Selection of Some Abstracts

Water availability
Hydrometeorology and Water Cycle
Coupling of a Meteorological and a Hydrological Model
Landuse Changes
Heterogeneity
Remote Sensing
Wet and Dry Deposition

Water availability

Evaluation of Simulated Water Budget by Means of Measurements at Brandis Lysimeter Station                  
Nicole Mölders, Ulrike Haferkorn, S.Knappe, J. Döring, G. Kramm
In: Tetzlaff, G., Grünewald, U.: WissenschaftlicheMitteilungen, Meteorologische Arbeiten aus Leipzig,16, 67-83 (1999).
Lysimeter-, tensiometer-, andsoil-temperature-datarecorded at Brandis (51.32°N, 12.62°E, 133 mNN, about 50 km south-eastof Leipzig) are used to evaluate a hydro-thermodynamical soil-vegetation-scheme (HTSVS) which has been further developed by including a parameterization of root effects. HTSVS is driven by the meteorological data measured at Brandis. Comparing simulated and observed yield of groundwater, matric potential, soil temperature, and evapotranspiration shows that HTSVS well performs in spring and fall. Discrepancies occurring in winter may be attributed to the lack of a snow- and frost-parameterization. In summer, HTSVS provides better results when precipitation events are equally distributedin time than for strong precipitation events following long dry periods. Although the day to day differences with and without simulation of root effects hardly differ, accumulated recharge and evapotranspiration will meet slightly better the observed sums after 2049 days of integration if root effects are considered.


Application of lysimeter- and tensiometer-data for evaluation of a moduleto couple hydrological and atmospheric modelsN. Mölders, U.Haferkorn, S. Knappe, J. Döring,G. KrammIn: Gerold, G. (Ed.) Heterogenitaet landschaftshaushaltlicher Wasser- und Stoffumsätze in Einzugsgebieten, Eco Regio, 8, 97-105
Lysimeter- and tensiometer-data recorded at Brandis (51.32°N, 12.62°E, 133 m NN,about 50 km SE of Leipzig) are used to evaluate a hydro-thermodynamical soil-vegetation-scheme (HTSVS) which is developed to couple hydrological and atmospheric models. Comparing simulated and observed yield of ground water, matric potential, and evapotranspiration shows that HTSVS is suitable for the demands of hydrological and atmospheric modeling.


Hydrometeorology and Water Cycle

Investigations on the impact of explicitly predicted snow metamorphism on the micro-climate simulated by a meso-beta/ gamma-scale non-hydrostatic model
Fröhlich, K., and N. Möldersinpress (2002)
A snow-model is developed, coupled to and tested within the framework of the meso- beta/gamma-scale non-hydrostatic model GESIMA (Geesthacht’ssimulation model of the atmosphere).An evaluation of the snow-model is conducted both in a stand-alone version and within GESIMA. In the stand-alone mode,it is evaluated at local scales using data routinely observed at Brandis (51.32°N,12.62°E, 133m NN, Saxony) between 1993 and 1997. The snow-model reproduces reasonably the temporal evolution of the snow-depth, but it slightly underestimates snow-depth, on average. In the coupled mode, simulations are performed with and without the snow-model for a winter-storm snow event and a melt-period in East-Germany to examine the influence of explicitly modeled snow metamorphism on the simulated microclimate. The snow-model reasonably predicts the effects typically associated with snow-cover. Accuracy of predicted snow-depth and extension depends on the lateral boundary conditions and snow prediction by the host model. Evaluation of the simulated air-temperatures as well as humidity shows that the inclusion of the snow-model improves the model performance as compared to the simulations without snow-model. The results show that changing only the values of albedo and emissivity to those typical for snow, as of tend one in meso-beta /gamma-scale modeling of snow events, can even lead to opposite effects in simulated latent heat fluxes, ground heat fluxes, soil- and near-surface air-temperatures than those typically associated with a snow-cover. A rigorous evaluation of the snow simulations in coupled meso-beta/gamma-scale non-hydrostatic models requires data-sets of snow properties (e.g., albedo and emissivity, snowcover extent, snow-depth, snow-water equivalent, snow-temperature) in a high quality and resolution for the region under study. The available data-sets are not yet ready to fulfil this objective.

