The Effect of Surface Heterogeneity on the Temperature–Humidity Correlation and the Relative Transport Efficiency

We derive a conceptual model of the flow over heterogeneous terrain consisting of patches with contrasting Bowen ratios. Upward moving eddies are assumed to carry heterogeneous properties, whereas downward moving eddies carry homogeneous properties. This results in a decorrelation of temperature and humidity as the contrast between the patches increases. We show that this model is able to reproduce the relationship developed by Lamaud and Irvine (Boundary-Layer Meteorol. 120:87–109, 2006). Some details differ from their expression but are in accordance with data obtained over African savannah. We extend the conceptual model to a combination of any scalars, not necessarily linked through the surface energy balance (as is the case for temperature and humidity). To this end we introduce a new parameter that describes the surface heterogeneity in surface fluxes. The results of the current model can be used to predict the discrepancy between similarity relationships for different scalars over heterogeneous terrain.     

The Theoretical Model of Atmospheric Turbulence Spectrum in Surface Layer

It is shown that the slope of energy spectrum obtained from the velocity solution of Kdv-Burgers equation lies between -5/3 and -2 in the dilogarithmic coordinates paper. The spectrum is very close to one of Kolmogorov’s isotropic turbulence and Frisch’s intermittent turbulence in inertial region. In this paper, the Kdv-Burgers equation to describe atmospheric boundary layer turbulence is obtained. In the equation, the 1 / Re, corresponds to dissipative coefficient v, to dispersive coefficient β, then (v/ 2β)2 corresponds to .We prove that the wave number corresponding to maximum energy spectrum decreases with the decrease of stability (i.e., the increase of in eddy-containing region. And the spectrim amplitude decreases with the increase of (i.e., the decrease of stability). These results are consistent with actual turbulence spectrum of atmospheric surface layer from turbulence data.     

An Analytical Formulation of the Monin–Obukhov Stability Parameter in the Atmospheric Surface Layer Under Unstable Conditions

A non-iterative analytical scheme is developed for unstable stratification that parametrizes the Monin–Obukhov stability parameter \(\zeta \) (\({=}z{/}L\), where z is the height above the ground and L is the Obukhov length) in terms of bulk Richardson number (\(Ri_B\)) within the framework of Businger–Dyer type similarity functions. The proposed scheme is valid for a wide range of roughness lengths of heat and momentum. The absolute relative error in the transfer coefficients of heat and momentum is found to be less than 1.5% as compared to those obtained from an iterative scheme for Businger–Dyer type similarity functions. An attempt has been made to extend this scheme to incorporate the similarity functions having a theoretically consistent free convection limit. Further, the performance of the scheme is evaluated using observational data from two different sites. The proposed scheme is simple, non-iterative and relatively more accurate compared to the schemes reported in the literature and can be used as a potential alternative to iterative schemes used in numerical models of the atmosphere.     

Flux–Gradient Relationships in the Atmospheric Surface Layer Over the Gobi Desert in China

A field campaign was conducted to collect high quality vertical wind speed and temperature profiles with simultaneous turbulent momentum and sensible heat fluxes over the flat Gobi surface located at 39°09′N, 100°06′E at an elevation of 1,458 m during the Pilot Intensive Observation Period in 1990. Careful evaluation of the observations in near-neutral conditions supports a value of the von Karman constant close to 0.39, which is in good agreement with the results obtained from many other field experiments conducted in low elevation regions. In near-neutral stratification the turbulent Prandtl number is found to be 1 but with lower confidence due to scarcity and scatter of the data points. For an expanded stability range, exponents of −1/4 and −1/2 are respectively best fitted to the functional relations for the non-dimensional wind and temperature profile functions in unstable stratification but linear relations still hold for stable stratification in this high elevation region.     

On Monin–Obukhov Scaling in and Above the Atmospheric Surface Layer: The Complexities of Elevated Scintillometer Measurements

In scintillometry Monin–Obukhov similarity theory (MOST) is used to calculate the surface sensible heat flux from the structure parameter of temperature (C_T²){(C_{T^2})} . In order to prevent saturation a scintillometer can be installed at an elevated level. However, in that case the observation level might be located outside the atmospheric surface layer (ASL) and thus the validity of MOST questioned. Therefore, we examine two concepts to determine the turbulent surface sensible heat flux from the structure parameter at elevated levels with data obtained at 60-m height on the Cabauw tower (the Netherlands). In the first concept (MOSTs) C_T²{C_{T^2}} is still scaled with the surface flux, whereas in the second (MOSTl) C_T²{C_{T^2}} is scaled with the local sensible heat flux. The C_T²{C_{T^2}} obtained from both concepts is compared with direct observations of C_T²{C_{T^2}} using a sonic anemometer/thermometer. In the afternoon (when the measurement height is located within the ASL) both concepts give results that are comparable to the directly observed values of C_T²{C_{T^2}} . In the morning (data outside the ASL), our data do not unequivocally support either of the two concepts. First, the peak in C_T²{C_{T^2}} that occurs when the measurement height is located in the entrainment zone disqualifies the use of MOST. Second, during the morning transition, local scaling shows the correct pattern (zero flux and a minimum in C_T²{C_{T^2}}) but underestimates C_T²{C_{T^2}} by a factor of ten. Third, from the best linear fit a we found that the slope of MOSTl gave better results, whereas the offset is closer to zero for MOSTs. Further, the correlation between the direct observations and MOST-scaled results is low and similar for the two concepts. In the end, we conclude that MOST is not applicable for the morning hours when the observation level is above the ASL.     

