Large-scale Atmospheric Conditions Research Articles

Ability of an ensemble of regional climate models to reproduce weather regimes over Europe-Atlantic during the period 1961–2000

One of the main concerns in regional climate modeling is to which extent limited-area regional climate models (RCM) reproduce the large-scale atmospheric conditions of their driving general circulation model (GCM). In this work we investigate the ability of a multi-model ensemble of regional climate simulations to reproduce the large-scale weather regimes of the driving conditions. The ensemble consists of a set of 13 RCMs on a European domain, driven at their lateral boundaries by the ERA40 reanalysis for the time period 1961–2000. Two sets of experiments have been completed with horizontal resolutions of 50 and 25 km, respectively. The spectral nudging technique has been applied to one of the models within the ensemble. The RCMs reproduce the weather regimes behavior in terms of composite pattern, mean frequency of occurrence and persistence reasonably well. The models also simulate well the long-term trends and the inter-annual variability of the frequency of occurrence. However, there is a non-negligible spread among the models which is stronger in summer than in winter. This spread is due to two reasons: (1) we are dealing with different models and (2) each RCM produces an internal variability. As far as the day-to-day weather regime history is concerned, the ensemble shows large discrepancies. At daily time scale, the model spread has also a seasonal dependence, being stronger in summer than in winter. Results also show that the spectral nudging technique improves the model performance in reproducing the large-scale of the driving field. In addition, the impact of increasing the number of grid points has been addressed by comparing the 25 and 50 km experiments. We show that the horizontal resolution does not affect significantly the model performance for large-scale circulation.

Palaeoflood and floodplain records from Spain: Evidence for long-term climate variability and environmental changes

Palaeoflood chronologies from seven Spanish river basins and floodplain aggradation chronologies from thirteen rivers are analysed. These fluvial records were divided in to two sub-sets, namely Atlantic (10 ka record) and Mediterranean (3 ka record) river basins, which represent distinct modern hydroclimatic conditions. In Atlantic basins floods result from intense, widespread rainfalls associated with Atlantic frontal systems transported by westerly airflow. Mediterranean river flooding is related to heavy rainfall induced by mesoscale convective systems (MCSs) during autumn months. Evidence from radiocarbon dates in slackwater flood deposits shows six periods of flood clusters at 10,750–10,240; 9550–9130; 4820–4440; 2865–2350; 960–790; and 520–290 cal BP. Despite the different flood-producing weather conditions in Atlantic and Mediterranean rivers, the radiocarbon sample clusters overlap and indicate changes in large-scale atmospheric circulation and climatic conditions in the Iberian Peninsula. Comparison with proxy records of mean temperature for the Northern Hemisphere demonstrates a relationship between the period of slackwater flood deposition and cold climatic phases (e.g. the 2650 yr BP climatic event or AD 1590–1650 period of the Little Ice Age). Radiocarbon dates from aggraded floodplain sediments were clustered at 2710–2320, 2000–1830, and 910–500 cal BP. The first cluster period is in phase with the timing of slackwater deposition, whereas the third (910–500 cal BP) occurs in between two periods of increased flood frequency as indicated by the palaeoflood and documentary flood records. It is argued that the 910–500 cal BP floodplain aggradation period reflects the first post-Roman evidence of environmental change related to generalised land-use changes at the catchment scale, which produced high sediment load transported to overbank areas during high flows.

On the Extreme Variability and Change of Cold-Season Temperatures in Northwest Canada

Abstract The Mackenzie River basin (MRB) in northwestern Canada is a climatologically important region that exerts significant influences on the weather and climate of North America. The region exhibits the largest cold-season temperature variability in the world on both the intraseasonal and interannual time scales. In addition, some of the strongest recent warming signals have been observed over the basin. To understand the nature of these profound and intriguing observed thermal characteristics of the region, its atmospheric heat budget is assessed by using the NCEP–NCAR reanalysis dataset. The composite heat budgets and large-scale atmospheric conditions that are representative of anomalous winters in the region are examined in unison to study the processes that are responsible for the development of extreme warm/cold winters in the MRB. It is shown that the large winter temperature variability of the region is largely a result of the strong variability of atmospheric circulations over the North Pacific, the selective enhancement/weakening of latent heating of the cross-barrier flow for various onshore flow configurations, and synoptic-scale feedback processes that accentuate the thermal response of the basin to the changes in upwind conditions. The improved understanding of mechanisms that govern the thermal response of the basin to changes in the upstream environment provides a theoretical basis to interpret the climate change and modeling results for the region. In particular, the large recent warming trend observed for the region can be understood as the enhanced response of the basin to the shift in North Pacific circulation regime during the mid-1970s. The strong cold bias that affected the region in some climate model results can be attributed to the underprediction of orographic precipitation and associate latent heating of the cross-barrier flow, and the subsequent weakening of mean subsidence and warming over the basin in the models.

