Long-term Average Values Research Articles

Simple ET0 Forms of Penman’s Equation without Wind and/or Humidity Data. I: Theoretical Development

In this paper, new algebraic expressions are derived for estimating reference evapotranspiration (ET0) from limited meteorological data. Reference evapotranspiration is commonly computed from readily available measured data at weather stations; e.g., solar radiation, RS (MJ/m2/d); relative humidity, RH (%); wind speed, u (m/s); and average temperature, T (°C). Recently, a simple algebraic formula, equivalent in accuracy to the Penman equation, was derived by Valiantzas for computing ET0 from readily available measured data. The derivation of the formula is based on simplifications made to the standardized form of the Penman equation. In a first place, an improved and more simplified form of Penman’s equation is proposed, requiring a full set of data. The new full set of data formula is obtained by calibration using meteorological data obtained from the CLIMWAT global database. For many places where reliable wind speed data are not available, an expression is also suggested that does not require wind data. Further simplifications were applied in the proposed formula to derive the following new formula based on RS and T measurements alone: ET0≈0.0393RST+9.5−0.19RS0.6φ0.15+0.0061(T+20)(1.12T−Tmin−2)0.7 where Tmin = minimum temperature; and φ (rad) = latitude of the station. The proposed formula, which requires limited data, can be also applied when taking the local long-term average wind speed value into account. Evaluation of the formulas and comparisons with other methods using daily meteorological data are given in the companion paper.

Spatio-temporal prediction of suspended sediment concentration in the coastal zone using an artificial neural network and a numerical model

A problem of predicting suspended particulate matter (SPM) concentration on the basis of wind and wave measurements and estimates of bed shear stress done by a numerical model is considered. Data at a location at 10 km offshore from Noordwijk in the Dutch coastal area is used. The time series data have been filtered with a low pass filter to remove short-term fluctuations due to noise and tides and the resulting time series have been used to build an artificial neural network (ANN) model. The accuracy of the ANN model during both storm and calm periods was found to be high. The possibilities to apply the trained ANN model at other locations, where the model is assisted by the correctors based on the ratio of long-term average SPM values for the considered location to that for Noordwijk (for which the model was trained), have been investigated. These experiments demonstrated that the ANN model's accuracy at the other locations was acceptable, which shows the potential of the considered approach.

Transport of dissolved load in the hydrologically extreme conditions in the Crnica river basin

During 2010, 62065.3 t of the dissolved load were transported from the Crnica Basin, which was 5.1 times higher than the long-term average value. In hydrological terms the studied year was specific. In the period from January to May the amount of runoff water was significantly above the average perennial values, while in the period from August to November the amount was below the perennial average. According to the hydrological conditions in the period January-May 82.3% were transported, and in the period August-November only 5.1% of the annual dissolved load amount. Most of the year (54.2% of the time) the specific runoff was less than 10 l/s/km2, the average water mineralization was 374.9 mg/l, and in that time 13% of the total annual amount of the dissolved load was evacuated. On the other hand, the specific runoffs greater than 50 l/s/km2 represented 13.4% of the annual frequency, the average water mineralization was 263.3 mg/l, but for that time period even 53.9% of the annual quantity of the dissolved load was evacuated.

Action Time Sharing Policies for Ergodic Control of Markov Chains

Ergodic control for discrete time controlled Markov chains with a locally compact state space and a compact action space is considered under suitable stability, irreducibility, and Feller continuity conditions. A flexible family of controls, called action time sharing (ATS) policies, associated with a given continuous stationary Markov control, is introduced. It is shown that the long-term average cost for such a control policy, for a broad range of one-stage cost functions, is the same as that for the associated stationary Markov policy. In addition, ATS policies are well suited for a range of estimation, information collection, and adaptive control goals. To illustrate the possibilities we present two examples. The first demonstrates a construction of an ATS policy that leads to consistent estimators for unknown model parameters while producing the desired long-term average cost value. The second example considers a setting where the target stationary Markov control q is not known but there are sampling schemes available that allow for consistent estimation of q. We construct an ATS policy which uses dynamic estimators for q for control decisions and show that the associated cost coincides with that for the unknown Markov control q.

