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1.
Summary Vertical profile of surface radiative fluxes in an area of heterogeneous terrain in south-west Germany is presented. Main
data sets utilized for the study were recorded during the REgio KLIma Projekt (REKLIP). Supporting observational data were
provided by the German weather service and German geophysical consultant service. Elevation of the study sites ranged from
212 m a.s.l. to 1489 m a.s.l. From May to September, monthly mean albedo was generally low at the study sites, ranging from
19% to 24%. For the other months, monthly mean albedo lie between 22% and 25% at the lowland site but extended between 27%
and 71% at the highly elevated mountain site. Following the altitudinal increase in surface albedo, net radiative flux and
radiation efficiency declined with elevation at an annual mean of 1.15 Wm−2/100 m and 0.008/100 m respectively. Absorbed shortwave radiation and effective terrestrial radiation showed mean decline
of 1.54 Wm−2/100 m and 0.34 Wm−2/100 m, respectively, with the mean sky-to-earth radiation deficit amounting to about 52 Wm−2 for the lowland site and 73 Wm−2 for the highest elevated site.
Some empirical models which express shortwave and longwave radiative fluxes in terms of meteorological variables have been
validated for the lowland and mountain sites. Monthly mean daily total estimates of solar radiation obtained from ?ngst?m-Prescott
relation were quite consistent with observed values. Parameterisation of downward atmospheric radiation under all sky condition
was achieved by extending Brutsaert clear sky atmospheric model. Relationship between outgoing longwave radiation and screen
temperature at the study sites was best described by an exponential function unlike the linear relationship proposed by Monteith
and Unsworth. Net radiative flux for the lowland and mountain sites has been expressed in terms of absorbed shortwave radiation,
cloud amount and screen temperature.
Received March 5, 2001 Revised October 29, 2001 相似文献
2.
T. Laurila H. Soegaard C. R. Lloyd M. Aurela J.-P. Tuovinen C. Nordstroem 《Theoretical and Applied Climatology》2001,70(1-4):183-201
Summary 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 (69° N); fen, heathland, and snowbed willow ecosystems in northeastern Greenland (74° N); and a polar semidesert
site in Svalbard (79° 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, GP
max, followed by the fen ecosystems. The polar semidesert ecosystem had the lowest GP
max. 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.
Received March 1, 2000 Revised October 2, 2000 相似文献
3.
Summary We investigated the ratio of photosynthetically active photon flux (Q
p
) to global solar radiation (R
s
) at three sites along different altitudes in Naeba Mountain, Japan at various temporal scales based on 3 years measurement
data (1999–2001). The lowest values of the ratio ever reported were found for all sites on both an hourly and a daily scale.
A similar slight diurnal pattern was found for all sites based on the monthly mean hourly values of the ratio. However, different
sites exhibited different seasonal courses. Statistically significant altitude dependencies were found for the hourly Q
p
/R
s
under both clear and cloudy weather conditions (t-test, P < 0.001). For clear weather conditions, the hourly Q
p
/R
s
exhibited an increasing trend with altitude at an average rate of 3.6% per km. The increasing rate was more noticeable below
900 m (8.8% per km) than above (0.7% per km). The inverse trend was found for hourly Q
p
/R
s
with the altitude under cloudy weather conditions. The hourly Q
p
/R
s
decreased from 550 m to 1500 m at a rate of 1.8% per km. Again, a major decrease occurred below 900 m, which had the rate
of 4.2% per km, compared with 0.2% per km over 900 m. Although the same tendencies were noted for daily Q
p
/R
s
, under clear sky conditions, they were not as statistically significant as the hourly counterpart (t-test, P < 0.021). The
increasing rate of Q
p
/R
s
at this scale under clear weather conditions was near that of the hourly rate, but below the 900 m rate was reduced to near
half of the hourly rate (4.7% per km). And the rate over 900 m increased to 2.7% per km. On the other hand, statistically
significant altitude effect was noted for the daily under cloudy weather conditions (t-test, P < 0.002). A rapidly decreasing
rate was found for it along the altitude gradient. The reason was due to the large decreasing rate below 900 m (12.4% per
km). But again similar to the hourly Q
p
/R
s
, a very small decreasing rate of daily Q
p
/R
s
was found over 900 m under cloudy weather conditions. These results suggest the necessity of considering the altitude dependency
of Q
p
/R
s
in future studies. 相似文献
4.
