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1.
Daily minimum and maximum air temperatures recorded in Naples (1872–1982) and in surrounding areas have been analysed in order to set up a statistical model for investigating climatic changes of extreme air temperature. We have analysed on various time-scales the mean values of minimum air temperature lower than the 10th percentile ( Tmin 10) and the mean values of the maximum air temperature greater than the 90th percentile ( Tmax 90). The results have shown for the city: (i) a significant secular trend both for yearly Tmin 10 and Tmax 90, mostly due to the process of urbanization, that is also responsible for (ii) the ascertained change in the character of the annual cycle, (iii) a reasonable ability to forecast winter Tmin 10 and summer Tmax 90 in statistical terms using a markovian model, and (iv) a significant 11-yr cycle with an amplitude of 0.5 °C directly related to solar activity which has never been succesfully determined before. 相似文献
2.
Coherent structures in turbulent flow above a midlatitude deciduous forest are identified using a wavelet analysis technique. Coupling between motions above the canopy ( z/h=1.5, where h is canopy height) and within the canopy ( z/h=0.6) are studied using composite velocity and temperature fields constructed from 85 hours of data. Data are classified into winter and summer cases, for both convective and stable conditions. Vertical velocity fluctuations are in phase at both observation levels. Horizontal motions associated with the structures within the canopy lead those above the canopy, and linear analysis indicates that the horizontal motions deep in the canopy should lead the vertical motions by 90°. On average, coherent structures are responsible for only about 40% of overall turbulent heat and momentum fluxes, much less than previously reported. However, our large data set reveals that this flux fraction comes from a wide distribution that includes much higher fractions in its upper extremes. The separation distance L
s between adjacent coherent structures, 6–10 h, is comparable to that obtained in previous observations over short canopies and in the laboratory. Changes in separation between the summer and winter (leafless) conditions are consistent with L
s being determined by a local horizontal wind shear scale. 相似文献
3.
Summary Summer-season (May–September) daily maximum temperature ( T
max) and daily minimum temperature ( T
min) observations and three types of heat spells obtained from these temperature observations at seven weather stations located
in southern Quebec (Canada) for the 60-year period from 1941 to 2000 are studied to assess temporal changes in their characteristics
(i.e. frequency of occurrence, seasonal hot days and extremal durations of heat spells). Type-A and Type-B heat spells are
obtained respectively from T
max and T
min observations and Type-C heat spells from simultaneous joint observations of T
max and T
min using suitable thresholds and spells of duration ≥1-day and ≥3-day. The results of this investigation show that the majority
of the selected percentiles (i.e. 5P, 10P, 25P, 50P, 75P, 80P, 90P, 92P, 95P, and 98P) of T
max observations show a negative time-trend with statistically significant decreases (at 10% level) in some of the higher percentiles
and in the maximal values at four out of seven stations. Almost all of the selected percentiles (same as for the T
max) and the maximal and minimal values of T
min observations show a positive trend, with statistically significant increases for all seven stations. Examination of frequencies
of occurrence of heat spells, seasonal hot days and annual extremes of heat spell durations indicate that many of these characteristics
of heat spells have undergone statistically significant changes over time at some of the stations for Type-A and Type-B heat
spells as compared to Type-C heat spells. The Type-C heat spells are generally small in number and are found to be relatively
temporally stable. More severe Type-C heat spells, i.e. the ones having T
max and T
min values simultaneously above very high thresholds and with duration ≥3-day have been rarely observed in southern Quebec. 相似文献
4.
This study focuses on changes in the maximum and minimum temperature over the Subansiri River basin for different climate change scenarios. For the study, dataset from Intergovernmental Panel on Climate Change (IPCC) fifth assessment report (AR5) (i.e., coupled model intercomparison project phase five (CMIP5) dataset with representative concentration pathway (RCP) scenarios) were utilized. Long-term (2011–2100) maximum temperature (T
max) and minimum temperature (Tmin) time series were generated using the statistical downscaling technique for low emission scenario (RCP2.6), moderate emission scenario (RCP6.0), and extreme emission scenario (RCP8.5). Trends and change of magnitude in T
max, T
min, and diurnal temperature range (DTR) were analyzed for different interdecadal time scales (2011–2100, 2011–2040, 2041–2070, 2070–2100) using Mann-Kendall non-parametric test and Sen’s slope estimator, respectively. The temperature data series for the observed duration (1981–2000) has been found to show increasing trends in T
max and T
min at both annual and monthly scale. Trend analysis of downscaled temperature for the period 2011–2100 shows increase in annual maximum temperature and annual minimum temperature for all the selected RCP scenarios; however, on the monthly scale, T
max and T
min have been seen to have decreasing trends in some months. 相似文献
5.
