Estimation of sampling error uncertainties in observed surface air temperature change in China

This study examines the sampling error uncertainties in the monthly surface air temperature (SAT) change in China over recent decades, focusing on the uncertainties of gridded data, national averages, and linear trends. Results indicate that large sampling error variances appear at the station-sparse area of northern and western China with the maximum value exceeding 2.0 K² while small sampling error variances are found at the station-dense area of southern and eastern China with most grid values being less than 0.05 K². In general, the negative temperature existed in each month prior to the 1980s, and a warming in temperature began thereafter, which accelerated in the early and mid-1990s. The increasing trend in the SAT series was observed for each month of the year with the largest temperature increase and highest uncertainty of 0.51 ± 0.29 K (10 year)⁻¹ occurring in February and the weakest trend and smallest uncertainty of 0.13 ± 0.07 K (10 year)⁻¹ in August. The sampling error uncertainties in the national average annual mean SAT series are not sufficiently large to alter the conclusion of the persistent warming in China. In addition, the sampling error uncertainties in the SAT series show a clear variation compared with other uncertainty estimation methods, which is a plausible reason for the inconsistent variations between our estimate and other studies during this period.

     

Atmospheric concentrations of PAHs, their possible sources and gas-to-particle partitioning at a residential site of Bursa, Turkey

Atmospheric PAH concentrations were determined in Gulbahce district of Bursa, Turkey between August 2004 and April 2005. Measured PAH concentrations were classified as heating and non-heating season samples. The concentrations of total PAHs in heating season were almost ten times higher than those in non-heating season. Diagnostic ratios and factor analysis results show that in the heating season traffic along with residential heating emissions heavily influence PAH concentrations. The plot of logK_p versus logP_L⁰ for all the data set of heating and non-heating season samples gave significantly different slopes. The slope for the heating season samples (− 0.92) was steeper than the one for the non-heating season samples (− 0.78). The partitioning results for individual samples further indicated that slope values varied depending on air parcel trajectories. Air parcels traveled over water (either over the Black Sea or Aegean Sea) prior to arriving at the sampling site had less steep slopes. Partitioning of PAHs was also investigated by comparing experimentally determined K_p values with the results obtained both from octanol-based model (K_p(Oct.)) and soot and octanol-based model (K_p (Soot + Oct.)). Both models were useful in predicting the experimental K_p values. However, they did not explain the observed variability in the experimental K_p values.     

Trends and uncertainties in surface air temperature over the Tibetan Plateau, 1951–2013

Trends and uncertainties of surface air temperature over the Tibetan Plateau (TP) are evaluated by using observations at 100 meteorological stations during the period 1951–2013. The sampling error variances of gridded monthly data are estimated for every month and every grid box of data. The gridded data and their sampling error variances are used to calculate TP averages, their trends, and associated uncertainties. It is shown that large sampling error variances dominate northern and western TP, while small variances appear over southern and eastern TP. Every month from January to December has a positive linear trend during the study period. February has the largest trend of 0.34 ± 0.18°C (10 yr)^–1, and April the smallest at 0.15 ± 0.11°C (10 yr)^–1. The uncertainties decrease steadily with time, implying that they are not large enough to alter the TP warming trend.     

The Diffuse Fraction of Global Solar Irradianceat a Tropical Location

Summary The annual and monthly mean diurnal variations of the diffuse fraction of global solar irradiance arriving on the ground at a tropical station in Sub-Sahel Africa is here been reported. The monthly mean hourly values of the diffuse fraction (K _d ) for such clear-sky months as February, March and November at this location, which approach a minimum at about local noon, are observed to lie generally below 0.50 during the period from 11:00 to 15:00 hrs (LST). Consequently, solar concentrators utilising parabolic mirrors are expected to have high performance during these months in this region. Like the mainly-cloudy and wet months (June to August) in which monthly mean hourly values of K _d higher than 0.62 have been recorded, the corresponding diffuse fraction for dust-haze months (mostly December and January) with high turbidity coefficients were generally above 0.50. Monthly mean hourly values of K _d for less cloudy months (April, May, September and October) ranged between 0.48 and 0.77 during the period from 11:00 to 15:00 hrs (LST). The effects of atmospheric dust-haze, clouds and albedo on the monthly mean diurnal variation of the diffuse fraction has been discussed. Also reported are the characteristic values of K _d for sets of months with relatively similar atmospheric and sky conditions at this location. The annual variations of the monthly mean daily values of K _d which exhibit strong seasonal dependence showed a peak in August for both years. Except for the months of February and March, the monthly mean daily totals of K _d exhibited similar annual marches during both years. The major discrepancy in the values of the monthly mean daily totals of K _d in both years were recorded in the months of February, November and December, with the corresponding K _d values for these months in both years agreeing only to within 32.9% in February, 15.4% in November and 16.2% in December. Apart from the aforementioned months, the corresponding monthly mean daily totals of K _d for the remaining nine months in both years agreed mostly to within less than 8.4%. The least monthly mean daily ratios of K _d were obtained in the relatively clear month of November for both years being 0.43 in 1993 and 0.49 in 1994. On an annual average, the diffuse component was found to constitute 59.6% of the global solar irradiance arriving on the ground at this region in 1993 and 60.9% in 1994. The results been reported here have been compared with a few others emanating from other tropical stations. Received February 5, 1998 Revised May 12, 1998     

