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1.
Summary ?Progress in technology as well as signal processing has promoted Wind Profiler Radar (WPR) or sodar with RASS additions to become standard tools in profiling of the atmospheric boundary layer. Apart from
these instruments’ basic abilities in profiling mean winds and temperature, this paper will give an emphasis on the profiling
of ABL height as well as the turbulent fluxes of sensible heat and momentum both, with respect to methods as well as with
respect to realization. The special focus will thereby be laid on the demands for vertical profiling, which were defined within
the LITFASS-project of the German Meteorological Service. In the frame of this project, some special measuring campaigns have
been performed where remote-sensing systems were used to assess their abilities in profiling ABL parameters. On the base of
some case studies from these campaigns comparisons are shown, where results from sodar/RASS and WPR/RASS measurements are
compared to measurements from airborne sensor systems and results from numerical models. Regarding turbulent heat fluxes,
we found excellent agreement for remotely-sensed flux profiles from WPR/RASS with both, numerical models and airborne in-situ
measurements. However, as the inherent errors of the remotely-sensed fluxes are in the order of ± 20 ⋯ 30 W/m2 typically, current signal processing does not allow to interpret small-scale vertical structures in the profiles with respect
to surface inhomogeneities yet.
Received June 16, 2001; revised February 20, 2002; accepted May 30, 2002 相似文献
2.
Summary ?At the Deutscher Wetterdienst (DWD) an internal project named LITFASS was running to determine the representative turbulent
fluxes of heat and momentum over heterogeneous land surfaces by observation and simulation. The project took advantage of
the infrastructure of the Research Division at the DWD, where model research capacity is combined with the measurements made
at and around the Meteorological Observatory Lindenberg.
The paper describes the simulation component of the LITFASS-project. It consists of a high-resolving model, derived from the
new operational non-hydrostatic, compressible Lokal-Modell (LM), which is denoted LLM (LITFASS-Lokal-Modell). The integration
area covers the lower atmosphere in the vertical up to 3000 m with 39 model layers. The horizontal size of the integration
area with 145 × 145 grid points (horizontal mesh width Δs = 96.5 m) corresponds to a typical grid box of a meso-scale model.
The LLM has to operate under real meteorological conditions. Therefore, the LLM is driven by time-dependent measured vertical
profiles of wind, temperature and humidity and surface-based measurements (of radiation, precipitation, soil properties) supported
by satellite information. The profiles are available for a great variety of weather situations occurring during the simulation
period (1–20 June 1998). First model results from extended 24 hour-integrations against different kinds of measurements are
discussed. They reveal the LLM to become a promising validation instrument, from which a systematic, sustainable validation
system can be established beyond LITFASS for improving parameterization schemes in the NWP models of the DWD.
Received July 18, 2001; revised March 15, 2002; accepted May 30, 2002 相似文献
3.
Summary ?This paper describes the configuration of measurement systems operated continuously at the Meteorological Observatory Lindenberg
with the aim of constructing combined profiles of wind and temperature – so-called composite profiles – covering the boundary
layer with high temporal and vertical resolution. This is required for the forcing of a micro-α-scale model in order to simulate
the atmospheric boundary layer structure over a heterogeneous landscape during the LITFASS-98 experiment. The problems of
combining measurements of different remote sensing and in-situ systems are briefly discussed. Although the measuring range
of individual remote sensing systems is variable, the height coverage of wind and temperature profile measurements by sodar/RASS
and two wind profiler radar/RASS complement each other very well. Using a simple merging procedure composite wind and temperature
profiles have been synthesized based on radiosonde, windprofiler/RASS, sodar/RASS and tower measurements. Time-height cross
sections of hourly composite profiles show considerably more details of the boundary layer structure than simple radiosonde
interpolation due to the higher sampling frequency, higher vertical resolution and increased accuracy at the lower levels.
Finally some qualifications of the formulated algorithm are suggested for future application.
Received June 18, 2001; revised May 30, 2002; accepted June 6, 2002 相似文献
4.