Summary Possible changes of mean climate and the frequency of extreme temperature events in Emilia-Romagna, over the period 2070–2100
compared to 1960–1990, are assessed. A statistical downscaling technique, applied to HadAM3P experiments (control, A2 and
B2 scenarios) performed at the Hadley Centre, is used to achieve this objective. The method applied consists of a multivariate
regression based on Canonical Correlation Analysis (CCA), using as possible predictors mean sea level pressure (MSLP), geopotential
height at 500 hPa (Z500) and temperature at 850 hPa (T850), and as predictands the seasonal mean values of minimum and maximum
surface temperature (T min and T max), 90 th percentile of maximum temperature (T max90), 10 th percentile of minimum temperature (T min10), number of frost days (T nfd) and heat wave duration (HWD) at the station level. First, the statistical model is optimised and calibrated using NCEP/NCAR
reanalysis to evaluate the large-scale predictors. The observational data at 32 stations uniformly distributed over Emilia-Romagna
are used to compute the local predictands. The results of the optimisation procedure reveal that T850 is the best predictor
in most cases, and in combination with MSLP, is an optimum predictor for winter T max90 and autumn T min10. Finally, MSLP is the best predictor for spring T min while Z500 is the best predictor for spring T max90 and heat wave duration index, except during autumn. The ability of HadAM3P to simulate the present day spatial and temporal
variability of the chosen predictors is tested using the control experiments. Finally, the downscaling model is applied to
all model output experiments to obtain simulated present day and A2 and B2 scenario results at the local scale. Results show
that significant increases can be expected to occur under scenario conditions in both maximum and minimum temperature, associated
with a decrease in the number of frost days and with an increase in the heat wave duration index. The magnitude of the change
is more significant for the A2 scenario than for the B2 scenario. 相似文献
6.
This study analyzes mid-21st century projections of daily surface air minimum (T min) and maximum (T max) temperatures, by season and elevation, over the southern range of the Colorado Rocky Mountains. The projections are from four regional climate models (RCMs) that are part of the North American Regional Climate Change Assessment Program (NARCCAP). All four RCMs project 2°C or higher increases in T min and T max for all seasons. However, there are much greater (>3°C) increases in T max during summer at higher elevations and in T min during winter at lower elevations. T max increases during summer are associated with drying conditions. The models simulate large reductions in latent heat fluxes and increases in sensible heat fluxes that are, in part, caused by decreases in precipitation and soil moisture. T min increases during winter are found to be associated with decreases in surface snow cover, and increases in soil moisture and atmospheric water vapor. The increased moistening of the soil and atmosphere facilitates a greater diurnal retention of the daytime solar energy in the land surface and amplifies the longwave heating of the land surface at night. We hypothesize that the presence of significant surface moisture fluxes can modify the effects of snow-albedo feedback and results in greater wintertime warming at night than during the day. 相似文献
7.
ARPEGE general circulation model simulations were dynamically downscaled by The Weather Research and Forecasting Model (WRF) for the study of climate change and its impact on grapevine growth in Burgundy region in France by the mid twenty-first century. Two time periods were selected: 1970–1979 and 2031–2040. The WRF model driven by ERA-INTERIM reanalysis data was validated against in situ surface temperature observations. The daily maximum and minimum surface temperature (T max and T min) were simulated by the WRF model at 8?×?8?km horizontal resolution. The averaged daily T max for each month during 1970–1979 have good agreement with observations, the averaged daily T min have a warm bias about 1–2?K. The daily T max and T min for each month (domain averaged) during 2031–2040 show a general increase. The largest increment (~3?K) was found in summer. The smallest increments (<1?K) were found in spring and fall. The spatial distribution of temperature increment shows a strong meridional gradient, high in south in summer, reversing in winter. The resulting potential warming rate in summer is equivalent to 4.7?K/century under the IPCC A2 emission scenario. The dynamically downscaled T max and T min were used to simulate the grape (Pinot noir grape variety) flowering and véraison dates. For 2031–2040, the projected dates are 8 and 12?days earlier than those during 1970–1979, respectively. The simulated hot days increase more than 50% in the two principal grapevine regions. They show strong impact on Pinot noir development. 相似文献
8.
