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1.
Ultrasonic wind measurements, sonic temperature and air temperature data at two heights in the advection experiment MORE II
were used to establish a complete budget of sensible heat including vertical advection, horizontal advection and horizontal
turbulent flux divergence. MORE II took place at the long-term Carbo-Europe IP site in Tharandt, Germany. During the growing
period of 2003 three additional towers were established to measure all relevant parameters for an estimation of advective
fluxes, primarily of CO2. Additionally, in relation to other advection experiments, a calculation of the horizontal turbulent flux divergence is proposed
and the relation of this flux to atmospheric stability and friction velocity is discussed. In order to obtain a complete budget,
different scaling heights for horizontal advection and horizontal turbulent flux divergence are tested. It is shown that neglecting
advective fluxes may lead to incorrect results. If advective fluxes are taken into account, the sensible heat budget based
upon vertical turbulent flux and storage change only, is reduced by approximately 30%. Additional consideration of horizontal
turbulent flux divergence would in turn add 5–10% to this sum (i.e., the sum of vertical turbulent flux plus storage change
plus horizontal and vertical advection). In comparison with available energy horizontal advection is important at night whilst
horizontal turbulent flux divergence is rather insignificant. Obviously, advective fluxes typically improve poor nighttime
energy budget closure and might change ecosystem respiration fluxes considerably. 相似文献
2.
Igor Esau Philbert Luhunga George Djolov C. J. de W. Rautenbach Sergej Zilitinkevich 《Meteorology and Atmospheric Physics》2012,118(3-4):129-142
Links between spatial and temporal variability of Planetary Boundary Layer meteorological quantities and existing land-use patterns are still poorly understood due to the non-linearity of air–land interaction processes. This study describes the results of a statistical analysis of meteorological observations collected by a network of ten Automatic Weather Stations. The stations were in operation in the highveld priority area of the Republic of South Africa during 2008–2010. The analysis revealed localization, enhancement and homogenization in the inter-station variability of observed meteorological quantities (temperature, relative humidity and wind speed) over diurnal and seasonal cycles. Enhancement of the meteorological spatial variability was found on a broad range of scales from 20 to 50?km during morning hours and in the dry winter season. These spatial scales are comparable to scales of observed land-use heterogeneity, which suggests links between atmospheric variability and land-use patterns through excitation of horizontal meso-scale circulations. Convective motions homogenized and synchronized meteorological variability during afternoon hours in the winter seasons, and during large parts of the day during the moist summer season. The analysis also revealed that turbulent convection overwhelms horizontal meso-scale circulations in the study area during extensive parts of the annual cycle. 相似文献
3.
High-Resolution Fibre-Optic Temperature Sensing: A New Tool to Study the Two-Dimensional Structure of Atmospheric Surface-Layer Flow 总被引:1,自引:0,他引:1
Christoph K. Thomas Adam M. Kennedy John S. Selker Ayla Moretti Martin H. Schroth Alexander R. Smoot Nicholas B. Tufillaro Matthias J. Zeeman 《Boundary-Layer Meteorology》2012,142(2):177-192
We present a novel approach based on fibre-optic distributed temperature sensing (DTS) to measure the two-dimensional thermal
structure of the surface layer at high resolution (0.25 m, ≈0.5 Hz). Air temperature observations obtained from a vertically-oriented
fibre-optics array of approximate dimensions 8 m × 8 m and sonic anemometer data from two levels were collected over a short
grass field located in the flat bottom of a wide valley with moderate surface heterogeneity. The objectives of the study were
to evaluate the potential of the DTS technique to study small-scale processes in the surface layer over a wide range of atmospheric
stability, and to analyze the space–time dynamics of transient cold-air pools in the calm boundary layer. The time response
and precision of the fibre-based temperatures were adequate to resolve individual sub-metre sized turbulent and non-turbulent
structures, of time scales of seconds, in the convective, neutral, and stable surface layer. Meaningful sensible heat fluxes
were computed using the eddy-covariance technique when combined with vertical wind observations. We present a framework that
determines the optimal environmental conditions for applying the fibre-optics technique in the surface layer and identifies
areas for potentially significant improvements of the DTS performance. The top of the transient cold-air pool was highly non-stationary
indicating a superposition of perturbations of different time and length scales. Vertical eddy scales in the strongly stratified
transient cold-air pool derived from the DTS data agreed well with the buoyancy length scale computed using the vertical velocity
variance and the Brunt–Vaisala frequency, while scales for weak stratification disagreed. The high-resolution DTS technique
opens a new window into spatially sampling geophysical fluid flows including turbulent energy exchange. 相似文献
4.
