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[en] By analyzing normalized variables, it was found that the latitudinal secular variations of the rainwater deuterium fractionation ratio δ2H, oxygen fractionation ratio δ18O, vapor pressure, and surface temperature were almost non-linear, occurred in parallel, and decreased with latitude. The rate of depletion around the equator is asymmetric and smaller to the south of 45o S than to the north of 45o N. In the east Mediterranean, the rate of change of δ18O with height was found to be -.2 %o per 100 m and that of δ2H is comparable with the dry lapse rate in the atmosphere. Analysis of the annual time series of δ2H at Alexandria has indicated that variations show sinusoidal waveform with a major cycle of two years that accounts for 68 % of the total variance. Although the quasi-biannual cycle in the atmosphere has small amplitude in the lower layers of the atmosphere at East Mediterranean latitudes, the major cycle in annual series of δ2H or δ18O may be linked to the quasi-biannual oscillation in the atmosphere. It was also found that the first three empirical orthogonal functions (EOF) account for 72 % of the seasonal variation of δ2H and share 68 % of the seasonal variation of δ18O. Share of variances of monthly EOF in the months of the year indicate that the main underlying factors that cause fractionation processes for δ2H and δ18O are similar across the East Mediterranean especially in late winter and early spring. (author)
[en] Net ecosystem CO2 exchange was measured over a mountain birch forest in northern Finland throughout the growing season. The maximal net CO2 uptake rate of about - 0.5 mg(CO2) m-2s-1 was observed at the end of July. The highest nocturnal respiration rates in early August were 0.2 mg(CO2)m-2s-1. The daily CO2 balances during the time of maximal photosynthesis were about -15 g(CO2)m-2d-1. The mountain birch forest acted as a net sink of CO2 from 30 June to 28 August. During that period the net CO2 balance was -448 g(CO2)m-2. The inter annual representativeness of the observed balances was studied using a simplified daily balance model, with daily mean global radiation and air temperature as the input parameters. The year-to-year variation in the phenological development was parameterized as a function of the cumulative effective temperature sum. The daily balance model was used for estimating the variability in the seasonal CO2 balances due to the timing of spring and meteorological factors. The sink term of CO2 in 1996 was lower than the 15-year mean, mainly due to the relatively late emergence of the leaves. (author)
[en] The carbon dioxide exchange in arctic and subarctic terrestrial ecosystems has been measured using the eddy-covariance method at sites representing the latitudinal and longitudinal extremes of the European Arctic sea areas as part of the Land Arctic Physical Processes (LAPP) project. The sites include two fen (Kaamanen and Kevo) and one mountain birch ecosystems in subarctic northern Finland (69o N); fen, heath land, and snow bed willow ecosystems in northeastern Greenland (74o N); and a polar semi desert site in Svalbard (79o N). The measurement results, which are given as weekly average diurnal cycles, show the striking seasonal development of the net CO2 fluxes. The seasonal periods important for the net CO2 fluxes, i.e. winter, thaw, pre-leaf, summer, and autumn can be identified from measurements of the physical environment, such as temperature, albedo, and greenness. During the late winter period continuous efflux is observed at the permafrost-free Kaamanen site. At the permafrost sites, efflux begins during the thaw period, which lasts about 3-5 weeks, in contrast to the Kaamanen site where efflux continues at the same rate as during the winter. Seasonal efflux maximum is during the pre-leaf period, which lasts about 2-5 weeks. The summer period lasts 6 weeks in NE Greenland but 10-14 weeks in northern Finland. During a high summer week, the mountain birch ecosystem had the highest gross photosynthetic capacity, GPmax, followed by the fen ecosystems. The polar semi desert ecosystem had the lowest GPmax. By the middle of August, noon uptake fluxes start to decrease as the solar elevation angle decreases and senescence begins within the vascular plants. At the end of the autumn period, which lasts 2-5 weeks, topsoil begins to freeze at the end of August in Svalbard; at the end of September at sites in eastern Greenland; and one month later at sites in northern Finland. (author)