Aerosol and rain samples were collected between 48°N and 55°S during the KH-08-2 and MR08-06 cruises conducted over the North
and South Pacific Ocean in 2008 and 2009, to estimate dry and wet deposition fluxes of atmospheric inorganic nitrogen (N).
Inorganic N in aerosols was composed of ~68% NH4+ and ~32% NO3– (median values for all data), with ~81% and ~45% of each species being present on fine mode aerosol, respectively. Concentrations
of NH4+ and NO3− in rainwater ranged from 1.7–55 μmol L−1 and 0.16–18 μmol L−1, respectively, accounting for ~87% by NH4+ and ~13% by NO3− of total inorganic N (median values for all data). A significant correlation (r = 0.74, p < 0.05, n = 10) between NH4+ and methanesulfonic acid (MSA) was found in rainwater samples collected over the South Pacific, whereas no significant correlations
were found between NH4+ and MSA in rainwater collected over the subarctic (r = 0.42, p > 0.1, n = 6) and subtropical (r = 0.33, p > 0.5, n = 6) western North Pacific, suggesting that emissions of ammonia (NH3) by marine biological activity from the ocean could become a significant source of NH4+ over the South Pacific. While NO3− was the dominant inorganic N species in dry deposition, inorganic N supplied to surface waters by wet deposition was predominantly
by NH4+ (42–99% of the wet deposition fluxes for total inorganic N). We estimated mean total (dry + wet) deposition fluxes of atmospheric
total inorganic N in the Pacific Ocean to be 32–64 μmol m−2 d−1, with 66–99% of this by wet deposition, indicating that wet deposition plays a more important role in the supply of atmospheric
inorganic N than dry deposition. 相似文献
5.
Ahmed A. Balogun Jimmy O. Adegoke Sajith Vezhapparambu Matthias Mauder Joseph P. McFadden Kevin Gallo 《Boundary-Layer Meteorology》2009,133(3):299-321
Previous measurements of urban energy balances generally have been limited to densely built, central city sites and older
suburban locations with mature tree canopies that are higher than the height of the buildings. In contrast, few data are available
for the extensive, open vegetated types typical of low-density residential areas that have been newly converted from rural
land use. We made direct measurements of surface energy fluxes using the eddy-covariance technique at Greenwood, a recently
developed exurban neighbourhood near Kansas City, Missouri, USA, during an intensive field campaign in August 2004. Energy
partitioning was dominated by the latent heat flux under both cloudy and near clear-sky conditions. The mean daytime Bowen
ratio (β) values were 0.46, 0.48, and 0.47 respectively for the cloudy, near clear-sky and all-sky conditions. Net radiation (R
n
) increased rapidly from dawn (−34 and −58W m−2) during the night to reach a maximum (423 and 630W m−2) after midday for cloudy and near clear-sky conditions respectively. Mean daytime values were 253 and 370W m−2, respectively for the cloudy and near clear-sky conditions, while mean daily values were 114 for cloudy and 171W m−2 for near clear-sky conditions, respectively. Midday surface albedo values were 0.25 and 0.24 for the cloudy and near clear-sky
conditions, respectively. The site exhibited an angular dependence on the solar elevation angle, in contrast to previous observations
over urban and suburban areas, but similar to vegetated surfaces. The latent heat flux (Q
E
), sensible heat flux (Q
H
), and the residual heat storage ΔQ
s
terms accounted for between 46–58%, 21–23%, and 18–31% of R
n
, respectively, for all-sky conditions and time averages. The observed albedo, R
n
, and Q
E
values are higher than the values that have been reported for suburban areas with high summer evapotranspiration rates in
North America. These results suggest that the rapidly growing residential areas at the exurban fringe of large metropolitan
areas have a surface energy balance that is more similar to the rural areas from which they were developed than it is to the
older suburbs and city centres that make up the urban fabric to which they are being joined. 相似文献
6.
