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1.
This study documents the new PLACE soil hydrology model, and examines the effects of various parameterization schemes on the solution of the Richards equation. Richards equation is the basis upon which many of the land surface schemes participating in the PILPS experiments model soil water transport. Generally, the integration is carried out using a coarse model grid, which makes the solution more sensitive to particulars of the parameterization scheme. Parameterization schemes for the lower boundary condition, lateral interflow, and for moisture fluxes between model layers are tested in PLACE using both high and low resolution grids. Simulations were made using PILPS-HAPEX forcing data and soil and vegetation parameters. The soil hydrology model is validated against the annual observed HAPEX soil moisture profiles. The predicted evapotranspiration is also compared to a value computed from the PILPS-HAPEX forcing data using the Penman-Monteith equation.When testing a low-resolution soil grid typical of land surface schemes, predicted soil moisture was found to be highly sensitive to the interpolation method for computing vertical moisture fluxes between model layers. A new interpolation method for low resolution models is proposed and tested. It reproduces the high resolution model results more faithfully, over the entire range of soil moisture, than two methods commonly applied in the literature. Further tests demonstrate that by varying the parameterizations for lower boundary condition and the treatment of lateral flow (collectively called drainage), the predicted total annual evapotranspiration may range between 74% and 97% of the incident precipitation in this case. Both of these parameterizations involve one free parameter, and both are largely unconstrained by the available observations. Good overall agreement between the PLACE predicted and HAPEX observed soil moisture profiles was attained by varying these two PLACE drainage parameters over their respective ranges for a series of model simulations. Root-mean square error tests were then used to determine the set of parameters which corresponded to the best predicted soil moisture profile. However, the best predicted soil moisture profiles do not correspond with the best predicted evapotranspiration. This inconsistency occurs not only for PLACE, but, to varying degrees, for all of the land-surface schemes participating in PILPS-HAPEX.  相似文献   

2.
The land-surface flux model (PROGSURF) designed jointly at the Universities of Vienna and Budapest is reviewed; it belongs to the broad spectrum of PILPS1 models. PROGSURF comprises one vegetation layer and three soil layers. Temperature prediction is made by the heat conduction equation in conjunction with the force-restore method. Turbulent heat fluxes are parameterized by gradient laws using the resistance concept. The formula for the canopy surface resistance involves both a parameter describing atmospheric demand and one describing moisture availability. Soil moisture prediction is made with Richards' equation. PROGSURF is tested in off-line mode for the Cabauw data set. The observed annual mean values of the state and flux quantities at the earth's surface are well reproduced. For example, the model yields latent and sensible heat fluxes of −35.3 and −2.4 W/m2, respectively; evapotranspiration and runoff is −449 and 326 mm/yr; and root zone soil moisture content is 0.344 m3/m3. Further, the seasonal changes of water and energy balance components are well simulated. The sensitivity of PROGSURF to the canopy resistance formulation is analysed. We find that the atmospheric demand is largely represented by the saturation value of the evapotranspiration/soil moisture curve with maximum summer impact upon the annual value and further that the moisture availability is represented by the slope of the evapotranspiration curve. Both saturation value and slope control the amplitude of the seasonal fluctuation of the water balance components; at Cabauw site the saturation value is the governing parameter. These results fit satisfactorily into the other PILPS models. In particular, we are able to reproduce with PROGSURF the total variability of most other PILPS models by simply changing the atmospheric demand and soil moisture availability parameters. PROGSURF presently serves to simulate observed surface fluxes for an atmospheric diagnostic model.  相似文献   

3.
A new land surface parameterization scheme (ALSIS), with emphasis on soil moisture prediction, is described and validated with observations from HAPEX-MOBILHY and Cabauw. An important feature of the scheme is the inclusion of vertical heterogeneity of soil hydraulic parameters is modelling unsaturated flow. The simulated soil moisture for HAPEX site using a vertically homogeneous soil has a positive bias in the upper soil layers and a negative bias in the deep soil layers. Taking into account the soil vertical heterogeneity greatly eliminates this discrepancy and results in an excellent agreement between annual cycles of modelled and observed soil moisture profiles. The mean annual soil moisture in the top 1.6 m of soil increased from 394 mm for homogeneous case to 433 mm for the heterogeneous case, consistent with 435 mm observed. The improvement in soil moisture simulation resulted in an improved skill in predicting the mean and the diurnal cycles of surface fluxes for the intensive observational period (28 May–3 July). The simulated monthly averages of surface temperature and fluxes follow observations over the year, except for January when the model overestimates the latent heat flux due to its failure in simulating high rates of dew fall. The deviation of modelled monthly mean surface fluxes from observations are well within the estimated observational errors. The simulated mean daily surface temperature, and surface fluxes are generally consistent with observations, except for some times in the winter period. The modelled diurnal cycles of temperature and fluxes are in agreement with those observed. However, the model overestimates the night-time latent heat flux, especially during January.  相似文献   

