Selection of Some Abstracts
- Water availability
- Hydrometeorology and Water Cycle
- Coupling of a Meteorological
and a Hydrological Model
- Landuse Changes
- Remote Sensing
- Wet and Dry Deposition
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,
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.)
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
- 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
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. LaubeThe 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
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
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
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.
Similarity of microclimate as simulated in response to a landscape of the 1930s
and the 1980s
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
Application of the principle
of superposition to detect nonlinearity in the short-term atmospheric response
to concurrent land-use changes associated with future landscapes
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.
On the impact
of 50-years-accumulated land-surface changes upon micrometeorological conditions
In: Arnold, K., Raabe, A.:
Wiss. Mitt., Meteorologische Arbeiten aus Leipzig, 17, 29-43
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.
On the atmospheric response to urbanization and open-pit mining under various
geostrophic wind conditions
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
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.
On the Influence of Surface Heterogeneity on Latent Heat-Fluxes and Stratus
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
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.
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.
A sensitivity study on the initialization of surface characteristics in meso-beta/gamma-modeling
using digitized vs. satellite derived landuse data
Ulrich Strasser, Karl Schneider, Wolfram Mauser, ArminRaabe
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
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
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.
Beurteilung der Modellierbarkeit des flächenbezogenen Eintrags von Spurenstoffen
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
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. .
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.
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