Long-term variations of solar radiation in Europe

Presented are the results of the analysis of the series of seasonal and annual means of short-wave solar radiation measured at 180 actinometric stations of Europe in 1964–2010. It is demonstrated that there are two strongly pronounced periods, namely, the decrease from the early 1960s to the late 1980s and the increase in the subsequent 20 years. Total solar radiation decreased by 1.8% per 10 years on average during the first period and increased by 2.9% per 10 years during the second period. The increase in solar radiation during the second period is observed at the majority of stations due to the increase in the direct solar radiation (by 8.3% per 10 years on average). The diffuse radiation decreased by 3.1% on average for that period. The highest values of the ratio of the diffuse radiation to the direct one were registered in the 1980s–early 1990s.     

On the estimation of long-wave radiation flux from clear skies

Summary Data from measurements of long-wave radiation at Barcelona were used to test the validity of several methods for computing this component of the radiation balance in clear sky conditions.Two types of formulae, the analytically derived formulae of Swinbank and Brutsaert 1 and 2 and the empirically obtained formulae of Brunt, Idso and Jackson and Idso 1 and 2 were used in the test.Most of these methods are derived for a particular location and utilize local empirical coefficients. However, there are several which have been considered more universal.Estimates by the two methods give approximately the same value when the screen level air temperature is above 0°C.In addition, the test for temperatures below 0°C shows several discrepancies between the observed and estimated values of long-wave atmospheric radiation. This fact suggests that modifications may be needed for both analytical and empirical formulae. However, since we have few measurements in the temperature regime below 0°C, this statement cannot be justified as a conclusion of this study.

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Zusammenfassung Es werden Daten der langwelligen atmosphärischen Strahlung bei Barcelona herangezogen, um verschiedene Methoden zur Bestimmung dieser Komponente der Strahlungsbilanz bei klarem Himmel zu vergleichen. Dazu werden zwei unterschiedliche Formeltypen, die analytischen nach Swinbank und Brutsaert (1 und 2) und empirische nach Brunt, Idso und Jackson sowie Idso (1 und 2) benützt.Von diesen Methoden wurden die meisten für einen bestimmten Ort entwickelt und verwenden daher lokale empirische Koeffizienten. Allerdings gibt es einige, die als allgemein verwendbar angesehen werden.Für beide Typen der Abschätzung ergeben sich für Lufttemperaturen über 0°C im Hüttenniveau ähnliche Werte. Bei Lufttemperaturen unter 0°C zeigen sich jedoch einige Unterschiede zwischen den beobachteten und geschätzten Werten der langwelligen atmosphärischen Strahlung. Das legt nahe, die Koeffizienten sowohl für die analytischen als auch die empirischen Formeln anzupassen. Leider war das auf Grund des geringen Datenmaterials bei Temperaturen unter 0°C innerhalb dieser Untersuchung nicht möglich.

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With 2 Figures     

Validation of an urban canyon radiation model for nocturnal long-wave fluxes

The urban canyon radiation model of Arnfield (1976, 1982) is validated using measurements of long-wave fluxes taken within a scaled down urban canyon constructed from concrete building blocks. A custom-designed traversing system allowed miniature radiometers to be automatically moved around the perimeter of a canyon cross-section, thereby providing for the validation of individual model grid-points. The agreement between measured and modelled radiation is generally very good. Some differences between the two over the canyon walls are attributed to difficulties in achieving precise instrument orientation. Model results derived from the measured surface temperature data are compared to results using various approximation schemes more likely to be used in practice. Approximations based on canyon surface temperatures are superior to those using air temperature.     

Long-term variations in thermal comfort in Vienna

Summary A human energy balance model is calculated using the homogeneous data set of Vienna, Austria (48°N and 16° E). Variations in the different stages of comfort since 1873 are discussed. The historical data are then used to generate scenarios of a changing climate and calculate the impact of these variations on thermal comfort.With 5 Figures     

Long-term summer temperature variations in the Pyrenees

Two hundred and sixty one newly measured tree-ring width and density series from living and dry-dead conifers from two timberline sites in the Spanish Pyrenees were compiled. Application of the regional curve standardization method for tree-ring detrending allowed the preservation of inter-annual to multi-centennial scale variability. The new density record correlates at 0.53 (0.68 in the higher frequency domain) with May–September maximum temperatures over the 1944–2005 period. Reconstructed warmth in the fourteenth to fifteenth and twentieth century is separated by a prolonged cooling from ∼1450 to 1850. Six of the ten warmest decades fall into the twentieth century, whereas the remaining four are reconstructed for the 1360–1440 interval. Comparison with novel density-based summer temperature reconstructions from the Swiss Alps and northern Sweden indicates decadal to longer-term similarity between the Pyrenees and Alps, but disagreement with northern Sweden. Spatial field correlations with instrumental data support the regional differentiation of the proxy records. While twentieth century warmth is evident in the Alps and Pyrenees, recent temperatures in Scandinavia are relatively cold in comparison to earlier warmth centered around medieval times, ∼1450, and the late eighteenth century. While coldest summers in the Alps and Pyrenees were in-phase with the Maunder and Dalton solar minima, lowest temperatures in Scandinavia occurred later at the onset of the twentieth century. However, fairly cold summers at the end of the fifteenth century, between ∼1600–1700, and ∼1820 were synchronized over Europe, and larger areas of the Northern Hemisphere.     

