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1.
We analyze gust probe measurements obtained in the convective boundary layer over the central equatorial Pacific as part of the Equatorial Pacific Ocean Climate Studies (EPOCS) program. From the lowest level flights, the bulk transfer coefficients are found to be 1.1 × 10-3 and 1.4 × 10-3 for latent and sensible heat fluxes, respectively. Vertical profiles of water vapor density, potential temperature and wind velocity are obtained as are the profiles of the fluxes of latent and sensible heat and momentum. From the extrapolated profiles, we obtain surface fluxes of 120 W m-2 and 13 W m-2 for latent and sensible heat, respectively, and 0.11 N m-2 for momentum. The 10 m drag coefficient is 1.5 × 10-3. Two convergence boxes, north and south of the ITCZ, are analyzed. Enhanced convergence is found in the northern trades relative to the southern trades. The advective acceleration is found to be comparable in magnitude to the other terms in the horizontal equations of motion. 相似文献
2.
The actinometric system installed aboard the Yak-42D "Roshydromet" research aircraft is presented. It is designed to study radiation processes in the troposphere. The system is based on standard Kipp&Zonen actinometric instruments for measuring solar, thermal, and ultraviolet radiation fluxes as well as on specially developed radiation models with high-precision methods for solving radiative transfer equations (Monte Carlo, k-distribution, and line-by-line calculations). The combination of actinometric measurements and detailed simulation of radiative transfer in the atmosphere allows examining the radiation balance components throughout the troposphere using in situ measurements at the aircraft location. Some results of studying radiation fluxes obtained during the flights over the Arctic region of the Russian Federation are presented. The data of measurements carried out using the presented system are useful for validating radiation codes utilized in general atmospheric circulation models and for processing satellite remote sensing data. 相似文献
3.
TOGA-COAREIOP海表通量估算 总被引：3，自引：0，他引：3
使用ＴＯＧＡ－ＣＯＡＲＥＩＯＰ１９９２年１１月５日至１９９３年２月１９日向阳红５号海上船舶（２°Ｓ，１５６°Ｅ）观测资料，通过３种不同的总体方法估算了这个点的海表面通量。首先得出一个中性拖曳系数和风速之间的准线性关系，然后用迭代法处理依赖于稳定度的拖曳系数和输送系数，在此基础上计算了动量、感热和潜热通量。在暖池区与西风相对应的通量远大于东信风相对应的通量，海表通量的量值也依赖于稳定度，特别是在弱风条件下。估算的海表净热量平衡表明从海洋向大气大量的热输送主要是由潜热通量和有效长波辐射产生的。其中潜热通量的数值最大、感热通量数值最小。最后和同期日本Ｒ／ＶＨａｋｕｈｏ考察船（０°，１５６°Ｅ）用涡动相关法得到的直接测量通量比较，作了精确度分析，表明用总体方法估算的通量是可靠的。并用向阳红５号船的资料估算的有效长波辐射和直接测量值作了比较，也和热带西太平洋ＴＯＧＡ调查作了比较分析。 相似文献
4.
With the marine ship observation data set obtained by three cruise-phases of Chinese Xi-angyanghong 5 from November 5,1992 to February 19,1993 in the TOGA-COARE IOP at 2°S,156°E.the sea surface fluxes at this point are estimated by three different bulk schemes.Firstly.aquasi-linear relation is found between the neutral drag coefficients and wind speed.Then,the sta-bility-dependent drag and heat transfer coefficients are solved in the iterative method.Based onthus-derived transfer coefficients,the momentum,sensible and latent heat fluxes are calculated.In the warm pool region,the fluxes corresponding to the westeily winds are much greater thanthose of the easterly trade winds.The magnitude of sea surface fluxes depends upon the atmo-spheric stability as well,in particular in the case of weak wind condition.The estimated sea sur-face net heat budget shows that considerable amount of heat transport from ocean to atmosphere ismainly produced by the effective longwave radiation,latent and sensible heat fluxes.Among themthe value of latent heat flux is the largest and the sensible heat flux is the smallest.Finally,an ac-curacy analysis is made by direct measurements with the eddy-correlation method on the JapaneseR/V Hakuho board at the same time.It is shown that the bulk-derived fluxes are acceptable withmuch confidence.The estimated effective longwave radiation is used to compare with those by di-rect observations on Xiangyanghong 5.This research is compared with TOGA investigation in thetropical western Pacific. 相似文献
5.
