Daytime boundary layer behavior over eastern region (per-humid climate) and western regions (semi-arid climate) of India: a case study

The annual variation in planetary boundary layer (PBL) height is determined from the profiles of conserved thermodynamic variables, i.e., virtual potential temperature ?? _v and equivalent potential temperature ?? _e, using radiosonde data at per-humid climate region, Ranchi (23°42??N, 85°33??E, 610?m asl) and semi-arid region, Anand (23°35??N, 72°55??E, 45.1?m asl), India. Of all the variables, the ?? _v profile seems to provide the most reasonable estimate of the PBL height. This has been supplemented by T-Phi gram analysis for specific days. It has been found that in winter the height of boundary layer is very low due to subsidence and radiational cooling, while pre-monsoon months exhibit the most variable convection. It may be inferred that synoptic conditions accompanied by a variety of weather phenomena such as thunderstorms, onset and withdrawal of monsoons, etc. control the ABL over Ranchi, while daytime solar insolation and nighttime radiative cooling mainly control the ABL over Anand.     

Circulation analysis in the northwest Indian Ocean using ARGO floats and surface drifter observations,and SODA reanalysis output

This study incorporates observations from Array of Real-time Geostrophic Oceanography (ARGO) floats and surface drifters to identify seasonal circulation patterns at the surface, 1000 m, 1500 m, and 2000 m in the northwest Indian Ocean, and quantify velocities associated with them. A skill comparison of the Simple Ocean Data Assimilation (SODA) reanalysis output was also performed to contribute to the understanding of the circulation dynamics in this region.Subsurface currents were quantified and validated using the ARGO float data. Surface currents were identified using surface drifter data and compared to the subsurface observations to enhance our previous understanding of surface circulations. Quantified Southwest Monsoon surface currents include the Somali Current (v_max = 179.5 cm/s), the East Arabian Current (v_max = 52.3 cm/s), and the Southwest Monsoon Current (v_max = 51.2 cm/s). Northeastward flow along the Somali coast is also observed at 1000 m (v_max = 26.1 cm/s) and 1500 m (v_max = 12.7 cm/s). Currents associated with the Great Whirl are observed at the surface (v_max = 161.4 cm/s) and at 1000 m (v_max = 16.2 cm/s). In contrast to previous studies, both ARGO and surface drifter data show the Great Whirl can form as early as the boreal Spring intermonsoon, lasting until the boreal Fall intermonsoon. The Arabian Sea exhibits eastward/southeastward flow at the surface, 1000 m, 1500 m, and 2000 m. Quantified Northeast Monsoon surface currents include the Somali Current (v_max = 97.3 cm/s), Northeast Monsoon Current (v_max = 30.0 cm/s), and the North Equatorial Current (v_max = 28.5 cm/s). Southwestward flow along the Somali coast extends as deep as 1500 m.Point-by-point vector and scalar correlations of SODA output to ARGO and surface drifter data showed that surface SODA output and surface drifter data generally produced a strong correlation attributed to surface currents strongly controlled by the monsoons, while subsurface correlations of SODA output and ARGO were mostly insignificant due to variability associated with intermonsoonal transitions. SODA output produced overall smaller velocities than both observational datasets. Assimilating ARGO velocities into the SODA reanalysis could improve subsurface velocity assimilation, especially during the boreal fall and spring when ARGO observations suggest that flow is highly variable.     

Distribution of CO2 parameters in the Western Tropical Atlantic Ocean

The variability of sea surface Total Alkalinity (TA) and sea surface Total Inorganic Carbon (C_T) is examined using all available data in the western tropical Atlantic (WTA: 20°S-20°N, 60°W-20°W). Lowest TA and C_T are observed for the region located between 0°N-15°N/60°W-50°W and are explained by the influence of the Amazon plume during boreal summer. In the southern part of the area, 20°S-10°S/40°W-60°W, the highest values of TA and C_T are linked to the CO₂–rich waters due to the equatorial upwelling, which are transported by the South Equatorial Current (SEC) flowing from the African coast to the Brazilian shore. An increase of C_T of 0.9 ± 0.3 μmol kg⁻¹yr⁻¹ has been observed in the SEC region and is consistent with previous published estimates. A revised C_T-Sea Surface Salinity (SSS) relationship is proposed for the WTA to take into account the variability of C_T at low salinities. This new C_T-SSS relationship together with a published TA-SSS relationship allow to calculate pCO₂ values that compare well with observed pCO₂ (R² = 0.90).     