An OGCM Simulation of Seasonal and Interannual Variabilities in the Surface—Layer Pacific of the Equatorial Band 总被引:1,自引:0,他引:1
The heat budget is analyzed in the surface-layer (0-50 m) Pacific of the equatorial band (10°S-10°N),using the simulation of an ocean general circulation model from 1945 to 1993. The analysis indicates that downward net surface heat flux from the atmosphere and ocean advective heat fluxes play distinct roles in seasonal and interannual variabilities of surface-layer ocean temperature. The surface heat flux dominantly determines the ocean temperature in the seasonal time-scale. But, it has a negative feedback to the ocean temperature in the interannual time-scale. The interannual variability of ocean temperature is largely associated with the cold advection from off-equatorial divergent flow in the central Pacific and from upwelling in the cold tongue. Both the surface heat flux and ocean advective heat fluxes are important to the ocean temperature during an El Nino event. The ocean advective heat fluxes are further associated with local westward trade wind in the central Pacific. These results are largely consistent with some regional observational analyses. 相似文献
5.
利用北京延庆站风廓线雷达水平风廓线资料进行大气温度平流的反演,详细分析2014年11月15日夜间冷空气入侵过程,并统计分析2015年9—11月6次冷空气入侵过程,同T639L60模式的预报风场及温度平流预报产品进行对比。结果表明:在一定预报时效内 (约6~12 h),风廓线雷达获取的水平风廓线与模式给出的预报风场有较好的一致性;由风廓线雷达反演的温度平流与模式给出的温度平流量级相同,温度平流属性一致;风廓线雷达6 min完成1次垂直高度分辨率为120 m的探测,高时空分辨率使风廓线雷达获取的温度平流较T639L60模式更能反映大气温度平流的细节。 相似文献
6.
Amplitude of El Niño and La Niña was significantly different during 1980–2016 but almost same during 1958–1979. The cause of this interdecadal change is investigated through an oceanic mixed-layer heat budget analysis. It was found that this interdecadal change was primarily attributed to the distinctive effects of nonlinear zonal temperature advection between the two periods. During 1980–2016 nonlinear zonal advection, working together with nonlinear meridional advection, contributes to the El Niño and La Niña amplitude asymmetry. During 1958–1979 the nonlinear zonal advection had an opposite effect. The difference in the nonlinear zonal advection between the two interdecadal periods was caused by distinctive longitudinal locations of El Niño centers. Maximum SST anomaly (SSTA) centers were confined near the coast of South America (east of 90° W) during the first period but appear near 110° W during the second period. Because of this difference, an anomalous eastward ocean surface current (caused by a positive thermocline depth anomaly during El Niño) would generate a negative (positive) nonlinear zonal advection before (after) 1980. The distinctive longitudinal locations of El Niño centers are possibly caused by the interdecadal changes of mean thermocline and high-frequency wind variability over the equatorial western-central Pacific. A hypothesis was put forth to understand distinctive initiation locations between El Niño and La Niña. 相似文献
7.
Mitsuaki Horiguchi Taiichi Hayashi Ahoro Adachi Shigeru Onogi 《Boundary-Layer Meteorology》2012,144(2):179-198
Large-scale turbulence structures in the near-neutral atmospheric boundary layer (ABL) are investigated on the basis of observations made from the 213-m tall meteorological tower at Tsukuba, Japan. Vertical profiles of wind speed and turbulent fluxes in the ABL were obtained with sonic anemometer-thermometers at six levels of the tower. From the archived data, 31 near-neutral cases are selected for the analysis of turbulence structures. For the typical case, event detection by the integral wavelet transform with a large time scale (180 s) from the streamwise velocity component (u) at the highest level (200 m) reveals a descending high-speed structure with a time scale of approximately 100 s (a spatial scale of 1 km at the 200-m height). By applying the wavelet transform to the u velocity component at each level, the intermittent appearance of large-scale high-speed structures extending also in the vertical is detected. These structures usually make a large contribution to the downward momentum transfer and induce the enhancement of turbulent kinetic energy. This behaviour is like that of “active” turbulent motions. From the analysis of the two-point space–time correlation of wavelet coefficients for the u velocity component, the vertical extent and the downward influence of large-scale structures are examined. Large fluctuations in the large-scale range (wavelet variance at the selected time scale) at the 200-m level tend to induce the large correlation between the higher and lower levels. 相似文献
8.