Some evaluations of drag and bulk transfer coefficients over water bodies of different sizes 总被引：1，自引：0，他引：1
B. B. Hicks 《Boundary-Layer Meteorology》1972,3(2):201-213
Three recent experiments allow evaluation of the bulk transfer coefficients for momentum, water vapour and sensible heat over water bodies of different sizes. As part of a study of evaporation rates from a swamp, measurements of latent and sensible heat fluxes were made over Lake Wyangan in southern N.S.W., Australia. This lake is of several kilometers diameter. In a later experiment, Reynolds stress and sensible heat transfer were measured from a natural-gas platform standing in Bass Strait, south of mainland Australia. The most recent experiment involved the direct measurement of each of these turbulent fluxes from a fixed tower erected in Lake Michigan, U.S.A.Perhaps the most important of the results is the finding that drag coefficients measured over Bass Strait are not significantly different from those over Lake Michigan, despite the obvious differences in depth, fetch, and hence surface wave structure. At both locations, drag coefficients are found to increase slightly with increasing wind speed, while at low wind speeds they are not significantly different from those corresponding to aerodynamic smoothness.Near-neutral bulk transfer coefficients for sensible heat and for water vapour are found to be similar. An average value of about 1.4 × 10–3 is obtained.It is emphasized that stability effects should be considered in any discussion of drag coefficients or bulk transfer coefficients. Large errors can result if near-neutrality is incorrectly assumed. 相似文献
6.
Turbulent characteristics and bulk transfer coefficients over the desert in the HEIFE area 总被引：1，自引：0，他引：1
Ichiro Tamagawa 《Boundary-Layer Meteorology》1996,77(1):1-20
Observations of surface-layer turbulence and turbulent fluxes were made over a desert in northwestern China as a part of HEIFE (HEIhe river Field Experiment). These show that the normalized variations of the vertical wind component and of the air temperature obey Monin-Obukhov similarity well, especially in free convective conditions. However, the variations of specific humidity do not obey Monin-Obukhov similarity.Mean bulk transfer coefficients of sensible heat and momentum flux are obtained as functions of stability over a wide stability range from the observed data of turbulent fluxes and mast profiles. However, the bulk transfer coefficient for water vapor could not be obtained because of the large scatter of the data. In free convective conditions, the sensible heat flux was found to be approximately proportional to the 1.4 power of temperature difference between the surface and 20m. The bulk transfer coefficient of sensible heat is also obtained as a function of the bulk Richardson number for practical convenience. 相似文献
7.
A Measure of Inhomogeneity of the Land Surface and Parametrization of Turbulent Fluxes under Natural Conditions 总被引：1，自引：0，他引：1
Summary The effects of surface heterogeneity and nonstationarity on turbulent fluxes are parametrized by introducing an additional
roughness length that corrects for deviations from Stationarity and Horizontal Homogeneity (SHH). Using data from the experiments
of FIFE, KUREX, TARTEX and SADE, a relationship was detected between the underestimation of turbulent fluxes (the lack of
balance in the surface energy budget) and terrain inhomogeneity.
Based on the assumption that the parametrization obtained from these data is applicable for complex terrain surfaces in general,
the paper presents some simple relationships for surface turbulent fluxes, bulk transfer coefficients, and roughness lengths.
Received August 8, 1997 Revised March 9, 1998 相似文献
8.
9.
Denny P. Alappattu D. Bala Subrahamanyam P. K. Kunhikrishnan Radhika Ramachandran K. M. Somayaji R. Venkatesh G. S. Bhat A. Bhagavath Singh 《Boundary-Layer Meteorology》2008,126(2):297-309
We report the spatio-temporal variability of surface-layer turbulent fluxes of heat, moisture and momentum over the Bay of
Bengal (BoB) and the Arabian Sea (AS) during the Integrated Campaign for Aerosols, gases Radiation Budget (ICARB) field experiment.
The meteorological component of ICARB conducted during March – May 2006 onboard the oceanic research vessel Sagar Kanya forms
the database for the present study. The bulk transfer coefficients and the surface-layer fluxes are estimated using a modified
bulk aerodynamic method, and then the spatio-temporal variability of these air-sea interface fluxes is discussed in detail.
