Global photosynthetically active radiation and its relationship with global solar radiation in the Eastern Mediterranean basin

Summary ?The relationship between global photosynthetically active radiation (PAR) and global solar radiation is studied with a 2-year data archive of hourly values H_PAR and H_SW of these irradiances obtained at Athalassa, Cyprus. These data are used to determine the temporal variability of H_PAR and its dependence on sky conditions. The seasonal variation of the ratio H_PAR/H_SW obtained from daily data ranges from 0.456 (during summer) to 0.451 (during winter) with an annual mean value of 0.454. The ratio increases from 0.454 to 0.467 (daily values) or from 0.460 to 0.501 (hourly values), as sky conditions change from clear to overcast. Finally, the effect of aerosol content on the H_PAR/H_SW ratio is found to incur substantial changes in the PAR fraction. Received June 27, 2001; revised April 17, 2002; accepted May 18, 2002     

Hourly estimation of soil heat flux density at the soil surface with three models and two field methods

Heat flux density at the soil surface (G ₀) was evaluated hourly on a vegetal cover 0.08 m high, with a leaf area index of 1.07 m² m^?2, during daylight hours, using Choudhury et al. (Agric For Meteorol 39:283–297, 1987) ( $ G_0^{\text{rn}} $ ), Santanello and Friedl (J Appl Meteorol 42:851–862, 2003) ( $ G_0^{\text{s}} $ ), and force-restore ( $ G_0^{\text{fr}} $ ) models and the plate calorimetry methodology ( $ G_0^{\text{pco}} $ ), where the gradient calorimetry methodology (G _0R ) served as a reference for determining G ₀. It was found that the peak of G _0R was at 1 p.m., with values that ranged between 60 and 100 W m^?2 and that the G ₀/Rn relation varied during the day with values close to zero in the early hours of the morning and close to 0.25 in the last hours of daylight. The $ G_0^{\text{s}} $ model presented the best performance, followed by the $ G_0^{\text{rn}} $ and $ G_0^{\text{fr}} $ models. The plate calorimetry methodology showed a similar behavior to that of the gradient calorimetry referential methodology.     

Relationships between photosynthetically active radiation and clearness index at Bloemfontein, South Africa

Summary Relationships between photosynthetically active radiation (PAR) and solar radiation (SR) and between diffuse radiation and global radiation at Bloemfontein, South Africa were investigated. The ratio of PAR to SR (PAR/SR) has been reported from many places in the northern hemisphere, but there were not many PAR/SR measurements documented from the southern hemisphere, including the study region. Based on the present observations, mean PAR/SR in the region (0.48) was not exceptionally different from other reported data (0.45–0.50). The effects of sky condition on PAR/SR were also investigated and confirmed the previous findings. PAR/SR increased as the clearness index (K_T=ratio of global to extraterrestrial SR) decreased, as sky conditions varied from clear to cloudy. Thus, PAR/SR can be a simple function of the clearness index (the global PAR model). In this study, PAR/SR was explained by a quadratic function of K_T. For the relationship between diffuse and global radiation, a simple linear threshold diffuse PAR model, as a linear function of K_T, was proposed for the study region using long-term data of diffuse and global SR. Using the previous findings on the relationship between the ratio of diffuse to global SR (K_SR) and the ratio of diffuse to global PAR (K_PAR), at high K_T, K_PAR can be estimated as 30% higher than K_SR, while at low K_TK_PAR is equivalent to K_SR.     

Analysis of photosynthetically active radiation and applied parameterization model for estimating of PAR in the North China Plain

As photosynthetically active radiation (PAR) variability and PAR estimating methods play an important role in climate change and ecological process research, PAR variation trends and broadband global solar radiation (R _s ) ratios (PAR/R _s ) in the North China Plain (NCP) are examined using in situ PAR and R _s observed data for 2005 to 2011. The annual average PAR value found in the NCP is 22.9 mol m^?2 d^?1. The highest and lowest values were recorded at Changwu and Luancheng sites, respectively. The highest PAR/R _s value was found in Jiaozhouwan due to large water vapor volumes present in this area. PAR/R _s levels have increased in the NCP due to a decrease in fine aerosols and increase in water vapor concentration. From these analysis results, a parameterization model that can be applied to all sky conditions was checked. Empirical estimation model comparisons for obtaining PAR values indicate that model was least accurate when R _s was used independently. When the model included R _s, the clearness index (K _s) and the solar zenith angle, the model estimated PAR values with acceptable accuracy. A parameterization model was constructed by considering K _s and attenuation factors of PAR under clear weather conditions (ρ _clear). The improved parameterization model more accurately predicts values for local sites and for various observation sites.     