4.
The characteristics of four wet deposition schemes widely used in dust modeling studies are examined within the framework of a regional scale dust model. Since these schemes are based on different formulations, the scavenging coefficients of them deviate by a factor of 103 depending on precipitation rate and particle size. The four schemes coupled with the dust model are applied to simulate a 2002 Asian dust event. The corresponding wet deposition patterns and scavenging efficiencies are compared. It is found that apart from the scheme derived from scavenging coefficient measurements, the other three schemes give similar wet deposition patterns although their scavenging efficiencies are different depending on the particle-size range. The results suggest that the performances of these schemes are affected by the particle size distribution of the dust emission, together with the model's performance of precipitation prediction.  相似文献   

5.
In model inter-comparisons one major obstacle is the format of the reported data. To facilitate the analysis of the results from the different models they should all be reported in the same format. This requires that the format is flexible enough to be easily implemented into the different land surface schemes. It should also be fault tolerant and allow a few consistence checks to avoid erroneous data to be submitted. The present note describes such a format developed for the PILPS project. After discussing the aim of this new format we present the routines which are used to write and read data. Finally two applications are described which allow the user to perform a number of consistency checks on the data.  相似文献   

6.
The energy components of sixteen Soil-Vegetation Atmospheric Transfer (SVAT) schemes were analyzed and intercompared using 10 years of surface meteorological and radiative forcing data from the Red-Arkansas River basin in the Southern Great Plains of the United States. Comparisons of simulated surface energy fluxes among models showed that the net radiation and surface temperature generally had the best agreement among the schemes. On an average (annual and monthly) basis, the estimated latent heat fluxes agreed (to within approximate estimation errors) with the latent heat fluxes derived from a radiosonde-based atmospheric budget method for slightly more than half of the schemes. The sensible heat fluxes had larger differences among the schemes than did the latent heat fluxes, and the model-simulated ground heat fluxes had large variations among the schemes. The spatial patterns of the model-computed net radiation and surface temperature were generally similar among the schemes, and appear reasonable and consistent with observations of related variables, such as surface air temperature. The spatial mean patterns of latent and sensible heat fluxes were less similar than for net radiation, and the spatial patterns of the ground heat flux vary greatly among the 16 schemes. Generally, there is less similarity among the models in the temporal (interannual) variability of surface fluxes and temperature than there is in the mean fields, even for schemes with similar mean fields.  相似文献   

7.
The parameterization scheme SPONSOR (Semi-distributed ParameterizatiON Scheme of the ORography-induced hydrology) participating in PILPS (Project for Intercomparison of Land-surface Parameterization Schemes) experiments since 1993 is described in more detail than before, taking into account a range of recent modifications. Improvement of the scheme in several aspects (e.g., soil water movement) resulted in significantly improved results for the Cabauw site (used for PILPS (2a) experiments). Then, parameterization of cold seasons/regions processes (water phase transformations within soil and snow cover) was developed for PILPS (2d) experiments carried out with Valdai data. Testing of the scheme against the data of Kolyma water balance station shows that it is able to reproduce the main features of heat and water exchange at the land surface in the permafrost zone quite satisfactorily. It was found that the scheme results are rather sensitive to the soil heat conductivity, especially in the cold seasons. The original method for the calculation of this parameter was developed using a square root function. The surface temperature and dates of crossing the 0°C temperature threshold for Kolyma station were reproduced with satisfactory accuracy. The temporal variation of the deep soil layers' temperatures was modelled satisfactorily too, but the seasonal amplitude of deep soil temperatures was overestimated by the scheme. This disadvantage can possibly be improved by inclusion of vertical inhomogeneity of soil thermal and hydraulic properties in the model.  相似文献   