It is observed that the sensible and latent heat fluxes over the AS are marginally higher than those over the BoB, which we
attribute to differences in the prevailing meteorological conditions over the two oceanic regions. The values of the wind
stress, sensible and latent heat fluxes are compared with those obtained for the Indian Ocean Experiment (INDOEX) period.
The variation of drag coefficient (C
D
), exchange coefficients of sensible heat and moisture (C
H
= C
E
) and neutral drag coefficient (C
DN
) with wind speed is also discussed.
相似文献
10.
In climate and weather prediction models the near-surface turbulent fluxes of heat and momentum and related transfer coefficients are usually parametrized on the basis of Monin–Obukhov similarity theory (MOST). To avoid iteration, required for the numerical solution of the MOST equations, many models apply parametrizations of the transfer coefficients based on an approach relating these coefficients to the bulk Richardson number \(Ri_{b}\). However, the parametrizations that are presently used in most climate models are valid only for weaker stability and larger surface roughnesses than those documented during the Surface Heat Budget of the Arctic Ocean campaign (SHEBA). The latter delivered a well-accepted set of turbulence data in the stable surface layer over polar sea-ice. Using stability functions based on the SHEBA data, we solve the MOST equations applying a new semi-analytic approach that results in transfer coefficients as a function of \(Ri_{b}\) and roughness lengths for momentum and heat. It is shown that the new coefficients reproduce the coefficients obtained by the numerical iterative method with a good accuracy in the most relevant range of stability and roughness lengths. For small \(Ri_{b}\), the new bulk transfer coefficients are similar to the traditional coefficients, but for large \(Ri_{b}\) they are much smaller than currently used coefficients. Finally, a possible adjustment of the latter and the implementation of the new proposed parametrizations in models are discussed. 相似文献
11.
Jens Bange Thomas Spieß Marcus Herold Frank Beyrich Barbara Hennemuth 《Boundary-Layer Meteorology》2006,121(1):127-151
Turbulent fluxes of sensible and latent heat were measured with the helicopter-borne turbulence probe Helipod over a heterogeneous landscape around the Meteorological Observatory Lindenberg during the STINHO-2 and LITFASS-2003 field experiments. Besides the determination of area-averaged heat fluxes, the analysis focused on different aspects of the response of the turbulent structure of the convective boundary layer (CBL) on the surface heterogeneity. A special flight pattern was designed to study flux profiles both over quasi-homogeneous sub-areas of the study region (representing the major land use types—forest, farmland, water) and over a typical mixture of the different surfaces. Significant differences were found between the heat fluxes over the individual surfaces along flight legs at about 80 m above ground level, in agreement with large-aperture scintillometer measurements. This flux separation was still present during some flights at levels near the middle of the CBL. Different scales for the blending height and horizontal heterogeneity were calculated, but none of them could be identified as a reliable indicator of the mixing state of the lower CBL. With the exception of the flights over water, the latent heat flux measurements generally showed a larger statistical error when compared with the sensible heat flux. Correlation coefficients a nd integral length scales were used to characterise the interplay between the vertical transport of sensible and latent heat, which was found to vary between ‘fairly correlated’ and ‘decoupled’, also depending on the soil moisture conditions. 相似文献
12.
We address the problem of the high-frequency correction of water vapour fluxes measured by eddy covariance with a closed-path
infrared gas analyser (IRGA). Different transfer functions are compared and evaluated at a forested (Vielsalm, Belgium) and
an agricultural (Lonzée, Belgium) site. Classical functions, usually applied to correct CO2 fluxes (Gaussian, Lorentzian), are found to be unsuited to water vapour cospectral corrections, being characterised by too
sharp a decrease at high frequency. Two other functions characterised by a lower decreasing slope are found to better fit
experimental transfer functions. They were calibrated and validated on experimental transfer functions and their dependency
on air humidity is parameterised. On this basis, new correction coefficients are estimated. The coefficients are found to
be larger than those based on the classical functions, even when the dependency of the latter on air humidity is taken into
account. The difference amounts to 10% at the forested site and to 5% larger at the crop site. The study highlights the necessity
of characterising the water transfer function shape and taking it into account in the correction factor at each site equipped
with a closed path IRGA. 相似文献
13.