Summary ?Microclimatological data obtained during a field experiment in the nongrowing winter period were used to study the microclimatologically
stable night conditions of a 200 × 150 m miscanthus (Miscanthus cv. giganteus) stand and compared to open field conditions. The microclimatological pattern within the miscanthus canopy
was characterized by long-wave radiative cooling of the plant stand and by an established temperature inversion within the
canopy at calm nights. The results show that there are significant differences in air temperature and energy balance components
between the open field and the miscanthus field during calm and clear nights. In general, net radiation difference during
the cold and calm nights was relatively constant and about 20 W m−2 less negative in miscanthus (because of lower surface temperatures) than at the open field. Air temperature differences also
remained fairly constant and were up to 3 °C lower than at the open field (at the height of 1 m). Through thermal inversion
cold air accumulated in the lower parts of the canopy as shown by the vertical air temperature profiles. They showed a greater
amplitude within the diurnal cycle in the miscanthus stand than in the open field. Through the onset of wind, temperature
profiles changed rapidly and differences diminished. Vertical katabatic air drainage into the canopy layers was estimated
indirectly by using the energy balance approach. It was calculated from the significant energy balance closure gap and showed
a mean air exchange rate of up to 22 m3 m−2 h−1, related to a stand volume of 1 m2 area and 4 m height, during the mostly calm and clear nights, depending on the canopy net radiation and turbulent heat exchange
forced by slight wind spells. Quantitative uncertainties in calculated cold air drainage which are introduced by the measurement
method and certain assumptions in the calculations, were considered in a sensitivity analysis. In spite of these uncertainties
evidence of katabatic cold air flow is given.
Received July 29, 1999; revised June 11, 2001; accepted March 14, 2002 相似文献
5.
A Study of the Internal Boundary Layer due to a Roughness Change in Neutral Conditions Observed During the LINEX Field Campaigns 总被引:1,自引:0,他引:1
Summary As an aspect of the LINEX field studies (1996–1997; Lindenberg near Beeskow, Germany), the characteristics of the internal
boundary layer (IBL) that is associated with a step change of the surface roughnesses in neutral constant stress layers was
investigated and is reported in this paper. Both smooth to rough (in 1996) and rough to smooth (in 1997) types of flow, have
been studied based upon the profiles of mean wind and temperature realised from a 10-m mast and eddy correlation measurements
taken at two levels (2 m and 5 m). Depending upon wind direction, the fetch at the site varied between 140 m and 315 m within
the wind sector (200° to 340°) used for the field investigations. The height of the IBL, δ, had been determined from the intersect
of the logarithmic wind-profiles below (< 2 m) and above (> 6 ) the interface. Values of δ obtained at the experimental site
compared fairly well to the existing theoretical/empirical fetch-height relationships of the form: δ=aċx
b
, where a, b, are empirical constants. The ratio for the friction velocities below and above the IBL as measured directly by the eddy
correlation techniques showed that for fetches less than 250 m there was an increase (decrease) of about 20% of the momentum
flux arising from the smooth to rough (rough to smooth) transitions. Influences of distant obstructions (e.g., bushes, pockets
of trees) on the surface flow were markedly important on the examined wind profiles and such can be indicative as multiple
IBLs.
Received September 1, 1997 Revised August 5, 1998 相似文献
6.
Summary A mobile RASS (Radio Acoustic Sounding System), which can be loaded onto a truck along with all the other equipment, including
the power supply, was developed for atmospheric temperature measurement. Also, since it is necessary to avoid noise pollution
in surrounding areas when conducting observations with the mobile RASS, a new method that allows measurement of the temperature
profile up to about 200 m using a single acoustic pulse was devised. We discuss the development of a truck-mounted mobile
RASS and the results of the first mobile observation conducted at various locations in the Tokyo area.
Received November 3, 1998 Revised June 16, 1999 相似文献
7.
Summary Near surface climate was observed through temperature profiling from the surface to 2.47 m height in an urban vegetated park
and its surroundings in central Stockholm, Sweden. Measurements were conducted during three summer days by mobile traverses.