An experimental micrometeorological set-up was established at the CARBOEURO-FLUX site in Tharandt, Germany, to measure all relevant variables for the calculation of the vertical and horizontal advective fluxes of carbon dioxide. The set-up includes two auxiliary towers to measure horizontal and vertical CO2 and H2O gradients through the canopy, and to make ultrasonic wind measurements in the trunk space. In combination with the long-term flux tower an approximately even-sided prism with a typical side-length of 50 m was established. It is shown that under stable (nighttime) conditions the mean advective fluxes have magnitudes on the same order as the daily eddy covariance (EC) flux, which implies that they play a significant, but not yet fully understood, role in the carbon budget equation. The two advective fluxes are opposite and seem to cancel each other at night (at least for these measurements). During the day, vertical advection tends to zero, while horizontal advection is still present implying a flow of CO2 out of the control volume. From our measurements, a mean daily gain of 2.2 gC m–2 d–1 for the horizontal advection and a mean daily loss of 2.5 gC m–2d–1 for the vertical advection is calculated for a period of 20 days. However the large scatter of the advective fluxes has to be further investigated. It is not clear yet whether the large variability is natural or due to measurement errors and conceptual deficiencies of the experiment. Similar results are found in the few comparable studies. 相似文献
9.
Summary The temporal variability of thermal turbulence and vertical velocity derived from sodar measurements during periods of atmospheric
free convection is studied using both spectral and wavelet analysis. A promising approach to analyse atmospheric processes,
an advanced high-resolution spectrum estimation technique is described. Variance spectra of meteorological and turbulent parameters
are shown to have their specific comb shape at a low-frequency range. Spectra and wavelet transforms of the data obtained
at different sites both indicate the existence of some representative predominant temporal scales in time variations of the
convective boundary layer structure. The most evident temporal scales revealed are centered around 7–9 and 18–22 minutes.
Received October 16, 1998 Revised April 15, 1999 相似文献
10.
The scaled-decomposed atmospheric water budget over North America is investigated through the analysis of 25 years of simulation
by the Canadian Regional Climate Model (CRCM) driven by the NCEP–NCAR reanalyses for the period 1975–1999. The time average
and time variability of the atmospheric water budget for the winter and summer seasons are decomposed into their large-scale
and small-scale components to identify the added value of the regional model. For the winter season, the intra-seasonal transient-eddy
variance is the main temporal variability. The large- and small-scale terms are of the same order of magnitude, and are large
over both coasts and weak over the continent. For the summer season, the time–mean atmospheric water budget is rather different
to that of winter, with maximum values over the south-eastern part of the continent. The summer intra-seasonal variance is
about twice stronger than in winter and also dominates the variability, but the inter-monthly variance is non-negligible and
can be in part associated to North American Monsoon System. Over the continent, the intra-seasonal climatological variance
is dominated by the variability of the small scales. The small scales, that is those scales that are only resolved in the
regional model but not in the reanalyses, contribute to the added value in a regional climate simulation. In the winter season,
the added value of the CRCM is large and dominated by oceanic forcing, while in summer, it is dominant (larger than the large
scales) and controlled mainly by convective processes. 相似文献
11.
Interdecadal variability of the meridional overturning circulation as an ocean internal mode 总被引:1,自引:1,他引:0
The meridional overturning circulation (MOC) in the coupled ECHAM5/MPIOM exhibits variability at periods of near 30 years
and near 60 years. The 30-year variability, referred to as interdecadal variability (IDV), exist in an ocean model driven
by climatological atmospheric forcing, suggesting that it is maintained by ocean dynamics; the 60-year variability, the multidecadal
variability (MDV), is only observed in the fully coupled model and therefore is interpreted as an atmosphere–ocean coupled
mode. The coexistence of the 30-year IDV and the 60-year MDV provides a possible explanation for the widespread time scales
observed in climate variables. Further analyses of the climatologically forced ocean model shows that, the IDV is related
to the interplay between the horizontal temperature-dominated density gradients and the ocean circulation: temperature anomalies
move along the cyclonic subpolar gyre leading to fluctuations in horizontal density gradients and the subsequent weakening
and strengthening of the MOC. This result is consistent with that from less complex models, indicating the robustness of the
IDV. We further show that, along the North Atlantic Current path, the sea surface temperature anomalies are determined by
the slow LSW advection at the intermediate depth. 相似文献
12.