Variability of energy fluxes in relation to the net-radiation of urban and suburban areas: a case study

This paper addresses the relation between the net-radiation (Q ^*) and the ground heat flux (Q _G), the energy stored in the soil ( $\Updelta Q_{\rm S}$ ), and the residual of the energy partition (R = Q ^* ? Q _H  ? Q _E ) of urban and suburban areas of Oklahoma City, USA. These three forms of energy were observed or estimated from observations taken during Joint Urban 2003 Campaign. The database includes net-radiation, soil temperature, ground heat flux, and turbulent fluxes. In most cases the estimates of the energy stored in the soil were obtained by assuming roughly a certain type of soil and an effective soil depth. From the residuals it seems to be possible to distinguish the urban boundary layer from the suburban boundary layer when plotted as a function of net-radiation. Hysteresis coefficients were computed for fits of net-radiation against R, $\Updelta Q_{\rm S}$ and Q _G. In particular, the hysteresis patterns show that Q ^* vs. R represents clearer urban areas or suburban areas under the influence of an urban “plume”. On the other hand, hysteresis curves obtained from $\Updelta Q_{\rm S}$ or Q _G account for better the ground composition. A possible consequence is that the land use of urban areas could be roughly inferred from curve shapes such as Q ^* vs. R, or Q ^* versus another input variable representing the storage term. The objective is to show the variability of the subsurface-related energy fluxes across an urban area using these three different quantities and also to show that $\Updelta Q_{\rm S}, \,Q_{\rm G}$ , or R (and their corresponding hysteresis curves) are likely to be quantitatively different, which have not been clearly stated in the literature.     

Dynamics of photosynthetic photon flux density (PPFD) and estimates in coastal northern California

Plants require solar radiation for photosynthesis and their growth is directly related to the amount received, assuming that other environmental parameters are not limiting. Therefore, precise estimation of photosynthetically active radiation (PAR) is necessary to enhance overall accuracies of plant growth models. This study aimed to explore the PAR radiant flux in the San Francisco Bay Area of northern California. During the growing season (March through August) for 2?years 2007?C2008, the on-site magnitudes of photosynthetic photon flux densities (PPFD) were investigated and then processed at both the hourly and daily time scales. Combined with global solar radiation (R _S) and simulated extraterrestrial solar radiation, five PAR-related values were developed, i.e., flux density-based PAR (PPFD), energy-based PAR (PARE), from-flux-to-energy conversion efficiency (fFEC), and the fraction of PAR energy in the global solar radiation (fE), and a new developed indicator??lost PARE percentages (LPR)??when solar radiation penetrates from the extraterrestrial system to the ground. These PAR-related values indicated significant diurnal variation, high values occurring at midday, with the low values occurring in the morning and afternoon hours. During the entire experimental season, the overall mean hourly value of fFEC was found to be 2.17???mol?J^?1, while the respective fE value was 0.49. The monthly averages of hourly fFEC and fE at the solar noon time ranged from 2.15 in March to 2.39???mol?J^?1 in August and from 0.47 in March to 0.52 in July, respectively. However, the monthly average daily values were relatively constant, and they exhibited a weak seasonal variation, ranging from 2.02?mol?MJ^?1 and 0.45 (March) to 2.19?mol?MJ^?1 and 0.48 (June). The mean daily values of fFEC and fE at the solar noon were 2.16?mol?MJ^?1 and 0.47 across the entire growing season, respectively. Both PPFD and the ever first reported LPR showed strong diurnal patterns. However, they had opposite trends. PPFD was high around noon, resulting in low values of LPR during the same time period. Both were found to be highly correlated with global solar radiation R _S, solar elevation angle h, and the clearness index K _t. Using the best subset selection of variables, two parametric models were developed for estimating PPFD and LPR, which can easily be applied in radiometric sites, by recording only global solar radiation measurements. These two models were found to be involved with the most commonly measured global solar radiation (R _S) and two large-scale geometric parameters, i.e., extraterrestrial solar radiation and solar elevation. The models were therefore insensitive to local weather conditions such as temperature. In particular, with two test data sets collected in USA and Greece, it was verified that the models could be extended across different geographical areas, where they performed well. Therefore, these two hourly based models can be used to provide precise PAR-related values, such as those required for developing precise vegetation growth models.     