Air temperature differences between the built-up area and the park were in the range of 0.5–0.8 °C during the day and reached
a maximum of 2 °C at sunset. The thermal stratification of the air was mainly stable in the park and unstable in the built-up
area. Inverse air temperature profiles in the park were less stable in open than in shady areas, and close to neutral at midday.
The most unstable air was found in the north–south orientated canyons in the early afternoon. Possible heat advection from
the surroundings, and thus uncoupling between the surface and the air, was identified through temperature gradients pointing
at different directions within the 2.47 m profile. Examples at midday indicated that warm air advected as far as 150 m into
the park. 相似文献
8.
Summary ?Simultaneous flight measurements with the research aircraft Do 128 and the helicopter-borne turbulence probe Helipod were
performed on 18 June 1998 during the LITFASS-98 field experiment. The area-averaged turbulent vertical fluxes of momentum,
sensible, and latent heat were determined on a 15 km × 15 km and a 10 km × 10 km flight pattern, respectively. The flights
were carried out over heterogeneous terrain at different altitudes within a moderately convective boundary layer with Cumulus
clouds.
Co-spectra-analysis demonstrated that the small scale turbulent transport was completely sampled, while the comparatively
small flight patterns were possibly of critical size regarding the large-scale turbulence. The phygoide of the airplane was
identified as a significant peak in some co-spectra. The turbulent fluxes of momentum and sensible heat at 80 m above the
ground showed systematic dependence on the location of the flight legs above the heterogeneous terrain. This was not observed
for the latent heat flux, probably due to the vertical distribution of humidity in the boundary layer.
Statistical error analysis of the fluxes F showed that the systematic statistical error ΔF was one order of magnitude smaller than the standard deviation σ
F
. The difference between area-averaged fluxes derived from simultaneous Helipod and Do 128 measurements was much smaller than
σ
F
, indicating that the systematic statistical error was possibly over-estimated by the usual method.
In the upper half of the boundary layer the airborne-measured sensible heat flux agreed well with windprofiler/RASS data.
A linear fit was the best approximation for the height dependence of all three fluxes. The linear extrapolations of the latent
and sensible heat fluxes to the ground were in good agreement with tower, scintillometer, and averaged ground-station measurements
on various surface types. Systematic discrepancies between airborne and ground-based measurements were not found.
Received June 18, 2001; revised December 21, 2001; accepted June 3, 2002 相似文献
9.
Reconstruction of Northern Hemisphere 500 hPa geopotential heights back to the late 19th century 总被引:2,自引:0,他引:2
Summary In this study the authors have developed a statistical method and have reconstructed Northern Hemisphere 500 hPa heights back
to the late 19th century using one temperature and three sea level pressure (SLP) data sets. First, the relationship between
ERA40 500 hPa heights and surface temperature and SLP was screened using stepwise multiple regression based on the calibration
period of 1958–2002 (1998/2000 according to the availability of SLP data). All selected predictors (temperature and SLP) were
significant and their variance contribution was greater than 1%. On average, there were 8.1 variables retained in the final
regression equations. Second, the regression equations were applied to compute the 500 hPa height through to the late 19th
century for the whole Northern Hemisphere. As the SLP and temperature coverage improved over time, the number of predictors
decreased by about 1 in the most recent periods, and the root mean squared error decreased by about 0.8 m. A leave-one-out
cross-validation method was used to test the skill and stability of the regression models. The reduction of error during the
cross-validation period of 1958–1997 varied from 0.33 to 0.56, depending on the SLP data. Reconstructions were also checked
using NCEP/NCAR 500 hPa heights from January 1949 to December 1957, and compared with the historical reconstruction over Europe.
Reconstructions show high consistency with these independent data sets. Generally, the reconstruction provides a valuable
opportunity to analyze, as well as to validate climate simulations of the variability in free atmosphere circulations over
the past one hundred years. 相似文献
10.