FAO-56 methodology for determining water requirement of irrigated crops: critical examination of the concepts,alternative proposals and validation in Mediterranean region

The present study evaluates firstly the ability of the FAO-56 methodology, based on the two-step approach “reference evapotranspiration (ET₀)—crop coefficient (K _c),” to accurately determine the actual evapotranspiration (ET) of irrigated crops and proposes, secondly, the alternative approaches for improving this determination. The FAO-56 methodology is supported by two hypotheses: (1) ET₀ represents all effects of weather and (2) K _c varies predominately with specific crop characteristics and only marginally with climate, which enables the transfer of K _c standard values among locations and climates. On the base of the theoretical analysis and experimental observations, a critical examination of the previous hypotheses demonstrates that they are not verified by reality. The first hypothesis is not verified for two reasons: (a) The formulation adapted by the Penman–Monteith equation and proposed in FAO-56 methodology for calculating ET₀ uses climatic variables determined at a 24-h average scale. However, in principle it is only valid in permanent regime, in other words at least on an hourly scale. (b) The FAO-56-proposed formulation attributes a constant value to the canopy resistance of the reference surface; but in reality, this resistance is variable in relation to the climatic variables. The second hypothesis, concerning the two-step approach, is also not verified because the values of K _c largely vary in relation to climatic variables (radiation, air vapour pressure deficit and wind speed). This fact does not support the possibility of the transferability of K _c values into locations where the local conditions deviate from the conditions where the adjusted values of K _c were determined. The weakness of the ET estimation, observed on several crops cultivated in the Mediterranean region, through the application of the FAO-56 methodology, is the result of errors accumulation, associated with that affects the determination of either ET₀ or K _c. The present study underlines the advantage of using a one-step approach in the calculation of ET, since it is based on fewer computation steps and, consequently, on fewer error sources than the two-step model. Two models adopting this approach are proposed and validated, one of which can be considered as operational, i.e. it only needs standard meteorological data as input. The use of these models enables an improvement of the ET estimation. This objective is a key component of any strategy to improve agricultural water management in Mediterranean region.     

Concentration and gas/particle partitioning of polychlorinated biphenyls (PCBs) at an industrial site at Bursa, Turkey

Gas and particle phase concentrations of atmospheric polychlorinated biphenyls (PCBs) were measured at an urban/industrial site in the city of Bursa, Turkey. PCB concentration levels were presented between July 2004 and May 2005. Average particle and gas phase concentrations of individual PCB congeners ranged from 0.08 (PCB-183) to 6.86 (PCB-49) pg m^− 3 and from 0.01 (PCB-209) to 47.2 (PCB-33) pg m^− 3, respectively. The mean concentration of total (gas + particle) PCBs varied between 24.27 and 666.21 pg m^− 3 with an average of 287.27 ± 174.80 pg m^− 3. PCB concentrations at the sampling site were higher than the concentrations reported at non-urban sites. PCBs partitioned between gas and particle phases and the partitioning was examined according to different approaches such as logK_p–logP_L^o, logK_p–logK_OA and the Junge–Pankow model. In order to present possible interactions, a correlation matrix based on PCB congeners and meteorological parameters was constructed. Application of the Clausius–Clapeyron equation yielded a low slope value indicating possible emissions from local and regional sources originating mainly from urban/industrial areas, landfill and waste incineration plant. Then, likely dry deposition fluxes were estimated depending on reported dry deposition velocity and atmospheric concentration values.     