8.
A simplified version of the coupled heat and moisture transport model   总被引：1，自引：0，他引：1  
In this paper, the analysis of the order of magnitude of different terms in energy and mass balance equations in complete coupled model (CM) used for either wet or dry soil moisture condition is conducted. It leads to a simplified version of the coupled model (SCM) but without losing accuracy. Then, through numerical simulation of CM and SCM by using 1-year observation data from HEIFE experiment, two tests with wet or dry moisture conditions for SCM verification are carried on. The results prove the reasonability of SCM. When compared with the numerical results from SCM, CM and observation data, the numerical results from SCM show very close agreement with CM and good agreement with observation data. It means the SCM can be used in climate study for either wet or dry region.  相似文献   

9.
Results from the 14 land surface parameterization schemes involved in the PILPS-RICE Workshop are compared for a soya crop growing season (from June to September). During this period, the transpiration flux dominates the total surface evapotranspiration and observed data from HAPEX-MOBILHY are available for comparison. Results indicate that during the month of June half of the models fall within the uncertainty range of the observations. The scatter between models behaviour is explained by three major reasons:
• The functional dependency between soil moisture and transpiration;
• the initial moisture content at the beginning of the period;
• the vertical discretization within the soil and the extension of the root system that defines the soil water holding capacity for plants
Examination of diurnal cycles of evaporation reveals that formulations based on the supply-demand concept are very sensitive to the specification of the root zone.This analysis underlines the need for more sensitivity experiments to be done with the current forcing data set and more detailed datasets to be collected in future field experiments (e.g. latent heat flux during all the growing season, root zone distribution).  相似文献   

10.
A 41-year-long reconstructed annual mean glacier mass balance record from the Cordillera Blanca, Peru, was investigated for its climate sensitivity toward temperature, humidity and precipitation, and its links with the large-scale atmospheric circulation. On interannual timescales precipitation variability appears to be the main driver for glacier mass balance fluctuations in the Cordillera Blanca. This is corroborated by an analysis of the relationship between mass balance variations and local- to regional-scale precipitation variability. Temperature tends to enhance precipitation in driving the mass balance signal, as dry years are often characterized by warm conditions, while wet years usually coincide with cold anomalies. In some years, however, warm and wet or cold and dry conditions coincide, under which circumstances temperature minimizes or even neutralizes the effects of precipitation. Surface energy balance studies have shown that changes in atmospheric humidity significantly affect the melt rates of tropical glaciers, but the lack of long and high-quality in-situ measurements precludes a detailed quantitative assessment of its role on interannual timescales in the Cordillera Blanca. Sea surface temperature anomalies (SSTA) in the tropical Pacific exert the dominant large-scale forcing on interannual time scales, leading to negative mass balance anomalies during El Niño and above average mass balance during La Niña episodes. In general the teleconnection mechanism linking ENSO with glacier mass balance is similar to what has previously been described for the Bolivian Altiplano region. Changes in the upper-tropospheric zonal flow aloft associated with ENSO conditions determine the amount of snowfall during the wet season and thereby significantly affect the glacier mass balance. Because this teleconnection mechanism is spatially unstable and oscillates latitudinally along the subtropical Andes, it affects the Cordillera Blanca in most, but not all years. The relationship between ENSO and glacier mass balance is therefore characterized by occasional ‘break downs’, more common since the mid-1970's, when El Niño years with above average mass balance and La Niña events with negative mass balance have been observed.  相似文献   

11.
《Planetary and Space Science》2007,55(10):1272-1282
  相似文献   

12.
Atmospheric and land surface data collected from the HAPEX-MOBILHY field experiment were used to compare the bare soil evaporation simulations of 13 land surface schemes and to examine the relationship between differences in evaporation and differences in soil moisture. For a 120-day period in which there was no vegetation present, computed total evaporation ranged between 100 and 250 mm. This large range in evaporation was not related to soil moisture differences. Prescribing surface soil moisture and temperature did not reduce the range in evaporation and instead the range was increased. The models' predictions of evaporation were in closer agreement with each other when they were allowed to select their own surface conditions than when they were forced to use the same conditions. The bare soil evaporation formulations used by the land-surface schemes are not consistent with each other and these inconsistencies produce widely-varying bare soil evaporation rates. The range in bare soil evaporation is unlikely to be reduced by improving the simulation of soil moisture and instead an assessment of why the bare soil evaporation formulations are inconsistent is required.  相似文献   