[en] Turbulent fluxes of CO2 were continuously measured by eddy correlation for three months in 1997 over a gramineous fen in a high-arctic environment at Zackenberg (74o28'12''N, 20o34'23''W) in NE-Greenland. The measurements started on 1 June, when there was still a 1-2 m cover of dry snow, and ended 26 August at a time that corresponds to late autumn at this high-arctic site. During the 20-day period with snow cover, fluxes of CO2 to the atmosphere were small, typically 0.005 mg CO2 m-s-1 (0.41 g CO2 m-2d-1), whereas during the thawed period, the fluxes displayed a clear diurnal variation. During the snow-free period, before the onset of vegetation growth, fluxes of CO2 to the atmosphere were typically 0.1 mg CO2 m-2s-1 in the afternoon, and daily sums reached values up to almost 9 g CO2 m-2d-1. After 4 July, downward fluxes of CO2 increased, and on sunny days in the middle of the growing season, the net ecosystem exchange rates attained typical values of about -0.23 mg m-s-1 at midday and max values of daily sums of -12 g CO2 m-2d-1. Throughout the measured period the fen ecosystem acted as a net-sink of 130 g CO2 m-2. Modeling the ecosystem respiration during the season corresponded well with eddy correlation and chamber measurements. On the basis of the eddy correlation data and the predicted respiration effluxes, an estimate of the annual CO2 balance the calendar year 1997 was calculated to be a net-sink of 20 g CO2 m-2yr-1. (author)
[en] Measurements of landscape-scale methane emission were made over an aapa mire near Kaamanen in Finnish Lapland (69o 8' N, 27o WE, 155 m ASL). Emissions were measured during the spring thaw, in summer and in autumn. No effect of water table position an CH4 emission was found as the water table remained at or above the surface of the peat. Methane emission fluxes increased with surface temperature from which an activation energy of -99 kJ mol-1 was obtained. Annual emission from the site, modeled from temperature regression and short-term flux measurements made in three separate years, was calculated to be 5.5 ± 0.4 g CH4 m-2y-1 of which 0.6 ± 0.1 g CH4 m-2y-1 (11 %) was released during the spring thaw which lasted 20 to 30 days. The effect of global warming an the CH4 budget of the site was estimated using the central scenario of the SILMU (Finnish Research Program on Climate Change) model which predicts annual mean temperature increases of 1.2, 2.4 and 4.4 oC in 2020, 2050 and 2100, respectively. Maximum enhancements in CH4 emission due to warming were calculated to be 18, 40 and 84 % for 2020, 2050 and 2100, respectively. Actual increases may be smaller because prediction of changes in water table are highly uncertain. (author)
[en] Current predictions of the effects of climate change indicate that the Arctic may experience a larger than average increase in temperature with consequent changes to the length of the snow-free active summer period, winter snow depth and amount and frequency of summer precipitation being highly probable. This paper reports on measurements of carbon dioxide flux at a high arctic site at Ny-Aalesund (78o 56' N, 11o 55' E), Svalbard and the physical climate variables that largely control this flux. lt is shown that during three important precipitation-free periods of the active summer period, namely post snow melt, high summer, and early autumn, the net balance between CO2 flux from the soil (due to respiration of roots and soil organisms) and CO2 assimilation by the vegetation is controlled largely by soil temperature and solar radiation. A simple combined photosynthetic assimilation-soil respiration model is shown to be capable of simulating the net CO2 flux during mid-summer, but is less proficient in the post snow melt period and in early autumn when the simple models' inability to simulate the effects of emergent growth and ponding during the former and senescence, freezing temperatures and dew during the latter indicates the need for a more complex descriptive model. The net CO2 flux during the measurement periods progresses from a net CO2 source of 0.3 gC m-2d-1 during late snow melt to a mid summer net CO2 sink of -0.39 gC m-2d-1, returning to a net CO2 source of 0.1 gC m-2d-1 in the early autumn. Simple extrapolation of the data indicates that, during the active summer season in 1995, this site was a net sink of CO2 of approximately -9 gC m-2. (author)
[en] This paper is a contribution towards the link between urban microclimate and building energy modelling using the Town Energy Balance model TEB as a new component embedded into the non-stationary building energy model TRNSYS. A number of comparative features between TEB and TRNSYS motivated this work, which includes commensurate time processing speed, similarity in describing the building facets, comparable inputs and simulation time scope, and the versatile modular architecture of TRNSYS. The paper describes the parameter tabs, inputs and outputs of TEB-Type 201, which offers (i) a user-friendly graphical interface, (ii) short time for data pre-processing with consistency check of inputs, (iii) versatility in selecting and storing outputs in small-sized files and (iv) easy installation. Besides illustrating the capabilities and practicality of this new component, an extensive sensitivity