Gordon A. McBean 《Boundary-Layer Meteorology》1973,4(1-4):265-274
In order to parameterize the surface fluxes, it is desirable first to understand the turbulent transfer processes. In this paper the spectral correlation coefficients for momentum, heat and moisture transfer from the Ladner, BOMEX and Suffield experiments are compared. Near-neutral to unstable stratifications were examined. Differences between heat and momentum transfer processes were found and the differences increased with instability. The transfer of a passive scalar, such as moisture was found to be dependent on the active-scalar/passive-scalar correlation. 相似文献
14.
Jens Bange Peter Zittel Thomas Spieß Jörg Uhlenbrock Frank Beyrich 《Boundary-Layer Meteorology》2006,119(3):527-561
The low-level flight method (LLF) has been combined with linear inverse models (IM) resulting in an LLF+IM method for the determination of area-averaged turbulent surface fluxes. With this combination, the vertical divergences of the turbulent latent and sensible heat fluxes were calculated from horizontal flights. The statistical errors of the derived turbulent surface fluxes were significantly reduced. The LLF+IM method was tested both in numerical and field experiments. Large-eddy simulations (LES) were performed to compare ‘true’ flux profiles with ‘measurements’ of simulated flights in an idealised convective boundary layer. Small differences between the ‘true’ and the ‘measured’ fluxes were found, but the vertical flux divergences were correctly calculated by the LLF+IM method. The LLF+IM method was then applied to data collected during two flights with the Helipod, a turbulence probe carried by a helicopter, and with the research aircraft Do 128 in the LITFASS-98 field campaign. The derived surface fluxes were compared with results from eddy-covariance surface stations and with large-aperture scintillometer data. The comparison showed that the LLF+IM method worked well for the sensible heat flux at 77 and 200 m flight levels, and also for the latent heat flux at the lowest level. The model quality control indicated failures for the latent heat flux at the 200 m level (and higher), which were probably due to large moisture fluctuations that could not be modelled using linear assumptions. Finally the LLF+IM method was applied to more than twenty low-level flights from the LITFASS-2003 experiment. Comparison with aggregated surface flux data revealed good agreement for the sensible heat flux but larger discrepancies and a higher statistical uncertainty for the latent heat flux 相似文献
15.
Estimation of areally-averaged surface fluxes 总被引：6，自引：1，他引：6
Martin Claussen 《Boundary-Layer Meteorology》1991,54(4):387-410
The concept of blending height is used to estimate areally averaged surface fluxes of momentum and heat in a stratified, horizontally inhomogeneous surface-layer flow. This concept is based on the assumption that at sufficiently large heights above a heterogeneous surface, subsequent surface modifications will not be recognizable in the flow individually, but overall flux and mean profiles will represent the surface condition of a large area. The height at which the flow becomes approximately independent of horizontal position is called blending height according to Wieringa (1986).Here, it is proposed to classify the ground surface in a surface-layer grid box of a larger-scale model into several land-use categories. Surface momentum and heat fluxes should be estimated for each category at the blending height. The grid-averaged surface fluxes are to be obtained by the average of surface fluxes on each land-use surface weighted by its fractional area. The postulate of computing the surface fluxes at the blending height leads to a new formulation of turbulent transfer coefficients.The proposed parameterization has been tested by employing a small-scale numerical model as a surface-layer grid box of a hypothesized larger-scale model. Several quite different flow configurations have been studied in order to investigate the performance of the new parameterization. Generally, the relative errors of estimated averaged surface fluxes are found to be well within ±10%. 相似文献
16.
Modelling surface turbulent fluxes in stable conditions 总被引：3，自引：0，他引：3
17.
A bulk model for the atmospheric planetary boundary layer 总被引：1，自引：0，他引：1
Mohamed S. Smeda 《Boundary-Layer Meteorology》1979,17(4):411-427
The integrated momentum and thermodynamic equations through the planetary boundary layer (PBL) are solved numerically to predict the mean changes of wind and potential temperature from which surface fluxes are computed using bulk transfer coefficients of momentum and heat. The second part of the study involves a formulation and testing of a PBL height model based on the turbulent energy budget equation where turbulent fluxes of wind and heat are considered as the source of energy. The model exhibits capability of predicting the PBL height development for both stable and unstable regimes of observed conditions. Results of the model agree favourably with those of Deardorff's (1974a) and Tennekes' (1973) models in convective conditions.Contribution number 396. 相似文献
18.