On the sensitivity of model results to the choice of surface parameters
Nicole Mölders In: Arnold, K., Raabe, A.: Wissenschaftliche Mitteilungen, Meteorologische Arbeiten aus Leipzig, 17, 1-18 (2000)

The uncertainty of predicted fluxes, variables of state, cloud- and precipitation formation to the choice of plant- and soil parameters, soil type, subgrid-scale heterogeneity and inhomogeneity is examined by results of simulations wherein one parameter is alternatively changed for all grid cells of the domain within its natural range of variability. A higher sensitivity of evapotranspiration to evaporative conductivity, roughness length, and subgrid-scale heterogeneity or inhomogeneity is found than for the other parameters examined. Except for wind velocity, the quantities of liquid and solid water substances the uncertainty is lower at night and early afternoon than at other times. Therefore, evaluation of meteorological models should be performed at those times of the day when the uncertainty in model results caused by the choice of plant and soil parameters is ata minimum. Furthermore, domain-specific parameters should be used when ever available.

On the influence of bulk-parameterization schemes of cloud microphysics on the predicted water cycle relevant quantities - A case study N. Mölders, G. Kramm, M. Laube, A. Raabe Meteorol. Zeitschr. 6, 21-32 (1997).

Two different bulk-parameterization schemes of cloud microphysics alternatively used in a meso-beta-scale meteorological model are compared to elucidate their influence on the predicted atmospheric water cycle. The different parameters (e.g., ice crystal types, density of ice) and parameterizations (e.g., terminal velocity, riming, accretion) used by the schemes cause differences in the mixing ratios of the predicted water substances and in the release and consumption of heat resulting in appreciable differences in the vertical motion. The first scheme leads to a larger and more stratiform cloud coverage than the second one which provides broken cloud fields. Consequently, the latter scheme predicts a more shower-like precipitation with locally greater intensities while the first scheme provides a homogeneous precipitation horizontally larger extended with lower intensity. Moreover, the domain averaged maximal precipitation occurs in the afternoon for the second scheme and in the evening for thefirst scheme. Altogether, the differences in predicted cloud coverage, insolation, vertical motions, precipitati on and soil wetness caused bythe different microphysical parameterizations applied, strongly affect the partitioning of energy between sensible and latent heat at the Earth's surface and hence, the amount of water locally reprovided to the atmosphere.

On the parameterization of ice microphysics in a mesoscale alpha weather forecastmodel N. Mölders, M. Laube, and G. Kramm Atmos. Res., 38, 207-235 (1995).

Numerical experiments with a three-dimensional mesoscale weather forecast model are performed to investigate the influence of parameterized microphysics on predicted cloud structures and precipitation. Both the warm and the cold path of cloud and precipitation formation aretaken into account. The parameterization of the warm path processes considers condensation, autoconversion, accretion, evaporation of both cloud water and rain water, and the sedimentation of rain. The parameterization of the cold path processes consists of water vapor deposition, sublimation, riming, melting, and also the sedimentation of ice crystals. Studies considering only the warm path processes showed that this scheme is overload when strong vertical motions and ice topped clouds are to be simulated. The inclusion of the cold path processes provides a more realistic description of the dynamics and microphysics of the troposphere, and leads to an improvement in the model performance. The results of sensitivity studies with and without riming show that the inclusion of riming leads only to slightly more adequate results. Further numerical experiments have been performed to investigate the sensitivity of the model to different parameters and processes. It is substantiated by all of these numerical studies that the relative humidity and water substance mixing ratio fields were only strongly altered by turning off the ice phase or the riming process. The results of the simulations are presented and discussed on the basis of the analysis and satellite data. Moreover, predicted precipitation rates over land are compared to observed data. Estimation of skill and uncertainty are determined for further model evaluation.

A numerical study on the influence of different cloud treatment in a chemical transport model on gas phase distribution N. Mölders and M. Laube

The long-range transport, the transformation and the deposition of atmospheric pollutants over Europe were simulated witha three-dimensional chemical transport model and its meteorological preprocessor for a three day episode, where two different cloud parameterization schemes (cumulus parameterization and ice parameterization) were used alternatively. Large discrepancies in the predicted distributions of gas concentrations, especially for gases participating ingas phase and aqueous chemistry, as well as in wet deposition occur. These discrepancies are caused by thelarge differences between the two simulations in the calculated cloud amountand in the vertical redistribution of the trace gases due to vertical mixing induced by cloud motions. The parameterized vertical mixing due to clouds and the presence of clouds themselves has been found to strongly affect how far pollutants are transported from their sources. The study shows that the choice of a cloud parameterization used in chemical transport model appreciably affects gas phase and aqueous chemistry calculations.

