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991.
In this study, the global Lorenz atmospheric energy cycle is evaluated using the Modern Era Retrospective analysis for Research and Applications (MERRA) and the National Center for Environmental Prediction and the Department of Energy (NCEP R2) reanalysis datasets over a 30-year period (1979–2008) for the annual, JJA, and DJF means. The energy cycle calculated from the two reanalysis datasets is largely consistent, but the energy cycle determined using the MERRA dataset is more active than that determined from the NCEP R2 dataset. For instance, with regard to the annual mean, the general discrepancy between the energy components in the global integral is about 5 %, whereas the discrepancy between the conversion components is about 16 %, with the exception of C(PM, KM), which has a different sign in the global integrals. The latitude-altitude cross-section indicates that the difference in the energy cycle of the two reanalysis datasets is larger in the southern hemisphere than in the northern hemisphere. The conversion rates of mean available potential energy to mean kinetic energy [C(PM, KM)] and eddy available potential energy to eddy kinetic energy [C(PE, KE)] are also calculated using two formulations (so-called ‘v·grad z’ and ‘ω·α’) for the two reanalysis datasets. The differences in the conversion rate between the two reanalysis datasets for the global integral are not appreciable for the two formulations. 相似文献
992.
993.
MA Dingguo CHEN Jie ZHANG Wenjiang ZHENG Lin LIU Ying 《地理学报(英文版)》2007,17(3):269-284
This paper quantitatively explores farmers' vulnerability to flood in the Poyang Lake Region (PLR) with the supports of GIS spatial functions. The analysis consists of three major steps, which is based on the spatial unit of township. Firstly, the spatial extent and characteristics of flood risk areas were determined using a digital elevation model (DEM) derived from the 1:50,000 topographic map. Secondly, for each of the township, six indices indicating the economic activities of local farmers were calculated. These indices are: rural population proportion, cultivated land proportion, GDP per unit area, employment proportion of primary industry, net rural income per capita and agricultural income proportion. These six indices were then normalized and used for later vulnerability assessment. Thirdly, the normalized indices (as GIS data layers) were overlaid with the flood risk areas to produce the risk coefficient for each township and to calculate the overall vulnerability for each township. The analysis results show that in the PLR there are high flood risk areas where the farmers' livings are seriously influenced or threatened. About 55.56% of the total 180 townships in the flood risk areas have a high degree of flood vulnerability. The townships under flood risk are mainly distributed in the areas around the Poyang Lake and the areas along the "five rivers". 相似文献
994.
Numerical weather prediction models are increasingly employed for providing meteorological data for urban air quality applications.
Model resolution, physiographic parameters and surface-layer parameterisations need to be adapted to the requirements of the
urban boundary layer. The Lokalmodell of the German Weather Service was triple-nested down to a horizontal grid resolution
of 1.1 km, urbanised physiographic parameters were implemented, and an additional anthropogenic heat source was introduced.
Results of a sensitivity study for a spring dust episode in Helsinki show a clear urbanisation effect of these measures on
temperature, humidity and the partitioning of surface fluxes, leading to an increased Bowen ratio and heat storage and an
urban heat island effect. 相似文献
995.
Thara V. Prabha Anandakumar Karipot Michael W. Binford 《Boundary-Layer Meteorology》2007,123(2):239-261
Large-eddy simulation is used to study secondary circulations in the convective boundary layer modulated as a result of horizontally
varying surface properties and surface heat fluxes over flat terrain. The presence of heat flux heterogeneity and its alignment
with respect to geostrophic wind influences the formation, strength and orientation of organized thermals. Results show boundary-attached
roll formation along heat flux maxima in the streamwise direction. The streamwise organization of the updrafts and downdrafts
formed downwind of heterogeneities leads to counter-rotating secondary circulations in the crosswind plane. The distribution
of resolved-scale pressure deviations shows large pressure gradients in the crosswind plane. Spanwise and vertical velocity
variances and heat flux profiles depict considerable spatial variability compared to a homogeneous forest simulation. Secondary
circulations are observed for various ambient wind scenarios parallel and perpendicular to heterogeneities. In the presence
of increased wind speed, thermals emerging from the heat flux heterogeneity are elongated, and organize along and downwind
of large-scale heterogeneity in the streamwise direction. Simulation with a reduced heat flux shows a shallower circulation
with a lower aspect ratio. Point measurements of heat flux inside the roll circulation could be overestimated by up to 15–25%
compared to a homogeneous case. 相似文献
996.