Exploring the vertical extent of breaking internal wave turbulence above deep-sea topography

A mooring equipped with 200 high-resolution temperature sensors between 6 and 404 m above the bottom was moored in 1890 m water depth above a steep, about 10° slope of Mount Josephine, NE-Atlantic. The sensors have a precision of less than 0.5 mK. They are synchronized via induction every 4 h so that the 400 m range is measured to within 0.02 s, every 1 s. Thin cables and elliptical buoyancy assured vertical mooring motions to be smaller than 0.1 m under maximum 0.2 m s⁻¹ current speeds. The local bottom slope is supercritical for semidiurnal internal tides by a factor of two. Exploring a one-month record in detail, the observations show: 1/semidiurnal tidal dominance in variations of dissipation rate ε, eddy diffusivity K_z and temperature, but no significant correlation between the records of ε and total kinetic energy, 2/a variation with time over four orders of magnitude of 100-m vertically averaged ε, 3/a local minimum in density stratification between 50 and 100 m above the bottom, 4/a gradual decrease in daily or longer averaged ε and K_z by one order of magnitude over a vertical distance of 250 m, upwards from 150 m above the bottom, 5/monthly mean values of <[ε]> = 2 ± 0.5 × 10⁻⁷ m² s⁻³, <[K_z]> = 8 ± 3 × 10⁻³ m² s⁻¹ averaged over the lower 150 m above the bottom.     

Investigations on meteorological conditions for elevated PM2.5 in Fairbanks,Alaska

The relationships between meteorological conditions (temperature, wind-speed and direction, relative humidity, surface-inversion depth and strength, and stability) and PM_2.5 concentrations in Fairbanks, Alaska were investigated using ten years of observational data. The results show that during wintertime (November through February) PM_2.5 concentrations exceeding the 24 h National Air Quality Standard (35 μg/m³) occurred under calm wind, extremely low temperature (≤20 °C) and moisture (water-vapor pressure < 2 hPa) multiday surface-inversion conditions that trap the pollutants in the breathing level and inhibit transport of polluted air out of Fairbanks. PM_2.5 concentrations tend to be higher under stable than other conditions, but are not sensitive to the degree of stability. The presence of a surface inversion and calm wind are necessary, but in combination with low temperatures and humidity, the conditions are sufficient for high PM_2.5 concentrations. The low temperatures are required because they lead to increased emission rates from domestic heating and power production. During multiday inversions with temperatures above ? 20 °C, high relative humidity (> 75%) partly caused by water-vapor emission reduces PM_2.5 concentrations.     

Variability of CO2 fugacity at the western edge of the tropical Atlantic Ocean from the 8°N to 38°W PIRATA buoy

Hourly data of CO₂ fugacity (fCO₂) at 8°N–38°W were analyzed from 2008 to 2011. Analyses of wind, rainfall, temperature and salinity data from the buoy indicated two distinct seasonal periods. The first period (January to July) had a mean fCO₂ of 378.9 μatm (n = 7512). During this period, in which the study area was characterized by small salinity variations, the fCO₂ is mainly controlled by sea surface temperature (SST) variations (fCO₂ = 24.4*SST-281.1, r² = 0.8). During the second period (August–December), the mean fCO₂ was 421.9 μatm (n = 11571). During these months, the region is subjected to the simultaneous action of (a) rainfall induced by the presence of the Intertropical Convergence Zone (ITCZ); (b) arrival of fresh water from the Amazon River plume that is transported to the east by the North Equatorial Countercurrent (NECC) after the retroflection of the North Brazil Current (NBC); and (c) vertical input of CO₂-rich water due to Ekman pumping. The data indicated the existence of high-frequency fCO₂ variability (periods less than 24 h). This high variability is related to two different mechanisms. In the first mechanism, fCO₂ increases are associated to rapid increases in SST and are attributed to the diurnal cycle of solar radiation. In addition, low wind speed contributes to SST rising by inhibiting vertical mixing. In the second mechanism, fCO₂ decreases are associated to SSS decreases caused by heavy rainfall.     