Simulation of the Recent Multidecadal Increase of Atlantic Hurricane Activity Using an 18-km-Grid Regional Model

In this study, a new modeling framework for simulating Atlantic hurricane activity is introduced. The model is an 18-km-grid nonhydrostatic regional model, run over observed specified SSTs and nudged toward observed time-varying large-scale atmospheric conditions (Atlantic domain wavenumbers 0–2) derived from the National Centers for Environmental Prediction (NCEP) reanalyses. Using this “perfect large-scale model” approach for 27 recent August–October seasons (1980–2006), it is found that the model successfully reproduces the observed multidecadal increase in numbers of Atlantic hurricanes and several other tropical cyclone (TC) indices over this period. The correlation of simulated versus observed hurricane activity by year varies from 0.87 for basinwide hurricane counts to 0.41 for U.S. landfalling hurricanes. For tropical storm count, accumulated cyclone energy, and TC power dissipation indices the correlation is ~0.75, for major hurricanes the correlation is 0.69, and for U.S. landfalling tropical storms, the correlation is 0.57. The model occasionally simulates hurricanes intensities of up to category 4 (~942 mb) in terms of central pressure, although the surface winds (< 47 m s−1) do not exceed category-2 intensity. On interannual time scales, the model reproduces the observed ENSO-Atlantic hurricane covariation reasonably well. Some notable aspects of the highly contrasting 2005 and 2006 seasons are well reproduced, although the simulated activity during the 2006 core season was excessive. The authors conclude that the model appears to be a useful tool for exploring mechanisms of hurricane variability in the Atlantic (e.g., shear versus potential intensity contributions). The model may be capable of making useful simulations/projections of pre-1980 or twentieth-century Atlantic hurricane activity. However, the reliability of these projections will depend on obtaining reliable large-scale atmospheric and SST conditions from sources external to the model.

On the occurrence of ocean sunfish Mola mola and slender sunfish Ranzania laevis in the Adriatic Sea

Presence and habitat preference of two pelagic fish species—Mola mola and Ranzania laevis—are investigated from all available records obtained in the Adriatic from 1781 up to today. Absence of systematic investigations is overcome by relating their occurrences to the long-term meteorological and oceanographic data sets representing local conditions and processes. Seasonal and interannual distributions of these two species are significantly different and point to a possible different causes of their appearance. On the seasonal scale almost all findings of M. mola, with only a few exceptions, are from the warm part of the year, whereas R. laevis is appearing throughout the year with the highest number of individuals in December. Analysis of the interannual meteorological and oceanographic conditions indicates that occurrence of M. mola coincides with the sea warming, whereas the oceanographic conditions favourable for appearance of R. laevis are more complex and could be related to the abrupt change in the large scale atmospheric conditions. Changeable atmospheric conditions coincided with increased productivity in the Adriatic and increased number of zooplankton and small pelagic fish, which are the main food for R. laevis.

Another deficient monsoon 2004 - A comparison with drought year 2002 and possible causes

The rainfall over India as a whole during the summer monsoon season of 2004 was deficient with –13% below normal. Earlier in 2002, India has faced another worst situation when large-scale drought occurred and all India rainfall was below –19%. In the present study, we have compared briefly salient observational features of both the monsoons to find out their distinct characteristics. Comparisons show appearance of many similar as well as contrasting features. Though, both seasons were deficient, their dates of onset of monsoon over Kerala were either before or near the normal date. Progress up to central India was also normal in both the seasons. While Indian Summer Monsoon Rainfall (ISMR) during June was good, a few longest stagnation periods during advancing stage in July of both the years made unexpected delay of monsoon in covering entire India. Rainfall of July also suffered the most in both the seasons with a record lowest ISMR in 2002. Not a single depression formed in 2002 while in 2004, their frequency was less than half of normal. Analysis of other large-scale monthly anomalous ocean and atmospheric conditions over Indo-Pacific region including El-Nino conditions confirms that ENSO and Equatorial Indian Ocean Oscillation or EQUINOO have caused drought in July 2002, but not in July 2004. This is because very high typhoon formation and their recurvature with significantly higher than normal convection over northwest Pacific associated with record lowest ISMR in July, 2002 in contrast to occurrence of deficient ISMR in July 2004 which was associated with few typhoon formation and less convection. Also in 2002, Indian region was happened to fall exactly under the subsidence branch of Walker circulation with ascending branch over the western Pacific in the season in contrast to 2004, when subsidence was observed to be both over large part of western Pacific and adjoining Indian region.