Increases of wet deposition at remote sites in Japan from 1991 to 2009

Temporal trends in wet deposition of major ions were explored at nationwide remote sites in Japan from April 1991 to March 2009 by using the seasonal Kendall slope estimator and the nonparametric seasonal Kendall test. For the trend analysis, datasets from eight remote sites (Rishiri, Echizenmisaki, Oki, Ogasawara, Shionomisaki, Goto, Yakushima, and Amami) were selected from the Japanese Acid Deposition Survey (JADS) conducted by the Ministry of the Environment. Deposition of H⁺ has been increasing at remote sites in Japan on a national scale. Significant (p????0.05) increases in H⁺ deposition were detected with changes of +3?C+9?%?year^?1 at seven sites, while insignificant increases were observed at one site. Depositions of non-sea salt (nss)-SO ₄ ^2? and NO ₃ ^? significantly increased at four and six sites, respectively, with changes of +1?C+3?%?year^?1. Significant increases in precipitation at four sites would have contributed to the increase in depositions of H⁺, nss-SO ₄ ^2? , and NO ₃ ^? . The emission trends of SO₂ and NO_x did not corresponded to the deposition trends of nss-SO ₄ ^2? and NO ₃ ^? . The different trends indicated that temporal variation of precipitation amount trend dominated the deposition trends.     

香河地区光合有效辐射的测量和计算

2004年9月12日—2006年10月31日,在河北省香河县对太阳辐射（包括光合有效辐射PAR、可见光辐射VIS和总辐射Q等）、气象参数等进行了综合测量,初步得到了PAR、VIS等的变化特征。观测表明,小时累计之比PAR/Q、VIS/Q、PAR/VIS相对稳定,2004—2006年的平均值分别为2.164、0.434 mol•MJ-1和4.967 mol•MJ-1,同时它们表现出明显的日、逐日和季节变化特征,并受到水汽、气溶胶、云等因素的影响。建立了实际天气条件计算PAR、VIS小时累计值的经验公式以及PAR与VIS转换关系式,计算值与观测值符合得较好。在考虑水汽和散射因子时,PAR、VIS计算值与观测值的相对偏差分别为9.9%和10.8%。限于实际情况,也可以只考虑水汽因子的作用来计算PAR和VIS小时累计值,它们的相对偏差分别为11.1%和11.8%。对于PAR、VIS的传输和计算来说,水汽因子的作用至关重要。散射因子的作用虽然弱于水汽因子,但它的作用不容忽视。     

禹城地区光合有效辐射的计算方法

利用2005年7月-2006年10月在山东禹城对太阳辐射（包括光合有效辐射PAR、可见光辐射VIS、总辐射Q等）、气象要素等进行的4次综合观测资料,初步得到了朋R,VIS的日、季节变化特征并对其进行了分析,结果表明：各辐射的小时累计之比vIS／Q,PAR／Q,PAR／VIS相对稳定,其平均值分别为0．39,1．95（mol／MJ）,4．97（mol／MJ）,但它们均有明显的日、逐日、季节变化,并受水汽、气溶胶、云等因素的影响。同时建立了实际天气PAR,VIS的小时累计经验公式及其转换关系,计算值与观测值均比较接近。当考虑水汽和散射因子时,PAR,VIS的计算值与观测值的相对偏差分别为11．1％,10．6％。限于实际情况,可以只考虑水汽因子的作用来计算PAR和VIS的小时累计值,它们的相对偏差分别为13．3％,12．6％。水汽因子对于PAR,VIS的传输和计算具有重要作用。     