Determination of the Turbulent Temperature–Humidity Correlation from Scintillometric Measurements

We report on the investigation and successful application of the bichromatic correlation of optical and microwave signals for determining the area-averaged correlation of temperature–humidity fluctuations. The additional technical effort is marginal compared to the common ‘two-wavelength method’, which has (in contrast) the restriction that only two of the three relevant meteorological structure parameters can be deduced. Therefore, in the past, it was often assumed that the turbulent humidity and temperature fluctuations are perfectly positively or negatively correlated. However, as shown in this study, over non-homogeneous terrain when the flow conditions are not ideal, this assumption is questionable. The measurements were analysed statistically, and were compared to in situ measurements of the Bowen ratio Bo and the correlation of temperature–humidity fluctuations using eddy-covariance techniques. The latter is in good agreement to that derived by scintillometry. We found that the correlation is not ±1 but as low as −0.6 for Bo smaller than −2, and up to 0.8 for Bo larger than 1.     

Trends in Extremes of Surface Humidity, Temperature, and Summertime Heat Stress in China

l. IntroductionPrevious studies have shown climatological and seasonal surface temperature and humld-ity dlstributlons over China (Wang and Gaffen, 200l ) and evaluated trends in seasonal meansof several surface humidity variables, rainfall, temperatures, and apparent temPerature for thelast half century (Easterling et al., 2000, Zhai et al., 1999, Zhai and Eskridge, l997, Zhai andRen, l997, Wang and Gaffen, 200l). However, trends in local temperatures, and particularlytrends in extreme he…     

Studies of Aerosols in The Marine Boundary Layer in the Coastal Area During The EOPACE’99 Campaign

Results are presented based on measurements taken using an FLS-12 lidar system and laser particle counters only on the Atlantic coast of the U.S.A. during a campaign within the scope of the international EOPACE experiment. The objectives of the EOPACE (Electro-optical Propagation Assessment in Coastal Environments) effort, which was conducted in Duck, N.C. (U.S.A.) between 25 February and 11 March 1999, involved investigating, developing and evaluating ocean and coastal aerosol models and their effects on visibility; integrating and developing simple, realistic models for infrared propagation near the ocean surface and developing a consistent chemical/optical model for aerosol particles suitable for inclusion in navy meteorological models.     

The 30–60-day Intraseasonal Variability of Sea Surface Temperature in the South China Sea during May–September

This study investigates the structure and propagation of intraseasonal sea surface temperature(SST) variability in the South China Sea(SCS) on the 30–60-day timescale during boreal summer(May–September). TRMM-based SST, GODAS oceanic reanalysis and ERA-Interim atmospheric reanalysis datasets from 1998 to 2013 are used to examine quantitatively the atmospheric thermodynamic and oceanic dynamic mechanisms responsible for its formation. Power spectra show that the 30–60-day SST variability is predominant, accounting for 60% of the variance of the 10–90-day variability over most of the SCS. Composite analyses demonstrate that the 30–60-day SST variability is characterized by the alternate occurrence of basin-wide positive and negative SST anomalies in the SCS, with positive(negative) SST anomalies accompanied by anomalous northeasterlies(southwesterlies). The transition and expansion of SST anomalies are driven by the monsoonal trough–ridge seesaw pattern that migrates northward from the equator to the northern SCS. Quantitative diagnosis of the composite mixed-layer heat budgets shows that, within a strong 30–60-day cycle, the atmospheric thermal forcing is indeed a dominant factor, with the mixed-layer net heat flux(MNHF) contributing around 60% of the total SST tendency, while vertical entrainment contributes more than 30%. However, the entrainment-induced SST tendency is sometimes as large as the MNHF-induced component, implying that ocean processes are sometimes as important as surface fluxes in generating the30–60-day SST variability in the SCS.     