In this study, the trends of the annual, seasonal and monthly maximum ( T max) and minimum ( T min) air temperatures time series were investigated for 20 stations in the western half of Iran during 1966?C2005. Three statistical tests including Mann?CKendall, Sen??s slope estimator and linear regression were used for the analysis. The annual T max and T min series showed a positive trend in 85% of the stations and a negative trend in 15% of the stations in the study region. The highest increase of T max and T min values were obtained over Kermanshah and Ahwaz at the rates of (+)0.597°C/decade and (+)0.911°C/decade, respectively. On the seasonal scale, the strongest increasing trends were identified in T max and T min data in summer. The highest numbers of stations with positive significant trends occurred in the monthly T max and T min series in August. In contrast, the lowest numbers of stations with significant positive trends were observed between November and March. Overall, the results showed similar increasing trends for the study variables, although T min generally increased at a higher rate than T max in the study period. 相似文献
9.
Western China experienced an extreme hot summer in 2015, breaking a number of temperature records. The summer mean surface air temperature (SAT) anomaly was twice the interannual variability. The hottest daytime temperature ( TXx) and warmest night-time temperature ( TNx) were the highest in China since 1964. This extreme hot summer occurred in the context of steadily increasing temperatures in recent decades. We carried out a set of experiments to evaluate the extent to which the changes in sea surface temperature (SST)/sea ice extent (SIE) and anthropogenic forcing drove the severity of the extreme summer of 2015 in western China. Our results indicate that about 65%–72% of the observed changes in the seasonal mean SAT and the daily maximum ( Tmax) and daily minimum ( Tmin) temperatures over western China resulted from changes in boundary forcings, including the SST/SIE and anthropogenic forcing. For the relative role of individual forcing, the direct impact of changes in anthropogenic forcing explain about 42% of the SAT warming and 60% (40%) of the increase in TNx and Tmin ( TXx and Tmax) in the model response. The changes in SST/SIE contributed to the remaining surface warming and the increase in hot extremes, which are mainly the result of changes in the SST over the Pacific Ocean, where a super El Niño event occurred. Our study indicates a prominent role for the direct impact of anthropogenic forcing in the severity of the extreme hot summer in western China in 2015, although the changes in SST/SIE, as well as the internal variability of the atmosphere, also made a contribution. 相似文献
10.
Summary A comparative study was performed to evaluate the performance of the UK Met Office’s Global Seasonal (GloSea) prediction General
Circulation Model (GCM) for the forecast of maximum surface air temperature (T max) over the Indian region using the model generated hindcast of 15-members ensemble for 16 years (1987–2002). Each hindcast
starts from 1 st January and extends for a period of six months in each year. The model hindcast T max is compared with T max obtained from verification analysis during the hot weather season on monthly and seasonal scales from March to June.
The monthly and seasonal model hindcast climatology of T max from 240 members during March to June and the corresponding observed climatology show highly significant (above 99.9% level)
correlation coefficients (CC) although the hindcast T max is over-estimated (warm bias) over most parts of the Indian region. At the station level over New Delhi, although the forecast
error (forecast-observed) at the monthly scale gradually increases from March to June, the forecast error at the seasonal
scale during March to May (MAM) is found to be just 1.67 °C. The GloSea model also simulates well T max anomalies on monthly and seasonal scales during March to June with the lower Root Mean Square Error (RMSE) of bias corrected
forecast (less than 1.2 °C), which is much less than the corresponding RMSE of climatology (reference) forecast. The anomaly
CCs (ACCs) over the station in New Delhi are also highly significant (above 95% level) on monthly to seasonal time scales
from March to June, except for April.
The skill of the GloSea model for the seasonal forecast of T max as measured from the ACC map and the bias corrected RMSE map is reasonably good during MAM and April to June (AMJ) with higher
ACC (significant at 95% level) and lower RMSE (less than 1.5 °C) found over many parts of the Indian regions.
Authors’ addresses: D. R. Pattanaik, H. R. Hatwar, G. Srinivasan, Y. V. Ramarao, India Meteorological Department (IMD), New
Delhi, India; U. C. Mohanty, P. Sinha, Centre for Atmospheric Sciences, Indian Institute of Technology, Hauz Khas, New Delhi
110016, India; Anca Brookshaw, UK Met Office, UK. 相似文献
11.