Some effects of different cloud parameterizations in a mesoscale model anda chemistry transport model Nicole Mölders, Heinz Hass, Hermann J. Jakobs, Manfred Laube, and Adolf Ebel J. Appl. Meteor., 33, 527-545 (1994).
Chemistry transport models often ignore the cloud parameters which can be provided by meteorological preprocessors like mesoscale meteorological models. They of ten recalculate these parameters with algorithms which differ from those used in the meteorological preprocessors. Hence, inconsistencies between the treatment of clouds in the meteorological andchemical part of the model package can occur. In this study the influence of five different cloud parameterization schemes, used in a well-known mesoscale meteorological model on the results of a stand-alone version of a cloud and scavenging module is illustrated. The differences between the results provided by five model runs with different cloud modules and those recalculated by the stand-alone version are discussed. Such differences occur due to the inconsistencies between the different cloud parameterization schemes in the meteorological model and the cloud and scavenging module. The results of the cloud and scavenging module differ due to the different meteorological input data provided by the meteorological model. It is manifested both in recalculated cloud parameters and in predicted wet deposition rates. As illustrated in this study, the rate of wet deposition strongly depends on the cloud parameterization scheme used in the meteorological model and, hence, on the model architecture itself.

Coupling of a Meteorologicaland a Hydrological Model

On the impact of explicitly predicted runoff on the simulated atmospheric response to small-scale land-use changes - An integrated modeling approach
N. Mölders and W. Rühaak Atmos. Res. 63: 3-38 (2002).

An integrated modeling approach was developed to simulate the water cycle in a closed manner. It consists of (1) procedures for up- and downscaling of the variables and fluxes important for both the hydrological and atmospheric processes, (2) a module to explicitly predict surface and channel runoff, (3) the hydro-thermo-dynamic soil-vegetation scheme (HTSVS) which was introduced in the (4) non-hydrostatic meso-beta/gamma-scale meteorological model GESIMA (Geesthacht’ssimulation model of the atmosphere). Comparison of the results provided by simulations with and without considerationof surface and channel runoff shows a remarkable impact of surface runoff on the water cycle within the domain. The results of simulations wherein, along the rivers, grassland and agriculturally used land were substituted by deciduous forest demonstrate that the atmospheric response to land-use changes is more distinct when surface runoff is considered explicitly thanif not. It can be concluded that an integrated modeling techniques of the water cycle, like presented here, can be an important tool for studies on water availability under altered future conditions.


Concepts for coupling hydrological and meteorologicalmodels Nicole Mölders Wiss. Mitt. Inst. Meteor. 22: 1-15 (2001).

Earth system modeling, climate modeling, water resource research as well as integrated modeling (e.g., climate impact studies) require the coupling of hydrological and meteorological models. The paper presents recent concepts on such a coupling. It points out the difficulties to be solved, and provides a brief overview on recently realized couplings. Furthermore, a concept of a hydrometeorological module to couple hydrological and meteorological models is introduced.

Sensitivity studies with a surface and channel runoff module coupled to a mesoscale atmospheric models Nicole Mölders, Wolfram Rühaak Wiss. Mitt. Inst. Meteor. 22: 16-25 (2001).

A module to investigate ground water recharge was developed, and implemented into the mesoscale meteorological model GESIMA (Geesthacht’s simulation model of the atmosphere) as well as coupled to a soil-vegetation scheme. Important features of the ground water module are the determination of surface and channel runoff. A comparison of the results provided by GESIMA with and without consideration of surface and channel runoff shows a re-markable impact of surface runoff on the soil moisture fluxes. Substituting water meadowsby willow-forests demonstrates their importance for soil moisture fluxes.

Testing the effect of a two-way-coupling of ameteorological and a hydrologic model on the predicted local weather Nicole Mölders and Armin Raabe Atmos. Res. 45, 81-107 (1997).

A land-surface module to couple a meteorological and a hydrologic model was developed to simulate the water cycle in a closed manner. The module allows to consider the hydrologic processes of the river catchment (translation, retention, lateral discharge) in the meteorological model which itself drives the hydrologic model by predicted evapotranspiration and precipitation. Besides this two-way-coupling the module allows to consider subgrid-scale surface processes and to heterogenize precipitation in the meteorological model. Theresults of 24-h simulations with and withouta two-way-coupling of the models substantiate that even on a short timescale surface runoff and lateral water flows affect soil wetness, soil temperature, cloudiness and the thermal regime of the atmospheric boundary layer within the catchment. As expected, the coupling results in a slight trend towards moister valleys and drier hills.