Monin–Obukhov Similarity Functions for the Structure Parameters of Temperature and Humidity

Monin–Obukhov similarity functions for the structure parameters of temperature and humidity are needed to derive surface heat and water vapour fluxes from scintillometer measurements and it is often assumed that the two functions are identical in the atmospheric surface layer. Nevertheless, this assumption has not yet been verified experimentally. This study investigates the dissimilarity between the turbulent transport of sensible heat and water vapour, with a specific focus on the difference between the Monin–Obukhov similarity functions for the structure parameters. Using two datasets collected over homogeneous surfaces where the surface sources of sensible heat and water vapour are well correlated, we observe that under stable and very unstable conditions, the two functions are similar. This similarity however breaks down under weakly unstable conditions; in that regime, the absolute values of the correlations between temperature and humidity are also observed to be low, most likely due to large-scale eddies that transport unsteadiness, advection or entrainment effects from the outer layer. We analyze and demonstrate how this reduction in the correlation leads to dissimilarity between the turbulent transport of these two scalars and the corresponding Monin–Obukhov similarity functions for their structure parameters. A model to derive sensible and latent heat fluxes from structure parameters without measuring the friction velocity is tested and found to work very well under moderately to strongly unstable conditions (−z/L > 0.5). Finally, we discuss the modelling of the cross-structure parameter over wet surfaces, which is crucial for correcting water vapour effects on optical scintillometer measurements and also for obtaining surface sensible and latent heat fluxes from the two-wavelength scintillometry.     

Variability of Surface Air Temperature in Italy 1870–1980

Summary The trends and the fluctuations in variability of surface air temperature in Italy has been investigated by statistical analysis of historical data covering the recent 100 years. 27 stations were used for the analysis and these were distributed all over the Italian territory divided into two climatically homogeneous zones. The temperature trends are different in each climatic zone and season, while the interannual variability shows a similar seasonal dependence for the North and South of Italy. In particular, summer temperature shows a characteristic pattern with alternating minima and maxima reaching significant values in the period 1940–1970: a maximum for the North between 1940–1960 and a minimum for the South between 1960–1970. Received February 1, 1996 Revised June 7, 1997     

Analysis of Mean Wind Characteristics in the Atmospheric Surface Lurface Layer

ＡＮＡＬＹＳＩＳＯＦＭＥＡＮＷＩＮＤＣＨＡＲＡＣＴＥＲＩＳＴＩＣＳＩＮＴＨＥＡＴＭＯＳＰＨＥＲＩＣＳＵＲＦＡＣＥＬＡＹＥＲＯＦＴＨＥＧＲＡＳＳＬＡＮＤＡＲＥＡＩＮＮＯＲＴＨＣＨＩＮＡＸｕｅＨｅｎｇ（薛桁），ＺｈｕＲｕｉｚｈａｏ（朱瑞兆）ａｎｄＷｕＨｏ...     

The Synoptic Climatology of Monthly Mean Surface Temperature in Asia in Relation to the 700 hPa Circulation

The synoptic climatology of monthly mean surface air temperature anomaly (MMATA) at 47 surface stations in Asia is assessed by two types of maps. The first consists of simple linear correlation coefficients between the MMATA at a station and the monthly mean 700 hPa height anomaly (MMHA) at 134 grid points in the Northern Hemisphere. In winter, these fields generally contain two equally important centers: a center of maximum positive correlation approximately 1300 km from the reference station and a negative center about 2800 km to its northwest. In summer, the positive center is located an average of 800 km from the reference station and strongly dominates the MMATA, while the negative center is no longer as important as in winter. The second kind of map is a special type of anomaly composite, constructed by multiplying the correlation coefficient at each grid point by the standard deviation of MMHA at the same point. This map shows the optimum distribution of height anomalies for abnormally warm (or c     

Trends and Uncertainties in Surface Air Temperature over the Tibetan Plateau,1951–2013

Trends and uncertainties of surface air temperature over the Tibetan Plateau(TP)are evaluated by using observations at 100 meteorological stations during the period 1951–2013.The sampling error variances of gridded monthly data are estimated for every month and every grid box of data.The gridded data and their sampling error variances are used to calculate TP averages,their trends,and associated uncertainties.It is shown that large sampling error variances dominate northern and western TP,while small variances appear over southern and eastern TP.Every month from January to December has a positive linear trend during the study period.February has the largest trend of 0.34±0.18°C(10 yr)~(–1),and April the smallest at 0.15±0.11°C(10 yr)~(–1).The uncertainties decrease steadily with time,implying that they are not large enough to alter the TP warming trend.     