Meteorological techniques were used to monitor evapotranspiration (ET) at two sites in a boreal forest drainage basin located in southeastern Manitoba, Canada. An energy balance method was used in which net radiation (R
N
) and ground heat flux (G) were measured directly. Sensible heat flux (H) was measured by the eddy correlation technique using a propeller anemometer and a fine-wire thermocouple. The energy components were calculated hourly on-line, and data were collected reliably over a five-month period.The R
N
and H instruments were mounted above the forest canopy and simultaneous measurements of H at heights of 12 and 6 m were in good agreement. Measurements at an open bare rock site indicated that G could be a substantial fraction of the daily RN at some locations, but over longer time periods, it was a small fraction and, therefore, was ignored.The two measurement locations represented upland (open bedrock/jack pine forest) and lowland (aspen/willow forest) sites in the drainage basin. The mean daily value of R
N
- H at the upland site was 0.57 times the value at the lowland location owing to differences in R
N
, H, and G. The mean ratio of daily H/R
N
was 0.6 for the upland site and 0.4 for the lowland site. A basin-wide ET was calculated by weighting the values for the two sites in proportion to their areas. The measured ET agreed well with precipitation minus runoff for the basin. Differences between these two quantities in summer and fall were attributed to water release and storage by the ground, respectively.Issued as AECL-9153. 相似文献
7.
The characteristics of net radiation (Rn)(0.3--10 μm) in Lhasa and
Haibei in the Tibetan Plateau were analyzed based on long-term in-situ
measurements of surface radiation data. The monthly average of daily
Rn reached a minimum during the winter period followed by an increase
until May and then a decline until January. This variation is consistent
with solar activity. The annual mean daily total Rn values were 0.92 MJ
m-2 d-1 and 0.66 MJ m-2d-1 in Lhasa and Haibei,
respectively.
A relationship between Rn and broadband solar radiation (Rs) was
demonstrated by a good linear correlation at the two sites. Rn can be an
accurate estimate from Rs. The estimated Rn values were similar to the
observed values, and the relative deviations between the estimates and
measurements of Rn were 2.8% and 3.8% in Lhasa and Haibei,
respectively. The application of the Rn estimating model to other
locations showed that it could provide acceptable estimated Rn values from the Rs data. Furthermore, we analyzed the influence of clouds on
Rn by different clear index (Ks), defined as the ratio of Rs to the
extraterrestrial solar irradiance on a horizontal surface. The results
indicate that more accurate results are associated with increased cloudy
conditions. The influence of the albedo was also considered, but its
inclusion in the model resulted in only a slight improvement. Because
surface albedo is not usually measured, an expression based solely on global
solar radiation could be of more extensive use. 相似文献
8.
Seasonal carbon dioxide balance and respiration of a high-arctic fen ecosystem in NE-Greenland 总被引:2,自引:0,他引:2
C. Nordstroem H. Soegaard T. R. Christensen T. Friborg B. U. Hansen 《Theoretical and Applied Climatology》2001,70(1-4):149-166
Summary 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 (74°28′12″N, 20°34′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−2 s−1 (0.41 g CO2 m−2 d−1), wheres 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−2 s−1 in the afternoon, and daily sums reached values up to almost 9 g CO2 m−2 d−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−2 s−1 at midday and max values of daily sums of −12 g CO2 m−2 d−1. Throughout the measured period the fen ecosystem acted as a net-sink of 130 g CO2 m−2. Modelling 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 calender year 1997 was calculated to be a net-sink of 20 g CO2 m−2 yr−1.
Received October 6, 1999 Revised May 2, 2000 相似文献
9.
Decreasing teleconnections with inter-site distance in monthly climatic data and tree-ring width networks in a mountainous Alpine area 总被引:3,自引:0,他引:3
C. Rolland 《Theoretical and Applied Climatology》2002,71(1-2):63-75
Summary The similarities in time series recorded at sites which are distant from each other are called teleconnections. In this paper,
the loss of such correlations with inter-site distance was investigated for both climatic and dendrochronological data sets,
with 70 tree-ring chronologies. A dense network of weather stations was studied in the southeastern French Alps, covering
complex climatic gradients over three departments. 78 sites with precipitation data (with a total of 48 756 monthly values),
and 48 stations that recorded temperature (with 20 722 monthly mean values) were analysed. In the same area, four coniferous
species (mountain pine and stone pine, European larch and Norway spruce) provided 37 ring-width chronologies for high elevation
sites near the timberline. Both silver fir and Norway spruce provided a second tree-ring chronology network for 33 different
sites at lower elevations.