A module to couple an atmospheric and a hydrologicmodel - description and preliminary results Nicole Mölders, Thomas Beckmann, and ArminRaabe In: Raabe, A., Heintzenberg, J.: Wissenschaftliche Mitteilungen, Meteorologische Arbeiten aus Leipzig, 4, 79-88.
A land-surface module to couple a meteorological and a hydrologic model is described. It was implemented and tested in the Leipzig's version of GESIMA. Preliminary results of a coupling with NASMO are presented, although this article mainly focuses on the description of the module and its effect on the atmospheric water cycle. One positive impact of the module is that it allows to produce subgrid-scale evapotranspiration in more details and to heterogenize precipitation. This strongly affects soil wetness, cloudiness and the thermal regime of the atmospheric boundary layer.

Landuse Changes

Similarity of microclimate as simulated in response to a landscape of the 1930s and the 1980s Nicole Mölders
J. Hydrometeor. 1, 330-352 (2000)
In the time between the 1930s and the 1980s land-use was modified by deforestation, urbani-zation, afforestation and recultivation of open-pit mines, further installation of open-pit mines, and drainage in about 45.99% of an 30000 km 2 area in South-Brandenburg/North-Saxony region . This study evaluates the short-term (1 d) impacts of these land-use changes assuming the same typical day in May for both landscapes. In so doing, a state-of-the-art, meso- b-scale atmospheric model is applied with a resolution of 5x5 km 2 on the coarse grid and 1x1 km2 on the subgrid.Under the land-use of the 1980s the simulated atmospheric boundary layer (ABL) is slightly warmer and drier than in the 1930s. The sensitivity of the ABL to the land-use changes varies over withtime. The calculated probability density functions show that the partitioning of incoming energy between sensible and latent heat and the partitioning of cloud-microphysical processes between the warm and cold paths of precipitation formation differ appreciably. The cloud and precipitation distributions are affected the most of all variables examined here. For precipitation, simply changing coniferous forest to its full extent in the 1980s may provide results even more dissimilar when compared to re-sults provided by a 1930s landscape than does a simulation with an 1980s landscape. Deviations from the principal of superposition of the responses of the simple land-use changes can be induced by primary (land-use changes) and secondary (e.g., altered cloud distributions as a response to the land-use modifications) differences. Diminution or enhancement of the atmospheric response depend on (1) the size of the resulting new patch as well as the uniformity ofits land-use, (2)the kind of change in the hydrologic and thermal characteristics, and (3)the type of land-use prevailing in the environments of land-use conversion. According to the results of this case study, areas dominated by grassland and forests are more sensitive to concurrent land-use changes than prevailingly agriculturally used areas.
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Application of the principle of superposition to detect nonlinearity in the short-term atmospheric response to concurrent land-use changes associated with future landscapes Nicole Mölders Meteor. and Atmos. Phys., 72, 47-68 (2000).

The changes in the atmospheric response (e.g.,in the variables of state, the amount of cloud- and precipitating particles, the water- and energy fluxes) to concurrent land-use changes are exemplarly examined for various landscape scenarios since the cessation of open-pit mining. The principle of superposition is applied to detect areas where the atmospheric response is either enhanced or diminished according to concurrent land-use changes as compared to simple land-use changes. The results show that nonlinear behavior of a given quantity may occur in areas without significant changes in this quantity and that a quantity may be significantly changed without finding nonlinearity. Moreover,the concurrent land-use changes do not necessarily yield a stronger atmospheric response than simple land-use changes. In addition to the size of the patches, where land-use changes, the contrast in the hydrologic and thermal behavior of the changes is decisive in measuring the magnitude of the response. Enhancement and diminishment seem also to depend on the land-use adjacent to the altered land-use.

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On the impact of 50-years-accumulated land-surface changes upon micrometeorological conditions . Nicole Mölders In: Arnold, K., Raabe, A.: Wiss. Mitt., Meteorologische Arbeiten aus Leipzig, 17, 29-43 (2000).

The influence of the concurrent land-use changes that took place in East-Germany from the Thirties to Eighties on micrometeorological conditions is examined. These land-use changes lead to a slightly warmer and drier atmospheric boundary layer (ABL). Moreover, they may significantly modify the partitioning of incoming energy between sensible and latent heat as well as partitioning of cloud-microphysical processes between the warm and cold path of precipitation formation. The atmospheric response to concurrent land-use changes deviates from superposition (of the responses to simple land-use changes) also in areas of nonsignificant changes.

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On the atmospheric response to urbanization and open-pit mining under various geostrophic wind conditions Nicole Mölders Meteor. and Atmos. Phys., 71, 205-228 (1999).