Spatial distribution of phytoplankton in the White Sea in the late summer period with regard to the water structure and dynamics

The species composition and biomass of the phytoplankton, as well as the hydrophysical and hydrochemical characteristics of the water masses, were estimated for different areas of the White Sea at 24 stations for the period of August 26 to September 3, 2007. The micronutrient concentrations were lower compared to the average long-term values for the summer period. The total biomass of phytoplankton (Bt) varied from 87 to 1914 mg C/m2. For most of the studied sites, Bt was low; dinoflagellates were the most abundant species. Diatoms dominated in the areas of elevated hydrodynamic activity, i.e., in the Gorlo (vertical mixing of the water layers), in intrusions of the Gorlo water masses into the basin of the White Sea, and in the peripheral areas of the Dvina outflow current. The Bt was also the highest in the listed areas.

Statistical Evidence on the Mean Reversion of Interest Rates

Based on two hundred years of annual data of the Netherlands , Germany , US and Japan we analyse the mean reversion of long-term interest rates, by unit root tests over rolling windows and taking into account structural breaks and regime changes. While short-term rates and the yield curve tend to revert to their long-term average value, long-term rates can persistently deviate from it. At the outside, we only find weak statistical evidence for mean reversion of long-term rates. Outcomes of smooth transition autoregressive ( STAR ) models for long-term interest rates, indicate that the speed of mean reversion is regime dependent, being stronger when rates are far from their equilibrium value.

Coastal Aerosol Profiling with a Camera Lidar and Nephelometer

Abstract A bistatic lidar configuration of a wide-angle camera (100°) and vertically pointed laser (532 nm) was used to profile aerosols at a coastal site. Aerosol profiles were measured on two evenings from the surface through the boundary layer. The site, on the eastern tip of the Big Island of Hawaii, is influenced by both marine boundary layer aerosols and breaking waves. Two nephelometers, located at 7 and 25 m above sea level, were compared directly with the 0.5-m-altitude resolution of the camera lidar (clidar). At 7 m, changes in aerosol were tracked quite well by the clidar. At 25 m the aerosol was fairly constant and a useful comparison could only be made with averaged values. The clidar results showed a steep gradient (decreasing with altitude) in the aerosol extinction from 7 to about 35 m. The gradient continued to 200 m at a lower rate. This demonstrated the use of the clidar in characterizing the environment for the in situ aerosol sampling. Both a measured and a NASA Aerosol Robotic Network (AERONET)-derived aerosol phase function, representing similar marine conditions but from different locations, were used to convert the single-angle clidar scatter to extinction. The measured function gave the best fit to the near-surface nephelometer data. The extinction/backscatter ratio, derived by comparing the NASA Moderate Resolution Imaging Spectroradiometer (MODIS) aerosol optical depth to the integrated clidar profile, was higher than the long-term average value from the AERONET aerosol phase function.

Spatial variability of the species composition, abundance, and productivity of the phytoplankton in the white sea in the late summer period

The species composition, cell concentration (N), and biomass (B) of the phytoplankton, as well as the chlorophyll a (Chl a) concentration, primary production (PP), and the concentrations of the dissolved inorganic micronutrients (phosphorus, silica, nitrogen as nitrite), were estimated for Kandalaksha Bay (KB), Dvina Bay (DB), and the basin (Bas) of the White Sea in August of 2004. The micronutrient concentrations were lower compared to the average long-term values for the summer period. The Chl a concentration varies from 0.9 to 2.0 mg/m3 for most of the studied areas, reaching up to 7.5 mg/m3 in the Northern Dvina River estuary. The surface water layer of the DB was the most productive area, where the PP reached up to 270–375 mg C/(m3 day). The phytoplankton biomass varied from 11 to 205 mg C/m3 with the highest values observed in the Bas and DB. Three groups of stations were defined during the analysis of the phytoplankton’s species composition similarity. The dinoflagellates Dinophysis norvegica and Ceratium fusus were particular to the phytoplankton assemblages in the KB; the diatom Ditylum brightwellii was particular to the upper and central parts of the DB. These three phytoplankton species were less abundant in the Bas.

SPECTRAL SURVEY OF X-RAY BRIGHT ACTIVE GALACTIC NUCLEI FROM THE ROSSI X-RAY TIMING EXPLORER

Using long-term monitoring data from the Rossi X-ray Timing Explorer (RXTE), we have selected 23 active galactic nuclei (AGN) with sufficient brightness and overall observation time to derive broadband X-ray spectra from 3 to >100 keV. Our sample includes mainly radio-quiet Seyferts, as well as seven radio-loud sources. Given the longevity of the RXTE mission, the greater part of our data is spread out over more than a decade, providing truly long-term average spectra and eliminating inconsistencies arising from variability. We present long-term average values of absorption, Fe line parameters, Compton reflection strengths and photon indices, as well as fluxes and luminosities for the hard and very hard energy bands, 2-10 keV and 20-100 keV respectively. We find tentative evidence for high-energy rollovers in three of our objects. We improve upon previous surveys of the very hard X-ray energy band in terms of accuracy and sensitivity, particularly with respect to confirming and quantifying the Compton reflection component. This survey is meant to provide a baseline for future analysis with respect to the long-term averages for these sources and to cement the legacy of RXTE, and especially its High Energy X-ray Timing Experiment, as a contributor to AGN spectral science.