13.
Two sensitivity experiments, in which CO2 is instantaneously doubled, have been performed with a general circulation model to determine the influence of the convective parametrization on simulated climate change. We have examined the spatial structure of changes in the annual mean and annual cycle for surface temperature and precipitation for both experiments; similarly we have examined changes in the variance for these two fields. We have also computed a range of test statistics in order to obtain reliable measures of the signal-to-noise ratio in the climate change signal from each experiment. We have computed test statistics for the entire globe and for five different region and we contrast the global response with the response in the Australian region taken as a representative sample.We find that the highest signal-to-noise ratios in the change from 1 * CO2 to 2 * CO2 are for the change in surface temperature for both experiments with little difference in the global averages between the experiments. Globally averaged precipitation shows a greater noise level but perhaps the greatest contrast between experiments. There are generally significant increases in the temporal and spatial variability of precipitation in the change from the 1 * CO2 to 2 * CO2 and with some differences apparent between the two experiments. The temporal variability of surface temperature does not change significantly in any of the 2 * CO2 cases, and there is little difference between the experiments. There is a significant decrease in the spatial variability of surface temperature in all 2 * CO2 experiments in all cases and with significant differences in the seasonal variations between different experiments. The spatial variability of precipitation increases in all 2 * CO2 cases and also with substantial differences in the seasonal variations between the experiments. There are accompanying significantly different spatial pattern correlations for both surface temperature and precipitation. In general we find that the global changes are fairly robust with the differences associated with convective parametrization schemes being very small. However, at the regional level, there are marked differences between experiments with changes both in the means and in the spatial and temporal variances but often with low levels of significance.  相似文献   

14.
We present the hydrometeorology of eastern Asia during April 1995 simulated by the Regional Climate System Model. The amount and location of simulated monthly precipitation agrees well with observations. Soil water content variation was closely correlated with precipitation. Land-surface evaporation and the surface energy budget were strongly controlled by soil moisture content. A sensitivity test with reduced initial soil moisture content suggested that near-surface soil moisture spins up quickly after heavy precipitation events. However, variations in the initial soil moisture field may alter details of the simulated precipitation which can introduce further complexity in climate simulations.  相似文献   

15.
Monthly runoff from the 34.3% glacierized tropical catchment of Llanganuco in the tropical Cordillera Blanca, Perú, is successfully simulated and compared with a measured 44 year time series. In the investigation area, the climate is characterized by all-year round homogenous temperature conditions and a strong variability in air humidity and moisture content of the atmosphere. Thus, contrary to the mid latitudes, the seasonal variation in glacier melt strongly depends on moisture-related variables, rather than on air temperature. The here presented ITGG-2.0-R model aims for these requirements. The lack of moisture-related input data other than precipitation demands for an intermediate calibration step. Net shortwave radiation, the emissivity of the atmosphere and a sublimation/melt ratio are related to precipitation amounts. Runoff is well simulated and correlates with the measured record with r2 = 0.76. Seasonally obtained r2 are only slightly smaller. On a long-term, the cumulative deviation is minor, and the mean annual cycle of runoff is reproduced rather well (r2 = 0.99). Based on four different IPCC climate change scenarios, future runoff is simulated. All runoff scenarios are modelled for the respective steady-state glacier extent. This leads to a reduction in the glacier size and a decreased amount of glacier melt. On the other hand, direct runoff increases due to larger glacier free areas. Consequently, mean annual runoff remains almost unchanged, but the seasonality intensifies considerably with more runoff during the wet and less runoff during the dry season.  相似文献   