Simulations alternatively assuming a real landscape with and without open-pit mines and grown settlements were performed with a non-hydrostatic meteorological model of the meso-beta-scale to elucidate whether the atmospheric response to such land-use changes is sensitive to the direction and magnitude of geostrophic wind. The results of simulations with the same geostrophic wind conditions substantiate that the daily domain-averages of the variables of state hardly differ for the different landscape realizations, except for cloud- and precipitating particles. However, land-use changes may significantly affect the local conditions the over and downwind of the altered surfaces. The significant differences in the cloud- and precipitating particles, however, are not bound to the surroundings of land-use changes. The vertical component of wind vector, which is modified by the different heating of converted land-use, strongly affects cloud- and precipitation formation by the interaction cloud microphysics-dynamics. The magnitude of atmospheric response changes under the various directions and speeds of geostrophic wind for most of the field quantities and fluxes.

On the effects of different flooding stages of the Oder and different land-use types on the distributions of evapotranspiration, cloudiness and rainfall in the Brandenburg-Polish border area Nicole Mölders, Contrib. Atmos. Phys., 72, 1-24 (1999).

Simulations of a typical summer day were performed with a non-hydrostatic meteorological model to examine the impact of natural (flooding) and anthropogenic land-surface changes (drainage of marshes and water meadows) on the local atmospheric water cycle. The results indicate that the changed hydrologic, thermal and dynamical conditions associated with different flooding stages or marshes may noticeably affect stability, the water supply to the atmosphere, cloud and precipitation microphysics. The magnitude and the kind of atmospheric response to the surface changes depend on the horizontal size of the converted patch and the kind of land-surface conversion. Cloudiness, for instance, may be reduced downwind of small flooded areas due to stabilization, while itmay be increased downwind of large flooded areas due to the modification of the moisture convergence. The findings of this study suggest that, during extreme flooding events, the local weather forecasts have to consider the modified surface conditions.

Landscape changes over a region in East Germany and their impact upon the processes of its atmospheric water-cycle Nicole Mölders Meteorol. Atmos Phys. 68, 79-98 (1998).
Simulations replicating urbanization and/or different landscapes following the cessation of open-pit mining were performed with a non-hydrostatic meso-beta-scale model. Except for cloud and precipitating particles the daily domain averages of the variables of state hardly differ under calm wind conditions. Nevertheless, the 'single land-use changes' which are associated with urbanization, open-pit mines or the flooding of open-pit mines may appreciably or even significantly affect the local processes of the atmospheric water-cycle over and downwind of the land-use changes. Of the three, urbanization affects the local weather the least significantly, and flooding the open-pit mines causes the most significant changes. Generally, the most significant differences (at 90 % or better statistical-significance level) occur for the liquid- and solid-water substances, the soil-wetness-factors, and the vertical component of the wind-vectors. The last changes strongly influence the paths of cloud and precipitation formation by the interaction of cloud-microphysics-dynamics. In contrast to all other quantities for which a land-use change causes significant differences, the differences between cloud and precipitating particles are often not reflected in the environs of the land-use change.

Heterogeneity

On the Influence of Surface Heterogeneity on Latent Heat-Fluxes and Stratus Properties Katja Friedrich, Nicole Mölders and Gerd Tetzlaff Theor. Appl. Clim. 65: 181-196 (2000)

The influence of surface heterogeneity on spatial distribution, temporal development,and on the domain-average of the ratio between sensible and latent heat-flux (Bowen-ratio) is investigated for synthetic landscapes of differing degrees of surface heterogeneity. In so doing, simulations are performed applying a 3-dimensional non-hydrostatic mesoscale model. The synthetic landscapes consist of patches of sandy loamcovered by mixed forest and loamy soil covered by grass. The results of the numerical experiments substantiate that land-surface distributions will non-linearly influence the Bowen-ratio if patches of equal type exceed a certain size. Moreover, the heterogeneity of the upwind region may play a role. Similarity coefficients show that the surface type dominating a landscape does not necessarily determine the mean Bowen-ratio representative for this area. Thus, when applying the strategy of dominant surface type, the margin of error in the regional Bowen-ratio depends on the horizontal resolution of the model or on available data.

On the Influence of Surface Heterogeneity on Latent Heat-Fluxes and Stratus Properties Katja Friedrich and Nicole Mölders Atmos. Res. 54, 59-85 (2000)

A mesoscale atmospheric model is used to examinethe three-dimensional structure and evolution of low extended stratus over various synthetic landscapes of different heterogeneity in mid-latitudes in spring. The simulation results substantiate that surface heterogeneity non-linearly influences the distributions of latent heat-fluxes, vertical motions, and cloud-water - presupposed thelength of the patches of equalsurface type is about 10 km or larger than that. For low degrees of heterogeneity (large patch-sizes) a great coverage by lowly evpotranspiring, but strongly heating patches may enhance vertical motion. Moreover, this constellation may increase the cloud-water amount oflow extended stratus as compared to that of the other heterogeneous landscapes or that with the highest domain-averaged daily sum of latent heat-fluxes. Although there exists a relationship between the degree of heterogeneity and the modulation of latent heat-fluxes as well as cloud-water amount, the kindof surface characteristics is also important for the modulation of the properties of low extended stratus.