Analysis of the Weighted Mean Temperature of China Based on Sounding and ECMWF Reanalysis Data

Weighted mean temperature (Tm) is one of the most important conversion parameters for calculating precipitable water vapor by the signal path wet delay in ground-based GPS meteorology. This paper first discusses the Tmregression models for Hong Kong (HK) and the associated error statistics relative to the true values of Tmfrom the numerical method. The results show that there is little difference in precision between annual and seasonal Tmregression models for HK. The Bevis Tm-Ts(surface temperature) regression model is more suitable for northeastern China and the Qinghai-Tibetan Plateau than the local models. For areas lack of historical sounding data, the Kriging interpolation method and the ECMWF reanalysis product ERA-interim were employed to set up local Tm-Ts models. The results indicate that the Tmderived by the ERA-interim data coincides well with that by the sounding data, and the Kriging interpolation method can successfully obtain the coefficients of local Tm-Tsmodels, suggesting that these two approaches may serve as effective ways in the acquisition and localization of Tm.     

Local Scales of Turbulence in the Stable Boundary Layer

Local, gradient-based scales, which contain the vertical velocity and temperature variances, as well as the potential temperature gradient, but do not include fluxes, are tested using data collected during the CASES-99 experiment. The observations show that the scaling based on the temperature variance produces relatively smaller scatter of empirical points. The resulting dimensionless statistical moments approach constant values for sufficiently large values of the Richardson number Ri. This allows one to derive predictions for the Monin–Obukhov similarity functions φ _m and φ _h , the Prandtl number Pr and the flux Richardson number Rf in weak turbulence regime.     

Parameterization of Sheared Convective Entrainment in the First-Order Jump Model: Evaluation Through Large-Eddy Simulation

In this note, two different approaches are used to estimate the entrainment-flux to surface-flux ratio for a sheared convective boundary layer (CBL); both are derived under the framework of the first-order jump model (FOM). That suggested by Sun and Wang (SW approach) has the advantage that there is no empirical constant included, though the dynamics are described in an implicit manner. The second, which was proposed by Kim et al. and Pino et al. (KP approach), explicitly characterizes the dynamics of the sheared entrainment, but uncertainties are induced through the empirical constants. Their performances in parameterizing the CBL growth rate are compared and discussed, and a new value of the parameter A ₃ in the KP approach is suggested. Large-eddy simulation (LES) data are employed to test both approaches: simulations are conducted for the CBL growing under varying conditions of surface roughness, free-atmospheric stratification, and wind shear, and data used when the turbulence is in steady state. The predicted entrainment rates in each case are tested against the LES data. The results show that the SW approach describes the evolution of the sheared CBL quite well, and the KP approach also reproduces the growth of the CBL reasonably, so long as the value of A ₃ is modified to 0.6.     

Henry's law coefficients of formic and acetic acids

The Henry's law constants, K _H, of dilute aqueous formic and acetic acids were determined experimentally as a function of concentration and temperature using a new counterflow packed-column technique. K _H was found to be (8.9±1.3)×10³ and (4.1±0.4)×10³ M atm^-1 at 25°C for HCOOH and CH₃COOH, respectively. The reaction enthalpies, H, were found to be –51±2 kJ mol^-1 and –52±1 kJ mol^-1 for formic and acetic acid, respectively. These are in good agreement with calculated thermochemical values.Whereas the K _H values are in reasonably good agreement with certain other experimentally determined values, K _H (HCOOH) is two to three times higher than calculated thermochemical values while K _H (CH₃COOH) is lower than the two calculated values.The best experimental values appear to be (11±2)×10³ M atm^-1 and (7±3)×10³ M atm^-1 for HCOOH and CH₃COOH, respectively.     

Determination of kolmogorov entropy of chaotic attractor included in one—dimensional time series of meteorological data

The 1970-1985 day to day averaged pressure dataset of Shanghai and the extension method in phase space are used to calculate the correlation dimension D and the second-order Renyi entropy K2 of the approximation of Kolmogorov’s entropy, the fractional dimension D = 7.7~7.9 and the positive value K2 ≈ 0.1 are obtained. This shows that the attractor for the short-term weather evolution in the monsoon region of China exhibits a chaotic mo-tion. The estimate of K2 yields a predictable time scale of about ten days. This result is in agreement with that ob-tained earlier by the dynamic-statistical approach.The effects of the lag time τ on the estimate of D and K2 are investigated. The results show that D and K2 are convergent with respect to τ. The day to day averaged pressure series used in this paper are treated for the extensive phase space with τ = 5, the coordinate components are independent of each other; therefore, the dynamical character quantities of the system are stable and reliable.     

Statistics of Scalar Fields in the Atmospheric Boundary Layer Based on Large-eddy Simulations. Part 1: Free Convection

Convection in a quasi-steady, cloud-free, shear-free atmospheric boundary layer is investigated based on a large-eddy simulation model. The performed tests indicate that the characteristic (peak) values of statistical moments at the top of the mixed layer are proportional to the interfacial scales (from gradients of scalars in the interfacial layer). Based on this finding a parameterization is proposed for profiles of scalar variances. The parameterization employs two, semi-empirical similarity functions F_m(z/z_i) andF_i(z/z_i), multiplied by a combination of the mixed-layer scales and the interfacial scales.     