Characterization of water-soluble inorganic ions in size-segregated aerosols in coastal city,Xiamen

The samples of water-soluble inorganic ions (WSIs), including anions (F^?, Cl^?, SO₄^2?, NO₃^?) and cations (NH₄⁺, K⁺, Na⁺, Ca²⁺, Mg²⁺) in 8 size-segregated particle matter (PM), were collected using a sampler (with 8 nominal cut-sizes ranged from 0.43 to 9.0 μm) from October 2008 to September 2009 at five sites in both polluted and background regions of a coastal city, Xiamen. The results showed that particulate matters in the fine mode (PM_2.1, Dp < 2.1 μm) comprised large part of mass concentrations of aerosols, which accounted for 45.56–51.27%, 40.04–60.81%, 42.02–60.81%, and 40.46–57.07% of the total particulate mass in spring, summer, autumn, and winter, respectively. The water-soluble ionic species in the fine mode at five sampling sites varied from 15.33 to 33.82 (spring), 14.03 to 28.06 (summer), 33.47 to 72.52 (autumn), and 48.39 to 69.75 μg m^? 3 (winter), respectively, which accounted for 57.30 ± 6.51% of the PM_2.1 mass concentrations. Secondary pollutants of NH₄⁺, SO₄^2? and NO₃^? were the dominant contributors of WSIs, which suggested that pollutants from anthropogenic activities, such as SO₂, NOx were formed in aerosols by photochemical reactions. The size distributions of Na⁺, Cl^?, SO₄^2? and NO₃^? were bimodal, peaking at 0.43–0.65 μm and 3.3–5.8 μm. Although some ions, such as NH₄⁺ presented bimodal distributions, the coarse mode was insignificant compared to the fine mode. Ca²⁺ and Mg²⁺ exhibited unimodal distributions at all sampling sites, peaking at 2.1–3.3 μm, while K⁺ having a bimodal distributions with a major peak at 0.43–0.65 μm and a minor one at 3.3–4.7 μm, were used in most of samples. Seasonal and spatial variations in the size-distribution profiles suggested that meteorological conditions (seasonal patterns) and sampling locations (geographical patterns) were the main factors determining the formation of secondary aerosols and characteristics of size distributions for WSIs.     

Impressions of the turbulence variability in a weakly stratified,flat-bottom deep-sea ‘boundary layer’

The character of turbulent overturns in a weakly stratified deep-sea is investigated in some detail using 144 high-resolution temperature sensors at 0.7 m intervals, starting 5 m above the bottom. A 9-day, 1 Hz sampled record from the 912 m depth flat-bottom (<0.5% bottom-slope) mooring site in the central-north Alboran Sea (W-Mediterranean) demonstrates an overall conservative temperature range of only 0.05 °C, a typical mean buoyancy period as large as 3 h and a 1 Hz-profile-vertically-averaged turbulence dissipation rate maximum of only 10⁻⁸ m² s⁻³. Nonetheless, this ‘boundary layer’ varies in height between <6 and >104 m above the bottom and is thus not homogeneous throughout; the temperature variations are seldom quiescent and are generally turbulent in appearance, well exceeding noise levels. The turbulence character is associated with small-scale internal waves; examples are found of both shear- and convection-driven turbulence; particular association, although not phase-locked, is found between turbulence variations and tidal rather than with inertial motions; the mean buoyancy frequency of a few times the inertial frequency implies the importance of ‘slantwise convection’ in the direction of the earth rotational vector rather than in the direction of gravity. Such convection is observed both in near-homogeneous and weakly stratified form.     

Size-resolved aerosol chemical concentrations at rural and urban sites in Central California,USA