The teleconnections between precipitation series were found to be higher than those observed for temperature over short distances,
but the maximum threshold distance was lower (193 km) compared to a positive correlation distance that exceeds 500 km for
temperature. The maximum temperatures had stronger teleconnections than minimum values (522 km versus 476 km), since the latter
are linked more with other site factors, such as slope, exposure and local topography.
As expected, the tree-ring chronologies showed weaker teleconnections than the climatic series, with a threshold distance
of 374 km obtained for all high elevation forests. The coniferous species with high intra-specific teleconnections over large
distances were, in decreasing importance, Pinus uncinata (> 500 km), Picea abies (477 km), Pinus cembra (over 254 km) and Larix decidua (over 189 km only). The two former species showed the highest intra-specific correlations (with mean correlation R=0.625 and 0.666). The dendrochronological teleconnections were found to have a extent lesser for trees species that depend
on rainfall (such as larch, and stone pine). They are enhanced, however, for temperature sensitive species such as spruce
and mountain pine (a drought resistant tree). Therefore, these two latter conifers appear to be especially suitable for climatic
reconstruction over large distances in mountainous areas. However, teleconnections within silver fir (Abies alba) and spruce chronologies were sharply reduced (over 131 km and 135 km) in lower elevation forests, underlining the interest
of timberline forests for dendroclimatology.
A better knowledge of the spatial correlations in climatic series and ring-width data may enable the optimisation of weather
station networks. It may also permit a better choice of weather stations used for dendroclimatology, either for tree-ring
and climate relationship calibration or for climate reconstructions. In dendrochronology, wood dating also requires the knowledge
of to what extent remote ring-width chronologies can be used.
Received September 11, 2000 Revised March 26, 2001 相似文献
10.
Summary ?Simultaneous flight measurements with the research aircraft Do 128 and the helicopter-borne turbulence probe Helipod were
performed on 18 June 1998 during the LITFASS-98 field experiment. The area-averaged turbulent vertical fluxes of momentum,
sensible, and latent heat were determined on a 15 km × 15 km and a 10 km × 10 km flight pattern, respectively. The flights
were carried out over heterogeneous terrain at different altitudes within a moderately convective boundary layer with Cumulus
clouds.
Co-spectra-analysis demonstrated that the small scale turbulent transport was completely sampled, while the comparatively
small flight patterns were possibly of critical size regarding the large-scale turbulence. The phygoide of the airplane was
identified as a significant peak in some co-spectra. The turbulent fluxes of momentum and sensible heat at 80 m above the
ground showed systematic dependence on the location of the flight legs above the heterogeneous terrain. This was not observed
for the latent heat flux, probably due to the vertical distribution of humidity in the boundary layer.
Statistical error analysis of the fluxes F showed that the systematic statistical error ΔF was one order of magnitude smaller than the standard deviation σ
F
. The difference between area-averaged fluxes derived from simultaneous Helipod and Do 128 measurements was much smaller than
σ
F
, indicating that the systematic statistical error was possibly over-estimated by the usual method.
In the upper half of the boundary layer the airborne-measured sensible heat flux agreed well with windprofiler/RASS data.
A linear fit was the best approximation for the height dependence of all three fluxes. The linear extrapolations of the latent
and sensible heat fluxes to the ground were in good agreement with tower, scintillometer, and averaged ground-station measurements
on various surface types. Systematic discrepancies between airborne and ground-based measurements were not found.
Received June 18, 2001; revised December 21, 2001; accepted June 3, 2002 相似文献
11.