In contrast to atmospheric surface-layer (ASL) turbulence, a linear relationship between turbulent heat fluxes ( FT) and vertical gradients of mean air temperature within canopies is frustrated by numerous factors, including local variation
in heat sources and sinks and large-scale eddy motion whose signature is often linked with the ejection-sweep cycle. Furthermore,
how atmospheric stability modifies such a relationship remains poorly understood, especially in stable canopy flows. To date,
no explicit model exists for relating FT to the mean air temperature gradient, buoyancy, and the statistical properties of the ejection-sweep cycle within the canopy
volume. Using third-order cumulant expansion methods (CEM) and the heat flux budget equation, a “diagnostic” analytical relationship
that links ejections and sweeps and the sensible heat flux for a wide range of atmospheric stability classes is derived. Closure
model assumptions that relate scalar dissipation rates with sensible heat flux, and the validity of CEM in linking ejections
and sweeps with the triple scalar-velocity correlations, were tested for a mixed hardwood forest in Lavarone, Italy. We showed
that when the heat sources ( ST) and FT have the same sign (i.e. the canopy is heating and sensible heat flux is positive), sweeps dominate the sensible heat flux.
Conversely, if ST and FT are opposite in sign, standard gradient-diffusion closure model predict that ejections must dominate the sensible heat flux. 相似文献
12.
本文选取1981年7月至2012年12月美国国家航空和航天局(NASA)制作的归一化的动态植被指数(NDVI)资料、根据NDVI值计算地表热力输送系数(C H)的参数化关系式(C H-I NDV)和青藏高原70个常规气象观测资料,计算了青藏高原全区的逐月地表热力输送系数(C H),讨论了其时空分布特征,并在此基础上计算了高原70个常规台站的感热通量(SSHF)序列,并与已有感热资料进行了对比。随后,探讨了地面感热通量的气候特征及其年际变化与气候因子的关系。结果表明:高原地区的C H值具有明显的空间差异和季节差异,表现为东高西低、夏季大、冬季小的特点。感热的年际变化在冬季主要响应于地气温差的变化,夏季则受地面风速影响较大;由于风速减小趋缓,地气温差增大,变化趋势在2003年前后由减弱趋势转变为增强趋势,这种趋势的转变最早发生在2001年秋季,且在高原全区具有较好的一致性。 相似文献
13.
In this study,the maximum wind speed(WSmax) changes across China from 1956 to 2004 were analyzed based on observed station data,and the changes of WS max for 2046-2065 and 2080-2099 are projected using three global climate models(GFDL CM2 0,CCCMA CGCM3,and MRI CGCM2) that have participated in the IPCC Fourth Assessment Report(AR4).The observed annual and seasonal WS max and the frequency of gale days showed obvious declining trends.The annual WS max decreased by approximately 1.46 m s-1 per decade,and the number of gale days decreased by 3.0 days per decade from 1956 to 2004.The amplitudes of the annual and seasonal WS max decreases are larger than those of the annual and seasonal average wind speeds(WSavg).The weakening of the East Asian winter and summer monsoons is the cause for the distinct decreases of both WS max and WS avg over the whole China.The decrease of WS max in the southeast coastal areas of China is related to the reduced intensity of cold waves in China and the decreasing number(and decreasing intensity) of land-falling typhoons originated in the Northwest Pacific Ocean.The global climate models GFDL CM2 0,MRI CGCM2,and EBGCM(the ensemble of above mentioned three global climate models) consistently suggest that the annual and seasonal WS max values will decrease during 2046-2065 and 2080-2099 relative to 1981-2000.The models also suggest that decreases in WS max for whole China during 2046-2065 and 2080-2099 are related to both the reduced intensity of cold waves and the reduced intensity of the winter monsoon,and the decrease in WS max in the southeast coastal areas of China is corresponding to the decreasing number of tropical cyclones over the Northwest Pacific Ocean in the summer during the same periods. 相似文献
14.
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 CO 2 fluxes. The seasonal periods important for the net CO 2 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
15.