Aerosol size distributions were measured with Micro Orifice Uniform Deposit Impactor (MOUDI) cascade impactors at the rural Angiola and urban Fresno Supersites in California's San Joaquin Valley during the California Regional PM₁₀/PM_2.5 Air Quality Study (CRPAQS) winter campaign from December 15, 2000 to February 3, 2001. PM_2.5 filter samples were collected concurrently at both sites with Sequential Filter Samplers (SFS). MOUDI nitrate (NO₃⁻) concentrations reached 66 μg/m³ on January 6, 2001 during the 1000–1600 PST (GMT-8) period. Pair-wise comparisons between PM_2.5 MOUDI and SFS concentrations revealed high correlations at the Angiola site (r > 0.93) but more variability (r < 0.85) at the Fresno site for NO₃⁻, sulfate (SO₄⁼), and ammonium (NH₄⁺). Correlations were higher at Fresno (r > 0.87) than at Angiola (r < 0.7) for organic carbon (OC), elemental carbon (EC), and total carbon (TC). NO₃⁻ and SO₄⁼ size distributions in Fresno were multi-modal and wider than the uni-modal distributions observed at Angiola. Geometric mean diameters (GMD) were smaller for OC and EC than for NO₃⁻ and SO₄⁼ at both sites. OC and EC were more concentrated on the lowest MOUDI stage (0.056 µm) at Angiola than at Fresno. The NO₃⁻ GMD increased from 0.97 to 1.02 µm as the NO₃⁻ concentration at Angiola increased from 43 to 66 µg m^− 3 during a PM_2.5 episode from January 4–7, 2001. There was a direct relationship between GMD and NO₃⁻ and SO₄⁼ concentrations at Angiola but no such relationships for OC or EC. This demonstrates that secondary aerosol formation increases both concentration and particle size for the rural California environment.     

Comparison of Monte Carlo simulation methods for the calculation of the nucleation barrier of argon

We compare two molecular Monte Carlo simulation methods, the discrete summation method and the growth/decay method, which calculate the vapor-liquid nucleation free energy barrier by simulating isolated clusters of fixed size without the surrounding vapor. The methods are applied to calculations of nucleation barriers of Lennard–Jones argon at 60 K and 80 K. Both of these methods are computationally efficient, as only isolated clusters without the surrounding vapor are simulated, and the methods can be applied with any given cluster definition. They give equivalent results to other methods where the vapor phase is also included. The discrete summation method is based on the calculation of the difference in free energies between two systems containing an n-cluster and an (n − 1)-cluster plus one non-interacting (free) molecule. We show that the configurational space is not equivalent in the two systems. Hence, there has to be an additional term in the free energy calculation that accounts for several kT in magnitude. In contrast to previous studies we also show that it is not correct to prevent the overlap of the non-interacting molecule and another molecule by a zero or an arbitrarily small repulsive potential, but with a small excluded space around the free molecule.     

Below-cloud rain scavenging of atmospheric aerosols for aerosol deposition models

Below-cloud aerosol scavenging is generally estimated from field measurements using advanced instruments that measure changes in aerosol distributions with respect to rainfall. In this study, we discuss various scavenging mechanisms and scavenging coefficients from past laboratory and field measurements. Scavenging coefficients derived from field measurements (representing natural aerosols scavenging) are two orders higher than that of theoretical ones for smaller particles (D_p < 2 μm). Measured size-resolved scavenging coefficients can be served as a better option to the default scavenging coefficient (e.g. a constant of 10^?4 s^?1 for all size of aerosols, as used in the CALPUFF model) for representing below-cloud aerosol scavenging. We propose scavenging correction parameter (C_R) as an exponential function of size-resolved scavenging coefficients, winds and width in the downwind of the source–receptor system. For a wind speed of 3 m s^?1, C_R decrease with the width in the downwind for particles of diameters D_p < 0.1 μm but C_R does not vary much for particles in the accumulation mode (0.1 < D_p < 2 μm). For a typical urban aerosol distribution, assuming 3 m s^?1 air-flow in the source–receptor system, 10 km downwind width, 2.84 mm h^?1 of rainfall and using aerosol size dependent scavenging coefficients in the C_R, scavenging of aerosols is found to be 16% in number and 24% in volume of total aerosols. Using the default scavenging coefficient (10^?4 s^?1) in the CALPUFF model, it is found to be 64% in both number and volume of total aerosols.     

Biogeophysical impacts of land use on present-day climate: near-surface temperature change and radiative forcing

Changes in land cover affect climate through the surface energy and moisture budgets, but these biogeophysical impacts of land use have not yet been included in General Circulation Model (GCM) simulations of 20th century climate change. Here, the importance of these effects was assessed by comparing climate simulations performed with current and potential natural vegetation. The northern mid-latitude agricultural regions were simulated to be approximately 1–2 K cooler in winter and spring in comparison with their previously forested state, due to deforestation increasing the surface albedo by approximately 0.1 during periods of snow cover. Some other regions such as the Sahel and India experienced a small warming due to land use. Although the annual mean global temperature is only 0.02 K lower in the simulation with present-day land use, the more local temperature changes in some regions are of a similar magnitude to those observed since 1860. The global mean radiative forcing by anthropogenic surface albedo change relative to the natural state is simulated to be −0.2 Wm², which is comparable with the estimated forcings relative to pre-industrial times by changes in stratospheric and tropospheric ozone, N₂O, halocarbons, and the direct effect of anthropogenic aerosols. Since over half of global deforestation has occurred since 1860, simulations of climate since that date should include the biogeophysical effects of land use.     