Variance methods to estimate regional heat fluxes with aircraft measurements in the convective boundary layer

Summary Turbulence data obtained by aircraft observations in the convective boundary layer (CBL) were analyzed to estimate the regional surface heat fluxes through application of the variance methods. Several heights within and above the CBL were flown repeatedly above the flux observation site in a homogeneous steppe region in Mongolia. The vertical profiles of the second moment about the mean, i.e., the variance, of temperature were found to follow in general the functional forms proposed in previous studies. These variance statistics were applied to the variance formulations to estimate surface sensible heat fluxes. First, the flux estimation was made with these equations and the constant parameters as proposed in previous studies. Then, the constants were re-calibrated with the current data set and used for flux estimation. In addition, a new simpler formulation was proposed and also calibrated with the current data set. Finally, additional variables, which represent the large scale atmospheric conditions namely baroclinity and advection, were considered for possible improvement of the flux estimation. The resulting rms difference of the estimated sensible heat flux and ground based measurements was reduced from about 40–100 W m −2 for the results obtained with the original constants and formulations, to 30 W m −2 or less for those obtained with locally calibrated constants and introduction of four additional variables. All formulations including the new simple equation performed equally well.

Large-scale atmospheric patterns associated with mesoscale features leading to extreme precipitation events in Northwestern Italy

The synoptic and large-scale atmospheric conditions for heavy rainfall events in Northwestern Italy are diagnosed through the joint analysis of surface precipitation gauges and reanalysis atmospheric fields. Quantiles of local surface gauge precipitation observations are used to estimate the much larger-scale composite maps (conditional mean fields) of vertically integrated moisture flux, low-level winds, sea-level pressure, and 500 hPa height across the Atlantic and European domains. Remarkably, coarse-resolution reanalysis data show distinct synoptic conditions for heavy precipitation in localized regions that are below the resolution of the reanalysis. In this paper the key attributes of the new approach that is based on the joint analysis of gridded reanalysis and station data are presented. The application of the methodology are used to establish supporting evidence for hydrometeorological processes that lead to extreme precipitation across Northwest Italy. The results confirm the role of large-scale flow features that interact with regional topography in producing localized extreme precipitation. Whereas previous studies were based on a few case studies (modeled or observational), in this study the approach to producing a large ensemble of cases and composite statistics are introduced.

Eastern Adriatic typical wind field patterns and large‐scale atmospheric conditions

AbstractThe famous Bora and Scirocco winds blow along the eastern coast of the Adriatic Sea, prevailing during the colder part of the year. Sea and land breezes, as well as Etesians, are also rather frequent, but they prevail during the warmer seasons. There are also some other less well known wind types in this region. This paper deals with the application of an objective procedure for the classification of all wind field patterns, regardless of the wind names. For this purpose, a complex principal component analysis technique has been applied. Time series of instantaneous (at 07 h, 14 h and 21 h local time) wind data have also been used, including the National Centres for Environmental Prediction–National Centre for Atmospheric Research reanalyses of the constant‐pressure levels of 1000 hPa and 850 hPa, as well as the thickness of 850–1000 hPa. All refer to the period 1981–98. The results indicate 11 typical wind field patterns over the Adriatic area. Some of them have the characteristics of Bora and Scirocco, whereas the other are Etesians, sea (land) breezes or a combination of these. There is also a near‐calm type. A rather high correlation between these mesoscale wind patterns and large‐scale (regional) atmospheric conditions has been established. Two controlling pressure centres, i.e. the Icelandic cyclone and the Azores anticyclone, appear as important large‐scale factors which, at least indirectly, influence the creation of the eastern Adriatic wind patterns. For types representing Scirocco and Bora conditions, regional open or closed synoptic‐scale circulation systems, however, have a dominant influence. Copyright © 2005 Royal Meteorological Society