Comparative measurements and seasonal variations in energy and carbon exchange over forest and pasture in South West Amazonia 总被引:1,自引:0,他引:1
C. von Randow A. O. Manzi B. Kruijt P. J. de Oliveira F. B. Zanchi R. L. Silva M. G. Hodnett J. H. C. Gash J. A. Elbers M. J. Waterloo F. L. Cardoso P. Kabat 《Theoretical and Applied Climatology》2004,78(1-3):5-26
Summary Comparative measurements of radiation flux components and turbulent fluxes of energy and CO2 are made at two sites in South West Amazonia: one in a tropical forest reserve and one in a pasture. The data were collected from February 1999 to September 2002, as part of the Large Scale Biosphere-Atmosphere Experiment in Amazonia (LBA). During the dry seasons, although precipitation and specific humidity are greatly reduced, the soil moisture storage profiles down to 3.4m indicate that the forest vegetation continues to withdraw water from deep layers in the soil. For this reason, seasonal changes observed in the energy partition and CO2 fluxes in the forest are small, compared to the large reductions in evaporation and photosynthesis observed in the pasture. For the radiation balance, the reflected short wave radiation increases by about 55% when changing from forest to pasture. Combined with an increase of 4.7% in long wave radiation loss, this causes an average reduction of 13.3% in net radiation in the pasture, compared to the forest. In the wet season, the evaporative fraction (E/Rn) at the pasture is 17% lower than at the forest. This difference increases to 24% during the dry season. Daytime CO2 fluxes are 20–28% lower (in absolute values) in the pasture compared to the forest. The night-time respiration in the pasture is also reduced compared to the forest, with averages 44% and 57% lower in the wet and dry seasons, respectively. As the reduction in the nocturnal respiration is larger than the reduction in the daytime uptake, the combined effect is a 19–67% higher daily uptake of CO2 in the pasture, compared to the forest. This high uptake of CO2 in the pasture site is not surprising, since the growth of the vegetation is constantly renewed, as the cattle remove the biomass. 相似文献
12.
R. R. Reddy K. Rama Gopal L. Siva Sankara Reddy K. Narasimhulu K. Raghavendra Kumar Y. Nazeer Ahammed C. V. Krishna Reddy 《Journal of Atmospheric Chemistry》2008,59(1):47-59
In the present study, an attempt has been made to examine the governing photochemical processes of surface ozone (O3) formation in rural site. For this purpose, measurements of surface ozone and selected meteorological parameters have been
made at Anantapur (14.62°N, 77.65°E, 331 m asl), a semi-arid zone in India from January 2002 to December 2003. The annual
average diurnal variation of O3 shows maximum concentration 46 ppbv at noon and minimum 25 ppbv in the morning with 1σ standard deviation. The average seasonal
variation of ozone mixing ratios are observed to be maximum (about 60 ppbv) during summer and minimum (about 22 ppbv) in the
monsoon period. The monthly daytime and nighttime average surface ozone concentration shows a maximum (55 ± 7 ppbv; 37 ± 7.3 ppbv)
in March and minimum (28 ± 3.4 ppbv; 22 ± 2.3 ppbv) in August during the study period. The monthly average high (low) O3 48.9 ± 7.7 ppbv (26.2 ± 3.5 ppbv) observed at noon in March (August) is due to the possible increase in precursor gas concentration
by anthropogenic activity and the influence of meteorological parameters. The rate of increase of surface ozone is high (1.52 ppbv/h)
in March and lower (0.40 ppbv/h) in July. The average rate of increase of O3 from midnight to midday is 1 ppbv/h. Surface temperature is highest (43–44°C) during March and April months leading to higher
photochemical production. On the other hand, relative humidity, which is higher during the rainy season, shows negative correlation
with temperature and ozone mixing ratio. It can be seen that among the two parameters are measured, correlation of surface
ozone with wind speed is better (R
2=0.84) in compare with relative humidity (R
2=0.66). 相似文献
13.
T. Gnauk K. Müller E. Brüggemann W. Birmili K. Weinhold D. van Pinxteren G. Löschau G. Spindler H. Herrmann 《Journal of Atmospheric Chemistry》2011,68(3):199-231
The fractions of local traffic (LT), urban background (UBG) and regional background (RBG) of the particle pollution at a traffic-influenced
kerbside in Dresden, Germany, were determined by measurements of size-segregated mass concentration, chemical composition
and particle size distributions in a network of five measurement stations partly existing and partly set up for this study.