A nocturnal gravity wave was detected over a south-western Amazon forest during the Large-Scale Biosphere–Atmosphere experiment
in Amazonia (LBA) in the course of the dry-to-wet season campaign on October 2002. The atmospheric surface layer was stably
stratified and had low turbulence activity, based on friction velocity values. However, the passage of the wave, an event
with a period of about 180–300 s, caused negative turbulent fluxes of carbon dioxide (CO2) and positive sensible heat fluxes, as measured by the eddy-covariance system at 60 m (≈30 m above the tree tops). The evolution
of vertical profiles of air temperature, specific humidity and wind speed during the wave movement revealed that cold and
drier air occupied the sub-canopy space while high wind speeds were measured above the vegetation. The analysis of wind speed
and scalars high frequency data was performed using the wavelet technique, which enables the decomposition of signals in several
frequencies allowed by the data sampling conditions. The results showed that the time series of vertical velocity and air
temperature were −90° out of phase during the passage of the wave, implying no direct vertical transport of heat. Similarly,
the time series of vertical velocity and CO2 concentration were 90° out of phase. The wave was not directly associated with vertical fluxes of this variable but the mixing
induced by its passage resulted in significant exchanges in smaller scales as measured by the eddy-covariance system. The
phase differences between horizontal velocity and both air temperature and CO2 concentration were, respectively, zero and 180°, implying phase and anti-phase relationships. As a result, the wave contributed
to positive horizontal fluxes of heat and negative horizontal fluxes of carbon dioxide. Such results have to be considered
in nocturnal boundary-layer surface-atmosphere exchange schemes for modelling purposes. 相似文献
13.
Measurement of the Sensible Eddy Heat Flux Based on Spatial Averaging of Continuous Ground-Based Observations 总被引:1,自引:0,他引:1
M. Mauder R. L. Desjardins E. Pattey Z. Gao R. van Haarlem 《Boundary-Layer Meteorology》2008,128(1):151-172
Using the standard eddy-covariance (EC) method to quantify mass and energy exchange at a single location usually results in
an underestimation of vertical eddy fluxes at the surface. In order to better understand the reasons for this underestimation,
an experimental set-up is presented that is based on spatial averaging of air temperature data from a network of ground-based
sensors over agricultural land. For eight days during the 34-day observational period in May and June 2007, additional contributions
to the sensible heat flux of more than 50Wm−2 were measured in the lower surface layer by applying the spatial EC method as opposed to the standard temporal EC method.
Smaller but still significant additional sensible heat fluxes were detected for four more days. The additional energy is probably
transported in organised convective structures resulting in a mean vertical wind velocity unequal to zero at the tower location.
The results show that convective transport contributes significantly to the surface energy budget for measurement heights
as low as 2–3 m. Since these structures may be quasi-stationary, they can hardly be captured by a single-location measurement.
The spatial EC set-up presented here is capable of quantifying contributions to the sensible heat flux from structures up
to the scale of our spatial sensor network, which covered an area 3.5 × 3.5 km. For future experiments aiming at closing the
energy balance, the spatial EC method should be employed to measure both the sensible and latent heat fluxes. Experimental
determination of the horizontal advection of sensible and latent heat should also be considered, since such transport must
occur due to convergence and divergence related to convection. 相似文献
14.
S. Khodayar N. Kalthoff M. Fiebig-Wittmaack M. Kohler 《Meteorology and Atmospheric Physics》2008,99(3-4):181-198
Summary The boundary-layer structure of the Elqui Valley is investigated, which is situated in the arid north of Chile and extends
from the Pacific Ocean in the west to the Andes in the east. The climate is dominated by the south-eastern Pacific subtropical
anticyclone and the cold Humboldt Current. This combination leads to considerable temperature and moisture gradients between
the coast and the valley and results in the evolution of sea and valley wind systems. The contribution of these mesoscale
wind systems to the heat and moisture budget of the valley atmosphere is estimated, based on radiosoundings performed near
the coast and in the valley.