Transition of the Large-Scale Atmospheric and Land Surface Conditions from the Dry to the Wet Season over Amazonia as Diagnosed by the ECMWF Re-Analysis

Abstract Using 15-yr instantaneous European Centre for Medium-Range Weather Forecasts Re-Analysis (ERA) data, the authors have examined the large-scale atmospheric conditions and the local surface fluxes through the transition periods from the dry to wet seasons over the southern Amazon region (5°–15°S, 45°–75°W). The composite results suggest that the transition can be divided into three phases: initiating, developing, and mature. The initiating phase is dominated by the local buildup of the available potential energy. This begins about 90 days prior to the onset of the wet season by the increase of local land surface fluxes, especially latent heat flux, which increases the available potential energy of the lower troposphere. The cross-equatorial flow and upper-tropospheric circulation remain unchanged from those of the dry season. The developing phase is dominated by the seasonal transition of the large-scale circulation, which accelerates by dynamic feedbacks to an increase of locally thermal-driven ra...

Inter-annual variability in cyanobacteria blooms in the Baltic Sea controlled by wintertime hydrographic conditions

We investigated inter-annual variability of late summer cyanobacteria (cb) blooms in the Baltic Sea using the 3D ecosystem model ERGOM. A long-term simulation for the period 1982-1993 was carried out with realistic forcing. The simulated variability in cb blooms was in good agreement with satellite observations. Further simulations were performed in order to separate the influence of wintertime nutrient conditions from the impact of weather conditions during the growth period. There is strong evidence that the late-winter phosphate concentration in the surface layer has a determinant influence on late summer cb blooms. A large fraction of the inter-annual variability in cb blooms can be attributed to the variability in excess dissolved inorganic phosphorus (eDIP) in the sur- face layer. The amount of available eDIP in the surface layer depends on the wintertime mixedlayer depth and on the magnitude and persistency of coastal upwelling. The simulation results suggest an impact of the large-scale atmospheric conditions in winter, namely the North Atlantic Oscillation (NAO), on the occurrence of cb blooms in the Baltic Sea. It is hypothesised that the impact of the NAO is transferred by a cause-and-effect chain starting in winter and developing until late summer: high NAO index → high wind stress, low ice cover → high mixed-layer depth, strong upwelling → high surface-layer eDIP concentration → (potentially) strong cb bloom.

広域の大気状態が中部日本山岳地域の夏季の夜間冷却に及ぼす影響

広域の大気状態が中部日本山岳地域の夏季の夜間冷却に及ぼす影響

Experimental study of five föhn events during the Mesoscale Alpine Programme: From synoptic scale to turbulence

AbstractAircraft measurements made during the Mesoscale Alpine Programme are used to investigate the atmospheric turbulence inside the large Rhine Valley on the north side of the Alps during five föhn events induced by a southerly to south‐westerly flow. Prior to that goal, an analysis based on the observations of different instruments provides the mesoscale and large‐scale atmospheric conditions encountered during the aircraft flights. The temporal and spatial structure of the föhn event of 20 October 1999 is presented as an example. In this case, the three‐dimensional structure of the turbulence is investigated. An estimate of the different components of the turbulent kinetic energy budget is attempted. It shows that the source of the turbulence is mainly mechanical. In spite of the high inhomogeneity of the turbulence in space and between the cases, the study of five cases allows the description of some general features of the föhn events, such as the plume of turbulence extending downwards in the valley and the near homogeneity of the dissipative length‐scale. Copyright © 2003 Royal Meteorological Society.

Regional effects of large-scale extreme wind events over orographically structured terrain