Numerical Investigations on the Influence of Subgrid-scaleSurface Heterogeneityon Evapotranspiration and Cloud Processes Nicole Mölders and Armin Raabe J. Appl. Meteor. 35, 782-795 (1996) .

Numerical experiments were performed with a meso-beta-scalemeteorological model to investigate the influence of subgrid-scale surface heterogeneity on the prediction of evapotranspiration, cloud and precipitation formation. The results of simulations using different horizontal grid resolutions and assuming the dominant landuse type within a grid box as the representative surface type for the entire grid element are compared with those obtained from model runs considering subgrid-scale heterogeneity by separately determining the fluxes of the respective subgrid-scale landuse types. The same surface parameterization scheme was applied in both cases. All of these numerical experiments show that the surface character istics and, hence, the subgrid-scale surface processes strongly affect the predicted microclimate close to the ground. Furthermore, the model results also evidence that in the case of applyingdominant landuse types the grid resolution may strongly affect the calculated water and energy fluxes because a landuse type being of subgrid-scale on a coarse grid and here of minor importance may be dominanton a finer grid. Moreover, if surface heterogeneity was considered thesimulation with coarser grid width also predicted many features provided by the run with a finer grid resolution with a sufficient degree of accuracy. The results substantiate that the degree of heterogeneity especially affects evapotranspiration, clouds, precipitation and soil wetness.

A comparison of two strategies on land surface heterogeneity used in a mesoscale beta meteorological model Nicole Mölders, Armin Raabe and Gerd Tetzlaff Tellus 48A, 733-749 (1996) .

Results of case studies with a mesoscale betameteorological model applying two different strategies to treat subgrid-scalesurface heterogeneity are compared with each other to evaluate the effectsof these strategies on the predicted hydrologically relevant quantities.In the first strategy, the mosaic approach, different landuse types areconsidered as separate patches within a grid cell independently interacting with mean atmospheric field quantities of that grid cell. Feedback to the grid scale is accomplished by forming area-weighted quantities from the fluxes provided by the individual patches for the soil-biosphere-atmosphereinteraction. In the second strategy, a higher resolution subgrid is established within each model grid cell and the soil-biosphere-atmosphere interaction is determined for each subgrid cell with its individual soil and biosphere conditions and near-surface meteorological forcing. Probability density functions are used to evaluate the statistical behavior of both the strategies. It is substantiated that the partitioning of the atmospheric radiativeand moisture forcing at the surface as well as cloud and precipitation ormation can significantly be affected by the type of strategy. Usingthe explicit subgrid strategy results in a shift in the partitioning of energy towards decreasing Bowen ratios ascompared to the mosaic approach. For very heterogeneous surfaces with strongly varying soil types and plant species an area-weighted meteorological near-surface forcing as used inthe mosaic approach may artificially reduce evapotranspiration. An explicit subgrid strategy or individual near-surface meteorological forcing within the mosaic approach seem to be more adequate under such surface conditions.

On the influence of grid resolution and land surface heterogeneity on hydrologic ally relevant quantities Nicole Mölders and Armin Raabe In: Raabe, A., G. Tetzlaff, W. Metz: Wissenschaftliche Mitteilungen, Meteorologische Arbeiten aus Leipzig, 1, 47-63 (1995).
Numerical experiments were performed to investigatethe influence of grid resolution and subgrid heterogeneity on the prediction of the quantities of the water cycle. The results were compared with eachother and with those provided by a simulation using the same surface parameterizationscheme buttaking subgrid scale surface heterogeneity into account. The model results substantiate that the evapotranspiration, cloudiness and precipitation are affected by the grid resolution and the heterogeneity. It was found that increasing the grid size but including the heterogeneity describes more realistically the surface processes and phenomena (e.g., heat island effect) than assuming one land use type for the whole grid element.

Remote Sensing

A sensitivity study on the initialization of surface characteristics in meso-beta/gamma-modeling using digitized vs. satellite derived landuse data Nicole Mölders, Ulrich Strasser, Karl Schneider, Wolfram Mauser, ArminRaabe Contrib. Atmos. Phys. 70, 173-187 (1997).