16.
Currently, and throughout much of the Amazonian, the mean annual surface temperatures of Mars are so cold that basal melting does not occur in ice sheets and glaciers and they are cold-based. The documented evidence for extensive and well-developed eskers (sediment-filled former sub-glacial meltwater channels) in the south circumpolar Dorsa Argentea Formation is an indication that basal melting and wet-based glaciation occurred at the South Pole near the Noachian–Hesperian boundary. We employ glacial accumulation and ice-flow models to distinguish between basal melting from bottom-up heat sources (elevated geothermal fluxes) and top-down induced basal melting (elevated atmospheric temperatures warming the ice). We show that under mean annual south polar atmospheric temperatures (?100 °C) simulated in typical Amazonian climate experiments and typical Noachian–Hesperian geothermal heat fluxes (45–65 mW/m2), south polar ice accumulations remain cold-based. In order to produce significant basal melting with these typical geothermal heat fluxes, the mean annual south polar atmospheric temperatures must be raised from today’s temperature at the surface (?100 °C) to the range of ?50 to ?75 °C. This mean annual polar surface atmospheric temperature range implies lower latitude mean annual temperatures that are likely to be below the melting point of water, and thus does not favor a “warm and wet” early Mars. Seasonal temperatures at lower latitudes, however, could range above the melting point of water, perhaps explaining the concurrent development of valley networks and open basin lakes in these areas. This treatment provides an independent estimate of the polar (and non-polar) surface temperatures near the Noachian–Hesperian boundary of Mars history and implies a cold and relatively dry Mars climate, similar to the Antarctic Dry Valleys, where seasonal melting forms transient streams and permanent ice-covered lakes in an otherwise hyperarid, hypothermal climate.  相似文献   

17.
Abstract— A simple thermal model is developed to determine the temperature history of the inlet tube of the Huygens probe gas chromatograph mass spectrometer (GCMS) after its fortuitous emplacement on the surface of Saturn's moon Titan. The model parameters are adjusted to match the recorded temperature history of a nearby heater, taking into account heat losses by conduction to the rest of the probe and to Titan's cold atmosphere. The model suggests that after impact when forced convective cooling ceased, the inlet temperature rose from ?110 K to an asymptotic value of only ?145 K. This requires that the inlet was embedded in a surface that acted as an effective heat sink, most plausibly interpreted as wet or damp with liquid methane. The data appear inconsistent with a tar or dry, fine‐grained surface, and the inlet was not warm enough to devolatilize methane hydrate.  相似文献   

18.
Abstract– Planetary surfaces are subjected to meteorite bombardment and crater formation. Rocks forming these surfaces are often porous and contain fluids. To understand the role of both parameters on impact cratering, we conducted laboratory experiments with dry and wet sandstone blocks impacted by centimeter‐sized steel spheres. We utilized a 40 m two‐stage light‐gas gun to achieve impact velocities of up to 5.4 km s?1. Cratering efficiency, ejection velocities, and spall volume are enhanced if the pore space of the sandstone is filled with water. In addition, the crater morphologies differ substantially from wet to dry targets, i.e., craters in wet targets are larger, but shallower. We report on the effects of pore water on the excavation flow field and the degree of target damage. We suggest that vaporization of water upon pressure release significantly contributes to the impact process.  相似文献   

19.
The partial heat fluxes of thermal radiation in an emitting, absorbing, and scattering finite medium bounded by diffusely-reflecting plates is studied, assuming the medium to scatter isotropically. Two algebraic equations connecting the partial heat fluxes relevant to this problem and the corresponding one with simple boundary conditions are obtained. The intergral equation is solved in a semi-analytical from by collection method, using Legendre polynomials as basis functions. Numerical results are presented and compared.  相似文献   

20.
In this account we present estimates of nannofossil fluxes in four sections and one borehole all belonging to the Early Jurassic western Tethys. This study aims to map the distribution of pelagic carbonate production across the Early Toarcian anoxic event (T-OAE), and to understand which environmental parameters did control such production. Our results indicate important changes in carbonate production by nannoplankton occurring within the western Tethys and its variations through time. Nannofossil fluxes (specimens per m2 per year) are extremely low during the T-OAE in all the studied settings. Higher fluxes are encountered in the westernmost part of the Tethys Ocean before the T-OAE, whilst pelagic carbonate production shifted towards the northern margin of the Tethys after the recovery from anoxic conditions. The dramatic decrease in nannoplankton production during the T-OAE has been interpreted in previous works as a biocalcification crisis related to high pCO2 in the atmosphere/hydrosphere system. Although a high pCO2 may have lowered the carbonate saturation state of Early Jurassic oceans and finally hampered biocalcification, we speculate that the most important effects of CO2 increase were indirect, and affected pelagic producers via changes on climate and sea-level. Namely, it seems that precipitation/evaporation budgets and continental runoff that controlled nutrient levels and salinity in surface oceanic waters were important factors for pelagic biocalcifiers.  相似文献   

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