Near the coast, a well-mixed cloud-topped boundary layer exists. Both, the temperature and the specific humidity do not change
considerably during the day. In the stratus layer the potential temperature increases, while the specific humidity decreases
slightly with height. The top of the thin stratus layer, about 300 m in depth, is marked by an inversion. Moderate sea breeze
winds of 3–4 m s−1 prevail in the sub-cloud and cloud layer during daytime, but no land breeze develops during the night.
The nocturnal valley atmosphere is characterized by a strong and 900 m deep stably stratified boundary layer. During the day,
no pronounced well-mixed layer with a capping inversion develops in the valley. Above a super-adiabatic surface layer of about
150 m depth, a stably stratified layer prevails throughout the day. However, heating can be observed within a layer above
the surface 800 m deep. Heat and moisture budget estimations show that sensible heat flux convergence exceeds cold air advection
in the morning, while both processes compensate each other around noon, such that the temperature evolution stagnates. In
the afternoon, cold air advection predominates and leads to net cooling of the boundary layer. Furthermore, the advection
of moist air results in the accumulation of moisture during the noon and afternoon period, while latent heat flux convergence
is of minor relevance to the moisture budget of the boundary layer.
Correspondence: Norbert Kalthoff, Institut für Meteorologie und Klimaforschung, Universit?t Karlsruhe/Forschungszentrum Karlsruhe,
Postfach 3640, 76021 Karlsruhe, Germany 相似文献
15.
水平非均匀对流边界层热量平衡和平流输送作用的大涡模拟 总被引:3,自引:2,他引:3
采用大涡模拟所获的数据结果,分析地面热通量沿平均风方向存在 突变的条件下对流边界层的热量平衡和平流输送作用。分析表明边界层内模拟所得结果 可以很好地满足热量平衡关系。除地面热通量项以外,平流项(包括水平平流和垂直平 流)对边界层加热率的作用可达地面热通量不均匀性差值的大小,是影响边界层内热量 平衡的最重要因子,平均速度散度项对热量平衡的作用也不可忽略,但湍流通量散度项 的作用则很小。 相似文献
16.
Surface Energy Budget Variability: A Case Study over Grass with Special Regard to Minor Inhomogeneities in the Source Area 总被引:5,自引:0,他引:5
Summary Eddy correlation measurements of surface energy fluxes above a meadow site are presented and discussed in terms of energy
balance closure. The degree of closure changed with time and wind direction, which can be explained by temporal and spatial
variations of the surrounding vegetation. More frequently than not, a tendency towards an energy “deficit” was observed, that
means, the sum of turbulent fluxes was less than the available energy. As a possible reason, we cautiously suggest that large-scale
flux components may have to be taken into account. If so, then a convenient way to obtain fairly accurate total surface energy
fluxes would be to correct the turbulent fluxes with an appropriate factor that forces the budget to perfect closure.
Received October 14, 1996 Revised October 1, 1998 相似文献
17.
采用地形坐标系下适合于复杂地形且满足地-气耦合的静力学三维中-β尺度气象预报模式,使用08时的实测流场经变分法初始化后得到的初始流场,模拟研究了上海地区的局地流场时空演变特征。模式较细致地考虑了湍流、长短波辐射、凝结、蒸发、地表热力平衡等因子,在此基础上,使用有限元法数值求解一阶闭合的三维欧拉平流扩散方程,模拟了上海地区的SO2浓度分布。结果表明:上海的局地流场具有明显的日变化特征,受海陆温差的影响明显,日间风速较夜间风速大,风向呈顺时针旋转;在不稳定层结情况下,高架点源排放的高空污染物对地面的污染物浓度有贡献,会造成地面污染物浓度升高。 相似文献
18.