Abstract Two dynamical models are used to perform a series of seasonal predictions. One model, referred to as GCM2, was designed as a general circulation model for climate studies, while the second one, SEF, was designed for numerical weather prediction. The seasonal predictions cover the 26‐year period 1969–1994. For each of the four seasons, ensembles of six forecasts are produced with each model, the six runs starting from initial conditions six hours apart. The sea surface temperature (SST) anomaly for the month prior to the start of the forecast is persisted through the three‐month prediction period, and added to a monthly‐varying climatological SST field. The ensemble‐mean predictions for each of the models are verified independently, and the two ensembles are blended together in two different ways: as a simple average of the two models, denoted GCMSEF, and with weights statistically determined to minimize the mean‐square error (the Best Linear Unbiased Estimate (BLUE) method). The GCMSEF winter and spring predictions show a Pacific/North American (PNA) response to a warm tropical SST anomaly. The temporal anomaly correlation between the zero‐lead GCMSEF mean‐seasonal predictions and observations of the 500‐hPa height field (Z 500) shows statistically significant forecast skill over parts of the PNA area for all seasons, but there is a notable seasonal variability in the distribution of the skill. The GCMSEF predictions are more skilful than those of either model in winter, and about as skilful as the better of the two models in the other seasons. The zero‐lead surface air temperature GCMSEF forecasts over Canada are found to be skilful (a) over the west coast in all seasons except fall, (b) over most of Canada in summer, and (c) over Manitoba, Ontario and Quebec in the fall. In winter the skill of the BLUE forecasts is substantially better than that of the GCMSEF predictions, while for the other seasons the difference in skill is not statistically significant. When the Z 500 forecasts are averaged over months two and three of the seasons (one‐month lead predictions), they show skill in winter over the north‐eastern Pacific, western Canada and eastern North America, a skill that comes from those years with strong SST anomalies of the El Niño/La Niña type. For the other seasons, predictions averaged over months two and three show little skill in Z 500 in the mid‐latitudes. In the tropics, predictive skill is found in Z 500 in all seasons when a strong SST anomaly of the El Niño/La Niña type is observed. In the absence of SST anomalies of this type, tropical forecast skill is still found over much of the tropics in months two and three of the northern hemisphere spring and summer, but not in winter and fall. 相似文献
16.
Annual variations of mixed-layer characteristics at New Delhi, India have been studied for a weak monsoon (1987) and a strong monsoon (1988) year. In the weak monsoon year (1987), the maximum mixing depth h
max was found to have a value of around 3000 m during the pre-monsoon, less than 2000 m during the summer monsoon, around 2000 m during the post-monsoon, and less than 1000 m in the winter season. For the strong monsoon year (1988), h
max values were less than 1987 values for comparable periods throughout the year. The seasonal and yearly differences of h
max were explained by the surface energy balance and potential temperature gradient at a time close to sunrise. According to the spatial patterns of obtained by an objective analysis of the 850 to 700 hPa layers. mixed-layer characteristics obtained at New Delhi are representative of the north and central regions of India. 相似文献
17.
We used an aerodynamic method to objectively determine a representative canopy height, using standard meteorological measurements.
The canopy height may change if the tree height is used to represent the actual canopy, but little work to date has focused
on creating a standard for determining the representative canopy height. Here we propose the ‘aerodynamic canopy height’ h
a as the most effective means of resolving the representative canopy height for all forests. We determined h
a by simple linear regression between zero-plane displacement d and roughness length z
0, without the need for stand inventory data. The applicability of h
a was confirmed in five different forests, including a forest with a complex canopy structure. Comparison with stand inventory
data showed that h
a was almost equivalent to the representative height of trees composing the crown surface if the forest had a simple structure,
or to the representative height of taller trees composing the upper canopy in forests with a complex canopy structure. The
linear relationship between d and z
0 was explained by assuming that the logarithmic wind profile above the canopy and the exponential wind profile within the
canopy were continuous and smooth at canopy height. This was supported by observations, which showed that h
a was essentially the same as the height defined by the inflection point of the vertical profile of wind speed. The applicability
of h
a was also verified using data from several previous studies. 相似文献
18.
The Regional Atmospheric Modeling System (RAMS)-based Forest Large-Eddy Simulation (RAFLES), developed and evaluated here,
is used to explore the effects of three-dimensional canopy heterogeneity, at the individual tree scale, on the statistical
properties of turbulence most pertinent to mass and momentum transfer. In RAFLES, the canopy interacts with air by exerting
a drag force, by restricting the open volume and apertures available for flow (i.e. finite porosity), and by acting as a heterogeneous
source of heat and moisture. The first and second statistical moments of the velocity and flux profiles computed by RAFLES
are compared with turbulent velocity and scalar flux measurements collected during spring and winter days. The observations
were made at a meteorological tower situated within a southern hardwood canopy at the Duke Forest site, near Durham, North
Carolina, U.S.A. Each of the days analyzed is characterized by distinct regimes of atmospheric stability and canopy foliage
distribution conditions. RAFLES results agreed with the 30-min averaged flow statistics profiles measured at this single tower.