H. Linné B. Hennemuth J. Bösenberg K. Ertel 《Theoretical and Applied Climatology》2007,87(1-4):201-211
Summary Water vapour flux profiles in the atmospheric boundary layer have been derived from measurements of water vapour density fluctuations
by a ground-based Differential Absorption Lidar (DIAL) and of vertical wind fluctuations by a ground-based Doppler lidar.
The data were collected during the field experiment LITFASS-2003 in May/June 2003 in the area of Lindenberg, Germany. The
eddy-correlation method was applied, and error estimates of ±50 W/m2 for latent heat flux were found. Since the sampling error dominates the overall measurement accuracy, time intervals between
60 and 120 min were required for a reliable flux calculation, depending on wind speed. Rather large errors may occur with
low wind speed because the diurnal cycle restricts the useful interval length. In the lower height range, these measurements
are compared with DIAL/radar-RASS fluxes. The agreement is good when comparing covariance and error values. The lidar flux
profiles are well complemented by tower measurements at 50 and 90 m above ground and by area-averaged near surface fluxes
from a network of micrometeorological stations. Water vapour flux profiles in the convective boundary layer exhibit different
structures mainly depending on the magnitude of the entrainment flux. In situations with dry air above the boundary layer
a positive entrainment flux is observed which can even exceed the surface flux. Flux profiles which linearly increase from
the surface to the top of the boundary layer are observed as well as profiles which decrease in the lower part and increase
in the upper part of the boundary layer. In situations with humid air above the boundary layer the entrainment flux is about
zero in the upper part of the boundary layer and the profiles in most cases show a linear decrease. 相似文献
11.
Stefan Emeis Klaus Sch?fer Christoph Münkel Roman Friedl Peter Suppan 《Boundary-Layer Meteorology》2012,143(1):25-35
Since 2006 different remote monitoring methods for determining mixing-layer height have been operated in parallel in Augsburg
(Germany). One method is based on the operation of eye-safe commercial mini-lidar systems (ceilometers). The optical backscatter
intensities recorded with ceilometers provide information about the range-dependent aerosol concentration; gradient minima
within this profile mark the tops of mixed layers. Special software for these ceilometers provides routine retrievals of lower
atmospheric layering. A second method, based on sodar observations, detects the height of a turbulent layer characterized
by high acoustic backscatter intensities due to thermal fluctuations and a high variance of the vertical velocity component.
This information is extended by measurements with a radio-acoustic sounding system (RASS) that directly provides the vertical
temperature profile from the detection of acoustic signal propagation and thus temperature inversions that mark atmospheric
layers. Ceilometer backscatter information is evaluated by comparison with parallel measurements. Data are presented from
2 years of combined ceilometer and RASS measurements at the same site and from comparison with a nearby (60 km) radiosonde
for larger-scale humidity information. This evaluation is designed to ensure mixing-layer height monitoring from ceilometer
data more reliable. 相似文献
12.
A numerical study of the influence of urban expansion on monthly climate in dry autumn over the Pearl River Delta, China 总被引:6,自引:0,他引:6
W. S. Lin C.-H. Sui L. M. Yang X. M. Wang R. R. Deng S. J. Fan C. S. Wu A. Y. Wang S. K. Fong H. Lin 《Theoretical and Applied Climatology》2007,89(1-2):63-72
Summary In this study, we employed a regional model to simulate the impact of urban expansion on monthly climate in Pearl River Delta
(PRD) region. Two experiments were performed by prescribing two different land covers in the PRD region. One land cover represents
vegetation in the 1970s which is derived from the United States Geological Survey (USGS) data with 24-category (hereafter
referred to as NU). The other land cover represents the current urban condition which is derived from remote sensing data
acquired by the Moderate Resolution Imaging Spectroradiometer (MODIS) in 2004 (hereafter referred to as HU). Using the two
land cover datasets, monthly climate of October 2004 was simulated, which was a very dry season in the PRD region. The results
obtained from the numerical simulation show a distinct difference in simulated shelter-level temperature, humidity, surface
fluxes and the height of planetary boundary layer (PBL) with two different land cover data sets being specified. The maximum
difference in simulated monthly mean temperature over urban areas was 0.9 °C. A large temperature difference was found in
urbanized area in Guangzhou, Dongguan, Zhongshan and Shenzhen. The monthly mean relative humidity in urban areas decreased
by 1.4% as a result of urban expansion (from 59.2% in NU to 57.8% in HU). The maximum decrease in mixing ratio was 0.4 g/kg
in Guangzhou and Dongguan, whereas the maximum decrease in relative humidity was 2.4%. There was an increase of sensible heat
flux in developed lands and the maximum increase was 90 W m−2. In contrast, latent hear flux in urban area decreased and the maximum decrease was 300 W m−2. In addition, the increase in mean height of PBL ranged from 20 to 80 m (HU compared with NU), and the maximum change of
the height was 180 m over urban area in city of Guangzhou. 相似文献
13.