¶Above orographically structured terrain considerable differences of the regional wind field may be identified during large-scale extreme wind events. So far, these regional differences could not be resolved by climate models. To determine the relationships between large-scale atmospheric conditions, the influence of orography, and the regional wind field, data measured in the upper Rhine valley within the framework of the REKLIP Regional Climate Project were analyzed and calculations were made using the KAMM mesoscale model. In the area of the upper Rhine valley, ratios of the wind velocity in the Rhine valley at 10 m above ground level, νval, and the large-scale flow velocity, νlar, are between νval/νlar ≈ 0.1 and νval/νlar ≈ 1. The νval/νlar ratio exhibits a strong dependence on thermal stratification, δ, and decreases from νval/νlar ≈ 1 at δ = 0 K m−1 to νval/νlar ≈ 0.2 at δ = 0.0075 K m−1. In areas, where the lateral mountainous border of the Rhine valley is interrupted, the νval/νlar ratio increases again with increasing stability or decreasing Froude number. This is obviously due to flow around the Black Forest under stable stratification. It is demonstrated by model calculations that a complex wind field develops in the Rhine valley at small Froude numbers (Fr < 1) irrespective of the direction of large-scale flow. The νval/νlar ratio is characterized by small values in the direct lee side (νval/νlar ≈ 0.2) and high values on the windward side of the lateral mountainous border of the Rhine valley (νval/νlar ≈ 0.8).

Downscaling recent streamflow conditions in British Columbia, Canada using ensemble neural network models

Variations in climate conditions during recent decades in British Columbia, Canada have occurred coincident to significant changes in streamflow conditions in the province. In the current study, the ability of empirical downscaling models to resolve these changes is investigated using ensemble neural networks forced with synoptic-scale atmospheric conditions. Five-day averages of streamflow data from 21 watersheds in the region are modelled using atmospheric data from the NCEP/NCAR reanalysis project as inputs. Ability of the downscaling models to predict streamflow and changes in streamflow between 1975–1986 and 1987–1998 is evaluated using a combination of model performance statistics, comparisons between long-term averages, and results from non-parametric statistical tests. While performance varied between systems, results suggest that empirical downscaling models for streamflow are capable of predicting changes in streamflow observed during recent decades using only large-scale atmospheric conditions as model inputs. Based on comparisons between stepwise linear regression and neural network models, the latter approach is recommended, particularly when trying to model systems with complex non-linear and interactive relationships between inputs and outputs. The use of ensemble averaging as a part of the modelling process is investigated and a number of recommendations are made with respect to this methodology.

A Growing-Season Hydroclimatology, Focusing on Soil Moisture Deficits, for the Ohio Valley Region

A hydroclimatology, or description of long-term means and interannual variation, that focuses on soil moisture deficits was constructed for the period of 1895‐1998 for a six-state region composing the Ohio Valley. The term ‘‘deficit’’ is considered from an agricultural point of view whereby moisture-induced crop stress is a combination of insufficient precipitation and soil moisture. Of particular concern are deficits that occur during the growing season (May‐September) when vegetation is most susceptible to moisture-induced stress. Evidence suggests that there is considerable temporal variability but no long-term trend toward either wetter or drier conditions in the Ohio Valley. The pattern of growing-season deficit is characterized by multiyear and multidecadal cycles of wet and dry periods. Decreases in precipitation during years with anomalously large growing-season deficits, however, are associated more with the reduced frequency of precipitation events than with any changes in intensity. These variations in precipitation frequency and the conditions conducive to droughts are intimately linked with largescale atmospheric conditions, including the low-level and upper-level flow patterns.

Impact of CO2-Induced Warming on Hurricane Intensities as Simulated in a Hurricane Model with Ocean Coupling

Abstract This study explores how a carbon dioxide (CO2) warming–induced enhancement of hurricane intensity could be altered by the inclusion of hurricane–ocean coupling. Simulations are performed using a coupled version of the Geophysical Fluid Dynamics Laboratory hurricane prediction system in an idealized setting with highly simplified background flow fields. The large-scale atmospheric boundary conditions for these high-resolution experiments (atmospheric temperature and moisture profiles and SSTs) are derived from control and high-CO2 climatologies obtained from a low-resolution (R30) global coupled ocean–atmosphere climate model. The high-CO2 conditions are obtained from years 71–120 of a transient +1% yr−1 CO2-increase experiment with the global model. The CO2-induced SST changes from the global climate model range from +2.2° to +2.7°C in the six tropical storm basins studied. In the storm simulations, ocean coupling significantly reduces the intensity of simulated tropical cyclones, in accord with ...