Influence of regional pollution and sandstorms on the chemical composition of cloud/fog at the summit of Mt. Taishan in northern China

Cloud/fog samples were collected during spring of 2007 in the highly polluted North China Plain in order to examine the impact of pollution and dust particles on cloud water chemistry. The volume weighted mean pH of cloud water was 3.68. The cloud acidity was shown to be associated with air mass origins. Cloud water with its air mass trajectories originating from the southern part of China was more acidic than those from northern China. Anthropogenic source and dust had obvious impact on cloud water composition as indicated by the very high mean concentrations of SO₄^2? (1331.65 μeq L^? 1), NO₃^? (772.44 μeq L^? 1), NH₄⁺ (1375.92 μeq L^? 1) and Ca²⁺ (625.81 μeq L^? 1) in the observation periods. During sandstorm days, cloud pH values were relatively high, and the concentrations of all the ions in cloud water reached unusual high levels. Significant decreases in the mass concentrations of PM_2.5 and PM₁₀ were observed during cloud events. The average scavenging ratio for PM_2.5 and PM₁₀ was 52.0% and 55.7%, respectively. Among the soluble ions in fine particles, NO₃^?, K⁺ and NH₄⁺ tend to be more easily scavenged than Ca²⁺ and Na⁺.     

Ensemble Square Root Filter Assimilation of Near-Surface Soil Moisture and Reference-Level Observations into a Coupled Land Surface-Boundary Layer Model

The potential for using the ensemble square root filter data assimilation technique to estimate soil moisture profiles, surface heat fluxes, and the state of the planetary boundary layer （PBL） is explored. An observing system simulation experiment is designed to mimic the assimilation of near-surface soil moisture observations （θo ） and in-situ measurements of 2-m temperature （To ）, 2-m specific humidity （Qo ）, and 10-m horizontal winds [Vo =（Uo , Vo ）]. The background forecasts are generated by a one-dimensional coupled land surface-boundary layer model （CLS-BLM） with soil, surface-layer and PBL parameterization schemes similar to those used in the Weather Research and Forecasting （WRF） model. Soil moisture, surface heat fluxes, and the state of the PBL evolve on different characteristic timescales, so the minimum assimilation time intervals required for skillful estimates of each target component are different. Correct estimates of the soil moisture profile are obtained effectively when a 6-h update time interval is used, while skillful estimates of surface fluxes and the PBL state require more frequent updates. The CLS-BLM requires a shorter assimilation time interval to correctly estimate the soil moisture profile than previously indicated by experiments using an off-line land surface model （LSM）. Results from assimilating different subsets of observations show that θo makes a larger contribution to soil moisture estimates, while To , θo , and Vo are more important for estimates of surface heat fluxes and the PBL state. It is therefore necessary to combine these variables to accurately estimate the states of both the land surface and the PBL. Experimentation with different prescribed observational errors shows that the assimilation system is more sensitive to increases in observational errors than to reductions in observational errors.     

Multi-gas emission envelopes to meet greenhouse gas concentration targets: Costs versus certainty of limiting temperature increase

This paper presents a set of technically feasible multi-gas emission pathways (envelopes) for stabilising greenhouse gas concentration at 450, 550 and 650 ppm CO₂-equivalent and their trade-offs between direct abatement costs and probabilities to meet temperature targets. There are different pathways within the envelope. Delayed response pathways initially follow the upper boundary of the emission envelope and reduce more by the end of the century. In contrast, early action pathways first follow the lower boundary and then the upper boundary. The latter require an early peak in the global emissions but keeps the option open for shifting to lower concentration targets in the future. Costs evaluations depend on the discount rate. Early action profiles have high costs early on, but learning-by-doing and smoother reduction rates over time lead to in most cases to lower costs across the century (net present value (NPV)). To achieve the 450 ppm CO₂-equivalent, the global emissions need to peak before 2020. The NPV of costs increase from 0.2% of cumulative gross domestic product to 1.0% as the shift is made from 650 to 450 ppm (discount rate 5%). However, the chances of limiting global mean warming to 2 °C above pre-industrial levels are very small for peaking and stabilisation at 650 ppm (1–23%) and 550 ppm (1–48%), but increase for a peaking at 510 ppm with subsequent stabilisation 450 ppm to 14–67%.     