Roe deer population growth and lynx predation along a gradient of environmental productivity and climate in Norway

The extent to which large carnivores compete with hunters for harvestable populations of wild ungulates is a topic of widespread controversy in many areas of the world where carnivore populations are recovering or are reintroduced. Theory predicts that predation impacts should vary with prey density and environmental conditions. To test this prediction, we analyzed trends in an index of population abundance of roe deer (Capreolus capreolus) over 9 y in 144 Norwegian municipalities. The municipalities span a wide range of landscapes and climatic conditions and were associated with a varying degree of Eurasian lynx (Lynx lynx) presence. There was a wide variation in trends of roe deer abundance (estimated long-term average λ ranging from 0.69 to 1.23) among municipalities. Roe deer population growth rates were lower in the municipalities with lynx and harsh climatic conditions than in municipalities with mild climatic conditions and/or without lynx. Thus, lynx presence appears to be having a negative impact on roe deer populations; this was especially evident in areas with unfavourable environmental conditions. Our finding that estimated long-term average values of λ were less than 1 in many municipalities indicates that roe deer populations in Norway may not be able to sustain current combined mortality from hunters and lynx, especially in marginal areas.

Characteristics of aerosol black carbon mass concentration over a high altitude location in the Central Himalayas from multi-year measurements

Multi-year measurements of near surface aerosol black carbon (BC) mass concentration, made from a high altitude station at Manora Peak (29.4° N, 79.5° E, 1958 m msl) in the Central Himalayas, using a 7-channel Aethalometer for 38 months from November 2004 to December 2007, are examined. Temporally, BC exhibited well-defined diurnal variations, comprising of a single prominent peak occurring in the late afternoon (before sunset) hours during the months from October to March, while these variations were insignificant during April to September. These were found to be closely associated with the dynamics of atmospheric boundary layer (ABL), and pose a form that is distinctly different from those reported for the plains. BC mass concentrations were always higher by a factor of about 2 during daytime than the concentrations during nighttime. Seasonally, BC mass concentrations were higher during spring (with a mean value of 1.34 ± 0.05 µg m − 3 ), which are attributed to lifting up of pollutants from the valley (below the mountain peak) by the convective boundary layer and increased local emissions. The concentration decreased by a factor of 2 in summer (0.53 ± 0.02) and recovered during autumn (1.03 ± 0.04). The long-term average value was 0.99 ± 0.02 µg m − 3 . Examination of the wavelength dependence revealed that BC observed at this location is generally dominated by fossil fuel combustion.

Mapping the performance of PV modules, effects of module type and data averaging

A method is presented for estimating the energy yield of photovoltaic (PV) modules at arbitrary locations in a large geographical area. The method applies a mathematical model for the energy performance of PV modules as a function of in-plane irradiance and module temperature and combines this with solar irradiation estimates from satellite data and ambient temperature values from ground station measurements. The method is applied to three different PV technologies: crystalline silicon, CuInSe 2 and CdTe based thin-film technology in order to map their performance in fixed installations across most of Europe and to identify and quantify regional performance factors. It is found that there is a clear technology dependence of the geographical variation in PV performance. It is also shown that using long-term average values of irradiance and temperature leads to a systematic positive bias in the results of up to 3%. It is suggested to use joint probability density functions of temperature and irradiance to overcome this bias.

Recent Declines in Western U.S. Snowpack in the Context of Twentieth-Century Climate Variability

Abstract A monthly snow accumulation and melt model was used with monthly Precipitation-elevation Regressions on Independent Slopes Model (PRISM) temperature and precipitation data to generate time series of 1 April snow water equivalent (SWE) for 1900 through 2008 in the western United States. Averaged across the western United States, SWE generally was higher than long-term (1900–2008) average conditions during the periods 1900–25, 1944–55, and 1966–82; SWE was lower than long-term average conditions during the periods 1926–43, 1957–65, and 1984–2008. During the period 1900–2008, the temporal pattern in winter precipitation exhibited wetter-than-average and drier-than-average decadal-scale periods with no long-term increasing or decreasing trend. Winter temperature generally was below average from 1900 to the mid-1950s, close to average from the mid-1950s to the mid-1980s, and above average from the mid-1980s to 2008. In general, periods of higher-than-average SWE have been associated with higher precipitation and lower temperature. Since about 1980, western U.S. winter temperatures have been consistently higher than long-term average values, and the resultant lower-than-average SWE values have been only partially offset by periods of higher-than-average precipitation. The post-1980 lower-than-average SWE conditions in the western United States are unprecedented within the context of twentieth-century climate and estimated SWE.