The impact of landuse data sets on the predictedvariables of state, water and energy fluxes was exemplarly investigatedby simulations alternatively applying digitized and satellite derived landuse data within the framework of a mosaic approach. The (domain) fractional coverage of the various landuse types differs about 5 %, but the location of occurrence appreciably differs. Although the distribution of daily averagesof temperature and humidity changes less than 0.2 C (1 %) and 0.2 g/kg (1.5 %), respectively, some locations reveal appreciable differences in the daily averages of soil moisture (0.19 m3m-3, 29 % ), surface temperature (2.3 C, 12 %),sensible (30 Wm-2, 29 %) and latent heat fluxes (32 Wm-2, 34 %). During the daytime the area average fluxes of regions dominated bythe same land use in bothdata sets differ up to 165 Wm-2 (35 %)except for grassland for which they are smaller than for all other landuse types. The greatest differences occur for a change from a dominance of low vegetation to settlements or forest because their surface characteristicsdiffer the strongest.The results suggest that, although on the mesoscale (locally) the predicted fluxes strongly differ, on the large scale (domain average) point of viewit only seems of importance that these fluxes occur somewhere within themodel domain.

Evaluation of model generated cloud cover by means of satellite data Nicole Mölders, Manfred Laube, and ErhardRaschke Atmos. Res. 39, 91-111 (1995).
An automated cloud retrieval algorithm has been developed and applied to determine cloud cover from NOAA9 AVHRR (AdvancedVery High Resolution Radiometer) satellite data. This satellite derivedcloud cover is used to evaluate the model generated cloud cover provided by two different cloud cover parameterization schemes established in a 3-D-chemical transport model. In the standard version of this model cloudcover depends on rain rate for raining clouds and on the relative humidityat cloud base for fair weather clouds. In the second cloudcover parameterization scheme predictions of liquid water content and ice content in combination with values of water content derived from several observations are used to generate the cloud cover by the model. Partial cloudiness is allowedto form when mesoscale relative humidity is less than 100 %. The comparison of the model generated with the satellite derived cloud cover shows that the second cloud cover parameterization scheme substantially improves the determination of cloud cover by the model.

Wet and Dry Deposition

On Modeling Dry Deposition of Long-Lived and Chemically Reactive Species over Heterogeneous Terrain Tetzlaff, G., R. Dlugi, K. Friedrich, G. Gross, D. Hinneburg, U. Pahl, M.Zelger, and N. Mölders J. Atm. Chem. (in press) (2002)
An explicit multi-layer subgrid-scheme was developedfor a meso-g/b-scalemodel to consider subgrid-scalesurface heterogeneity, dry deposition, biogenic and anthropogenic emissionof trace gases. Since dry deposition measurements of highly reactive tracespecies are scarce we try to evaluate this scheme by heuristic principles.The results of simulations conducted for a 5x5 km 2  resolution with and withoutthis scheme are evaluated by using results ofa model run with 1x1 km2 resolution, whichis taken as a 'grand thruth' and which has the same resolutionas the subgrid. The explict multi-layer subgrid scheme provides a similar distribution ofdry deposition fluxes as the much more computationally expensive simulation with the 1x1 km2 resolution.
Dry deposition fluxes determined from observations give evidence that the explicit multi-layer subgrid scheme which does not require a constant flux approximation for a layer of several decameters leads to an improvement in determining the exchange between the atmosphere and the ground. Results of simulation with a microscale model show that the inhomogeneity at forest edges leads to an increase of theturbulent transports of up to a factor 4 compared to horizontally homogeneous terrain, which is assumed to be the conditions of the subgrid cells (andwhich is usually the assumption for the entire grid cell in mesoscale models). Inhomogeneity inside an extended stand of trees causes an overall increaseof 5-10% with high local extremes, i.e. such an inhomogeneity results toan underestimation of dry deposition in meso- g/b-scalemodels.The effects are most pronounced for a wind direction perpendicularto theforest edge.
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Beurteilung der Modellierbarkeit des flächenbezogenen Eintrags von Spurenstoffen durch Deposition Tetzlaff, G., und N. Mölders In: Tetzlaff, G., von Hoyningen-Huene, Wiss. Mitt.Leipzig, Band 6