Relationship Between Fine-Particle Pollution and the Urban Heat Island in Beijing,China: Observational Evidence

Urbanization has led to a significant urban heat island (UHI) effect in Beijing in recent years. At the same time, air pollution caused by a large number of fine particles significantly influences the atmospheric environment, urban climate, and human health. The distribution of fine particulate matter (PM_2.5) concentration and its relationship with the UHI effect in the Beijing area are analyzed based on station-observed hourly data from 2012 to 2016. We conclude that, (1) in the last five years, the surface concentrations of PM_2.5 averaged for urban and rural sites in and around Beijing are 63.2 and 40.7 µg m^?3, respectively, with significant differences between urban and rural sites (ΔPM_2.5) at the seasonal, monthly and daily scales observed; (2) there is a large correlation between ΔPM_2.5 and the UHI intensity defined as the differences in the mean (ΔT_ave), minimum (ΔT_min), and maximum (ΔT_max) temperatures between urban and rural sites. The correlation between ΔPM_2.5 and ΔT_min (ΔT_max) is the highest (lowest); (3) a Granger causality analysis further shows that ΔPM_2.5 and ΔT_min are most correlated for a lag of 1–2 days, while the correlation between ΔPM_2.5 and ΔT_ave is lower; there is no causal relationship between ΔPM_2.5 and ΔT_max; (4) a case analysis shows that downwards shortwave radiation at the surface decreases with an increase in PM_2.5 concentration, leading to a weaker UHI intensity during the daytime. During the night, the outgoing longwave radiation from the surface decreases due to the presence of daytime pollutants, the net effect of which is a slower cooling rate during the night in cities than in the suburbs, leading to a larger ΔT_min.     

Polarimetric rainfall retrieval from a C-Band weather radar in a tropical environment (The Philippines)

We evaluated the potential of polarimetric rainfall retrieval methods for the Tagaytay C-Band weather radar in the Philippines. For this purpose, we combined a method for fuzzy echo classification, an approach to extract and reconstruct the differential propagation phase, Φ _DP , and a polarimetric self-consistency approach to calibrate horizontal and differential reflectivity. The reconstructed Φ _DP was used to estimate path-integrated attenuation and to retrieve the specific differential phase, K _DP . All related algorithms were transparently implemented in the Open Source radar processing software wradlib. Rainfall was then estimated from different variables: from re-calibrated reflectivity, from re-calibrated reflectivity that has been corrected for path-integrated attenuation, from the specific differential phase, and from a combination of reflectivity and specific differential phase. As an additional benchmark, rainfall was estimated by interpolating the rainfall observed by rain gauges. We evaluated the rainfall products for daily and hourly accumulations. For this purpose, we used observations of 16 rain gauges from a five-month period in the 2012 wet season. It turned out that the retrieval of rainfall from K _DP substantially improved the rainfall estimation at both daily and hourly time scales. The measurement of reflectivity apparently was impaired by severe miscalibration while K _DP was immune to such effects. Daily accumulations of rainfall retrieved from K _DP showed a very low estimation bias and small random errors. Random scatter was, though, strongly present in hourly accumulations.     

A Test Pattern Identification Algorithm and Its Application to CINRAD/SA(B) Data简

A variety of faulty radar echoes may cause serious problems with radar data applications,especially radar data assimilation and quantitative precipitation estimates.In this study,＂test pattern＂ caused by test signal or radar hardware failures in CINRAD （China New Generation Weather Radar） SA and SB radar operational observations are investigated.In order to distinguish the test pattern from other types of radar echoes,such as precipitation,clear air and other non-meteorological echoes,five feature parameters including the effective reflectivity data percentage （Rz）,velocity RF （range folding） data percentage （RRF）,missing velocity data percentage （RM）,averaged along-azimuth reflectivity fluctuation （RNr,z） and averaged along-beam reflectivity fluctuation （RNa,z） are proposed.Based on the fuzzy logic method,a test pattern identification algorithm is developed,and the statistical results from all the different kinds of radar echoes indicate the performance of the algorithm.Analysis of two typical cases with heavy precipitation echoes located inside the test pattern are performed.The statistical results show that the test pattern identification algorithm performs well,since the test pattern is recognized in most cases.Besides,the algorithm can effectively remove the test pattern signal and retain strong precipitation echoes in heavy rainfall events.     