Mixing and transport of water in a karst catchment: a case study from precipitation via seepage to the spring

Abstract. One of the best-known and largest karst areas in Germany, the Blautopf Catchment, offers unique access to waters of the unsaturated zone through a large cave system. It was investigated with stable isotopes (18O/16O and D/H ratios expressed in permille = ‰) in precipitation, seepage- and groundwater as tracers for water flow, mixing, and storage. The precipitation showed a distinct seasonality with δ18O values between −2.9 and −24.6‰ during summer and winter, respectively. However, the isotope signals in seepage water in the caves as well as the discharge were almost completely buffered and ranged around an average δ18O value of −10‰. This value was also close to the long-term average value of local precipitation, −9.3‰. The homogeneous isotopic composition of the Blautopf Spring was unexpected, as its highly variable discharge (0.3 to 32 m3 s−1) is typical for a fast responsive karst system. These isotopic similarities could be explained by nearly complete mixing of the water already in the vadose zone. The data set therefore presents a case study to narrow down zones of mixing in karst catchments. It also confirms the minor role of the fast conduit system in the water balance of the Blautopf Catchment.

Trophic relations of capelin Mallotus villosus and polar cod Boreogadus saida in the Barents Sea as a factor of impact on the ecosystem

Abstract The purpose of the study is to assess the role of trophic relations of the dominant pelagic fishes capelin and polar cod in the Barents Sea with regard to distribution and accessibility as prey for the Atlantic cod in warm years (2004–2005). Unlike in the previous period, during these warm years a dramatic increase of the polar cod population resulted in a northwards expansion of the feeding grounds where overlapping of polar cod and capelin concentrations was observed. This caused an increased competition for copepods, which are the main food item for young fish. In the areas dominated by polar cod the shortage of copepods forced immature capelin to switch to the chaetognath Sagitta , which affected their fatness negatively. During the warm years the feeding grounds of Atlantic cod also expanded, to a large degree caused by the shortage of their main food, the capelin. In 2004–2005 the cod formed feeding concentrations in the north and northeast Barents Sea where they fed on the capelin. In this area the consumption of polar cod by cod increased, and in some local areas the polar cod practically replaced the capelin in the diet of cod. In general polar cod in the diet of Atlantic cod were more important in the northern than in the southern part of the Barents Sea. The fatness of cod was extremely low during the whole spring–summer period (until August), and after the feeding period the fatness index of the Atlantic cod became lower than the average long-term autumn value.

Changes in Runoff and Sediment Yield along the Yellow River during the Period from 1950 to 2006

In this paper, the changes in runoff and sediment yield have been assessed by using long-term observation data from 9 gauging stations on the Yellow River and 12 climate stations in the Yellow River watershed in China. It was observed that the annual precipitation depth at 3 climate stations in the headwater region of the Yellow River has an upward trend. However, in the lower section of the Upper Reach sub-watershed of the Yellow River, the annual precipitation depth has a slightly downward trend. In the Middle Reach sub-watershed, annual precipitation depth has a clear downward tendency. In the Lower Reach sub-watershed of the Yellow River, annual precipitation depth has a slightly upward tendency. Results indicate that, both annual sediment yield and annual runoff depth have a tendency of reduction in the past half century. The annual sediment yield in the Middle Reach is extremely high, with a long-term annual sediment yield of 1543.65 t/km^2 at the Longmen station and 1631.39 t/km^2 at the Tongguan station. In the Lower Reach, both annual runoff depth and sediment yield have a clearly downward trend. However, the long-term average annual sediment yield in the Lower Reach varies from 1035 to 1330 t/km^2 which is still extremely high but less than those at gauging stations on the Middle Reach. The average annual sediment yield decreased significantly in recent 10 years. Examplewise, for the Yellow River at Lijin Station, the average runoff depth of the recent 10 year s is only 1/3 of the long-term average value, and the average annual sediment yield of the recent 10 years is only 1/4 of the long-term average value. Additionally, the impacts of human activities on both runoff depth and sediment yield have been discussed.