On the Blocking Flow Patterns in the Euro–Atlantic Sector:A Simple Model Study

The flow patterns of Euro-Atlantic blocking events in winter are investigated by dividing the sector into three sub- regions： 60°-30°W （Greenland region）; 20°W-30°E [eastern Atlantic-Europe （EAE） region]; and 50°-90°E （Ural region）. It is shown that blocking events in winter are extremely frequent in the three sub-regions. Composite 500-mb geopotential height fields for intense and long-lived blocking events demonstrate that the blocking fields over Greenland and Ural regions exhibit southwest-northeast （SW-NE） and southeast-northwest （SE-NW） oriented dipole-type patterns, respectively, while the composite field over the EAE region exhibits an Ω-type pattern. The type of composite blocking pattern seems to be related to the position of the blocking region relative to the positive center of the climatological stationary wave （CSW） anomaly existing near 10°W.
The physical cause of why there are different composite blocking types in the three sub-regions is identified using a nonlinear multiscale interaction model. It is found that when the blocking event is in almost the same position as the positive CSW anomaly, the planetary-scale field can exhibit an Ω-type pattern due to the enhanced positive CSW anomaly. Neverthe- less, a SW-NE （SE-NW） oriented dipole-type block can occur due to the reduced positive CSW anomaly as it is farther in the west （east） of the positive CSW anomaly. The total fields of blocking in the three regions may exhibit a meandering flow comprised of several isolated anticyclonic and cyclonic vortices, which resembles the Berggren-Bolin-Rossby meandering jet type.     

The Southern Oscillation / Northern Oscillation Cycle Associated with Sea Surface Temperature in the Equatorial Pacific

This paper analyzed the time evolution of the global 1000 hPa height anomalies related to the sea surface temperature (SST) in the eastern equatorial Pacific by using ECMWF data in the period 1979-1988, in which two Pacific warm events, 1982/83 and 1986/787, are included. It is found that there are distinct evidences of eastward propagation of alternate positive / negative height anomalies not only in the tropical South Pacific but also in the tropical North Pacific. The former is associated with the Southern Oscillation (SO) and the latter is associated with the so-called Northern Oscillation (NO).It is noteworthy that the alternate positive / negative anomaly centers associated with SO and NO can be traced back to the middle and higher latitudes of the South Indian Ocean and the East Asian continent respectively, which may be significant for the understanding of the causes and mechanism of SO and NO and for the monitoring of ENSO.Furthermore, these evolution processes have a strong symmetry about the     

An Analysis of the Turbulent Structure in the Unstable Surface Layer nearby a Shelter Belt

An analysis was performed of the turbulent data obtained from Yucheng experimental station in the Shandong Province in 1984. [t is shown that at variant wind speed, the spectra of streamwise velocity remain similar and the intensity of wind fluctuations is proportional to wind speed in the downwind area of shelter belt. Therefore, we may decide the similarity of wind fluctuations by a speed scale and a length scale which is not correlated with stability, σu /V0 = F(X / H). The -5/3 power range of temperature spectra extends to lower frequency. The variation of ratio σ0 /T. with stability becomes σ0 / T . = C(X / H)( - Z / L)-1/3 . There is not such an extension of -5 / 3 power range in the humidity spectra.     

A Quasi-Linear Relationship between Planetary Outgoing Longwave Radiation and Surface Temperature in a Radiative-Convective-Transportive Climate Model of a Gray Atmosphere

In this study, we put forward a radiative-convective-transportive energy balance model of a gray atmosphere to examine individual roles of the greenhouse effect of water vapor, vertical convection, and atmospheric poleward energy transport as well as their combined effects for a quasi-linear relationship between the outgoing longwave radiation(OLR)and surface temperature(TS). The greenhouse effect of water vapor enhances the meridional gradient of surface temperature,thereby directly contributin...     

A Primary Study of Interaction Between Monsoon and Sea Surface Temperature in the Neighborhood Sea Area in South Aisa

1. Introduction South Asian monson is an important weather and climate phenomenon, and it is also an important con- stituent of the global atmospheric circulation, thus people pay more attention to it (Hahn and Manabe, 1975; Zhu and Zhao, 1987; Zhu et al., 1991; Zhou and Yang, 1994; Wu and Huang, 2001; Li et al., 1999). For example, Zhu and Zhao (1987) studied the effects of terrain on South Asian monsoon by the equato- rial atmospheric balance model, indicating that ter- rain effect is …     

Acoustic Travel Time Tomography – A Method for Remote Sensingof the Atmospheric Surface Layer

Summary Acoustic travel time tomography is demonstrated as a technique for remote monitoring of near surface air temperature and wind fields. An experimental procedure is presented which provides line-averaged values of the effective sound speed changing with air temperature and wind vector. In this study the travel times of sound signals at defined propagation paths between different acoustic sources and receivers were measured. The travel time data were inverted into effective sound speed values by using a special tomographic algorithm (Simultaneous Iterative Reconstruction Technique) to obtain area-averaged meteorological quantities (air temperature, wind speed). The method of acoustic travel time tomography will be applied to the atmosphere in order to directly provide spatially averaged data which are needed for evaluation of large-eddy simulation and microscale meteorological models as well as to complete conventional point measurements. Received November 4, 1998 Revised April 7, 1999