华北地区光合有效辐射的计算方法研究

2004年9月—2006年10月,选择华北地区的4个观测站开展了太阳辐射（光合有效辐射PAR、可见光辐射VIS、总辐射Q等）、气象参数等的综合测量,得到了PAR、VIS等的变化特征,结果表明：PAR/Q、VIS/Q、PAR/VIS相对稳定,有明显的日、逐日和季节变化,并受到水汽、散射因子、云等因素的影响。2004—2006年禹城、栾城、香河、兴隆地区VIS/Q,PAR/Q和PAR/VIS的平均值分别为0.39,1.95 mol/MJ和4.97 mol/MJ;0.39,1.94 mol/MJ和4.95 mol/MJ;0.43,2.16 mol/MJ和4.97 mol/MJ;0.42,2.03 mol/MJ和4.89 mol/MJ。建立了计算华北地区实际天气PAR、VIS小时累计值的经验公式及PAR与VIS转换关系式,计算值与观测值符合得都比较好。考虑水汽和散射因子时,PAR、VIS计算值与观测值的相对偏差分别为13.0%、12.4%。由于某些站点可能缺少直接或散射辐射,也可以只考虑水汽因子,此时,PAR、VIS的相对偏差分别为13.2%、12.8%。对于PAR、VIS的传输和计算来说,水汽因子的作用最为重要;散射因子的作用虽弱于水汽因子,但也不应该忽视。     

Estimation of ground heat flux from soil temperature over a bare soil

Ground soil heat flux, G ₀, is a difficult-to-measure but important component of the surface energy budget. Over the past years, many methods were proposed to estimate G ₀; however, the application of these methods was seldom validated and assessed under different weather conditions. In this study, three popular models (force-restore, conduction-convection, and harmonic) and one widely used method (plate calorimetric), which had well performance in publications, were investigated using field data to estimate daily G ₀ on clear, cloudy, and rainy days, while the gradient calorimetric method was regarded as the reference for assessing the accuracy. The results showed that harmonic model was well reproducing the G ₀ curve for clear days, but it yielded large errors on cloudy and rainy days. The force-restore model worked well only under rainfall condition, but it was poor to estimate G ₀ under rain-free conditions. On the contrary, the conduction-convection model was acceptable to determine G ₀ under rain-free conditions, but it generated large errors on rainfall days. More importantly, the plate calorimetric method was the best to estimate G ₀ under different weather conditions compared with the three models, but the performance of this method is affected by the placement depth of the heat flux plate. As a result, the heat flux plate was recommended to be buried as close as possible to the surface under clear condition. But under cloudy and rainy conditions, the plate placed at depth of around 0.075 m yielded G ₀ well. Overall, the findings of this paper provide guidelines to acquire more accurate estimation of G ₀ under different weather conditions, which could improve the surface energy balance in field.     

Characteristics of the precipitation recycling ratio and its relationship with regional precipitation in China

A dynamic recycling model (DRM) with an analytical moisture trajectory tracking method, together with Japan Meteorological Agency 25-year reanalysis data, is used to study the regional precipitation recycling process across China, by calculating the regional recycling ratio (ρ _r ) at the daily time scale during 1979–2010. The distribution of ρ _r shows that, in western China, especially the Tibetan Plateau and its surrounding areas, precipitation is strongly dependent on the recycling process associated with regional evaporation. In Southeast China, however, the contribution from the recycling processes is much smaller due to the influence of the summer monsoon. A precipitation threshold value of about 4 mm/day is obtained from detailed analysis of both extreme and all-range ρ _r years. According to this threshold, China is classified into three types of sub-regions: low-precipitation sub-regions (mainly in the northwest), high-precipitation sub-regions (mainly in the south), and medium-precipitation sub-regions (mainly in the northeast). It is found that ρ _r correlates positively with precipitation, as well as convective precipitation (P _CP) and large-scale precipitation (P _LP) in the low-precipitation sub-regions. However, negative ρ _r ?～?P _LP correlations are found in the high-precipitation sub-regions and nonsignificant correlations exist in the medium-precipitation sub-regions. As P _CP is mainly locally generated due to mid-latitude mesoscale systems and the cumulus parameterization used in producing the reanalysis, the recycling ratio positively correlates to the ratio P _CP/P _LP in almost all sub-regions, particularly in the Tibetan Plateau and its surrounding areas. The correlation between radiation flux and ρ _r suggests more net radiation supports more evaporation and higher ρ _r , especially in the high-precipitation sub-regions. The influence of clouds on shortwave radiation is crucial, since evaporation is suppressed when the amount of cloudiness increases, especially in the high-precipitation sub-regions. Together with the consideration of soil moisture, it can be inferred that limited soil moisture inhibits evaporation in the low-precipitation sub-regions, while the energy or radiation is the dominant factor controlling evaporation in the high-precipitation sub-regions.     