Tilt corrections over complex terrain and their implication for CO<Subscript>2</Subscript> transport
Jielun Sun 《Boundary-Layer Meteorology》2007,124(2):143-159
Observational data from sonic anemometers are commonly rotated from sonic to streamline coordinates, a procedure that is called
tilt correction. Tilt corrections are often used to post-process air velocity data collected from sonic anemometers to allow
objective interpretation of air flow data relative to the Earth. Since streamline coordinates depend on dynamical characteristics
of the flow, the tilt correction depends not only on temporal and spatial variations of the flow, but also on local circulations.
We found that ensemble- averaged slope flows are approximately parallel to the terrain slope close to the ground within the
canopy layer, but not above, due to the influence of the diurnal variation of local vertical circulations. As a result, the
diurnal variation of the observed vertical velocity in streamline coordinates at 21.5 m above the ground over 11-m tall forest
canopies can be opposite to that calculated from the continuity equation. To estimate CO2 transport over sloping terrain, a workable reference coordinate system is needed such that multiple sonic anemometers have
a common reference relative to the Earth. Streamline coordinate systems can be the choice of the common reference coordinate
system only if flow, at least ensemble-averaged flow, is parallel to terrain slopes. The choice of the reference coordinate
system and its implication in investigation of CO2 transport are discussed.
The National Center for Atmospheric Research is sponsored by the National Science Foundation. 相似文献
997.
Stable carbon isotopic composition of ethane and propane over the western North Pacific and eastern Indian Ocean between 31°N
and 26°S was investigated from February through March 2004. The isotopic composition of ethane ranged from −28 to −18‰ and
showed a gradual increase from north to south. Conversely, that of propane was between −31 and −24‰; it showed no systematic
latitudinal variation. Investigation of the ethane/propane ratio indicates that ethane and propane that originated from northern
mid-latitude countries in the eastern part of Eurasia were both transported into the western North Pacific region. However,
the results of the isotopic analyses indicate the contribution of oceanic emission to the atmospheric propane during transport,
although that contribution can not be discerned for ethane. A ship based stationary observation conducted in the western equatorial
North Pacific showed that the isotopic composition of ethane varied from −25 to −19‰ and showed clear systematic diurnal variation:
propane ranged between −32 to −26‰ and no such isotopic diurnal signal was observed. The diurnal variation for ethane is explained
by entrainment of free tropospheric air, whereas the variation for propane was influenced by oceanic emissions as well as
the entrainment. The contribution of oceanic emissions to the atmospheric propane inventory was considered from our isotopic
observation. Isotopic composition of dissolved propane is estimated to be less than −38‰, and the contribution up to 79% was
calculated when the isotopic composition of dissolved propane is assumed to be −40‰. Our study demonstrates that isotopic
analysis can be more useful than ratio-based analysis to improve our present understanding of transport processes, especially
for impact of the oceanic emissions on the atmospheric distribution of low level C2–C5 non-methane hydrocarbons such as propane in the remote marine atmosphere. 相似文献
998.