Aspects of CO2 advection measurements

Observations of vegetation–atmosphere exchange of carbon dioxide (CO₂) by the eddy covariance (EC) technique are limited by difficult conditions such as nighttime and heterogeneous terrain. Thus, advective flux components are included into the net ecosystem exchange (NEE) budget. However, advection measurements are experimentally challenging and do not always help to solve the night flux problem of the EC technique. This study investigates alternative methods for the observation of horizontal advection, in particular horizontal concentration gradients, as well as different approaches to coordinate rotation and vertical advection. Continuous high-frequency measurements of the horizontal CO₂ concentration field are employed and compared to the often used discontinuous sequential sampling. Significant differences were found in the case of 30-min mean concentration values between the conventional discontinuous sampling approach and the complete observation of the time series by continuous sampling. Estimates of vertical advection rely on accurate estimates of vertical wind velocity ( $\emph{w}$ ). Therefore, different approaches to the planar fit coordinate rotation have been investigated. Sector-wise rotation was able to eliminate directional dependencies of mean $\emph{w}$ . Furthermore, the effect of the data set length used for rotation (window length) was investigated and was found to have significant impact on estimates of vertical advection, with larger window lengths yielding about 50% larger vertical advection. A sequential planar fit with controlled window length is proposed to give reproducible results. The different approaches to the measurement and calculation of horizontal and vertical advection presented are applied to data obtained during the exchange processes in mountainous region experiment at the FLUXNET site Waldstein–Weidenbrunnen (DE-Bay). Estimates of NEE including advection are compared to NEE from turbulent and storage flux alone without advection. NEE including vertical advection with sector-wise planar fit rotation and controlled window length and including horizontal advection from continuous gradient measurements, which were comprehensively bias corrected by a new approach, did compare well with the expected night flux error, with meteorological drivers of the fluxes and with soil chamber measurements. Unrealistically large and noisy values of horizontal advection from the conventional discontinuous sampling approach, which lead to unrealistic values of NEE, could be eliminated by the alternative approaches presented. We therefore suggest the further testing of those approaches at other sites in order to improve the accuracy of advection measurements and, subsequently, estimates of NEE.     

Climatic comfort of the Southern Federal Okrug and its regionalization using the computed values of the pathogenicity index and coefficient of the atmosphere self-purification potential

Bioclimatic conditions of the Southern Federal Okrug that characterize how comfort the climate conditions are for the human organism are studied. The territory is regionalized based on the estimated values of the pathogenicity index I and coefficient of the atmosphere self-purification potential K _p .     

Intensity Evolution of Zonal Shear Line over the Tibetan Plateau in Summer: A Perspective of Divergent and Rotational Kinetic Energies

Based on the ERA5 reanalysis datasets during 1980–2019, a total of eleven zonal shear lines (ZSLs) that caused heavy precipitation and lasted more than 60 hours over the Tibetan Plateau in summer are selected for composite analysis. By decomposing the kinetic energy (K) near the ZSL into divergent and rotational kinetic energies (K_D and K_R) and the kinetic energy of interaction between the divergent wind and the rotational wind (K_RD), the influence of the rotational and divergent winds on the evolution of the ZSL intensity is investigated from the perspective of K_D and K_R. The main results are as follows. The ZSL is a comprehensive reflection of rotation and convergence. The intensity evolution of ZSL is essentially synchronized with those of K, K_R, and K_RD but lags behind K_D by about three hours. The enhancement of K is mainly contributed by K_R, which is governed by the conversion from K_D to K_R. Furthermore, the increase in the conversion from K_D to K_R is controlled by the geostrophic effect term Af, which is determined by the joint enhancement of the zonal rotational and meridional divergent wind components (u_R and v_D). Therefore, the joint enhancement of u_R and v_D controls the increase of the ZSL intensity, leading to increased precipitation.     

A numerical study of daily transitions in the convective boundary layer

We examine daily (morning–afternoon) transitions in the atmospheric boundary layer based on large-eddy simulations. Under consideration are the effects of the stratification at the top of the mixed layer and of the wind shear. The results describe the transitory behaviour of temperature and wind velocity, their second moments, the boundary-layer height Z _m (defined by the maximum of the potential temperature gradient) and its standard deviation σ _m , the mixed-layer height z _i (defined by the minimum of the potential temperature flux), entrainment velocity W _e, and the entrainment flux H _i . The entrainment flux and the entrainment velocity are found to lag slightly in time with respect to the surface temperature flux. The simulations imply that the atmospheric values of velocity variances, measured at various instants during the daytime, and normalized in terms of the actual convective scale w_*, are not expected to collapse to a single curve, but to produce a significant scatter of observational points. The measured values of the temperature variance, normalized in terms of the actual convective scale Θ_*, are expected to form a single curve in the mixed layer, and to exhibit a considerable scatter in the interfacial layer.     