The 183-WSL fast rain rate retrieval algorithm: Part I: Retrieval design

The Water vapour Strong Lines at 183 GHz (183-WSL) fast retrieval method retrieves rain rates and classifies precipitation types for applications in nowcasting and weather monitoring. The retrieval scheme consists of two fast algorithms, over land and over ocean, that use the water vapour absorption lines at 183.31 GHz corresponding to the channels 3 (183.31 ± 1 GHz), 4 (183.31 ± 3 GHz) and 5 (183.31 ± 7 GHz) of the Advanced Microwave Sounding Unit module B (AMSU-B) and of the Microwave Humidity Sounder (MHS) flying on NOAA-15-18 and Metop-A satellite series, respectively.The method retrieves rain rates by exploiting the extinction of radiation due to rain drops following four subsequent steps. After ingesting the satellite data stream, the window channels at 89 and 150 GHz are used to compute scattering-based thresholds and the 183-WSLW module for rainfall area discrimination and precipitation type classification as stratiform or convective on the basis of the thresholds calculated for land/mixed and sea surfaces. The thresholds are based on the brightness temperature difference Δ_win = T_B89 ? T_B150 and are different over land (L) and over sea (S): cloud droplets and water vapour (Δ_win < 3 K L; Δ_win < 0 K S), stratiform rain (3 K < Δ_win < 10 K L; 0 K < Δ_win < 10 K S), and convective rain (Δ_win > 10 K L and S). The thresholds, initially empirically derived from observations, are corroborated by the simulations of the RTTOV radiative transfer model applied to 20000 ECMWF atmospheric profiles at midlatitudes and the use of data from the Nimrod radar network. A snow cover mask and a digital elevation model are used to eliminate false rain area attribution, especially over elevated terrain. A probability of detection logistic function is also applied in the transition region from no-rain to rain adjacent to the clouds to ensure continuity of the rainfall field. Finally, the last step is dedicated to the rain rate retrieval with the modules 183-WSLS (stratiform) and 183WSLC (convective), and the module 183-WSL for total rainfall intensity derivation.A comparison with rainfall retrievals from the Goddard Profiling (GPROF) TRMM 2A12 algorithm is done with good results on a stratiform and hurricane case studies. A comparison is also conducted with the MSG-based Precipitation Index (PI) and the Scattering Index (SI) for a convective-stratiform event showing good agreement with the 183-WSLC retrieval. A complete validation of the product is the subject of Part II of the paper.     

Greenhouse gas mitigation in Chinese agriculture: Distinguishing technical and economic potentials

China is now the world's biggest annual emitter of greenhouse gases with 7467 million tons (Mt) carbon dioxide equivalent (CO₂e) in 2005, with agriculture accounting for 11% of this total. As elsewhere, agricultural emissions mitigation policy in China faces a range of challenges due to the biophysical complexity and heterogeneity of farming systems, as well as other socioeconomic barriers. Existing research has contributed to improving our understanding of the technical potential of mitigation measures in this sector (i.e. what works). But for policy purposes it is important to convert these measures into a feasible economic potential, which provides a perspective on whether agricultural emissions reduction (measures) are low cost relative to mitigation measures and overall potential offered by other sectors of the economy. We develop a bottom-up marginal abatement cost curve (MACC) representing the cost of mitigation measures applicable in addition to business-as-usual agricultural practices. The MACC results demonstrate that while the sector offers a maximum technical potential of 402 MtCO₂e in 2020, a reduction of 135 MtCO₂e is potentially available at zero or negative cost (i.e. a cost saving), and 176 MtCO₂e (approximately 44% of the total) can be abated at a cost below a threshold carbon price ≤¥ 100 (approximately €12) per tCO₂e. Our findings highlight the relative cost effectiveness of nitrogen fertilizer and manure best management practices, and animal breeding practices. We outline the assumptions underlying MACC construction and discuss some scientific, socioeconomic and institutional barriers to realizing the indicated levels of mitigation.     