Generation of available potential energy due to the long-wave radiation influx in the atmosphere

Investigated are the features of the distribution of the generation of available potential energy (APE) due to the influx of long-wave radiation in the atmosphere. The reanalysis (ERA-Interim) data of the European Center for Medium-Range Weather Forecast are used as the reference values of fields for computing APE generation. The obtained results indicate the influence of cloudiness and atmospheric stratification on APE generation due to the inflow of long-wave radiation which values are by 4–5 times smaller than the values of APE generation due to the phase transitions of moisture in the atmosphere.     

Analysis of long time series of long-wave radiation fluxes above a pine forest

Summary ?The long-term variations of upward terrestrial (E) and downward atmospheric (A) long-wave radiation fluxes above a pine stand in the southern part of the upper Rhine valley plain are analysed based on monthly mean values from 27 years of monitoring. Equivalent blackbody temperatures of the canopy and the atmosphere are calculated and compared to air temperatures at nearby sites. Based on 324 monthly values each, correlations between A and E as well as A and global radiation G are analysed. Only the former are highly correlated. Monthly mean values of long-wave radiation A can be calculated from air temperature, water vapour pressure and cloud cover. The long-term yearly average of equivalent blackbody temperature of the canopy is 0.6 K lower than kinetic air temperature at nearby sites. Only small, insignificant increases of both blackbody temperatures and air temperature are found. Despite the strong forest growth, it is surprising that the ratio of canopy emission temperature to air temperature did not change significantly. Relationships between the changes of general atmospheric circulation and equivalent blackbody temperatures of the canopy point to a strong dependence on shifts of general atmospheric flow. Received February 24, 2000; revised April 18, 2002; accepted July 20, 2002     

Long-term variations of cyclone activities in East Asia

A statistical analysis is made of the temporal and spatial variability of cyclone activities in middle latitudes in East Asia for 52 years during the period from 1934 to 1985.Three principal tracks of cyclones are distinguished in East Asia almost all year around except for the disappearance of the south one in summer.A longer-term variation in frequency of cyclones passing over the Japanese Islands with a period of about 20 years is found, in addition to a shorter-term variation with a period of a few years. A significant decreasing trend in cyclone frequency is noted between the late 1960s to around 1980.     

Peculiarities of seasonal variations of atmospheric aerosol concentration in the surface air of Moscow environs

The seasonal variations of the concentration of particles of different sizes in the atmospheric surface layer are studied on the basis of the data of daily measurements of atmospheric aerosol characteristics in the town of Dolgoprudny (20 km from the center of Moscow) carried out in 2006–2009. It is revealed that the steady variations of monthly mean aerosol concentration are observed within the particle diameter interval of 0.02–1 μm. The annual course of concentration of these particles has two maxima, in February-March and in September–October, and one minimum in June. The concentrations of particles with the size of 0.01–0.02 μm defined by the general atmospheric background and the concentrations of particles of >1 μm associated with the local sources do not have clearly pronounced seasonal variations. It is shown that the regularities of the annual concentration variations of particles with the size of 0.02–1 μm are mainly explained by the sign and value of the lapse rate in the layer up to 925 hPa that indicates the prevalence of the vertical mixing in the processes of aerosol scattering in the surface layer as compared with the horizontal transfer.     

Long-term variations of annual and growing season rainfalls in Nigeria

Summary Evidence for changes in the annual and growing season rainfall series for the period 1919 to 1985 in Nigeria are examined on a regional basis, using power-spectral and lowpass filter techniques, and the Mann-Kendall rank statistic. Four regions, the Coastal Zone, the Guinea-Savanna Zone, the Midland area and the Sahel, are used in the investigation of rainfall variation from south to north across the country.Quasi-periodic oscillations in the annual and growing season rainfall series are found to be concentrated in four spectral bands: 2.0–2.4, 2.7–2.9, 3.2–3.6 and 5.6–6.3 years. The spatial coherence of the fluctuations in annual and growing season rainfall is found to be limited to Nigeria south of 11 degrees north latitude. Evidence also emerges of a progressive decline in annual and growing season rainfall for northern Nigeria, north of nine degrees north latitude, for the period 1939–1985.With 5 Figures     