Is the Water Temperature of the Danube River at Bratislava, Slovakia, Rising?

Abstract This paper aims to reveal the annual regime, time series, and long-term water temperature trends of the Danube River at Bratislava, Slovakia, between the years 1926 and 2005. First, the main factors affecting the river’s water temperature were identified. Using multiple regression techniques, an empirical relationship is derived between monthly water temperatures and monthly atmospheric temperatures at Vienna (Hohe Warte), Austria, monthly discharge of the Danube, and some other factors as well. In the second part of the study, the long-term trends in the annual time series of water temperature were identified. The following series were evaluated: 1) The average annual water temperature (To) (determined as an arithmetic average of daily temperatures in the Danube at Bratislava), 2) the weighted annual average temperature values (Toυ) (determined from the daily temperatures weighted by the daily discharge rates at Bratislava), and 3) the average heat load (Zt) at the Bratislava station. In the long run, the To series is rising; however, the trend of the weighted long-term average temperature values, Toυ, is near zero. This result indicates that the average heat load of the Danube water did not change during the selected period of 80 yr. What did change is the interannual distribution of the average monthly discharge. Over the past 25 yr, an elevated runoff of “cold” water (increase of the December–April runoff) and a lower runoff of “warm” water (decrease of the river runoff during the summer months of June–August) were observed.

Seasonal primary production cycle in Lake Onega

A long-term average curve of seasonal changes in the primary production of phytoplankton in the pelagial zone of Lake Onega has been plotted on the basis of experimental data approximated by a specified function. Long-term average values of primary production for each day of the growing season and its integrated and daily average values for different growing seasons have been calculated. Interannual variation of the seasonal process of primary production has been analyzed, and its quantitative estimations are given. The influence of basic environmental factors on the seasonal dynamics of primary production is discussed.

Modeling Potential Distribution and Carbon Dynamics of Natural Terrestrial Ecosystems: A Case Study of Turkey

We derived a simple model that relates the classification of biogeoclimatezones, (co)existence and fractional coverage of plant functional types (PFTs), and patternsof ecosystem carbon (C) stocks to long-term average values of biogeoclimatic indices in atime- and space-varying fashion from climate-vegetation equilibrium models. ProposedDynamic Ecosystem Classification and Productivity (DECP) model is based on the spatialinterpolation of annual biogeoclimatic variables through multiple linear regression (MLR)models and inverse distance weighting (IDW) and was applied to the entire Turkey of780,595 km² on a 500 m x 500 m grid resolution. Estimated total net primary production(TNPP) values of mutually exclusive PFTs ranged from 108 26 to 891 207 Tg C yr-1under the optimal conditions and from 16 7 to 58 23 Tg C yr-1 under the growth-limiting conditions for all the natural ecosystems in Turkey. Total NPP values ofcoexisting PFTs ranged from 178 36 to 1231 253 Tg C yr-1 under the optimalconditions and from 23 8 to 92 31 Tg C yr-1 under the growth-limiting conditions. Thenational steady state soil organic carbon (SOC) storage in the surface one meter of soil wasestimated to range from 7.5 1.8 to 36.7 7.8 Pg C yr-1 under the optimal conditions andfrom 1.3 0.7 to 5.8 2.6 Pg C yr-1 under the limiting conditions, with the national range of 1.3 to 36.7 Pg C elucidating 0.1% and 2.8% of the global SOC value (1272.4 Pg C), respectively. Our comparisons with literature compilations indicate that estimated patterns of biogeoclimate zones, PFTs, TNPP and SOC storage by the DECP model agree reasonably well with measurements from field and remotely sensed data.

Wind turbines power curve variability

A comprehensive measurement programme was carried through 300 kW Nordtank stall-regulated horizontal axis wind turbine. These turbines were erected at the test station for windmills by Hurghada Wind Energy Technology Centre. To the extent necessary to understand the measurement carried out, all experimental set up systems must be described. This paper describes the annual wind speed variability in Hurghada city in period (1973–2001). The wind speed and direction were measured on the latitude of meat masts as, 10, 24.5, and 31 m. These stations were operated since 1986. The wind data was recorded from the instruments with a scanning rate of about 2 Hz and the data was subsequently stored as consecutive 1-h average values. Simultaneously, various types of monthly statistics were accumulated. Also, the study discusses the effect of this wind variability on the power curve of Hurghada farm wind turbines. The results show that, if the annual mean wind speed varies by ±10% around a long-term average value, the corresponding natural variability of the available wind energy is about ±25%.