Die Bestimmung des atmosphärischen Eintrags in Ökosysteme durchtrockene und nasse Deposition verlangt oft räumlich detailliertere Verteilungen als sie mit der herkömmlichen Auflösung von Chemie-Transport-Modellen geliefert werden kann . Deshalb verfolgt man in der derzeitigen Modellierung zwei Hauptrichtungen nämlich (1) die feinere Auflösung von Teilgebieten des Modellgebiets durch 'Nesting'-Verfahren oder Vielskalenmodellierung und (2) Verfahren zur Berücksichtigung der subskaligen Heterogenität - sogenannte Flächenwichtungsverfahren. Letztere sind aber bisher kaum zur Bestimmung des flächengewichteten atmosphärischen Eintragsverwendet worden. Im vorliegenden Beitragwerden die verschiedenen Methoden vorgestellt, soweit wie möglichmiteinander verglichen und bezüglich ihres numerischen und datentechnischen Aufwands, ihrer Vor- und Nachteile sowie Anwendbarkeit zur Bestimmung des flächengewichteten atmosphärischen Eintrags bewertet. Die Literaturstudie zeigt, daß 'Nesting'-Verfahren und Vielskalenmodellierung am rechenzeit- und speicherplatzintensivsten sind, aber sowohl den Eintrag durch nasse und trockene Deposition liefern können, solange die Aufloesung nicht feiner erforderlich ist, als die verwendeten Parametrisierungen es zu lassen. Das Mosaikverfahren ist i.a. numerisch am effektivsten, hat aber den Nachteil,dass für detaillierte Verteilungen eine Disaggregation erforderlich ist. Um auch subskalige Emissionen behandeln zu koennen, ist von den Flächenwichtungsverfahren wahrscheinlich ein in der vertikalen Richtung ausgedehntes Untergitterver fahren zu bevorzugen. Es wird empfohlen, ein alpha-mesoskaliges Modellzur Bestimmung der Randwerte- und Anfangskonzentrationen zu verwenden. In dieses sollte ein beta-mesoskaliges Modell eingebettet werden, das ein in der Vertikalen ausgedehntes Untergitter- oder Mosaikverfahren zur Berücksichtigung der Oberflächenheterogenität und folglich zur Berechnung der flächengewichteten Flüsse verwendet. Mit dieser Modellkonfiguration könnte der flächengewichtete atmosphärische Jahreseintragmit 20 - 30 repräsentativen Szenarien hochgerechnet werden. Wegender derzeitigen Meßungenauigkeiten und der Ungenauigkeiten in den Emissions- und Anfangsbedingungen erscheint eine Evaluierung nur integriertüber das Jahr möglich.

Determining the Dry Deposition of SO2,O3, NO, and NO2 at the SANA Core Station Melpitz Gerald Spindler, Nicole Mölders, JörnHansz, Norbert Beier, GerhardKramm Meteorol. Zeitsch. 5, 205-220 (1996)

In 1992 the SANA core station was installed atMelpitz near Torgau providing,am ong other things, vertical profile dataof the concentrations of SO2, O3 ,NO, and NO2, wind speed, dry-and wet-bulb temperatures. Basedon the data of July and October 1992, dry deposition fluxes were determined applying a one-dimensional diagnostic modelof the atmospheric surface layer, where in the case of the triad NO-NO2-O3 the model calculations were carried out with and withoutchemical reactions to investigate the influence of the latter on dry deposition.The numerical results substantiate that the vertical profiles of fluxes and,hence, deposition velocities can strongly be affected by chemical reactionsleading to larger absolute values of fluxes and deposition velocity. Furthermore,the calculated fluxes also depend slightly on vegetation activity, photochemically active radiation as well as on the turbulent mixing of the atmospheric surface layer.
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On the Role of Parameterized Ice Microphysicson Cloud Structures, Dynamicsand Sulfate Distributions Nicole Mölders, Manfred Laube, Gerhard Kramm Transactions of the A&WMA. 108-127 (1995).

A mesoscale alpha chemical transport model andits meteorological preprocessor were used to invesigate the influence of parameterized ice microphysics on cloud structure, dynamics and sulfate distributions. The results of simulations with and without ice and withand without riming were compared with those obtained with the original model packages using a cumulus parameterization. These numerical experiments substantiated that the relative humidity, water substance mixing ratio fields, and, hence, cloud structures were strongly altered by turning off the ice phase or the riming process. The differencesin dynamics may be mainly attributed to the different assumptions made upon cloud and precipitation formation, and, hence, to the treatment of the consumption and release of latent heat and the sedimentation of hydrometeors. The differences in predicted cloud amount, cloud distribution, cloud structure and cloud type cause large differences in the calculated sulfate and SO2 concentration distributions. The cloud lifetime and the treatment of aqueous chemistry (cloud mean values versus height-dependent values) strongly influence sulfate and SO2 concentrations in the gasphase and wet deposition rates. All results indicate that the predicted concentration distributions and the wet and dry deposition fluxes of the atmospheric trace constituents are strongly sensitive to the model assumptions and the model architecture itself.

For further information or reprints please contact molders@gi.alaska.edu