Besides the kerbside station, one urban background site and three rural sites were included in the study. Using data from
these different sites, the LT, UBG, and RBG contributions were calculated, following the approach of Lenschow et al. (2001). At the kerbside site, 19% of the total number concentration (DpSt = 10–600 nm) could be attributed to the RBG, 15% to the UBG, and 66% to the LT immediately nearby. Particle mass concentrations
up to Dpaer = 420 nm RBG amounts to 68%, UBG to 21%, and LT only to 11%. Highest mass concentrations were observed at all stations in
autumn and winter during easterly inflow directions. The local traffic fraction of PM10 mass at the kerbside station was found to be 30% for westerly inflow, but only 7% for southeasterly inflow due to the dominating
transport fraction from up to 80% of the particle mass at this inflow direction. Size-resolved investigation showed the main
fractions in both the particle size ranges of Dpaer = 0.42 to 1.2 and 0.14 to 0.42 μm at all stations. The main components sulphate, ammonium and total carbon showed higher
concentrations at south-eastern/eastern inflow in autumn at all stations, while nitrate at the kerbside and urban background
site was higher during westerly inflow in winter. The chemical composition at the regional background site at westerly inflow
(12% nitrate, 8% sulphate, 11% total carbon) was significantly different from that at easterly inflow (3% nitrate, 15% sulphate,
22% total carbon). The prevailing part of the ionic mass was always found in the fine particle range of Dpaer = 0.14 to 1.2 μm at all stations. For all inflow directions highest total carbon concentrations were observed at the kerbside
station, especially in the ultra-fine size range of Dpaer = 0.05 to 0.14 μm with up to 30% of the whole carbon. PAH concentrations were always higher at south-eastern/eastern inflow
especially during wintertime. Trace metal components and silicon were found mainly in the coarse mode fraction at the kerbside
resulting from abrasion or resuspension. 相似文献
14.
Summary 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−2 s−1 was observed at the end of July. The highest nocturnal respiration rates in early August were 0.2 mg(CO2) m−2 s−1. The daily CO2 balances during the time of maximal photosynthesis were about −15 g(CO2) m−2 d−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 interannual 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 parameterised 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.
Received October 11, 1999 Revised April 25, 2000 相似文献
15.
Summary Cloud parameters and surface radiative fluxes predicted by regional atmospheric models are directly compared with observations
for a 10-day period in late summer 1995 characterized by predominantly large-scale synoptic conditions. Observations of total
cloud cover and vertical cloud structure are inferred from measurements with a ground-based network of Lidar ceilometers and
IR-radiometers and from satellite observations on a 100 kilometer scale. Ground-based observations show that at altitudes
below 3 km, implying liquid water clouds, there is a considerable portion of optically non-opaque clouds. Vertical distributions
of cloud temperatures simultaneously inferred from the ground-based infrared radiometer network and from satellite can only
be reconciled if the occurrence of optically thin cloud structures at mid- and high tropospheric levels is assumed to be frequent.
Results of three regional atmospheric models, i.e. the GKSS-REMO, SMHI-HIRLAM, and KNMI-RACMO, are quantitatively compared
with the observations. The main finding is that all models predict too much cloud amount at low altitude below 900 hPa, which
is then compensated by an underestimation of cloud amount around 800 hPa. This is likely to be related with the finding that
all models tend to underestimate the planetary boundary layer height. All models overpredict the high-level cloud amount albeit
it is difficult to quantify to what extent due to the frequent presence of optically thin clouds. Whereas reasonably alike
in cloud parameters, the models differ considerably in radiative fluxes. One model links a well matching incoming solar radiation
to a radiatively transparent atmosphere over a too cool surface, another model underpredicts incoming solar radiation at the
surface due to a too strong cloud feedback to radiation, the last model represents all surface radiative fluxes quite well
on average, but underestimates the sensitivity of atmospheric transmissivity to cloud amount.
Received August 31, 2000 Revised March 15, 2001 相似文献
16.
Concurrent measurements of the surface energy balance components (net radiation, heat storage, and sensible and latent heat fluxes) were made in three communities (open water, Phragmites australis, Scirpus acutus) in a wetland in north-central Nebraska, U.S.A., during May-October, 1994. The Bowen ratio – energy balance method was used to calculate latent and sensible heat fluxes. This paper presents results from the open water area. The heat stored in water (G) was found to play a major role in the energy exchange over the water surface. During daytime, G consumed 45–60% of R
n
, the net radiation (seasonally averaged daytime G was about 127 W m–2). At night, G was a significant source of energy (seasonally averaged nighttime G was about -135 Wm–). The diurnal pattern of latent heat flux ( E) did not follow that of R
n
. On some days, E was near zero during midday periods with large R
n
. The diurnal variability in E seemed to be significantly affected by temperature inversions formed over the cool water surface. The daily evaporation rate (E) ranged from 2 to 8 mm during the measurement period, and was generally between 70 and 135% of the equilibrium rate. 相似文献
17.