Climate change impacts on ecosystems and the terrestrial carbon sink: a new assessment

Climate output from the UK Hadley Centre's HadCM2 and HadCM3 experiments for the period 1860 to 2100, with IS92a greenhouse gas forcing, together with predicted patterns of N deposition and increasing CO₂, were input (offline) to the dynamic vegetation model, Hybrid v4.1 (Friend et al., 1997; Friend and White, 1999). This model represents biogeochemical, biophysical and biogeographical processes, coupling the carbon, nitrogen and water cycles on a sub-daily timestep, simulating potential vegetation and transient changes in annual growth and competition between eight generalized plant types in response to climate.Global vegetation carbon was predicted to rise from about 600 to 800 PgC (or to 650 PgC for HadCM3) while the soil carbon pool of about 1100 PgC decreased by about 8%. By the 2080s, climate change caused a partial loss of Amazonian rainforest, C₄ grasslands and temperate forest in areas of southern Europe and eastern USA, but an expansion in the boreal forest area. These changes were accompanied by a decrease in net primary productivity (NPP) of vegetation in many tropical areas, southern Europe and eastern USA (in response to warming and a decrease in rainfall), but an increase in NPP of boreal forests. Global NPP increased from 45 to 50 PgC y⁻¹ in the 1990s to about 65 PgC y⁻¹ in the 2080s (about 58 PgC y⁻¹ for HadCM3). Global net ecosystem productivity (NEP) increased from about 1.3 PgC y⁻¹ in the 1990s to about 3.6 PgC y⁻¹ in the 2030s and then declined to zero by 2100 owing to a loss of carbon from declining forests in the tropics and at warm temperate latitudes — despite strengthening of the carbon sink at northern high latitudes. HadCM3 gave a more erratic temporal evolution of NEP than HadCM2, with a dramatic collapse in NEP in the 2050s.     

A numerical comparison study of cloud seeding by silver iodide and liquid carbon dioxide

A comparison study on dynamic and microphysical effects of cloud seeding by silver iodide (AgI) and liquid carbon dioxide (liquid CO₂) was made using a 3D cloud model with seeding processes. The model was initialized based on the rawinsonde sounding taken from Pinliang station located in the western China on 20 April 2001. The sounding air reflects moist and stable characteristics at middle and low layers. The model results show that the seeding by liquid CO₂ and AgI at − 15 to − 20 °C levels of cloud has almost the same dynamic effect on the simulated clouds. The seeding is able to induce the formation of weak convective cells in both seeded and unseeded regions due to latent heat released by the transformation from liquid saturation to ice saturation. However, the initial seeding conducted by liquid CO₂ in the region of maximum supercooled water with temperature of 0 to − 5 °C enable to produce much stronger dynamic effect and precipitation by forming many convective new cells at low levels in the later stage of seeded clouds. The accumulated precipitation at the surface can be increased and redistributed, and more concentrated in the downstream region of seeded clouds.     

A method for determining thermophysical properties of organic material in aqueous solutions: Succinic acid

A method for determining evaporation rates and thermodynamic properties of aqueous solution droplets is introduced. The method combines evaporation rate measurements using modified TDMA technique with data evaluation using an accurate evaporation model. The first set of data has been collected and evaluated for succinic acid aqueous solution droplets.Evaporation rates of succinic acid solution droplets have been measured using a TDMA system at controlled relative humidity (65%) and temperature (298 K). A temperature-dependent expression for the saturation vapour pressure of pure liquid phase succinic acid at atmospheric temperatures has been derived by analysing the evaporation rate data with a numerical model. The obtained saturation vapour pressure of liquid phase succinic acid is ln(p) = 118.41 − 16204.8/T − 12.452ln(T). The vapour pressure is in unit of Pascal and the temperature in Kelvin. A linear expression for the enthalpy of vaporization for liquid state succinic acid is also presented.According to the results presented in the following, a literature expression for the vapour pressure of liquid phase succinic acid defined for temperatures higher than 461 K [Yaws, C.L., 2003. Yaws' Handbook of Thermodynamic and Physical Properties of Chemical Compounds, Knovel] can be extrapolated to atmospheric temperatures with very good accuracy. The results also suggest that at 298 K the mass accommodation coefficient of succinic acid is unity or very close to unity.