‘Surface Drag in the Arctic Marginal Sea-ice Zone: A Comparison of Different Parameterisation Concepts’ 总被引：1，自引：0，他引：1
Two parameterisation schemes for the turbulent surface fluxes and drag coefficients over the Arctic marginal sea-ice zone
(MIZ) are (further) developed, and their results are compared with each other. Although the schemes are based on different
principles (flux averaging and parameter averaging), the resulting drag coefficients differ only slightly in the case of neutral
and stable stratification. For unstable stratification and sea-ice conditions being typical for the north-eastern Fram Strait,
the drag coefficients resulting from the parameter-averaging concept are 5–10% larger than those of the flux-averaging concept.
At a sea-ice concentration of 45%, the parameter-averaging method overestimates the heat fluxes by a factor of 1.2. An inclusion
in the schemes of form drag caused by floe edges and ridges has a much larger effect on the drag coefficient, and on the momentum
fluxes, than the choice between the parameter-averaging or flux-averaging methods. Based on sensitivity studies with the flux-averaging
scheme, a simple formula for the effective drag coefficient above the Arctic MIZ is derived. It reduces the computational
costs of the more complex parameterisations and could also be used in larger scale models. With this simple formula, the effective
drag coefficient can be calculated as a function of the sea-ice concentration and skin drag coefficients for water and ice
floes. The results obtained with this parameterisation differ only slightly from those using the more complex schemes. Finally,
it is shown that in the MIZ, drag coefficients for sea-ice models may differ significantly from the effective drag coefficients
used in atmospheric models. 相似文献
19.
西太平洋暖池区的海气通量及整体交换系数 总被引：3，自引：1，他引：2
根据西太平洋海域弱风、高温、潮湿的大气状态特征,提出了在光滑面存在粘性副层气流中的廓线的层结订正方案。用此模式对西太平洋暖池区ＴＯＧＡＣＯＡＲＥＩＯＰ期间,在向阳红５号船（２°Ｓ,１５４°Ｅ）获取的海面风、温、湿梯度资料进行了处理。计算结果显示西太平洋暖池区贴水层气流中不稳定层结占５０％－８０％,其中很不稳定的占１０．３％;该海区海气通量和整体交换系数受层结影响远大于受风速的影响;海气通量和整体交换系数随不稳定程度增加而增大,在相同风速下量值可相差４倍以上;其变化范围为０．３×１０－３—３．２×１０－３。由此可见,层结的影响使它们的变化大于其它海区的结果。在ｕ１０＝０－１０ｍ／ｓ范围内,中性化整体交换系数平均为ＣＤＮ＝１．２×１０－３,ＣＨＮ＝１．１４×１０－３,ＣＥＮ＝１．１９×１０－３,与Ｌａｒｇｅ和Ｐｏｎｄ（１９８１,１９８２）不稳定条件的研究结果相差无几。 相似文献
20.
Matthias Mauder Raymond L. Desjardins Ian MacPherson 《Boundary-Layer Meteorology》2008,129(3):431-450
The objective of this study is to produce two-dimensional maps of the sensible and the latent heat fluxes from airborne measurements,
based on the analysis of a flight pattern, called grid flights. A footprint model with along-wind and cross-wind components
was used to project the measured fluxes onto the surface map. The method was applied to measurements over Arctic tundra during
the Mackenzie Area GEWEX (Global Energy and Water Cycle Experiment) Study (MAGS) 1999. The resulting flux estimates were computed
by integration of a wavelet transform, and corrected for long wavelength losses using information from 100 km long regional
runs that were conducted close to the grid flights. The random flux error was estimated based on the flight length that is
represented in each map element, and a map resolution of 3 × 3 km was chosen in order to keep the average random error of
the latent heat flux below 25%. The random error of the sensible heat flux was smaller by a factor of 1.4 on average. An analysis
of airborne flux measurements at different altitudes showed no significant increase of flux estimates for measurement heights
below 90 m. Thus, the fluxes measured at heights between 48 and 64 m were not corrected for vertical flux divergence. The
resulting flux maps provide quantitative two-dimensional estimates of the energy exchange between the surface and the atmosphere
during the snow melt period in an Arctic environment, which are well-suited for calibration and validation of numerical models. 相似文献