The growing interest in and emphasis on high spatial resolution estimates of future climate has demonstrated the need to apply
regional climate models (RCMs) to that problem. As a consequence, the need for validation of these models, an assessment of
how well an RCM reproduces a known climate, has also grown. Validation is often performed by comparing RCM output to gridded
climate datasets and/or station data. The primary disadvantage of using gridded climate datasets is that the spatial resolution
is almost always different and generally coarser than climate model output. We have used a Bayesian statistical model derived
from observational data to validate RCM output. We used surface air temperature (SAT) data from 109 observational stations
in California, all with records of approximately 50 years in length, and created a statistical model based on this data. The
statistical model takes into account the elevation of the station, distance from coastline, and the NOAA climate region in
which the station resides. Analysis indicates that the statistical model provides reliable estimates of the mean monthly SAT
at any given station. In our method, the uncertainty in the estimates produced by the statistical model are directly determined
by obtaining probability density functions for predicted SATs. This statistical model is then used to estimate average SATs
corresponding to each of the climate model grid cells. These estimates are compared to the output of the RCM to assess how
well the RCM matches the observed climate as defined by the statistical model. Overall, the match between the RCM output and
the statistical model is good, with some deficiencies likely due in part to the representation of topography in the RCM. 相似文献
999.
Drag partition measurements were made in the atmospheric inertial sublayer for six roughness configurations made up of solid
elements in staggered arrays of different roughness densities. The roughness was in the form of a patch within a large open
area and in the shape of an equilateral triangle with 60 m long sides. Measurements were obtained of the total shear stress
(τ) acting on the surfaces, the surface shear stress on the ground between the elements (τS) and the drag force on the elements for each roughness array. The measurements indicated that τS quickly reduced near the leading edge of the roughness compared with τ, and a τS minimum occurs at a normalized distance (x/h, where h is element height) of
(downwind of the roughness leading edge is negative), then recovers to a relatively stable value. The location of the minimum
appears to scale with element height and not roughness density. The force on the elements decreases exponentially with normalized
downwind distance and this rate of change scales with the roughness density, with the rate of change increasing as roughness
density increases. Average τS : τ values for the six roughness surfaces scale predictably as a function of roughness density and in accordance with a shear
stress partitioning model. The shear stress partitioning model performed very well in predicting the amount of surface shear
stress, given knowledge of the stated input parameters for these patches of roughness. As the shear stress partitioning relationship
within the roughness appears to come into equilibrium faster for smaller roughness element sizes it would also appear the
shear stress partitioning model can be applied with confidence for smaller patches of smaller roughness elements than those
used in this experiment. 相似文献
1000.
Soon-Il An 《Theoretical and Applied Climatology》2004,78(4):203-215
Summary The interannual variability of sea surface temperature (SST) anomalies in the tropical Indian Ocean is dominated mainly by a basin-scale mode (BM) and partly by an east–west contrast mode (zonal mode, ZM). The BM reflects the basin-scale warming or cooling and is highly correlated with El Nino with 3- to 6-month lags, while the ZM is marginally correlated with El Nino with 9-month lags.During an El Nino, large-scale anomalous subsidence over the maritime continent occurs as a result of an eastward shift in the rising branch of the Walker circulation suppresses convection over the eastern Indian Ocean, allowing more solar radiation over the eastern Indian Ocean. At the same time, the anomalous southeasterly wind over the equatorial Indian Ocean forces the thermocline over the western Indian Ocean to deepen, especially in the southern part. As a result, SST over the whole basin increases. As El Nino decays, the subsidence over the maritime continent ceases and so does the anomalous southeasterly wind. However, the thermocline perturbation does not quickly shoal back to normal because of inertia and it disperses as Rossby waves. These Rossby waves are reflected back as an equatorial Kelvin wave, causing deepening of the thermocline in the eastern Indian Ocean, and preventing SSTs from cooling in that region. Moreover, the weaker wind speed of the monsoon circulation results in less latent heat loss, and thus warms the eastern Indian Ocean. These two processes therefore help to maintain warm SSTs over the eastern Indian Ocean until fall. During the fall, the warm SST over the eastern Indian Ocean and the cold SST over the western Indian Ocean are enhanced by air–sea interaction and the ZM returns. The ZM dissipates through the seasonal reversal of the monsoon atmospheric circulation and the boundary-reflected Kelvin wave. In the same manner, a basin-scale cooling in the tropical Indian Ocean can induce the ZM warming in the west and cooling in the east. 相似文献