H51D-01
Foliage Temperature Profile Modeling: The Role of Canopy Density and Stomatal Resistance Profiles
Land surface energy fluxes play a key role in the hydrology, weather and climate of a region, and the land surface temperature (Ts) is a key variable in most land surface models (LSMs) used to calculate them. Many LSMs make use of remotely sensed (radiometric) Ts. Most of them use either a single lumped Ts value or distinguish between the soil surface temperature and the lumped foliage temperature. However, even within the foliage itself, recent measurements by two of the present investigators have shown well-defined vertical leaf temperature (Tf) profiles. Such profiles are handled explicitly in very few LSMs. To address this problem, a Localized Near Field (LNF) Lagrangian transport canopy model has been developed. This model combines the LNF theory proposed by M. Raupach with the combination equation applied to thin horizontal layers of the canopy to determine the energy budget for each layer. Required input data are net radiation, canopy density distribution, stomatal resistance distribution, and wind speed, air temperature, and humidity above the canopy. The model calculates momentum flux, H, and LE, as well as vertical distributions of heat and vapor source strengths, air temperature, humidity, and foliage temperature. The model is applied to data from the Southern Great Plains (SGP-97) experiment from a dense (LAI-4.0, canopy height 0.6 m) grassy site. The model was run with three different assumed foliage density distributions, all of which had a total LAI of 4.0, and two different stomatal resistance profile shapes. A key finding of this study is that the shape of the modeled Tf profiles can vary considerably depending on the assumed foliage density and stomatal resistance profiles. For example, during the middle of the day, foliage density profiles that have maximum density near the middle of the canopy also developed Tf maxima near the middle of the canopy, but uniform foliage density profiles developed Tf maxima at the top of the canopy. A better understanding of these interactions is essential for proper interpretation of remotely sensed values of Ts.
H51D-02
An Initial assessment of Soil Moisture Fields Simulated by the Noah Land Surface Model at Regional and Local Scales
Soil moisture data, measured as a volumetric content fraction, produced by multi-year runs of the Noah Land Surface Model were compared with soil moisture point measurements available from the Soil Climate Analysis Network (SCAN). The comparison area covered the Lower Mississippi Delta region. All Noah model runs were configured and performed using the NASA Land Information System (LIS) software. Noah retrospective runs were performed at horizontal grids with different spatial resolutions (ranging from 1km to 25km) to examine a scale-dependence accuracy/quality of simulated soil moisture fields. The North American Land Data Assimilation System (NLDAS) atmospheric forcing data were used in these simulations. The sensitivity of soil moisture fields to uncertainties associated with the specification of atmospheric forcing and soil parameters within the Noah model will be estimated and discussed.
H51D-03
On the impact of surface heterogeneity on the diurnal evolution of the convective boundary layer
It is well-known that vigorous turbulent interactions between heterogeneous surface and overlying convective boundary layer (CBL) during the daytime have strong impacts on short-term flow properties (e.g. velocity, temperature, and humidity) as well as local and regional weather and climate. A significant amount of experimental and modeling work has been performed to attempt to build our understanding of the impact of surface heterogeneities (i.e. fluxes and roughness) on the ABL. However, for practical reasons, these efforts have often been undertaken for idealized surface conditions. This research attempts to further our understanding by using realistic heterogeneous surface flux fields obtained from the Soil-Moisture Atmosphere Coupling Experiment 2002 (SMACEX) as boundary conditions in a Large-Eddy Simulation (LES). Specifically, two main questions are investigated: 1) How explicitly must the surface fluxes be resolved in order to accurately predict CBL states and dynamics? and 2) What is the relationship between length scales of surface heterogeneities and the CBL states and dynamics? To answer the first question, a set of statistically similar fields (relative to the actual fields at SMACEX) are used in the LES as boundary conditions. These realizations are designed to exactly replicate the mean and covariance between the surface roughness and sensible and latent heat fluxes. The second question is addressed by varying the correlation length of the flux fields while maintaining the mean and variance. Results from this study not only illustrate the impact of surface heterogeneity on CBL structure and dynamics, but also offer insight into developing better parameterizations of surface characteristics used in regional climate models.
H51D-04
The Impact of the Physical Initialization in the Global Analysis and Short Range Forecast Over South America Using the GPSAS-CPTEC/INPE Initial Conditions
The Brazilian Center for Weather Prediction and Climate Studies (CPTEC/INPE) seeks to improve its global analysis as well as the short range forecast over South America by assimilating precipitation. The Tropical Rainfall Measuring Mission (TRMM) merged high quality (HQ)/infrared (IR) precipitation estimates were assimilated in the atmospheric general circulation model as an initial test. The experiments were performed using the initial conditions generated by Global Physical-space Statistical Analysis System (GPSAS- CPTEC/INPE), for March 2004. Two experiments were carried out: (i) with physical initialization (PI), where the precipitation was assimilated in the region between -40oS to 40oN; and (ii) without physical initialization (no-PI). Evaluations of the impact on the prognostic variables, such as air temperature, specific humidity, and horizontal wind are provided based on comparisons with the control experiment, global analyses, and observations.
H51D-05
Regulation of Soil Moisture on Water Transport in an Oak Savanna Ecosystem at Plant and Stand Scales
Study of water exchange between soil, plant and the atmosphere in response to seasonal or periodic droughts is critical to model the hydrologic cycle and many other processes in water-controlled ecosystems. The difficulties in such studies arise from insufficient understanding of the complex interactions between the various processes and their scale-dependence. The purpose of our study is to investigate the regulation of root water uptake and evaporative fluxes by water deficits and climatic conditions at a plant scale (a few m2) and at a stand scale (a few hundreds to a few thousands m2). Our study site is an oak savanna ecosystem that is located in Mediterranean climate zone and experiences annual summer droughts. The influence of soil moisture on actual evapotranspiration (ET) at the stand scale is studied using spatially distributed soil moisture measurements and tower-based ET measurements, and it is separately investigated for trees, grasses and mixture of trees and grasses in the ecosystem. On the other hand, study at the plant scale is based on stem sap flow measurements using the heat ratio method and soil moisture measured in the local root zone. Potential tree transpiration and stand-level ET are estimated from meteorological variables using the Penman-Monteith equation. The regulation patterns of soil moisture on water transport at the plant and stand scales are studied by examining the change of ratio between the actual and potential water fluxes with soil moisture. The regulation patterns at the two scales will be compared and appropriate models will be identified and parameterized based on the observations.
H51D-06
Why is an LSM augmented with an aquifer model less sensitive to parameter choices than a standard LSM?
Previous work has shown that the addition of a lumped, unconfined aquifer model to a land-surface model (LSM) decreases the sensitivity of modeled monthly change in terrestrial water storage (dTWS) to selection of subsurface hydrologic parameters. In the work presented here, we investigate why adding an aquifer model as the lower boundary condition increases the robustness of LSM-simulated dTWS. We also evaluate the sensitivity of modeled runoff and modeled partitioning of terrestrial water storage to parameter choices. We compare two versions of the National Center for Atmospheric Research Community Land Model (CLM): (1) the standard CLM, which has a 10-layer, 3.43-m soil profile and no explicit aquifer representation; and (2) the standard CLM augmented with a lumped, unconfined aquifer model as its lower boundary. We simulate 1997 to 2005, driving the models offline as a single column representing Illinois, USA. The two versions of CLM are each run 20,000 times using a random sample of the parameter space for soil texture and key hydrologic parameters. We use the model covariance structures to identify how the shift in sensitivity occurs and perform detailed analysis of the interaction between parameters and model processes under a range of hydrologic conditions.