Trend analysis of rainfall time series for Sindh river basin in India

The main goal of this paper is to estimate a set of optimal seasonal, daily, and hourly values of atmospheric turbidity and surface radiative parameters Ångström’s turbidity coefficient (β), Ångström’s wavelength exponent (α), aerosol single scattering albedo (ω_o), forward scatterance (F_c) and average surface albedo (ρ_g), using the Brute Force multidimensional minimization method to minimize the difference between measured and simulated solar irradiance components, expressed as cost functions. In order to simulate the components of short-wave solar irradiance (direct, diffuse and global) for clear sky conditions, incidents on a horizontal surface in the Metropolitan Area of Rio de Janeiro (MARJ), Brazil (22° 51′ 27″ S, 43° 13′ 58″ W), we use two parameterized broadband solar irradiance models, called CPCR2 and Iqbal C, based on synoptic information. The meteorological variables such as precipitable water (u_w) and ozone concentration (u_o) required by the broadband solar models were obtained from moderate-resolution imaging spectroradiometer (MODIS) sensor on Terra and Aqua NASA platforms. For the implementation and validation processes, we use global and diffuse solar irradiance data measured by the radiometric platform of LabMiM, located in the north area of the MARJ. The data were measured between the years 2010 and 2012 at 1-min intervals. The performance of solar irradiance models using optimal parameters was evaluated with several quantitative statistical indicators and a subset of measured solar irradiance data. Some daily results for Ångström’s wavelength exponent α were compared with Ångström’s parameter (440–870 nm) values obtained by aerosol robotic network (AERONET) for 11 days, showing an acceptable level of agreement. Results for Ångström’s turbidity coefficient β, associated with the amount of aerosols in the atmosphere, show a seasonal pattern according with increased precipitation during summer months (December–February) in the MARJ.     

Anthropogenic sulphate aerosols and large Cl-deficit in marine atmospheric boundary layer of tropical Bay of Bengal

Our long-term study provides an unequivocal evidence for near-quantitative (80–100%) depletion of chloride from sea-salts in the marine atmospheric boundary layer (MABL) of tropical Bay of Bengal. During the late NE-monsoon (Jan-Mar), continental outflow from south and south-east Asia dominate the wide-spread dispersal of pollutants over the Bay of Bengal. Among anthropogenic constituents, SO ₄ ^2? (range: 0.6–35 μg m^?3) is the most dominant. The non-sea-salt SO ₄ ^2? (nss-SO ₄ ^2? ) constitutes a major fraction (55–65%) of the aerosol water-soluble ionic composition (WSIC), whereas contribution of NO ₃ ^? is relatively minor. The magnitude of Cl-deficit (with respect to its sea-salt proportion) exhibits linear increase with the excess-nss-SO ₄ ^2? (excess over NH ₄ ⁺ ). We propose that displacement of HCl from sea-salt aerosols by H₂SO₄ is a dominant reaction mechanism for the chloride-depletion. These results also suggest that sea-salts could serve as a potential sink for anthropogenic SO₂ in the downwind polluted marine environment. Furthermore, loss of hydrogen chloride, representing a large source of reactive chlorine, has implications to the oxidant chemistry in the MABL (oxidation of hydrocarbons and dimethyl sulphide).     