Annual methane emission from Finnish mires estimated from eddy covariance campaign measurements 总被引:4,自引:0,他引:4
K. J. Hargreaves D. Fowler C. E. R. Pitcairn M. Aurela 《Theoretical and Applied Climatology》2001,70(1-4):203-213
Summary Measurements of landscape-scale methane emission were made over an aapa mire near Kaamanen in Finnish Lapland (69° 8′ N,
27° 16′ E, 155 m ASL). Emissions were measured during the spring thaw, in summer and in autumn. No effect of water table position
on 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, modelled from temperature regression and short-term flux measurements made in
three separate years, was calculated to be 5.5 ± 0.4 g CH4 m−2 y−1 of which 0.6 ± 0.1 g CH4 m−2 y−1 (11%) was released during the spring thaw which lasted 20 to 30 days.
The effect of global warming on the CH4 budget of the site was estimated using the central scenario of the SILMU (Finnish Research Programme on Climate Change) model
which predicts annual mean temperature increases of 1.2, 2.4 and 4.4 °C 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.
Received September 17, 1999 Revised October 16, 2000 相似文献
18.
19.
Joe Kidston Christian Brümmer T. Andrew Black Kai Morgenstern Zoran Nesic J. Harry McCaughey Alan G. Barr 《Boundary-Layer Meteorology》2010,136(2):193-218
Components of the surface energy balance of a mature boreal jack pine forest and a jack pine clearcut were analysed to determine
the causes of the imbalance that is commonly observed in micrometeorological measurements. At the clearcut site (HJP02), a
significant portion of the imbalance was caused by: (i) the overestimation of net radiation (R
n
) due to the inclusion of the tower in the field of view of the downward facing radiometers, and (ii) the underestimation
of the latent heat flux (λE) due to the damping of high frequency fluctuations in the water vapour mixing ratio by the sample tube of the closed-path
infrared gas analyzer. Loss of low-frequency covariance induced by insufficient averaging time as well as systematic advection
of fluxes away from the eddy-covariance (EC) tower were discounted as significant issues. Spatial and temporal distributions
of the total surface-layer heat flux (T), i.e. the sum of sensible heat flux (H) and λE, were well behaved and differences between the relative magnitudes of the turbulent fluxes for several investigated energy
balance closure (C) classes were observed. Therefore, it can be assumed that micrometeorological processes that affected all turbulent fluxes
similarly did not cause the variation in C. Turbulent fluxes measured at the clearcut site should not be forced to close the energy balance. However, at the mature
forest site (OJP), loss of low-frequency covariance contributed significantly to the systematic imbalance when a 30-min averaging
time was used, but the application of averaging times that were long enough to capture all of the low-frequency covariance
was inadequate to resolve all of the high-frequency covariance. Although we found qualitative similarity between T and the net ecosystem exchange (NEE) of carbon dioxide (CO2), forcing T to closure while retaining the Bowen ratio and applying the same factor to CO2 fluxes (F
C
) cannot be generally recommended since it remains uncertain to what extent long wavelength contributions affect the relationship
between T, F
C
and C. 相似文献
20.
Summary Net Ecosystem CO2 Exchange (NEE) was studied during the summer season (June–August) at a high Arctic heath ecosystem for 5 years in Zackenberg,
NE Greenland. Integrated over the 80 day summer season, the heath is presently a sink ranging from −1.4 g C m−2 in 1997 to −23.3 g C m−2 in 2003. The results indicate that photosynthesis might be more variable than ecosystem respiration on the seasonal timescale.
The years focused on in this paper differ climatically, which is reflected in the measured fluxes. The environmental conditions
during the five years strongly indicated that time of snow-melt and air temperature during the growing season are closely
related to the interannual variation in the measured fluxes of CO2 at the heath. Our estimates suggest that net ecosystem CO2 uptake is enhanced by 0.16 g C m−2 per increase in growing degree-days during the period of growth. This study emphasises that increased summer time air temperatures
are favourable for this particular ecosystem in terms of carbon accumulation. 相似文献