A primitive equation model is used to investigate the warm pool equilibrium of the tropical Pacific ocean. Attention is focused
on the upper ocean. The oceanic response is described using an isothermal approach applied to warm waters contained in the
TOGA-COARE domain. The heat balance shows that all the terms, atmospheric surface fluxes, advection and diffusion, operate
in the heat bugdet with different time scales. Over long periods, diffusive heat fluxes transfer heat received from the atmosphere
out of the warm pool trough the top of the main thermocline. Over short periods, the impact of westerly wind bursts modifies
this balance: atmospheric heating is reversed, diffusion is enhanced and advective heat transports out of the warm pool operate
through zonal and vertical contributions. We were able to relate the two latter processes to zonal jets and Ekman pumping,
respectively. Conversely, the meridional contribution always represents a source of heat, mainly due to the tropical wind
convergence. The modelling results clearly show that except during strong wind events, entrainment cooling is not an important
component of the budget. The inability to remove heat is due to the salt stratification which needs to be first reduced or
even destroyed by westerly wind bursts to activate heat entrainment into deeper layers. Finally, we suggest that the near
zero estimate for the surface heat flux entering the warm pool may be extended to longer periods including seaosnal to interannual
time scale.
Received: 16 December 1996 / Accepted: 8 July 1997 相似文献
19.
Analysis of the wind field and heat budget in an alpine lake basin during summertime fair weather conditions 总被引:2,自引:0,他引:2
M. Kossmann A. P. Sturman P. Zawar-Reza H. A. McGowan A. J. Oliphant I. F. Owens R. A. Spronken-Smith 《Meteorology and Atmospheric Physics》2002,81(1-2):27-52
Summary ?Observational data collected in the Lake Tekapo hydro catchment of the Southern Alps in New Zealand are used to analyse the
wind and temperature fields in the alpine lake basin during summertime fair weather conditions. Measurements from surface
stations, pilot balloon and tethersonde soundings, Doppler sodar and an instrumented light aircraft provide evidence of multi-scale
interacting wind systems, ranging from microscale slope winds to mesoscale coast-to-basin flows. Thermal forcing of the winds
occurred due to differential heating as a consequence of orography and heterogeneous surface features, which is quantified
by heat budget and pressure field analysis.
The daytime vertical temperature structure was characterised by distinct layering. Features of particular interest are the
formation of thermal internal boundary layers due to the lake-land discontinuity and the development of elevated mixed layers.
The latter were generated by advective heating from the basin and valley sidewalls by slope winds and by a superimposed valley
wind blowing from the basin over Lake Tekapo and up the tributary Godley Valley.
Daytime heating in the basin and its tributary valleys caused the development of a strong horizontal temperature gradient
between the basin atmosphere and that over the surrounding landscape, and hence the development of a mesoscale heat low over
the basin. After noon, air from outside the basin started flowing over mountain saddles into the basin causing cooling in
the lowest layers, whereas at ridge top height the horizontal air temperature gradient between inside and outside the basin
continued to increase.
In the early evening, a more massive intrusion of cold air caused rapid cooling and a transition to a rather uniform slightly
stable stratification up to about 2000 m agl. The onset time of this rapid cooling varied about 1–2 h between observation
sites and was probably triggered by the decay of up-slope winds inside the basin, which previously countered the intrusion
of air over the surrounding ridges. The intrusion of air from outside the basin continued until about mid-night, when a northerly
mountain wind from the Godley Valley became dominant. The results illustrate the extreme complexity that can be caused by
the operation of thermal forcing processes at a wide range of spatial scales.
Received June 25, 2001; Revised December 21, 2001 相似文献
20.
Thomas Foken 《Boundary-Layer Meteorology》2006,119(3):431-447
In weak wind stable conditions, eddy-correlation fluxes calculated using conventional averaging times of 5 min or longer to define the perturbations are severely contaminated by poorly sampled mesoscale motions. A method is developed to identify the averaging time for each individual data record that captures the turbulence while excluding most of the mesoscale motions. The method is based on multiresolution decomposition of the heat flux, and provides an objective procedure for selecting the averaging time for calculating eddy-correlation fluxes. Eddy-correlation data collected in weak turbulence conditions over grass, snow, a pine forest and the ocean are used to demonstrate the approach.When the small-scale turbulence and mesoscale motions are clearly separated by a gap region in the heat flux cospectra, the variable window width reduces the influence of nonstationarity by more effectively filtering out mesoscale motions compared to traditional methods using constant averaging time. For records where turbulence and mesoscale motions overlap in scale, the method is not well posed, although such records occur infrequently for our datasets. These ambiguous cases correspond to significant nonstationarity at scales that overlap with turbulence scales. The improved turbulence fluxes calculated with the proposed method are the appropriate fluxes for evaluating flux-gradient relationships and Monin–Obukov similarity theory for developing improved model parameterizations of turbulence for weakly turbulent flows 相似文献