Time-expanded sampling approach for Ensemble Kalman Filter: Experiment assimilation of simulated soundings

In the Ensemble Kalman Filter (EnKF) data assimilation-prediction system, most of the computation time is spent on the prediction runs of ensemble members. A limited or small ensemble size does reduce the computational cost, but an excessively small ensemble size usually leads to filter divergence, especially when there are model errors. In order to improve the efficiency of the EnKF data assimilation-prediction system and prevent it against filter divergence, a time-expanded sampling approach for EnKF based on the WRF (Weather Research and Forecasting) model is used to assimilate simulated sounding data. The approach samples a series of perturbed state vectors from N _b member prediction runs not only at the analysis time (as the conventional approach does) but also at equally separated time levels (time interval is Δt) before and after the analysis time with M times. All the above sampled state vectors are used to construct the ensemble and compute the background covariance for the analysis, so the ensemble size is increased from N _b to N _b+2M×N _b=(1+2M)×N _b) without increasing the number of prediction runs (it is still N _b). This reduces the computational cost. A series of experiments are conducted to investigate the impact of Δt (the time interval of time-expanded sampling) and M (the maximum sampling times) on the analysis. The results show that if Δt and M are properly selected, the time-expanded sampling approach achieves the similar effect to that from the conventional approach with an ensemble size of (1+2M)×N _b, but the number of prediction runs is greatly reduced.     

The influence of stratification on heat and momentum turbulent transfer in antarctica

Data from the Antarctic winter at Halley Base have been used in order to evaluate qualitatively and quantitatively how the stratification in the low atmosphere (evaluated with the gradient Richardson number, Ri) influences the eddy transfers of heat and momentum. Vertical profiles of wind and temperature up to 32 m, and turbulent fluxes ( , and ) measured from three ultrasonic thermo-anemometers installed at 5, 17 and 32 m are employed to calculate Ri, the friction velocity (u _*) and the eddy diffusivities for heat (K _h ) and momentum (K _m ). The results show a big dependence of stability onK _m ,K _h andu _*, with a sharp decrease of these turbulent parameters with increasing stability. The ratio of eddy diffusivities (K _h /K _m ) is also analyzed and presents a decreasing tendency as Ri increases, reaching values even less than 1, i.e., there were situations where the turbulent transfer of momentum was greater than that of heat. Possible mechanisms of turbulent mixing are discussed.     

Chemical Composition of Wet Precipitation in Irbid, Jordan

Rainwater samples were collected in Irbid city using 24 hour sampling periods from December 1996 to April 1998. All samples were analyzed for major cations (Na⁺, K⁺, Ca²⁺ and Mg²⁺), major anions (Cl^–, NO₃ ^– and SO₄ ^2–) and pH. High levels of Ca²⁺ and SO₄ ^2– were observed. Together, Ca²⁺ and SO₄ ^2– made up more than 52.4% of the total ion mass, while Ca²⁺ alone contributed over 39.0% of the total cation. The majority of the rain samples collected had pH values higher than 5.6. The average pH was 6.4±0.9. High values of pH are attributed to the neutralization by natural alkaline local dusts which contain large fractions of calcite. Correlation and mineralogical analyses indicated that Ca²⁺, K⁺ and fractions of Na⁺, SO₄ ^2– and Mg²⁺ are of crustal origin. Results of the present study suggested that the atmospheric composition in the city is strongly influenced by natural sources rather than anthropogenic.     

Kinetic and Available Potential Energy Transport during the Stratospheric Sudden Warming in January 2009

The local features of transient kinetic energy and available potential energy were investigated using ECMWF(European Centre for Medium-Range Weather Forecasts) Interim Reanalysis data for the stratospheric sudden warming(SSW) event of January 2009.The Western Europe high plays important roles in the propagation of the energy from North America to Eurasian.When the Western Europe high appeared and shifted eastward,energy conversions increased and energy propagated from North America to Eurasian as a form of interaction energy flow.The baroclinic conversion between transient-eddy kinetic energy(Ke) and transient-eddy available potential energy(Ae) and the horizontal advection of geopotential height were approximately one order of magnitude less than Ke and Ae generation terms.So,these terms were less important to this SSW event.