The influence of large‐scale atmospheric circulation on the surface energy balance of the King George Island ice cap

AbstractDuring the austral summer 1997–1998 three automatic weather stations were operated at different altitudes on the sub‐Antarctic ice cap of King George Island (South Shetland Islands). Snowmelt was derived from energy balance computations. Turbulent heat fluxes were calculated from meteorological measurements using the bulk aerodynamic approach, with net radiation being measured directly. Modelled ablation rates were compared with readings at ablation stakes and continuously measured snow height at a reference site. Snow depletion and daily snowmelt cycles could be well reproduced by the model. Generally, radiation balance provided the major energy input for snowmelt at all altitudes, whereas sensible heat flux was a second heat source only in lower elevations. The average latent heat flux was negligible over the entire measuring period. A strong altitudinal gradient of available energy for snowmelt was observed. Sensible heat flux as well as latent heat flux decreased with altitude. The measurements showed a strong dependence of surface energy fluxes and ablation rates on large‐scale atmospheric conditions. Synoptic weather situations were analysed based on AVH RR infrared quicklook composite images and surface pressure charts. Maximum melt rates of up to 20 mm per day were recorded during a northwesterly advection event with meridional air mass transport. During this northwesterly advection, the contribution of turbulent heat fluxes to the energy available for snowmelt exceeded that of the radiation balance. For easterly and southerly flows, continentally toned, cold dry air masses dominated surface energy balance terms and did not significantly contribute to ablation. The link between synoptic situations and ablation is especially valuable, as observed climatic changes along the Antarctic Peninsula are attributed to changes in the atmospheric circulation. Therefore, the combination of energy balance calculations and the analysis of synoptic‐scale weather patterns could improve the prediction of ablation rates for climate change scenarios. Copyright © 2001 Royal Meteorological Society

INFLUENCES OF LARGE-SCALE CLIMATIC VARIABILITY ON EPISODIC TREE MORTALITY IN NORTHERN PATAGONIA

In the context of potential global warming, it is critical that ecologists bridge the typically local spatial scale of ecology to the regional scale of climatology by linking ecosystem responses to variations in the large-scale synoptic controls of regional climates. In northern Patagonia, Argentina, we related regional-scale tree mortality events over the past ∼100 years to annual and decadal-scale climatic variations associated with changes in the major synoptic climatic controls of the southeastern Pacific region, including the El Niño–Southern Oscillation (ENSO). In nine stands of Austrocedrus chilensis a xeric conifer, we used dendrochronological techniques to date the outermost tree ring on dead-standing and fallen trees to estimate the dates of tree death for 336 trees. To evaluate climatic conditions during periods of high tree mortality, we used regional records of precipitation and temperature from six climate stations and also used a regional set of 24 tree ring chronologies from Austrocedrus. Good preservation of the resinous wood of Austrocedrus allowed relatively precise dating of tree deaths over the past ∼90 years. Episodes of massive tree mortality coincide with exceptionally dry springs and summers during the 1910s, 1942–1943, and the 1950s. Although there is a general regional synchroneity of tree death associated with drought, intra-regional variations in the intensity of droughts, as interpolated and mapped from the regional network of tree ring chronologies, are also reflected by north-to-south variations in tree mortality patterns. Periods of drought and associated tree mortality during the 20th century in northern Patagonia are strongly associated with above average sea level atmospheric pressure off the coast of Chile at the same latitudes. Temperature and precipitation in northern Patagonia are highly influenced by the intensity and latitudinal position of the southeastern Pacific anticyclone, which, in turn, are greatly affected by ENSO. Tree mortality in northern Patagonia appears to be intensified by extreme events of the Southern Oscillation and is more strongly coincident with El Niño events along the coast of northern Peru. These results, in combination with previously established climatic influences on fire occurrence and tree seedling establishment, strongly link stand-level and regional-scale forest dynamic processes in northern Patagonia with variations in large-scale atmospheric conditions.

Using Similarity Theory to Parameterize Mesoscale Heat Fluxes Generated by Subgrid-Scale Landscape Discontinuities in GCMs

Abstract Similarity theory was used to develop a parameterization of mesoscale heat fluxes induced by landscape discontinuities for large-scale atmospheric models (e.g., general circulation models). For this purpose, Buckingham Pi theory, a systematic method for performing dimensional analysis, was used to derive a set of dimensionless groups, which describes the large-scale atmospheric background conditions, the spatial variability of surface sensible heat flux, and the characteristic structure of the landscape. These dimensionless groups were used to calculate the coefficients of a fourth-order Chebyshev polynomial, which represents the vertical profiles of dimensionless mesoscale heat fluxes obtained for a broad range of large-scale atmospheric conditions and different landscapes. The numerous three-dimensional numerical experiments performed to evaluate this similarity relationship suggest that the parameterization is quite robust.