Long-term comparisons of net radiation calculation schemes

Six commonly used models for calculating daily net radiation were tested against measured net radiation. Meteorological data from 32 and 7 consecutive years obtained at two temperate sites were used. The extensive duration of the datasets ensured that all weather conditions and extreme events were captured. A set of statistical procedures was used to evaluate the performance of the models. The mean bias errors ranged from 0.0 W m⁻² to 24.8 W m⁻² and 0.1–24.7 W m⁻² and root mean square error from 11.0 W m⁻² to 28.1 W m⁻² and 10.0–27.9 W m⁻² at the two sites respectively, for days without snow cover on the ground. The best agreement was found when locally calibrated model coefficients were used. Only negligible differences in model performances were found between the two sites and the differences were lower than the inaccuracies of the net radiation instruments used. Including days with snow cover in the analysis lead to a slight increase in the bias and scatter of the predictions. Model performances were in general better during summertime than wintertime. Altered albedo values during winter caused by generally low sun angles were likely the cause of this. Analysis showed that at least 5 years of data were needed to obtain stable calibration coefficients for local calibration of the models. Based on the results from this study, and due to their physical background, two physical based models were recommended for calculating daily values of net radiation under temperate climate regimes. A simple adjustment of the calibration coefficients based on climate regime was suggested for these models.     

Outgoing long-wave radiation over the Tropical Pacific and Atlantic Ocean and Indian summer monsoon rainfall

Summary In this paper, the interannual variability of satellite derived outgoing longwave radiation (OLR) is examined in relation to the Indian summer monsoon rainfall (June to September total rainfall; ISMR). Monthly grid point OLR field over the domain i.e. the tropical Pacific and Atlantic region (30°N to 30°S, 110°E to 10°W) and the ISMR for the period 1974–2001 are used for the study. A strong and significant north–south dipole structure in the correlation pattern is found between the ISMR and the OLR field over the domain during January. This dipole is located over the west Pacific region with highly significant negative (positive) correlations over the South China Sea and surrounding region (around north-east Australia). The dipole weakens and moves northwestward during February and disappears in March. During the month of May, the OLR over the central Atlantic Ocean shows a significant positive relationship with the ISMR. These relationships are found to be consistent and robust during the period of analysis and can be used in the prediction of the ISMR.A multiple regression equation is developed, using the above results, for prediction of the ISMR and the empirical relationships are verified using an independent data set. The results are encouraging for the prediction of the ISMR. The composite annual cycle of the OLR, over the west Pacific regions during extreme ISMR is found to be useful in the prediction of extreme summer monsoon rainfall conditions over the Indian subcontinent.     

Long-term variations of elements of hydrometeorological regime of the Rybinsk Reservoir

Variations of hydrometeorological variables of the Rybinsk Reservoir area from 1947 to 2005 are analyzed. A special attention is given to the global warming period started since 1976. It is shown that the intensity of air temperature increase on the reservoir shore during recent 30 years made up 0.46–0.56°C/10 years. The maximum increase in the water temperature at shore stations and in the surface layer was registered in July at an increase rate of 0.7–1.2°C/10 years. The change in climate conditions resulted in the increase in low-water runoff, decrease in snowmelt flood volumes, and shift in the time of snowmelt flood start.     

Principal component analysis of satellite-observed outgoing long-wave radiation during the monsoon period (June–September) over India

Summary In this study, Principal Component Analysis (PCA) has been used to identify the major modes of the outgoing long-wave radiation data for the period (1979–2002) during the Indian monsoon period (June–September), using seasonal mean values over the Indian region covering 143 grid points (5° N–35° N and 70° E–95° E at 2.5° Longitude–Latitude intervals. The five principal components explain up to 98.0% of the total variance. The first principal component explains 60% of the total variance with a pronounced variation in the outgoing long-wave radiation over the region 10° N to 25° N. It appears that the major reason for the monsoon variability is the intensity and associated fluctuations in the two major semi-permanent seasonal systems. This is largely indicative of strong seasonal shift of the major area of cloudiness associated with convergence zone. The second principal component explaining 20% of the total variance exhibits higher positive component loadings along 25° N and east of 80° E. The possible reason for this could be the synoptic systems such as monsoon depression/lows over the north bay and trough/vortices off the west-coast in the Arabian sea.     

依安县近50a气温变化趋势分析

通过对依安县气象站1961-2010年气温资料进行统计分析,得出依安县的年平均气温呈上升趋势﹙0.45℃/10 a﹚,四季气温也呈上升趋势,尤其是冬季变暖最明显﹙0.58℃/10 a﹚;年平均最低气温的上升趋势﹙0.73℃/10 a﹚远大于年平均最高气温的上升趋势﹙0.22℃/10 a﹚。以20世纪80年代末为界分为冷暖两个阶段,前为冷期,后为暖期。