analysis highlights in a hierarchical form the main decisive urban and building parameters responsible in the formation of urban canopy heat or cool islands. The anthropogenic heat, the canyon geometry (aspect ratio, roof plan density) as well as the thermo-physical and radiative properties of the building envelope (thermal insulation, thermal inertia, albedo, emissivity) considered individually or in combination with each other appear to have clear effects on the formation of a microclimate in-canyon on the one hand, and in the magnitude and frequency of canopy heat or cool island episodes at daily and monthly basis on the other hand. The warming of canyon air is heavily influenced by the combination of high urban density (deep canyons and high plan density), high level of anthropogenic heat and weak thermal insulation. Low emissivity, no or low anthropogenic heat, better thermal insulation and low thermal mass favour the cooling of the canyon. These findings reveal the decisiveness of urban and building design choices on the outdoor thermal environment and hence on the energy demand for heating and cooling indoors. As outlook, the paper also notes the necessity of a synchronised coupling of urban canopy and building energy models.
[en] An appraisal of the recent changes in the present climate (1970–2005) followed by the possible future (2006–2100) changes in the climate has been carried out in the current study using the observations and regional climate model (REMO) over the Northeast Indian region. The regional climate model simulation has been used from the COordinated Regional climate Downscaling EXperiment (CORDEX) South Asia framework. A consistent warming for the winter (December, January, and February (DJF)) and post-monsoon (October and November (ON)) has been observed for the present climate especially in the northern and eastern parts of the region. The changes in the near future (2020–2049) and far future (2070–2099) temperature climatology suggest a rise in temperature by ~ 3–8 °C across different representative concentration pathways (RCPs). The rate of long-term (1970–2099) increase in temperature has been found ranging between 0.01 and 0.07 °C/year across the region in the least emission (RCP2.6) to strongest emission (RCP8.5) scenarios. The daily mean precipitation statistics suggests an overall increasing trends of precipitation during the pre-monsoon (March, April, and May (MAM)) for the present across the region with a mixed trend in other seasons. A change in daily mean precipitation ranging from − 60% (during winter) to + 40% during post-monsoon has been projected by the model across different RCPs. RCP4.5 and RCP8.5 show a strong deficit in precipitation in the warmer climate across the region as compared to RCP2.6. This fact is also confirmed from the long-term trend of precipitation where a consistent decreasing trend dominates in the RCP4.5- and RCP8.5-simulated precipitations by the end of the twenty-first century. A large model bias in temperature and precipitation along with high amount of uncertainty is associated with the model simulations; thus, in order to use the projections, a more careful approach to improve the utility of downscaled product should be adopted.
[en] This study documents the inter-decadal change of the lagged inter-annual relationship between the TC frequency (TCF) and the local sea surface temperature (SST) in the western North Pacific (WNP) during 1979–2014. An abrupt shift of the lagged relationship between them is observed to occur in 1998. Before the shift (1979–1997), a moderately positive correlation (0.35) between previous-year local SST and TCF is found, while a significantly negative correlation (− 0.71) is found since the shift (1998–2014). The inter-decadal change of the lagged relationship between TCF and local SST over the WNP is also accompanied by an inter-decadal change in the lagged inter-annual relationship between large-scale factors affecting TCs and local SST over the WNP. During 1998–2014, the previous-year local SST shows a significant negative correlation with the mid-level moisture and a significant positive correlation with the vertical wind shear over the main development region of WNP TC genesis. Almost opposite relationships are seen during 1979–1997, with a smaller magnitude of the correlation coefficients. These changes are consistent with the changes of the lagged inter-annual relationship between upper- and lower-level winds and local SST over the WNP. Analyses further suggests that the inter-decadal shift of the lagged inter-annual relationship between WNP TCF and local SST may be closely linked to the inter-decadal change of inter-annual SST transition over the tropical central-eastern Pacific associated with the climate regime shift in the late 1990s. Details on the underlying physical process need further investigation using observations and simulations.