Following this intercomparison, two case studies are numerically considered representing end-members of foliage and midday
atmospheric stability conditions: one representing the winter season with strong winds above a sparse canopy and a slightly
unstable boundary layer; the other representing the spring season with a dense canopy, calm conditions, and a strongly convective
boundary layer. In each case, results from the control canopy, simulating the observed heterogeneous canopy structure at the
Duke Forest hardwood stand, are compared with a test case that also includes heterogeneity commensurate in scale to tree-fall
gaps. The effects of such tree-scale canopy heterogeneity on the flow are explored at three levels pertinent to biosphere-atmosphere
exchange. The first level (zero-dimensional) considers the effects of such heterogeneity on the common representation of the
canopy via length scales such as the zero-plane displacement, the aerodynamic roughness length, the surface-layer depth, and
the eddy-penetration depth. The second level (one-dimensional) considers the normalized horizontally-averaged profiles of
the first and second moments of the flow to assess how tree-scale heterogeneities disturb the entire planar-averaged profiles
from their canonical (and well-studied planar-homogeneous) values inside the canopy and in the surface layer. The third level
(three-dimensional) considers the effects of such tree-scale heterogeneities on the spatial variability of the ejection-sweep
cycle and its propagation to momentum and mass fluxes. From these comparisons, it is shown that such microscale heterogeneity
leads to increased spatial correlations between attributes of the ejection-sweep cycle and measures of canopy heterogeneity,
resulting in correlated spatial heterogeneity in fluxes. This heterogeneity persisted up to four times the mean height of
the canopy ( h
c
) for some variables. Interestingly, this estimate is in agreement with the working definition of the thickness of the canopy
roughness sublayer (2 h
c
–5 h
c
). 相似文献
19.
利用北京325 m气象塔上安装的7层CO 2涡动相关系统在2014年12月到2015年11月的观测资料,分析了北京城区不同高度上CO 2浓度、通量时空分布及湍流谱的特征。结果表明:城市CO 2浓度日变化除了冬季都呈现双峰型,冬季由于人为碳源排放的大幅增加,双峰型不明显。每层的CO 2浓度、通量都有明显的季节变化:冬季最高,春末、夏季最低。CO 2浓度整体随高度的增加而降低。北京城区是CO 2源,CO 2通量的日变化不如CO 2浓度日变化规律明显。CO 2通量在47 m以下为负,47 m以上为正。通量在140 m以下随高度的增加而增加;140m以上随高度的增加而减少。根据对CO 2时空分布的分析可知:边界层CO 2浓度、通量强烈受到碳源、下垫面植被、大气稳定度、环境温度和天气过程等因素的影响。各变量谱与Kaimal等的研究结果接近:归一化速度谱和CO 2谱在惯性子区有-2/3的斜率,在低频区与稳定度参数(Z/L)有一定的关系。这说明复杂地形的城市下垫面的湍流谱结构与平坦地形相比没有太大的实质性差异。 相似文献
20.
利用1960~2006年我国地温、气温逐日4个时次[02:00(北京时间,下同)、08:00、14:00和20:00]的台站观测资料,计算并分析了我国东南、西北地区各季地气温差的年代际变化特征。分析结果表明:我国东南部地区各季地气温差在20世纪70年代末以前,大部分年份偏高,高于平均值,而在20世纪70年代末以后,我国东南部地区各季地气温差偏低,在夏季和冬季表现尤为明显。我国西北地区春季和夏季地气温差在20世纪70年代末以前大部分年份偏低,低于平均值;而在20世纪70年代末以后,地气温差则大部分年份明显偏高。我国西北地区秋季地气温差的年代际变化特征不明显,而冬季地气温差的年代际变化趋势与春夏季相反,在20世纪70年代末以前大部分年份偏高,高于平均值,而在20世纪70年代末以后偏低。另外,发现地温和气温对我国东南、西北地区各季地气温差的年代际变化在各季所起的贡献作用不同。 相似文献
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