, suggesting a transition to the interglacial. Taiga-dominant phase lasted until ca. 117.4 ky BP, e.g. about 10 ky. The most favourable climate conditions occurred during the first half of the LI. P _ann reached 500 mm soon after 128 ky BP. However, temperature changed more gradually. Maximum values of T _c ~ −20°C and T _w~16–17°C are reconstructed from about 126 ky BP. Conditions became gradually colder after ca. 121 ky BP. T _c dropped to ~ −27°C and T _w to ~15°C by 119.5 ky BP. The reconstructed increase in continentality was accompanied by a decrease in P _ann to ~400–420 mm. However, the climate was still humid enough (α~0.9) to support growth of boreal evergreen conifers. A sharp turn towards a dry climate is reconstructed after ca. 118 ky BP, causing retreat of forest and spread of cool grass-shrub communities. Cool steppe dominated the vegetation in the area between ca. 117.5 ky and 114.8 ky BP, suggesting the end of the interglacial and transition to the last glacial (MIS 5d). Shift to the new glaciation was characterised by cool and very dry conditions with T _c ~ −28 to −30°C, T _w~14–15°C, P _ann~250 mm and α~0.5.     

Atmospheric inorganic nitrogen in marine aerosol and precipitation and its deposition to the North and South Pacific Oceans

Aerosol and rain samples were collected between 48°N and 55°S during the KH-08-2 and MR08-06 cruises conducted over the North and South Pacific Ocean in 2008 and 2009, to estimate dry and wet deposition fluxes of atmospheric inorganic nitrogen (N). Inorganic N in aerosols was composed of ~68% NH₄⁺ and ~32% NO₃^– (median values for all data), with ~81% and ~45% of each species being present on fine mode aerosol, respectively. Concentrations of NH₄⁺ and NO₃⁻ in rainwater ranged from 1.7–55 μmol L⁻¹ and 0.16–18 μmol L⁻¹, respectively, accounting for ~87% by NH₄⁺ and ~13% by NO₃⁻ of total inorganic N (median values for all data). A significant correlation (r = 0.74, p < 0.05, n = 10) between NH₄⁺ and methanesulfonic acid (MSA) was found in rainwater samples collected over the South Pacific, whereas no significant correlations were found between NH₄⁺ and MSA in rainwater collected over the subarctic (r = 0.42, p > 0.1, n = 6) and subtropical (r = 0.33, p > 0.5, n = 6) western North Pacific, suggesting that emissions of ammonia (NH₃) by marine biological activity from the ocean could become a significant source of NH₄⁺ over the South Pacific. While NO₃⁻ was the dominant inorganic N species in dry deposition, inorganic N supplied to surface waters by wet deposition was predominantly by NH₄⁺ (42–99% of the wet deposition fluxes for total inorganic N). We estimated mean total (dry + wet) deposition fluxes of atmospheric total inorganic N in the Pacific Ocean to be 32–64 μmol m⁻² d⁻¹, with 66–99% of this by wet deposition, indicating that wet deposition plays a more important role in the supply of atmospheric inorganic N than dry deposition.     

Micrometeorological Conditions for Dust-Devil Occurrence in the Atacama Desert

We report on field observations in January 2009 (austral summer) of atmospheric dust devils in the northern part of the Atacama Desert in South America (≈20^◦S). An extremely high level of dust-devil activity over the study site has been observed, dependent on local meteorological conditions. We found a high correlation between the dust-devil frequency of occurrence and the Obukhov length scale, L, calculated from meteorological gradient measurements, with a clear tendency for this frequency to increase with decreasing −L. The upper threshold values of −L ≈ 20–30 m, and the 2-m mean wind speed, V ₂ ≈ 8m s⁻¹, for dust-devil occurrence have been found, but the minimal V ₂ threshold was not observed. Parallel routine meteorological measurements enabled us to calculate the main constituents of the surface energy balance, to obtain direct estimates of the surface albedo (α ≈ 0.21 at the solar noon) and to summarize the local conditions.     

Critical Evaluation of Scalar Roughness Length Parametrizations Over a Melting Valley Glacier

We present a field investigation over a melting valley glacier on the Tibetan Plateau. In the ablation zone, aerodynamic roughness lengths (z _0M ) vary on the order of 10⁻⁴–10⁻² m, whose evolution corresponds to three melt phases with distinct surface cover and moisture exchange: snow (sublimation/evaporation), bare ice (deposition/condensation), and ice hummocks (sublimation/evaporation). Bowen-ratio similarity is validated in the stably stratified katabatic winds, which suggests a useful means for data quality check. A roughness sublayer is regarded as irrelevant to the present ablation season, because selected characteristics of scalar turbulence over smooth snow are quite similar to those over hummocky ice. We evaluate three parametrizations of the scalar roughness lengths (z _0T for temperature and z _0q for humidity), viz. key factors for the accurate estimation of sensible heat and latent heat fluxes using the bulk aerodynamic method. The first approach is based on surface-renewal models and has been widely applied in glaciated areas; the second has never received application over an ice/snow surface, despite its validity in (semi-)arid regions; the third, a derivative of the first, is proposed for use specifically over rough ice defined as z _0M > 10⁻³ m or so. This empirical z _0M threshold value is deemed of general relevance to glaciated areas (e.g. ice sheet/cap and valley/outlet glaciers), above which the first approach gives notably underestimated z _0T,q . The first and the third approaches tend to underestimate and overestimate turbulent heat/moisture exchange, respectively, frequently leading to relative errors higher than 30%. Comparatively, the second approach produces fairly low errors in energy flux estimates both in individual melt phases and over the whole ablation season; it thus emerges as a practically useful choice to parametrize z _0T,q in glaciated areas. Moreover, we find all three candidate parametrizations unable to predict diurnal variations in the excess resistances to humidity transfer, thus encouraging more efforts for improvement.