Summary ?The LITFASS project (‘Lindenberg Inhomogeneous Terrain – Fluxes between Atmosphere and Surface: a Long-term Study’) of the Deutscher Wetterdienst (DWD, German Meteorological Service) aims to develop and to test a strategy for the determination
and parameterisation of the area-averaged turbulent fluxes of heat, momentum, and water vapour over a heterogeneous land surface.
These fluxes will be representative for an area of about 10 * 10 km2 (while the typical patch size is between 10−1 to 100 km2) corresponding to the size of a grid cell in the present operational numerical weather prediction model of the DWD.
LITFASS consists of three components:
– the development of a non-hydrostatic micro-α-scale model (the LITFASS local model – LLM) with a grid-size of about 100 * 100 m2,
– experimental investigations of land surface – atmosphere exchange processes and boundary layer structure within a 20 * 20 km2 area around the Meteorological Observatory Lindenberg,
– the assimilation of a data base as an interface between measurements and modelling activities.
The overall project strategy was tested over a three-week period in June 1998 during the LITFASS-98 field experiment. This
paper gives an overview on the LITFASS project, on the design and measurement program of the LITFASS-98 experiment, and on
the weather conditions during the period of the experiment. Conclusions are formulated for the operational realisation of
the LITFASS measurement concept and for future field experiments aimed at studying the land surface – atmosphere interaction
in the Lindenberg area. Selected results from both experimental and modelling activities are presented in a series of companion
papers completing this special issue of the journal.
Received June 18, 2001; revised March 18, 2002; accepted April 2, 2002 相似文献
14.
A new method for deduction of the sensible heat flux is validated with three sets of published SODAR (sound detection and ranging) data. Although the related expressions have previously been confirmed by the author with surface layer data, they have not yet been validated with observations from the boundary layer before this work. In the study, selected SODAR data are used to test the method for the convective boundary layer. The sensible heat flux (SHF) retrieved from SODAR data is found to decrease linearly with height in the mixed layer. The surface sensible heat fluxes derived from the deduced sensible heat flux profiles under convective conditions agree well with those measured by the eddy correlation method. The characteristics of SHF profiles deduced from SODAR data in different places reflect the background meteorology and terrain. The upper part of the SHF profile (SHFP) for a complicated terrain is found to have a different slope from the lower part. It is suggested that the former reflects the advective characteristic of turbulence in upwind topography. A similarity relationship for the estimation of SHFP in a well mixed layer with surface SHF and zero-heat-flux layer height is presented. 相似文献
15.
John R. Taylor Nathan J. Segal Michael R. Bradshaw David J. Low 《Meteorology and Atmospheric Physics》2013,119(3-4):197-206
Potential sonic temperature profiles from a continuous electromagnetic, pulsed acoustic, radio acoustic sounding system (RASS) were compared with profiles recorded by a commercially available temperature, relative humidity and pressure recorder mounted in a radio-controlled model motor-glider. The glider profiles covered the period of the morning transition in the lowest 200 m of an initially stably stratified boundary layer. Comparison of the profiles shows that the sonic temperature can be calculated based on the average speed of sound in the boundary layer; this removes the need to correct for vertical velocity in each temperature profile, thus avoiding the possibility of contaminating the temperatures with measurement noise from the vertical velocity profiles. Further, the low-level cold bias that occurs with the spatially separated transmit and receive antennas of a bistatic RASS system was not significant for the present measurements as the separation between the antennas was minimised. The comparison of RASS and glider temperatures gives confidence in the use of RASS-derived temperatures for investigating the performance of boundary layer models. 相似文献
16.