Estimating a Lagrangian Length Scale Using Measurements of CO2 in a Plant Canopy

Analytical Lagrangian equations capable of predicting concentration profiles from known source distributions offer the opportunity to calculate source/sink distributions through inverted forms of these equations. Inverse analytical Lagrangian equations provide a practical means of estimating source profiles using concentration and turbulence measurements. Uncertainty concerning estimates of the essentially immeasurable Lagrangian length scale ( ${\mathcal{L}}$ ), a key input, impedes the operational practicality of this method. The present study evaluates ${\mathcal{L}}$ within a corn canopy by using field measurements to constrain an analytical Lagrangian equation. Measurements of net CO₂ flux, soil-to-atmosphere CO₂ flux, and in-canopy profiles of CO₂ concentration provided the information required to solve for ${\mathcal{L}}$ in a global optimization algorithm for 30-min time intervals. For days when the canopy was a strong CO₂ sink, the optimization frequently located ${\mathcal{L}}$ profiles that follow a convex shape. A constrained optimization then fit the profile shape to a smooth sigmoidal equation. Inputting the optimized ${\mathcal{L}}$ profiles in the forward and inverse Lagrangian equations leads to strong correlations between measured and calculated concentrations and fluxes. Coefficients of the sigmoidal equation were specific to each 30-min period and did not scale with any measured variable. Plausible looking ${\mathcal{L}}$ profiles were associated with negative bulk Richardson number values. Once the canopy senesced, a simple eddy diffusivity profile sufficed to relate concentrations and sources in the analytical Lagrangian equations.     

Bulk characteristics of heat transfer in the unstable,baroclinic atmospheric boundary layer

Field data for the unstable, baroclinic, atmospheric boundary layer over land and over the sea are considered in the context of a general similarity theory of vertical heat transfer. The dependence of δθ/θ_* upon logarithmic functions of h _c z _T and stability (through the similarity function C) is clearly demonstrated in the data. The combined data support the conventional formulation for the heat transfer coefficient δθ/θ_* when,

1. the surface scaling length is z _T (« z ₀), the height at which the surface temperature over land is obtained by extrapolation of the temperature profile
2. the height scale is taken as the depth of convective mixing h _c
3. the temperature profile equivalent of the von Karman constant is taken as 0.41
4. areal average, rather than single point, values of δθ are employed in strongly baroclinic conditions. No significant effect of baroclinity or the height scale ratio as proposed in the general theory is found. Variations in C about a linear regression relation against stability are most probably due to uncertainties in the areal surface temperature and to experimental errors in general temperature measurements.

     

Wet deposition of precipitation chemistry during 2005–2009 at a remote site (Nam Co Station) in central Tibetan Plateau

Chemical compositions of precipitation samples collected from a remote and high elevation site (Nam Co Station, 30°46.44??N, 90°59.31??E, 4730?m?a.s.l.) in central Tibetan Plateau (TP, hereafter) from August 2005 to August 2009 are investigated. During the study period, Ca²⁺ and HCO ₃ ^- have the highest concentrations among ions and are the dominant cation and anion in precipitation, taking 27.46?% and 30.84?% to the total ions respectively. Empirical Orthogonal Functions (EOFs) analyses reveal that crustal aerosol inputs significantly contributed to the loading of Ca²⁺, Mg²⁺, SO ₄ ^2- and HCO ₃ ^- in precipitation, while lake salt plays a major source of K⁺ and Cl^-. Seasonal variations of ionic wet deposition fluxes show high values during monsoon seasons due to large precipitation amount. Among the cations, annual Ca²⁺ flux is the largest (86.26?eq hm^?2), Na⁺ and NH ₄ ⁺ fluxes are following. Among anions, HCO ₃ ^- has the highest flux (98.66?eq hm^?2) while that of NO ₃ ^- is the lowest. Annual wet deposition of nitrogen has varied considerably with the average value of 0.70?kg?ha^?1 a^?1 at Nam Co Station. About 80?% of total nitrogen flux occurs during the monsoon seasons when precipitation is concentrated, in which NH ₄ ⁺ and NO ₃ ^- contributed to 61?% and 39?% of the total nitrogen deposition. Thus, our ionic concentrations and wet deposition fluxes in precipitation can provide a useful dataset to assess atmospheric environment and its impacts on ecosystem in the inland TP.