H. Kraus C. M. Ewenz M. Kremer J. M. Hacker 《Meteorology and Atmospheric Physics》2000,73(3-4):157-175
Summary In Southern Australia summertime deep cold fronts are frequently preceded by a shallow cold frontal line connected to a prefrontal
lower tropospheric trough. The advance of this line defines a “cool change” which in many cases causes severe weather events.
The goal of this paper is to analyze the multi-scale structure of these cool changes using aircraft observations and synoptic-scale
analyses. The aircraft measurements on cross-frontal tracks of horizontal lengths of up to 300 km are performed with an average
resolution of 3 to 4 m along the track. Thus a multi-scale analysis from micro-scale events up to the synoptic-scale phenomena
can be presented. All flights and thus all meso- and micro-scale analyses are performed over water only. The obviously very
different characteristics of the cool change structure elements over land are not investigated.
The synoptic analyses for one very typical case show a prefrontal trough as characterized by its position in relation to the
main deep cold front, its source region in Western Australia and its extent to the southeast. Fields of strong wind shear,
temperature gradients, vertical wind and Q-vectors are displayed.
The meso-β-scale x, z-cross-sections derived from two aircraft missions (data of the second one in brackets) show: a shallow cold front with a
160 (60) km wide transition zone in which the near surface potential temperature drops rather steadily by 9 °C (20 °C); a
shallow feeder flow topped by a strong inversion with a vertical gradient of potential temperature up to 5 °C/100 m between
the top of the feeder flow at 400 (200) m and 1500 (700) m; a cross-frontal circulation expressed by the ageostrophic wind
components u
ϕ,subscale and w with a center at 1200 m over the frontal edge of the feeder flow (for one mission only); a strong shear of the along-frontal
wind component v
ϕ with a large increase of the negative v
ϕ-values with height, which very well fits to the synoptic-scale view of the wave structure of the geostrophic wind (well-known
from the upper level synoptic charts) at different heights; a jet core of this along-frontal wind in the center of the cross-frontal
circulation, again for one mission only.
A very striking example of a micro-scale event is an approximately 1 km wide head of a frontal squall line. It shows dramatic
changes of all meteorological parameters. The event is displayed in a horizontal domain of 4 km with full resolution (∼ 4 m).
Derivatives of the measured parameters in the cross-frontal direction add information to the space series of the parameters
themselves. Deformation frontogenesis of potential temperature and specific humidity show very large values on the scale resolved
here. Fortunately the squall line could be sampled again at the same height, but in a somewhat degenerated state 1? h later.
Received September 3, 1999 Revised December 14, 1999 相似文献
17.
A global ocean temperature and altimeter data assimilation system for studies of climate variability 总被引:4,自引:0,他引:4
An ocean data assimilation (ODA) system which can assimilate both temperature and altimeter observations has been applied
to the global ocean and tested between January 1993–October 1996. A statistical method has been used to convert sea surface
height (SSH) anomalies observations from TOPEX/POSEIDON into synthetic temperature profiles. The innovative aspect of this
method is the introduction of time dependency in the correlations used to transform the altimeter observations into temperature
corrections. The assimilation system is based on a univariate variational optimal interpolation scheme applied to assimilate
both in situ and synthetic temperature profiles. In addition, a longer global analysis for the upper-ocean temperature starting
from January 1979 and ending November 1997, has been produced to examine the skill of sea temperature assimilation with a
rather simple and practical method. The temperature analysis shows encouraging improvement over a corresponding ocean simulation
when compared to independent (not assimilated) temperature data both at seasonal and interannual time scales. However, the
univariate data assimilation of hydrographic data does not result in an improvement of the velocity field. In fact the assimilation
of sparse in situ data can introduce unrealistic spatial variability in the temperature field which affects the velocity field
in a negative way. This deficiency is partially overcome when we also assimilate altimeter observations since the coverage
is complete and uniform for this data. In particular, our study shows that temperature corrections due to the altimeter signal
have a positive impact on the current system in the tropical Pacific.
Received: 28 May 2000 / Accepted: 6 November 2000 相似文献
18.
Summary A wind‐profiling Doppler radar equipped with a radio acoustic sounding system (RASS) may be used to estimate the vertical
profile of the vertical flux of heat in the atmosphere. Simultaneous measurements of the time‐varying temperature and vertical
air velocity are combined to give the convective heat flux using the eddy‐correlation method. The accuracy of the estimates
depends on the fundamental accuracy of the temperature and vertical velocity measurements. Also, in common with all eddy‐correlation
methods, uncertainties are introduced by the need to define a suitable averaging time and to remove trends. A problem unique
to RASS is the possible presence of ground and intermittent clutter at close ranges, which can cause errors in the vertical
air velocity measurements. These considerations are discussed with particular reference to observations using a UHF radar
wind profiler situated in an urban environment, where clutter is a serious problem.
A Rank‐Order Signal Processing Algorithm (ROSPA) for recognizing and eliminating outliers in the vertical velocity, is introduced.
It is explained how ROSPA uses both a minimum filter and a median filter on the velocity data. It is shown, using a comparison
with nearly clutter free data from a rural site, that the filtering substantially improves the quality of the noisy urban
data. The paper then compares RASS‐measured urban and rural heat flux profiles, along with the heat flux profile measured
by an instrumented airplane. It is concluded that the main obstacles to RASS heat flux measurements are the effects of winds
and turbulence in the boundary layer, rather than clutter.
Received September 24, 1998 Revised January 27, 1999 相似文献
19.
L. Cvitan 《Meteorology and Atmospheric Physics》2006,93(3-4):235-246
Summary The stability parameter μ is suggested as the one which is determinable with satisfying accuracy for routine application by
means of commonly accessible meteorological data at the Molve location (Croatia). The similarity functions applied for vertical
wind speed simulation in the planetary boundary layer (PBL) at Molve were useful for the determination of local stability
classes. Universal similarity functions were applied for unstable and neutral stability, whereas local similarity functions
were established for stable stratification. Wind speed simulations were performed using two types of wind models. The Monin-Obukhov
similarity theory was included in both types. However, it turned out that for the operative determination of the stability
of the 35 m deep lowest layer, the stability parameter μ was locally a better stability parameter than the Monin-Obukhov parameter
z/L. That was possibly because 35 m deep lowest layer sometimes (depending upon stability) includes a large proportion of
the Ekman layer and parameter μ is originally designed for the deeper part of PBL than z/L that is originally designed for
the surface layer. At Molve, the input data for local wind models as well as for the stability parameter μ were wind speed
at 35 m and temperature at 2 and 35 m above the ground. 相似文献
20.
基于湍流散射理论,运用边界层风廓线雷达 (WPR) 联合RASS (Radio Acoustic Sounding System), GPS/PWV (Global Position System/Precipitable Water Vapor) 进行全遥感系统的大气比湿廓线反演试验,并对影响因子进行分析。利用2011年8—9月云南大理综合探测试验数据的反演结果与探空数据进行比较分析,结果表明:WPR联合探空的温度廓线和起始边界比湿 (q0) 反演大气比湿廓线,与探空大气比湿廓线相比具有相同的变化趋势,标准差为0.84 g·kg-1,误差随高度增加呈递增趋势;WPR联合RASS, GPS/PWV数据反演大气比湿廓线,与探空大气比湿廓线的标准差为0.85 g·kg-1。参加反演的数据中,折射指数结构常数Cn2与谱宽σturb2对反演影响最大,反演算法中大气折射指数梯度M符号的判断对反演精度也有较大影响。 相似文献